The weight of supermassive black holes found in the center of galaxies is usually estimated by measuring the effects of the huge gravitational fields on the objects located in the vicinity of the black holes in question. Now, a new and precise weighing method developed at the University of California with the help of data provided by NASA's Chandra X-ray Observatory, estimates the mass of supermassive black holes simply by measuring temperature peaks in the center of the galaxy.

"This is tremendously important work since black holes can be elusive, and there are only a couple of ways to weigh them accurately. It's reassuring that two very different ways to measure the mass of a big black hole give such similar answers," said leader of the study Philip Humphrey of the University of California.

NGC 4649 is a giant elliptical galaxy housing a supermassive black hole in its center. The previous method used to measure the weight of the black hole indicated a possible mass 3.4 billion times that of the Sun. Measuring the temperature of the material in the vicinity of the black hole confirmed the accuracy of the previously used method, making the black hole of NGC 4649 the only known such object whose mass was measured through two distinct methods, and the biggest black hole in the local universe.

Fabrizio Brigheti of the University of Bologna and William Mathews of the University of California predicted more than a decade ago that gas in the center of the galaxy gets compressed and hotter as it spirals towards the black hole. The bigger the black hole, the higher the temperature of the material.

"It was wonderful to finally see convincing evidence of the effects of the huge black hole that we expected. We were thrilled that our new technique worked just as well as the more traditional approach for weighing the black hole," said Brighenti.

Currently, the black hole of the NGC 4649 galaxy appears to accrete little material, thus it produces relatively low amounts of light, which is why it has been mostly studied by observing the gravitational effects of the motions of the stars and gas in its vicinity.

"Monster black holes like this one power spectacular light shows in the distant, early universe, but not in the local universe. So, we can't wait to apply our new method to other nearby galaxies harboring such inconspicuous black holes," said Humphrey.