A supermassive black hole pushed out of galactic core by gravitational waves

The quasar 3C 186 and its galaxy (Image NASA, ESA, and M. Chiaberge (STScI and JHU))
The quasar 3C 186 and its galaxy (Image NASA, ESA, and M. Chiaberge (STScI and JHU))

An article published in the journal “Astronomy & Astrophysics” describes the discovery of a supermassive black hole pushed out from its galaxy’s core. A team of astronomers led by Marco Chiaberge of the Space Telescope Science Institute in the USA used the Hubble Space Telescope to observe the quasar 3C 186 in which this phenomenon occurred. Another interesting element is that the black hole’s movement may have been accelerated by gravitational waves.

The quasar 3C 186 is located within a galaxy cluster about 8 billion light years from Earth. The researchers discovered it while they were conducting a survey of distant galaxies that emit huge amounts of radiation as a result of galactic mergers. They had quite a surprise when they found a quasar that was clearly offset from the core of a normally shaped galaxy because generally the supermassive black holes that power quasars are at the center of the galaxies that host them.

According to calculations, the supermassive black hole traveled over 35,000 light years from the center of its galaxy. The surprises were not over because the gas surrounding the black hole is estimetated to be moving from the galactic center about 7.5 million km/h (about 4.7 million mph). Since the gas is locked to the black hole, that means that from our point of view they will leave the galaxy in about 20 million years.

Studying the images captured by the Hubble Space Telescope, the researchers noticed traces of a galaxy merger now complete, suggesting that in the distant past the two supermassive black holes in the middle of the two galaxies also merged. This event was the culmination of an approach with the two black holes whirling around each other generating gravitational waves as illustrated by the sequence in the image below.

Two black holes with different rotation speed and mass emit gravitational waves more intense along a certain direction. The consequence is that when they collide they stop producing gravitational waves and the new black hole “recoils” in the opposite direction of the most intense gravitational waves.

Another hypothesis is that the quasar is actually in another galaxy of that cluster, in line with the observed one, giving the illusion that it’s within it. It’s unlikely because the researchers should have detected that other galaxy’s traces even though it’s in the background but it’s important to consider all the possibilities.

The hypothesis that the supermassive black hole was pushed out of the galaxy core is still by far the most likely. In this case, being able to observe it was a lucky event and the researchers plan to keep on studying it with the Hubble Space Telescope but also with other instruments such as the ALMA radio Telescope. Observations of electromagnetic emissions at diverse wavelengths such as infrareds and radio waves can help to have a more complete picture of this object’s nature.

Sequence of supermassive black hole merger and its consequences (Image NASA, ESA, and A. Feild (STScI))
Sequence of supermassive black hole merger and its consequences (Image NASA, ESA, and A. Feild (STScI))

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