Scientists have discovered the terrifying secret behind the apparent youth of some stars at the heart of the Milky Way; stars participating in a kind of cosmic destruction derby around our galaxy’s supermassive black hole, Sagittarius A*, or Sgr A*.
Like a cosmic version of Elizabeth Bathory, the 17th-century serial killer who allegedly tried to maintain her youthful glow by bathing in the blood of her victims, some of these stars appear to continue looking youthful by colliding with neighboring stars and covering themselves. stolen star material. This cannibalistic process leaves the star victim as a grotesque, stripped-down “zombie” star, dooming the cannibal star to an early death.
That’s just some of the strange findings that emerged from a simulation of 1,000 dense stars orbiting the supermassive black hole at the center of the Milky Way, a study led by scientists at Northwestern University.
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“The centers of other galaxies are very difficult to observe because they are so far away,” research leader and scientist Sanaea C. Rose of Northwestern University told Space.com. “Studying our own Galactic Center can give us information about what’s going on at the centers of all galaxies.”
The heart of the Milky Way is one of the most extreme environments astronomers can observe from Earth. This region is home to Sgr A*, not only a black hole with a mass equivalent to 4.5 million suns, but also a cosmic monster orbiting more than a million stars.
These stars are squeezed into an area about 4 light-years wide, roughly the distance between the sun and its nearest stellar neighbor, Proxima Centauri. This means that events such as stellar collisions, which are relatively rare in the sparsely populated region of the Milky Way, are almost commonplace around Sgr A*.
“The supermassive black hole at the heart of the Milky Way is surrounded by a very dense cluster of stars, and many of these stars are orbiting at speeds ranging from hundreds to thousands of miles per second,” Rose said.
Studying the Milky Way’s violent heart could reveal how stars behave, evolve and interact under the influence of the extreme gravity of a supermassive black hole.
Episode about cosmic demolition derby
While the team’s simulations took into account many factors and properties, such as stellar mass and star cluster density, one factor stood out as particularly important when determining the fate of a star near the heart of the Milky Way.
Rose explained that in general, a star’s distance from Sgr A* is a good indicator of whether it will collide with another star and what type of collision it will be.
“As we get closer to the supermassive black hole, the population of the cluster gradually increases, so the probability of collision increases,” he said. ” “It’s a bit like running through rush hour traffic in an incredibly crowded subway station in New York City. “If you’re not colliding with other people, you’re passing too close to them.”
The closer a star is to Sgr A*, the faster the black hole’s immense gravity spins it. As a result, stars right next to the supermassive black hole can move at speeds of around 18 million miles per hour (29 million kilometers per hour), making the heart of the Milky Way more like a demolition derby than a packed New York subway.
This means that collisions in the innermost region of Sgr A*, an area approximately 2000 times the distance between the Earth and the sun, or 0.01 parsecs, tend to be destructive in nature.
Such stars at a distance of about 0.01 parsec from Sgr A* constantly collide with each other, but this is rarely a head-on collision. This means that, just like a demolition derby car’s bumper being removed before it hits the road, grazing effects can shed a star’s outer layers, resulting in it racing on a collision course alongside another neighbor.
“They bump into each other and move on. They graze each other like they’re giving a very violent high-five,” Rose said.
However, how much matter a star experiencing this chaos will lose depends on how fast it is moving and how close it is to the star it collides with. One result of these catastrophic collisions is a strange population of stripped stars and starlets that appear young thanks to their bathing in hydrogen-rich material falling from the stars.
However, gaining this youthful appearance comes with a price. The more massive a star is, the faster it burns through its fuel supply for internal nuclear fusion, a process that prevents it from collapsing under its own gravity. So these big stars shorten their own lives by piling on this stolen material.
Further away from Sgr A*, about 0.1 parsec, or about 21,000 times the distance between the Sun and Earth, stars collide less frequently and at more relaxed speeds. Rose and colleagues’ simulation showed that when these slower collisions occur, a complete merger in which two stars become one massive star is likely.
“Collisions outside 0.01 parsecs are more likely to merge colliding stars,” he added. “Stars within 0.1 parsec of Sgr A* are very likely to experience at least one collision in their lifetime.”
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Rose explained that one of the most satisfying aspects of using this model to address some unexplained observations of stars at the heart of the Milky Way is the fact that it relies on a relatively simple calculation.
“One thing that I personally find very special about my research is that it is based on calculating collision timelines, something that is taught relatively early in undergraduate physics education,” he said. “It was great to use a relatively simple calculation to learn about an extremely complex environment unlike anything we’ve encountered in our solar neighborhood.”
The team has produced two studies using the model so far; one was published this month in The Astrophysical Journal Letters and the other was published in September 2023, but they are not yet finished.
“The next steps will be to extend the physics currently in the model,” Rose said. “The Galactic Center is an extremely complex environment, so there are always things we can add and we are never done!”
Rose presented this research at the American Physical Society’s April meeting, held as part of the “Particle Astrophysics and Galactic Center” session on Thursday, April 4, in Sacramento, California.