First middle-weight black hole found hiding in dense star cluster
middle : One more cosmic missing link has been found: a middle sized black hole. Till now, scientists had found either small black holes weighing a few Suns or supermassive black holes weighing millions or billions of Suns, like the one at the center of our galaxy, the Milky Way.
But in an ancient cluster of stars some 13,000 light years away from Earth, scientists discovered an intermediate-mass black hole (IMBH) weighing 2,200 Suns. It was hiding at the center of the globular star cluster 47 Tucanae.
“We want to find intermediate-mass black holes because they are the missing link between stellar-mass and supermassive black holes. They may be the primordial seeds that grew into the monsters we see in the centers of galaxies today,” says lead author Bulent Kiziltan of the Harvard-Smithsonian Center for Astrophysics(CfA).
47 Tucanae is a 12-billion-year-old star cluster located in the southern constellation of Tucana the Toucan. It contains thousands of stars in a ball only about 120 light-years in diameter. It also holds about two dozen pulsars that were important targets of this investigation.
47 Tucanae has been examined for a central black hole before without success. In most cases, a black hole is found by looking for X-rays coming from a hot disk of material swirling around it. This method only works if the black hole is actively feeding on nearby gas. The center of 47 Tucanae is gas-free, effectively starving any black hole that might lurk there.
A black hole also betrays its presence by its influence on nearby stars causing them to speed up. But the crowded center of 47 Tucanae makes it impossible to watch the motions of individual stars.
Scientists studying 47 Tucanae found that heavy stars nearer the center were getting speeded up and flung away as if a cosmic “spoon” was stirring the pot. This was measured by the astronomers and compared with computer simulations, leading them to conclude that there was some very heavy body at the center causing this gravitational stirring.