An article published in the “Astrophysical Journal” describes the discovery of the remnants of a galaxy of which only a small core remained after passing through a larger galaxy. A team of astronomers used the VLBA radio telescope to find this unique object cataloged as B3 1715+425 with a diameter that is now only 3,000 light-years and a supermassive black hole at its center.
The discovery of B3 1715+425, part of a huge galactic cluster located about two billion light years from Earth, was made by chance during a search for supermassive black holes and in particular of pairs of these objects. The observations with the VLBA (Very Long Baseline Array) of the US National Science Foundation showed that the supermassive black holes of almost all galaxies were at their center. One of these objects offset from the center would be proof of a galaxy merger.
In the galaxy cluster cataloged as ZwCl 8193, astronomers have found B3 1715+425, a very small object in a galactic scale thinking that the Milky Way, which is not particularly large, has a diameter of about 100,000 light years. As if that weren’t enough, B3 1715+425 is moving away from the core of a much larger galaxy at a remarkable speed, more than 2000 km/s (more than 1,200 mps), leaving a trail of ionized gas behind it.
These clues suggest that B3 1715+425 is the remnant of a normal galaxy after it passed through another larger galaxy. Most of its stars and its gas were ripped off during that transition by a galaxy that had a greater global gravity force leaving a nearly “naked” supermassive black hole, surrounded only by a small galactic core.
The long-term consequences of that passage are ongoing because B3 1715+425 is leaving behind a trail of gas. If it keeps on losing mass, in the future it won’t have enough gas to create new stars. According to James Condon of the National Radio Astronomy Observatory, in a billion years it will no longer be visible.
B3 1715+425 was discovered by accident but it’s possible that there are many other supermassive black holes that are “naked” or surrounded by just a few stars. Establishing if these objects are common will require specific research that will help us better understand the evolution of galaxies with their interactions, typically within galaxy clusters.
