Largest Black Holes in the Universe

[ErnieM]

After wathing this video http://www.youtube.com/watch?v=KHSZcSowpgg titled Largest Black Holes in the Universe a few questions came to me:

Is a black hole(s) always present in the center of all Quasars and Galaxies of different shapes and sizes?
Are black holes a form of dark matter?
Are there dark galaxies composed mainly of dead stars, black holes and dark matter? After all, there are more dark matter than visible matter in the entire universe. If so, what kind of signature would these type of galaxies give?
Do known energy spectra pass through dark matter rendering dark matter "invisible"?
What happens to dark matter as it approaches the event horizon?
What is the eventual fate of black holes? Even discounting the expanding universe, would these black holes, dark matter and dark energy eventually, in the very distant future, fill up the cold and dark universe?

[Chris Peterson]

After wathing this video http://www.youtube.com/watch?v=KHSZcSowpgg titled Largest Black Holes in the Universe a few questions came to me:

Is a black hole(s) always present in the center of all Quasars and Galaxies of different shapes and sizes?

Quasars almost certainly are a manifestation of supermassive black holes in the center of galaxies. But it appears that not all galaxies have central black holes, although most do. Where they are absent, it isn't known if they never existed, or became separated during an earlier galactic collision. Many models of galaxy formation require a supermassive black hole as part of the process.

Are black holes a form of dark matter?

No. Dark matter is probably made up of a particular subatomic particle (or group of them). Black holes are regions of very high mass density.

Are there dark galaxies composed mainly of dead stars, black holes and dark matter?

Probably not. There hasn't been enough time since the beginning of the Universe for galaxies to die a "natural" death, where all their stars have stopped fusing. All galaxies, however, are made up mostly of dark matter.

Do known energy spectra pass through dark matter rendering dark matter "invisible"?

Dark matter is invisible to electromagnetic radiation because it is (probably) non-baryonic, and doesn't interact via the electromagnetic force. So in a sense, light and other electromagnetic radiation does "pass through" the dark matter. However, dark matter isn't really invisible; we can observe it using other forms of energy, such as gravity, which it does interact with.

What happens to dark matter as it approaches the event horizon?

Since dark matter interacts gravitationally just like normal matter, it is probably pulled into a black hole the same as any matter. However, since it doesn't interact electromagnetically, it may not experience anything like drag forces, and therefore is unlikely to play a part in accretion disc behavior near a black hole. An open question is whether dark matter interacts with itself. If so, it may undergo momentum transfer, and therefore experience orbital decay and fall into black holes. If it doesn't interact with itself, there may be no mechanism other than direct collision for it to fall into a black hole, in which case (given the tiny collisional cross section of black holes), almost no dark matter may be lost to black holes.

What is the eventual fate of black holes? Even discounting the expanding universe, would these black holes, dark matter and dark energy eventually, in the very distant future, fill up the cold and dark universe?

Black holes appear to lose mass over time due to quantum mechanical effects. The time scales involved for massive black holes is huge, but still finite. So presumably, the ultimate fate of all black holes is to evaporate away.

[neufer]

After wathing this video http://www.youtube.com/watch?v=KHSZcSowpgg titled Largest Black Holes in the Universe a few questions came to me:

Is a black hole(s) always present in the center of all Quasars and Galaxies of different shapes and sizes?

All Quasars and many (if not all) Galaxies

Are black holes a form of dark matter?

Black holes contribute to the universe's dark matter

Are there dark galaxies composed mainly of dead stars, black holes and dark matter? After all, there are more dark matter than visible matter in the entire universe.

Possible but unlikely.

If so, what kind of signature would these type of galaxies give?

Gravitational lensing where there seem to be no galaxies.

Do known energy spectra pass through dark matter rendering dark matter "invisible"?

Known energy spectra pass through dark matter rendering the dark matter "visible" :
. http://apod.nasa.gov/apod/ap080823.html

What happens to dark matter as it approaches the event horizon?

It speeds up then (likely) falls in like everything else.

