Researchers put all this into a false-color image, where orange represents high-intensity radio waves and black represents low-intensity. “But each telescope only picks up a tiny fraction of the radio signal,” explains Fulvio Melia, an astrophysicist at University of Arizona who has written about our galaxy’s supermassive black hole. Because we’re missing much of the signal, “instead of seeing a crystal clear photo, you see something that’s a little foggy … a little blurred.”
The image helps reveal more about the black hole’s event horizon — the closest point to which anything can approach the black hole without being sucked in. Beyond the event horizon, not even light can escape.
From the image, scientists have been able to better estimate the size of the event horizon and deduce that the accretion disk is tilted by more than 40 degrees from the Milky Way’s disk, so that we’re seeing the round face of the flat accretion disk, rather than the thin sliver of its edge.
But even if the black hole’s accretion disk were oriented edge-on relative to Earth, the gravity around the black hole warps the space around it so much that light emitted from the backside of the black hole would be bent around to come toward us, making a ringlike image regardless of its orientation. So, how do scientists know its orientation? Because the ring is mostly round; if we were viewing the accretion disk edge-on, then the ring would be more squished and oblong.
Markoff thinks that this new ability to look into the heart of our galaxy will help to fill in gaps in our understanding of the evolution of galaxies and the large-scale structure of the universe. A dense, massive object such as a black hole at the center of a galaxy influences the movements of the stars and dust near it, and that influences how the galaxy changes over time. Properties of the black hole, such as in which direction it spins, depend on the history of its collisions — with stars or other black holes, perhaps. “A lot of people … look at the sky and think of it all as static, right? But it’s not. It’s a big ecosystem of stuff that’s evolving,” Markoff says.
So far, the fact that the image matches the scientists’ expectations so precisely makes it an important confirmation of current theories of physics. “This has been a prediction that we’ve had for two decades,” Bower says, “that we would see a ring of this scale. But, you know, seeing is believing.”
Katie McCormick is a quantum physicist-turned-science writer based in Sacramento, California. Read more of her work at www.katiemccormickphd.com.
This article originally appeared in Knowable Magazine, an independent journalistic endeavor from Annual Reviews. Sign up for the newsletter.
10.1146/knowable-110822-1
