Scientists think they’ve come up with an explanation for what they initially believed to be a “runaway” black hole speeding through the universe, which has been the subject of much debate in the scientific community.
Scientists have discovered a chain of stars 200,000 light-years long that was originally thought to follow a runaway black hole described as an “unseen unseen monster”, but it may actually be a disguised galaxy belonging to a relatively common type of galaxy known as flat galaxies.
Astronomers announced the “runaway” black hole, which has a mass of 20 million suns, earlier this year, based on observations of the Hubble Space Telescope.
The team was amazed at the size of the tail of stars that the black hole appears to be dragging away from its home galaxy.
It is believed that this stellar tail arose when the black hole, which is moving at a great speed equivalent to covering the distance between the Earth and the Moon in just 14 minutes, made its way through the gas, causing the formation of dense regions and the birth of stars in its wake.
But scientists weren’t sure why this black hole wasn’t greedily gobbling up gas and creating more turbulence as it moved through it. The galaxy from which the supermassive black hole was ejected was also supposed to be surrounded by a huge amount of gas.
These factors cast some doubt on the “runaway black hole followed by stars” scenario, and multiple teams of astronomers have begun to explore different, less exotic explanations for the observations.
In a recent study, a team from the Institute of Astrophysics of the Canary Islands (IAC) suggested that the intriguing observation could in fact be a galaxy without the appearance of a bulge at the edge. These thin or flat disk galaxies are fairly common in the universe.
“The movements of the stars, their size and quantity, are consistent with what has been seen in galaxies within the local universe,” said team member and researcher at the Institute of Astrophysics of the Canary Islands, Jorge Sanchez-Almeida, in a statement.
He added, “It is very satisfying to find a solution to this puzzle. The new proposed scenario is much simpler. On the other hand, it is unfortunate, because runaway black holes are expected, and this may be the first scenario that can be observed.”
To examine their interpretation of the Hubble observations, the team compared the supposed trail of stars to a well-known, less bulging galaxy called IC5249. This thin galaxy is located near our own Milky Way galaxy, and has a cluster of stars similar to the “tail” observed by Hubble.
Observations of the two dissimilar objects – the presumed runaway black hole’s tail and IC5249 – were surprisingly similar.
“When we analyzed the velocities of this distant structure of stars, we realized that they were very similar to those obtained from the rotation of galaxies. So we decided to compare a much closer galaxy and found it to be extraordinarily similar,” said co-researcher and team member Mireya Montes.
The relationship between the mass of what the team assumed to be a flat galaxy and its top speed of rotation convinced the team that the supposed “star tail” was in fact a galaxy behaving like a galaxy. However, this conclusion is unlikely to dampen interest in this object..
Astronomer Ignacio Trujillo added: “It is an interesting object because it is a very large galaxy at a very great distance from Earth, where the majority of galaxies are smaller.”