What is the eventual fate of black holes? Even discounting the expanding universe, would these black holes, dark matter and dark energy eventually, in the very distant future, fill up the cold and dark universe?

All black holes eventually evaporate (by the Hawking mechanism) starting with the smallest.

[Chris Peterson]

Black holes contribute to the universe's dark matter

To suggest this is very confusing. The term "dark matter" now has a very specific meaning, and it doesn't include black holes. You might say that black holes contribute to the Universe's unseen mass, but not its dark matter.

[neufer]

Black holes contribute to the universe's dark matter

To suggest this is very confusing. The term "dark matter" now has a very specific meaning, and it doesn't include black holes. You might say that black holes contribute to the Universe's unseen mass, but not its dark matter.

WIMP

<<Although dark matter had historically been inferred by many astronomical observations, its composition long remained speculative. Early theories of dark matter concentrated on hidden heavy normal objects, such as black holes, neutron stars, faint old white dwarfs, brown dwarfs, as the possible candidates for dark matter, collectively known as MACHOs. Astronomical surveys failed to find enough of these hidden MACHOs. Some hard-to-detect baryonic matter, such as MACHOs and some forms of gas, were additionally speculated to make a contribution to the overall dark matter content, but evidence indicated such would constitute only a small portion.

Furthermore, data from a number of lines of other evidence, including galaxy rotation curves, gravitational lensing, structure formation, and the fraction of baryons in clusters and the cluster abundance combined with independent evidence for the baryon density, indicated that 85–90% of the mass in the universe does not interact with the electromagnetic force. This "nonbaryonic dark matter" is evident through its gravitational effect. Consequently, the most commonly held view was that dark matter is primarily non-baryonic, made of one or more elementary particles other than the usual electrons, protons, neutrons, and known neutrinos. The most commonly proposed particles then became axions, sterile neutrinos, and WIMPs (Weakly Interacting Massive Particles, including neutralinos).

The dark matter component has much more mass than the "visible" component of the universe. Only about 4.6% of the mass of the Universe is ordinary matter. About 23% is thought to be composed of dark matter. The remaining 72% is thought to consist of dark energy, an even stranger component, distributed diffusely in space. Determining the nature of this missing mass is one of the most important problems in modern cosmology and particle physics. It has been noted that the names "dark matter" and "dark energy" serve mainly as expressions of human ignorance, much like the marking of early maps with "terra incognita".

Historically, three categories of dark matter candidates had been postulated. The categories cold, warm, and hot refer to the speed at which the particles are traveling rather than an actual temperature.

Cold dark matter – objects that move at classical velocities
Warm dark matter – particles that move relativistically
Hot dark matter – particles that move ultrarelativistically>>

[Ann]

ErnieM wrote:

Is a black hole(s) always present in the center of all Quasars and Galaxies of different shapes and sizes?

Large Magellanic Cloud. Credit and Copyright: Yuri Beletsky (ESO)

No central black hole of any "galactic significance" here, probably!







Ann

[neufer]

[b][color=#0000FF]This composite image shows the distribution of dark matter, galaxies, and hot gas in the core of the merging galaxy cluster Abell 520, formed from a violent collision of massive galaxy clusters. Image Credit: NASA, ESA, CFHT, CXO, M.J. Jee (University of California), and A. Mahdavi (San Francisco State)[/color][/b]

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<<Astronomers are left scratching their heads over a new observation of a “clump” of dark matter apparently left behind after a massive merger between galaxy clusters. What is so puzzling about the discovery is that the dark matter collected into a “dark core” which held far fewer galaxies than expected. The implications of this discovery present challenges to current understandings of how dark matter influences galaxies and galaxy clusters.

Initially, the observations made in 2007 were dismissed as bad data. New data obtained by the Hubble Space Telescope in 2008 confirmed the previous observations of dark matter and galaxies parting ways. The new evidence is based on observations of a distant merging galaxy cluster named Abell 520. At this point, astronomers have a challenge ahead of them in order to explain why dark matter isn’t behaving as expected.

