Astronomers are reporting evidence that points to a massive star-eating black hole at the center of our Milky Way galaxy. The evidence comes from a powerful U.S. telescope that has orbited Earth for two years detecting x-ray sources in the universe. This finding shows that the Milky Way is not unique among galaxies after all.
Astronomers believe that the centers of most galaxies have massive black holes. Black holes of any size are extremely dense objects with gravity so powerful that they suck in stars, gas, and everything near them, like water swirling down a drain.
Despite the observations indicating the presence of massive black holes in other galaxy centers, U.S. space agency astronomer Alan Bunner says the Milky Way was once thought to be different. He said, "We always thought that our galaxy is benign in this respect - no special active nucleus at the core of our galaxy, peacefully avoiding this maelstrom of activity that we see in other active galaxies."
But in recent years, scientists have come to observe activity in the Milky Way's center that hints of a hungry massive black hole. Nearby stars are in frantically fast orbits as if they are being pulled by a powerful object.
Such activity is crucial to detecting black holes because the holes themselves cannot be seen. This is because their gravity is so enormous not even light can escape. But one of the best clues to a massive black hole, x-ray emissions, has been lacking at our galactic center, causing skepticism that one exists there. X-rays come from objects piling up as they enter the swirling vortex and generate extreme heat.
Now, astronomers from several U.S. and Japanese institutions have filled the x-ray gap and detected the best evidence ever for a massive black hole at the Milky Way's nucleus. Using the Chandra X-Ray Observatory, they have witnessed a powerful three-hour long x-ray flare that hints of one consuming a meal of stars and gas.
Team leader Frederick Baganoff of the Massachusetts Institute of Technology said the flash was seen where the edge of black hole's entrance would be. "This amount of energy," he said, "is 50 times the total output of our sun. Yet, the rise time is only about three hours, and after three-and-a-half to four, the entire event is over and it returns to its quiescent luminosity."
The previous faintness of the x-ray source had bothered the astronomers. They expected matter falling into the hole would shine more brightly. Team member Gordon Garmire of Pennsylvania State University says this left room for doubt about the black hole's existence - until the flash occurred. "You can't imagine the excitement when we saw that light curve," he said. "I mean, everyone was dancing up and down the hallways. So this gives us the first glimpse of the closest massive black hole that we have to us."
Earlier calculations indicate this black hole is 2.5 million times as massive as our sun. The latest ones hint that this huge mass is tightly packed into an area only the distance between Earth and the sun - 150 million kilometers.
University of Arizona astrophysicist Fulvio Melia says that according to Albert Einstein's theory of relativity, only a black hole can be that dense. Mr. Melia said, "Modern physics doesn't have any theory that could adequately account for such an object if this is not a black hole. There is only one category of massive objects. There is nothing else that we know about in the universe that would have a mass of 2.6 solar masses that could be confused with a black hole."
Despite the x-ray evidence, team leader Frederick Baganoff says it is not conclusive. He wants to conduct longer Chandra Observatory observations to find more flashes and link them to radio emissions from the same source. He hopes to have definitive evidence within a year.