Black Hole invisibly triggers star formation

Pamela L. Gay, Ph.D.
3 min readApr 24, 2023

There is a lot of stuff going on out in space.

One of my favorite recent news items is the story of a 200,000 ly long filament of baby stars and the black hole that likely triggered their formation.

According to a new paper in the Astrophysical Journal Letters, in 2022 the Hubble Space Telescope spotted a line of stars extending away from the dwarf galaxy RCP 28. Both the galaxy and the streak are quite faint, and remarkably, they are essentially the same color, which usually means they are made of the kinds of stars. According to the paper, this kind of a pairing hasn’t been seen before, and the team, led by Pieter van Dokkum, included this feature in a scheduled observing run with the Keck observatory.

HST/ACS image of the linear feature and its surrounds. [from 10.3847/2041–8213/acba86]

This new data revealed the galaxy has star formation and an irregular shape that are both consistent with the galaxy experiencing a recent merger. It also showed that the streak was truly weird.

We see streaks in astronomy all the time. Generally, they are caused by jets: Jets from disks around black holes or other high density stellar remnants, and jets from extremely young stars. When jets interact with their environment, we see them spread out and lose power as they move farther away from their source. This is consistent with what we see from water fountains, and even laser beams passing through dust or air.

This streak, however, is more tightly focused further from the galaxy than near the galaxy… and the streak is made of young stars, not tightly beamed gas… and while we’ve seen jets that caused star formation in the past, those jets, like all jets. Were associated with a disk of material … a disk that isn’t evident around the black hole or black holes in the center of this particular galaxy.

Note I said “Black holes”… plural.

Dokkum and his team postulate that what we might be seeing is a trail of star formation left behind by a runaway supermassive black hole that has been flung out of the dwarf galaxy after a merger. The physics of 3-body systems isn’t entirely stable, and if this system had 3 super massive black holes in its core, brought together through mergers between systems, it is possible one of those 3 dark objects was flung out. As it has traveled through space, it has shocked…



Pamela L. Gay, Ph.D.

Astronomer, technologist, & creative focused on using new media to engage people in learning and doing science. Opinions & typos my own.