How Do Scientists 'Weigh' Stars?

This image shows an Einstein ring (middle right), which occurs when a massive object

acts like a lens for light coming toward the observer from a background object. This phenomenon is known as gravitational lensing, and recently used for the first time to measure the mass of an individual star. Credit: ESA/Hubble & NASA Stars are enormous balls of hot gas located many trillions of miles away, but when they're observed from the Earth, they appear as tiny shining dots visible in the night sky. In a new study, astronomers made a precise measurement of the mass of a nearby "white dwarf," a star that has reached the end of its life cycle. But how, exactly, can that be done? How do scientists "weigh" the mass of a gaseous sphere light-years away? "Just about the only way we have as astronomers for measuring masses of stars and planets and galaxies is by their gravitational influence on one another," said Terry Oswalt, a professor of engineering physics at Embry-Riddle Aeronautical University, who wrote a commentary about the recent white-dwarf measurement for the journal Science. In other words, if a satellite is in orbit around Jupiter, it's possible to estimate Jupiter's mass by measuring the effects of the planet's gravity on the satellite's orbit. [The 18 Biggest Unsolved Mysteries in Physics]           https://www.livescience.com/59436-how-do-scientists-weigh-stars.html