The image you see here is a computer-generated model of the black hole at the center of the Milky Way, which we call Sagittarius A*. More precisely, it is a model of the “shadow” that Sagittarius A*, with its mass of four million suns, should cast. The glowing blob in the lower right corner is a hotspot–a clump of nearly annihilated matter orbiting the black hole at relativistic speeds. The bright ring that marks the circumference comes from photons that have orbited the black hole many times.
“That ridge”–the slender bright ring–”delineates the edge of the black hole,” says Avery Broderick, an astrophysicist at the Perimeter Institute for Theoretical Physics and the University of Waterloo who created the model. “Everything inside that ridge is the shadow. But there’s still stuff in front of the black hole you can see–that’s why the shadow isn’t completely black.”
The Event Horizon Telescope (EHT) is a massive astronomical undertaking intended to directly observe this shadow–to take a picture of a black hole. An international team of astronomers is working to link radio telescopes in Hawaii, California, Arizona, Chile, Mexico, the South Pole, France, Spain and Greenland to create an Earth-size interferometer capable of peering at the event horizon of Sagittarius A* and other supermassive black holes. If all goes well, a version of the EHT capable of imaging Sagittarius A* will see first light next year. And if the mathematical models are correct, it should see something resembling Broderick’s simulation.
I’m writing a book about this undertaking. I’ve been reporting on the EHT for the past two years, and I’ll be embedded with the project in the years ahead as the real action begins. Along the way, I’ll be writing about the journey on this blog.
The title of the blog is a reference to the 18th-century astronomer John Michell’s conception of a “dark star,” an object so massive that light cannot escape it. Black holes as we now understand them are very different from Michell’s dark stars, but “Dead Star Diaries” is a little too morbid for a blog title.
In the coming weeks I’ll be writing a series of introductory posts that will make things clearer. There is a lot to explain, starting with how, exactly, the Event Horizon Telescope will work, what it will take to create it, and what seeing the event horizon of a black hole could tell us.
I’ll also use this blog to track other matters related to black holes and the galactic center. Watch this space in the coming days for news about a highly anticipated cosmic event–the possible collision of a dusty blob (called G2) with Sagittarius A*. The object should be making its closest approach to the black hole any day. (Technically, this approach happened almost 30,000 years ago; that’s how far away the galactic center is in light years.) Some astronomers say G2 is a simple dust cloud, which Sagittarius A* could rip to shreds and perhaps even partially swallow. Others say fireworks are unlikely because the “cloud” is probably a star that the black hole won’t be able to destroy. With astronomers around the world watching, we’ll soon know which it is.