WASHINGTON -- 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 Thursday called a 鈥済entle giant鈥� on a near-starvation diet.
Astronomers believe nearly all galaxies, including our own, 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 super heated gas and dust.
The colourized image unveiled Thursday is from an international consortium behind the Event Horizon Telescope, a collection of eight synchronized radio telescopes around the world. Getting a good image was a challenge; previous efforts found the black hole too jumpy.
鈥淚t burbled and gurgled as we looked at it,鈥� the University of Arizona's Feryal Ozel said.
She described it as a 鈥済entle giant鈥� while announcing the breakthrough along with other astronomers involved in the project. 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 Ozel said this one is 鈥渆ating very little.鈥� It's the equivalent to a person eating a single grain of rice over millions of years, another astronomer said.
鈥淧ictures of black holes are the hardest thing to think about,鈥� said astronomer Andrea Ghez of the University of California, Los Angeles. She wasn't part of the telescope team bu t earned a Nobel Prize for the discovery of the Milky Way's black hole in the 1990s.
She said the image of 鈥渕y baby鈥� is exactly how it should be - an eerie-looking orange-red ring with utter blackness in the middle.
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.
鈥淚t is the cowardly lion of black holes,鈥� said project scientist Geoffrey C. Bower of Taiwan's Academia Sinica Institute of Astronomy and Astrophysics.
Because the black hole 鈥渋s on a starvation diet鈥� 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 A (with an asterisk denoting star). 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, 鈥渏ust sitting there doing very little.鈥�
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 1,500 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 5.9 trillion miles (9.5 trillion kilometres).
To get the picture, the eight telescopes had to coordinate so closely 鈥渋n a process similar to everyone shaking hands with everyone else in the room,鈥� 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
The project cost nearly US$60 million with $28 million coming from the U.S. National Science Foundation.
Even though it is quieter than expected, the centre of the Milky Way is an important place to study, Ghez said.
It's 鈥渓ike an urban downtown, everything is more extreme. It's crowded. Things move fast,鈥� Ghez said in an interview. 鈥淲e live out in the suburbs (in a spiral arm of the galaxy). Things are calm out here.鈥�
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