Milky Way Black Hole Predicted To Swallow Gas Cloud Might 'Light' Up The Skies, Astronomers Say
The black hole at the center of our galaxy, the Milky Way, is expecting a visitor about as massive as the earth sometime this spring. It's a gas cloud, and scientists can only wait to see what will happen as it passes by. "Astronomers have never seen anything like this, much less with a front-row seat," the University of Michigan said in a recent news release.
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Scientists believe there's a black hole at the center of most galaxies in the universe. The one at the center of our galaxy, about 25,000 light-years away, is called Sagittarius A*. (The asterisk is pronounced by scientists as "star.") The gas cloud in its front yard is called G2. Right now, it's kind of circling the drain. Its molecules have been stretched out and are being spun by the black hole's gravitational pull. If it collides with other matter around Sagittarius A* and plunges into it, scientists say it would heat up into a specular light show before being swallowed in a hail of X-rays.
Or, they say, it might do nothing. "I would be delighted if Sagittarius A* suddenly became 10,000 times brighter," said Dr. Jon Miller, a University of Michigan astronomer on the team observing the collision. "However, it is possible that it will not react much — like a horse that won't drink when led to water."
Black holes aren't really holes at all. They're actually the leftover material from enormous dead stars that have exploded in a supernova. That matter gathers into an extremely tiny space: NASA compares it to the matter and energy of 10 suns being packed into New York City. The result is a gravitational force so great that nothing can escape — not even light (thus, "black" hole). That gravity is what keeps the spiral of the Milky Way spinning, and it often sucks asteroids and comets away from their host stars and into a whirling cloud around it. The result is friction and, in turn, bright flares of heat and light.
That's kind of what could happen here. In August, scientists at the Max Planck Institute for Extraterrestrial Physics in Germany were watching the cloud get stretched, yo-yo like, around the black hole, ScienceNews.org reported at the time. They said the gas cloud is moving at about 1,900 miles per second but that Sagittarius A* — which is 4.3 million times more massive than the sun — is causing the cloud to speed up.
Part of what makes this event so interesting to astronomers is that our black hole is a rather dim one, and we don't know a lot about how things get sucked into it, an event known as accretion. If that happens here, the G2 cloud will heat up around the perimeter of the black hole and start giving off X-rays. If it crosses the edge of the hole, called the event horizon, there's no escape, and there won't be any more trace of it. "If Sagittarius A* consumes some of G2, we can learn about black holes accreting at low levels — sneaking midnight snacks. It is potentially a unique window into how most black holes in the present-day universe accrete," Miller said.
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