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Missing Red Giant

Old stars may not be missing, they’ve just grown dim

The core of the Milky Way galaxy, shown here in infrared, appears to have many young stars but very few old ones.


New computer simulations provide a conclusive test for a hypothesis explaining why the center of the Milky Way galaxy appears to be filled with young stars but has very few old ones. According to the theory, the remnants of older, red giant stars are still there — they just aren’t bright enough to be detected with telescopes.

Simulations conducted at Georgia Tech investigated the possibility that these red giants were dimmed after they were stripped of tens of percent of their mass millions of years ago during repeated collisions with an accretion disk at the galactic center. The very existence of the young stars, seen in astronomical observations today, is an indication that such a gaseous accretion disk was present in the galactic center because the young stars are thought to have formed from it as recently as a few million years ago.


“Red giants could have lost a significant portion of their mass only if the disk was very massive and dense,” said Tamara Bogdanovic, the Georgia Tech assistant professor of physics who co-led the study. “So dense, that gravity would have already fragmented the disk on its own, helping to form massive clumps that became the building blocks of a new generation of stars.”

The study was published in The Astrophysical Journal. — Jason Maderer

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