HE 0437-5439 - Mechanism of Ejection From The Milky Way

Mechanism of Ejection From The Milky Way

Studies say that a triple-star system was traveling through the center of the Milky Way when it came too close to the galactic center (which is thought to have a giant black hole). One of the stars was captured by the black hole causing the other two to be ejected from the Milky Way, where they merged to form a hot blue star. The star is moving at a speed of 1,600,000 miles per hour (2,600,000 km/h), about three times faster than the Sun's orbital velocity around the galaxy's center, and also faster than the galaxy's escape velocity.

The star is about 200,000 light years from the galaxy's center now. Some doubt has surrounded the previous studies based on the speed and position of HE 0437-5439. The star would have to be at least 100 million years old to have traveled that distance from the galactic core, yet its mass and blue color indicate that it had burned only for 20 million years, which led to the explanation that it was part of a triple-star system consisting of two closely bound stars and one outer star. The black hole pulled the outer star away, which granted the star's momentum to the tight binary system, boosting both stars to escape velocity from the galaxy. And as they traveled away they went into normal stellar evolution, with one of them becoming a red giant and engulfing the other, forming one superstar - a blue straggler.

In 2008 a team of astronomers found a match between the star's chemical composition and the characteristics of stars in the Large Magellanic Cloud. Support that the star originated in the LMC is strengthened since the star is only 65,000 light-years away from the nearby galaxy.