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Dim Galaxy Could Give Clues to Dark Matter
chamblah writes "Reuters is reporting that the dimmest galaxy has been found. 'In fact, it is dimmest galaxy ever detected, which means it could give clues to the mysterious dark matter that appears to be pushing regular matter around.' Since this galaxy is '...100 times dimmer than the night sky', it could only be detected using 'instruments involved in the Sloan Digital Sky Survey, the sky-mapping project.' The galaxy is also part of the Andromeda galaxy, only 2 million light years from us. The article goes on to explain how finding these dim galaxies can be useful, 'Andromeda IX fits the profile for the small, dim galaxies that cosmic theorists predict should exist as leftovers from the formation of big galaxies.'"
They're just eco-friendly and power saving.
It's not "part of" Andromeda; it's a satellite galaxy, like the Magellanic Clouds are to the Milky Way. It wouldn't make a whole lot of sense to talk about a dim galaxy that's part of a regular galaxy, anyway ...
The correlation between ignorance of statistics and using "correlation is not causation" as an argument is close to 1.
Exactly, just like I-90 is part of the Honda freeway!
Our intelligent designer has never created an animal that we couldn't improve by strapping a bomb to it.
So ... I've R'd TFA, but I'm still not an astrophysicist ...
Does one infer from this that the 'missing' dark matter is possibly just a bunch of stuff we haven't been able to see yet? Or is the magnitude of the dark matter just too big to be accounted for by dim structures in space?
Just askin'.
Lost at C:>. Found at C.
> Reuters is reporting that the dimmest galaxy has been found
Yeah, I always that galaxy wasn't too bright...
Scientists have now found the brightest dark-sucker galaxy to date...
From the article:
"How dim is Andromeda IX? At least twice as faint as the previous record holder,"
Obviously, they turned up the gain on their faintness detectors.
Alright, I hope this doesn't come off as condescending, but IAAA (grad student, at least), and *one* dim, tiny dwarf galaxy will tell us very little about dark matter.
You can measure its velocity dispersion to infer its total mass, and you can measure its light and spectra to attempt to infer its mass in baryons (protons, neutrons, and electrons), and you can measure the spectral lines to determine its metallicity, but this has nothing to do with inferring dark matter.
Dark Matter is inferred, at least when it comes to galaxies and clusters of galaxies (to keep it simple), because the mass required to provide the galaxy/cluster with the internal velocities observed is much more than what we see in starlight. Therefore, some of the matter is non-luminous, or "dark". Dark matter exists, on AVERAGE, so that 1/7 of the total mass in a galaxy is in baryons, and 6/7 is in dark matter. This ratio varies widely for different galaxies, and I do not see how *one* galaxy is going to tell us anything?
Also, if this satellite galaxy is less than ~100 kpc from Andromeda, the main galaxy's dark halo will envelop the satellite, too, further complicating the matter.
Of course I haven't read the article :-) I better go and have a look at it.
Also I thought these days what mattered is the redshift, not faintness.
Forgive the scepticism, but it may be worth noting that there are electrical discharge theories of the cosmos that do not need to invoke "dark matter" at all (though these theories are, for reasons unknown, not accepted by mainstream astrophysicists and cosmologists). The point being that maybe there ain't no such thing as "dark matter".
You obviously don't live in a city.
[TMB]
Also, since there is so much matter in the universe, and it was all in a very tiny place just after the big bang, we know for sure that we were inside a black hole. But nothing can escape a black hole, not even light. So we live inside a black hole. A gigantic black hole. Why don't we see the universe collapsing? Simply because time is a continuous and in the black hole event horizon, time doesn't flow. If you stay at the horizon, your clock doesn't go forward nor backward. Therefore as time is continuous, time must go backwards in the black hole, because it goes forward outside the black hole.
To my knowledge, there are several mistakes in this description. However, I have never heard that reasoning before and after correcting these technical mistakes the reasoning as a whole may still be sound if it were phrased more accurately. First of all, matter can escape from a black hole, it gets radiated away in a thermal spectrum as described here. Secondly, if you're sitting on the event horizon, you would observe your clock to tick normally, time does flow. An observer far removed from the black hole would indeed observe your clock as stopped however. Thirdly, I don't think that you can simply say that time "flows backward" inside a black hole. Although I have never taken a GR course, I am familiar with special reletivity and I imagine the frame of reference inside the event horizon to be somewhat analagous to a frame of reference travelling faster than light (at least when comparing them to a traditional inertial frame). There's nothing theoretically wrong with such a coordinate system, but there is simply no way you can transform values measured there into a traditional frame of reference without getting nonsense for an answer. In other words, if you were sitting inside the event horizon, there is simply no way to translate the ticks you observe on your clock to what a far removed observer would observe.
Any portion of sky which doesn't have a star/galaxy in it is black, black black!
Not totally black... there is a fair bit of light that reflects off dust in the solar system (zodiacal light). So it's entirely possible for this galaxy to appear 101% as bright as the background sky.
And just for general info... there are lots of low-surface brightness galaxies out there - Malin1 for example.
Have you seen the Deep Field images? The Universe is positively thick with stars and galaxies. If you have a very dark object, you might well see it as a silhouette against a brighter background; cf. the Horsehead Nebula, or the Coal Sack.
Real Daleks don't climb stairs - they level the building.
...the mysterious dark matter that appears to be pushing regular matter around
That must be the extra mysterious version of dark matter that works opposite to gravity (pushes).
