Astronomers ‘weigh’ white dwarf stars via gravitational lensing
Astronomers have determined the mass of a scorched star directly using a phenomenon known as gravity lens effect. An international team, led by Peter McGill from the University of Cambridge (UK), used data from two telescopes to measure how light from a distant star was deflected by the white dwarf star LAWD 37, causing the The distant star’s temporary distance from the star’s position seemed to change. This is the first time this effect has been observed with a star other than our Sun, and the first time the mass of such a lensed star has been measured directly (Royal Astronomical Society Monthly NoticesFebruary 2).
LAWD 37 is a white dwarf, the compact remnant of a star like our sun. When a Sun-like star runs out of nuclear fuel, it swells and propels its outer layers into space. Only its warm, compact core remains. Under these conditions, matter as we know it behaves very differently and transforms into something that degenerate matter is called. LAWD 37 has been extensively researched as it is relatively close. Located 15 light-years away in the southern constellation of Fly, the white dwarf is the remnant of a dead star more than a billion years ago.
Mass is one of the most important factors in the evolution of a star. For most stellar objects, astronomers derive the mass indirectly, based on strong and often untested model assumptions. In the rare cases where the mass can be inferred directly, the star must have a companion, as in a binary star system. But for single objects, such as LAWD 37, other methods are needed to determine the mass.
McGill and his colleagues have now succeeded – with ESA’s Gaia Astrometric Space Telescope and NASA and ESA’s Hubble Space Telescope – in making the first accurate determination of LAWD’s mass. Using Gaia, astronomers were able to predict the motion of LAWD 37 and determine the point where it would be close enough to a background star to cause the desired lensing effect. With this information, astronomers were able to point the Hubble Space Telescope at the right place in the sky at the right time to actually observe the phenomenon, which happened in November 2019.
From the lensing strength, which is proportional to the mass of the object acting as a lens, it has now been calculated that the mass of LAWD 37 is 0.56 solar masses. This agrees well with previous theoretical predictions of the mass of this white dwarf, and confirms the reliability of existing theories on the evolution of these objects. (EE)
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