Free Astronomy Magazine September-October 2015

SPACE CHRONICLES host black holes with masses less than one percent of the galaxy. In CID-947, the black hole mass is 10 percent that of its host galaxy. Because of this remarkable dispa- rity, the team deduced this black hole grew so quickly the host galaxy was not able to keep pace, calling into question previous thinking on the co-evolution of galaxies and their central black holes. “The measurements of CID-947 cor- respond to the mass of a typical ga- laxy,” Trakhtenbrot said. “We there- fore have a gigantic black hole wi- thin a normal size galaxy. The result was so surprising, two of the astro- nomers had to verify the galaxy mass independently. Both came to the same conclusion.” “Black holes are objects that possess such a strong gravitational force that nothing – not even light – can escape,” said Professor Meg Urry of Yale University, co-author of the study. ”Einstein’s theory of relativity describes how they bend space-time it- self. The existence of black holes can be proven because mat- ter is greatly acceler- ated by the gravita- tional force and thus emits particularly high- energy radiation.” Until now, observa- tions have indicated that the greater the number of stars pres- ent in the host gal- axy, the bigger the black hole. “This is true for the local Uni- verse, which merely reflects the situation in the Universe’s re- cent past,” Urry said. Furthermore, previ- ous studies suggest the radiation emitted I n this illustration a black hole emits part of the accreted matter in the form of ener- getic radiation (blue), without slowing down star formation within the host galaxy (purple regions). [M. Helfenbein, Yale Univ./OPAC] n during the growth of the black hole controlled, or even stopped, the creation of stars as the released energy heated up the gas. This cu- mulative evidence led scientists to assume the growth of black holes and the formation of stars go hand-in-hand. The latest results, however, suggest that these processes work different- ly, at least in the early Universe. The distant young black hole observed by Trakhtenbrot, Urry and their col- leagues had roughly 10 times less mass than its galaxy. In today’s local Universe, black holes typically reach a mass of 0.2 to 0.5 percent of their host galaxy’s mass. “That means this black hole grew much more efficiently than its gal- axy – contradicting the models that predicted a hand-in-hand develop- ment,” he said. The researchers also concluded stars were still forming even though the black hole had reached the end of its growth. Contrary to previous as- sumptions, the energy and gas flow propelled by the black hole did not stop the creation of stars. "From the available Chandra data for the source, we also concluded that the black hole has a very low accretion rate, and is therefore reached the end of its growth. On the other had, other data sug- gests that stars were still forming throughout the host galaxy," Trakh- tenbrot said. The galaxy could continue to grow in the future, but the relationship between the mass of the black hole and that of the stars would remain unusually large. The researchers believe CID-947 could be a precursor of the most extreme, massive systems that we observe in today’s local Universe, such as the galaxy NGC 1277 in the constellation of Perseus, some 220 million light years away from our Milky Way.