The James Webb Telescope has detected a 200,000 light-year long trail of gas and stars, perhaps caused by a black hole hurtling through a galaxy at great speed.
Astronomers have discovered an extremely long “cosmic trail” of gas and dust in a distant galaxy. This trail — similar to a “contrail” — could have been generated by the passage of a very massive object, perhaps a black hole, although an alternative origin is not ruled out, according to a new study.
Where it was found. The trail was spotted in the spiral galaxy NGC 3627 (also known as M 66), which is located about 31 million light-years away in the constellation Leo. NGC 3627 is part of the group known as the “Leo Triplet”, which also includes other nearby interacting galaxies. The “contrails” (or “contrails“) had already been observed in the Milky Way, but the one discovered in NGC 3627 is the clearest and most defined ever detected so far, and notable above all for its size.
Characteristics. The trail extends about 20,000 light-years (or ~6 kiloparsecs in the study’s model), which corresponds to about a fifth of the diameter of the galaxy itself. It is surprisingly narrow: the study speaks of a width of about 200 parsecs (~650 light years). Inside the trail, a “supersonic turbulence” is observed with dispersion of material at a speed of the order of 10 km/s and the trail is visible both thanks to the wavelength of the dust emission (in the infrared data of the JWST) and the movement of particular molecules (carbon monoxide), detected with radio waves by the ALMA telescope).
the origin of the trail. According to researchers Zhao and Li, who conducted the study based on a model developed by Li in 2021, the trail may have formed when a compact, massive object passed through the galactic disk and “gravitationally focused” the surrounding gas, leaving behind this linear structure of gas and dust. From the model and data, the researchers estimate that the object in question had a mass on the order of 10⁶ solar masses (one million times the mass of the Sun) and was traveling at a speed greater than 300 km/s as it passed through the galaxy.
Personal data. The model also suggests that the trail formed about 20 million years ago, a relatively short time in cosmic terms. According to the two researchers, the estimated mass of the object is compatible with both a massive black hole and the dense core of a dwarf galaxy that has crossed the main galaxy. Therefore, with current data, it is not possible to establish the identity of the object with certainty, even if Zhao explains: «From the data in our possession, however, the balance tips towards the passage of a black hole, but we cannot absolutely exclude the second hypothesis. In any case, if the object were a dwarf galaxy it could be too faint to be detected directly at that distance.”
In the future, very deep optical campaigns or even higher resolution ALMA observations may be able to identify it and thus solve the mystery.
Implications. If this interpretation is correct, the trail could be an example of how “dark objects” — black holes or galactic nuclei — interact with the interstellar medium as they pass through a galactic disk. The authors suggest that discovering other similar trails could help estimate how common these phenomena are, and therefore better understand the population of invisible massive objects passing through galaxies.