View Full Version : Black holes and the CMBR
2001-Dec-23, 03:05 PM
A young friend recently asked my if black holes were currently evaporating. I started to answer in the affirmative, but it crossed my mind that all black holes (if they indeed exist) must be bathed in the CMBR. Ignoring primordial (i.e., less than stellar mass) black holes for the moment, my question is simply this: are black holes (even those in intergalactic environs) gaining more mass through CMBR influx than they are losing through Hawking radiation?
2005-Nov-03, 05:24 PM
I see that no one at the time was able to answer this, its an interesting subject which I too would be interested in finding out more about.
Is there anyone now aware of the answer? And is it true, as jgates states, that there were primordial black holes of less than stellar mass? That sounds amazing, particularly given that the black holes we generally hear about are those at the centre of galaxies.
2005-Nov-03, 06:02 PM
I found an answer here (http://www.answers.com/main/ntquery;jsessionid=b4i79bemqsh2s?method=4&dsid=2222&dekey=Hawking+radiation&gwp=8&curtab=2222_1&sbid=lc03a&linktext=Hawking%20radiation). The Hawking temperature of a stellar mass black hole is around 60 nanokelvin, less than a billionth the temperature of the current CMB. So they gain a lot more weight from being bathed in the CMB than they lose through the Hawking process.
I didn't (and can't) do the math, but the same (and then some) would probably be true if you just let the black holes gobble up the hydrogen atoms of interstellar space which they might encounter on their rounds around their respective galactic centers, leaving out even what might be left of any (former) stellar neighbourhoods (solar wind, planets, dust etc).
2005-Nov-04, 06:01 AM
I found an answer here (http://www.answers.com/main/ntquery;jsessionid=b4i79bemqsh2s?method=4&dsid=2222&dekey=Hawking+radiation&gwp=8&curtab=2222_1&sbid=lc03a&linktext=Hawking%20radiation).
If you don't feel like crunching the numbers in all the formulas on that page (I like formulas), try this. The radiative temperature of a black hole is about (6x10-8/mass) kelvins, where the mass is measured in solar masses. Likewise, the radiative lifetime of a black hole is about 1071*M3, where M is the mass in solar masses. The lifetime assumes that the black hole is only radiating, not absorbing. As already pointed out, it's likely that they are all absorbing more than they emit.
2005-Nov-08, 09:40 PM
"And is it true, as jgates states, that there were primordial black holes of less than stellar mass? That sounds amazing, particularly given that the black holes we generally hear about are those at the centre of galaxies."
Today’s paper on the subject:
If this piques your interest, go to the arxiv homepage: http://arxiv.org Under astrophysics, select ‘find’. There are three searches of interest. First, type in ‘primordial black hole’ in the Title block, and submit the search. If this doesn’t yield enough results, enter the same phrase in the Abstract block and submit. Lastly, at the bottom of the Search page is the Experimental Full Text Search— it gives … unpredictable results. Enjoy! Steve
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