In November 2019, the nearby single, isolated white dwarf LAWD 37 aligned closely with a distant background source and caused a so-called microlensing event. Leveraging astrometry from ESA’s Gaia mission and follow-up data from the NASA/ESA Hubble Space Telescope, astronomer measured the astrometric deflection of the background source and obtain a mass for LAWD 37.
LAWD 37 is located approximately 15 light-years away in the constellation of Musca.
Also known as WD 1142-645, this white dwarf has been extensively studied.
“Because this white dwarf is relatively close to us, we’ve got lots of data on it — we’ve got information about its spectrum of light, but the missing piece of the puzzle has been a measurement of its mass,” said Dr. Peter McGill, an astronomer at the University of California, Santa Cruz.
In his general theory of relativity, Albert Einstein predicted that when a massive compact object passes in front of a distant star, the light from the star would bend around the foreground object due to its gravitational field. This effect is known as gravitational microlensing.
In 1919, British astronomers Arthur Eddington and Frank Dyson first detected this effect during a solar eclipse, in what was the first popular confirmation of general relativity.
In 2017, astronomers detected this gravitational microlensing effect for another nearby white dwarf in a binary system, Stein 2051b, which marked the first detection of this effect for a star other than our Sun.
Now, Dr. McGill and colleagues have detected the effect for LAWD 37, giving the first direct mass measurement for a single white dwarf.
Using data from Gaia, they were able to predict the movement of the star and identify the point where it would align close enough to a background star to detect the lensing signal.
They then pointed Hubble in the right place at the right time to observe this phenomenon, which happened in November 2019, 100 years after the famous Eddington/Dyson…
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