Why can't LIGO detect collisions of super massive black holes?

In summary: If I understand correctly, anyway...If I understand correctly, anyway...they are proposing using an indirect detection - observing the effect of gravitational waves on the detected tick rate of distant pulsars. And they are proposing looking for much much longer times before the final inspiral - millions of years, not seconds. I don't think this methodology would have the sensitivity to pick up what LIGO looks for. On the other hand, I think it can detect enormously lower frequencies. Which is why they're looking at SMBHs (huge power output) early in the inspiral (enormous wavelength). Exactly right, they are proposing looking for signals from the inspiral of black holes. The final parsec problem is that the
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mitosis
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Does anyone know, and is there an instrument that could?
 
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Why do you think LIGO can't detect collisions of supermassive black holes? What do you think LIGO has been detecting?
 
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I think the OP is considering supermassive black holes to be black holes with masses of millions or billions of solar masses, and is asking why LIGO doesn't detect collisions of them. The collisions LIGO has detected so far have been stellar mass black holes. The answer is that LIGO would detect a SMBH collision if it occurred, but they are very rare. I don't know the exact number, but they probably only occur in the observable universe on million year time scales.
 
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We are indulging in that favorite PF activity "guess what the poster meant". Maybe we should let him or her tell us what he or she means.
 
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  • #5
Vanadium 50 said:
We are indulging in that favorite PF activity "guess what the poster meant". Maybe we should let him or her tell us what he or she means.

I disagree. The phrase "super massive black hole" has a well-defined astrophysical meaning. For example, Wikipedia says:

"A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, containing a mass of the order of hundreds of thousands, to billions times, the mass of the Sun (M☉)."
 
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phyzguy said:
I disagree. The phrase "super massive black hole" has a well-defined astrophysical meaning. For example, Wikipedia says:

"A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, containing a mass of the order of hundreds of thousands, to billions times, the mass of the Sun (M☉)."
 
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Exactly right, they have been recording stellar black hole collisions. I was hoping it was just the frequency/ timing issue but I thought I heard a LIGO scientist in an interview say they couldn't measure a super massive black hole collision, so I wanted to check with this wonderful community! I appreciate that this exists.
 
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mitosis said:
but I thought I heard

Can you tell us where?
 
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I thought it was on a segment of Science Friday on NPR.
 
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Well, the frequency of the gravitational waves emitted by a SMBH collision will be much lower than a stellar mass black hole, so I guess it is possible that it is outside of the LIGO bandwidth. One of the things that LISA hopes to detect is SMBH inspirals, that is the oscillations that occur before the collision. I would think that an actual coalescence of SMBHs would produce a huge burst of gravitational waves, and that part of it would be within the LIGO bandwidth, but I really don't know for certain.
 
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Figure 3 in this paper suggests that LIGO isn't sensitive to signals from the inspiral of black holes above about 1000 solar masses (the chirp mass isn't the same as individual masses, but you get the idea). I think it's simply the frequency of the waves emitted by that size of binary black hole. Like any antenna, LIGO only works well for picking up waves in a limited range of frequencies.
 
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Ibix said:
Figure 3 in this paper suggests that LIGO isn't sensitive to signals from the inspiral of black holes above about 1000 solar masses (the chirp mass isn't the same as individual masses, but you get the idea). I think it's simply the frequency of the waves emitted by that size of binary black hole. Like any antenna, LIGO only works well for picking up waves in a limited range of frequencies.
I guess if you had to pick one range to measure it is logical to select the one to record the much more frequently occurring events. It still blows my mind that LIGO could be made to be sensitive enough to measure such small changes.
 
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  • #14
jedishrfu said:
Heres an article on it

https://www.simonsfoundation.org/2017/11/13/gravitational-waves-supermassive-black-hole-merger/
They say it happens too fast relative to what is detected today.
I think that isn't quite the same issue. That article is proposing using an indirect detection - observing the effect of gravitational waves on the detected tick rate of distant pulsars. And they are proposing looking for much much longer times before the final inspiral - millions of years, not seconds. I don't think this methodology would have the sensitivity to pick up what LIGO looks for. On the other hand, I think it can detect enormously lower frequencies. Which is why they're looking at SMBHs (huge power output) early in the inspiral (enormous wavelength).

If I understand correctly, anyway...
 
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I've also read about the "final parsec problem" about how the final mergers of binary smbh can be very drawn out.
 
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  • #16
Ibix said:
Figure 3 in this paper suggests that LIGO isn't sensitive to signals from the inspiral of black holes above about 1000 solar masses (the chirp mass isn't the same as individual masses, but you get the idea). I think it's simply the frequency of the waves emitted by that size of binary black hole. Like any antenna, LIGO only works well for picking up waves in a limited range of frequencies.
Thanks for solving IBEX!
 
  • #17
Sorry, Ibix!
 

1. Why is it difficult for LIGO to detect collisions of super massive black holes?

Super massive black holes are extremely massive and have a much lower frequency of collisions compared to smaller black holes. This means that the gravitational waves produced by these collisions have a lower frequency and are therefore harder to detect by LIGO's current sensitivity range.

2. Can LIGO be upgraded to detect collisions of super massive black holes?

Yes, LIGO is constantly being upgraded and improved to increase its sensitivity range. However, detecting collisions of super massive black holes would require a significant upgrade in terms of sensitivity and frequency range, which may not be feasible with current technology.

3. Are there other methods or instruments that can detect collisions of super massive black holes?

Yes, there are other methods and instruments being developed to detect gravitational waves from super massive black hole collisions. These include space-based detectors like LISA (Laser Interferometer Space Antenna) and pulsar timing arrays.

4. How do we know that super massive black hole collisions are happening if LIGO can't detect them?

Scientists use other methods to indirectly observe the effects of super massive black hole collisions, such as studying the behavior of stars and gas around these black holes. They also use computer simulations to predict the gravitational waves that would be produced by these collisions.

5. Will future advancements in technology make it easier for LIGO to detect collisions of super massive black holes?

It is possible that future advancements in technology and upgrades to LIGO could make it more sensitive to gravitational waves from super massive black hole collisions. However, it may still be a challenging task due to the extremely low frequency of these collisions.

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