“This result is a puzzle,” said astronomer James Jee (University of California, Davis). “Dark matter is not behaving as predicted, and it’s not obviously clear what is going on. Theories of galaxy formation and dark matter must explain what we are seeing.”

Current theories on dark matter state that it may be a kind of gravitational “glue” that holds galaxies together. One of the other interesting properties of dark matter is that by all accounts, it’s not made of same stuff as people and planets, yet interacts “gravitationally” with normal matter. Current methods to study dark matter are to analyze galactic mergers, since galaxies will interact differently than their dark matter halos. The current theories are supported by visual observations of galaxy mergers in the Bullet Cluster, and have become a classic example of our current understanding of dark matter.

Studies of Abell 520 are causing astronomers to think twice about our current understanding of dark matter. Initial observations found dark matter and hot gas, but lacked luminous galaxies – which are normally detected in the same regions as dark matter concentrations. Attempting to make sense of the observations, the astronomers used Hubble’s Wide Field Planetary Camera 2 to map dark matter in the cluster using a gravitational lensing technique.

“Observations like those of Abell 520 are humbling in the sense that in spite of all the leaps and bounds in our understanding, every now and then, we are stopped cold,” said Arif Babul (University of Victoria, British Columbia).

Jee added, “We know of maybe six examples of high-speed galaxy cluster collisions where the dark matter has been mapped, but the Bullet Cluster and Abell 520 are the two that show the clearest evidence of recent mergers, and they are inconsistent with each other. No single theory explains the different behavior of dark matter in those two collisions. We need more examples.”

The team has worked on numerous possibilities for their findings, each with their own set of unanswered questions. One such possibility is that Abell 520 was a more complicated merger than the Bullet Cluster encounter. There may have been several galaxies merging in Abell 520 instead of the two responsible for the Bullet Cluster. Another possibility is that like well-cooked rice, dark matter may be sticky. When particles of ordinary matter collide, they lose energy and, as a result, slow down. It may be possible for some dark matter to interact with itself and remain behind after a collision between two galaxies.

Another possibility may be that there were more galaxies in the core, but were too dim for Hubble to detect. Being dimmer, the galaxies would have formed far fewer stars than other types of galaxies. The team plans to use their Hubble data to create computer simulations of the collision, in the hopes of obtaining vital clues in the efforts to better understand the unusual behavior of dark matter.>>

http://asterisk.apod.com/viewtopic.php?t=27615

[ErnieM]

From the post by neufer:

Studies of Abell 520 are causing astronomers to think twice about our current understanding of dark matter. Initial observations found dark matter and hot gas, but lacked luminous galaxies – which are normally detected in the same regions as dark matter concentrations. Attempting to make sense of the observations, the astronomers used Hubble’s Wide Field Planetary Camera 2 to map dark matter in the cluster using a gravitational lensing technique.

What if the stars in these "missing" galaxies were the "short lived super giants" that have long ago turned into black holes or chunks of exploded cosmological debris? Maybe regions of mostly dark matter and little visible matter is not so uncommon after all. Humans think these are inconceivable given our present understanding and are only beginning to look for them.

[Chris Peterson]

What if the stars in these "missing" galaxies were the "short lived super giants" that have long ago turned into black holes or chunks of exploded cosmological debris? Maybe regions of mostly dark matter and little visible matter is not so uncommon after all. Humans think these are inconceivable given our present understanding and are only beginning to look for them.

The problem is, there is no known mechanism for galaxies to form that contain only supergiant stars, and no observational evidence to support their existence. The conditions that allow for the formation of supergiants also allow for the formation of much smaller (and longer lived) stars, and in greater abundance.

[neufer]

What if the stars in these "missing" galaxies were the "short lived super giants" that have long ago turned into black holes or chunks of exploded cosmological debris? Maybe regions of mostly dark matter and little visible matter is not so uncommon after all. Humans think these are inconceivable given our present understanding and are only beginning to look for them.

The problem is, there is no known mechanism for galaxies to form that contain only supergiant stars, and no observational evidence to support their existence. The conditions that allow for the formation of supergiants also allow for the formation of much smaller (and longer lived) stars, and in greater abundance.

