A white dwarf is not your typical kind of star.
While main sequence stars like our Sun melt nuclear material in their cores to keep them from collapsing under their own weight, white dwarfs use an effect known as quantum degeneration. The quantum nature of electrons means that no two electrons can have the same quantum state.
When you try to squeeze electrons into the same state, they exert a degenerative pressure that keeps the white dwarf from collapsing.
But there is a limit to how much mass a white dwarf can have.
Subrahmanyan Chandrasekhar made a detailed calculation of this limit in 1930 and found that if a white dwarf has more mass than about 1.4 suns, gravity will crush the star into a neutron star or a black hole.
But the Chandrasekhar limit is based on a fairly simple model. One where the star is balanced and does not rotate. True white dwarfs are more complex, especially when undergoing collisions.
Binary white dwarfs are quite common in the universe. Many sun-like stars and red dwarfs are part of a binary system.
(ESA / XMM-Newton, L. Oskinova / Univ. Potsdam, Germany)
When these stars reach the end of their main sequence life, they become a binary system of white dwarfs.
Over time, their orbits can decay, eventually causing the two white dwarfs to collide. What happens next depends on the situation.
Often times they can explode as a nova or supernova, creating a leftover neutron star, but sometimes they can form something unusual, like a recent article in Astronomy and Astrophysics shows.
In 2019, an X-ray source that resembled a white dwarf but was too bright to be caused by a white dwarf was discovered. It has been suggested that the object could be an unstable fusion of two white dwarfs. In this new study, a team used the XMM-Newton X-ray telescope to create an image of the object, seen above.
They confirmed that the object has a mass greater than the Chandrasekar limit. The super Chandrasekar object is surrounded by a remnant nebula with high wind speeds.
The nebula is usually made of neon, as seen as green in the image above. This is consistent with the fact that the object was created by a fusion of white dwarfs. It probably has a high rotation, which prevents the object from collapsing into a neutron star.
Ultimately, this object will collapse over the next 10,000 years and become a neutron star. It will likely create a supernova in the process. It looks like a white dwarf can break the Chandrasekhar limit, but only for a while.
This article was originally published by Universe Today. Read the original article.