First Image of Supermassive Black Hole Sagittarius A*

First Image of Supermassive Black Hole Sagittarius A*
This image shows Sagittarius A*, the black hole at the center of the Milky Way galaxy. EHT Collaboration, CC BY-SA

At simultaneous press conferences around the world, astronomers have revealed the first image of the supermassive black hole at the center of the Milky Way galaxy: Sagittarius A*. The result provides compelling evidence that the object at the heart of our galaxy is indeed a black hole, and provides valuable clues about the workings of such giants, many of which are thought to reside at the center of galaxies.

Image using observations from a worldwide network of radio telescopes Center for Astrophysics | It was produced by a global research team called the Event Horizon Telescope (EHT), which includes scientists from Harvard & Smithsonian (CfA).

The image, which was announced today in a special issue of the Astrophysical Journal Letters, has long been awaited for the image of the massive object located in the very center of the Milky Way.

Scientists have previously seen stars orbiting something invisible, compact, and very large at the core of our galaxy. This strongly suggested that the object known as Sagittarius A* or Sgr A* was a black hole; today's image provides the first direct visual evidence of this.

"For decades, astronomers have wondered what lies at the heart of our galaxy, whose stars are held in gravitational fields by enormous gravity," says CfA astrophysicist Michael Johnson.

“With the EHT image, we got a thousand times closer than these orbits, where gravity is a million times stronger. At this close range, the black hole brings matter closer to the speed of light and bends the paths of photons in warped spacetime.”

The black hole itself is completely dark, but it reveals an image of glowing gas around it.

A dark central region surrounded by a bright ring-like structure called the shadow in these images. This new view shows light bent by the strong gravity of the black hole, which is four million times larger than the Sun.

"We now see the black hole swallowing nearby gas and light and pulling them into a bottomless pit," says Ramesh Narayan, a theoretical astrophysicist at Cfa. "This image confirms decades of theoretical work to understand how black holes eat."

Sagittarius A* is located 27.000 light-years away.

To arrive at the image, the team created the powerful EHT that connects eight existing radio observatories on the planet to form a single "Earth-sized" virtual telescope.

Based on the summit of Maunakea Hawaii, the Submillimeter Array (SMA), a joint operation between the CfA and the Academia Sinica Institute for Astronomy and Astrophysics, was one of eight instrumental telescopes used to capture the image.

Together, the telescopes observed Sgr A* on multiple nights in 2017, collecting data for hours in a row, similar to using a long exposure time on a camera.

“More than 10 years ago, we connected radio dishes in California and Arizona to the SMA and other telescopes in Hawaii, allowing us to explore features the size of the black hole shadow in Sgr A*.

“This breakthrough launched EHT and led us to the wonderful Sgr A* image that emerged today,” says Sheperd Doeleman, founding director of Eht.

Today's breakthrough follows the EHT collaboration sharing with the scientific world in 2019 the first image of a black hole called M87* at the center of the more distant Messier 87 galaxy.

The image of Sgr A*, only the second image taken of a black hole, shows that the black holes look remarkably similar, although Sgr A* is a thousand times smaller and less massive than M87*.

"Even though the sizes and surrounding environments of these two black holes are very different, it's surprising how similar the images look," says NASA Einstein and CfA astrophysicist Sara Issaoun. “This similarity stems from the most fundamental property of black holes: their extreme gravity.

The effect of this extreme environment on the orbit of the light we observe from the orbiting gas creates the shadow.

However, despite Sgr A* being much closer to Earth, the process of imaging Sgr A* was much more difficult than M87*.

“One day in the life of M87* is only one minute in the life of Sgr A*, and our telescopes have to observe for hours to gather enough data to form an image, so Sgr A*'s appearance is constantly changing, even as we try to view it. ” says Dominic Pesce, CfA astrophysicist.

Researchers have had to develop sophisticated new tools that take into account gas movement around Sgr A*.

While the M87* is an easier, more stable target, nearly all images look the same, this was not the case for the Sgr A*. Therefore, today's image of the Sgr A* black hole is the average of the different images the team has extracted, eventually revealing the giant lurking in the center of the Milky Way galaxy.

This effort was made possible by the creativity of more than 80 researchers from 300 institutes around the world who together make up the EHT Collaboration.

In addition to developing sophisticated tools to meet the Sgr A* imaging challenges, the team has worked diligently for five years.

All supercomputers were used to combine and analyze data while compiling an unprecedented library of simulated black holes to compare with observations.

The team is excited to finally have images of two very different sizes of black holes, providing an opportunity to understand how they compare and contrast.

Scientists have also begun using the new data to test theories and models of how gas behaves around supermassive black holes. This process is not yet fully understood, but is thought to play a key role in shaping the formation and evolution of galaxies.

 About the Event Horizon Telescope (EHT) 

EHT Consortium;

  • The Academia Sinica Institute of Astronomy and Astrophysics
  • The University of Arizona
  • The University of Chicago
  • The East Asian Observatory
  • Goethe-Universitaet Frankfurt
  • Institut de Radioastronomie Millimétrique
  • Large Millimeter Telescope
  • Max Planck Institute for Radio Astronomy
  • MIT Haystack Observatory
  • National Astronomical Observatory of Japan
  • Perimeter Institute for Theoretical Physics
  • Radboud University
  • The Center for Astrophysics | Harvard & Smithsonian.

It consists of 13 separate institutions.


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