Astronomers have uncovered the unusual history of a distant red giant star by “listening” to tiny vibrations rippling through it.
These vibrations, known as starquakes, revealed that the star may have gone through a violent past involving a collision or merger with another star. Today, it orbits a quiet black hole in a system known as Gaia BH2.
The discovery was made by researchers at the University of Hawaiʻi’s Institute for Astronomy using data from NASA’s Transiting Exoplanet Survey Satellite (TESS).
Although TESS is best known for searching for exoplanets, it is also capable of detecting slight changes in a star’s brightness.
In this case, those subtle flickers were caused by waves moving through the inside of the red giant, much like earthquakes that move through the Earth.
By studying these starquakes, the researchers were able to peer beneath the star’s surface and measure the properties of its core.
What they found was surprising. The star contains a high amount of elements known as “alpha elements,” which usually appear in very old stars formed in the early universe.
However, the vibrations revealed that this star is only about 5 billion years old. This strange mix of youth and ancient chemistry suggests the star did not evolve alone. Instead, it may have stolen mass from a nearby companion or merged with another star in the past, changing its structure and composition.
Other observations show that the star is also spinning much faster than expected. It completes one full rotation in just 398 days, which is unusually quick for a red giant of its age.
Scientists believe this rapid spin was likely caused by powerful gravitational interactions with its companion — the black hole. These interactions could have “spun up” the star over time, further pointing to a dramatic history.
The team also studied another black hole system, Gaia BH3, which has an even more unusual companion star.
Models predicted that this star should also produce detectable starquakes, but none were seen.
This puzzling result suggests that current theories about certain types of stars, especially those with very low metal content, may need to be revised.
Both Gaia BH2 and BH3 are considered “quiet” black holes because they are not actively pulling in material and do not emit strong X-rays.
They were discovered by measuring the subtle movements of the stars orbiting them. As future observations continue, scientists hope to learn more about how such hidden black hole systems form and evolve over time.
Source: KSR.
