Are The Black Holes LIGO Detected the Missing Matter of the Universe?

rbpeake
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Interesting speculative blog about the LIGO merging black hole gravity wave discovery by Sean Carroll.
http://www.preposterousuniverse.com/blog/2016/03/10/did-ligo-detect-dark-matter/

Mike Hewson
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Are The Black Holes LIGO Detected the Missing Matter of the Univ

That's a very good article Bob. Sean Carroll is certainly a theorist worth listening to. He has made an intriguing point about the LIGO detection. That is, what is the population of bodies that we may now sample via the GW detectors and hence what might we legitimately expect as the discovery rate of that category of system ( colliding black holes with the quoted mass range ) ? The other great point is that primordial black holes are such a simple consequence of well known physics. We don't need any new stuff for this. Plus the essential requirement of being testable ie. a halo distribution and little if any EM fuss indicating accretion disks etc.

NB : Primordial means really close to the moment of 'infinite' density when relatively small 'knots of spacetime' may form and become these black holes that we detect today. Initially they were randomly distributed and then went with the general Hubble Flow over the aeons but radiated ( ie. GW emission ) causing clusters around much larger masses ie. galaxies. This is rather like an electron emitting light and thus being captured by a nucleus. This would give a straight forward uniform distribution of dark matter around a galaxy ie. an extended halo.

Cheers, Mike.

( edit ) Ooops. My misunderstanding. The paper referred to by Sean Carroll states :

Quote:
In any galactic halo, there is some small chance that two BHs will undergo a hard scatter and in so doing lose energy to a soft gravitational wave (GW) burst and thereby become gravitationally bound. This binary will then merge via emission of GWs in less than a Hubble time.


and so the BH's are already bound within some galaxy's halo by now, but then lose energy by their mutual interaction. So the logic now reaches towards attributing the total BH-BH merger detection rate ( to be observed/assessed from now on ) as made up of 'traditional' BH mergers in co-evolving binary systems PLUS these primordial guys which later undergo chance close encounter.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

rbpeake
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Thanks for your insights,

Thanks for your insights, Mike, very interesting to ponder! And with the dawn of gravity wave astronomy just upon us, I feel like we are at the beginning of a new era of many amazing discoveries! Exciting times!

Mike Hewson
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Indeed. To be very

Indeed. To be very Rumsfeldian : we don't yet know what it is that we don't yet know ! :-)

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Bill592
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RE: 5 mergers per cubic

Quote:
5 mergers per cubic gigaparsec per year.

hmmm..... a cubic gigaparsec ? sounds like a pretty decent
sized area )

Will Ligo be instrumental in proving\disproving this theory ?

or, are alot of these going to be too far away to detect
with (current) Ligo ?

Bill

AgentB
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RE: Indeed. To be very

Quote:
Indeed. To be very Rumsfeldian : we don't yet know what it is that we don't yet know ! :-)


Just imagine if the next observed event is another pair at exactly 30 solar masses, or a 60 and 30!

If all the DM is made of these, there must be a lot of them flying around and occasionally bumping into one another, i do find it odd they would live mainly is some halo, and not one seen moving things about in our neighbourhood.

Exciting times ahead.

AgentB
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RE: Will Ligo be

Quote:
Will Ligo be instrumental in proving\disproving this theory ?


I think LIGO are expecting to see about 5 BH mergers per year so i'm sure this will be one of many theories which will be tested.

Quote:
or, are alot of these going to be too far away to detect
with (current) Ligo ?


Even if we can only detect close mergers, we would just have to observe for a longer time i would think to get accurate estimates. GW150914 was ~0.4 Gparsecs away and i know they have plans to improve the detectors to see (hear?) at least twice current sensitivity, so they could detect twice as far (and hear 8 times more events).

I have been wondering if, at the LIGO / Virgo conference next week, another announcement will be made.

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