Survey of Super Massive Black Holes Completed

relativity by macadamia_harold · 2006-10-07 18:47 · Score: 1

The average density of a supermassive black hole can be very low, and may actually be lower than the density of water.

I'm starting to feel very lucky to have grown up in the Milky Way Galaxy.

He might as well be saying he feels lucky that he grew up in Kansas instead of Hawaii.

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Re:relativity by Tablizer · 2006-10-07 19:23 · Score: 2, Insightful

The average density of a supermassive black hole can be very low, and may actually be lower than the density of water.

That sounds suspicious, especially coming from wikipedia. Something with a density that low could not likely bend light enough to keep it from escaping, even if very large.

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Re:relativity by Anonymous Coward · 2006-10-07 19:35 · Score: 0

You're correct. It should read, "The average density of a supermassive black hole can be very high, and may actually be higher than the density of of the typical slashdotter."
Re:relativity by ajs · 2006-10-07 22:50 · Score: 4, Informative

That sounds suspicious, especially coming from wikipedia.

It would sound more reasonable coming from Slashdot? What source of information on the Web do you think is more reliable? I've certainly fixed my share of errors on Wikipedia, but that's becuase I hunt them down, as do many others. That kind of fact-checking is almost non-existant on most of the Web, so if I'm going to trust any one source (and I don't) for such information, it would be Wikipedia.

And, as others have noted, you were mis-understanding the definition of "average density". There's a fairly well-known calculation that states that a spherical volume of material with the density of water, and a diameter less than that of Jupiter's orbit would form an event horizon, effectively constituting a black hole. It's a nice visualization of a complex phenomenon. R. Huber has done the math for us (pdf) if you want to check for yourself.
Re:relativity by Impy+the+Impiuos+Imp · 2006-10-07 23:01 · Score: 2, Informative

Suspicious? Let's see. "The solar system"/supermassive black hole is about 16 light-hours across.

57600 light-seconds

10713600000 miles

The sun is 800,000 miles across. So, width-wise, the solar system is

13392 suns wide

Volume is the cube of the linear width, so the solar system could fit

2,401,797,132,288 sunc

in its volume.

Although the density of the core of the sun is very high, I'm thinking it's not so high that "billions" of suns would make such a volume be denser than water when that volume could hold two and a half trillion suns just to be as dense as one sun.

It may be more on the order of as dense as a helium baloon, or even lighter.

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Re:relativity by Anonymous Coward · 2006-10-07 23:59 · Score: 0

And the average density of the Sun is less than that of air. So what? Astronomical objects aren't required to fit into a human defined notion of common sense.
Re:relativity by Ckwop · 2006-10-08 02:36 · Score: 3, Informative

That sounds suspicious, especially coming from wikipedia. Something with a density that low could not likely bend light enough to keep it from escaping, even if very large.

It's nice to see a skeptic; It's a virtue to be a skeptic and not a sin. However, in this case your skepticism is misplaced.

The simplest black hole solution to the equations that govern General Relativity is Schwarzschild's solution. In this he shows that the radius of a black hole is directly proportional to its mass. Elementary geometry tells us that the volume of a sphere is proportional to the cube of the radius. Therefore, the density, which is just mass over volume, that is required to create a blackhole decreases the more mass you have.

I find the figure fairly reasonable for the amount of mass these super-massive black-holes contain.

Simon
Re:relativity by KarMann · 2006-10-08 15:14 · Score: 1

Density of Sun: 1.408 g/cm^3, or about 1.4 times the density of water
Density of air: about 0.0012 g/cm^3

I'll leave the "greater than or less than" part of the math for you. You have a good point about them not fitting common sense, but your example here is atrocious.

P.S. Damn, couldn't they at least let us use <sup> and <sub>, finally?

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Re:relativity by KarMann · 2006-10-08 15:18 · Score: 1

An afterthought: Saturn would have been a much better example. Less dense than water, about 0.7 g/cm^3 if I recall correctly. Still somewhat irrelevant, as a black hole can have arbitrarily low density by increasing its mass (somewhat counterintuitive, granted; and assuming you define its volume from its event horizon). But at least correct, and gets that counterintuitivity point across.

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400 light years isn't that far... by mhotchin · 2006-10-07 18:50 · Score: 5, Informative

400 lightyears? Didn't the submitter read the article?

It's 400 *million* light years.

Re:400 light years isn't that far... by Ignorant+Aardvark · 2006-10-07 18:53 · Score: 1

Yeah, no kidding. I was reading the Slashdot summary and I was thinking "Exactly how many galaxies are we supposed to think are within 400 light-years of ours? Especially considering that the diameter of our galaxy is 100,000 light-years?"

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Re:400 light years isn't that far... by forgotten_my_nick · 2006-10-07 20:02 · Score: 4, Interesting

Exactly.. here is a nice video to put the whole thing in perspective.

http://www.youtube.com/watch?v=mcBV-cXVWFw
Re:400 light years isn't that far... by CodeBuster · 2006-10-07 20:02 · Score: 3, Informative

Indeed, the nearest major galaxy in the local group is actually the Andromeda Galaxy at ~2.5 million light years distance, give or take a few thousand since the distance can only be measured relatively indirectly via Cepheid variable stars. The Andromeda galaxy is also thought to be on a collision course with the Milky Way (although it is impossible to know for sure if they will actually collide because the tangential velocity of the Andromeda Galaxy with respect to the Milky Way is not known). So, assuming that some other disaster does not befall humanity in the meantime, which would certainly be miraculous given our recorded history and more recent events, we will know the answer in ~3 billion years or so (predicted time to impact or convergence rather since both galaxies are mostly empty space).
Re:400 light years isn't that far... by Kamineko · 2006-10-07 20:22 · Score: 1

"You humans, when're you gonna learn that size doesn't matter? Just 'cause something's important, doesn't mean it's not very, very small."
Re:400 light years isn't that far... by Impy+the+Impiuos+Imp · 2006-10-07 23:12 · Score: 1

> since the distance can only be measured relatively indirectly via Cepheid [wikipedia.org] variable stars.

Well, if you can get a rough estimate of the size of our galaxy, you could judge the distance to the Andromeda galaxy via angular size, assuming they are roughly in the same ballpark of size.

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Re:400 light years isn't that far... by FhnuZoag · 2006-10-08 00:43 · Score: 1

Maybe we should tag this article (and such future errors) 'erroneous' or something, so that they'll get fixed?
Re:400 light years isn't that far... by jftitan · 2006-10-08 01:17 · Score: 1

I've always been one looking up into the stars, but never have I heard or seen anything as awesome as this youtube clip. What I don't understand is... our universe is 250 billion lightyears in size? I thought we couldn't measure our universe? I mean I know our galaxy is... huge! and our solar system is roughly... less huge (HAHAHAH big numbers!)

Have we been able to size our Universe? because if that has happened WTF has happened to all the news about it. "Tonight at 11! The universe gets a size, and it larger than XXXXXXL" "back to you Diane, and your small tits!"

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Re:400 light years isn't that far... by Profane+MuthaFucka · 2006-10-08 02:59 · Score: 1

The number is an estimate based on what we know. What they left out was the error bar, which is oddly enough, also based on what we know!

Nobody knows perfectly, but we can make some guesses. Expect that number to change in the future.

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Re:400 light years isn't that far... by Anonymous Coward · 2006-10-08 03:27 · Score: 0

...but I wouldn't want to walk it.
Re:400 light years isn't that far... by NormalVisual · 2006-10-08 06:29 · Score: 1

Those pugs are some pretty wise dogs.

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Re:400 light years isn't that far... by empesey · 2006-10-08 07:11 · Score: 2, Insightful

> I thought we couldn't measure our universe?

Really, we only have to measure half of it and multiply 2.
Re:400 light years isn't that far... by Anonymous Coward · 2006-10-08 11:24 · Score: 1, Interesting

So if it's 250 billion light years across, than the 'ends' would be 125 billion light years from the center. If the universe is only 14 billion years old, how did galaxies get 125 billion light years from the center at that time? They would have to travel at 10x the speed of light, and that's supposed to be impossible...
Re:400 light years isn't that far... by Kheng · 2006-10-08 12:20 · Score: 1

Inflation isnt governed by the speed of light
Re:400 light years isn't that far... by KarMann · 2006-10-08 15:26 · Score: 1

The sizes of galaxies similar in appearance to ours (which, I might remind you, we've never even seen from outside) varies quite a bit, rendering such a technique rather useless. Even with the error range of Cepheid variable measurements, it's still much more accurate than that could ever be.

Unless you were just nitpicking on the "can only be measured" point. I guess I'd have to grant that it might give some vague idea of how close it is. Kind of the way assuming the Moon were the same size as the Earth would get us within an order of magnitude of its distance, assuming we knew the Earth's size. (And how do you suppose we measure our own Milky Way's size?)

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Re:400 light years isn't that far... by Anonymous Coward · 2006-10-09 01:58 · Score: 0

Um. Why not? Everything else in the universe seemes to be limited by it. Can you elaborate? Is there an explanation for it, or is it some handwaving to fit the model?
Re:400 light years isn't that far... by Anonymous Coward · 2006-10-09 02:03 · Score: 0

Relativity places restrictions on how fast matter and energy can travel through space, but it places no restrictions on how fast space itself can expand. You can write down solutions of the Einstein field equation that expand at any arbitrarily high rate, even so high that matter itself gets ripped apart.
Re:400 light years isn't that far... by Profane+MuthaFucka · 2006-10-09 03:24 · Score: 1

Inflation is an expansion of space itself and is not limited to the speed of light, which limits travel through space. http://en.wikipedia.org/wiki/Cosmic_inflation is a pretty good introduction.

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Re:400 light years isn't that far... by suitti · 2006-10-09 06:08 · Score: 1

A new technique, involving looking for eclipsing binary stars in the target galaxy, has been used to measure the distance to m33. m31 is next. This technique is still based on the brightness of stars, but the intrinsic brightness is supposed to be better known.

Also of interest is that proper motion has been measured for m33. No proper motion has yet been detected for m31.

