Watching the Changing M87 Black Hole Event Horizon

Observed and theoretical images of M87*. The left panels display EHT images of M87* from the 2018 and 2017 observation campaigns. The middle panels show example images from a general relativistic magnetohydrodynamic (GRMHD) simulation at two different times. The right panels present the same simulation snapshots, blurred to match the EHT's observational resolution.

The event horizon is a fascinating part of a black hole’s anatomy. In 2017, telescopes around the world gathered data on the event horizon surrounding the supermassive black hole at the heart of M87. This was the first time we had ever seen an image of such a phenomenon. Since then, 120,000 more images of the region have been captured and, as astronomers sift through the data, their model of M87’s event horizon has evolved. 

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Recent Observations Challenge our Understanding of Giant Black Holes

Artist's impression of a white dwarf embedded in the disk of a giant black hole. Credit: NASA/Sonoma State University, Aurore Simonnet

Black holes are among the most mysterious and powerful objects in the Universe. These behemoths form when sufficiently massive stars reach the end of their life cycle and experience gravitational collapse, shedding their outer layers in a supernova. Their existence was illustrated by the work of German astronomer Karl Schwarzschild and Indian-American physicist Subrahmanyan Chandrasekhar as a consequence of Einstein’s Theory of General Relativity. By the 1970s, astronomers confirmed that supermassive black holes (SMBHs) reside at the center of massive galaxies and play a vital role in their evolution.

However, only in recent years were the first images of black holes acquired by the Event Horizon Telescope (EHT). These and other observations have revealed things about black holes that have challenged preconceived notions. In a recent study led by a team from MIT, astronomers observed oscillations that suggested an SMBH in a neighboring galaxy was consuming a white dwarf. But instead of pulling it apart, as astronomical models predict, their observations suggest the white dwarf was slowing down as it descended into the black hole – something astronomers have never seen before!

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About a Third of Supermassive Black Holes are Hiding

A supermassive black hole surrounded by a torus of gas and dust is depicted in four different wavelengths of light in this artist’s concept. Visible light (top right) and low-energy X-rays (bottom left) are blocked by the torus; infrared (top left) is scattered and reemitted; and some high energy X-rays (bottom right) can penetrate the torus. Image Credit: NASA/JPL-Caltech

Supermassive black holes can have trillions of times more mass than the Sun, only exist in specific locations, and could number in the trillions. How can objects like that be hiding? They’re shielded from our view by thick columns of gas and dust.

However, astronomers are developing a way to find them: by looking for donuts that glow in the infrared.

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The Hubble and FU Orionis: a New Look at an Old Mystery

This is an artist's concept of the early stages of the young star FU Orionis (FU Ori) outburst, surrounded by a disk of material. A team of astronomers has used the Hubble Space Telescope's ultraviolet capabilities to learn more about the interaction between FU Ori's stellar surface and the accretion disk that has been dumping gas onto the growing star for nearly 90 years. NASA-JPL, Caltech

In 1936 astronomers watched as FU Orionis, a dim star in the Orion constellation, brightened dramatically. The star’s brightness increased by a factor of 100 in a matter of months. When it peaked, it was 100 times more luminous than our Sun.

Astronomers had never observed a young star brightening like this.

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Astronomers Map the Shape of a Black Hole's Corona for the First Time

Illustration of material swirling around a black hole highlights the corona, that shines brightly in X-ray light. Credit: NASA/Caltech-IPAC/Robert Hurt

If you were lucky enough to observe a total eclipse, you are certain to remember the halo of brilliant light around the Moon during totality. It’s known as the corona, and it is the diffuse outer atmosphere of the Sun. Although it is so thin we’d consider it a vacuum on Earth, it has a temperature of millions of degrees, which is why it’s visible during a total eclipse. According to our understanding of black hole dynamics black holes should also have a corona. And like the Sun’s corona, it is usually difficult to observe. Now a study in The Astrophysical Journal has made observations of this elusive region.

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Simulating the Accretion Disk Around a Black Hole

Supercomputer simulations reveals the nature of turbulence in black hole accretion disks

Black holes are by their very nature, challenging to observe and difficult to spot. It’s usually observations of the accretion disk that reveal properties of the hidden black hole. There is often enough material within the accretion disk to make them shine so brightly that they can often be among the brightest objects in space. A wonderful image has been released which shows the highest resolution simulation of a black hole accretion disk ever created. 

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Not All Black Holes are Ravenous Gluttons

This artist’s impression shows the record-breaking quasar J059-4351, the bright core of a distant galaxy that is powered by a supermassive black hole. The light comes from gas and dust that's heated up before it's drawn into the black hole. Credit: ESO/M. Kornmesser

Some Supermassive Black Holes (SMBHs) consume vast quantities of gas and dust, triggering brilliant light shows that can outshine an entire galaxy. But others are much more sedate, emitting faint but steady light from their home in the heart of their galaxy.

Observations from the now-retired Spitzer Space Telescope help show why that is.

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A Black Hole Has Cleared Out Its Neighbourhood

An artist's illustration of a supermassive black hole (SMBH.) The JWST has revealed SMBHs in the early Universe that are much more massive than our scientific models can explain. Could primordial black holes have acted as "seeds" for these massive SMBHs? Image Credit: ESA

We can’t see them directly, but we know they’re there. Supermassive black holes (SMBHs) likely dwell at the center of every large galaxy. Their overwhelming gravity draws material toward them, where it collects in an accretion disk, waiting its turn to cross the event horizon into oblivion.

But in one galaxy, the SMBH has choked on its meal and spit it out, sending material away at high speeds and clearing out the entire neighbourhood.

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A Bizarre Pulsar Switches Between Two Brightness Modes. Astronomers Finally Figured Out Why.

Credit: ESO/M. Kornmesser

Pulsars are the lighthouses of the universe. These rotating dead stars shoot twin jets of radiation from their poles, usually with a predictable rhythm. But sometimes pulsars behave strangely, and one pulsar in particular has had astronomers scratching their heads for years. It’s called PSR J1023+0038, and a decade ago, it shut off its jets and began oscillating between two brightness levels in an unpredictable pattern. Now, scientists think they understand why: it is busy eating a neighboring star.

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Hungry Black Hole was Already Feasting 800 Million Years After the Big Bang

Artist view of an active supermassive black hole. Credit: ESO/L. Calçada

Black holes swallow everything—including light—which explains why we can’t see them. But we can observe their immediate surroundings and learn about them. And when they’re on a feeding binge, their surroundings become even more luminous and observable.

This increased luminosity allowed astronomers to find a black hole that was feasting on material only 800 million years after the Universe began.

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