Hubble Sees Dark Shadows That Could Be Cast by a Supermassive Black Hole

We use the term ‘supermassive black hole’ with a kind of casual familiarity. But stop and think about what they really are: Monstrous, beguiling singularities where the understood laws of physics and cosmology are brought to their knees. A region where gravity is so powerful that it warps everything around it, drawing material in—even light itself—and sometimes spitting out jets of energy at near-light-speed.

It was only recently that we got our first image of one of these monstrosities. Now, the Hubble has captured an image of a supermassive black hole (SMBH), or what might be part of its shadow, anyway.

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Merging Black Holes and Neutron Stars. All the Gravitational Wave Events Seen So Far in One Picture

The Theory of Relativity predicted the existence of black holes and neutron stars. Einstein gets the credit for the theory because of his paper published in 1915, even though other scientists’ work helped it along. But regardless of the minds behind it, the theory predicted black holes, neutron stars, and the gravitational waves from their mergers.

It took about one hundred years, but scientists finally observed these mergers and their gravitational waves in 2015. Since then, the LIGO/Virgo collaboration has detected many of them. The collaboration has released a new catalogue of discoveries, along with a new infographic. The new infographic displays the black holes, neutron stars, mergers, and the other uncertain compact objects behind some of them.

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Do neutron star collisions produce black holes?

In principle, creating a stellar-mass black hole is easy. Simply wait for a large star to reach the end of its life, and watch its core collapse under its own weight. If the core has more mass than 2 – 3 Suns, then it will become a black hole. Smaller than about 2.2 solar masses and it will become a neutron star. Smaller than 1.4 solar masses and it becomes a white dwarf.

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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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