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Behind the amazing photo of the Milky Way’s own black hole

Sagittarius A*, the supermassive black hole at the center of our galaxy, has fascinated cosmologists for years. Now we have pictures.

One of the reasons scientists are so fascinated by black holes is that they grip the fabric of time and space, slowing time to creep as matter swirls to a point of no return. The fact that black holes play a game with time captured the imagination of Lia Medeiros, a postdoctoral researcher at the Institute for Advanced Study, and part of the team that used an array of eight telescopes to create the first image of matter swirling around the Earth. supermassive black hole at the center of the Milky Way.

She was still a high school student when she first read that black holes warp time – and decided to find a way to make studying them her life’s work. Not only does time slow down near a supermassive black hole, but theoretically time and space within it would somehow switch places. Efforts to understand black holes could lead scientists to a more comprehensive understanding of the rest of our universe and its still mysterious origins.

The ambitious black hole imaging project is called the Event Horizon Telescope because it aims to look as close as possible to the boundary beyond which even light cannot escape the black hole’s gravity. Eight telescopes placed around the world work together to create each image. In 2019, the same team revealed a similar bright donut of matter swirling around a much larger but more distant supermassive black hole at the center of a galaxy called M87.

While both images required years of work and a team of more than 300 scientists, our own galaxy’s black hole posed more of a challenge. Although the black hole itself has a mass equivalent to 4 million suns, the glowing donut in the image occupies a relatively small area of ​​space, smaller than the size of Mercury’s orbit. It is also 27,000 light-years away and shrouded in a thick haze of gas and dust. Medeiros said to take their picture, they chose a particular wavelength in the radio spectrum that penetrated this thick wall of dust — similar to the way X-rays penetrate the human body.

As one of the theorists on the team, she helped figure out which wavelength would bring them closest to the black hole’s true event horizon, which is called Sagittarius A* because it’s in the constellation Sagittarius, although it’s much further away. than the other. stars that make up the shape.

A mass of 4 million suns is amazing, but this black hole is no freak of nature. That seems to be typical of the hearts, except for the smallest galaxies. And yet no one knows exactly when or how they originated.

That is, it is not known whether Sagittarius A* grew so large by consuming 4 million stars, or whether it was born from a lump in the primordial matter of the universe, after which stars began to light up around it. Or maybe black holes and galaxies are taking shape together. Our black hole is relatively silent, which is why it was so difficult to photograph anything up close. Team member Feryal Ozel of the University of Arizona called it “our gentle giant.”

Other black holes, far away, are engaged in much more violent, visible activity. The action of stars being torn apart and drawn to the event horizon creates light that shines at us from the far reaches of the cosmos, giving us a glimpse back to an earlier stage in the evolution of the universe.

Our black hole is currently in a quiescent phase, said Avi Loeb, a professor of astrophysics at Harvard. That’s because it has consumed most of the material within its reach. But it could erupt into new activity when our galaxy merges with our neighbor, Andromeda, shaking things up and bringing new stars and matter close enough to be drawn in. That won’t happen for another few billion years.

Black holes, like the origin of the universe, are considered singularities because time and space are curved to infinity. When cosmologists talk about the Big Bang, they extrapolate our expanding universe back in time until everything becomes infinitely dense and space becomes infinitely curved. The mass of the universe would be packed into an infinitesimal point. But many physicists take this as a sign that what is really happening can only be described with natural laws that have yet to be discovered.

It is at the Big Bang and in black holes that the laws of physics begin to falter — their behavior cannot be described by Einstein’s relativity, which works on a large scale, or quantum mechanics, which rules things on a micro-scale.

While nature is said to abhor a vacuum, Princeton University cosmologist James Peebles says physicists loathe singularities. “We hope the universe has a similar distaste,” said Peebles, who won a Nobel Prize in physics in 2019. If you extrapolate back in time, you start calculating “arbitrarily high temperature, arbitrarily high curvature of space … that’s a bad thing, we think.”

Bad, that is, it means that our laws of physics are not complete. Good thing because it leaves the door open for new theories that could be more revealing, more complete, and even useful to us here on Earth.

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