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Universe Teeming With Black Holes
Porfiry writes "For the first time, astronomers believe they have proof black holes of all sizes once ruled the universe. NASA's Chandra X-ray Observatory provided the deepest X-ray images ever recorded (a million-second exposure), and those pictures deliver a novel look at the past 12 billion years of black holes. Combining infrared and X-ray observations, the Penn State team found veils of dust and gas are common around young black holes. 'The discovery of this object, some 12 billion light years away, is key to understanding how dense clouds of gas form galaxies, with massive black holes at their centers,' said Colin Norman of Johns Hopkins University."
Black holes "evaporate" via a process known a Hawking radiation. Basically, it works as follows:
1) A particle/anti-particle pair forms just above the event horizon.
2) One of the particle gets sucked in, the other escapes.
The energy to form the particle pair comes from the black hole itself, so that escaping particle carries off some energy. And E=mc^2 so it's exactly the same as if it had carried off some mass from the black hole.
- Blah blah blah, missing scientist. Blah blah blah, atomic bomb. -
Why's it so surprising that there's tons of black holes out there?
I agree: it doesn't seem very surprising. But this leads us to the opposite question: Why's there so much non-black hole stuff out there? According to the article, black holes were much more active in the past. Why did the situation change?
I can't hold a camera steady for that long, what with all the crazy spinning going on and all...
Oh, and the earth moving, too.
Seriously, does anyone know how exactly that works? The article just says
The images, known as the Chandra Deep Fields, were obtained during many long exposures over the course of more than a year[...]The group's 500,000-second exposure included the Hubble Deep Field North, allowing scientists the opportunity to combine the power of Chandra and the Hubble Space Telescope, two of NASA's Great Observatories. The Penn State team recently acquired an additional 500,000 seconds of data, creating another one-million-second Chandra Deep Field, located in the constellation of Ursa Major.
-j
I forget what 8 was for.
How do black holes form? Normally when matter coalesces it rotates, forming a galaxy , cloud, solar system, etc. I believe the accepted theory on formation of black holes is that a massive star supernovas, exerting huge compression on it own core and collapsing the matter into a black hole which then consumes the rest of the star.
As there were presumably no old stars to supernova at the beginning of the universe, how did these form? Possibly they are remnants from the big bang or perhaps there were huge amounts of matter which collapsed quickly shortly after the big bang, although these should also leave microwave imprints.
It's also worth noting that black holes could solve the convex/concave universe problem. It's been postulated that there is "dark matter" we cannot see accounting for the rest of the mass of the universe. If there are lots of small black holes out there it could explain this. This could prove that the universe will eventually collapse back in on itself creating a new big bang, instead of expanding forever.
Now, can anyone tell me whether this is definitive proof of the existence of black holes, or could these signals be produced by any type of dense matter?
Okay, so we're teaming with stars, the universe is teaming with black holes. My bet is that the universe goes for pulsars next; if so, planets will be our next choice.
When it comes down to nebulae, we'll probably do the usual "I don't care if it's my turn, you can have him." "I don't want him!" thing. Nobody likes the fat kid. We'll get stuck with them anyway; it's not so bad, they're not entirely useless.
The universe will probably win though. It's a lot older than us.
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What if black holes are the " rivits " of the fabric of the universe, or anchors ther emust be more to it , because if the universe was teeming with them , and lets say that in the beggining teeming phase the universe was a great deal smaller , there fore more black holes in less space , each exerting a vast amount of gravity , would they attract or repel each other like magnets ? and if they repled , would it enhacne the push from the big bang , or act as anchor weights to slow down the furious fast explosion, maybe they were used in the beggining to make sure the intial " bang " never totaly ripped itself up , kind of held it in cheque ? Damit i know what this means , no sleep for me for a week again !
Probably not. Isn't Dark Matter supposed to account for something along 90+% of the 'missing' mass of the universe?
Although, how did they get that figure (or whatever the real figure is) at all? It's not like we can point to a spot in the sky and say the universe ends there. So how do they (they being the astronomers and astrophysicists) know how much mass is missing? (Sounds like I really need to pick up that book by Hawking...)
Kierthos
Mr. Hu is not a ninja.
