How much does a dead star weigh? That’s a question now with at least one solid answer – thanks to an experiment first suggested by Albert Einstein a century ago.
This month astronomers led by Howard Bond NASA’s Space Telescope Science Institute announced they had successfully measured the mass of a type of shrunken dead star called a white dwarf.
They did so using the Hubble space telescope and a test first devised by Einstein as a test of his general theory of relativity.
Einstein theorised that light should be affected by the mass of huge objects, such that light beams should bend around them. The theory was essentially proven during a solar eclipse in 1919 – catapulting the physicist to world fame.
Using the same principle, Bond and his colleagues aimed Hubble at a particular white dwarf known as Stein 2051B as it passed in front of another star, taking multiple images in the process.
Relativity predicts that the light emanating from the background star should bend as the dwarf moves in and out of its way. The difference in the bent and straight line light arrival times is the crucial variable that permits the dwarf to be measured.
That difference turned out to be about two milliarcseconds – a unit of measurement used in astronomy, and equivalent to 0.0000005555555556 of one degree.
This equates to roughly 68 per cent of the mass of our own sun – a measurement, the scientists reported, that accorded well with earlier theoretical estimates based on the dwarf’s known radius and other values.
“The agreement of the theoretical prediction with the measurement we were able to make with Hubble was astonishingly good,” Bond said.
The research was published in the journal Science.
The team’s next project is to make good use of Einstein, Hubble and bending light to measure the mass of the sun’s nearest neighbour, the star Proxima Centauri.
Source: http://bit.ly/2s5OW8n
