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The Milky Way’s Black Hole

Sagittarius A*. Image credit: Chandra

Sagittarius A*. Image credit: Chandra

Most galaxies are home to a black hole at their center, and the Milky Way is no exception. The black hole that lives in the center of our galaxy is named Sagittarius A* (pronounced “Sagittarius A-star”) or Sgr A* for short.

It’s 26,000 light-years from Earth and  Sgr A* is measured to be about 14 million miles across. This means that the black hole itself would easily fit inside the orbit of Mercury. How much mass is crammed inside this relatively small space? The lower mass limit of the black hole itself is calculated to be more than 40,000 Suns. However, the radio-emitting part of Sgr A* is a bit bigger, about the size of the Earth’s orbit around the Sun (93 million miles), and weighs much, much more – 4 billion Suns.

Black holes have such a strong gravitational pull that nothing – not even light, which is the fastest anything can go in our Universe – can escape it. You may think that black holes should be invisible because they don’t emit light, and suck up everything in the vicinity, but they can actually be very bright. This is because as matter bunches up around them, friction causes the gas and dust to heat up and emit light. Here are a few images of our very own black hole in the X-ray, radio and infrared spectrum.

Sgr A*, like all other black holes, will try to eat anything that goes near it. But it’s not all destruction all of the time: the area around it is a good place for new stars to form. The black hole at the center of the Milky Way is very active, spitting out flares of gas from stars it has eaten.

If you want to know more, there is a whole book written just about our very own supermassive black hole. NOVA has a whole show (viewable online) about the history of Sgr A*, and the European Organisation for Astronomical Research in the Southern Hemisphere (ESO) has a video about a 16-year long  study to measure its mass.

Astronomy Cast covered black holes in detail in Episode 18, and the Milky Way in Episode 99, and there’s more about the Center of the Milky Way in the Guide to Space.

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