Chandra spies a pair of stars tossed from their host galaxy

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Scientists have been pouring over all the data that the Chandra X-ray observatory gathers. Chandra has discovered one of the clearest examples of a stellar pair being expelled from their galactic base. The binary stars are a pair of stars that orbit around each other and can include stars like our sun, neutron stars, and even black holes.

Scientists say that neutron stars form when a massive star explodes as a supernova, and the core of the star collapses onto itself. In some conditions, the monstrous blast that creates a neutron star isn’t symmetric, and the recoil effect can expel the star away from the galaxy where it resides. Chandra’s data shows that sometimes a companion star is forced to exit the galaxy as well.

The scientists liken this to a guest being asked to leave a party with a rowdy friend. In this case, the companion star is drug from the galaxy simply because it orbits the star that went supernova. Scientists can find these banished pairs if the companion star is close enough because it swirls around the dense neutron star and forms a disc around it. Strong gravitational forces cause the material in the disc to move rapidly, creating heat in tens of millions of degrees and causing the disc to glow in x-rays.

The binary pair that the team discovered was found while studying the Fornax galaxy cluster using observations taken with Chandra between 1999 and 2015. Combining Chandra data with optical observations allows astronomers to conclude that about 30 sources of X-rays in the Fornax cluster were likely from pairs of stars that had been tossed from the center of their host galaxies.

The clusters now exist in the space between galaxies and are on their way out of their home galaxies. The team also found another 150 sources of X-rays that appear to be outside stellar boundaries of galaxies within the Fornax cluster that aren’t believed to be caused by expulsion. The team says that there may be many more “evicted” binaries that are too faint to be seen in Chandra data.

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