Dark Matter and Black Hole!!

A few days back, I was having an interesting discussion with one of my friend in a public forum known as Actaphysica http://www.actaphysica.com/ . He seemed to be an expert in Black Hole physics who opened various threads related to some interesting aspects related to black holes, hawking radiation(HR) as well as dark matter. He talked about the possibility of a black hole formed out of two unstable micro black holes. As we know the black body temperature associated with a black hole in inversely proportional to the mass squared. Thus smaller the mass is , higher is the temperature and sooner the black hole will evaporate. I had a doubt while discussing the possibility of an atom formed out of a black hole with charge -1 and mass $m_e$ which we call and eBH (electron black hole) and another with charge +1 and mass $m_p$ which we call a pBH (proton black hole). I raised the doubt saying that eBH being tiny will evaporate soon by emitting HR and hence there won't be any bound state forming between eBH and pBH. But my friend pointed out that only isolated black holes can radiate HR and finally evaporate. Thus within a bound state eBH and pBH won't be emitting HR. However if the radius of their bound state is smaller than the corresponding Schwarzchild Radius then the bound state itself can behave like a black hole and hence emit HR since the bound state is an isolated state by itself. This would be , according to him, a ground breaking result since so far people have no idea about internal substructure of black holes. One more interesting aspect of such bound state could be the relation with dark matter. If the bound state does not become a black hole then it would be a stable entity and hence can be studied from dark matter point of view. I do not know how much work is done in this direction but it seems like an interesting field to explore.

The Darker Black Hole...

Black holes as we know are the infinitely dense objects in the Universe which keeps sucking the matter around it. They are generally formed from the gravitational collapse of stars . They are dark in the sense that even light can't escape their gravitational field. But from quantum mechanical point of view they are not so dark as they keep radiating( so called Hawking Radiation). So far the observed black holes are formed from the collapse of ordinary matter we see around us. However its worth investigating the possibility of a black hole which cud have formed from the collapse of dark matter: the darker black hole so to say. I had a few words with Dr. Yajnik regarding this couple of days back. He was saying the number of such darker black holes may be very much constrained from the structure formation data. Since dark matter particles will decouple very early (compared to usual standard model particles) and hence will start forming potential wells....and finally collapsing on its own. If such formation takes a long time like billion years from the big bang then it won't be constrained from structure formation data. But early formation will be tightly constrained.
I am just wondering how such black holes can be formed. One obvious thought comes to mind which says it may be formed from the collapse of a dark star. But does such dark star exist? Very difficult to predict. I found a paper(http://arxiv.org/abs/0902.3662) by two fellows from SUNY, Buffalo where they assume neutralino as dark matter particle and show that neutralino star can't exist. I have no idea how reliable their calculation is but it sounds really interesting. So is there any other way by which such darker black holes can form? If yes how and how tightly it will be constrained from cosmology observations?
After few day I saw a news which indeed talked about such stuffs. According to some physicist in University College London very highly massive black holes can be formed from collapse of dark matter. They call it "Dark Gulping". Only future observations will tell how much truth is there in their model. But the topic is really interesting. In fact although in the above mentioned paper people have shown that dark stars can't exist, they are assuming that the dark matter particles only have weak interaction. But it may well be true and worth exploring that there is a dark sector where the dark matter particles may have strong self-interaction which can arise from some hidden sector gauge group. People have worked on such dark sector models but I have not found any paper where they talk about star or black hole formation from dark particles. I am really excited about this new field and would be looking forward to work on it as well...:)