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-- Stephen.
Re:400 light years isn't that far... by rpresser · 2006-10-09 06:15 · Score: 1

There is indeed an explanation: cosmic inflation, as others have pointed you to.

But here is a handwaving analogy: Imagine two ants on the surface of a balloon. Neither can crawl faster than a, the maximum running speed of an ant[1]. But if somebody is blowing up the balloon, the ants can recede from each other much faster than a.

[1] I dunno, maybe a few mm per second? I'm no ant expert.

I'm starting to feel very lucky... by RyanFenton · 2006-10-07 18:51 · Score: 5, Funny

I'm starting to feel very lucky to have grown up in the Milky Way Galaxy.

Yes. Living near one of those super-massive black holes would certainly suck. Being one with everything around you sounds nice and radiant - but it leaves you all strung out over time, and it seems to take forever! The light at the end of the tunnel is you.

Ryan Fenton

Re:I'm starting to feel very lucky... by Oronar · 2006-10-07 20:53 · Score: 2, Interesting

I guess it sucks for you then.

Because there's a supermassive black hole at the center of our galaxy.
http://en.wikipedia.org/wiki/Sagittarius_A*

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Re:I'm starting to feel very lucky... by ajs · 2006-10-07 21:00 · Score: 1

It would not suck, and we do live near one. It's questionable how much living near an active galactic core would suck, but we'll find out eventually when something hefty gets munched by our galaxy's black hole.
Re:I'm starting to feel very lucky... by Anonymous Coward · 2006-10-07 21:05 · Score: 0

Well, it seems to take forever, but only from the outside. You'll reach the singularity in finite time. And if the black hole is massive enough, you'll be still alive when passing the event horizons.
Re:I'm starting to feel very lucky... by Ruie · 2006-10-08 04:46 · Score: 1

I'm starting to feel very lucky to have grown up in the Milky Way Galaxy.

Our black hole is located near Sagittarius A.
Re:I'm starting to feel very lucky... by Broken+scope · 2006-10-08 04:59 · Score: 1

Feel free to make fun of me but couldn't that have already happened? The time dilation+the huge distance mean that it would take a very very long for anything to get to us. No force or particle can travel faster than light.

(I've gotten really cocky since i started reading the elegant universe so feel free to deride my small intellect.)

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Re:I'm starting to feel very lucky... by YU+Nicks+NE+Way · 2006-10-08 05:19 · Score: 1

Ask not up whom the black hole sucks...it sucks up you.

(Parent is right, btw. There's at least one multi-million solar mass black hole within 70K light-years of you. It holds the core of our galaxy together.)
Re:I'm starting to feel very lucky... by ajs · 2006-10-10 07:05 · Score: 1

Yes, the core could already have "gone active" and we would not know about it yet. Something along these lines was the basis for a plot in some of Niven's stories, in fact, where humanity's first clue that something was wrong came in the form of a race of highly advanced beings that were fleeing the center of the galaxy ahead of a shock-wave that they had gained advanced warning of. At least that's how I recall it. I haven't read the story for decades.
Re:I'm starting to feel very lucky... by Broken+scope · 2006-10-10 07:32 · Score: 1

WOOHOO! I said something about science that made sense. cough.

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400 light years?!?! by philgross · 2006-10-07 18:51 · Score: 3, Informative

That would be 400 million light years. 400 light years wouldn't get you out of our local arm of the Milky Way.

Re:400 light years?!?! by heatdeath · 2006-10-07 19:13 · Score: 2, Funny

It's a good thing we have an army of a millionth of an editor keeping slashdot submissions high quality.

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SUPERMASSIVEBLACKHOLE by m0biusAce · 2006-10-07 18:51 · Score: 1, Interesting

I can't be the only one that thought of the british band, "Muse" =D

Re:SUPERMASSIVEBLACKHOLE by maroberts · 2006-10-07 18:57 · Score: 1

I can't be the only one that thought of the british band, "Muse" =D

Or goatse :-)

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Re:SUPERMASSIVEBLACKHOLE by kiwipeso · 2006-10-07 20:22 · Score: 1

I was thinking about some african-american pornstar called jeannie pepper.
Damn that one got real big in the last ten years.

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- Kaos games and encryption systems developer
Re:SUPERMASSIVEBLACKHOLE by bloobloo · 2006-10-07 21:36 · Score: 1

Yeah - and it came up on iTunes for me just as I read the headline which was odd!
Re:SUPERMASSIVEBLACKHOLE by Conanymous+Award · 2006-10-07 21:37 · Score: 1

"I can't be the only one that thought of the british band, "Muse" =D"

Nope, you aren't. Me and my GF had a laugh when we saw the headline. "Glaciers melting in the dead of night and the superstars sucked into the supermassive..."
Re:SUPERMASSIVEBLACKHOLE by stunt_penguin · 2006-10-08 05:12 · Score: 1

1 : what prick modded you offtopic? meh,

2: I think I need to give these guys a bell as there's a supermassive black hole on my desk right now ^^

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Re:SUPERMASSIVEBLACKHOLE by Gli7ch · 2006-10-08 16:11 · Score: 1

I didn't, I thought of the piece of shit album that the British band Muse released which had Supermassive Black Hole as its first single and is going to completely destroy the section of their fanbase that isn't completely retarded.

(For those who are looking to mod me troll, I'd like to point out that Muse was and to an extent still is one of my favourite bands, It's just a shame that their latest album was a Supermassive Hunk of Crap.)
Re:SUPERMASSIVEBLACKHOLE by iainl · 2006-10-08 21:49 · Score: 1

I'm not modding you troll, but to be fair resisting the temptation would be a lot easier if there was a "-1, has rubbish taste and accuses others of being retarded" mod. Personally, I think it's the best thing they've done yet, despite a slightly saggy section between A Soldier's Poem and Exo-Politics.

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"I Know You Are But What Am I?"
Re:SUPERMASSIVEBLACKHOLE by Gli7ch · 2006-10-09 09:13 · Score: 1

Corrupt, you corrupt, Bring corruption to all that you touch. Hold, you'll behold, And behold and for all that you've done. And Spell, cast a spell, Cast a spell on the country you run. And risk, you will risk, You will risk all their lives and their souls.
We're wacked, out on acid, too much acid to write decent lyrics. But release, we'll release it, because all the emos and angsty teens will love it.

Personally I think the album has a slump right up until Knights of Cydonia.
Re:SUPERMASSIVEBLACKHOLE by Gli7ch · 2006-10-09 09:17 · Score: 1

Interesting, the blockquote tag isn't working. What's with that?
Re:SUPERMASSIVEBLACKHOLE by iainl · 2006-10-09 21:55 · Score: 1

I've no idea about the quote tag, sorry.

As for the lyrics, yes they're completely nuts - it's not acid; they've just got carried away with their conspiracy theory nonsense. But that was something of a running theme in Absolution, too.

I don't care, really - it's the music I like.

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"I Know You Are But What Am I?"
Re:SUPERMASSIVEBLACKHOLE by Gli7ch · 2006-10-09 22:20 · Score: 1

I'm down with that.

That's 400 Million not just 400. by SauroNlord · 2006-10-07 18:52 · Score: 0

From the article:
"We are confident we are seeing every, active supermassive black hole within 400-million-light-years of Earth," said Jack Tueller of NASA Goddard Space Flight Center in Maryland who led the census effort."

Considering our own galaxy is about a 100,000 light years across. Wikipedia:Milky Way

We Live in a (semi-)Active Galaxy by idsfa · 2006-10-07 18:52 · Score: 3, Informative

Hate to break it to you, but there's a >million solar mass black hole at the center of our galaxy. We're not considered an "Active Galaxy" only because it is on a diet.

Apparently by Timesprout · 2006-10-07 18:53 · Score: 1

They are black and holey

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Re:Apparently by Tablizer · 2006-10-07 19:20 · Score: 5, Funny

They are black and holey

Oh great, did you have to bring race *and* religion into this?

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Table-ized A.I.
Re:Apparently by Anonymous Coward · 2006-10-07 23:06 · Score: 0

They are black and holey

Oh great, did you have to bring race *and* religion into this?

And they smell like fish :(

Why is he feeling lucky? by maroberts · 2006-10-07 18:54 · Score: 3, Interesting

Almost every major galaxy including the Milky Way has been found to have a supermassive black hole at its core. The only lucky part is our sun not being near to the core of the galaxy, not which galaxy it is in.

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Re:Why is he feeling lucky? by Rakshasa+Taisab · 2006-10-07 19:04 · Score: 1

Yeah, I was going to comment on that same thing... We got an aprox. ~2.6 billion solar-mass black hole according to our latest calculations. (From amongs other things observing stars orbiting rather close to it)

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Re:Why is he feeling lucky? by Rakshasa+Taisab · 2006-10-07 19:07 · Score: 1

That would be million, not billion, thinko.

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Re:Why is he feeling lucky? by Entropy · 2006-10-07 19:19 · Score: 1

He is probably feeling lucky because the supermassive blackhole at the center of our galaxy is not an AGN .. not active. Not "feeding". Of course, given that the article says only a few percent are active, it's not exactly "lucky". *shrug*

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Re:Why is he feeling lucky? by MillionthMonkey · 2006-10-07 19:20 · Score: 1

That would be million, not billion, thinko.
Actually the active nucleus in M87 is 2-3 billion solar masses, billion with a "B".
Re:Why is he feeling lucky? by kestasjk · 2006-10-07 19:29 · Score: 1

That's like saying "Isn't it lucky we live on a planet which has water to drink!"; it's not "lucky", we could only have evolved on a planet which had water to drink.

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Re:Why is he feeling lucky? by LakeSolon · 2006-10-07 19:44 · Score: 1

This is known as the Anthropic Principle.
Re:Why is he feeling lucky? by gomoX · 2006-10-07 20:33 · Score: 1

If we were unlucky enough we could have evolved on a planet were the timing for our understanding of supermassive black holes and the annihilation of our solar system were perfectly synchronized. Actually, given the amount of different "universes" there are out there (observable universes) this is very likely to happen somewhere at some point.

