Scientists can’t see the supermassive black hole, called Sagittarius A*, at the center of our Milky Way galaxy. But they can sense the enormous gravitational power it has on the stars around it. Stars, which astronomers can see, orbit the black hole at staggering speeds.
See for yourself. This video includes 16 years of observations from the European Southern Observatory. This isn’t an animation — it’s real images of stars sped up by a factor of 32 million. Watch them dance around a mysterious blank center.
And here’s a cleaner, illustrated version of similar observations, from the Keck Observatory in Hawaii.
On Tuesday, Andrea Ghez, an astronomer at UCLA, and Reinhard Genzel, of the Max Planck Institute for Extraterrestrial Physics in Germany and UC Berkeley, shared half of the Nobel Prize in physics for leading teams who made these extraordinary observations captured over three decades. (Ghez made them at the Keck Observatory, and Genzel led the European effort.) Ghez is now the fourth woman to have won the Nobel Prize in physics.
“Stretching the limits of technology, [Ghez and Genzel] refined new techniques to compensate for distortions caused by the Earth’s atmosphere, building unique instruments and committing themselves to long-term research,” the Nobel Committee writes. “Their pioneering work has given us the most convincing evidence yet of a supermassive black hole at the centre of the Milky Way.”
Ghez and Genzel share this year’s prize with Roger Penrose, an emeritus professor at Oxford, who theorized that the existence of black holes is compatible with Einstein’s theory of gravity.
“Einstein did not himself believe that black holes really exist,” the Nobel Committee writes. “In January 1965, ten years after Einstein’s death, Roger Penrose proved that black holes really can form and described them in detail; at their heart, black holes hide a singularity in which all the known laws of nature cease. His groundbreaking article is still regarded as the most important contribution to the general theory of relativity since Einstein.”
Ghez and Genzel also proved in their work how Einstein’s theory of gravity is fundamentally correct.
Star S2, which is marked in the video above with a yellow line, is around 15 times as massive as our sun. But it’s nothing compared with the black hole, which is estimated to be some 4 million times more massive than our sun. The gravity it produces whips S2’s orbit to around 11 million miles per hour, which is about 200 times the speed the Earth orbits around the sun. S2 completes one orbit in around 16 Earth years.
Recently, both Genzel’s and Ghez’s teams witnessed S2 passing by Sagittarius A* at a speed greater than 15.5 million miles per hour. That’s more than 4,300 miles every second, or nearly 3 percent of the speed of light. S2 completes its orbit around the black hole in just 16 years, which allows these teams of astronomers to precisely compare the predictions of Einstein’s gravitational theory of something orbiting such a massive black hole with actual observations, proving the theory is watertight.
All the work awarded with the Nobel Prize Tuesday laid the groundwork for scientists to peer even deeper and closer at the black holes that live at the center of galaxies. In 2019, a worldwide effort called the Event Horizon Telescope published the first up-close image of a black hole (the center of the Messier 87 galaxy). In the coming years, they may also resolve an image of the mysterious, powerful Sagittarius A* at the center of our galaxy. And finally, we’ll see the source of all this gravitational power.