Astronomers have measured the mass of a lone white dwarf star for the first time. This type of smoldering stellar remnant is formed at the end of the life of low-mass stars and will be what it will leave behind when the Sun dies in about 5 billion years. Space Hubble telescope mass measured white dwarf It was named LAWD 37, which burned more than 1 billion years ago.

Scientists used a phenomenon first predicted in 1915 in their study. Albert Einstein It’s called “gravitational lensing,” which involves the bending of light by large objects. The team determined that LAWD 37 has a mass of about 56% of its own mass. Sun. The finding supports existing theories about how these stellar remnants formed and evolved. This particular white dwarf is well studied as it is relatively close. SoilIt is only 15 million light-years away in the constellation of the Amulet.

“Because this white dwarf is relatively close to us, we have a lot of data on it – we know about the light spectrum, but the missing piece of the puzzle is measuring its mass,” University of Astronomer Peter McGill said. Santa Cruz, California, who led the research, says expression.

This is the first time astronomers have calculated the mass of a lone white dwarf, but have previously made similar measurements for white dwarfs in binary partnerships with others. stars.

By applying Newton’s theory of gravity to the motion of two stars rotating against each other, astronomers can obtain mass measurements in pairs. But this can be an uncertain process, especially if the companion star has a long orbit of hundreds or thousands of years. The researchers turned to Einstein’s gravitational formula to measure the mass of this uniform star. general theory of relativity.

How did Einstein help measure a dead star?

The general theory of relativity assumes that massive objects “deform” the fabric of space-time. The greater the mass, the larger the “pit” it creates in space. When light from a background object passes through this curvature, it is deflected; this is an effect that can amplify the light and even make the background object appear in multiple places at once. However, more often the distortion causes a shift in the apparent position of the background object.

The mass of the lensing object causing the effect can be obtained by measuring how much light is deflected and thus caused by the change in position when astronomers look at the background object. This is true even if this shift is small, as with microlensing events such as the event involving this particular white dwarf.

In the new observations, LAWD 37 acts as a gravitational lens in the foreground, slightly deflecting light passing through the background star and changing its position in the sky. This change in position allowed McGill and his team to measure the mass of LAWD 37. Researchers used a similar process to determine the mass of another white dwarf in 2017, but this stellar remnant was in a binary system rather than a single dead star. LAW 37.

McGill and colleagues, thanks to LAWD 37 Gaia missions The European Space Agency, which accurately measures the position of about 2 billion stars. Using multiple Gaia images allows astronomers to track the movement of the star, so the team was able to predict that LAWD 37 would pass in front of the background star in November 2019. Armed with this prediction, scientists have used Hubble for several years to measure the change in the apparent position of the background star as the white dwarf passes in front of it.

“These cases are rare and the consequences are minor,” McGill said. Said. “For example, the extent of the slip we measured is similar to measuring the length of a car on the Moon when viewed from Earth.”

The team also had to select the faint light of background stars from the glow of LAWD 37, which is about 400 times brighter. Fortunately, Hubble is powerful enough to make such high-contrast observations in visible light.

“Even if you encounter one-in-a-million events like this, it’s still extremely difficult to make these measurements,” said Leigh Smith, an astronomer at the University of Cambridge in England and co-author of the study. in practice. “The flare from a white dwarf can cause streaks in unpredictable directions, which means we need to analyze each of the Hubble observations and their limitations extremely carefully to model the event and estimate the mass of LAWD 37.”