Even when that happens, though, the black hole still will emit x-rays and such, so it is still detectable.
If the black hole is wandering through the universe having eaten its host galaxy, it'd be damn hard to detect. Even if it's emitting Hawking radiation, this would in no way compare to the emissions of, eg, Cygnus X-1. 'Detectable' is the operative word, here; Chandra is looking back twelve billion years; it's not going to detect anything that isn't (wasn't?) truly spectacular. Sissy Hawking radiation would be damn hard to detect in our own galaxy, let alone one that died before the sun formed.
--
Vidi, Vici, Veni
Two words: gravitational lensing...
Ok, imagine for a second that you're looking at a distant galaxy. Since matter bends light, you get an image of it from one angle. Now, suppose you look for galaxies at an angle just slightly different from the first angle. You see a galaxy. Upon inspection, it looks eerily like the first galaxy... in fact, neighboring galaxies seem to have 'clones' like the first galaxy too! What is going on?!?
What's happening is you're experiencing a 'lensing' effect by some matter that you can't see, allowing you to see one galaxy from many different angles. You plug the numbers into your computer model of the universe, try to figure out how much matter would produce said effect, (by laws of general relativity), and lo and behold, you get this figure for large amounts of invisible matter!
Now, what I'm interested in is how many galaxies have 'eaten' all their surrounding dust. If there was any dust, the black hole would compress it to unimaginable degrees as it drew said dust in, producing x-rays of incredible magnitude... some of the brightest/most energy-producing objects in the universe are thought to be such super-holes. So, either those billions of black holes have mostly 'evaporated', (see another poster's explanation of the process), or they have sucked up all nearby gasses/dust... this discovery is going to produce some interesting fodder for the cosmologists. (and no, a cosmologist doesn't worry about makeup, guys, and the modeling careers of universes. Well, maybe some of them do, but that's not their job ;)
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IANASRP- I am not a self-referential phrase
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IANASRP- I am not a self-referential phrase
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email: proprietary becomes free, org to com
By and large they are still there, they have just cleaned out most of the matter in their immediate vicinities, so that they are no longer very easy to detect -- bloack holes are mainly detectable by the energy given off by the matter in the process of falling in, which gets VERY hot.
Black holes do radiate Hawking radiation, but most big ones radiate less than they absorb from the cosmic microwave background (let alone any remaining infall), so they are mostly still growing. Only when the universe is much, much, much older will they radiate away their mass and evaporate.
It now seems that most large galaxies have a pretty big (millions of solar masses) central black hole. One theory is that the black hole came first and the galaxy accumulated around it.
These black holes may have formed from large clumps of matter relatively soon after the big bang, or from very early, super-large, short-lived stars. They could then have grown by absorbing matter from their vicinities in the relatively dense universe of the time.
It seems unlikely that black holes make up much of the dark matter in the universe, although they could be a part. We know by looking at the way galaxies rotate and move, that most of the dark matter is in galaxies, but reasonably evenly distributed through them rather than collected at the center. If this was small black holes we'd notice their Hawking radiation. If it was bigger ones, we'd notice their gravity in various ways.
Finally the X-ray signatures could possibly be other small and very hot objects, but we don't know of anything that could be that small and that hot except matter falling into a black hole.
ESO has also issued a press release on this topic, which IMHO is better than the NASA press release (more facts, less marketspeak).
A star is basically a diffuse cloud of gas that collapses in on itself due to its own gravity right? Fine. Let's just consider the life cycles of stars then. A typical star, such as our sun, will 'live' about 10 billion years. Right now, and for the past 5 billion or so years it's been burning hydrogen, to make helium. This takes a fair amount of energy and in return releases quite a bit. Helium on the other hand releases much more, but also requires a great deal more pressure. When the hydrogen runs out, the sun will then ignite the helium burning phase and pretty much expand to somthing like the orbit of venus and make the earth look not unlike mercury. In a zone surrounding the helium burning core, hydrogen burning will still continue, but now the burning of helium provides most of the star's energy. And where this hydrogen burning phase lasted billions of years, the accumulated helium will last a few hundred million. But our sun is an unremarkable star. After it is done burning helium it will generate a small nova revealing its white hot core and, in time, a beautiful planitary nebula. Let's consider what might happen if we could add more gas to our sun.
