If you were attacked by a ravenous vampire star or risked falling into two dueling black holes, you’d probably run too!
One of these terrifying scenarios is likely responsible for sending a low-mass star flying through the Milky Way at a staggering million miles per hour (1.6 million kilometers per hour). That’s about 1,500 times faster than the speed of sound.
The star is called CWISE J124909+362116.0 (J1249+36) and was first discovered by citizen science volunteers from the Backyard Worlds: Planet 9 project, who are exploring the vast amount of data collected by NASA’s Wide-field Infrared Survey Explorer ( WISE) mission over the course of nearly a decade and a half. J1249+36 immediately stood out because of its enormous speed of specifically 2.1 million km per hour, which is almost three times as fast as the speed of the Sun in its orbit around the heart of the Milky Way. In fact, the speed of this ‘hypervelocity’ star is so great that it will probably escape from our Milky Way entirely.
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To unravel the secrets of this superfast star, Adam Burgasser, professor of astronomy and astrophysics at the University of California, San Diego, turned to the WM Keck Observatory in Maunakea, Hawaii, with the aim of observing its infrared spectrum.
This research showed that the star belongs to a class of the oldest stars in the Milky Way: L-subdwarfs. These stars are very rare and notable for their very low masses and relatively cool temperatures.
The team’s spectral data was combined with a new set of atmospheric models created specifically to study L subdwarfs. This revealed the position and speed of J1249+36 through the Milky Way. “This is where the source became very interesting,” Burgasser said in a statement. “Its speed and trajectory showed it was moving fast enough to possibly escape the Milky Way.”
The question is: what launched this subdwarf star on its rapid escape trajectory? Which brings us to our two suspects.
Is this star on the run from a white dwarf vampire?
In the first scenario used to explain the hypervelocity nature of J1249+36, Burgasser and colleagues hypothesized that the low-mass star was once the stellar companion of a type of “dead” star called a white dwarf.
White dwarfs are born when smaller stars like the Sun deplete the hydrogen supply in their cores. When that happens, a star’s nuclear fusion stops. This interrupts the outward flow of energy that supports the star against the inward pressure of its own gravity. While this ends the lives of lonely, isolated stars like the Sun, white dwarfs in binary systems can return from the grave by cannibalistically feeding on stellar material stripped from a nearby ‘donor’ star.
This material piles up on the white dwarf until the mass of that stellar remnant exceeds the Chandrasekhar limit of about 1.4 times the mass of the Sun, above which a star can become a supernova. This results in a type of cosmic explosion called a “Type Ia supernova” that completely destroys the white dwarf.
“In this type of supernova, the white dwarf is completely destroyed, so its companion is released and flies away at the orbital speed at which it was originally moving, plus a small jolt from the supernova explosion,” Burgasser explains. ‘Our calculations show that this scenario works. However, the white dwarf is no longer there and the remnants of the explosion, which probably took place several million years ago, have already disappeared, so we have no definitive proof that this is the cause. origin.”
Could two black holes have something to do with it?
In the second scenario the team considers, this superfast star begins life in a globular cluster, a dense and compact conglomeration of stars linked together by gravity. These globular clusters can contain tens of thousands to many millions of stars.
The stars are concentrated in the centers of globular clusters, where scientists theorize that black holes of varying masses also lurk. These black holes can come together to form binary stars that are adept at launching stars that come too close to them out of their home systems.
“When a star encounters a binary star with a black hole, the complex dynamics of this three-body interaction can throw that star straight out of the globular cluster,” said Kyle Kremer, a rising assistant professor in the Department of Astronomy and Astrophysics at UC San Diego.
Simulations generated by Kremer revealed that these types of interactions can, in rare cases, kick a low-mass subdwarf out of a globular cluster and put it on trajectories similar to what is observed with J1249+36.
The team also traced the trajectory of this hypervelocity star to an extremely busy region of space, which could indeed be the location of a currently undiscovered globular cluster – or perhaps it is. more than one.
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The team will now look at the elemental composition of J1249+36 in an attempt to determine which of these ejection scenarios is correct. The composition could be a possible indication of their origin, because white dwarfs, when they go ‘nova’, pollute the stars they kick away. Furthermore, stars born in globular clusters have different chemical compositions.
Whatever the origin of this star, its discovery provides scientists with a unique opportunity to investigate hypervelocity stars as a whole. And it’s all very cool.
Burgasser presented the team’s results at a press conference on Monday (June 10) during the 244th national meeting of the American Astronomical Society (AAS) in Madison, Wisconsin.