Besides which, only a fraction of such supergiants end up as black holes and the exploded cosmological debris quickly turns into new stars.

[b][color=#0000FF]Possible glow of Population III stars imaged by NASA's Spitzer Space Telescope. Credit: NASA / JPL-Caltech / A. Kashlinsky (GSFC)[/color][/b]

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<<Population III, or metal-free stars is a hypothetical extinct population of extremely massive and hot stars with virtually no surface metals, except for a small quantity of metals formed in the Big Bang, such as lithium-7. These stars are believed to have been formed in the early universe. Their existence is inferred from cosmology, but they have not yet been observed directly. Indirect evidence for their existence has been found in a gravitationally lensed galaxy in a very distant part of the universe. They are also thought to be components of faint blue galaxies. Their existence is proposed to account for the fact that heavy elements, which could not have been created in the Big Bang, are observed in quasar emission spectra, as well as the existence of faint blue galaxies. It is believed that these stars triggered a period of reionization. UDFy-38135539, a galaxy recently discovered, is believed to have been a part of this process. Some theories hold that there were two generations of Population III stars.

Current theory is divided on whether the first stars were very massive or not. One theory, which seems to be borne out by computer models of star formation, is that with no heavy elements from the Big Bang, it was easy to form stars with much more total mass than the ones visible today. Typical masses for Population III stars would be expected to be about several hundred solar masses, which is much larger than the current stars. Analysis of data on extremely low-metallicity Population II stars such as HE0107-5240, which are thought to contain the metals produced by Population III stars, suggest that these metal-free stars had masses of 20 to 130 solar masses instead. On the other hand, analysis of globular clusters associated with elliptical galaxies suggests pair-instability supernovae were responsible for their metallic composition. This also explains why there have been no low-mass stars with zero metallicity observed, although models have been constructed for smaller Population III stars. Clusters containing zero-metallicity red dwarfs or brown dwarfs (possibly created by pair-instability supernovae) have been proposed as dark matter candidates, but there is disagreement on this theory. Confirmation of these theories awaits the launch of NASA's James Webb Space Telescope. New spectroscopic surveys, such as SEGUE or SDSS-II, may also locate Population III stars.

Recent theories suggest the first star groups may have consisted of a massive star surrounded by several smaller stars.>>

Art (former chunk of exploded cosmological debris) Neuendorffer

[Beyond]

Art (former chunk of exploded cosmological debris) Neuendorffer

AHA That explains it! Our resident Quotidian Quotationist is a 2-Q Super Nova Neufer. No wonder he's so bright and fast with the quoting.

[ErnieM]

ErnieM wrote:

What if the stars in these "missing" galaxies were the "short lived super giants" that have long ago turned into black holes or chunks of exploded cosmological debris? Maybe regions of mostly dark matter and little visible matter is not so uncommon after all. Humans think these are inconceivable given our present understanding and are only beginning to look for them.

Chris Peterson wrote:
The problem is, there is no known mechanism for galaxies to form that contain only supergiant stars, and no observational evidence to support their existence. The conditions that allow for the formation of supergiants also allow for the formation of much smaller (and longer lived) stars, and in greater abundance.

Neufer wrote:
Besides which, only a fraction of such supergiants end up as black holes and the exploded cosmological debris quickly turns into new stars.

Then as often happens, the best explanation is the simplest. There are no missing galaxies. There is simply not enough material in the region to form any more galaxy than what is there and in this region, the ratio of dark matter is much higher than expected.

[Chris Peterson]

Then as often happens, the best explanation is the simplest. There are no missing galaxies. There is simply not enough material in the region to form any more galaxy than what is there and in this region, the ratio of dark matter is much higher than expected.

Very likely. The higher concentration is somewhat at odds with existing cosmological theory, but not radically so. Most likely it will (if confirmed) lead to some minor modifications to the theory, or to refinements in some parameters of the theory that are currently not well constrained (and are at least somewhat empirical).

