Darkness and light

Things are heating up in the field of dark matter.

One interesting idea making the rounds is that the very first stars may have actually been powered by dark matter!

It sounds paradoxical, since dark matter is dark now because it doesn't interact with anything, so how can it burn to power a star? But back in the early universe there could have been a lot more of it around, enough so that the dark matter particles could annihilate against each other to make large amounts of energy.

These "dark stars" would be pretty odd creatures. They could reach vast proportions, comparable to the size of our solar system, and weighing in at 1000 times a much as our own sun. They would be extremely bright as well, around one million times the luminosity of our own sun. And oddly enough the dark matter would actually form just a tiny fraction of their mass, the vast majority of which is normal matter.

When the dark matter runs out, after a few hundred thousand years, the normal matter would collapse to a supermassive normal star, and ultimately into a black hole. This could help resolve a puzzle: very large black holes appear to exist in the early universe, but nobody understands how they could grow so large in the time available.

To see the papers, check out Katherine Freese's website: http://www-personal.umich.edu/~ktfreese/index.html.

And in other dark matter news...

In the same Minnesota mine where the CDMSII experiment reported two possible dark matter detections earlier this month, another experiment called CoGeNT is reporting hundreds of events: http://www.nature.com/news/2010/100226/full/news.2010.97.html. These events are doubly interesting because they suggest an unexpectedly light dark matter particle.

Well, we should not get too excited just yet, since it is only one experiment and there are many possible complicating factors - but we can get a little excited...

and especially so, because the LHC turned on again yesterday, hopefully for real this time! With luck we will see results from the world of 7 trillion electron volts before year-end.