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21 votes
Accepted

What is the mechanism through which mass is converted to thermal energy in the accretion disc of a black hole?

The "mass" falling in is the rest mass (at infinity). As the matter falls it gains kinetic energy. Most of the matter cannot fall directly into the black hole because it encounters a ...
ProfRob's user avatar
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14 votes
Accepted

What is a "Gentle Giant" Black Hole?

There's no "authoritative" definition, this is just the common meaning of the word "gentle" used in a popular science and science fiction context. A black hole might be gentle ...
James K's user avatar
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7 votes

How can Kerr black holes have a 'speed limit' to how fast they can spin?

Yes, general relativity does not contain anything preventing spacetime from expanding or moving superluminally (e.g. "warp drive spacetimes"): normally other constraints (e.g. the lack of ...
Anders Sandberg's user avatar
5 votes

Is it possible to detect gravitational lensing of both light and gravitational waves originating from the same event?

Yes; typically, if the light is lensed, the gravitational waves are also lensed, and vice versa. The main exception is if the lens is small. The current observatories, LIGO/Virgo/KAGRA, are sensitive ...
Sten's user avatar
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3 votes

Could the revolution of super-massive black holes around each other create a pulsar-array gravitational wave signal despite 'final parsec' problem?

TL;DR: We do have gravitational wave emission from supermassive black hole binaries (SMBHBs) at larger separations, but a background created from solely those binaries won't have the characteristic ...
HDE 226868's user avatar
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3 votes

Could a super massive black hole actually be primordial black hole in disguise?

Some people certainly think that primordial black holes could account for a significant fraction of dark matter and at least provide the seeds for growing supermassive black holes in the early ...
ProfRob's user avatar
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3 votes

What is the mechanism through which mass is converted to thermal energy in the accretion disc of a black hole?

All else being equal, the same object will produce less far-field gravitational force, the deeper it is in a gravitational well. This is not intuitive if you are used to newtonian gravity, but it’s ...
QuadmasterXLII's user avatar
3 votes
Accepted

How bright in the night sky would J0529-4351 (brightest quasar ever found) be if it were in our galaxy?

The (boldly titled) omnicalculator can do luminosity calculations. At 500 trillion solar luminosities, this object would have an absolute magnitude of -32, and if placed at 26000 light years distance,...
James K's user avatar
  • 123k
3 votes

How can Kerr black holes have a 'speed limit' to how fast they can spin?

As an addendum to @Anders Sandberg's excellent answer: The maximum limit on the spin is a consequence of two (not fully proven) conjectures that each imply the existence of this limit individually. ...
TimRias's user avatar
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2 votes

How can Kerr black holes have a 'speed limit' to how fast they can spin?

Spin too fast and you have a "naked" singularity Basically, yeah, that's exactly what's limiting the rotational speed of a black hole. Rotating black holes, also known as Kerr black holes, ...
Alastor's user avatar
  • 2,658
2 votes

ER=EPR and information fuelling cosmic expansion

It is a very possible interesting possibility. In fact this is already accounted for in a theory, and this hypothesis adds more to it. So Quantum entanglement could form casual boundries, according to ...
Arjun's user avatar
  • 1,464
2 votes

Is it possible to detect gravitational lensing of both light and gravitational waves originating from the same event?

I also posted my question on https://www.quora.com/Is-it-possible-to-detect-gravitational-lensing-of-both-light-and-gravitational-waves-originating-from-the-same-event/ There I received an answer from ...
Alex's user avatar
  • 701
2 votes

Do all black holes, including stellar-mass ones, rotate at nearly the speed of light? Also, what exactly does that do to their shape?

The maximum angular momentum, $J$, for a spinning black hole is given by $$ J \leq \frac{GM^2}{c}\ . $$ This corresponds to a maximally spinning black hole having a "spin speed" of $\leq c$ ...
ProfRob's user avatar
  • 153k
2 votes

Do all black holes, including stellar-mass ones, rotate at nearly the speed of light? Also, what exactly does that do to their shape?

If a black hole rotates, it decreases its Schwarzschild radius. Physics SE: Why does angular momentum shorten the Schwarzschild Radius of a black hole? Wikipedia: Rotating black hole; Formation are ...
Astrovis's user avatar
  • 705
2 votes

How do two supermassive black holes reach "the last parsec" in the case of merging galaxies?

There's a paper that gives exactly the formulae you are looking for by Sobolenko et al. (2021). They describe the merger of supermassive black holes as a three-phase process. These phases may overlap ...
ProfRob's user avatar
  • 153k
1 vote
Accepted

Could macroscopic primordial black holes have created metals shortly after the big bang?

I am a new user so if you find any error in my answer kindly correct it. Perhaps, but indirectly Heavier elements are made in nuclear furnaces, where processes such as nucleosynthesis/neutron capture ...
Arjun's user avatar
  • 1,464
1 vote

If black holes contain dark energy would the expansion of the universe be uniform?

In that model, black holes are assumed to spread out uniformly throughout the universe after their formation. This is typical behavior for dynamical dark energy models, but it's particularly necessary ...
Sten's user avatar
  • 4,693
1 vote

Could a super massive black hole actually be primordial black hole in disguise?

I am a new user so if there is any error in this post kindly send it in the comment section so that I can improve my answer Maybe, but it all comes down to the recessional velocity of the early ...
Arjun's user avatar
  • 1,464

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