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Stellar collisions produce strange, merged star survivors

For stars, these near collisions still cause them to interact gravitationally.

A star-forming region in the Large Magellanic Cloud. Image by ESA/Hubble, CC BY 4.0
A star-forming region in the Large Magellanic Cloud. Image by ESA/Hubble, CC BY 4.0

A study has traced the fates of stars living near the Milky Way’s central black hole and showed how densely packed, fast-moving stars at the Milky Way’s centre can collide with each other.

To support predictions as to what happens next, the research uses simulations to explore the outcomes of these collisions. This finds that some collisions are more like ‘violent high fives’ while others are full-on mergers.

Using a new model, Northwestern University astrophysicists traced the violent journeys of 1,000 simulated stars orbiting our galaxy’s central supermassive black hole, Sagittarius A* (Sgr A*). This region commonly experiences brutal stellar collisions.

By simulating the effects of these intense collisions, the new work finds that collision survivors can lose mass to become stripped down, low-mass stars or can merge with other stars to become massive and rejuvenated in appearance.

According to lead researcher Sanaea C. Rose: “The region around the central black hole is dense with stars moving at extremely high speeds. It’s a bit like running through an incredibly crowded subway station in New York City during rush hour. If you aren’t colliding into other people, then you are passing very closely by them. For stars, these near collisions still cause them to interact gravitationally. We wanted to explore what these collisions and interactions mean for the stellar population and characterize their outcomes.”

According to Rose, the centre of our Milky Way is a strange and wild place. The gravitational pull of Sgr A* accelerates stars to whip around their orbits at terrifying speeds. And the sheer number of stars packed into the galaxy’s centre is upwards of a million. The densely packed cluster plus the lightning-fast speeds equal a high-speed demolition derby. In the innermost region — within 0.1 parsecs of the black hole — few stars escape unscathed.

Since the supermassive black hole has a strong gravitational pull, as stars orbit the black hole, they begin to move at thousands of kilometres per second. This hectic neighbourhood can cause star to collide with other stars.

The simulation takes several factors into account: density of the stellar cluster, mass of the stars, orbit speed, gravity and distances from the Sgr A*. This revealed one factor that is most likely to determine a star’s fate: its distance from the supermassive black hole.

Within 0.01 parsecs from the black hole, stars — moving at speeds reaching thousands of kilometers per second — constantly bump into one another. continue speeding along the collision course. These destructive collisions result in a population of strange, stripped down, low-mass stars.”

Outside of 0.01 parsecs, stars move at a slower pace — hundreds of kilometers per second. Because of the slower speeds, these stars collide with one another but then do not have enough energy to escape. Instead, they merge to become more massive. The research has been published in the Astrophysical Journal Letters.

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Dr. Tim Sandle is Digital Journal's Editor-at-Large for science news. Tim specializes in science, technology, environmental, business, and health journalism. He is additionally a practising microbiologist; and an author. He is also interested in history, politics and current affairs.

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