An Ancient Star Is Visible Zooming 600 km/s Through Space

While this is true for the majority of Milky Way stars, not all of them follow a calm and systematic orbit around the galactic center. Occasionally, a maverick is observed surpassing other players by traveling at a speed that will ultimately cause it to be thrown out of the galaxy.

We have just discovered a really unique example of one of these “hypervelocity” stars, which are incredibly uncommon. CWISE J124909+362116.0, or J1249+36 for short, is a very unusual kind of tiny, ancient, main sequence star known as a L subdwarf. It is also one of the oldest stars in the Milky Way. This star not only surpasses the galactic escape velocity at around 600 kilometers (373 miles) per second.

J1249+36 is one of the few hypervelocity stars found in the Milky Way; while it is by no means the fastest star, its incredible speed begs the question of how it came to be. It was first noticed by citizen scientists searching through telescope data for evidence of the enigmatic Planet Nine.

The discovery was presented at the American Astronomical Society’s 244th Meeting, and an article about it was just submitted to The Astrophysical Journal Letters.

The star’s velocity can be explained in a variety of ways. Three were investigated by the researchers.

There are three reasons why the star is moving so quickly. Burgasser and associates
The first is the white dwarf star’s expulsion from a binary system, which is the leftover core left over after a star similar to the Sun runs out of hydrogen, ejects most of its outer material, dies, and passes into the afterlife. Ultra-dense white dwarfs may be rather unstable if they have a binary companion and radiate brightly due to leftover heat rather than fusion.

The white dwarf can take material from the companion star if their orbits are near together. The upper mass limit of the white dwarf is the issue. It can sustain its existence through recurring eruptions known as novae if it obtains a little amount of mass. But if it acquires too much mass, it will burst as a Type Ia supernova, destroying the white dwarf entirely.

According to astrophysicist Adam Burgasser of the University of California San Diego, “in this kind of supernova, the white dwarf is completely destroyed, so its companion is released and flies off at whatever orbital speed it was moving, plus a little bit of a kick from the supernova explosion as well.”

“Our calculations show this scenario works. However, the white dwarf isn’t there anymore and the remnants of the explosion, which likely happened several million years ago, have already dissipated, so we don’t have definitive proof that this is its origin.”

A second option is an unstable many-body interaction that pushes one of the objects out into the galaxy. Within the Milky Way, there are conditions known as globular clusters—dense globs that can hold millions of stars—that increase the likelihood of these interactions. Black hole binary pairs are more prevalent than typical in globular clusters, which are thought to feature swarms of black holes at their centers.

According to astrophysicist Kyle Kremer of Caltech, who will soon join UC San Diego, “when a star encounters a black hole binary, the complex dynamics of this three-body interaction can toss that star right out of the globular cluster.”

This is also conceivable, however researchers have not yet been able to pinpoint a particular globular cluster as the star’s birthplace by retracing the star’s path backward.

The third possibility is that J1249+36 is actually one of the numerous satellite dwarf galaxies that orbit the Milky Way rather than being a part of the Milky Way itself. An extragalactic origin for hypervelocity stars was deemed feasible in a 2017 study investigating their origins. Additionally, J1249+36 can also achieve this, according to the researchers’ computations.

There are still three possibilities available. The best method to determine it will be to do a more thorough analysis of the star’s chemical makeup. In the event that J1249+36 was a white dwarf’s partner, the L subdwarf’s atmosphere may have been contaminated by trace elements left behind by the supernova. On the other hand, stars in globular clusters share comparable compositional characteristics, suggesting that the star can be associated with a home population in this manner.

If both of those options prove unsuccessful, we might have to investigate the Milky Way’s satellites to find out if this small, faint star is an alien passing through the galaxy or only a blink.

The discovery was announced at the American Astronomical Society’s 224th meeting.

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