The “tail” of stars in the M61 galaxy suggests that M61 engulfed a smaller galaxy in the past, leaving behind a trace that is still visible today.
A few months after its official debut, the Vera C. Rubin Observatory keeps its promise: to rewrite the observable history of the Universe. Even before the scientific investigation began, the giant camera mounted on a Chilean mountain returned a test image that hid an unexpected discovery: a long trail of stars — a stellar stream — unfolding from a well-known galaxy, a sign that that galaxy may have in the past engulfed and dismembered a much smaller companion.
A very active galaxy. “This is the first stellar flow detected by Rubin,” explains Sarah Pearson, an astrophysicist at the University of Copenhagen. “It’s just a taste of how many structures of this type we will discover.” The result was described in the Research Notes of the American Astronomical Society.
The protagonist of the scene is Messier 61 (M61), identified for the first time in 1779 in the Virgo Cluster and since then the object of attention due to its intense activity. Messier 61 is in fact a “starburst” galaxy: it hosts extremely vigorous star formation phenomena and has produced several supernovae observed by astronomers.
It is located in the constellation Virgo (Virgo) and is a member of the Virgo cluster. It is located about 50-55 million light years from our galaxy. Its diameter is on the order of 100,000 light years: therefore of dimensions comparable to those of our Milky Way.
A record for Rubin. Despite in-depth observations conducted with first-rate instruments – including the Hubble and James Webb space telescopes – “no one had previously highlighted this stellar flux”, comments Aaron Romanowsky of San Jose State University, one of the authors of the study.
Carefully analyzing Rubin’s first image, obtained with the largest digital camera built to date, the team applied filtering to remove stray light and bring out the faintest trace. The flow extends for about 55 kiloparsecs — that is, about 180,000 light years — and is thus among the longest ever measured.
Swallowed by a dwarf galaxy. Its origin appears to be a dwarf galaxy torn apart by the tidal force of Messier 61: an encounter that may have triggered the very explosion of star formation observed in the larger galaxy. That single image, however, contains millions of galaxies and this work is only a preview.
Galactic Census. Over the next few years, Rubin will collect light from orders of magnitude larger celestial objects, providing an unprecedented census that should reveal how, where and when galaxies assemble and transform.
“We expect almost every galaxy to be surrounded by these flows — they are an integral part of the history of galaxy formation,” concludes Romanowsky. «Rubin will allow us to identify them even when they are very weak as in the case of M61».