Even if you’re a huge star, you’re not always safe outside. When the orbit of a star three times heavier than ours brought it too close to a supermassive black hole, the black hole’s gravity tore out the star’s entrails and scattered them across a cosmic crime scene.
Nearly a decade ago, this tidal disruption phenomenon attracted the attention of scientists not only because of its enormity, but also because the carnage occurred relatively close to Earth, “just” 290 million light-years away. It’s also because it happened. The phenomenon, called ASASSN-14li, was almost mistaken for a supernova when it was discovered in 2014. Since then, even closer tidal disruption events have been discovered, but ASASSN-14li continues to attract the attention of astronomers. That’s because the star involved may be one of the largest, if not the largest, known to have been swallowed by a black hole. Now, new forensic analysis of the case reveals even more about this famous victim.
Although ASASSN-14li’s approach and the cause of the star’s death were already known, the research team needed to think like a space coroner to determine the star’s size. For this they relied on the following data: NASA’s Chandra and ESA’s XMM-Newton X-ray telescope. When a star is torn apart by the black hole’s gravity, the strength of the force heats up the star’s remains so much that a flare occurs. Such flares can be observed not only in visible and ultraviolet light, but also in X-rays.
During a flare, the black hole’s accretion disk pulls in gas from the collapsing star incredibly quickly, and energy is also released in the process. Chandra and her XMM-Newton observed this when the event was first discovered. Detections of such rapid accretion are rare because most stars annihilated by black holes tend to be smaller and therefore contain less gas.
By observing this phenomenon at X-ray wavelengths, telescopes were able to detect the carbon and nitrogen ejected into the black hole’s accretion disk. How much nitrogen was present compared to carbon helps scientists figure out a star’s mass when comparing that amount to the levels of the element in the Sun. Massive stars contain more nitrogen than carbon, so how they merge Converts hydrogen into heavier elements.
Previous simulations of tidal disruption events like ASASSN-14Li were unable to show whether the nitrogen and carbon that ended up in the black hole’s accretion disk came from high-mass stars. The research team could not rule out that possibility. Black holes are eating low-mass stars that have already shed their outer layers of matter.
Determining whether a massive star really met its end in ASASSN-14li is similar to reviewing DNA evidence from a crime scene, except with elements instead of genes. The gas in the black hole’s accretion disk contained nitrogen levels up to 100 times higher than the Sun’s and much lower carbon levels (only about 40 percent of that found in the Sun). This suggests that the black hole gutted a star with about three times the mass of the Sun.
Ramírez-Ruiz and his team believe that the gas observed by Chandra and XMM Newton’s X-ray vision suggests that the gas in the black hole’s accretion disk may be from just one star, due to the extreme ratio of nitrogen to carbon. He suggested that this indicates that it is most likely that It is difficult to find combinations of stars that produce similar ratios.
“ASASSN-14li is exciting because one of the most difficult things about tidal disruption is being able to measure the mass of an unlucky star, as we have done here,” said one of the paper’s authors. said Enrico Ramirez Ruiz, an astrophysicist at the University of California, Santa Cruz. Research at NASA press release.
ASASSN-14li now sets a precedent on which to base the search for larger stars destroyed by black holes. Its mass is similar to the mass of stars in star clusters near our galaxy’s supermassive black hole, Sagittarius A*. If star clusters in other galaxies are located in similar locations to supermassive black holes, tidal disruption events involving massive stars may occur more frequently than previously thought. However, a forensic investigation is required.
Astrophysical Journal Letters, 2023. DOI: 10.3847/2041-8213/ace03c