SCIENTISTS have used the Hubble telescope to weigh a white dwarf for the first time, offering new insights into the evolution and death of stars.

Efforts to study white dwarves, the burnt-out remains of stars, have been held back because the closest one to Earth is a companion of Sirius, the brightest star in the sky, which swamps its faint glow. Astronomers led by Martin Barstow, of the University of Leicester, have used Hubble to isolate the light from the Sirius B white dwarf, enabling them to measure the defunct star’s mass. Sirius B has a diameter of about 7,300 miles (11,700km), making it smaller than Earth, but it is so dense that its mass is 98 per cent of that of the Sun.

The observations will enable scientists to understand more about how stars like the Sun end up as white dwarves when they exhaust their nuclear fuel and collapse to form smaller, fainter bodies.

“Studying Sirius B has challenged astronomers for more than 140 years,” Dr Barstow said. “Only with Hubble have we at last been able to obtain the observations we need.”

In the study, published in Monthly Notices of the Royal Astronomical Society, the researchers relied on the effect that Sirius B’s strong gravity has on the light it gives off. The star is about the same size as Earth, but is so dense that its gravitational field is 350,000 times stronger: a person weighing 68kg (10st 10lb) would weigh almost 25,000,000kg if standing on its surface.

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