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Milky Way’s black hole seen at last!

Milky Way's black hole: Blurred orange ring amidst a black bakground
Astronomers using the Event Horizon Telescope (EHT) have obtained the 1st direct image of the Milky Way’s black hole, a giant some 4 million times the mass of our sun. Image via EHT Collaboration.

1st direct image of Milky Way’s black hole

At press conferences around the world, scientists from the Event Horizon Telescope (EHT) and the European Southern Observatory (ESO) have revealed the first-ever image of the supermassive black hole at the center of our Milky Way galaxy.

The image shows a glowing ring of gas surrounding a dark area known as the black hole shadow, which measures around 72 million miles (115 million km) across. In other words, if this black hole shadow were in place of our sun, its outer edge would nearly coincide with the orbit of the planet Mercury. Our Milky Way’s supermassive black hole – designated Sagittarius A* or simply Sag A* (pronouced Sagg A-Star) lies some 26,000 light-years away. The actual black hole is at the center of the shadow, but is of course invisible.

This incredible scientific achievement is the result of the work of 300 scientists and engineers from many scientific institutions, working together around the world to create the EHT: a global array of radio telescopes linked together to form a radio telescope the size of the Earth.

Sag A* vs. M87’s black hole

In 2019, the EHT presented the first-ever image of a black hole: the one at the center of the M87 galaxy, some 54 billion light years away. Astronomers call it M87* (pronounced M87-star). M87’s black hole is vastly more massive than the black hole in our Milky Way. The black hole shadow for M87* is slightly larger than the diameter of our entire solar system.

Visually, the image of Sag A* looks remarkably similar to the one of M87*, with the difference that the glowing ring of gas around Sag A* is more elliptical: less circular and instead more like a circle someone sat down on. The ring is more unevenly-shaped than the near-circular ring around M87*. But the two black holes are hugely different in mass as well as size: M87* has 6 billion times the mass of the sun as against Sag A*’s 4 million solar masses.

And the rate at which the two black holes consume the material surrounding them is also vastly different: M87* is far more active and consumes the equivalent of 900 Earth-masses per day. Sag A* in our Milky Way is quieter, consuming just a thousandth of that.

Confirms Einstein, reveals fascinating details

Initial studies of the image have revealed that Sag A* confirms Einstein’s theory of general relativity to within an error margin of 10%; this was similarly confirmed by the pioneering image of M87*. Black holes, where physical laws are pushed to their limits, are superb testbeds for theories of gravity, magnetism and the behavior of matter in extreme environments. The two images are so similar because black holes are extremely simple objects, affected in the same way by gravity. The image has also revealed that Sag A* is rotating, and is face-on to us; in other words, we are not looking down on its poles. Both the black hole and the ring of gas around it are rotating in the same direction.

The new image was processed from more than 5.5 petabytes of data acquired during the EHT’s observing run in 2017. If you were to print that data out, the stack of paper would reach the moon! It has taken so long to process because of the motion of gas around Sag A*, which as seen from the Earth changes over hours. It’s like trying to photograph a moving car so that the image is not blurred. This has necessitated the development of thousands of computer simulations on powerful supercomputers to assist with extracting the image of the black hole without the blurring effect of the gas.

Since 2017, the EHT has added another three telescopes to the array, which will improve its resolution. The team will now study the new image in depth, while searching for new black hole targets in the sky that can be imaged with this remarkable technology. As one of the scientists at the presentation said, this is just the beginning, the start of a new chapter in astronomers’ quest to understand black holes and the nature of gravity.

Fuzzy, irregular orange and yellow ring with a black center.
The Event Horizon Telescope group announced May 12, 2022, that they captured the first image ever of Sagittarius A*, the black hole at the heart of our Milky Way galaxy.

Bottom line: Astronomers gave the world the first-ever direct image of our Milky Way’s supermassive black hole on May 12, 2022.

Via ESO

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