Burnin' Dark Matter

Yesterday I gave a talk on "Stars Powered by Dark Matter" that I think came out pretty well. The overall gist, after giving a really brief overview of WIMPy dark matter, that stars tend to accumulate dark matter particles in their interiors, and at high enough concentrations this starts to have potentially interesting effects. In particular, WIMPs (i.e. particles of dark matter) probably self-annihilate. That is to say, if you bring two WIMPs together, they will annihilate just like matter and antimatter. However, you have to get them really, really close together for this to happen -- we know this, because otherwise you'd see lots of gamma rays and whatnot from all over due to WIMPs annihilating in the halo of dark matter surrounding our own galaxy.

I considered four cases. First, working mostly off this 2002 paper by Bottino, I discuss the amount of dark matter likely to build up in our own Sun. You get some 1024 or so particles per second, which annihilate to add a few petawatts of energy to the Sun's core. Sounds like a lot, but it's completely negligible to a star, and the effects are too small for us to detect.

Next, Fairbairn et al have a preprint out discussing what happens if you ramp up the dark matter concentration. Turns out, if you make the dark matter particles a billion times more common than we think they are around us (here, we think it's probably several per cubic meter, depending on how massive you think the particles are), the dark matter annihilation produces more energy in the star's core than would nuclear burning, and you get a so-called "WIMP burner". Of couse, finding such a high concentration of dark matter might be tricky...

So I also talked about some work from earlier this year (this conference proceeding and this paper) by Igor Moskalenko and Lawrence Wai. They think you can get such huge concentrations of WIMPs near the supermassive black hole at the center of a galaxy. Apparently, you could have a white dwarf -- a dense, dead, burned-out star -- that swings within a milliparsec of the black hole and captures enough dark matter to put out ten times the luminosity of the sun. That's twice the distance from us to the Voyager probes, but still pretty close when you're talking about a million-solar-mass black hole.

Finally I mentioned this paper by Spolyar et al that suggests that WIMP annihilation could have prevented the first stars from forming right away (or possibly, at all). Instead, they would remain the dense, dark clouds that we normally expect to form protostars, prevented from continuing their collapse because they can't get rid of the dark matter energy fast enough. If this model is right, that's an effect that the folks who study the first stars and their effects are going to have to find a way around.

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This page contains a single entry by Milligan published on December 11, 2007 3:13 PM.

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