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<\/p>\nOf the trillions of stars scattered throughout the universe, one of the most common are the white dwarfs, which are the dormant, burned out, and leftover cores of low\/medium mass stars. For decades, scientists have only measured the masses of white dwarfs within binary star systems. While these measurements provide insight into the true masses of white dwarfs, the measurements typically feature high amounts of uncertainty.<\/p>\n
With help from the joint NASA\/European Space Agency (ESA) Hubble Space Telescope, a team of researchers directly measured the mass of an isolated white dwarf outside of a binary star system. Found to be approximately 56% of the Sun\u2019s mass, the team\u2019s results agree with previous white dwarf mass predictions and provide insight into the evolutionary processes of dead stars.<\/p>\n<\/p>\n
To measure the mass of the white dwarf, named LAWD 37, the team utilized gravitational microlensing \u2014 a natural phenomenon in which the gravity from a cosmic object in front of another warps the light from the background object. In the case of LAWD 37\u2019s observations, light from a star behind the white dwarf was slightly warped as the white dwarf passed in front of the star, seemingly moving the background star to a different location in the sky.<\/p>\n
Precisely measuring the amount of light deflected by LAWD 37\u2019s gravity allowed the team to determine the mass of the white dwarf. Interestingly, using gravitational microlensing to measure the mass of a white dwarf is not new, and was first used in 2017 by Kailash Sahu of the Space Telescope Science Institute in Maryland to measure the mass of Stein 2051 b. However, much like the observations before Sahu\u2019s, the white dwarf was a member of a binary star system.<\/p>\n
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Artist\u2019s illustration showing how the gravity of a white dwarf can warp the light of a star behind it. (Credit: NASA, ESA, Ann Feild (STScI))<\/p>\n
\u201cOur latest observation provides a new benchmark because LAWD 37 is all by itself,\u201d said Sahu, who served as the principal Hubble investigator during the LAWD 37 observations.<\/p>\n
But what about LAWD 37 made it the perfect candidate for the team to study?<\/p>\n
First, LAWD 37 is a single, isolated white dwarf that is not part of a binary star system. This means that the gravity measurements the team collected would not be warped by the gravity of a second star within a binary, giving them clear and precise measurements for LAWD 37\u2019s mass.<\/p>\n
Space Technology (adsbygoogle = window.adsbygoogle || []).push({});<\/p>\n Second, LAWD 37 is very close to Earth \u2014 only 15 light-years away from our solar system in the constellation Musca. Using multiple observations from ESA\u2019s Gaia space observatory, the team was able to predict when LAWD 37 would pass in front of a background star. Gaia takes extraordinarily precise measurements of the positions of nearly two billion stars in the universe, and the motion of a specific star can be determined over multiple observations by Gaia.<\/p>\n \u201cBecause this white dwarf is relatively close to us, we\u2019ve got lots of data on it \u2014 we\u2019ve got information about its spectrum of light, but the missing piece of the puzzle has been a measurement of its mass,\u201d said lead author Peter McGill of the University of California, Santa Cruz.<\/p>\n The Gaia data showed McGill et al. that LAWD 37 would pass in front of the background star in November 2019. With this information, the team then enlisted the help of Hubble, which was used to precisely measure the (apparent) positional change of the background star over several years.<\/p>\n \u201cThese events are rare, and the effects are tiny. For instance, the size of our measured offset is like measuring the length of a car on the Moon as seen from Earth,\u201d McGill said.<\/p>\n What\u2019s more, extracting the light from the faint background star proved challenging for the team, as the glare from LAWD 37 is approximately 400 times brighter than the observed light of the background star. Hubble is the only space telescope that can perform high-contrast observations in visible light, making it the perfect tool for the team.<\/p>\n Graphic showing Hubble\u2019s observations of the movement of LAWD 37. (Credit: NASA\/ESA\/Peter McGill (UC Santa Cruz, IoA)\/Kailash Sahu (STScI)\/Joseph DePasquale (STScI))<\/p>\n After Hubble had collected all the needed data, McGill et al. were able to precisely calculate the mass of LAWD 37, which came to be around 56% of the mass of our Sun. The mass measurements will allow the team to test the mass-radius relationship for white dwarfs, which will then allow them to test the theory of degenerate matter \u2014 which states that within stars and other extreme cosmic objects, gas is so compressed under the object\u2019s gravity that it begins to behave like solid matter.<\/p>\n \u201cThe precision of LAWD 37\u2019s mass measurement allows us to test the mass-radius relationship for white dwarfs. This means testing the theory of degenerate matter under the extreme conditions inside this dead star,\u201d said McGill.<\/p>\n McGill et al.\u2019s mass calculation method is expected to open the door for predicting future white dwarf occultation events using Gaia. Furthermore, NASA\u2019s James Webb Space Telescope is capable of observing these occultation events like Hubble. With Webb\u2019s extreme sensitivity to infrared light, the white dwarf in Webb\u2019s observations will appear dimmer than the background star \u2014 perfect for measuring the change in the apparent position of the background star.<\/p>\nSee Also<\/h4>\n
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