Free Astronomy Magazine May-June 2023

26 MAY-JUNE 2023 ASTRO PUBLISHING First direct mass measurement of a lone white dwarf by NASA/ESA Bethany Downer A stronomers us- ing the NASA/ ESA Hubble Space Telescope have for the first time directly measured the mass of a single, isolated white dwarf star – the surviv- ing core of a burned- out sunlike star. Researchers found that the white dwarf is 56 percent of the mass of our Sun. This agrees with earlier theoretical predictions of its mass and corroborates cur- rent theories of how white dwarfs evolve as the end product of a typical star’s evolution. The unique observation yields insights into the- ories of the structure and composition of white dwarfs. Until now, previous white dwarf mass meas- urements have been gleaned from observing white dwarfs in binary star systems. By watch- H ubble has used microlensing to measure the mass of a white dwarf star called LAWD 37. It is a burned-out star in the centre of this Hubble image. Though its nuclear fusion furnace has shut down, trapped heat is sizzling on the surface at roughly 100,000 degrees Celsius, causing the stellar remnant to glow fiercely. The white dwarf has a ‘spike’ because it is so bright that the light ‘bled’ into the Hubble camera’s CCD detector. [NASA, ESA, P. McGill (Univ. of California, Santa Cruz and University of Cambridge), K. Sahu (STScI), J. Depasquale (STScI)]