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Re:Why is he feeling lucky? by Anonymous Coward · 2006-10-07 21:37 · Score: 0

Milky way != M87

Wait a minute here by MsWillow · 2006-10-07 19:05 · Score: 1

Our galaxy is about 100,000 light years in diameter. Every galaxy that revolves around a supermassive black hole within 400 light-years of our own galaxy has been cataloged.

Given the size of our galaxy, just how many other galaxies are within 400 lightyears of us, AGN or not? Or am I just massively confused here?

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Re:Wait a minute here by Tablizer · 2006-10-07 19:26 · Score: 1

just how many other galaxies are within 400 lightyears of us

Thousands, according to this website.

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Table-ized A.I.

Is this survey to be trusted? by EmbeddedJanitor · 2006-10-07 19:07 · Score: 2, Insightful

Considering our space boffins have a problem seeing large asteroids really close up -- not even one light second away -- http://www.cnn.com/2002/TECH/space/06/20/asteroid. miss/ why should we believe that they have seen all the black holes many light years away?

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Engineering is the art of compromise.

Re:Is this survey to be trusted? by Harmonious+Botch · 2006-10-07 19:38 · Score: 4, Informative

Considering our space boffins have a problem seeing large asteroids really close up -- not even one light second away...why should we believe that they have seen all the black holes many light years away?"

Because black holes - or, to be precise, the region in space right next to them - emit a lot more radiation. A LOT MORE.
Re:Is this survey to be trusted? by Anonymous Coward · 2006-10-08 01:24 · Score: 0

That, and the center of a given galaxy is rather trivial to find, as opposed to a random lump of rock that's not even constrained to the plane of the ecliptic.
Re:Is this survey to be trusted? by CK2004PA · 2006-10-08 12:55 · Score: 1, Funny

You are an idiot. Asteroids to galactic core? That's like comparing the Atlantic ocean to tiny microscopic organisms, that only live at the bottom of the ocean floor. Actually thats not even a good analogy.
A better analogy is an asteroid to a galactic core. Moron.

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Science for science sake by bripod82 · 2006-10-07 19:09 · Score: 1

In an era where there's no funding for anything, where I'd like the secrets of the universe revealed in my small lifetime, I'm genuinely excited that observations and projects like these are being conducted. Thank you NASA. I'll add that I wish that NASA's budget wasn't so tied to defense subsidy. Science for science's sake is a dream I hope we achieve soon.

Re:Science for science sake by gomoX · 2006-10-07 20:30 · Score: 1

That's not gonna happen. The axis of evil doesn't wan't you to know the secrets of the universe, because they are *evil*. They must be terminated. Now give me all your science budget for my military program please.

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Re:Science for science sake by Impy+the+Impiuos+Imp · 2006-10-07 23:18 · Score: 1

> In an era where there's no funding for anything

An odd statement given the US government is spending $2 trillion (with a T, not a B or M) per year, a rate that, adjusted for inflation, exceeds per capita any other year in history except for one year during WWII, in which we were engaged in two major war fronts simultaneously and were building a major capital ship per week.

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Re:Science for science sake by Ant+P. · 2006-10-08 03:08 · Score: 1

Source? 2 trillion on what? It's definitely not on the space program.
Re:Science for science sake by fireboy1919 · 2006-10-08 08:20 · Score: 1

To quote Star Trek (specifically Q, in the last episode of TGN), the future is "not mapping stars and studying nebula but charting the unknown possibilities of existence."

This isn't science for science's sake. Figuring out how things work is science for science's sake. This is science for scientists that are hunting for something to figure out; it's science for accountancy. I'm not sure that this isn't worse than science for practical applications.

Which do you think kills the imagination faster? Busy-work counting stellar phenomena, or making things that are actually useful but aren't at all based on new, theoretical concepts?

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Family Feud? by KewlioMZX · 2006-10-07 19:12 · Score: 3, Funny

100 black holes surveyed, top 5 answers on the board...

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Re:Family Feud? by uvajed_ekil · 2006-10-07 20:03 · Score: 1

100 black holes surveyed, top 5 answers on the board...
Show me "protoid capsules"!

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Wrong by WhiteSpade · 2006-10-07 19:23 · Score: 5, Interesting

The article says that it is every super massive black hole within 400 million light years. Also, as for being "lucky" to be in the Milky Way, our Galaxy has a super massive black hole at the center of it. Actually, we are a very typical galaxy. We are slightly larger than the average and we are a spiral galaxy (there are more elliptical galaxies and irregular galaxies than spiral). We are very typical. Also, as for being lucky about not being closer to the center of the galaxy (someone above mentioned that as well) if we were closer to the black hole at the center, it would not mean much. We are in an orbit around it and thus we won't be falling into it any time soon, even if we were closer to it. We do, though, have a great location in the galaxy. We are far enough out that we can look across the plane of our galaxy (only at some wavelengths because dust obscures a lot) and get a good view of it. We also can look out pretty well too. And to make things even cooler, our solar system actually bobs up and down through the main plane of the galaxy. It take about 30 million years to complete a complete cycle, but in 5 or so million years we will have a pretty cool view from above of the Milky Way. I don't remember exactly what the angle is that we would be viewing the galaxy from, not huge, but enough to be useful. The point of all this is that the advantage of this survey is to have a complete list of super massive black holes so as we are testing out theories we can apply these theories (and how they measure up) across not only a wide data set, but also a very complete set. There is so much left to be learned about black holes and this catalogue will certainly help.

Re:Wrong by Anonymous Coward · 2006-10-07 20:39 · Score: 0

And maybe in another 5 billion years, you will figure out how to break your text into paragraphs so it doesn't seem like one gigantic run-on sentence, but of course no human will be left alive in 5 billion years so it won't actually make any difference, and in fact, by that time the sun will have expanded and destroyed the Earth so there won't even be semi-intelligent pond slime left alive to look across the galactic plane and wonder where the hell it all went so very wrong.
Re:Wrong by jamesh · 2006-10-07 22:03 · Score: 1

One good thing about being out where we are (the unfashionable end :) is that there should be less crap flying around to crash into us, eg like other solar systems.
Re:Wrong by Anonymous Coward · 2006-10-08 00:27 · Score: 0

Actually to be slightly more technical, the Milky Way is a barred Spiral Galaxy. We are also a bit more lucky in our placement than you described. If we were too close to the center of the Galaxy where the density and the sizes of stars are greater, radiation from a significant number of supernovas in our galaxy's history would have probably destroyed any chance at life or at least have made it much more primitive due to periodic mass extinctions. But if we were a little further out we wouldn't have gotten the complexity of our solar nebula necessary for life as we know it (where we are at least the remnants of the nuclear processes and subsequent novas of 2 previous generations of stars).

but in 5 or so million years we will have a pretty cool view from above of the Milky Way.

Umm, great. That's really useful. It's like telling me that we can perform another Voyager Grand Tour in another 100 years. It is technically useful, but just not to anyone who is actually living.
Re:Wrong by ZorbaTHut · 2006-10-08 02:27 · Score: 1

It probably says a lot about me that I just thought "Wow! Only 5 million years! I can hardly wait!"

24 years down, 4,999,976 to go!

--
Breaking Into the Industry - A development log about starting a game studio.

Whoop-te-doo by Anonymous Coward · 2006-10-07 19:32 · Score: 0

That's big news.

Super Miniature Particles by c0d3r · 2006-10-07 19:33 · Score: 1

Now if they will announce a completion of a survey of super Miniature fundamental particles...

Survey? by talkingc · 2006-10-07 19:38 · Score: 1

"NASA has announced the completion of a survey of nearby supermassive black holes. Every galaxy that revolves around a supermassive black hole within 400 light-years of our own galaxy has been cataloged.

I'm sure they didn't get every galaxy... You know how things go with censuses; there were probably some galaxies that didn't care about it and claim the form they sent back was lost in the mail or something.

The Milky Way Galaxy by Kamineko · 2006-10-07 19:41 · Score: 1

The other galaxies are nowhere near as tasty!

But, today I learned an interesting fact about the milky way bar.

Re:The Milky Way Galaxy by Anonymous Coward · 2006-10-08 16:15 · Score: 0

Your post reminds me of an old scifi short story called "Thang", by Sturgeon or Van Vogt or somebody --- Thang was a creature who wandered around the Galaxy eating moons, planets, and stars like so many grapes. Then one day he felt himself being grabbed by the nape of his neck and lifted up, and he barely had time to see the giant-toothed maw beneath him getting ready to gobble him up. The last line in the story was something along the lines of, "There are greater things in creation than you, Thang."

Say, that reminds me --- If THEY are out there, are THEY friendly? What if THEY are hungry? I wonder how many solar systems are within a sixty light-year radius of the earth? Could the fleet from Yug-Suggoth be on its way already?

Comments from NASA on the survey by elmartinos · 2006-10-07 19:44 · Score: 1

Unfortunately, the survey everything but a a success. From the many questionnaires sent out by NASA, none of the black holes returned a completed form. Fortunately, NASA seems to learn from its mistake. The next questionaire will have much less and easier questions which should dramatically increase the response ratio.

--
Open Source Alternatives

Re:Comments from NASA on the survey by Ed_1024 · 2006-10-07 20:02 · Score: 1

Ah but they DID fill in the questionnaires - unfortunately the postmen can't make it back past the event horizons. Maybe they should start examining the Hawking Radiation for replies...

Density of black holes by Harmonious+Botch · 2006-10-07 19:47 · Score: 4, Informative

The average density of a supermassive black hole can be very low, and may actually be lower than the density of water.

That sounds suspicious, especially coming from wikipedia. Something with a density that low could not likely bend light enough to keep it from escaping, even if very large.

The singularity that bends light does not have that low density. It has an incredibly high density. But the AVERAGE density is the mass of the singularity divided by all that space inside the event horizon.

