Astronomers have detected the fastest runaway star ever seen in the Milky Way galaxy: the shell of a star thrown at breakneck speeds from a gigantic cosmic explosion. The white dwarf, named J0927, was seen flying through space at a staggering speed of 5.112 million miles per hour (8,226.967 kilometers per hour). Called a hypervelocity star because its speed will one day allow it to completely escape the gravitational pull of the Milky Way, J0927 was seen along with three other fast-moving stars, all of which are believed to be the result of a Type Ia supernova. one of the most violent explosions in the universe. The researchers published their findings on June 6 on the arXiv preprint server, and the findings have not yet been peer-reviewed.

Type Ia supernovae occur when two stars, one of them the collapsed shell of a star called a white dwarf, orbit one another. This causes the white dwarf to emit hydrogen from the spiraling star, creating a runaway reaction that ends in a gigantic thermonuclear explosion.

But a simple stellar explosion is not enough to launch stars at this speed. Astronomers suspect that hypervelocity stars are sent flying by a special type of Type Ia supernova called a dynamically driven double degeneracy double detonation (D6) supernova. In D6 supernovae, two white dwarf stars spiral around each other, one stripping the other of its remaining surface layers of helium. This process produces so much energy at the white dwarf’s surface that it snatches up helium that starts nuclear fusion in the shell once more, sending a shock wave deep into its core that causes it to detonate.

“If a significant fraction of type Ia supernovae produce a D6 star, it is likely that the galaxy has launched more than 10 million of them into intergalactic space,” the researchers wrote in the study. “An interesting corollary is that there should be large numbers of faint, nearby D6 stars thrown from galaxies throughout the local volume that pass through the solar neighborhood.” Despite the apparent abundance of these powerful supernovae, evidence for them and the white dwarfs that shoot like bullets remains elusive. To search for some candidates, the researchers turned to the Gaia Star Catalog, an ongoing project with the goal of creating the most detailed star map of our galaxy ever made.

Using the Gaia data, astronomers detected the white dwarfs and confirmed with follow-up observations of their chemical compositions (almost entirely oxygen and carbon) that the runaway white dwarfs were the product of an explosion that stripped them of helium and carbon. hydrogen.

Measurements of the white dwarfs revealed that J0927 was the fastest runaway star ever observed in our galaxy, surpassing the previous record of 4,921,200 mph (7,919,904 km/h) held by the white dwarf D6-1. An additional white dwarf observed in the new study also earned the title of the second fastest star ever observed in our galaxy. The researchers estimate that D6 supernovae could account for half of all Type Ia supernovae, but to know for sure, they will have to locate even more runaway stars streaking through space. “There is now a sizeable population of hypervelocity stars associated with thermonuclear supernovae,” the researchers wrote.

source: https://arxiv.org/abs/2306.03914