The first ever image of the supermassive black hole at the center of our galaxy has been published by the Event Horizon Telescope (EHT). It comes from the same team of over 300 international scientists who produced the first ever image of a black hole in another galaxy in 2019.
The dramatic new image—above—of what astronomers call Sagittarius A* (pronounced “Sagittarius A-Star”) was revealed today at a press conference at the European Southern Observatory (ESO) headquarters as well as a series of simultaneous events around the world. It follows 10 days of rumors and conjecture about what exactly was going to be announced.
You can download the incredible image for yourself here and take a virtual trip into the heart of the Milky Way here:
Taken using a network of 11 telescopes across the globe to produce an “Earth-size” telescope, the image actually shows not the black hole itself, but the shadow of the event horizon around Sagittarius A*—hence the name of the EHT.
A black hole is a massive, dense place in space where a gravitational field is so strong that not even light can not get out.
An event horizon is the boundary marking the limits of a black hole, effectively its surface. It’s where an object could escape from the black hole’s gravitational pull. However, beyond it everything is doomed.
With this image the EHT has completed what it set out to do back in 2015. The results are being published today in a special issue of The Astrophysical Journal Letters.
“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,” said EHT Project Scientist Geoffrey Bower from the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei.
What is Sagittarius A*?
It’s the supermassive black hole at the center of our Milky Way galaxy. It’s about 22 million miles across and a powerful sources of radio waves.
It was first discovered in 1974, but until now it’s not been possible to image it. It’s hoped that this new image will help astronomers study the properties of the accretion and outflow around our galaxy’s center. It will also further the study of fundamental black hole physics.
Where is Sagittarius A*?
About 27,000 light-years distant from us, Sagittarius A* is near the border of the constellations of Sagittarius (the Archer) and Scorpius (the Scorpion). It’s in that black, dusty lane in the above image of the Milky Way.
However, today’s image provides the first direct visual evidence of it.
Here’s a labeled map of our galaxy’s center, with the exact location of Sagittarius A* marked upon it:
What is the EHT?
The Event Horizon Telescope (EHT) project creates images of black holes. It uses a global network of radio observatories in unison to effectively create an Earth-sized telescope.
“The brightness and pattern of the gas around Sgr A* were changing rapidly as the EHT Collaboration was observing it — a bit like trying to take a clear picture of a puppy quickly chasing its tail,” said EHT scientist Chi-kwan (‘CK’) Chan, from Steward Observatory and Department of Astronomy and the Data Science Institute of the University of Arizona.
The final image of the Sgr A* black hole is an average of the different images the team extracted using the EHT’s 11 telescopes around the world:
What about the previous black hole image?
In 2019 the EHT released the first ever image of black hole at the center of the supergiant elliptical galaxy M87, which is in the constellation Virgo. It revealed a bright ring-like structure with a dark central region — the black hole’s shadow.
The second-largest black hole as seen from Earth, it’s about 1,000 times larger than the Milky Way’s black hole, but 2,000 times more distant.
The initial image published in 2019 was updated in 2021 to include the polarized light around the M87 black hole.
Black hole head-to-head: Sagittarius A* vs. M87
However, the two black holes imaged by the Event Horizon Telescope (EHT) Collaboration are very different. Our own Sagittarius A* black hole is over a thousand times smaller than the black hole at the center of the galaxy M87.
There are differences and similarities between the two black holes. “The gas in the vicinity of the black holes moves at the same speed—nearly as fast as light—around both Sgr A* and M87*,” said Chan. “But where gas takes days to weeks to orbit the larger M87*, in the much smaller Sgr A* it completes an orbit in mere minutes.”
“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,” said Sera Markoff, Co-Chair of the EHT Science Council and a professor of theoretical astrophysics at the University of Amsterdam, the Netherlands. “This tells us that General Relativity governs these objects up close, and any differences we see further away must be due to differences in the material that surrounds the black holes.”
Wishing you clear skies and wide eyes.