admin Until recently, only ten known stars in orbit could escape the Milky Way after being lost by a powerful supernova explosion. A new study using data from the ESA’s Gaia survey in June of this year found six more runaway stars, two of which set the fastest radial velocity records for a runaway star ever observed. Some 1,694km/s and 2,285km/s were updated.
The supernovae that produced these stars are of a special type known as type 1a. Type 1a supernovae are known to help determine astronomical distances (because they always explode at the same size). Type 1a supernovae occur in binary star systems. There, one white dwarf slowly digests the other, releasing stellar material as they orbit each other. When enough matter is transported from one star to another, the star eventually gains what is known as a “Chandrasekhar mass,” named after Indian-American theoretical physicist Subramanyan Chandrasekhar. reaches a mass of
Upon reaching this critical mass, the growing star can no longer withstand the gravitational pressure and collapses on its own, causing a violent explosion.
There are still some unanswered questions about Type 1a supernovae. In theory, white dwarf binaries reaching Chandrasekhar mass should be rarer than they actually are. This has led astronomers to consider another method of triggering similar supernovae: double explosions.
In this scenario, a white dwarf steals helium from a neighboring star’s envelope, causing the helium to explode first, creating a shock wave, then her second explosion, this time within the star’s carbon core. .
Under these conditions, a white dwarf can supernova without approaching the Chandrasekhar limit, as long as the solid star has a sufficiently large carbon core.
In a double explosion scenario, the remnant of a neighboring star is ejected into space at a velocity similar to that orbiting its now-defunct partner. This process allows the outliers to reach breakneck velocities, pass through the Milky Way Galaxy, and eventually out of the Milky Way Galaxy.
“These runaway white dwarfs are doubly degenerate smoking weapons,” write the authors of a new study published on the preprint server arXiv.
A single exploding supernova can also produce a runaway star. In such cases, it is the exploding star debris, not the other star, that is reaching extreme velocities. Such events are called type 1ax supernovae, in which the explosion does not completely destroy the star, leaving behind the rapid remnants of the white dwarf core.
These runaways are still very fast, but not as fast as the runaway caused by double explosions.
Researchers can use velocity differences and spectroscopic signatures to identify different origins of runaway stars and classify them accordingly. Ultimately, it should help limit the frequency with which each type of supernova occurs as the number of observed outliers increases.
Currently, the fastest nova in the galaxy is J0927, followed by the newly discovered J1235.
J0927 has almost twice the radial velocity of other stars in the galaxy, with a few exceptions. For example, the stars closest to the black hole’s orbit at the center of our galaxy are orbiting the black hole at breakneck velocities, sometimes reaching velocities of J0927. However, these objects are trapped in orbit and not on a runaway orbit.
