Astronomers have discovered a rare stellar phenomenon inside a strangely shaped nebula - two white dwarfs are on the verge of fusion.
During the study, in an attempt to understand the specific forms of nebulae in our galaxy, astronomers, with the help of the Very Large Telescope of the European Southern Observatory (VLT) in Chile, looked at the planetary nebula Henize 2-428. Planetary nebulae are formed in the later stages of a star's life after the hydrogen in its center ends. At this stage, the star throws out its outer layers through the powerful stellar winds.
But some distant planetary nebula has a strange asymmetric form - a cloud of dust and gas in it expands into a heterogeneous form. This became a mystery to astronomers, since if the nebula was formed by a single dying star, then all external material had to be ejected in all directions with the same speed.
But now, the mystery of asymmetry Henize 2-428 is revealed. Deep inside the cloud is not one, but two stars.
“Further observations made with telescopes located on the Canary Islands allowed us to determine the orbit of two stars and calculate their mass, as well as the distance between them. And this was a big surprise for us,” says Romano Corradi, researcher at the Canary Institute of Astrophysics and co-author of an article published in Nature magazine on Monday (February 9th). Both stars were dense tiny white dwarfs with a mass slightly smaller than our Sun. According to the calculations of researchers, the stars make a spiral rotation every 4 hours and after 700 million years, the pair will merge.
The crooked shape of the Henize 2-428 planetary nebula. Picture taken by Very Large Telescope at the European Southern Observatory of Paranal, Chile.
But what happens when these stars collide and merge together? Their combined mass will be 1, 8 times the Sun, which is higher than the mass of the threshold (also known as the Chandrasekhar limit), which will cause the object to fall inward. In other words, it will explode like a supernova!
"Until now, the formation of type Ia supernovae by merging two white dwarfs was purely theoretical," said David Jones, co-author of the study and an employee of ESO. "A pair of stars in Henize 2-428 is the real thing!".
"This is a very mysterious system," says lead researcher Santander Garcia of the Madrid Institute of Materials Science. "The study of type Ia supernovae will have important implications. Type Ia supernovae are widely used to measure astronomical distances and are key to discovering the expansion of the Universe is accelerating due to dark energy."