Re:Density of black holes by Beale · 2006-10-07 21:29 · Score: 1

Bad Analogy O'Clock: Defining the size of a black hole by it's event horizon is like defining a river by its watershed. The actual physical object is a point in the middle, not the large sphere of non-escaping stuff around it.
Re:Density of black holes by gedhrel · 2006-10-07 22:05 · Score: 1

By what definition of "actual" and "physical" (and "is")?
Re:Density of black holes by GeffDE · 2006-10-08 01:13 · Score: 4, Informative

No, the actual physical object is the volume inside the event horizon. Why is it called a black hole? Because anything that entered the event horizon does not escape. So a black hole is the volume enclosed by the event horizon. The singularity is the extraordinarily dense pit of gravity at the center of a black hole. They are two different things. Defining the size of a black hole by its event horizon is...how it should be done, if you think about it. The "object" in the middle is was causes all the action to happen, but that doesn't make it the only part of a black hole.

--
It has been a nervous year, with people beginning to feel like Christian Scientists with appendicitis.
Re:Density of black holes by Omnifarious · 2006-10-08 03:29 · Score: 1, Interesting

The actual physical object is a point in the middle, not the large sphere of non-escaping stuff around it.

So, you've seen this thing in the middle? What's it look like? Enquiring minds want to know!

You are possibly a troll, but it's rather standard to define the size of a black hole by the size of its event horizon. This is largely because we can't actually know anything about what there is behind the event horizon. Maybe there's a singularity there, and maybe there isn't. What we know of physics says there ought to be, but it seems impossible to observe, and trusting our physical theories in such extreme conditions is a big step of faith.

So, yes, in all the various articles about black holes that I've read, their size is defined by the size of their event horizon.

There are theories that posit the Universe is actually two-dimensional and that our experience of it as three-dimensional is actually more like a holographic projection of the two-dimensional reality. These theories are based on the relationship between a black hole's mass and its size that suggest that all the mass of a black hole is actually on the surface of the event horizon.

--
Need a Python, C++, Unix, Linux develop
Re:Density of black holes by Anonymous Coward · 2006-10-08 04:43 · Score: 0

There are theories that posit the Universe is actually two-dimensional and that our experience of it as three-dimensional is actually more like a holographic projection of the two-dimensional reality. These theories are based on the relationship between a black hole's mass and its size that suggest that all the mass of a black hole is actually on the surface of the event horizon.

The mass of a black hole is a global property of spacetime and is not "located" at any particular place. Holography states that the dynamical degrees of freedom are encoded in the horizon of the black hole, which is a somewhat different idea.
Re:Density of black holes by cbacba · 2006-10-09 01:53 · Score: 1

Sorry, but the original poster and wiki are correct. For a non rotating black hole - the classical original one - The schwartzchild radius (event horizon) is a function of Mass and 1/r - size. It's linear while density is a function of mass and 1/r^3 (volume).

There are the assumptions that 1) the equations are accurate inside the radius and 2) that there is nothing left to stop the collapse from happening further - hence that there must be a singularity (single point) inside the event horizon. However, to the distant observer, time slows down for a body falling into the event horizon. Hence, a question occurs - does a black hole form during the lifetime of the universe (according the distant or relatively unaffected observer) or is it still in the process of forming. Another question is do the same laws of physics apply within the even horizon? Does it work without the point mass (singularity) but rather with a mean density? Finally, the question arises that since it's not a condition of high density, is it possible that the schwartzchild radius is an artifact or a problem of the mathematics?

In any case, it might not be a matter of luck that we are in an area without AGN or quasars. It might simply be that life couldn't exist very long in such an area. It's also possible (or even probably) that all supermassive black holes have 'feeding binges', perhaps even the puny multimillion solar mass critter in the milky way, but I doubt it takes that one to obliterate any prospects of life in our galazy. After all, andromeda has something 10x the size of ours - and it's headed our way eventually to merge and that could be a real humdinger.

Global warming can happen in an instant. One moment you're breathing air, the next breathing a vacuum, and the next you're just floating atoms in space, surrounded by all of the atoms of all the oceans of the earth. It doesnt make for a good movie - and there's no chance of a sequal.
Re:Density of black holes by Anonymous Coward · 2006-10-09 02:29 · Score: 0

Sorry, but the original poster and wiki are correct.

What do you mean, "sorry"? The parent agreed with the original poster and Wikipedia, just clarifying that what was being referred to was the average density of the black hole, not the density of the singularity. (However, the parent did refer incorrectly to the "mass" of the singularity; the singularity's mass is undefined, and the mass of a black hole is associated with the entire spacetime in which it resides, not just the singularity within.)

Hence, a question occurs - does a black hole form during the lifetime of the universe (according the distant or relatively unaffected observer) or is it still in the process of forming.

A distant observer never sees the black hole "fully form" (although there is a finite time at which a distant observer can see any light from the hole). However, an infalling observer can enter a fully-formed black hole, so in that sense, the black hole does form, regardless of whether a distant observer ever sees that happen.

Another question is do the same laws of physics apply within the even horizon?

Yes. If they broke down just inside the horizon, you wouldn't even have a black hole, which by definition involves spacetime both inside and outside of a horizon. However, the laws of physics as we know them probably break down near the singularity.

Does it work without the point mass (singularity) but rather with a mean density?

No; there are no solutions of the Einstein field equations which have a static mean density inside. You could, however, perrhaps continually fill a growing black hole with a mean density of continuously infalling matter.

Finally, the question arises that since it's not a condition of high density, is it possible that the schwartzchild radius is an artifact or a problem of the mathematics?

No. It's just that event horizons don't have anything directly to do with "density". We could be inside an event horizon right now and not know it.
Re:Density of black holes by Omnifarious · 2006-10-11 15:36 · Score: 1

Ahh. :-) That's actually an interesting distinction. I'm not sure how I can state that in a way that reduces the MEGO factor of the people who read it.

--
Need a Python, C++, Unix, Linux develop
Re:Density of black holes by Anonymous Coward · 2006-10-13 04:01 · Score: 0

Well, it depends upon what your definition of "definition" is, after we agree on the definition of "is"

There are no black holes by viking80 · 2006-10-07 19:53 · Score: 5, Interesting

First, the diameter of a "black hole" is proportional to its mass. The sun, for example, must be compressed to a diameter of about 3km to become a black hole. A black hole with the mass of billion suns would have a dameter=3 billion km or 1000 times our solar system. The density of this black hole would be "low" as in much thinner than air. (Do the math yourself. Mass of sun is 2x10E30kg)

Anyway, as a region of space gets denser, time slows down, and as the density approaches the density required to become black hole, time just freezes.

What you will see when looking at a "black hole" is just a region of space with the eventual event horizon of the hole just frozen in time, and as you move outside, time goes through the "molasses" stage, and as you get further away, gets normal.

The black hole will not form in any finite time since time there just stopped!

For the observer falling towards the "hole", time in the rest of the universe just speeds up. In a matter of minutes the universe will age billions of years, and the observer will first hand know the ultimate fate of the universe in a distant future.

--
don't cut it off www.mgmbill.org

Re:There are no black holes by Anonymous Coward · 2006-10-07 20:05 · Score: 0

Small correction:

The 3km diameter and 3 billion km diameters you are refering to are the diameters of the event horizon. The black hole itself is a singularity, where the density of matter approaches infinity.

So no, density of the black hole is not 'low'.
Re:There are no black holes by Anonymous Coward · 2006-10-08 01:18 · Score: 0

We must be careful not to be too loose and fast with the word 'time'. The black hole would take infinitely long to form according to an outside observer's watch, but in the proper time of the matter which is collapsing it is a nice, smooth process completed in a finite amount of time.

For the observer falling into the hole, the rest of the universe appears to run faster and faster, then he/she moves smoothly past the event horizon. Inside of the horizon experience would be very different than it is outside, since the metric in that region is somewhat backwards in that time and radial distance change signs.
Re:There are no black holes by 72Nova · 2006-10-08 02:12 · Score: 1

So here is a common misconception. The "size" of the blackhole that you are talking about is it's Swarzchild radius, which has nothing to do with where the mass actually is. Nearly all of the mass is compacted into a tiny volume at the center. The Swarzchild radius is simply the point at which anything that comes closer will inevitably fall into the center, and has no way of escaping. Black holes do form in finite amounts of time. An observer, or any mass, which is falling into the blackhole will not feel any different passing the "event horizon" which is roughly at the swarzchild radius. Life will continue basically as normal until tidal forces from the differential gravitational force on the part of his body closer to the center compared the parts which are further away rips them to shreds. It would not be so pleasant as watching the ultimate fate of the universe.
Re:There are no black holes by Progman3K · 2006-10-08 04:52 · Score: 1

That is considering the observer's vantage point remains stable until the end of the universe...

I expect that if you were close enough to a black hole to experience time outside going by whizzingly fast WITHOUT you being torn apart by gravitational forces it would indeed be quite a show, but just as likely some other object would whiz right into you billions of years hence and your lookout would end.

--
I don't know the meaning of the word 'don't' - J
Re:There are no black holes by mark_osmd · 2006-10-08 06:27 · Score: 1

"black hole with the mass of billion suns would have a dameter=3 billion km or 1000 times our solar system" You think the solar system is 3 million km wide? It's more like 12 billion km wide if you use the orbit of pluto which is 39.5 AUs in radius. Mark
Re:There are no black holes by Black.Shuck · 2006-10-08 07:51 · Score: 1

The black hole itself is a singularity
You sound very sure of yourself. ;)
Re:There are no black holes by Xerxes314 · 2006-10-08 11:30 · Score: 1

Way to make yourself look like a jackass by spouting off about something you don't understand. Time only appears to distant observers to stop at the event horizon, because there is a coordinate singularity at that point. Essentially, all the light that is being emitted from the body falling in gets hung up at that point for an arbitrarily long amount time. Over the rest of the age of the universe, that light (ever more redshifted) will trickle out from just above the horizon. The object itself will fall onto the singularity in a very short amount of time.
For more information, read Falling into a Black hole (with nifty animations). Specifically, see answer to question 5. Or see question 3 of the Black Hole FAQ.
Re:There are no black holes by Anonymous Coward · 2006-10-08 17:11 · Score: 0

I don't have a slashdot account and don't care to create one for just this one reply.

