Are hints of quantum gravity in LIGO echoes?

[notFritzArgelander]

https://phys.org/news/2020-01-gravitati ... hesis.html

[helicon]

This is some really interesting research. Postulating that there might not even be an event horizon around some BH's throws a monkey wrench into General Relativity. Curious to see what the source of these lingering gravitational waves might be. And the authors won a prize for their research, too.

[AntennaGuy]

OK, sorry for the dumb question, but how can a black hole not have an event horizon? Isn't the event horizon the thing that makes it black?

[notFritzArgelander]

OK, sorry for the dumb question, but how can a black hole not have an event horizon? Isn't the event horizon the thing that makes it black?

Hawking radiation is a quantum mechanical effect which would make an event horizon not black. There would be radiation from the event horizon at a temperature that is inversely proportional to the BH mass. So if a BH is larger then the temperature of radiation is lower. With quantum effects a BH is only truly black if its temperature is lower than its environment. Otherwise it could be luminous.

https://en.wikipedia.org/wiki/Hawking_radiation

Note that a solar mass BH has a radiation temperature of about 6x10^(-8) K. So to be in equilibrium with the CMB a BH would need to be about 2x10^(-8) solar mass.

But in addition there's the possibility that there is quantum structure at the event horizon. That's the main point.

Also.... note that a freely falling observer never sees an event horizon. It's really an artifact of choosing a non inertial reference frame.

[AntennaGuy]

OK, sorry for the dumb question, but how can a black hole not have an event horizon? Isn't the event horizon the thing that makes it black?

Hawking radiation is a quantum mechanical effect which would make an event horizon not black. There would be radiation from the event horizon at a temperature that is inversely proportional to the BH mass. So if a BH is larger then the temperature of radiation is lower. With quantum effects a BH is only truly black if its temperature is lower than its environment. Otherwise it could be luminous.

https://en.wikipedia.org/wiki/Hawking_radiation

Note that a solar mass BH has a radiation temperature of about 6x10^(-8) K. So to be in equilibrium with the CMB a BH would need to be about 2x10^(-8) solar mass.

But in addition there's the possibility that there is quantum structure at the event horizon. That's the main point.

Also.... note that a freely falling observer never sees an event horizon. It's really an artifact of choosing a non inertial reference frame.

Thanks. I knew about Hawking radiation. But, truly black or not, it seems a "black hole" still needs to have an "event horizon" (defined as where the escape velocity is equal to the speed of light), right? Yet the article said a black hole might not have an event horizon. Hence my confusion. They say "black holes may be radically different from what Einstein's theory of relativity predicts, and lack event horizons."

[notFritzArgelander]

OK, sorry for the dumb question, but how can a black hole not have an event horizon? Isn't the event horizon the thing that makes it black?

Hawking radiation is a quantum mechanical effect which would make an event horizon not black. There would be radiation from the event horizon at a temperature that is inversely proportional to the BH mass. So if a BH is larger then the temperature of radiation is lower. With quantum effects a BH is only truly black if its temperature is lower than its environment. Otherwise it could be luminous.

https://en.wikipedia.org/wiki/Hawking_radiation

Note that a solar mass BH has a radiation temperature of about 6x10^(-8) K. So to be in equilibrium with the CMB a BH would need to be about 2x10^(-8) solar mass.

But in addition there's the possibility that there is quantum structure at the event horizon. That's the main point.

Also.... note that a freely falling observer never sees an event horizon. It's really an artifact of choosing a non inertial reference frame.

Thanks. I knew about Hawking radiation. But, truly black or not, it seems a "black hole" still needs to have an "event horizon" (defined as where the escape velocity is equal to the speed of light), right? Yet the article said a black hole might not have an event horizon. Hence my confusion. They say "black holes may be radically different from what Einstein's theory of relativity predicts, and lack event horizons."

