Wednesday, April 10, 2019

Black hole seen

We can now see a black hole for the first time. Science magazine explains:

Astronomers today revealed that they have taken a picture of a gargantuan black hole at the heart of the nearby galaxy Messier 87. The result is a powerful confirmation of Albert Einstein’s general theory of relativity, which was used to predict black holes more than a century ago. It is also a feat for the team of more than 200 scientists who toiled for years to produce the image by combining signals from eight separate radio observatories spanning the globe. . . .

Black holes have gravitational fields so strong that even light cannot escape, so they are defined by a black, featureless sphere called an event horizon. But the holes can nevertheless be seen because they acquire a disk of gas and whip it up to high temperatures so that it glows brightly at different wavelengths.

By seeing the shape of this ring, bent into an asymmetric crescent by the black hole’s gravity, a new era of astrophysics will begin. The precise size and shape of the ring will help researchers test Einstein’s gravitational equations to see if they stand up to the test or if some other theory of gravity may be needed.
For scale: black hole, sun:

(Image by XKCD.)