Free Astronomy Magazine November-December 2015

31 SPACE CHRONICLES holes via the nature of their ultra- violet light emission," said Youjun Lu of the National Astronomical Observatories of China, Chinese Academy of Sciences. "The structure of our universe, such as those giant galaxies and clus- ters of galaxies, grows by merging smaller systems into larger ones, and binary black holes are natural consequences of these mergers of galaxies," added co-investigator Xinyu Dai of the University of Okla- homa. The central black hole is esti- mated to be 150 million times the mass of our sun, and the compan- ion weighs in at 4 million solar mas- ses. The dynamic duo completes an orbit around each other every 1.2 years. The lower-mass black hole is the remnant of a smaller galaxy that merged with Mrk 231. Evidence of a recent merger comes from the host galaxy's asymmetry, and the long tidal tails of young blue stars. The result of the merger has been to make Mrk 231 an ener- getic starburst gal- axy with a star- formation rate 100 times greater than that of our Milky Way galaxy. The in- falling gas fuels the black hole "engine," triggering outflows and gas turbulence that incites a fire- storm of star birth. The binary black holes are predicted to spiral together and collide within a few hundred thou- sand years. Mrk 231 is located 581 million light- years away. T his artistic illustration is of a binary black hole found in the center of the nearest quasar host galaxy to Earth, Markarian 231. Like a pair of whirling skaters, the black-hole duo generates tremendous amounts of energy that makes the core of the host galaxy outshine the glow of the galaxy's population of billions of stars. Quasars have the most luminous cores of active galaxies and are often fueled by galaxy collisions. [NASA, ESA, and G. Bacon (STScI)] T his simplified spectral plot shows the radiation emitted from the center of a nearby galaxy that hosts a quasar. Visible and infra- red light coming from a disk surrounding a central black hole in the middle of the galaxy is measured. Surprisingly, ultraviolet light from the disk, as mea- sured by the Hubble Space Telescope, shows a drop in radiation from the disk. This is evidence for a large gap in the center of the disk that is likely carved out by a second black hole orbiting the primary black hole. [NASA, ESA, and P. Jeffries (STScI)] n