Today I’ll be writing about the very first topic I ever did research in, during my Bachelor’s thesis: Tidal Disruption Events (or TDEs), or the most dramatic way in which a star’s life can end.
Before getting into cool astrophysics stuff, let me remind you of how tides (roughly) work. Because of gravitation, the Moon attracts the Earth; however, because gravitation depends on the distance between two objects, points on the Earth that are closer to the Moon are attracted more, and vice versa. If the thing that’s being attracted isn’t solid – say, an Ocean – the result is that the Ocean gets deformed by gravity:
In practice it’s more complicated than that (the Sun also plays a role), but this is an easy enough schematic. So what does this have to do with stars?
Well, a similar thing happens to any fluid – including a star close to a supermassive black hole. In fact, if the star passes close enough to a black hole, this tidal force can be strong enough to completely rip it apart in a spectacular explosion, which we call a Tidal Disruption Event.
These events are interesting for many different reasons. First off, it turns out that the black hole devours the star very quickly, meaning that lots of matter falls onto it. This regime of lots of matter falling on a black hole is called super-Eddington accretion, and it’s very poorly understood. Second, TDEs occur mostly for relatively “small” supermassive black holes, meaning they weigh between a few hundred thousand and a few million times the mass of the Sun. These supermassive black holes also tend to be quiescent (meaning little gas falls on them), making them very hard to observe. A TDE going off is the exception to this rule – the black hole lights up as it devours the star, allowing astronomers to study these objects.
