Astronomers Image Ring of cold gas around the central black hole of our galaxy

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Scientists have recently produced the first images of a giant black hole in a distant galaxy, but there is a supermassive black hole much closer to home. At the center of our own galaxy lies an invisible monster, whose gravity can help maintain the milky way. We can not see this black hole, but the observations have detected some of its effects as a sphere of overheated gas. A new study has now revealed the flip side, a relatively cold ring of gas around the black hole.

This black hole, known as Sagittarius A * (pronounced "Sagittarius A Star") is about 26 000 light-years from Earth. This is difficult to observe because we have to look through the Milky Way disk, but observations have shown that this region of space is populated by stars, nebulae, and hot and cold gas clouds. The gas must form a rotating accretion disk that extends over several tenths of a light-year from the horizon of the black hole events.

Until now, all we have seen is the hot part of this gas via the millimeter wave observations, which gives an incomplete picture of the effects of the black hole on the near space. All scientists have been able to say before that there was a component of cold gas, but we now have a faithful picture.

Of course, "cold" gas is a relative term here. The hot gases around Sagittarius A * are about 10 million degrees Celsius, which is two-thirds of the temperature in the center of the sun. This gas emits X-rays, one of the distinctive signs of a black hole. In comparison, cold hydrogen only reaches 10,000 degrees Celsius (18,000 degrees Fahrenheit). The researchers used Atacama's Large Millimeter / Subillimeter Array (ALMA) system to look for the low radio frequency signal from this cooling gas ring.

The resulting image (top) shows the flow of cold gas around Sagittarius A *. The mapping of the Doppler shift in the spectrum as the gas moves towards us and moves away from us revealed a ring structure. The red part moves away from the Earth and the blue part moves towards the Earth. The team said this ring of gas extended to one hundredth of a light year from the event horizon (about 1,000 times the distance from the Earth to the sun).

These data could provide new information on how black holes consume the nearby material. Hopefully this is something that will never concern us on Earth, but it can help us understand what is happening in other parts of the universe.

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