Science: Black Holes

Washington Post staff writer Marc Kaufman and Juna Kollmeier, an astrophysicist and fellow with the Observatories of the Carnegie Institution, will be online today at 2 p.m. ET to discuss "supermassive" black holes which were recently discovered to be the core of all galaxies.

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In Kaufman's story today, he writes:

Discoveries by a UCLA professor, along with the work of scientists studying other galaxies, have in a short time led researchers to the surprising conclusion that most, if not all, of the universe's hundreds of billions of galaxies have supermassive black holes at their core. Even more striking, the astronomers have found that the black holes' mass and nature are closely related to the size and makeup of the surrounding galaxies.

It also appears that these cosmic monsters -- which can "eat" stars whole -- are key to understanding how galaxies were formed and are still being formed today.

Read more: Huge Black Holes May Hold Keys to Galaxy Formation

A transcript follows.

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Falls Church, Va.: What is it that's been newly discovered? I thought the existence of a supermassive blackhole at the center of the Milky Way had been known for some time now? Is it new that they have been found in other galaxies?

Marc Kaufman: Good afternoon, folks. This is Marc Kaufman, and I have with me black hole researcher and expert Juna Kollmeier of the Observatories of the Carnegie Institution of Washington. I first met Juna this summer during a five-day training course for journalists on "The Universe" at MIT. She spoke on the subject of today's chat, and she did it with such enthusiasm and knowledge that I knew I had to write a story about it all.

In response to the question, it seems like there is something new coming out about supermassive black holes every day. You are correct that the existence of a central black hole in the middle of the Milky Way is not brand new, but the subject is little known or understood by most people, and I thought it would be useful and interesting to fill in that blank. The work by Suvi Gezari-- where her team followed the "feeding" of a distant black hole on a star--came out this year, and there is a lot more in the works.

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Alexandria, Va.: Do supermassive black holes rotate?

Juna Kollmeier: We believe that supermassive black holes rotate indeed.

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Marc Kaufman: By the way, the vastness of the galaxies and universe becomes very apparent when you study black holes -- especially these supermassive ones. There are, for instance, hundreds of billions of galaxies in the universe, and each one may well have a central black hole.

That scale led to an error I made in the story: I wrote that the central supermassive for the Milky Way is 27,000 light years away, and I translated that as 158 trillion miles. As several careful readers pointed out, that should be quadrillion, and not trillion. So it's pretty far away, yet researchers can now peer into the center and find orbiting stars and other indirect signs of a supermassive black hole.

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Washington, D.C.: Pardon my lack of knowledge in this arena, but I thought black holes were full of nothing-ness so how do can you measure it?

Juna Kollmeier: Black holes have mass and we can measure that mass by watching the motions of stars or gas around that massive body. Definitely not nothingness! The black hole at the center of our Galaxy weighs more than 3 million suns!

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Miami, Fla.: Beyond curiosity - why do scientists study black holes?

Marc Kaufman: There certainly is no direct application to the knowledge they're gaining, but it helps enormously in the eternal human effort to learn more about our world. Supermassive back holes themselves tell us a lot about Einstein's theory of relativity, they tell us about how galaxies may have been formed and how they are at times destroyed, and they give us a window into the way that enormous and extremely powerful jets of radiation and matter are spewed out into the atmosphere. Stellar black holes, which are much, much smaller, tell us more about how stars live and die, and were the entry point for astronomy's study of black holes and the mysteries they present.

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Arlington, Va.: What would a supermassive black hole look like to an outside observer? Obviously, the hole itself cannot be seen. My recollection of relativity, however, is that to an outside observer, an object falling into a black hole would seem to hang forever on the event horizon. So, would the black hole at the center of the galaxy look to an observer like an enormous pile of every bit of matter that ever reached the event horizon?

Juna Kollmeier: You recall correctly. To an ouside observer, objects falling in just appear frozen. This is because of the way spacetime "works" around a black hole.

Juna Kollmeier: In fact, as the object falls in the photons emitted become redder and dimmer so eventually the outside observer sees nothing. So it wouldn't actually look like an enormous "kitchen sink" of accretion events.

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Pentwater, MI: What is inside a supermassive black hole? Not matter as we know it. Probably not neutrons; they would not be dense enough. Is is Quarks?

Juna Kollmeier: In classical General Relativity, the space time inside a black hole has no matter in it except at the very center--the singularity--which has all the mass. Recent arguments from String theory indicate that there is matter continuously distributed between the very center and the event horizon of the black hole. Within the context of string theory, this matter is strings--more primitive particles than neutrons or even quarks which we are familiar with.

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Marc Kaufman: One of the most interesting -- and elegant -- aspects of these supermassive black holes is, as Juna explained to us learners, that there appears to be a close correlation between the mass of the central bulge of the galaxy and the mass of the black hole. This leads to the theory that the black hole, in effect, regulates the structure and relative size of its galaxy. This is, to me, a stunning discovery that tells us something fascinating about the structure of our world.

