Six recent runaway stars were discovered racing through the Milky Way. Two of the super-speedster stars, designated J0927 and J1235, are moving faster than any object of this kind ever seen.
In line with recent research, these record breaking stars are traveling at an incredible 5.1 million miles per hour (2,285 kilometers per second) and three.8 million miles per hour (1,694 kilometers per second), respectively. J0927 has the fastest sun-orbiting velocity ever seen, making it able to racing between Recent York and Mississippi in under a second, if it were a terrestrial object. At that speed, an object could race around Earth 694 times in only an hour.
The 4 other stars aren’t any slouches within the speed department, either, all traveling at over 2.2 million miles per hour (1,000 kilometers per second). These hypervelocity stars are traveling through the Milky Way so rapidly that they’ve the speed needed to flee the gravitational influence of our galaxy , also generally known as its escape velocity.
“These stars are extraordinary because they’re traveling much faster than normal stars within the Milky Way. Because they’re faster than the galactic escape velocity, they’ll soon be launched into intergalactic space,” team leader and Harvard/Smithsonian Center for Astrophysics researcher Kareem El-Badry told Space.com. “We were in search of objects like this, so we had some hope and expectation that they might exist, but their properties were different than we expected.”
The team behind the invention thinks that the incredible velocity of those 4 stars might be the results of them being launched by a selected kind of cosmic explosion called a Type Ia supernova. This also gave them extraordinarily high surface temperatures, which El-Badry said surprised the team.
“Also they are much hotter than normal stars — likely a results of their unusual formation history, which involves a supernova exploding right next to them!” the astrophysicist explained.
Type Ia supernovas occur in binary systems containing a stellar remnant called a white dwarf, which forms when stars just like the sun die, feeding on material from a companion star.
White dwarfs — also called “degenerate stars” — are incredibly dense because of this of being created from the collapse of a stellar core with a mass around that of the sun squashed into an Earth-sized sphere, but they don’t seem to be massive enough to cross the so-called Chandrasekhar limit — the mass a star must trigger a “normal” supernova and create a neutron star or perhaps a black hole when it dies.
When material from their donor star companion falls to the surface of a white dwarf, the stellar remnant gathers mass. This implies this stellar material donation process may give a white dwarf the critical mass needed to push it over the Chandrasekhar limit, thus triggering a thermonuclear explosion called a Type Ia supernova.
Not only do these blasts constitute a number of the brightest events within the universe, but they’re so uniform that astronomers check with them as “standard candles” as they’ll use them to measure cosmic distances.
While any supernova would release enough energy to create runaway stars, the team thinks it could take a fair more violent and powerful supernova to speed up these stars to hypervelocity status. These particular explosions are called “helium ignited violent mergers” or “dynamically driven double-degenerate double-detonations,” with this mouthful of a moniker shortened to D⁶ supernovas.
D⁶ supernovas occur when white dwarfs strip helium slightly than hydrogen from the outer layers of their companion star, which is believed to be one other white dwarf (hence double degenerate). This leads to a second massive explosion (hence double-detonation), with the companion white dwarf launched as a hypervelocity runaway star because of this.
“The composition of the runaway stars may be very unusual,” El Badry explained. “Just about all stars within the Milky Way have atmospheres made mostly of hydrogen and helium, but these objects haven’t any hydrogen or helium in any respect and consist mostly of carbon and oxygen.”
This means these runaway stars are degenerate white dwarf stars and further supports the concept that they were blasted to extreme velocities by a D⁶ supernova.
El-Badry and his colleagues used the usual light output of Type Ia standard candles to calculate the speed at which runaway stars are launched. They found the creation rate of hypervelocity stars was consistent with the speed at which Type Ia supernovas proceed, suggesting that lots of these events might be D⁶ blasts.
This led them to conclude that there’s a significantly large population of those superspeed stars racing through the universe that astronomers are yet to find.
Though discovered inside the Milky Way, these recent runaway stars, all with velocities in excess of two.2 million miles per hour (1000 kilometers per second), will at some point exit our galaxy, which has an escape velocity of around 1.2 million miles per hour (550 kilometers per second). And the team thinks they will not be the primary stars launched by the Milky Way.
“If a major fraction of Type Ia supernovas produces a D6 star, the galaxy has likely launched greater than 10 million of them into intergalactic space,” El-Badry and his co-authors write.
In fact, turnabout is fair play, and just as our galaxy has blasted hypervelocity stars at its neighbors, the researchers led by El Badry think other galaxies have been blasting super-speed stars at us. They are saying this means there must be numerous faint runaway stars launched from galaxies within the Milky Way’s local grouping hurtling through our galaxy within the vicinity of the solar system.
The research is described in a paper that has been submitted for publication within the journal Open Journal of Astrophysics and is currently published on the paper repository arXiv.