A super-dense white dwarf star about 730 light years from Earth has been caught in the act of "cannibalising" its companion, astronomers said Friday.

The pair form a binary star system named Gaia14aae after the European Space Agency's Gaia satellite which discovered it in August 2014.

The system was first spotted when it suddenly became five times brighter over the course of a single day.

Further observations have determined that the outburst was due to the white dwarf stealing gas from its larger companion, said the University of Cambridge, whose experts took part in the study.

The smaller of the two stars is so dense that a teaspoon of its material would weigh as much as an elephant.

"The gravitational effects from the hot and superdense white dwarf are so strong that it has forced the companion star to swell up like a massive balloon and move towards it," said a university statement.

The companion star is about 125 times the volume of our Sun, and towers over the Earth-sized dwarf -- about the size ratio of a hot air balloon to a marble.

"However, the companion star is lightweight, weighing in at only one percent of the white dwarf's mass," the statement said.

The two are in tight orbit around one another.

Astronomers do not know whether the dwarf will completely devour its companion, or whether the two will collide and cause a supernova explosion.

Studying such explosions may help scientists measure the expansion of the Universe.

The findings were published in the journal Monthly Notices of the Royal Astronomical Society.
Source: AFP