ALMA helps to take black hole snapshot
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Have you ever seen a black hole? Impossible, you’d probably say. After all, a black hole doesn’t emit any light – that’s why it’s called black. So there’s nothing to see, right? Still, astronomers hope to take the first ‘photo’ of the giant black hole in the center of our Milky Way galaxy. And ALMA will play an important role in the project.
It’s true: black holes don’t emit light or any other kind of radiation – not even the millimeter and submillimeter waves that ALMA can observe. They only suck in matter from their surroundings. But surrounding the black hole are clouds of gas and dust that do emit millimeter waves. So, it should be possible to see the black hole as a dark silhouette on a glowing background.
There’s one problem, though: the black hole in the center of the Milky Way is very far away: about 26,000 light-years. As a result, the image of the black hole’s ‘shadow’ is incredibly tiny. To see it, you would need a millimeter-wave telescope almost as large as the Earth!
No one has the money to build such a huge instrument. But astronomers use a clever trick. They link up many smaller telescopes, in Europe, North America, South America, on Hawaii, and at the South Pole. When working together, this network can take pictures just as sharp as one Earth-sized telescope would.
In early April, the 66 dishes of the ALMA observatory will take part in the new photo session. All millimeter waves from the Milky Way’s center will be precisely measured and timed. The same happens at the other observatories that take part in the project. The computer tapes carrying the observations will then be brought together, to be analyzed by a powerful supercomputer.
This all will take many months. Astronomers expect their first results no earlier than in the spring of 2018. And it won’t be a very sharp picture either. But the hope is that the shadow of the black hole will be visible. If that is the case, the snapshot will help us to better understand these mysterious objects.
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