The mysterious stars at the heart of the Milky Way hide a dark secret

The mysterious stars at the heart of the Milky Way hide a dark secret

Legend has it that 16th century Hungarian Countess Elisabeth Bathory had a shocking method for preserving her youthful beauty.

Historical records say that the noblewoman was accused and imprisoned for killing hundreds of girls to bathe in their supposed blood. The veracity of these accusations is questionable, at best, but the idea of ​​resorting to arcane black magic in the search for eternal youth persists.

While gorging on the blood of our fellow humans may not work well on humans, new evidence suggests it could be extremely powerful at rejuvenating stars. A study of shattered stars at the center of the Milky Way suggests that they are much older than they appear, and that their youthful, beautiful appearance is the result of cosmic cannibalism.

“A few stars win the collision lottery,” says astrophysicist Sanya Rose of Northwestern University in Illinois.

“Through collisions and mergers, these stars accumulate more hydrogen. Although they are formed from older clusters, they are masquerading as young, regenerating stars. They are like zombie stars, eating their neighbors.”

The center of the galaxy is a hectic place. First, there’s a massive supermassive black hole about 4 million times the mass of the Sun. Around it, stars spin, reaching absolutely insane speeds in their long orbits. And there are many of them. The center of the galaxy is favorably clashing with stars, and is the densely crowded center of the Milky Way.

It’s an environment ripe for star crimes.

“It’s a bit like running through an incredibly crowded subway station in New York City during rush hour,” Rose explains. “If you’re not colliding with other people, you’re passing by them. For stars, these close collisions are still causing them to interact with gravity. We wanted to explore and characterize what these collisions and interactions mean for star clusters.” Results.”

Studying the stars directly at the galactic center is very difficult, because there is a lot of stuff there, including dense clouds that obscure the view at most wavelengths. Rose and her colleagues turned to simulations, creating a model of the galactic center and everything inside it, and observing the results once the stars moved.

They found that the fate of the colliding stars appears to be directly related to their proximity to the black hole. Within 0.01 parsec – about a thirtieth of a light-year – interactions between stars are even in path, but because of their high velocities, they tend to remain constant. The interactions tend to be grazing collisions that leave both stars more or less intact, although they may lose a fair portion of their outer matter in the process.

But beyond 0.01 parsec, things get a little more violent. Because stars move much slower, they don’t have the angular momentum to keep moving when they encounter each other. Instead, they become trapped in each other’s gravity, resulting in a complete collision that causes the stars to fuse together into one large star.

In this process, some stars gain enough hydrogen to give them a more youthful appearance, even though they may be slightly older. But there is a trade-off. The more massive a star is, the shorter its age.

“Massive stars are like giant cars that consume huge amounts of fuel,” Rose explains. “They start with a lot of hydrogen, but they burn up in it very quickly.”

The comparison with vampires falls a little flat there. But the results explain a strange feature of star clusters at the galactic center: the puzzling absence of ancient red giant stars. The researchers found that mass loss from collisions and mergers that create larger, short-lived stars would reduce the number of red giants you would expect to see in a normal star population.

Additional observational and theoretical research can help shed light on these processes, revealing the complex dynamics at play in a cosmic environment unlike any other in the galaxy.

The results, which have not been peer-reviewed, have been submitted to Astrophysical Journal Letterswhich was presented at the American Physical Society meeting in April, and is available on arXiv here and here.

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