Time doesn't "freeze."
For an observer falling into a black hole time would pass normally for them; they wouldn't see the universe age before them, they would just fall in and get eventually get torn apart by tidal forces or killed by blueshifted radiation. As they fell in they would see the universe above them get smaller until it was concentrated into a single point (if they lived that long, depending on the size of the black hole), but that's it.

On Purpose? by tokki · 2006-10-07 19:54 · Score: 2, Insightful

I wonder if the editors purposefully put factual errors in there just to sit back and watch the orgie of "OMG NO THATS WRONG" comments that invariably follow. 400 light years? Of course it's a mistake. Is there anyone who reads /. that doesn't know that 400 light years is a little close for a galaxy? Of course, there are those that get positively horny over the propsect of correcting factual errors.

Because hey, trivia = intelligence, right?

Re:On Purpose? by Anonymous Coward · 2006-10-07 21:07 · Score: 0

No, it's because lol=yuo.
Re:On Purpose? by Tim+C · 2006-10-07 22:16 · Score: 1

Is there anyone who reads /. that doesn't know that 400 light years is a little close for a galaxy?

Yes, I'd expect most of the readership to not realise that in fact. This is a general techy website, not an astro one. Would you expect most people here to know how solar cells work, or how to construct a thermocouple?

--
It's official. Most of you are morons.
Re:On Purpose? by gardyloo · 2006-10-08 06:15 · Score: 1

Yes, I'd expect most of the readership to not realise that in fact. This is a general techy website, not an astro one. Would you expect most people here to know how solar cells work, or how to construct a thermocouple?

Perhaps not. But I'd expect someone who is consolidating this information to at least do rudimentary fact-checking so as to not spread misinformation.
Re:On Purpose? by tokki · 2006-10-08 15:07 · Score: 1

You really don't think that something that anyone who payed attention in 7th grade science class (which would be just about any /. read) would pick up a little bit of a sense of galactic scale? I think you underestimate the comprehensive ability of the readership, or you overestimate yours (or both).

If you're gonna say that by Rhinobird · 2006-10-07 20:07 · Score: 1

If you're gonna say that, you need to do that Dr Evil pinky thing.

--
If Mr. Edison had thought smarter he wouldn't sweat as much. --Nikola Tesla

But we do live next to one.. by plasmacutter · 2006-10-07 20:13 · Score: 0, Troll

well americans do anyway.. the federal budget has been sucking up everything in sight for over 40 years now.

--
VLC FOR MAC IS DYING! IF YOU DEVELOP, PLEASE SAVE IT!!

Look! A Klemperer Rosette! by jvance · 2006-10-07 20:18 · Score: 1

Was that the Fleet of Worlds that just zoomed past?

hm... by FFT99 · 2006-10-07 20:36 · Score: 1

It seems to me that humans wouldn't have evolved on Earth if these super massive black holes were not located at just the right distance.

It reminds me of the series finale of Star Trek TNG.

BUT by traveller604 · 2006-10-07 20:50 · Score: 0

Do they have hair?

You might enjoy this: by PaulBu · 2006-10-07 20:51 · Score: 1

http://www.reason.com/rb/rb100606.shtml

Paul B.

Re :2 Wrongs don't... by MollyB · 2006-10-07 21:43 · Score: 1

I think your criticism is unwarranted. Slashdot is a place where people's ideas outrun their grammatical and paragraph structure awareness. This naturally produces some messy results. Would you want a brainstorming session to consist of complete sentences Only? Some documents would benefit from your prescription, for others it is just nitpicking.

Consider the context of the discussion before satirizing with mean spirit. I'll admit that your rejoinder was humorous--just a cheap shot, imho.

README by leonbrooks · 2006-10-07 21:46 · Score: 1

Read Me now!

Yes, it does make a difference. (-:

--
Got time? Spend some of it coding or testing

Re:README by Anonymous Coward · 2006-10-08 02:44 · Score: 0

Not just a creationist but a physics crackpot too. You're not doing to good on the "understanding of science" front, are you? Why don't you go over to the global warming thread and deny the existence of anthropogenic global warming to make a clean sweep of it?

That explains things by ndogg · 2006-10-07 21:52 · Score: 1

So it wasn't aliens abducting people and probing their asses all these years.

--
// file: mice.h
#include "frickin_lasers.h"

Re:Re :2 Wrongs don't... by Tim+C · 2006-10-07 22:09 · Score: 0, Offtopic

While the AC could have made his point in a rather less confrontational way, he *does* have a point. When I see a large block of text like that, my immediate reaction is to move on and read something else instead.

Would you want a brainstorming session to consist of complete sentences Only?

This isn't a brainstorming session. There is nothing at all to be gained (or lost) based on time to posting, and no reason other than inability or lack of respect for your reader to not structure your post well.

English has certain rules, and I am frequently surprised that in a place mainly frequented by techies well used to having to get config files and code syntactically and structurely correct that so many people seem to delight in ignoring them.

--
It's official. Most of you are morons.

The catalog (karma whoring) by nyri · 2006-10-07 22:14 · Score: 2, Funny

Every galaxy that revolves around a supermassive black hole within 400 light-years of our own galaxy has been cataloged.

The whole catalog:
1. Our own galaxy

Breaking news from the starship 'Long Shot'... by meringuoid · 2006-10-07 22:24 · Score: 1

Hate to break it to you, but there's a >million solar mass black hole at the center of our galaxy. We're not considered an "Active Galaxy" only because it is on a diet.

Hate to break it to you, but, er, that information's actually a little out of date...

Hey, where the hell did all the puppeteers just go?

-- B. Shaeffer

--
Real Daleks don't climb stairs - they level the building.

Shouldn't That Be 400 MILLION Light Years? by DaWalrus · 2006-10-07 22:47 · Score: 1

400 light years is a tad close for Active Galactic Nuclei...

Black and holy? That'd be Archbishop Desmond Tutu. by Channard · 2006-10-07 22:51 · Score: 1

So just what do Nasa think they're doing focusing their telescopes on his house? Are they trying to see what lottery numbers he uses?

rules of English. by MollyB · 2006-10-07 22:53 · Score: 0, Offtopic

I agree that languange usage should be prescriptive, rather than descriptive. However, language evolves, and those that prefer strict rules usually insist on the ones they learned at a formative stage. This contributes to an unending conflict of whose rules have currency.

I used the example of brainstorming in general. I didn't say /. was such. Your point misconstrues my justification of an enthusiastic poster; he/she was more interested in the content rather than the form. If you don't want to read long blocks of text, so be it.

I'm not a fan of sloppy construction. However, I don't take the view that I'm being dissed if a poster happens not to *know* the rulz.

Further, since your user# is what it is, you may have not noticed that a good deal of posters here are not necessarily coders anymore, but they like to discuss other relevant topics as well.

Oh, well. I've gone off-topic for too long. (/rant)

Sure, they took a survey... by Anonymous Coward · 2006-10-07 23:22 · Score: 0

but how many responded?

Super Massive Black Hole by webgeek2point0 · 2006-10-08 01:27 · Score: 1

That's not a Super Massive Black Hole. It's a space station!

--
"End of Line." - MCP

There are black holes by Anonymous Coward · 2006-10-08 02:03 · Score: 0

The black hole will not form in any finite time since time there just stopped!

This is wrong. There is a finite set of events at which the horizon forms; we can just never see it form. See this FAQ.

For the observer falling towards the "hole", time in the rest of the universe just speeds up. In a matter of minutes the universe will age billions of years,

This is also wrong. A similar misconception is described in this FAQ.

Lucky Or Inevitable? by Anonymous Coward · 2006-10-08 02:13 · Score: 0

" I'm starting to feel very lucky to have grown up in the Milky Way Galaxy."

Maybe the Anthropic Principle wouldn't have it any other way...

Re:Lucky Or Inevitable? by antispam_ben · 2006-10-08 12:24 · Score: 1

" I'm starting to feel very lucky to have grown up in the Milky Way Galaxy."

Maybe the Anthropic Principle wouldn't have it any other way...

In fact, The Anthropic Principle was invented just for such people.

--
Tag lost or not installed.

DON'T TRUST THESE RESULTS!!! by Anonymous Coward · 2006-10-08 02:34 · Score: 0

I am a massive black hole, I took this survey, and I answered C on every question, because even powerful galactic anomalies like myself think surveys suck.

Re:DON'T TRUST THESE RESULTS!!! by chris.evans · 2006-10-08 15:30 · Score: 1

Straight in down the middle and the gravity is too powerful to resist.

Corrections by usmc1944 · 2006-10-08 04:43 · Score: 1

>I'm starting to feel very lucky to have grown up in the Milky Way Galaxy." And why is that? Your galaxy has one too, puny human! >Every galaxy that revolves around a supermassive black hole within 400 light-years of our own galaxy has been cataloged eHM... That's supposed to be 400 MILLION light years, not 400. The nearest Galaxy, Andromeda, is 2 million light years away.

Black hole opinions overwhelmingly negative by Kohath · 2006-10-08 06:27 · Score: 1

They black holes who answered the survey overwhelmingly disapprove of the Bush Administration. Most blame Bush directly for their woes. "George Bush doesn't care about black holes" was a common sentiment.

Blame for Dick Cheney was surprisingly sparse, despite the gravitas he added to Bush's presidential bid in 2000.

Time distortion by Anonymous Coward · 2006-10-08 06:40 · Score: 0

My understanding is that if we did live next to a black hole there would be time distortion, relative to the rest of the universe. If that's the case, then our solar system's lifespan (local perception) would still be the same... wouldn't it?

While on the subject... supposedly time distortion reaches infinity at the event horizon. So, doesn't that mean that black holes have never had the time to actually "swallow" anything?

...but 78 billion light years is TOO far by Roger+W+Moore · 2006-10-08 09:08 · Score: 2, Informative

The narrator on the video keeps going on about look 78 billion light years into the universe but that is wrong. The universe only formed 13.7 billion years ago so the furthest we can see is 13.7 billion light years due to relativity. Inflation may mean the Universe is bigger bit we will not be able to see it if it is.

