Did LIGO detect dark matter

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  • #1
wolram
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https://www.sciencedaily.com/releases/2016/06/160615134951.htm
From science daily
Date:
June 15, 2016
Source:
Johns Hopkins University
Summary:
When an astronomical observatory detected two black holes colliding in deep space, scientists celebrated confirmation of Einstein's prediction of gravitational waves. A team of astrophysicists wondered something else: Had the experiment found the "dark matter" that makes up most of the mass of the universe?

Apparently there are pages of calculations in the original paper, what do you think are these objects dark matter?
 

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  • #3
BiGyElLoWhAt
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Well, it seems as though the researchers are unsure. They're merely exploring the possibility and looking for new constraints.
I'm assuming this is the paper they are talking about (or a pre-print thereof).
https://arxiv.org/abs/1603.00464
arxiv said:
In this Letter, we show that if DM consists of 30 M BHs, then the rate for mergers of such PBHs falls within the merger rate inferred from GW150914.
 
  • #4
Chalnoth
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Well, it seems as though the researchers are unsure. They're merely exploring the possibility and looking for new constraints.
I'm assuming this is the paper they are talking about (or a pre-print thereof).
https://arxiv.org/abs/1603.00464
It definitely sounds like it's plausible given the observations, there will need to be a lot more data needed to confirm.

Naively, I'd say it's highly unlikely, but not impossible. What it would take to convince me:
1. Measurements of many more BH-BH mergers (at least a hundred), so that we can actually get some reasonable statistics on their properties to see if they actually match the primordial black hole hypothesis.
2. At least one completely independent method of measuring the primordial black holes, such as signatures in the CMB or measurements of their collisions with normal matter.
 
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  • #5
BiGyElLoWhAt
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I've somewhat lost faith in dark matter. It's too "perfect" of a solution, sort of like the Ether. 100% Opinion, there.
Well, the problem with that observation limitation is that there are only ~2/year/gigiparsec^3. (I believe that's what they said).
I'm not sure what the volume of our universe is estimated to be, but a cubic gigiparsec is pretty dang huge! That means a pretty low rate. What this says to me (not a cosmologist, also not an astrophysicist, or really anything... yet...), is expect between 0-2 a year.
 
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Chalnoth
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I've somewhat lost faith in dark matter. It's too "perfect" of a solution, sort of like the Ether. 100% Opinion, there.
There's quite a lot of diverse evidence for dark matter, while all of the alternatives have failed to fit with observations. There's just no reason to doubt it any longer.

Well, the problem with that observation limitation is that there are only ~2/year/gigiparsec^3. (I believe that's what they said).
I'm not sure what the volume of our universe is estimated to be, but a cubic gigiparsec is pretty dang huge!
The size of the observable universe is approximately 12,000 Gpc^3. So yes, the rate is quite small, but it's a very big universe.

That means a pretty low rate. What this says to me (not a cosmologist, also not an astrophysicist, or really anything... yet...), is expect between 0-2 a year.
Depends upon how sensitive our instruments are. More sensitive instruments means being able to detect them from much further away. They're currently working on some pretty dramatic improvements to the sensitivity of LIGO.
 
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This sort of equipment may speed up the detection rate a bit.
 
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  • #8
BiGyElLoWhAt
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It depends on what you mean by dark matter. The lightest susy? Or just "something"? Perhaps they've come off the first for something else, but last I knew that was the idea.
 
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  • #9
BiGyElLoWhAt
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This sort of equipment may speed up the detection rate a bit.
Haha, well, when we can mine asteroids... ;-)
It's probably more feasible than that, but I think it will be difficult to maintain if we don't have bots to repair that stuff; I would assume we would use very large distances between mirrors.
 
  • #10
Drakkith
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It depends on what you mean by dark matter. The lightest susy? Or just "something"? Perhaps they've come off the first for something else, but last I knew that was the idea.
I'd just call it cold dark matter (CDM). While we don't know its exact properties, I believe the CDM version is the best fit at this time.
 
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Haha, well, when we can mine asteroids... ;-)
sooner than anyone thinks would be my guess, never underestimate a profit driven private corporation. :wink:
very large distances between mirrors.
Are you referring to the LISA?, I'm not certain but I believe this equipment doesn't use the same mirror arrangement that LIGO on earth does. I could be wrong and will look into it but I believe LISA is measuring the two blocks distance apart or at least their interaction between one another. I'll do some reading and post what I can find,
 
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  • #12
Chalnoth
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Haha, well, when we can mine asteroids... ;-)
It's probably more feasible than that, but I think it will be difficult to maintain if we don't have bots to repair that stuff; I would assume we would use very large distances between mirrors.
It's not nearly so bad as that. We have a number of satellites in orbit that are functional for multiple years without any maintenance. The main issue is just getting the funding to launch them. With regard to the long term, it is generally much cheaper to simply launch a new satellite than it is to maintain an existing one.

Now that gravity waves have been definitively detected, I'm really hoping that there will be more enthusiasm behind LISA or another similar proposal. But it will still take many years to build and launch the satellites. For the next decade or so, further improvements to LIGO and Virgo are likely to be our best bet for detecting additional black hole-black hole mergers.
 
  • #13
Chalnoth
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Are you referring to the LISA?, I'm not certain but I believe this equipment doesn't use the same mirror arrangement that LIGO on earth does. I could be wrong and will look into it but I believe LISA is measuring the two blocks distance apart or at least their interaction between one another. I'll do some reading and post what I can find,
They're very similar. It's the same basic idea of measuring changes in length across a large distance. The primary difference is that the eLISA satellites would be much further apart from one another than it is possible for a ground-based system to be, and that the satellites will actually be in an orbit revolving around a central point (LISA Pathfinder is at L1, which is between the Earth and Sun).

As I understand it, the main distinction in terms of the observations are that eLISA will be much more sensitive (as it won't have to deal with pesky noise due to the Earth) and has different wavelength sensitivity (the much larger distance between the detectors should allow eLISA to be much better at detecting long wavelength signals in particular).

Apparently eLISA, which will actually be able to detect gravity waves, is currently scheduled for launch in 2034. The current LISA Pathfinder is pretty much just and instrumentation test to make sure the technology works.
 
  • #14
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Apparently eLISA, which will actually be able to detect gravity waves, is currently scheduled for launch in 2034. The current LISA Pathfinder is pretty much just and instrumentation test to make sure the technology works.
Thanks for the info, I forgot to post this link while I posted the video.
http://www.jpl.nasa.gov/news/news.php?release=2016-143
It seems they are pretty pleased with the test results so far, (As they should be) I didn't realize Pathfinder was a only a test of the tech and not the mission, thanks again.
 

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