We actually don’t know how fast the Milky Way’s supermassive black hole is spinning but there might be a way to find out

Unless Einstein is wrong, a black hole is defined by three properties: mass, spin, and electric charge. The charge of a black hole should be nearly zero since the matter captured by a black hole is electrically neutral. The mass of a black hole determines the size of its event horizon, and can be measured in several ways, from the brightness of the material around it to the orbital motion of nearby stars. The spin of a black hole is much more difficult to study.

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Astronomers Watch a Star Get Spaghettified by a Black Hole

The gravitational dance between massive bodies, tidal forces occur because the pull of gravity from an object depends upon your distance from it. So, for example, the side of Earth near the Moon is pulled a bit more than the side opposite the Moon. As a result, the Earth stretches and flattens a bit. On Earth, this effect is subtle but strong enough to give the oceans high and low tides. Near a black hole, however, tidal forces can be much stronger, creating an effect known as spaghettification.

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Black Holes Make Complex Gravitational-Wave Chirps as They Merge

Gravitational waves are produced by all moving masses, from the Earth’s wobble around the Sun to your motion as you go about your daily life. But at the moment, those gravitational waves are too small to be observed. Gravitational observatories such as LIGO and VIRGO can only see the strong gravitational waves produced by merging stellar-mass black holes.

The chirp of a gravitational merger is clear. Credit: LIGO/Caltech/MIT/University of Chicago (Ben Farr)
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Einstein. Right again

Most of what we know about black holes is based upon indirect evidence. General relativity predicts the structure of a black hole and how matter moves around it, and computer simulations based on relativity are compared with what we observe, from the accretion disks that swirl around a black hole to the immense jets of material they cast off at relativistic speeds. Then in 2019, radio astronomers captured the first direct image of the supermassive black hole in M87. This allows us to test the limits of relativity in a new and exciting way.

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The Shadow from M87’s Supermassive Black Hole has Been Observed Wobbling Around the Galaxy for Years

In April 2019, the Event Horizon Telescope (EHT) released the first direct image of a black hole. It was a radio image of the supermassive black hole in the galaxy M87. Much of the image resulted from radio light gravitationally focused toward us, but there was also some light emitted by gas and dust near the black hole. By itself, the image is a somewhat unimpressive blurry ring, but the data behind the image tells a more detailed story.

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Behold! The Black Hole Collision Calculator!

Black holes have been the subject of intense interest ever since scientists began speculating about their existence. Originally proposed in the early 20th century as a consequence of Einstein’s Theory of General Relativity, black holes became a mainstream subject a few decades later. By 1971, the first physical evidence of black holes was found and by 2016, the existence of gravitational waves was confirmed for the first time.

This discovery touched off a new era in astrophysics, letting people know collision between massive objects (black holes and/or neutron stars) creates ripples in spacetime that can be detected light-years away. To give people a sense of how profound these events are, Álvaro Díez created the Black Hole Collision Calculator (BHCC) – a tool that lets you see what the outcome of a collision between a black hole and any astronomical object would be!

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Why Can Black Hole Binaries Have Dramatically Different Masses? Multiple Generations of Mergers

On the 12th of April, 2019, the LIGO and Virgo gravitational wave observatories detected the merger of two black holes. Named GW190412, one of the black holes was eight solar masses, while the other was 30 solar masses. On the 14th of August that year, an even more extreme merger was observed, when a 2.5 solar mass object merged with a black hole nearly ten times more massive. These mergers raise fundamental questions about the way black hole mergers happen.

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Supermassive black holes can cloak themselves in a cocoon of dust, making them invisible even when they should be bright quasars

Quasars are the most powerful sources of light in the universe, but sometimes they’re hard to find. A team of astronomers used the Chandra X-ray Space Telescope to find some diamonds in the rough.

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A Black Hole Popping Out of a Traversable Wormhole Should Give Off a Very Specific Signal in Gravitational Waves

Gravitational wave astronomy has changed the way we view the cosmos. In only a few years we have observed the collisions of black holes and neutron stars, confirming our theoretical understanding of these strange objects. But as gravitational wave astronomy matures, it will allow us to probe the very nature of space and time itself. While that day is a long way off, it hasn’t stopped the theory folks from dreaming up new discoveries. For example, how it might look if a black hole and a wormhole interact.

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