'Death sentence for star formation', yet Andromeda XXXV survived. How?

The Andromeda Galaxy, the nearest major galaxy to the Milky Way, has something lurking around its outskirts, something that should not exist at all. Astronomers have discovered a satellite galaxy called Andromeda XXXV. It is the dimmest and smallest satellite galaxy to be ever discovered. Experts are shocked to see this satellite galaxy since according to calculations, it should not be there.

Scientists are now trying to solve the mystery, since while Milky Way's satellite galaxies stopped churning out stars billions of years ago, Andromeda XXXV has continued to birth more stars.

The discovery of this satellite galaxy on the outer edges of the Andromeda was published in Astrophysical Journal Letters. A team of researchers led by the University of Michigan found the structure and the finding has changed their ideas about how galaxies form and survive in different cosmic environments.

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The dwarf galaxy is about 3 million light-years away and is proof that the universe harbours more mysteries and "helps correct what we do know and reveals more about what we don’t," Marcos Arias, lead author of the study, said.

Milky Way's satellite galaxies

The Milky Way is also surrounded by several satellite galaxies, and this is not the first one seen around Andromeda. However, what's different is that the earlier satellite galaxies were too big and bright, while this one is the faintest one yet seen.

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“These are fully functional galaxies, but they’re about a millionth of the size of the Milky Way,” the study’s senior author, Eric Bell, U-M professor and associate chair of astronomy said.

Till now, scientists have only managed to study the tiny galaxies around the Milky Way because of their proximity. Bell said, "It’s the first time we’ve done that outside our system.”

Hubble helped find the satellite galaxy

Bell and Eric used the Hubble Space Telescope to study the galaxy. The National Science Foundation and NASA, through the Space Telescope Science Institute, also supported the program.

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'Murder mystery' in Andromeda

What they found fascinated them. They saw that Andromeda XXXV was still churning out more stars, while stars in the satellite galaxies around the Milky Way mostly only had ancient stars.

“Most of the Milky Way satellites have very ancient star populations. They stopped forming stars about 10 billion years ago,” Arias said. “What we’re seeing is that similar satellites in Andromeda can form stars up to a few billion years ago—around 6 billion years.”

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Bell says there is a "murder mystery in Andromeda", where the larger host likely sucked the gas supply from the smaller galaxies, ending star formation.

Bell further said that when the universe got extremely hot for a second time after its birth, it was "a death sentence for star formation."

“We thought they were basically all going to be fried because the entire universe turned into a vat of boiling oil,” Bell said. However, why was Andromeda XXXV not fried is a question that might not get an answer anytime soon.