From Manu: “Merging galaxies has concealed black holes.”

Manu Garcia, a friend from IAC.

The universe around us.
Astronomy, everything you wanted to know about our local universe and never dared to ask.


Credit: NASA / CXC / M.Weiss / NAOJ
This illustration compares the growth of supermassive black holes in two different types of galaxies. A growing massive black hole in a normal galaxy would have a donut – shaped structure of gas and dust around it (left). In a galaxy fusion, a sphere material obscures the black hole (right).

Black holes have a bad reputation in popular culture swallow everything nearby. Actually, the stars, the gas and dust can orbit black holes for long periods of time, until a disturbance pushes the material inward.

A fusion of two galaxies is one of those disturbances. As galaxies are combined and their central black holes are close, the gas and dust in the vicinity are pushed their black holes. A huge amount of high energy radiation is released as material quickly spirals into the black hole hungry, it becomes what astronomers call an active galactic nucleus (AGN).

A study using the telescope NuSTAR NASA shows that in the later stages of galaxy mergers, both gas and dust fall into a black hole where the very bright AGN is wrapped. The combined effect of gravity of the two galaxies slows the rotation speeds of gas and dust that would otherwise be orbiting freely. This energy loss drops the material onto the black hole.

“The later fusion to occur, the AGN be more covert,” said Claudio Ricci, lead author of the study published in the Royal Astronomical Society Monthly Notices. “Galaxies that are far away in the melting process are completely covered in a cocoon of gas and dust”.

Ricci and his colleagues observed penetrating X – ray emission of high energy of 52 galaxies. About half of them were in the final stages of the merger. Because NuSTAR is very sensitive to the detection of X – rays of higher energy, was instrumental in setting the amount of light which escapes the field of gas and dust covers an AGN.


The study was published in the Monthly Notices of the Royal Astronomical Society. The researchers compared the observations of NuSTAR of galaxies with data from observatories NASA Swift and Chandra and ESA ‘s XMM-Newton , who observe lower energy components of the X-ray spectrum If high energy X rays are detected in a galaxy, but low energy X – rays are not, that’s a sign that an AGN is very dark.

NASA/Chandra Telescope

NASA/SWIFT Telescope

ESA/XMM Newton

The study helps confirm the long-standing idea that an AGN black hole does most of its consumption while involved in the latter stages of a merger.

“A supermassivo black hole grows rapidly during these mergers,” Ricci said. “The results improve our understanding of the mysterious origins of the relationship between a black hole and its host galaxy.”

NuSTAR is a small scouting mission led by Caltech and managed by the Jet Propulsion Laboratory for NASA’s Science Mission Directorate at NASA Headquarters in Washington. NuSTAR was developed in collaboration with the Technical University of Denmark and the Italian Space Agency (ASI). The spacecraft was built by Orbital Sciences Corp., Dulles, Virginia. The mission operations center of NuSTAR is at UC Berkeley, and file official data is at the Scientific Research Center Archives High Energy Astrophysics NASA. ASI provides the ground station of the mission and a mirror file. JPL is managed by Caltech for NASA.

Published in NuSTAR on 9 May 2017.

See the full article here .

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