What Are "Black Holes?"

Question: What are black holes?

Katie Freese: Inside the Milky Way and every other galaxy\r\n there is a giant black hole at the center and it is hard to explain \r\nwhere these came from, but even more peculiar is the fact that already \r\nat early times there are billion solar mass black holes.  These weigh a \r\nbillion times as much as the sun and this it at a redshift of six.  \r\nRedshift tells you how much more dense the universe was at that time and\r\n so you have to in very rapid fire do something from forming these first\r\n proto stellar objects collapsing them probably to make…  Before my work\r\n people thought you made relatively small stars and how you’re going to \r\ngrow those up to making million and billion solar mass black holes is a \r\npuzzle and so one of the contributions we made was to say hey, but we \r\nthink that the first stars can be quite a bit larger and then it would \r\nmake sense for the large black holes to be able to form.

We think\r\n that these black holes grow by accretion, but the accretion is in a \r\ndisk, so it is a flat ring around the black hole, so the stuff is \r\nswirling around in the accretion disk and it is moving pretty rapidly \r\nand before it falls into the black hole it’s giving off radiation, so \r\nwhat you’re looking for is the radiation of this stuff that is falling \r\ninto the black hole and from studying that in addition to what you’re \r\nalready saying about the motions of other things around the black hole \r\nyou can infer that the black hole should be there. 

What is dark matter, and how does it affect our picture of\r\n the Universe?

\r\nKatie Freese:
the galaxy is and in fact, the universe as a whole \r\nhave the…  they’re made of different pieces and the atomic matter \r\nactually is only a very small portion, so the rest being the dark \r\nmatter.  In fact, it’s kind of…  It’s revolutionary over the past decade\r\n that this had become clear that if you add up everything that we’re \r\nfamiliar with on a daily basis such as your body, the walls, the \r\nplanets, all these things, all the atomic matter only adds up to 4% of \r\nthe total content of the universe and the other breakdown is in terms of\r\n dark matter and dark energy and right we’re talking about the dark \r\nmatter, which is the predominant bulk of the mass in the galaxies and \r\nclusters and so on, so when people study these first stars they were \r\naware that they form inside these big globes of dark matter and at the \r\ncenter of this… of the dark matter you have a proto stellar cloud of \r\nhydrogen and helium that starts to collapse, so our contribution was to \r\nsay well but what about that huge bulk of material that’s out there, \r\ndoesn’t it play a role in this star formation process especially because\r\n these first stars are forming smack in the middle of these…  These \r\nspherical regions are called halos, so these halos of dark matter, \r\nespecially near the centers is where a lot… there is a huge amount of \r\ndark matter in there and that is where your star is forming, so what we \r\nthink happens is that there is a kind of dark matter power basically.

The\r\n dark matter particles and the ones that we believe…  There is a lot of \r\nexperiments going on right now to try to detect these particles and I \r\nthink that it is going to be resolved in the next five years, ten years \r\nat most and the most likely candidate they’re called WIMPs, which stands\r\n for weakly interacting massive particles and these WIMPs whenever there\r\n is two of them that find each other they interact among themselves and \r\n they actually annihilate, so they lose their original identity and they\r\n turn into something else, but in that annihilation process dumps a lot \r\nof heat into this proto stellar material, so you’ve got this \r\nproto-stellar cloud that is trying to collapse to make a small star, but\r\n all of the sudden you’re stopped because you have this heat source that\r\n stabilizes the cloud and prevents it from collapsing anymore, so and it\r\n is actually really a star.  The nomenclature dark star could be a \r\nlittle misleading in the sense that people think well it is probably \r\nmade of dark matter, but it really isn’t.  It’s really made of hydrogen \r\nand helium and just a smattering of dark matter.  It is a very powerful \r\nheat source and less than 1% of the mass is dark matter and the \r\nannihilation process gives a heat source that powers the star and it \r\nshines.  Very bright objects, they really are stars, so they’re atomic \r\nobjects that shine due to the dark matter power.

Recorded May 7, 2010
Interviewed by David Hirschman

Inside the Milky Way and every other galaxy there is a giant black hole at the center. Even in early times there were these types of holes, each weighing a billion times as much as the sun.

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