Things can get pretty messy when a black hole swallows a star. Take, for example, the event known as ASASSN-14li, where a massive star came very close to a supermassive black hole and paid the ultimate price. There are two main dangers associated with a black hole. First, there is an event horizon. The curved masses of space and black holes contain so much mass in such a small space that space-time collapses on itself, creating a cosmic trap. Anything that crosses the event horizon is lost forever. The second is the threat of tidal forces.

When an object approaches a dense mass such as a planet, star, or black hole, the part closest to the mass is pulled slightly more strongly than the part farthest from the mass. Gravity tries to compress the body into an oval or egg shape, not a spherical shape. Since these forces between the Earth and the Moon cause ocean tides, they are known as tidal forces. Normally, tidal forces are quite small, but near massive objects such as a black hole, tidal forces can be so strong that they can tear objects apart and cause what’s called a tidal disruption event (TDE).

When a star approaches a black hole, tidal forces often tear the star apart long before it reaches the event horizon. So how much of the star is absorbed by the black hole depends on the star’s initial orbit. In the ASASSN-14li sample, most of the star was not being absorbed by the black hole. TDE smashed the star and superheated its remnants; which emitted strong X-ray and ultraviolet light. While this was bad news for the star, it was great news for astronomers.

NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton telescope recorded the X-ray spectra of the event, and follow-up observations from other observatories provided the UV spectra. This gave astronomers a detailed look at the composition of the doomed star. In this latest work, the team was able to analyze the spectra of both the material captured in orbit around the black hole and the gases escaping from the black hole. By comparing parameters such as the nitrogen and carbon content of the stellar remnants, the team confirmed that the mass of the star was about 3 Suns.

Earlier this year, astronomers observed another TDE called Scary Barbie; this could be a 14 solar mass star, but this estimate is based on the overall luminosity of the event, not its spectrum. ASASSN-14li is currently the largest TDE with approved mass.

This event is a prime example of how stars move near a supermassive black hole. With further developments, we will even be able to study star clusters around supermassive black holes in other galaxies, helping us understand how the central cores of galaxies might evolve and the role they play in the evolution of stars. Source