A Giant Black Hole Destroys a Massive Star

Astronomers have made an unprecedented forensic study of a star that was torn apart when it ventured too close to a giant black and then had its insides tossed out into space.

NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton studied the amount of nitrogen and carbon near a black hole known to have torn apart a star. Astronomers think these elements were created inside the star before it was ripped apart as it neared the black hole.

Astronomers have found many examples of “tidal disruption events” in recent years, where the gravitational forces from a massive black hole destroy a star. This causes a flare, often seen in optical and ultraviolet light and X-rays, as the star’s debris is heated up. This one, called ASASSN-14li, stands out for several reasons.

At the time of discovery in November 2014, it was the closest tidal disruption to Earth — about 290 million light-years — in about a decade. Because of this proximity, ASASSN-14li has provided an extraordinary level of detail about the destroyed star. The research team applied new theoretical models to make improved estimates, compared to previous work, of the amount of nitrogen and carbon around the black hole.

The relative amount of nitrogen to carbon that was found points to material from the interior of a doomed star weighing about three times the mass of the Sun. This would make the star in ASASSN-14li one of the most massive — and perhaps the most massive — that astronomers have seen ripped apart by a black hole to date.

In addition to the unusual size of the destroyed star and the ability to conduct the detailed forensics on it, ASASSN-14li is also exciting because of what it means for future studies. Astronomers have seen moderately massive stars like ASASSN-14li’s in the star cluster containing the supermassive black hole in the center of our galaxy. Therefore, the ability to estimate stellar masses of tidally disrupted stars potentially gives astronomers a way to identify the presence of star clusters around supermassive black holes in more distant galaxies.

Until this study, there was a strong possibility that the elements observed in X-rays might have come from gas released in previous eruptions from the supermassive black hole. The pattern of elements analyzed here, however, appears to have come from a single star.

Credit: NASA/CXC/A. Hobart