New method to measure gravity on distant stars

Scientists have found a new way to measure the pull of gravity at the surface of a star, an advance that could be key to determining whether any planets orbiting distant stars can harbour life.

Knowing the surface gravity of a star is essentially knowing how much you would weigh on that star. If stars had solid surfaces on which you could stand, then your weight would change from star to star, researchers said.

The method developed by researchers from University of British Columbia in Canada and University of Vienna in Austria allows scientists to measure surface gravity with an accuracy of about four per cent, for stars too distant and too faint to apply current techniques.

Since surface gravity depends on the star's mass and radius, this technique will enable astronomers to better gauge the masses and sizes of distant stars.

It will help study planets beyond the Solar System, many so distant that even the basic properties of the stars they orbit can not be measured accurately, researchers said.

"The size of an exoplanet is measured relative to the size of its parent star," said study co-author Jaymie Matthews, from UBC.

"If you find a planet around a star that you think is Sun-like but is actually a giant, you may have fooled yourself into thinking you've found a habitable Earth-sized world," Matthews said.

"Our technique can tell you how big and bright is the star, and if a planet around it is the right size and temperature to have water oceans, and maybe life," he said.

The new technique called the autocorrelation function timescale technique, or timescale technique, uses subtle variations in the brightness of distant stars recorded by satellites like Canada's MOST and NASA's Kepler missions.

Future space satellites will hunt for planets in the 'Goldilocks Zones' of their stars. Not too hot, not too cold, but just right for liquid water oceans and maybe life, researchers said.

Future exoplanet surveys will need the best possible information about the stars they search, if they are to correctly characterise any planets they find.

"The timescale technique is a simple but powerful tool that can be applied to the data from these searches to help understand the nature of stars like our Sun and to help find other planets like our Earth," said study lead author, Thomas Kallinger, from University of Vienna.

The research was published in the journal Science Advances.