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A black hole is a volume from which matter cannot escape. More formally, the coordinate speed of light at the event horizon - the boundary of a black hole - is zero, as measured by a sufficiently separated observer.

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Both are correct. During the inspiral, the frequency of wave is simply twice the frequency at which the holes revolve around their center of mass. It increases as the holes get closer and closer and r …
answered Feb 24 by G. Smith
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You can think of the information being discussed as being the precise arrangement of matter and radiation around the black hole. This should not seem strange as the information in books is the arrange …
answered Apr 4 by G. Smith
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No. Interplanetary, interstellar, and intergalactic space is a near vacuum because the matter from the Big Bang, which was originally more-or-less uniformly distributed throughout space, gravitated …
answered Nov 9 '18 by G. Smith
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In the widely-accepted Lambda-CDM model of cosmology, the Hubble constant is decreasing but approaching a constant value of 57 km/s/Mpc. (See https://en.wikipedia.org/wiki/Hubble%27s_law#Time-dependen …
answered Dec 4 '18 by G. Smith
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The angular momentum of a Kerr or Kerr-Newman black hole causes the event horizon to have an equatorial bulge. It emerges from solving the Einstein field equations for gravity and has nothing to do wi …
answered Dec 28 '18 by G. Smith
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Photons are their own antiparticle, so they are the same in an universe of matter and a universe of antimatter.
answered May 2 by G. Smith
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If it is not a black hole, then light can escape from it. Why? Because a black hole is defined as something light cannot escape from.
answered Jan 15 by G. Smith
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A Schwarzschild black hole has no charge and no electrostatic potential. This is the potential of a Reissner-Nordström black hole, in Gaussian units. If you are talking about the potential of a point …
answered Feb 9 by G. Smith
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A black hole evaporates by radiating away energy in the form of photons, gravitons, neutrinos, and other elementary particles in a process that involves quantum field theory in curved spacetime. This …
answered May 25 by G. Smith
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Yes, black holes are four-dimensional. Spacetime is four-dimensional (three dimensions of space and one dimension of time), and black holes are just a particular type of curved spacetime. No, black h …
answered Jun 30 by G. Smith
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The mass of a black hole cannot be spread around its event horizon. The solution to Einstein’s equations representing a black hole has zero energy density at the horizon. It also has zero energy densi …
answered Jan 13 by G. Smith
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The jets are not ejected from inside the black hole. They are ejected from the accretion disk outside the event horizon. There is no paradox, and no violation of the laws of physics.
answered Apr 9 by G. Smith
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The project is using a network of radio telescopes to measure radio waves emitted by ionized matter in the accretion disk around the black hole, and by ionized matter in relativistic jets that are bei …
answered Apr 5 by G. Smith
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General Relativity is a classical theory, not a quantum theory. There is nothing in General Relativity that makes a black hole have a minimum radius for its event horizon. It can be arbitrarily small. …
answered Feb 26 by G. Smith
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A black hole in a stationary state is believed to be specified by only three parameters: its mass, charge, and angular momentum. (This is the famous “no-hair conjecture”.) These three parameters dete …
answered Jul 2 by G. Smith

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