[ErnieM]

ErnieM wrote:
Then as often happens, the best explanation is the simplest. There are no missing galaxies. There is simply not enough material in the region to form any more galaxy than what is there and in this region, the ratio of dark matter is much higher than expected.

Chris wrote:

Very likely. The higher concentration is somewhat at odds with existing cosmological theory, but not radically so. Most likely it will (if confirmed) lead to some minor modifications to the theory, or to refinements in some parameters of the theory that are currently not well constrained (and are at least somewhat empirical).

As a follow up, the ratio of dark matter to visible matter in the Bullet cluster must be lower than in Abell 520 and in both cases, as the visible galaxies and galaxy groups merge, the clump(s) of dark matter appears separated from the galaxies and from each other. Does this not imply that mass of dark matter is uniformly less dense and the "gravitational force" binding the dark matter together and onto galaxies is "weaker" than what binds the visible matter together? I imagine loosely fitted hats flying off the heads of kids holding hands in a lean back position, feet touching and spinning around.
Does this "uniformity" not imply that the composition of dark matter is less complex as compared to number of elements making up visible matter? Could it be that dark matter is the simplest and lightest "element", lighter than hydrogen and impervious to known forces except gravity.

[Chris Peterson]

As a follow up, the ratio of dark matter to visible matter in the Bullet cluster must be lower than in Abell 520 and in both cases, as the visible galaxies and galaxy groups merge, the clump(s) of dark matter appears separated from the galaxies and from each other. Does this not imply that mass of dark matter is uniformly less dense and the "gravitational force" binding the dark matter together and onto galaxies is "weaker" than what binds the visible matter together?

I wouldn't draw that conclusion... or any other conclusion based on the weight of evidence presented so far.

Does this "uniformity" not imply that the composition of dark matter is less complex as compared to number of elements making up visible matter? Could it be that dark matter is the simplest and lightest "element", lighter than hydrogen and impervious to known forces except gravity.

I don't know what "complex" or "simple" mean in terms of matter. I don't think dark matter can in any sense be considered an element. "Element" has a specific meaning, that of an atom comprised of protons, neutrons, and electrons. It seems nearly certain that none of these are components of dark matter.

[ErnieM]

Chris wrote:

I don't know what "complex" or "simple" mean in terms of matter. I don't think dark matter can in any sense be considered an element. "Element" has a specific meaning, that of an atom comprised of protons, neutrons, and electrons. It seems nearly certain that none of these are components of dark matter.

Really? Hydrogen has no neutron, only proton and electron. It is so light it escapes the pull of earth's gravity. It is the most abundant element/visible matter in the known universe. Only the stars and gas giant planets has enough gravity to hold down hydrogen. By extension, only gravity at galactic level can "hold down" dark matter.

[Chris Peterson]

Chris wrote:

I don't know what "complex" or "simple" mean in terms of matter. I don't think dark matter can in any sense be considered an element. "Element" has a specific meaning, that of an atom comprised of protons, neutrons, and electrons. It seems nearly certain that none of these are components of dark matter.

Really? Hydrogen has no neutron, only proton and electron.

Hydrogen certainly can have a neutron in its nucleus! The fact that elements have different isotopes, which in the case of hydrogen includes one with no neutrons at all, doesn't change my point. If you prefer, I can say that elements are made up of hadrons (such as protons and neutrons) and fermions (such as electrons). Dark matter appears to be made of something else entirely.

It is so light it escapes the pull of earth's gravity.

I don't think that's a particularly accurate statement. Hydrogen experiences the same gravitational forces that any element does. And any element in a gaseous form can be knocked out of our atmosphere by other forces. The lighter the element, the easier this will typically be... but there's nothing different about the process with hydrogen than with anything else.

Only the stars and gas giant planets has enough gravity to hold down hydrogen. By extension, only gravity at galactic level can "hold down" dark matter.

Again, I disagree with your first assertion. Even a tiny pebble has enough gravity to hold hydrogen to it. It's simply that in most environments, there are other forces that are strong enough to overcome hydrogen's gravitational attraction; basically, it blows away. When we look around the Universe, we see vast areas of "free" hydrogen that isn't bound to any stars, but is held together by gravitational self-attraction.