With more gas, there would be more gravity, so there would be more pressure over a greater volume so hydrogen burning would be more prolific. Hmmmm, by adding more fuel, we're increasing the rate at which it is consumed. So our billions of years of hydrogen burning might be short a billion. So we'll reach the following phase of helium burning sooner, and it too will proceed more quickly. Now we might be able to go beyond helium burning, and burn carbon. In fact this is what the super large stars do. A star of great mass, like a red super giant might be up to 10 billion km in diameter and would not be unlike an onion with different zones of fusion. And this star would be at the end of a life that progressed very quickly. Some lasting only a hundred million years or so, 1/100th the life span of our sun. But what happens at the end of a stars life? It's the energy from the nuclear fusion that literally holds stars up. Without it they collapse. Some stars collapse on an iron core that is so large, that the pressure inside the core forces some electrons into the interiors of all the protons in the iron core of the star. This produces a super nova, but the core, now a vastly smaller ball of neutrons with a 1 km iron crust is what remains. Even neutrons have their limit. They cannot bear an infinite burden. If the core were to be about 2 to 3 times the mass of the sun, it would be so great as to exceed the ability of neutrons to resist gravitation. So a black hole would be born. At least that's the short course.
Check out Black Holes by Jean-Pierre Luminet from Cambridge University Press ISBN 0521409063.
--Jimmy has fancy plans; and pants to match.
As far as astronomers know, black holes have a bimodal mass distribution, that is, they basically come in two sizes. There are stellar black holes, and supermassive black holes.
Stellar black holes are formed through total gravitational collapse of very massive stars; stars with more than, say, 30 solar masses. This event is known as a hypernova and produces a gamma-ray burst (GRB), which can easily be seen from billions of light-years away (other GRBs may be produced by mergers of neutron-star pairs, or a neutron star and a black hole). Stellar black holes commonly have masses between roughly 3 and 20 solar masses at formation, but can of course grow by swallowing gas. A well-known example of a stellar BH is Cygnus X-1.
Supermassive black holes (SMBH) reside in the centers of many galaxies (in all larger galaxies, it is thought) and have masses between, say 100 000 and 10 billion solar masses. The one in the center of the Milky Way is rather smallish for a SMBH with "only" 2.6 million solar masses, and is fairly inactive right now. Active SMBHs are observed as the central "engines" in Seyfert galaxies, Radio galaxies, Quasars and Blazars. The differences between these are primarily due to the angle from which it is observed, and how much gas and dust is around. The larger the SMBH mass, the larger the luminosity it can sustain.
The ratio between the mass of the central SMBH and the mass of the bulge component of stars in the galaxy has turned out to be astonishingly constant, about 0.5 percent IIRC. This indicates a connection between the formation of the SMBH and the formation of the bulge stars, which happened when the galaxy formed.
No one really knows for sure how SMBHs form. They are too large and the Universe is too young for them to have been early stellar BHs that simply have grown by swallowing gas. Some think that dense clusters of tens of thousands of stellar BHs and/or neutron stars in the galaxy cores collapsed together and merged in one big crunch. If so, this would be the most energetic events in the Universe, excepting the Big Bang itself. Others think that the SMBHs were formed directly in the Big Bang, and that the galaxies formed around them - that the SMBHs were "gravitational seeds" for galaxies, sort of.
Actually they seem to have found a few examples of mid-size BHs now, with masses between 100 and 10 000 solar masses, in the cores of globular star clusters. They could conceivably have formed in the same way as SMBHs, only in a smaller scale. And then there might exist tiny BHs formed in the Big Bang, now decaying thru emittance of quantum Hawking radiation, but AFAIK no one has found their very special gamma ray burst signature yet (observed GRBs do not fit).
As to Dark Matter, most scientists agree on that it cannot be dominated by inactive BHs, because then we would have much more gravitational lensing than we observe.
