Science & Technology

Scientists capture first image of supermassive black hole in Milky Way and it is starving

The image produced is a strong proof of Einstein’s Theory of Relativity, say experts

By Rohini Krishnamurthy
Published: Thursday 12 May 2022

Over 300 scientists from across the globe have captured the image of Sagittarius A* (Sgr A*), the supermassive black hole sitting in the heart of the Milky Way galaxy — about 27,000 light-years away from the Earth.

Sgr A*, which is about four million times the mass of our sun, is starving, scientists said. Supermassive black holes typically feed on dust and gas from their surroundings.

It is like the black hole is eating one grain of rice every million years, Sara Issaoun, NASA Einstein Fellow at the Harvard & Smithsonian Center for Astrophysics, Boston, United States, said in a press briefing. She was a part of the international Event Horizon Telescope (EHT) group that imaged the black hole.

The image produced is a strong proof of Einstein’s Theory of Relativity, which had predicted that a massive yet compact object occupying the centre of the galaxy, Preeti Kharb from the National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, told Down To Earth.

Although we cannot see the black hole itself because it is entirely dark, glowing gas around it reveals a tell-tale signature: A dark central region (called a shadow) surrounded by a bright ring-like structure, the EHT researchers noted.

The image is thanks to eight radio telescopes located in remote corners of the world, which combined to form a single ‘Earth-sized’ virtual telescope called EHT.

A thick cloud of gas and dust envelopes Sgr A*, preventing ordinary telescopes from viewing it. Radio telescopes, on the other hand, allow astronomers to observe the naturally occurring radio waves emitted from stars, planets, galaxies, clouds of dust and molecules of gas.

The EHT observed our supermassive galaxy on multiple nights in 2017, collecting data for many hours in a row. The researchers collected 6,000 terabytes of data from this exercise.

They fed the data into a supercomputer, which analysed the information to create a high-resolution image of the black hole, according to the researchers.

This announcement comes three years after scientists produce the first-ever image of a black hole, M87*, which is 500 times more massive and 2,000 times more distant. M87 is a part of the Messier 87 galaxy, about 53.49 million light-years away from the Earth.

“Sagittarius A*and M87* are different, but the former is more common in the universe,” Kharb pointed out. “Most galaxies in the universe are supposed to host black holes like the one in our galaxy,” the expert said.

However, despite the differences between the two black holes, they share resemblances, surprising researchers.

“We have two completely different types of galaxies and two very different black hole masses, but close to the edge of these black holes, they look amazingly similar,” Sera Markoff, co-chair of the EHT Science Council and a professor of theoretical astrophysics at the University of Amsterdam, the Netherlands, said.

This is because Sgr A* is smaller but closer while M87 is bigger but distant, Kharb said.

Also, the environment around Sgr A* is more dynamic, posing challenges for experts trying to image it.  M87*, in contrast, was relatively easier, experts said.

The gas in the vicinity of the black hole takes days to weeks to orbit the larger M87* and minutes in the much smaller Sgr A*. This means the brightness and pattern of the gas around Sgr A* were changing rapidly, EHT scientist Chi-kwan (‘CK’) Chan, from Steward Observatory and Department of Astronomy and the Data Science Institute of the University of Arizona, US, said.

“It is a bit like trying to take a clear picture of a puppy quickly chasing its tail, he added.

The EHT team will continue spying on the Sgr A*. “The current image is the average image. They will get another average picture a couple of years from now,” Kharb said.

“The group will compare the two and create a movie that captures the motion of the gas around the black hole,” she added.

The EHT is adding more telescopes to its network. The ongoing expansion and significant technological upgrades will allow scientists to share even more impressive images and movies of black holes in the near future, the EHT scientists said in a press note.

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