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Astronomers Unveil Growing Black Holes in Colliding Galaxies

An international team of researchers, including Claudio Ricci, professor of the Nucleo de Astronomia, performed the largest survey of the cores of nearby galaxies in near-infrared light, using high-resolution images taken by NASA’s Hubble Space Telescope and the W. M. Keck Observatory in Hawaii. The Hubble observations represent over 20 years’ worth of snapshots from its vast archive. The team discovered that a large number of AGNs, or rapidly growing black holes, especially those with high luminosities, are generated by collisions between galaxies. High-resolution observations were used to perform this work, which permitted to look through the thick layers of gas and dust that cover these regions. This is the largest study of this type, and the professor of the Institute of Astrophysics of the Pontificia Universidad Catolica de Chile, Ezequiel Treister, also participated. The study was published today on the prestigious scientific journal Nature.

AGNs release large amounts of energy due to the accretion of gas and dust onto the supermassive black hole that lies at the center of almost all massive galaxies. During this period of accretion they become some of the brightest energy sources in the Universe. With this study it was possible to observe the nuclei of galaxies just before the fusion of the black holes with such a high resolution that it was possible to resolve very small separations.

The video shows simulations of  galaxy mergers, along with the observations of the Keck Telescope.

 

The observations were carried out, using adaptive optics, at the Keck Observatory (Hawaii), and were complemented with data from the Hubble Space Telescope. The sample included a wide range of luminosity, as well as sources obscured by dust and gas.

Left: Tricolor images from the SDSS catalog of some of the galaxies of the sample, with the nuclei obscured by gas and dust. Right: Infrared images, obtained by the Keck Observatory, of the nuclei of these galaxies that show that they are merging.

Left: Images from the SDSS catalog of some of the galaxies of the sample, with the nuclei obscured by gas and dust. Right: Infrared images, obtained by the Keck Observatory, of the nuclei of these galaxies that show that they are merging.

 

Thanks to these observations at very high resolution we discovered that almost twenty percent of the AGNs are associated with the last stages of the galaxy collision process, that is, shortly before they merge and form a single, colossal black hole.  The interesting thing is that all this can be compared with simulations, which predict a very similar behaviour“, says Ezequiel Treister, who is also a researcher at the Centro de Astrofísica y Tecnologías Afines CATA.

The research detected nuclei of galaxies in these merging systems, and the analysis led to the conclusion that obscured black holes have a greater probability of being found in mergers. “The merger of galaxies is an important mechanism to obscure and feed supermassive black holes,” says Claudio Ricci.

According to Michael J. Koss (Eureka Scientific Inc.) the first author of this work, the images in this study show what will happen when our galaxy, the Milky Way, will merge with Andromeda. When black holes at the center of galaxies collide, they release energy in the form of gravitational waves, so this research could lead to predictions about the type of galaxies where these important cosmic events could be found.
Source: Nature