In actual fact the WMAP probe is the furthest we have seen, NOT the Hubble deep field since that looks at the Universe ~300k years after the Big Bang before there were any stars, let alone galaxies.

That said it was a nice video but it would have been nicer if they got their facts correct when trying to sound impressive!

Re:...but 78 billion light years is TOO far by Anonymous Coward · 2006-10-08 13:34 · Score: 0

The narrator on the video keeps going on about look 78 billion light years into the universe but that is wrong. The universe only formed 13.7 billion years ago so the furthest we can see is 13.7 billion light years due to relativity.

No, you're wrong. That ignores the nonlinear expansion of the universe. Actually, the observable universe can be any size, depending on how the universe expands; it can be far larger then 13.7 billion years. See this FAQ.
Re:...but 78 billion light years is TOO far by Anonymous Coward · 2006-10-08 20:41 · Score: 0

78 billion light years is the comoving distance between the Hubble telescope and the further-away galaxies in the ultra deep field study (HUDF).

At an apparent distance of a little more than 13 billion light years, the acceleration due to Hubble exapnsion is huge. As a result, the redshift is significant -- light in the visible spectrum emitted at the source is shifted into the infrared by the time it gets to us. Hubble was scanning in the visible spectrum here, so it was really looking at ultraviolet emissions from the source, which are redshifted down to the visible range.

The 78 billion light year figure is the distance now between us and the highly redshifted galaxies in HUDF. The universe kept expanding during the ca 13 billion years since those photons were emitted, carrying our part of the universe and theirs ever further apart.

Describing the figure as the present distance between us and the furthest galaxies would be clearer and more accurate than describing it as the proper-distance radius of the observable universe. However, the 78 billion light year figure was arrived at through the WMAP observations.

Guth, who first formally proposed cosmic inflation, has made good estimates of the ratio of the observable universe to the entire universe (most of which is beyond the particle horizon) of on the order of 1:1e23.

At these scales, small differences in estimates of dark energy non-linearities and calculations of the Hubble law lead to large error bars, but essentially the universe is a biiiiiiiiig place, and the volume of space with a present radius of ca. 7.4e26 metres is only that part of it that contains particles which we can "see" by looking into the past up to ca. 14 billion years. This volume of space is considered "small" given WMAP observations' consistency with cosmic inflation.
Re:...but 78 billion light years is TOO far by Roger+W+Moore · 2006-10-09 12:26 · Score: 1

Sorry but that is an absolutely crazy thing to quote the "distance to the object now". First we cannot measure it - we are extrapolating based on WMAP data as to the expansion of the universe - linear or otherwise it doesn't matter - and as this data suggests that we don't know what 96% of the universe is I have some doubts as to how reliable this is. Secondly there is no guarentee that the object even exists any more!

In summary it seems like saying "This computer I just bought will be over 1,000 years old in the year 3006 so it's a valuable antique!".
Re:...but 78 billion light years is TOO far by Roger+W+Moore · 2006-10-09 12:32 · Score: 1

As I pointed out to the previous poster it seems crazy to quote the distance now to an object which we are no longer sure even exists and for which, as you mention, we really can't do the extrapolation....but then again I'm an experimentalist and like to stick with real numbers rather than wild extrapolations.
Re:...but 78 billion light years is TOO far by Anonymous Coward · 2006-10-09 13:21 · Score: 0

Sorry but that is an absolutely crazy thing to quote the "distance to the object now".

Sorry, but it's the only thing that makes sense in this context, because the only preferred spatial slices in an expanding homogeneous spacetime are the ones of constant proper cosmological time. The rate of the universe's expansion is measured by how quickly the universe changes its size between two times. If you want to know how much bigger the universe has gotten before "then" and "now", the only meaningful way of doing it is by comparing the size of the universe "then" to the size of the universe "now".

But if you doubt me, go ahead, try to define some other way of measuring the rate of the universe's expansion when spacetime is curved. Tell me what your definition is.

First we cannot measure it - we are extrapolating based on WMAP data as to the expansion of the universe

Of course we can measure it. Most of the measurements we make in physics are inferred indirectly. Do you think we measure the size of a proton with a tiny little ruler? No, we infer it based on scattering amplitudes.

and as this data suggests that we don't know what 96% of the universe is I have some doubts as to how reliable this is.

We don't have to know what 96% of the universe is in order to know how big it is. In fact, it is our measurements of the universe's size (or rather its rate of expansion) that tells us that there is more to the universe than what we know, not the other way around. Furthermore, we have a much better handle on distances by combining CMBR measurements with the independent measurement of standard candle luminosities.

Secondly there is no guarentee that the object even exists any more!

That's irrelevant to the question of how big the universe is or how fast it expands.
Re:...but 78 billion light years is TOO far by Anonymous Coward · 2006-10-09 13:46 · Score: 0

As I pointed out to the previous poster it seems crazy to quote the distance now to an object which we are no longer sure even exists

We can be pretty sure it doesn't exist, at least not in the same form. Thirteen billion years is a long time, much longer than stellar lifetimes of more massive stars, and enough time for many of the mid-sized stars to have fallen out of the main sequence.

However, this is simply an exercise in (very) large scale dynamic field distribution, as is done at many other scales in physical disciplines. The only thing that makes it "spooky" is the expansion of the universe, and there are analogues to that in other field theory using disciplines as well.

as you mention, we really can't do the extrapolation.

We can do the extrapolation, which is limited by the proper distance of the furthest causally connected particle and much closer to here.

There is a limit to the distance of the photons moving through expanding space in all directions, and we can factor in a reasonable (as in consistent with observations) Hubble law, and take the longest and shortest vectors (particles moving at various speeds directly along a geodesic crossing the distant galaxy).

At the scales involved, local motion of the galaxy relative to its local group (and us) is insignificant unless something really unexpected happens, so we can reasonably assume (and expect observational evidence) that the mass of the galaxies is moving with respect to us only at Hubble speeds.

This gives us a range between the maximum and minimum distances if the entire galaxy suddenly exploded 13 billion years ago and turned into highly energetic photons, neutrinos, or whatnot moving at close to the speed of light, and the more probable distance to the evolved galaxy (new stars, new gas clouds, and similar objects, about which we have good observation-backed theory) that has moved almost entirely by the expansion of the universe over the past 13 billion years along a path directly away from us (relatively speaking).

The critical assumption is that space expands uniformly enough at large scale

WMAP provides good observational evidence backing that critical assumption.

It is fair to claim that our estimates of the present distances to the galaxies visible in HUDF are known to +/- 2e21 m and with those error bars the furthest is at 1.2e26 m. The uncertainty is almost entirely with respect to the Hubble flow.

WMAP's data is consistent with a Hubble flow of 71+/-4 (km/s)/Mpc.

There is a great deal of observational data available in the sky; cosmology's take on experimental science is to formulate a hypothesis and look for evidence. There were a strong set of hypotheses involved in the cosmic inflation part of WMAP's mission, and several flavours of that theory (and a number of competing theories) are inconsistent with WMAP's observations.

All that said, it is fair to think that the video was using the largest number consistent with our understanding of the size of the causally connected (visible) part of the universe mostly because 78 is a bigger number than 14, and so gets a bigger "wow".

(Heh, sorry that you're being tag-teammed by Anonymous Cowards).
Re:...but 78 billion light years is TOO far by Roger+W+Moore · 2006-10-10 05:38 · Score: 1

I think you and I are addressing different questions. I completely agree that the existance of a distant galaxy is irrelevant to the size of the Universe but when the narrator in the video says "these galaxies are 78 billion light years away" they are NOT 78 billion light years away in the photograph shown and likely do not existing in anything like the same form now. Thus my objection is to extrapolating the distance observed to the distance now without saying so.

If I understand correctly you can get from the WMAP data by itself the age and expansion of the universe which is all you need to calculate the current size so how does this image improve on that? You can't measure the Hubble constant from this image can you?

Regarding the inference of measurements there is a HUGE difference between inferring the proton size from scattering amplitudes and estimating the size of the Universe from WMAP data. Particle physics is an experimental science which means that we can (and have) repeated the experiment many times in a fully controlled laboratory setting where we can control (to some extent) what is going on. The WMAP data are based on observation: you have no control over the conditions. Additionally the WMAP data predict the existance of things we have no current explanation for like dark matter and dark energy which have lead some cosmologists to suggest that perhaps gravity doesn't work like we think it does at large distances. While I persomally think the dark metter/energy scenario is far more likely there are sufficient unknowns in there to make the WMAP extrapolations no where near as robust as proton scattering experiments.
Re:...but 78 billion light years is TOO far by Roger+W+Moore · 2006-10-10 06:15 · Score: 1

Ok I have a couple of questions:

What if the small group of cosmologists pushing the "gravity is different at large distances" is correct? Doesn't that change the WMAP predictions to the size of the Universe? (and if so how?) I personally think this unlikely but my understanding is that we can't rule out this possibility yet. So doesn't this put any extrapolations on somewhat questionable ground?

Secondly (just for my interest!) I can understand how the expansion of space will give apparent superluminal velocities over large distances what is less clear to me is how we stay causally connected. This is particularly puzzling given that my understanding of inflation is that the expansion of space was superluminal and resulted in causally disconnected regions of space. So what's the difference between the two? I know we don't really know a lot about inflation but clearly we know enough to be sure that there is a difference between this and normal expansion.

(Heh, sorry that you're being tag-teammed by Anonymous Cowards).

No problem - nothing like a vigourous discussion with fellow physicists (I'm guessing!) for understanding things outside my area better! That being said if you could recommend a good graduate level cosmology text I'd be grateful. I'm a particle physicist without much GR background but with the recent developments in cosmology our fields are becoming ever closer together.
Re:...but 78 billion light years is TOO far by hr+raattgift · 2006-10-10 15:29 · Score: 1

I'm going to jump around a bit:

my understanding of inflation is that the expansion of space was superluminal
... for a very brief period, on the order of 1e-33 seconds.

During that period, the universe expanded by a factor of on the order of 1e26.

What had been causally connected beforehand became causally disconnected as a result.