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Juna Kollmeier: Just another comment to Alexandria, Va on rotation:

Black holes must be spinning at some level because they are consuming material that has angular momentum. They may even be spinning extremely rapidly (for example, if the black holes at the centers of two galaxies collide when the galaxies collide this will lead to a very large amount of angular momentum and a large spin in the final product)

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Atlanta, Ga.: Thanks for this great research and interesting topic. I'm by no means an astronomer, or scientist-minded person. But I was curious. You say black holes have a mass, is this the same mass as you or the Earth? Or is this a "dark" mass or some other type, because my understanding of black holes was they were created by a supernova event, and the extreme gravity pulled all objects within the event horizon into a...we aren't sure?

I've heard of the potential for them serving as worm holes. For these supermassive black holes, would it be possible to send a sattelite or other human construction in and test what happens? Or is the mass and gravity too dense for that to happen?

Thanks again!

Juna Kollmeier: Great questions Atlanta! The notion of mass becomes tricky when it comes to black holes (see my response to Pentwater, MI). When we make measurements of the mass, however, we are directly measuring the gravitational field that the black hole's mass is causing via the motions of material in that gravitational field. In the same way that the Earth's orbit around the Sun depends on the Sun's mass.

Juna Kollmeier: Unfortunately, even if we could make such a craft that could withstand the incredible tidal forces around the black hole, we could never get the information out back to us here on Earth. Photons cannot escape and therefore cannot tell us what is going on inside the event horizon.

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Fairfax, Va.: Are black holes at the center of every observable galaxy where a search has been made for them? Are black holes necessary for galaxy formation?

Marc Kaufman: Yes, they have been found wherever and whenever astronomers have had the means to look for them. This has led to the expectation that they will be found at the heart of every galaxy. And as to galaxy formation, it appears that they play a central role, but that role is definitely not fully understood. Active supermassive black holes send out huge and highly energized jets of matter and radiation, and researchers are exploring how those jets may well seed the galaxies with the forces that lead to stars and later structure. Generally, the active supermassives are found in galaxies that are still in the process of formation, while more mature and sedate galaxies like our Milky Way have central black holes that are often described as dormant.

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Arlington, Va.: Can you tell us more about the Keck telescope that was used to discover the supermassive black holes? What other discoveries have come from it?

Juna Kollmeier: The Keck telescope has an *extremely* long list of very exciting discoveries and I couldn't possibly list them all here today! I think among the most exciting results, however, have been the discovery of galaxies at very early epochs in the universe as well as the discovery of extra-solar planets. These are just two of the many groundbreaking results from Keck.

Juna Kollmeier: One thing is for certain: whenever we open a new window in astronomy, we always see something unexpected and amazing!

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Washington, D.C.: What makes a supermassive black hole different from a stellar black hole? Is there anything other than the size?

Marc Kaufman: The primary difference, as I understand it, is the scale -- stellar black holes are created when stars die and implode (or explode) and generally have a mass of some 10 times our sun. But supermassive black holes have masses of hundreds of thousands or billions times our sun. Nobody knows how they are formed, but theories abound -- that they are the result of the implosion of a massive star from the early universe (when stars were much bigger) or that they are created when galaxies collide and black holes merge. But the basic dynamics of how they work -- to the extent that is known -- are thought to be similar or the same.

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Arlington, Va.: I just have to ask, what's the best black hole joke you've ever heard?

Juna Kollmeier: Black holes are no laughing matter. Just kidding.

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Glen Arm, Md.: Dark matter (if it exists) must also fall into black holes - have phyicist every tried to observe any possible "sigiture" that would be unique to such events?

Marc Kaufman: Interesting question. I believe the answer is that no signature has been found because no signature has ever been found for dark matter in any context. Astrophysicists now believe much of the universe consists of dark matter and dark energy, but that isn't based on observation but rather on theory. Indeed, one of the features of dark matter is that it does not emit or reflect enough electromagnetic radiation to be observed.

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Washington, D.C.: At the risk of sounding soulless, are there any practical applications of galactic and extra-galactic astronomy? Or is this area of science pure research at this point?

Marc Kaufman: Pure science at this point -- although it seems to me that humans have an unquenchable desire (need?) to learn more about the universe. The huge public response to the remarkable images from the Hubble Space Telescope suggest that desire remains alive and well.

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Cicero, Ill.: The mass of the central singularity is related to the bulge of the galaxy, as states. Recent data (L. Ferrareze) shows that this singularity is also related to the dark matter of the halo surrounding the galaxy. THAT is SPECTACULAR.

John Boguta

Marc Kaufman: I'm not familiar with that research, but if supported in future work it would certainly be fascinating and important.

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Washington, D.C.: Hi,

I'm having trouble grasping the vastness of "hundreds of billions of galaxies." Would that mean that our galaxy is to the universe of galaxies as one grain of sand is to a beach?