Yes, they did. I think that's remote as a possibility, though. I'd buy some structure at smaller than Planck lengths but I think that the fact that a freely falling observer would see nothing gives it some credence.

[starguru]

String theory predicts BHs are really “Fuzzballs”. They are exactly the same as a BH from the outside, but inside instead of increasingly warped space time lies a mass of compressed strings. When a new particles falls onto the FB its string just gets added to the jumble already there.

The EH of a FB is actually a physical boundary of the string structure, and it’s “fuzzy”, hence the name.

To be clear a FB is a BH to the outside observer, only at the EH and inside would its nature differ. The interesting thing about FB is the radius of the FB is calculated to be the exact same as the Schwartzchild radius of a Bh. Moreover, this treatment resolved some of the problems of BHs, particularly the information loss issue.

You can read more in Wikipedia.

[notFritzArgelander]

String theory predicts BHs are really “Fuzzballs”. They are exactly the same as a BH from the outside, but inside instead of increasingly warped space time lies a mass of compressed strings. When a new particles falls onto the FB its string just gets added to the jumble already there.

The EH of a FB is actually a physical boundary of the string structure, and it’s “fuzzy”, hence the name.

To be clear a FB is a BH to the outside observer, only at the EH and inside would its nature differ. The interesting thing about FB is the radius of the FB is calculated to be the exact same as the Schwartzchild radius of a Bh. Moreover, this treatment resolved some of the problems of BHs, particularly the information loss issue.

You can read more in Wikipedia.

This is more of a proposed hypothesis within String Theory than a necessary consequence.

[starguru]

String theory predicts BHs are really “Fuzzballs”. They are exactly the same as a BH from the outside, but inside instead of increasingly warped space time lies a mass of compressed strings. When a new particles falls onto the FB its string just gets added to the jumble already there.

The EH of a FB is actually a physical boundary of the string structure, and it’s “fuzzy”, hence the name.

To be clear a FB is a BH to the outside observer, only at the EH and inside would its nature differ. The interesting thing about FB is the radius of the FB is calculated to be the exact same as the Schwartzchild radius of a Bh. Moreover, this treatment resolved some of the problems of BHs, particularly the information loss issue.

You can read more in Wikipedia.

This is more of a proposed hypothesis within String Theory than a necessary consequence.

That's definitely true. What I find appealing about the idea is that

1. ST calculates the diameter of a fuzzball to be equal to the SR of a black hole
2. Resolves information loss paradox
3. Doesn't have the issue that general relativity basically predicts an infinite spacetime curvature at the singularity.
4. Sort of makes more intuitive sense that the BH is just an even more extreme form of degenerate matter.

This is all related to the OP because of what string theory says about the EH -- since it's a physical object in the fuzzball model, if LIGO can actually probe the EH there might be insights.

[75sinbad]

This is some really interesting research. Postulating that there might not even be an event horizon around some BH's throws a monkey wrench into General Relativity. Curious to see what the source of these lingering gravitational waves might be. And the authors won a prize for their research, too.

Not sure what you mean about lingering gravitational waves. And they won a prize for this?

[notFritzArgelander]

This is some really interesting research. Postulating that there might not even be an event horizon around some BH's throws a monkey wrench into General Relativity. Curious to see what the source of these lingering gravitational waves might be. And the authors won a prize for their research, too.

Not sure what you mean about lingering gravitational waves. And they won a prize for this?

Don't forget that folks doubt that these "lingering" echoes exist. Physics is not decided by prizes, it's decided by Nature. I'm not sure what prize you are referring to since I don't give a ripe red plum about prizes.

[75sinbad]

What do you mean that folks doubt this, from what I have seen there are more than 1 group who agree with this

[notFritzArgelander]

What do you mean that folks doubt this, from what I have seen there are more than 1 group who agree with this

So what?! There are many more that don't. LIGO data is shared and many groups have tried and failed to find the claimed echoes. If you would read and comprehend the material you would see your remark is off base.