The Event Horizon Telescope (EHT) project, which famously captured the first-ever image of a black hole in 2019, has done it again — this time capturing an image of a black hole within our own galaxy.
They have released an image of the enormous supermassive black hole at the center of the Milky Way, called Sagittarius A* or Sgr A* (pronounced “sadge-ay-star”). This monster black hole has a mass 4.3 million times the mass of the sun — though that makes it considerably smaller than the black hole previously imaged at the heart of Messier 87, which is an almost incomprehensible 2.4 billion times the mass of the sun.
Imaging a black hole is no easy task as these objects are so dense that they absorb anything that comes near them, even light. But that doesn’t mean that they are invisible, as the gas which comes close to them but has not yet been sucked into them glows brightly.
It is this glowing gas that the EHT astronomers searched for, which forms a ring with a distinctive dark shadow region in the center which represents the black hole itself.
“We were stunned by how well the size of the ring agreed with predictions from Einstein’s Theory of General Relativity,” said EHT Project Scientist Geoffrey Bower from the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, in a statement. “These unprecedented observations have greatly improved our understanding of what happens at the very center of our galaxy, and offer new insights on how these giant black holes interact with their surroundings.”
Imaging this black hole required international cooperation, as the EHT project brings together astronomers and telescopes from across the entire planet. To image Sagittarius A*, which is located 27,000 light-years away from Earth, the EHT project used data from eight radio observatories around the globe to create an enormous virtual telescope equivalent in size to the whole planet. It was the power of this virtual telescope collecting data across multiple nights which was able to create the image seen above.
Even though Sagittarius A* is much closer to Earth than Messier 87, imaging it was much harder due to Sagittarius A*’s smaller size, with the gas around it completing an orbit much faster. That meant the gas moved and changed as the astronomers tried to observe it, so they had to develop new software to allow for this. The project as a whole took more than five years and the work of over 300 researchers from 80 different institutions.
The result is this remarkable image, which is a stunning demonstration of the value of collaborative science in achieving that which was previously thought to be impossible. The discovery has been hailed by members of the space community around the world, including NASA Administrator Bill Nelson:
“The Event Horizon Telescope has captured yet another remarkable image, this time of the giant black hole at the center of our own home galaxy,” Nelson said in an emailed statement. “Looking more comprehensively at this black hole will help us learn more about its cosmic effects on its environment, and exemplifies the international collaboration that will carry us into the future and reveal discoveries we could never have imagined.”
The research is published in The Astrophysical Journal Letters.