The normally mysterious version of dark matter is simply dark and mysterious. It pulls.
Karma police, I've given all I can, it's not enough, I've given all I can, but we're still on the payroll.
>>Simply because time is a continuous and in the black hole event horizon, time doesn't flow. If you stay at the horizon, your clock doesn't go forward nor backward. Therefore as time is continuous, time must go backwards in the black hole, because it goes forward outside the black hole.
Well that sounds very neat and I'm sure any moderator with no knowledge of GR will mod you up. Unfortunately, though, if you do the maths you will discover that time does not run backwards inside a black hole. As someone pointed out, at the event horizon time does not stop for a local observer, but it appears to stop from the viewpoint of someone observing the horizon from outside.
Inside the black hole, what happens is even stranger than time running backwards. As you are no doubt aware, spacetime has 4 dimensions: 3 of space and one of time. Inside the black hole, the time dimension is swapped with one of the space dimensions - the radial dimension pointing at the centre of the hole. (For a spherical black hole, the maths is easiest in polar coordinates so your spatial dimensions are radial, axial and azimuthal rather than x, y and z). Because it's now a time-like dimension, and time marches ever onwards, you are inevitably drawn along the radial direction into the centre of the black hole; you can no more escape it than you can stop time locally. On the other hand, time has now become a spatial dimension, so presumably you can move along the time axis freely (until you hit the centre of the black hole and are crushed into nothingness).
That's what the maths says anyway. What it means philosophically (and biologically) to have your dimensions switched round is another question, and quite beyond my imagining.
The author of this post asserts his moral rights.
We can't be inside a black hole, we would all be dead by now because of the strong tidal forces.
Aside from all of the errors in the original post, that is false as well. The more massive and larger a black whole gets the weaker the tidal forces become at the event horizon. Given a black hole equal to the mass of the entire universe, the tidal forces of entering the black hole would be essentially zero.
Of course this really just brings us back to the fact that anying inside the event horizon is almost totally undefined by current physics.
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"there are electrical discharge theories of the cosmos that do not need to invoke "dark matter" at all" I was all ready to mod you up but, alas, no examples or links....
Sorry, I keep forgetting to add the tongue-in-cheek emoticon to the bottom of my posts...
sorry, didn't have the links on-hand when I posted and just figured ppl would google for them. Here are a couple of good ones. http://www.catastrophism.com/texts/bruce/ http://www.catastrophism.com/texts/bruce/era.htm I bring up Electrical Discharge Theory at all just because too few ppl think to question basic assumptions. In this case, most everyone presumes there's "dark matter" just because most physicists and astronomers tell them so, but history tells us that physicists and astronomers have been wrong about a lot of things (think Ptolemy and epicycles). It's just human nature, it's rooted in uncertainty, yet humans presume to know things as fact when all they have are interpretations. A case in point is "dark matter". It is only an interpretation for the observable data, an interpretation backed by not that much data (I mean, we can't even see this stuff), and "dark matter" is certainly not the only interpretation for the observable data.
Sigh. I really meant this to be a "the first error is... type dismissal - in particular that event horizon tital forces must be destructive. But I don't like being missquoted:
So you say it would be possible to live inside a hugely massive black hole, right?
I don't know what post you were reading, but it wasn't anything I wrote. The closest thing I said to that was "anying inside the event horizon is almost totally undefined by current physics." That says nothing about the inside of a black hole, much less indicate it would be possible to live inside.
Some major theories have everything going splat on the surface of the event horizon and a vacuum-like space inside. Most others have you rapidly going splat on the singularity or somesuch. There are many competing and contradictory theories, but not many that expect sustaining life.
according to GR, you can't distinguish between the following two scenarios:
1. You floating in space.
2. You falling into another object.
Right - within a sufficently narrow refference frame.
However it's usually pretty easy to tell the difference later when you eventually go splat against that object.
In fact if the big bang theory is true, we can only be inside a black hole, because the whole universe was condensed in such a tiny space.
I can't even begin to address this properly. You are lookign at the ordinary behavior of ordinary lumps of matter and ordinary patch of space within the space of our universe, and trying to apply with the origin of universe itself. An origin that is no ordinary lump of matter and no ordinary patch of space, and which is *NOT* lying within space. You need to get into some really serious physics and equations to even begin to look at it.
I'm going to wade in over my head and take a stab at it, hopefully I won't botch this too badly:
The earliest moments of the universe are believed to have been characterized by hyper-inflation of space itself (don't ask me why), inflation vastly exceeding the speed of light. Normally it is impossible for mass or energy to escape the gravity of a black hole, but space itself expanding faster than the speed of light can carry that mass and energy outwards reguardless of any gravitational issues. After an instant of hyper-inflation the mass-energy density is below the black-hole threshhold, thus no black hole exists or is formed anywhere in the process.
Sigh. I should have stuck with "Your first error is..." and quit. LOL.
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I don't know where you get that space expands inside an event horizon. Toss up a link if you like. The "classical" view is that everything splats on the singularity. The recent suspicion is that everything may just splat on the event horizon without crossing it.
Or maybe it just turns into blueberry pie, heh heh.
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Everything crosses the event horizon according to an observer that is outside the event horizon.
False. An outside observer NEVER sees anything cross the event horizon. He sees infinite time dilation as the object gets infinitely close to the horizon. This portion is not in dispute. Any google will confirm it. Here is the first Google result:
to an outside observer any objects approaching the Schwarzschild radius appear to take an infinite time to penetrate toward the inside
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