Stellar collision

Stellar collision is the coming together of two stars caused by stellar dynamics within a star cluster, or by the orbital decay of a binary star due to stellar mass loss or gravitational radiation, or by other mechanisms not yet well understood. Astronomers predict that events of this type occur in the globular clusters of our galaxy about once every 10,000 years.

While the concept of stellar collision has been around for several generations of astronomers, only the development of new technology has made it possible for it to be more objectively studied. For example, in 1764, a cluster of stars known as Messier 30 was discovered by astronomer Charles Messier. In the twentieth century, astronomers concluded that the cluster was approximately 13 billion years old.

The Hubble Space Telescope resolved the individual stars of Messier 30. With this new technology, astronomers discovered that some stars, known as “blue stragglers”, appeared younger than other stars in the cluster. Astronomers then hypothesized that stars may have “collided”, or “merged”, giving them more fuel so they continued fusion while fellow stars around them started going out.

On 2 September 2008 scientists first observed a stellar merger in Scorpius, though it was not known to be the result of a stellar merger at the time.

©Universe Today

Type Ia supernova occurs when two white dwarfs orbit each other closely.[8] Emission of gravitational waves causes the pair to spiral inward. When they finally merge, if their combined mass approaches or exceeds the Chandrasekhar limit, carbon fusion is ignited, raising the temperature.

Since a white dwarf consists of degenerate matter, there is no safe equilibrium between thermal pressure and the weight of overlying layers of the star. Because of this, runaway fusion reactions rapidly heat up the interior of the combined star and spread, causing a supernova explosion.

Neutron star mergers occur in a fashion similar to the rare type Ia supernovae resulting from merging white dwarfs. When two neutron stars orbit each other closely, they spiral inward as time passes due to gravitational radiation. When they meet, their merger leads to the formation of either a heavier neutron star or a black hole.

A gravitational wave event that occurred on 25 August 2017, GW170817, was reported on 16 October 2017 to be associated with the merger of two neutron stars in a distant galaxy.

If a neutron star collides with red giant of sufficiently low mass and density, both can survive in the form of a peculiar hybrid known as Thorne–Żytkow object, with the neutron star surrounded by the red giant.

About half of all the stars in the sky are part of binary systems, with two stars orbiting each other. Some binary stars orbit each other so closely that they share the same atmosphere, giving the system a peanut shape. While most contact binary stars are stable, a few have become unstable and have merged in the past for reasons not well understood.

When two low-mass stars in a binary system merge, mass may be thrown off in the orbital plane of the merging stars, creating an excretion disk from which new planets can form.

However the mechanism behind binary star mergers is not yet fully understood, and remains one of the main focuses of those researching contact binaries.

©The Independent

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