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Question: What are black holes?

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

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

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

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

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

Recorded May 7, 2010
Interviewed by David Hirschman

More from the Big Idea for Monday, July 12 2010


What Are "Black Holes?"

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