One of the most famous stars in the sky has a secret companion, astronomers have discovered. The bright star, called Beta Crucis, is one of four forming the Southern Cross that features on five national flags.

Researchers stumbled across a second star orbiting Beta when they examined observations of it from a space telescope.

The team from Swarthmore College, Philadelphia, wanted to study X-rays from the star being detected by the Chandra satellite. They were astonished to find a second source of X-rays from the same direction.

David Cohen, asssociate professor of astronomy, said: “We were interested in how the highly supersonic stellar winds of hot, luminous stars produce X-rays. We were surprised to see two strong X-ray sources where we had expected to see only one.”

Beta is the star on the left in the Southern Cross which features on the flags of Australia, Brazil, New Zealand, Papua New Guinea and Samoa. A paper describing the discovery is to be published in the Monthly Notices of the Royal Astronomical Society.

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