Mysterious stars at the center of the Milky Way were hiding a dark secret

Astrophysicists have uncovered the hidden habit of celestial bodies

Legend has it that the 16th century Hungarian Countess Elisabeth Bathory used a grisly method to preserve her youthful beauty. Astrophysicists say the bloody countess was right about something: the stars in the Milky Way galaxy are deceiving scientists by showing their youthful side while hiding their age. This phenomenon could happen due to the fact that a self-luminous celestial body absorbs its “relatives”.

Historical records state that the noble lady Bathory was accused and imprisoned for killing hundreds of girls in order to bathe in their supposedly healing blood. The credibility of these accusations is dubious at best, but the belief that she resorted to arcane black magic in search of eternal youth persists.

While drinking blood can be bad for people, new evidence suggests it can actually significantly rejuvenate celebrities, for example. A study of the stars orbiting the center of the Milky Way galaxy suggests they are much older than they appear, and that their youthful appeal is the result of cosmic cannibalism.

“A few stars win the collision lottery,” explains astrophysicist Sanya Rose of Northwestern University in Illinois. “As a result of mergers, they accumulate more hydrogen. Although the stars formed from an older population, they masquerade as renewed, youthful looking ones. They’re like zombie stars eating their neighbors.”

The center of the galaxy is a turbulent place. The fact is that there is a huge supermassive black hole there, the mass of which is approximately 4 million times the mass of the Sun. The stars revolve around it, and there are a lot of them there.

“It’s a little like running through an incredibly crowded subway station in New York City during rush hour,” Rose explains. — If you don’t run into other people, you pass them very close. As for stars, these close encounters still lead to their gravitational interaction. We wanted to explore what these collisions and interactions mean for the stellar population and characterize their consequences.”

Studying the stars directly in the center of the galaxy is quite difficult, because there is a lot there, including dense clouds that block the view. Sanea Rose and her colleagues began modeling, creating a model of the center of the galaxy and everything inside it, and observing the results as the stars moved.

They found that the fate of colliding stars appears to be directly related to their proximity to the black hole. Within 0.01 parsecs – about one-thirtieth of a light year – their high speeds mean they survive a glancing impact. However, beyond this limit the situation becomes different. Because stars move much slower, they don’t have enough angular momentum to keep moving when they collide with each other. Instead, they become trapped in each other’s gravity, resulting in a total collision that merges the stars into one large star. And it is during this process that some stars receive enough hydrogen, which rejuvenates them.

“Massive stars are like giant cars that consume a lot of gas,” Rose explains. “At first they contain a lot of hydrogen, but it burns very, very quickly.”

Comparisons with vampires, according to scientists, are somewhat inappropriate. But the findings explain a curious feature of the stellar population at the center of the galaxy: the mysterious absence of old red giants. The researchers found that both mass loss due to random collisions and mergers that lead to the formation of larger, short-lived stars would reduce the number of red giants that would be expected to be seen in a typical stellar population.

Further observations and theoretical studies could help shed light on these processes and reveal the complex dynamics occurring in the cosmic environment, the likes of which are not found in any other galaxy.