Saturday science subject: Seeing a black hole

Einstein's general theory of relativity predicts the existence of black holes, but nobody's ever actually seen one. As New Scientist reports, however, a team led by Shep Doeleman of MIT's Haystack Observatory is working to snap the first images of the supermassive black hole at the center of our galaxy.

That's no easy task. The object lies 30,000 light years away from Earth, and although it has about 4.5 million times the mass of our Sun, it's also only about the size of the "inner solar system." To put things in perspective, New Scientists says imaging Sagittarius A*'s event horizon (the point of no return for light around a black hole) is like trying to get a picture of a football on the Moon.

How do Doeleman and his team plan to do it?

No ordinary telescope could see such a small dark smudge. Instead, Doeleman is using a well-tested technique called very long baseline interferometry or VLBI. By combining the observations from widely separated dishes across the planet, radio astronomers can effectively reconstruct what would be seen by one enormous dish - even one as large as the Earth (see map). Because small dishes collect less light, a VLBI image is less bright than the image from a real planet-sized dish would be, but it can reveal just as much detail.

Using the part-built VLBI device, the team has already captured images "almost good enough" to show Sagittarius A*. You can see them in the gallery below, courtesy of

Of course, even though general relativity calls for Sagittarius A* to be a supermassive black hole, Doeleman and his team could end up with an image of something else. New Scientist says the team might see a boson star or something stranger yet—like an event horizon in a weird shape. That would imply relativity "is radically wrong when it comes to super-strong gravity," the article says.

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