How do you weigh the biggest black holes in the universe? One answer now comes from a completely new and independent technique that astronomers have developed using data from NASA's Chandra X-ray Observatory.
By measuring a peak in the temperature of hot gas in the center of the giant elliptical galaxy NGC 4649, scientists have determined the mass of the galaxy’s supermassive black hole. The method, applied for the first time, gives results that are consistent with a traditional technique.
Located about 51 million light years from Earth, NGC 4649 contains one of the biggest black holes in the local Universe, but there are no overt signs of its presence because the black hole is in a dormant state. The lack of a bright central point in either the X-ray or optical images shows that the supermassive black hole does not appear to be rapidly pulling in material towards its event horizon, nor generating copious amounts of light as it grows. Also, the very smooth appearance of the Chandra image shows that the hot gas producing the X-rays has not been disturbed recently by outbursts from a growing black hole.
Reassuringly, the estimate of the black hole's mass using the new technique is consistent with a more traditional technique using the motions of stars near the black hole. NGC 4649 is now one of only a handful of galaxies for which the mass of a supermassive black hole has been measured with two different methods.
Image Credit: X-ray (NASA/CXC/Univ. of California Irvine/P.Humphrey et al.); Optical (NASA/STScI)