The mystery of the stellar eruption a trillion times more powerful than the largest of those of the Sun

2023-06-23 12:15:20

FU Ori, located about 1,200 light-years distant from Earth, brightened remarkably 85 years ago and has not yet dimmed to the level of luminosity it should have.

Also, FU Ori isn’t even a proper star, but a protostar, so it’s still in the process of formation.

Although it is believed that the increase in luminosity of FU Ori is due to the fall on the protostar of extra material from a cloud of gas and dust called a protoplanetary disk, the details about it have been a mystery.

Those protoplanetary disks feed growing stars more material, but they also feed planets. Previous observations provided hints of the existence of a massive young planet orbiting very close to this star. Could a planet be the trigger for the colossal stellar eruption 85 years ago?

Sergei Nayakshin and Vardan Elbakyan of the University of Leicester, as well as James E Owen of Imperial College London, both institutions in the UK, created a simulation for FU Ori, modeling a gas giant planet formed in a very deep area of ​​the disk. away from the center, occupied by the star. Through a process of gravitational instability, a massive disk can fragment to form concentrations of matter with more mass than the planet Jupiter but much less dense than it.

The simulation shows that such a planetary seed tends to migrate towards the interior of its host star very quickly, pulled by its gravitational pull. When it reaches the equivalent of a tenth of the distance between Earth and our Sun, the material surrounding the star becomes so hot that it causes a kind of ignition in the outer layers of the planet’s atmosphere. The planet then becomes a massive source of extra material that feeds the star at a higher than normal rate and makes it grow bigger and brighter.

A simulation of the early stages of the process. A gas giant planet is pushed towards its star, getting too close to it. Due to the proximity, the terrible heat begins to evaporate the planet, tearing off its outer layers that become integrated into the surrounding disk. The extra material causes the disk to get much hotter than before the start of the eruption. When the planet loses most of its mass, it is ripped apart completely through the process colloquially described as “spaghetting.” This process is how stars that pass too close to a supermassive black hole break apart. The disappearance of the planet puts an end to the eruption. (Image: Sergei Nayakshin/Vardan Elbakyan/University of Leicester)

The study is titled “Extreme evaporation of planets in hot thermally unstable protoplanetary discs: the case of FU Ori”. And it has been published in the academic journal Monthly Notices of the Royal Astronomical Society. (Source: NCYT from Amazings)