World’s Weirdest Galaxy: NASA's Hubble Telescope Finds New Secrets About Sombrero

NASA's Hubble Space Telescope has recently revealed that the popular Sombrero galaxy may have had a more violent past than previously thought. Hubble's sharpness and sensitivity resolves tens of thousands of individual stars in the Sombrero's vast, extended halo, the region beyond a galaxy's central portion, typically made of older stars. Based on the huge number of metal-rich stars Hubble detected in the galaxy’s extended halo, astronomers believe the Sombrero galaxy could have once gone through a major merger with another galaxy.

"The Sombrero has always been a bit of a weird galaxy, which is what makes it so interesting," said Paul Goudfrooij of the Space Telescope Science Institute (STScI), Baltimore, Maryland. "Hubble's metallicity measurements (i.e.: the abundance of heavy elements in the stars) are another indication that the Sombrero has a lot to teach us about galaxy assembly and evolution," he added.

"Hubble's observations of the Sombrero's halo are turning our generally accepted understanding of galaxy makeup and metallicity on its head," said co-investigator Roger Cohen of STScI.

Sombrero Galaxy (M104) is a favourite of astronomers and amateur skywatchers due to the stunningly smooth brim of its disk. As with most galaxies, the Sombrero’s stars also extend far beyond the galaxy’s disk. This area of space surrounding the Sombrero is known as the Halo. Halos are packed with old, metal-poor stars. But using Hubble, astronomers resolved tens of thousands of stars in the Sombrero’s dim halo. They surprisingly found it contains many more younger, metal-rich stars than expected.

According to an official press release from Hubble, Sombrero Galaxy (M104) has a new chapter in its strange story — an extended halo of metal-rich stars with barely a sign of the expected metal-poor stars that have been observed in the halos of other galaxies.

"The absence of metal-poor stars was a big surprise," said Goudfrooij, "and the abundance of metal-rich stars only added to the mystery."

Utilising models and simulations, astronomers probed different ways the metal-rich stars could have ended up in the Sombrero’s halo. Based on the evidence, researchers feel that billions of years ago, the galaxy merged with another galaxy of similar mass.

However, Sombrero galaxy’s disk and halo don’t show any other signs that such an event happened though. Both have a silky smooth appearance, which doesn’t seem to suggest a turbulent past. Therefore, the team of researchers will continue to observe the Sombrero galaxy, especially when the powerful James Webb Space Telescope is launched in 2021.

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It is worth mentioning here that the unusual findings and possible explanations are published in the Astrophysical Journal.

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