The expansion became subluminal, leaving (from the perspective of any individual particle) islands of causal connectivity bounded by the particle horizon. The particle horizon is the present largest comoving distance from which light could have reached the observer. Today, here, that's ~78 Mly in all directions.

In GR here is also a related event horizon, which is the largest comoving distance from which a photon can ever reach an observer at some (any!) future time.

The ultimate end of the universe (crunch, asymptotic fade, big rip, false vacuum and other possibilities) has a huge impact on how the particle horizon evolves over large timescales, and whether there *is* a cosmological event horizon for an observer, and what its characteristics are (especially those that can be tested by observational cosmologists).

That being said if you could recommend a good graduate level cosmology text I'd be grateful.

Guth, Alan H. (1997). The Inflationary Universe. London: Vintage Press (Random House). ISBN 0-09-995950-X.

Although Cosmic Inflation has been evolving in the past almost ten years, the book is absorbing and gives a good overview of not only CI but cosmology in general, outlining the various cosmological problems and ways in which they have tackled. The maths are there, but there are plenty of appendices that help out people with varying exposures to cosmology, astronomy, and particle physics. As a particle physicist you will enjoy the parts that focus on the Higgs field and GUT, I imagine.

The importance of GUT work to cosmologists cannot be overstated, especially for inflationists; the large scale structure of the universe in CI is driven by gravitation as it falls out. The quark-gluon plasma's characteristics as it cools is also essential, and there are tight constraints upon these if cosmic inflation is true.

What if the small group of cosmologists pushing the "gravity is different at large distances" is correct?

Uh... well, gravitation and inertia can be firmly in the weird category (well, weirder), but most mainstream cosmology relies upon GR since it has routinely passed every unambiguous test put to it. A refinement of GR might be useful, but an overthrowing of it would raise lots of questions about why we see what we see through telescopes, and why we have been good at predicting what we will see when we look in different ways.

Returning to what triggered this (expansion and inflation), with respect to CI, there are a number of forthcoming experiments (SDSS, Planck Surveyor and some 21cm tomology) that will test CI predictions about the CMBR. So far predictions of the simpler CI models have held up remarkably well, with the key being a strong prediction of an adiabatic, nearly scale-invariant, Gaussian random field with more power at longer wavelengths. The characteristics of the field are critical in order for CI to explain that the large scale structure of the universe are caused by the gravitational collapse of perturbations during the inflationary period that were formed by QM fluctuations. If the field is not what is predicted, CI is false, and this in turn opens the door for "beyond GR" theories to answer the Big Bang cosmological problems.
Re:...but 78 billion light years is TOO far by Anonymous Coward · 2006-10-11 00:44 · Score: 0

I completely agree that the existance of a distant galaxy is irrelevant to the size of the Universe

I was addressing the claim that the furthest we can see is 13.7 billion light years. That assumes that spacetime has not expanded while the light was traveling.

but when the narrator in the video says "these galaxies are 78 billion light years away" they are NOT 78 billion light years away in the photograph shown and likely do not existing in anything like the same form now.

If they do still exist, they ARE 78 billion light years away. (And the Milky Way has certainly survived for many billions of years.)

When astronomers quote a distance to a galaxy, they can only quote two possible numbers. One is the distance now, and one is the distance the galaxy was from us when the light we see from it was emitted. Frankly, most people are not interested in how far away the galaxy used to be, and if you say "the distance to the galaxy is X lightyears" they will assume that means the distance now.

If I understand correctly you can get from the WMAP data by itself the age and expansion of the universe which is all you need to calculate the current size so how does this image improve on that? You can't measure the Hubble constant from this image can you?

I don't know what image you're talking about, since I didn't watch the original video. Are you talking about the Hubble Deep Field? No, you can't get the Hubble constant from that. The Hubble Deep Field is most useful in determining galactic structure in the early universe. If you want cosmology, look at the CMBR or supernovae luminosity/redshift relations.

Particle physics is an experimental science which means that we can (and have) repeated the experiment many times in a fully controlled laboratory setting where we can control (to some extent) what is going on. The WMAP data are based on observation: you have no control over the conditions.

That's true, but it's absurd to claim that you can use WMAP to measure anything. If you prefer an observational example, ALL of astronomy is observational, but astronomers certainly can measure lots of things! Perhaps a closer particle analogy would be SuperK measurements of neutrino masses with atmospheric/solar neutrinos.

Additionally the WMAP data predict the existance of things we have no current explanation for like dark matter and dark energy which have lead some cosmologists to suggest that perhaps gravity doesn't work like we think it does at large distances.

You mean, the cosmological constant? How does that cast doubt on our ability to measure things with WMAP? WMAP is what has given us our best evidence for the cosmological constant! The evidence is even better when combined with the original supernova surveys.

While I persomally think the dark metter/energy scenario is far more likely

I think you're confused. The "modification of gravity on large distances" that cosmologists have proposed to explain the accelerating universe observations is the inclusion (or rather, re-inclusion) of the cosmological constant term in general relativity. The cosmological constant is a form of dark energy, not an alternative to dark energy!

there are sufficient unknowns in there to make the WMAP extrapolations no where near as robust as proton scattering experiments.

WMAP isn't as robust as proton scattering, but it's not nearly so fragile as you imply, either. It definitively excludes the "no dark matter, no dark energy" scenario. And, as I said, you can combine it with supernova surveys. Those have the advantage that you don't even need to assume GR dynamics, since with both luminosities and redshifts you can measure distances and times more or less directly.

Responding to another message:

What if the small group of cosmologists pushing the "gravity is different at large distances" is correct?

See above, unless you're referring to something else I haven'
Re:...but 78 billion light years is TOO far by Roger+W+Moore · 2006-10-11 15:57 · Score: 1

Frankly, most people are not interested in how far away the galaxy used to be, and if you say "the distance to the galaxy is X lightyears" they will assume that means the distance now.

If I take a photo from the platform of a train pulling out of York station for Kings Cross and show it to someone saying "this is a picture of a train which is 200 miles away" I'd bet the first reaction would be "no it isn't" which would then be followed by "oh you mean now" but only because they know how big a train is. Repeat with a picture of a galaxy which you say is 78 billion light years away and I bet the understanding someone will take away from that will be this is a picture showing a galaxy that is 78 billion light years away. The reason being is that you usually describe what a picture shows in the picture not how things have changed since the picture was taken.

(Or are you talking about the MOND alternative to dark matter? It doesn't do well on the cosmological front, or even so much on the dark matter front nowadays.)

Sorry I should have been clearer - I meant MOND and variants. My understanding was that the cosmologocal constant was part of GR and not a modification to it (other than dropping Einstein's original conclusion that it had to be zero because there was no evidence for it!).

And, as I said, you can combine it with supernova surveys. Those have the advantage that you don't even need to assume GR dynamics, since with both luminosities and redshifts you can measure distances and times more or less directly.

This precisely demonstrates my point about observation being a lot riskier than experiment since it was only last week that I read of the observation of a supernova that was substantially brighter than it was supposed to be which now puts in doubt how accurate these supernova surveys are since the "standard candle" model is perhaps not correct. So how robust are predictions based on WMAP?

What I find fascinating about the WMAP data is that we either have to find some new particles to explain the dark matter and who knows what to explain the dark energy or some of the assumptions used to predict the dark matter/energy are wrong. Not being a cosmologist, and given that most cosmologists point at dark matter/energy I'm happy to take that as the most likely explanation....but until we can find the missing particles and understand what the dark energy is are you really extremely confident that all the assumptions used to mke that prediction are correct?

Look at the solar neutrino problem: people were convinced for years that the solar model was wrong (or the experiments were wrong) and in the end it simply turned out to be a wrong assumption that an electron neutrino remained an electron neutrino. Given that experience I can't help but wonder if there is not at least a small possibility of such another "obvious" (but wrong) assumption being made with the conclusions drawn from the WMAP data.
Re:...but 78 billion light years is TOO far by Roger+W+Moore · 2006-10-11 16:13 · Score: 1

Thanks for the book recommendation as well as the educational discussion! I know an overthrowing of GR would be a very unlikely prospect but my understanding was that some refinements could explain the galactic rotation curves (instead of dark matter haloes) but I did not know what the implications of that would be for the WMAP predictions. Although I understand that these models keep getting squeezed harder and harder and are becomming increasingly less believable.
Re:...but 78 billion light years is TOO far by Anonymous Coward · 2006-10-12 01:32 · Score: 0

The reason being is that you usually describe what a picture shows in the picture not how things have changed since the picture was taken.

The difference, which you're ignoring, is that the picture was not taken 10+ billion years ago.

Sorry I should have been clearer - I meant MOND and variants

MOND doesn't fit cosmological data that well (although you can sort of get it to work if you go to some fairly ad-hoc models with lots of free parameters), and when combined with all the other data, it is quite unlikely. Or rather, it is quite unlikely alone. It's possible that MOND works in addition to dark matter and dark energy, and that it accounts for merely some (but not all) of the results normally attributed wholly to dark matter. This is not an appealing scenario, but people are still looking at it. The Planck mission should settle it if other experiments haven't.

Furthermore, even if you do find a way to get MOND to work, that doesn't change the conclusions from the WMAP data regarding the age and size of the universe (which was the original issue)! It just explains how the universe got to the present state in a different way.

My understanding was that the cosmologocal constant was part of GR and not a modification to it (other than dropping Einstein's original conclusion that it had to be zero because there was no evidence for it!).

It's a matter of semantics; the CC was originally part of GR, as you say, and was later dropped. However, in order to explain dark energy, cosmologists did turn to a modification of the gravitational dynamics they were using (GR without or with a CC), and not to some other explanation.

This precisely demonstrates my point about observation being a lot riskier than experiment since it was only last week that I read of the observation of a supernova that was substantially brighter than it was supposed to be which now puts in doubt how accurate these supernova surveys are since the "standard candle" model is perhaps not correct.

Yes, I read that too; it was way overhyped, on the basis of one statistical anomaly. In particular, read this Slashdot comment from one of the authors of that paper, who says explicitly that this does not cast doubt on standard candles.