/Dervak
Chandra has two instruments, ACIS (Advanced Camera for Imaging and Spectroscopy) and HRC (High Resolution Camera). Almost all results going to the general public are made with ACIS. ACIS allows simultanoeus imaging AND spectroscopy. HRC was intended for really high resolution spectroscopy OR imaging.
ACIS is working nominally, and the Chandra team deserves all the credit for this. However, you do not hear that much about HRC. Why is that?
This is well documented: Have a look at the Chandra User Manual . See section 7.8.2.
Quote: The anti-coincidence shield of the HRC-S is not working because of a timing error in the electronics. The error is not correctable. As a result the event rate is very high and exceeds the total telemetry rate limit. So, they can not tell particles from X-rays.
The same in plain english: We are detecting more background than our data transfer can handle. The instrument is f*ked due to a silly electronics design error. We are very sorry, but that is all we can do about it.
You can read their latest news here, if you so want.
(Yes, IAAPA)
"I will take the Ring," he said, "though I do not know the way."
I propose that there have been multiple "big bangs" within the same section of space. Then the stellar-sized black holes can be left over from a prior creation (they didn't quite get enough time to evaporate).
It's silly. There's no real evidence. But I don't know why it couldn't be true. And it gets away from worrying about stars that are older than the universe.
Caution: Now approaching the (technological) singularity.
I think we've pushed this "anyone can grow up to be president" thing too far.
500,000 seconds? I could have made this image in about 15 seconds in PhotoShop....
No! You were doing great up to the comment about the Hawking radiation. As several people have pointed out, Hawking radiation for stellar black holes is in the neighborhood of a nanokelvin above absolute zero -- colder than the microwave background.
You actually can have a galactic dark halo composed of black holes, but lensing studies rule out most of the possible mass ranges. Earth-mass primordial black holes are still a candidate, but since they only form by fairly exotic processes a couple of seconds after the big bang, nobody takes them seriously.
The bit about the super-massive primordial stars is very possibly right on. An upcoming issue of Astrophysical Journal Letters is going to have an article on Pop. III massive black holes, which formed from >100-solar mass stars that formed at the center of primordial density fluctuations. This is very cool -- not only do the resultant black holes do a nice job of nucleating galaxies, but they shine brighly in the early universe before aggregating through mergers into a central supermassive black hole. Neat, yes?
Quantum mechanics: the dreams that stuff is made of.
In a word, no. Only black holes in the last fraction of their life-span produce enough Hawking radiation to be noticed, and there is no obvious source for black holes small enough to be decaying now.
The key thing is that, for a given system, you come up with some way to determine the total mass, and then compare that with the luminous mass (ie, the stuff you can see) -- that's really all it comes down to. The trick, of course, is in figuring out a way to get that estimate of the total mass.
There are several possible solutions. If you're looking at some systems (like, say, a cluster of galaxies), you can look at the "velocity dispersions" of the component galaxies, and from those (and using the assumption that the cluster has more-or-less virialized) get an estimate of the total mass that is "pulling" on each galaxy. You can also use gravitational lensing, as suggested by another poster. With clusters, you actually have another (very spiffy) option, which is to look at the X-ray emission from the hot gas between the galaxies in the cluster -- the temperature of the gas, which relates to the X-ray luminosity, is also related to the mass of the cluster.) The results with all of these methods suggest that a great deal of the mass in large clusters of galaxies is non-luminous.
In our own galaxy (and others), you can do a similar sort of analysis and come up with the same sort of result (that much of the mass must be dark). (Here, the usual procedure is to form a "rotation curve," which shows the velocity as a function of radius from galactic center; if you do this, you find that the radial velocity "flattens out" and stays that way for much longer than we'd expect unless there is a substantial "dark" mass in a halo surrounding the galaxy.) It's a little dangerous to make comparisons like these, since it's possible that the source of "extra" mass may be different on large (ie cluster) and small (ie galaxy) scales, but the basic idea is the same: that a big, big chunk of the matter in the Universe is probably not luminous.
A large answer to a short question. :-)
Same sort of deal here. Chandra can remain pointed to reasonably high accuracy on something as it moves in its orbit. Sure, it's moving (and so is the Earth, and so is the distant object, etc.), but as long as the telescope remains pointed at the object in question, you're fine.