Marc Kaufman: Yes -- and as a tiny planet in orbit around a smallish, garden-size star in the exurbs of a medium size galaxy, we are indeed a grain of sand (or maybe a part of a grain of sand) in the context of the universe.

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D.C.: What would happen if, all of a sudden, light trapped inside a black hole, escaped?

Marc Kaufman: As I understand it, it cannot escape and will not escape. However, a great deal of light and other forms of radiation are created as gas and other matter is sucked into a black hole. An "accredition disk" that swirls around the black hole moves the material and creates a great deal of friction -- and as a result heat and various forms of radiation. But once it goes into the black hole, it's gone...

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Falls Church, Va.: I have a mental image of black holes as ravenous creatures, ever-growing, ever-devouring, but that's not necessarily true, is it? A black hole can co-exist with its neighbors in a stable fashion without eventually consuming them, can't it? Or is the supermassive black hole at the center of the Milky Way eventually going to swallow the whole galaxy?

Juna Kollmeier: Have no fear Falls Church! Supermassive black holes can peacefully coexist with galaxies and this remarkable relationship seems to hold true even for galaxies outside of the Milky Way. The black hole can only grow when material comes sufficiently close to it--inside what is called the "sphere of influence" where the black hole's gravity is dominant. So the Galaxy is safe!

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Bethesda, Md.: Good afternoon!

I was wondering, I have heard of "Hawking" Radiation, and how it (I think) describes how a black hole eventually would irradiate itself away. Does this tie in with the "active" and "dormant" designations for black holes?

Are scientists currently thinking that the galaxies could be products of minature "Big Bangs" that produced black holes instead of...whatever the Big Bang produced in addition to all the atomic material?

Thanks for answering!

Juna Kollmeier: Hawking Radiation refers to the eventual evaporation of black holes due to the process known as pair-production. This process is *extremely* slow to occur so isn't the same type of activity we mean when we say a black hole is "active".

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D.C., bs in astronomy: What sorts of jobs are out there for people with a BS in astronomy but no PHD? I have a friend with such credentials who's been teaching HS physics but he really wants to do more with astrophysics. For what it's worth, as an immigrant he is unable to accept employment with NASA or any other government or defense agencies.

Thanks!

Juna Kollmeier: Excellent question D.C.! Most jobs in astronomy are either with academic institutions or with government labs. Plenty of universities employ research assistants and often only a B.S. degree in physics or astronomy is required.

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NY, NY: Thanks for taking the time to talk about this topic. It seems to me that if light can't escape black holes, then black holes must be very very luminous inside. More so than any other light source we know of.

So while it isn't visible on the outside, shouldn't they be called "bright holes"?

Also, the idea that every galaxy has a central black hole and that there might be a regulatory relationship between them is fascinating. Can you talk a little more about this?

Juna Kollmeier: In fact, when supermassive black holes "feed" they emit a tremendous amount of radiation. The brightest of these are called quasars and they outshine the galaxies they live in by orders of magnitude. Of course, this light is coming from the accretion disk around the black hole, but it is extremely bright!

Juna Kollmeier: The relationship between supermassive black holes and their hosts is truly fascinating. Astronomers have observed that there is very tight correlation between the mass of the supermassive black hole and the motions of the stars that surround it. Because these things have widely different scales of relevance, and because this correlation seems to be very tight, it indicates that the formation of supermassive black holes and the formation of galaxies is inextricably linked. There are many theories as to how this relationship is set up, but we do not yet know which one (if any) is correct!

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Marc Kaufman: Thanks for your questions everyone. Fascinating topic...

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Juna Kollmeier: One more comment to Bethesda, MD: When I say Hawking Radiation is a slow process, I am referring to the case for large astrophysical black holes. For very small black holes (with the size of a proton and the mass of a mountain) such as could have been produced in the Big Bang, this process can be very fast and lead to an explosion. This has not been observed yet but people have looked!

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NY, NY: Does dark matter and dark energy interact with a blackhole in the same way as classical matter and energy?

Also, does this discovrey have any effect on string theory?

Juna Kollmeier: Dark matter does interact with black holes in the same way as classical matter, but the situation is not so clear for Dark Energy since we don't know the equation of state of the Dark Energy.

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Juna Kollmeier: One comment to Glen Arm, Md: Our knowledge of Dark Matter comes from indirect evidence based on the rotation curves of galaxies as well as the effect that such mass has on light (gravitational lensing). Dark matter should interact with a supermassive black hole in the same way as ordinary matter.

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Juna Kollmeier: Comment to Cicero, Ill: Yes, there is a recent study that indicates that the connection between supermassive black holes may extend even beyond the bulges of galaxies to the dark matter halos they sit in. This is somewhat controversial but, if true, would demonstrate an amazing connection between the growth of dark matter (which seeds galaxy formation) and the growth of supermassive black holes.

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