Binary Stars on the Move

In 2005, astronomers from CfA stumbled upon a remarkable and fortunate finding: a star moving at an incredibly high speed of over three million kilometers per hour. This star seems to have been expelled from the vicinity of the supermassive black hole at the center of our galaxy approximately 80 million years ago, due to the powerful gravitational forces it experienced while passing by the black hole. As it races away from the galaxy, this star provides further evidence for the existence of a massive black hole at the galactic center, as well as supports calculations regarding the interactions between black holes and their surrounding stellar environments.

Additional hypervelocity stars, as well as runaway stars with lower velocities, have also been discovered. Most of these stars have been accelerated by one of two other gravitational mechanisms: either they were ejected from a dense cluster of stars due to random motions that propelled them into a slingshot-like orbit, or they were expelled from a binary system involving a supernova explosion that released them from their orbit. A binary star refers to a pair of stars that orbit around each other, and it is believed that many, if not most, stars are part of binary systems. Thus far, no hypervelocity binary stars have been found, although they have been predicted. One theory suggests that the identification of a hypervelocity binary pair could indicate the presence of a binary black hole at the core of the galaxy.

Astronomers Warren Brown and Scott Kenyon, along with their colleagues, have undertaken a study on the peculiar runaway binary LP400-22. This binary system consists of two highly evolved white dwarf stars that are currently located approximately 1400 light-years away from us. What makes this object unique is that it is the only known runaway white dwarf pair, and it possesses a higher velocity compared to most other runaway stars. The astronomers carefully observed its movement across the sky for a period of five years and based on its trajectory within the galaxy, they have concluded that it is highly unlikely that the binary pair was ejected from the vicinity of the galactic center. Additionally, they have found no evidence of X-ray remnants from a supernova, making the supernovae mechanism also improbable. The team suggests that the most probable origin of this binary pair is within a dense stellar cluster. They have tentatively traced its path back to one of several possible globular clusters. It is speculated that the runaway pair may have been involved in a multi-body interaction within the cluster or may have originally been part of a triple-star system that was disrupted by an intermediate mass black hole. Although the investigation did not directly address the properties of the black hole at the galactic center, it has provided valuable insights into runaway stars, white-dwarf binaries, and the intricate interactions occurring within dense stellar clusters.

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