In an incredible stroke of luck, Tess exoplanet-hunter satellite captured an unusual scene: a black hole swallowing a star. With that, he confirmed what astronomers already suspected: he is a gentleman, breaks the food before swallowing. It also cools it.
This process, technically called tidal disturbance, is a relatively rare occurrence that happens, estimated on average once every 10,000 to 100,000 years on the Milky Way. Of course, as it produces a powerful light signal, it can be seen even when it happens in other galaxies, which multiplies the chances of observing the phenomenon. Tess caught in a galaxy about 375 million light-years from Earth in the constellation Volans (Flying Fish) in the southern celestial hemisphere.
This is the first time the satellite has caught such a thing, but astronomers have seen about 40 similar occasions. The expectation was that Tess, during its initial two-year mission, would catch one or two of these occurrences. The fact that it happened so early was a stroke of luck. The satellite began its scientific operations in July 2018, and the first detection of the phenomenon, called ASASSN-19bt, took place in January of this year by Supernova Automatic Full-Sky Search (if you guessed that the acronym of the name, it's ASAS-SN, it's right).
The biggest prize, however, was that the cosmic event happened well in the area of the sky that is permanently monitored by Tess. Most of the celestial vault is observed by the satellite for periods of only 27 consecutive days. But in that corner, monitoring was virtually uninterrupted, allowing for the first time such a comprehensive collection of the phenomenon from start to finish.
The results, which involved observations with various ground and space telescopes, as well as precious Tess data, were gathered by Thomas Holoien's team from the Carnegie Observatories in California in an article published in The Astrophysical Journal.
Thanks to the temporal coverage of the Tess data, it was possible to confirm that it was indeed a tidal disturbance, which is basically the effect of gravity in the vicinity of the black hole that varies significantly within the star itself, between the most closer and farther from the black hole, causing it to shatter. (The Sun does this routinely with comets that pass too close to it, but it's much easier, since the gravity of the comets themselves is too weak to keep them whole.)
The data also showed that there is a cooling of the star during the shattering process from 40,000 to 20,000 degrees Celsius in a matter of days. This is the first time this process has been observed, although it was already predicted by some theoretical models of the phenomenon.
Apparently, the episode involved a supermassive black hole about 6 million times the mass of the Sun, swallowing a star similar to ours.