NASA Spots Starquakes in a Red Giant Orbiting One of the Galaxy’s Quietest Black Holes

With an unusual spin and internal structure, a distant red giant star orbiting a quiet black hole is defying expectations. Tiny vibrations in the star's light, captured by NASA's TESS satellite, suggest it may have collided with another star in the past, spinning much faster than normal. Its chemical makeup indicates it should be ancient, yet internal “starquakes” reveal it is only about five billion years old. The star, part of the Gaia BH2 system first identified by ESA's Gaia mission in 2023, provides a rare glimpse into the hidden history of stars quietly orbiting dormant black holes.

Stellar “Quakes” Reveal Rapidly Rotating Star's Hidden History

According to an Astronomical Journal report, researchers at the University of Hawaiʻi Institute for Astronomy (IfA) used these vibrations to probe the star's interior. Lead author Daniel Hey noted that “just like seismologists use earthquakes to study Earth's interior, stellar oscillations reveal unexpected details of the star's history.” Co-author Joel Ong added that the star's unusually rapid rotation, completing a full spin every 398 days, points to interactions with its companion or a past merger.

Unusual Chemistry and Oscillations Challenge Models of Red Giant Evolution

The star's alpha-rich chemistry suggests it should be much older, creating a puzzle about its formation. Comparison with another resting black hole system, Gaia BH3, reveals surprising differences in the oscillations, which are inconsistent with current models of low-metallicity stellar evolution.

Future observations by TESS will seek to determine whether the red giant's peculiarities stem from an earlier stellar merger and investigate how quiet black hole systems like this evolve.