The lifeless core of a star that exploded a billion years ago is the white
dwarf.
For the first time, astronomers have used the Hubble Space Telescope to
directly estimate the mass of a single white dwarf. The dwarf, also known as
LAWD 37, is the core remnant of a star that went supernova around a billion
years ago.
A group of astronomers used Hubble to see how light from a background star
temporarily curved around the dwarf as it passed in front of the former. The
scientists were able to estimate the mass of the dwarf based on how much of
the ambient light was bent by it. The Monthly Notices of the Royal
Astronomical Society reported their findings.
A white dwarf mass for a star remnant in a binary system was previously
measured by Kailash Sahu, a co-author of the current research. In a
statement issued by the European Space Agency, Sahu stated that "our most
recent observation gives a new benchmark since LAWD 37 is all by
itself."
The surface of LAWD 37 is still a scorching 180,000 degrees Fahrenheit
(100,000 degrees C) even if nuclear fusion is no longer taking place on the
star. About 15 light-years from Earth, the star remnant is currently roughly
56% the mass of the Sun.
Gravitational microlensing, a scaled-down variation of gravitational
lensing, is a technique used to measure the dwarf's mass. In gravitational
lensing, a big object bends space such that light from behind it bends
around the object, enabling us to view objects that would otherwise be
obscured. We can see objects that would otherwise be too faint to notice
thanks to the lensing effect, which also intensifies the light.
For instance, Earendel, a star that is around 13 billion years old, was
discovered last year as a result of this natural magnifying glass
phenomena.
The scientists had to wait for the dwarf to pass in front of the background
star in order to measure LAWD 37, an occurrence that could be predicted
owing to information from the ESA's Gaia mission. The scientists then
painstakingly separated the background star's light from the blinding glare
of the considerably closer LAWD 37.
According to main author of the research Peter McGill of UC Santa Cruz,
"the extent of our measured offset is like measuring the length of a vehicle
on the Moon as seen from Earth." Since the white dwarf's glare may produce
streaks in unpredictable directions, it was necessary to carefully consider
each of Hubble's observations and their limitations in order to model the
event and determine LAWD 37's mass.
Astronomers will be able to use this knowledge to investigate the link
between mass and radius for additional white dwarfs, learning more about how
matter behaves under such strong gravitational fields.
Our Sun will eventually turn into a white dwarf, which will happen in
around 5 billion years. The Sun will go through its own spectacular death
process when it runs out of fuel for its nuclear fusion, possibly leaving a
dazzling nebula in its wake.
The Webb Space Telescope, Hubble's successor, will be able to detect white
dwarfs in the same way via gravitational microlensing, however it primarily
studies light at redder wavelengths than Hubble. Webb has already, in fact.
Another white dwarf, LAWD 66, was the subject of several Webb observations
in 2022, and more are scheduled for 2024.
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