Surprising new data from NASA’s Hubble Space Telescope suggest that the soft, settled “wing” of the Sombrero Galaxy’s disk may be hiding a troubled past. Hubble’s acuity and sensitivity has resolved tens of thousands of individual stars in the vast and extended Halo of the Sombrero, the region beyond the central portion of the galaxy, typically made of older stars.

These latest observations of the Sombrero are putting a twist on conventional theory, showing only a small fraction of the oldest, metal-poor stars in the halo, plus an unexpected abundance of metal-rich stars normally only found in the disk. of a galaxy, and the central bulge. One possible explanation would be one or more galaxy mergers in the past, although the majestic Sombrero shows none of the messy evidence of a recent merger of massive galaxies through galactic collisions.

“The Hat has always been a bit of a strange galaxy, which makes it very interesting,” said Paul Goudfrooij of the Space Telescope Science Institute (STScI) in Baltimore, Maryland. “Hubble’s measurements of metallicity (that is, the abundance of heavy elements in stars) are another indication that the Hat has a lot to teach us about the assembly and evolution of galaxies.”

“Hubble’s observations of the Hat halo are altering our generally accepted understanding of the composition of galaxies and their metallicity,” added STScI co-investigator Roger Cohen.

Long a favorite of astronomers and amateur sky watchers for its brilliant beauty and curious structure, the Sombrero Galaxy (M104) now has a new chapter in its strange history: an extensive halo of metal-rich stars with only a faint signal. of the expected metal-poor stars that have been observed in the halos of other galaxies. The researchers, puzzled by the Hubble data, turned to sophisticated computer models to suggest explanations for such a strange reversal of conventional galactic theory.

Those results suggest the equally surprising possibility of large mergers in the galaxy’s past, although the majestic structure of the Sombrero shows no evidence of a recent galactic collision. The unusual findings and possible explanations are published in the Astrophysical Journal.