General relativity makes very specific predictions about what black holes are and how they should appear, as shown in this simulation.
While working on his doctorate in theoretical physics in the early 1970s, Saul Teukolsky solved a problem that seemed purely hypothetical. Imagine a black hole, the ghostly knot of gravity that forms when, say, a massive star burns out and collapses to an infinitesimal point. Suppose you perturb it, as you might strike a bell. How does the black hole respond?
Other things to check out:
Alternatives to black holes are scarce and strange | Science
At one time, many physicists resisted the notion of a black hole, a ghostly, self-sustaining gravitational field so intense that not even light can escape. Now, theorists have few alternatives to these creepy holes in the universe.
Any alternative to a black hole must be some dark, dense material orb that's slightly bigger than a black hole of the same mass. (Were the thing smaller, its own gravity would create a black hole around it.) Observers might detect the orb's surface by spotting matter crashing onto it and heating up. Or they might deduce the greater size of the object as it swirls around a companion and tears into it before merging.
Missing supermassive black hole at centre of distant galaxy baffles scientists | Science & Tech
Researchers detect something highly unusual about bright cluster galaxy A2261-BCG, which could be a "recoiling" black hole.
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Scientists are baffled by a missing supermassive black hole which should by normal expectations sit in the centre of a distant galaxy.
Instead, according to researchers at a handful of North American universities, there appears to be something highly unusual about the bright cluster galaxy A2261-BCG.
Missing: Supermassive Black Hole With up to 100 BILLION Times the Mass of the Sun - Universe Today
The massive galaxy cluster Abell 2261 should have a supermassive black hole in its center. But it doesn’t. Astronomers have looked everywhere – even between the couch cushions. What’s going on?
Giant black holes, also known as supermassive black holes, are basically everywhere, sitting in the heart of almost every single known galaxy. Even our own Milky Way sports one, a beast over 4 million times the mass of the sun, known as Sagittarius A* (and the subject of the most recent award of the Nobel Prize in physics ).
And here's another article:
Scientists discover first-ever 'recoiling' black hole, Science News | wionews.com
Galaxy cluster's Abell 2261's brightest cluster galaxy, hosts a very massive black hole which is a result of a supermassive black hole merger
Scientists have discovered a 'recoiling' black hole at the center of a bright cluster of a distant galaxy that has baffled them.
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The National Aeronautics and Space Administration's Hubble Space Telescope and Subaru Space Telescope revealed a galactic core is larger than expected for a galaxy its size.
Are primordial black holes really giant gravitinos? | Space
Astronomers don't understand the origins of the biggest black holes in the universe. These black holes appear so early in the cosmological record that we might have to invoke new physics to explain their appearance.
New research proposes an intriguing origin story: the first black holes didn't come from stars but from clumps of super-exotic, super-hypothetical particles known as gravitinos that managed to survive the first chaotic years of the Big Bang .
Primordial black holes and the search for dark matter from the multiverse
The recent progress in fundamental theory, astrophysics, and astronomical observations in search of PBHs has been made by an international team of particle physicists, cosmologists and astronomers, including Kavli IPMU members Alexander Kusenko, Misao Sasaki, Sunao Sugiyama, Masahiro Takada and Volodymyr Takhistov.
To learn more about primordial black holes, the research team looked at the early universe for clues. The early universe was so dense that any positive density fluctuation of more than 50 percent would create a black hole. However, cosmological perturbations that seeded galaxies are known to be much smaller. Nevertheless, a number of processes in the early universe could have created the right conditions for the black holes to form.
Brian Cox admitted 'we know nothing' about black holes as expert dissected Einstein
They have since proved to be one of the universe's biggest enigmas, with the first one not spotted until 1971.
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Yet, as physicist Professor Brian Cox, in the same year, told Joe Rogan on his 'PowerfulJRE' podcast, scientists still grapple with understanding what exactly happens inside the vast, apparently empty and almost invisible phenomena found nearly everywhere in space.
Talking about black holes that aren't at the centre of galaxies, he said: "These little black holes, they're a few times the mass of the Sun.
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