They decipher the riddle of the runaway black hole

A mysterious trail of stars formed eight billion years ago and recently discovered by the Hubble Space Telescope has kept numerous research teams in check. With a size similar to that of our Milky Way, this enormous and narrow structure has given rise to numerous speculations about its origin.

According to a controversial first hypothesis, this trail of stars could be the result of the passage of a supermassive black hole through a huge cloud of gas. This assumption immediately fired the imagination of the astronomical community as it requires a large number of very complex and exceptional circumstances to occur simultaneously. For this reason, different scientific teams have continued to explore different less exotic scenarios capable of explaining what has been observed.

In a recent work, researchers from the Instituto de Astrofísica De Canarias (IAC) in Spain have concluded that this unusual star structure can be interpreted as a bulgeless galaxy seen edge-on. These types of galaxies, also called thin or flat galaxies, are relatively common. “The movements, size and number of stars match what has been seen in galaxies in the local universe,” explains Jorge Sánchez Almeida, IAC researcher and co-author of the study. “It is a huge relief to have found the solution to the mystery; the new proposed scenario is much simpler. In a sense it’s also a shame because we expect the existence of runaway black holes, and this could have been the first to be observed.”

To support the galaxy hypothesis, the scientific team compared the enigmatic structure with a known local bulge galaxy, IC 5249, which has a similar stellar mass, and found a striking agreement. In the words of Mireia Montes, a researcher at the IAC and co-author of the study, “when analyzing the speeds of this distant star structure, we realized that they were very similar to those obtained by the rotation of galaxies, so we decided to compare with a closer one and we notice that they are extraordinarily similar”.

Above: image of the object observed with the Hubble Space Telescope. Shows emission in the ultraviolet part of the spectrum. Middle: ultraviolet image of a local edge-on bulgeless galaxy (IC 5249). The similarities are obvious. Bottom: The same galaxy IC 5249 observed in the visible part of the spectrum. The spatial scales of the three images are identical. (Photos: ESA/Hubble/NASA)

“We also explored the relationship between the mass of this supposed galaxy and its maximum speed of rotation, and we discovered that it is indeed a galaxy acting like a galaxy,” says Ignacio Trujillo, an IAC researcher who has participated in the study. “It is a very interesting object since it is a fairly large galaxy at a very distant distance from Earth where most of the galaxies are smaller,” he adds.

Future observations will allow us to study this object in greater detail.

The study is titled “Supermassive black hole wake or bulgeless edge-on galaxy?”. And it has been published in the academic journal Astronomy and Astrophysics. (Source: IAC)