If a black hole were to appear between the Earth and an observer, the Earth would appear ... [+] gravitationally lensed in a fashion similar to this, dependent on the Earth's position relative to the black hole and the observer. If a black hole were to form from the Earth itself, it would create an event horizon just 1.7 centimeters in diameter.
As it turns out, gravity doesn't need to be the only force: just the dominant one. As the matter collapses, it crosses a critical threshold for the amount of mass within a certain volume, leading to the formation of an event horizon. Eventually, some time later, any object at rest — no matter how far away from the event horizon it initially was — will cross that horizon and encounter the central singularity.
Other things to check out:
Physicists keep trying to break the rules of gravity but this supermassive black hole just said
That image of the supermassive black hole at the center of galaxy M87 was the first direct observation of a black hole's shadow — the imprint of the event horizon, a sphere around the black hole's singularity from which no light can escape. Einstein's theory predicts the size of the event horizon based on the mass of the black hole; and in April 2019, it was already clear that the shadow fits general relativity's prediction pretty well.
But no test is perfect. Watch how the sun's gravity tugs Mercury along its orbit, and you can measure general relativity in action. But telescopes can't measure the movement of Mercury down to the nanometer. And other forces — the tug of Jupiter's gravity, and Earth's gravity and the force solar wind, to name just a few — impact Mercury's movement in ways that are difficult to separate from the effects of relativity.
The spin of the supermassive black hole in the Milky Way
The Milky Way galaxy hosts a supermassive black hole (SMBH) at its center, Sagittarius A, with about four million solar-masses. At a distance of about twenty-seven thousand light-years, it is by far the closest such object to us, and even though it is not nearly as active or luminous as other supermassive galactic nuclei, its relative proximity provides astronomers with a unique opportunity to probe what happens close to the "edge" of a massive black hole.
CfA astronomers Giacomo Fragione and Avi Loeb realized that the spatial distribution of one group of cluster objects, the so-called S-stars, could be used to probe the spin. There are currently about forty known S-stars that orbit the SMBH in as little as 9.9 years, and recent analyses argue that collectively they lie in two nearly edge-on disks, with the stars in each disc rotating around the black hole but in opposite directions.
A Nobel for your black hole thoughts
This may worth something:
Watch a black hole eat a star | Boing Boing
Ever seen a black hole chow down on a star? Well, now you can. OK, it's a kind of crummy animated rendering, but the event is still cool and rare.
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The unusual "tidal disruption event" was visible in telescopes across the world. It appeared as a bright flare of energy, the closest of its kind ever recorded, at just 215 million light-years away.
Such events happen when a star gets too near to a black hole, and is pulled in by its extreme gravity.
Magnetic Fields on Earth: Black Hole-Sized Magnetic Fields
Think of a microwave running with nothing inside. It doesn’t spontaneously form a growing marshmallow. But if you put a marshmallow in there, now you can watch the marshmallow grow to many times its original size. Seeding the microtube reaction with a small magnetic field gives it something to blow up. In this case, the seed field is “by an external laser-plasma device such as a capacitor coil” also stimulated by a laser.
The scientists say their approach makes for more robust and practical magnetic fields partly because of the “geometrically unique” shape the mechanism induces. They explain:
The black hole always chirps twice: New clues deciphering the shape of black holes -- ScienceDaily
A team of gravitational-wave scientists led by the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) reveal that when two black holes collide and merge, the remnant black hole 'chirps' not once, but multiple times, emitting gravitational waves -- intense ripples in the fabric space and time -- that inform us about its shape. Today the study appears in Communications Physics (published by Nature).
Black holes are one the most fascinating objects in the Universe. At their surface, known as the 'event horizon', gravity is so strong that not even light can escape from them.
This supermassive black hole could reveal secrets of the early universe
This spider of a black hole first emerged when the universe was barely a billion years old and grew to gargantuan size almost as fast as Hagrid's acromantula Aragog (above) from Harry Potter and the Chamber of Secrets. Astronomers who used ESO's Very Large Telescope (VLT) to peer into space as it was billions of light years away, meaning billions of years back in time, have observed an unusual structure that an actromantula wouldn't mind hanging out in.
"This is the first spectroscopic identification of a galaxy overdensity around a supermassive black hole in the first billion years of the Universe," astronomer Marco MIgnoli, said in a study he recently led, published in Astronomy and Astrophysics . "Our finding lends support to the idea that the most distant and massive black holes form and grow within massive haloes in large-scale structures."
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