The newly-discovered supermassive black hole resides in a compact star-forming galaxy around 7.7 billion years away and has a mass of 20 million solar masses. The object has left behind a never-before-seen 200,000-light-year-long ‘contrail’ of newborn stars, twice the diameter of our Milky Way Galaxy.
There are several ways for a supermassive black hole to escape from the center of a galaxy.
The first step is always a galaxy merger, which leads to the formation of a binary supermassive black hole at the center of the merger remnant.
The binary can be long-lived and if a third supermassive black hole reaches the center of the galaxy before the binary merges, a three-body interaction can impart a large velocity to one of the supermassive black holes leading to its escape from the nucleus.
Even in the absence of a third supermassive black hole, the eventual merger of the binary can impart a kick to the newly formed black hole through gravitational radiation recoil.
The velocity of the ejected supermassive black hole depends on the mechanism and the specific dynamics.
Generally the kicks are expected to be higher for slingshot scenarios than for recoils, although in exceptional cases recoils may reach approximately 5,000 km per second.
In both scenarios the velocity of the supermassive black hole may exceed the escape velocity of the host galaxy.
Identifying such runaway supermassive black holes is of obvious interest but difficult.
“We think we’re seeing a wake behind the black hole where the gas cools and is able to form stars,” said Dr. Pieter van Dokkum, an astronomer at Yale University.
“So, we’re looking at star formation trailing the black hole.”
“What we’re seeing is the aftermath. Like the wake behind a ship we’re seeing the wake behind the black hole.”
“The trail must have lots of new stars, given that it is almost half as bright as the host galaxy it is linked to.”
“The black hole lies at one end of the column, which…
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