Black Hole at Milky Way centre a monster going hungry
The world’s first image of the chaotic supermassive black hole at the centre of our Milky Way galaxy doesn’t portray a voracious cosmic destroyer but what astronomers yesterday called a “gentle giant” on a nearstarvation diet.
Astronomers believe nearly all galaxies have these giant black holes at their bustling and crowded centre, where light and matter cannot escape, making it extremely hard to get images of them. Light gets bent and twisted around by gravity as it gets sucked into the abyss along with superheated gas and dust.
The colourised image unveiled yesterday is from an international consortium behind the Event Horizon Telescope, a collection of eight synchronised radio telescopes around the world. Getting a good image was a challenge; previous efforts found the black hole too jumpy.
The picture also confirms Albert Einstein’s general theory of relativity: The black hole is precisely the size that Einstein’s equations dictate. It is about the size of the orbit of Mercury around our sun.
Black holes gobble up galactic material but University of Arizona’s Feryal Ozel said this one was “eating very little”. It’s the equivalent to a person eating a grain of rice over millions of years, another astronomer said.
Scientists had expected the Milky Way’s black hole to be more violent, especially since the only other image from another galaxy shows a far bigger and more active black hole.
“It is the cowardly lion of black holes,” said project scientist Geoffrey C Bower of Taiwan’s Academia Sinica Institute of Astronomy and Astrophysics.
Because the black hole “is on a starvation diet” — so little material is falling into the centre — and that allows astronomers to gaze deeper, Bower said.
The Milky Way black hole is called Sagittarius. It’s near the border of Sagittarius and Scorpius constellations and is 4 million times more massive than our sun. Bower said it is probably more typical of what’s at the centre of most galaxies, “just sitting there doing very little.”
It is incredibly hot, trillions of degrees, Ozel said.
The same telescope group released the first black hole image in 2019. The picture was from a galaxy 53 million light-years away that is 1500 times bigger than the one in our galaxy. The Milky Way black hole is much closer, about 27,000 light-years away. A light year is 9.5 trillion kilometres.
To get the picture, the eight telescopes had to coordinate so closely “in a process similar to everyone shaking hands with everyone else in the room,” said astronomer Vincent Fish of the Massachusetts Institute of Technology.
Astronomers worked with data collected in 2017 to get the new images. The next step is a movie of one of those two black holes, maybe both, Fish said.