So how robust are predictions based on WMAP?

They are probably robust at least at the 10% level, given all the cross-checks they've been subjected to; there have been at least three or four other complementary surveys that all point to rather similar conclusions.

but until we can find the missing particles and understand what the dark energy is are you really extremely confident that all the assumptions used to mke that prediction are correct?

We don't have to detect dark matter directly to have evidence that it's there; dark energy is even vaguer, it's just a generic label for "whatever makes the universe's expansion accelerate", although the cosmological constant turns out to fit that dynamics rather well. Our evidence that the expansion is accelerating is independent of any assumptions about what dark energy is. It could be modified gravity (nonzero cosmological constant), dynamical fields, or something else.

Look at the solar neutrino problem: people were convinced for years that the solar model was wrong (or the experiments were wrong) and in the end it simply turned out to be a wrong assumption that an electron neutrino remained an electron neutrino.

Actually, a lot of people suspected neutrino mixing the whole time — a neutrino mixing solution to the solar neutrino problem was proposed by Bahcall in 1972 — and everybody knew that better measurements would be needed to settle the problem.

But once again, you're mostly missing the point. Our combined observations tell us a lot about cosmological evolution that is fairly model-independent; you can come
Re:...but 78 billion light years is TOO far by Roger+W+Moore · 2006-10-12 14:30 · Score: 1

The difference, which you're ignoring, is that the picture was not taken 10+ billion years ago.

I'm ignoring it for a good reason - it doesn't make any difference to the photo. Effectively it was taken 10+ billion years ago. There would be no difference between a photo of the galaxy taken 9 billion years ago at a distance 9 billion light years nearer to the galaxy and the one taken today from earth assuming red shift is corrected for. Essentially the photo is a 10+ billion year old pictures of galaxies which were a heck of a lot closer than 78 billion light years when the photo was effectively taken.

Our combined observations tell us a lot about cosmological evolution that is fairly model-independent; you can come up with different models to explain the same data, but the ultimate conclusions about the universe and how it is expanding are constrained to be mostly the same.

Yes but you are missing the point that I am trying to make. You are fitting models to the data to draw your conclusions which you state as observations. This is a lot different than a simple direct observation. Perhaps a better example, but far less well known, would be the theoretical calculation of the direct CP violation parameter e'/e which the leading theorists swore blind could not be above 1E-3 no matter how far they pushed their models. The experiment I worked on (and a similar one at Fermilab) both published measurements a few years later putting e'/e above 1E-3 in a statistically significant fashion and low and behold the theory groups re-evaluated some of their assumptions and suddenly could account for it.

Now in some ways this is an unfair comparison since non-perturbative QCD is fiendishly hard to get right since you have to make simplifying assumptions to be able to solve problems at all. On the other hand it only involves known physics. Plus, to be honest, I do believe that the WMAP/SN survey/etc. data really does point to dark matter and energy....just like I believe that at the LHC we will find a Higgs boson. In fact the Standard Model (with Higgs) is probably an excellent comparison. It is an excellent fit to the data - there is no better model out there. In fact you can even use the data to predict the mass of the Higgs boson. However you will not find any particle physicist who will tell you that the Higgs definitely exists (although I bet almost all of us believe that it does). The reason being that we have not yet directly observed the Higgs and so the possibility remains that there could be another explanation which nobody has thought of.

So how big is that possibility? I haven't a clue - I'd guess rather low but that is a guess. Being a particle physicist I (rightly or wrongly!) apply the same logic to the WMAP/Boomerang etc models. These are the best models out there, they agree with all the data but they predict something that we have not seen so I cannot help but think are there different models that we have not thought of with different new physics?

I suppose the point which I am trying to make is that once you have a model which requires new physics you are far less constrained than models which are consistent with known physics and you have to ask yourself is it possible you come up with some different new physics to explain the data? Historically we seem to have been pretty good at getting it right...but as I've heard them say in US financial commercials: past success is no guarentee of future performance!

Guys from nasa are narrow minded... by digihans · 2006-10-08 09:46 · Score: 1

First line proves it's wrong:
"Every galaxy that revolves around a supermassive black hole within 400 light-years of our own galaxy has been cataloged."

My wife's wallet has an blackhole. And I seen nobody from NASA.
And that black hole is nothing in comparison to the blackholes from several ministeries of finance of several countries, including NL ;>

BUt, but, but... by antispam_ben · 2006-10-08 12:22 · Score: 1

things get compressed by Black Holes.

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Tag lost or not installed.

There are no black holes - WRONG by rmerry72 · 2006-10-08 16:53 · Score: 1

First, the diameter of a "black hole" is proportional to its mass. The sun, for example, must be compressed to a diameter of about 3km to become a black hole. A black hole with the mass of billion suns would have a dameter=3 billion km or 1000 times our solar system. The density of this black hole would be "low" as in much thinner than air. (Do the math yourself. Mass of sun is 2x10E30kg)

Actually the volume of a black hole is propertial to its mass (that's what density is). For the densisty to remain the same the diamater would only increase 1000 fold, ie to 3000km according to your calcs. Besides, 3 billion km is within our solor system - ex-planet Pluto is 4.7 billion km on average.

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We do not inherit the Earth from our parents. We borrow it from our children.

Re:There are no black holes - WRONG by Anonymous Coward · 2006-10-09 00:13 · Score: 0

Actually the volume of a black hole is propertial to its mass (that's what density is)."

Wrong. Density is mass per unit volume. The mass of a black hole is proportional to its radius (or more accurately, the square root of its event horizon's surface area divided by 4pi). It's difficult to uniquely define the volume of a black hole, since inside the horizon there is no preferred spatial slice over which to take a volume integral, but any volume measure must be proportional to the cube of a distance. Therefore, volume must be proportional to the cube of its mass by dimensional analysis.

Quite possibly the simplest survey ever by QuantumFTL · 2006-10-08 19:11 · Score: 1

The survey was apparently completed so quickly because it simply consisted of the question "How much do you suck?"

They're Not AGN by neurostar · 2006-10-09 00:29 · Score: 1

'Called active galactic nuclei, or AGN, these black holes have masses of up to billions of Suns compressed into a region about the size of our solar system. The all-sky census, performed using NASA's Swift satellite over a nine-month period, detected more than 200 nearby AGN.'

This is wrong. Active Galactic Nuclei are not the same as supermassive black holes. AGN are cases where one of these supermassive black holes is actively accreting on a large scale. The result is an accretion disk which shines brightly. Generally the region around the black hole is more luminous than the rest of the galaxy. These are observationally evident in various forms (quasars, radio galaxies, seyferts, etc...). The Milky Way does have a supermassive black hole, but it is not accreting, so it is not an AGN. However, I believe there is some evidence that it was part of an AGN in the past.

A little background on AGN.. they are seen in roughly 10% of all galaxies. This hints that the duty cycle is roughly 10% for a galaxy, and that all galaxies go through an "active" period as part of their evolution. Feedback from the AGN can affect the evolution and star formation of the host galaxy. Which is why they're important to study.

Re:They're Not AGN by Phist · 2006-10-09 04:15 · Score: 1

See that super-massive black-hole over there about 350 million light years away? I bet it gets bigger in 350 million years from now.

Re: Geometry and Black Holes by Anonymous Coward · 2006-10-09 03:50 · Score: 0

Elementary geometry tells us that the volume of a sphere is proportional to the cube of the radius.

Except that elementary geometry doesn't apply in the vicinity of a Black Hole, because the Black Hole distorts space-time.
In Euclidean space, the volume V of a sphere is

v = 4/3 pi r^3

, where r is the radius of the sphere.
Since the geodesic circumference c of a sphere is

c = pi r^2

, the volume could also be given by

V = 4/3 pi (c/pi)^1.5

.
My understanding (which may not be correct, as IANA physicist) is that the volume of a sphere surrounding a Black Hole is actually less than 4/3 pi r^3, but greater than 4/3 pi (c/pi)^1.5.

MOD PARENT DOWN by Anonymous Coward · 2006-10-09 04:09 · Score: 0

His math is WAY off (doesn't properly define his terms, then fails to perform either a square or cube root, depending on what he actually meant) and his understanding of relativity is painfully shallow.

Re: Geometry and Black Holes by Anonymous Coward · 2006-10-09 04:48 · Score: 0

Except that elementary geometry doesn't apply in the vicinity of a Black Hole, because the Black Hole distorts space-time.

While volume may not strictly obey 4pi/3 r^3 in non-Euclidean geometry, it must be proportional to r^3 on dimensional grounds alone, if it's defined at all. Volume always has units of distance cubed.

My understanding (which may not be correct, as IANA physicist) is that the volume of a sphere surrounding a Black Hole is actually less than 4/3 pi r^3, but greater than 4/3 pi (c/pi)^1.5.

It's rather difficult to define the volume of a sphere surrounding a black hole, because you can only integrate volume down to the horizon, not within it. Or rather, you can integrate volume within a black hole, but there is no unique choice of how to do so. In order to determine the volume of a region of space, you have to slice spacetime into "space" and "time" in order to say what the geometry of space is. While there is a preferred way of doing that outside a black hole (the spatial slices orthogonal to the worldlines of stationary observers), there is no unique way of doing it inside a black hole.

Andromeda Strain by singingjim · 2006-10-09 07:48 · Score: 0

I can't wait for the light show that will be Andromeda when our two galaxies collide 10 billion years from now. How cool will that be??!

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Terrible karma and aiming lower, which in this environment of one-sided reason, is higher.

400 light years, yeah, right by Anonymous Coward · 2006-10-09 18:10 · Score: 0

Every galaxy that revolves around a supermassive black hole within 400 light-years of our own galaxy

Another galaxy within 400 ly of our own galaxy? Hello-hoh? Don't Slashdot editors have any feel of galactic proportions anymore? 400 ly is, like, not even outside the spiral arm we're living in ... It's 400 MILLION light years of course.

Sheesh, what has become of the true geeks of old, who could recite the 50 nearest stars and their distance from earth by heart?

Slashdot Mirror

Survey of Super Massive Black Holes Completed

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