Similarly, there is no reason to think that you need a galaxy to hold dark matter. In fact, since the dark matter forms something like 80% of the galactic mass, it is really the self-gravity of the dark matter that is holding everything together- including the luminous galaxy that we observe. And it is generally believed that dark matter exists in orbit around stars, planets, anyplace where there is a gravitational force.

[ErnieM]

Chris wrote:

Again, I disagree with your first assertion. Even a tiny pebble has enough gravity to hold hydrogen to it. It's simply that in most environments, there are other forces that are strong enough to overcome hydrogen's gravitational attraction; basically, it blows away. When we look around the Universe, we see vast areas of "free" hydrogen that isn't bound to any stars, but is held together by gravitational self-attraction.

From Wikipedia:

Hydrogen, as atomic H, is the most abundant chemical element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms (most of the mass of the universe, however, is not in the form of chemical-element type matter, but rather is postulated to occur as yet-undetected forms of mass such as dark matter and dark energy).[68] This element is found in great abundance in stars and gas giant planets. Molecular clouds of H2 are associated with star formation. Hydrogen plays a vital role in powering stars through proton-proton reaction and CNO cycle nuclear fusion.[69]
...
Under ordinary conditions on Earth, elemental hydrogen exists as the diatomic gas, H2 (for data see table). However, hydrogen gas is very rare in the Earth's atmosphere (1 ppm by volume) because of its light weight, which enables it to escape from Earth's gravity more easily than heavier gases. However, hydrogen is the third most abundant element on the Earth's surface,[71] mostly in the form of chemical compounds such as hydrocarbons and water.[37]

Chris wrote:

Similarly, there is no reason to think that you need a galaxy to hold dark matter. In fact, since the dark matter forms something like 80% of the galactic mass, it is really the self-gravity of the dark matter that is holding everything together- including the luminous galaxy that we observe. And it is generally believed that dark matter exists in orbit around stars, planets, anyplace where there is a gravitational force.

Let me paraphrase what you wrote. Dark matter is so abundant it is all around visible matter acting like a "very large container" of some sort. The "containers" collided with such a force causing the galaxies inside to break free off the gravitational hold. In relation to the galaxies accelerating towards one another, the dark matter "containers" appear like slow moving large chunks left behind in space.
Now this makes more sense than my original example of hats flying off the heads of spinning children.

[Chris Peterson]

From Wikipedia:

Under ordinary conditions on Earth, elemental hydrogen exists as the diatomic gas, H2 (for data see table). However, hydrogen gas is very rare in the Earth's atmosphere (1 ppm by volume) because of its light weight, which enables it to escape from Earth's gravity more easily than heavier gases.

Precisely. It is still subject to the same kind of gravitational forces as all the other atmospheric gases. Because it is light, the magnitude of the gravitational force is small, and it takes smaller countering forces to carry it away from the atmosphere. In fact, it is mainly solar wind that is responsible. If the Earth existed in isolation, between the stars, it would lose almost none of its atmospheric hydrogen, because there would be no forces acting on it stronger than gravity.

In every respect, hydrogen behaves like other elements. No elements behave remotely like dark matter.

Chris wrote:

Similarly, there is no reason to think that you need a galaxy to hold dark matter. In fact, since the dark matter forms something like 80% of the galactic mass, it is really the self-gravity of the dark matter that is holding everything together- including the luminous galaxy that we observe. And it is generally believed that dark matter exists in orbit around stars, planets, anyplace where there is a gravitational force.

Let me paraphrase what you wrote. Dark matter is so abundant it is all around visible matter acting like a "very large container" of some sort. The "containers" collided with such a force causing the galaxies inside to break free off the gravitational hold. In relation to the galaxies accelerating towards one another, the dark matter "containers" appear like slow moving large chunks left behind in space.
Now this makes more sense than my original example of hats flying off the heads of spinning children.

That's not what I said. It may be fairly accurate, or not. The problem is, we don't know if or how dark matter interacts with itself, so understanding galactic collisions is still quite limited.