- 3924 - WHITE
DWARF STAR -
measuring its mass. Astronomers
using NASA’s Hubble Space Telescope have for the first time directly measured
the mass of a single, isolated white dwarf star which is the surviving core of
a burned-out, Sun-like star.
-
------------------------------------ white dwarf stars merge
------------ 3924 - WHITE DWARF STAR - measuring its mass.
- These
astronomers found that the white dwarf
is 56 percent the mass of our Sun. This agrees with earlier theoretical
predictions of the white dwarf’s mass and corroborates current theories of how
white dwarfs evolve as the end product of a typical star’s evolution.
-
- The unique
observation yields insights into theories of the structure and composition of
white dwarfs. Until now, previous
white dwarf mass measurements have been gleaned from observing white dwarfs in
binary star systems.
-
- By
watching the motion of two co-orbiting stars, straightforward Newtonian physics
can be used to measure their masses. However, these measurements can be
uncertain if the white dwarf’s companion star is in a long-period orbit of
hundreds or thousands of years. Orbital motion can be measured by telescopes
only over a brief slice of the dwarf’s orbital motion.
-
- For this
companion-less white dwarf, researchers had to employ a trick of nature, called
gravitational microlensing. The light from a background star was slightly
deflected by the gravitational warping of space by the foreground dwarf star.
As the white dwarf passed in front of the background star, microlensing caused
the star to appear temporarily offset from its actual position on the sky.
-
- Hubble
telescope was used to precisely measure
how light from a distant star bent around the white dwarf, “LAWD 37”, causing
the background star to temporarily change its apparent position in the sky.
-
- Astronomers
first used microlensing in 2017 to measure the mass of another white dwarf,
“Stein 2051 B”. But that dwarf is in a widely separated binary system. These latest observation provides a new benchmark
because LAWD 37 is all by itself.
-
- The
collapsed remains of a star that burned out 1 billion years ago, LAWD 37 has
been extensively studied because it is only 15 light-years away in the
constellation Musca. Astronomers got information
about its spectrum of light, but the missing piece of the puzzle has been a
measurement of its mass.
-
- ESA’s Gaia
space observatory was used to make extraordinarily precise measurements of
nearly 2 billion star positions. Multiple Gaia observations can be used to
track a star’s motion. Based on this data, astronomers were able to predict
that LAWD 37 would briefly pass in front of a background star in November 2019.
-
- Once this
was known, Hubble was used to precisely measure over several years how the
background star’s apparent position in the sky was temporarily deflected during
the white dwarf’s passage. The size of
our measured offset is like measuring the length of a car on the Moon as seen from
Earth.
-
- Since the
light from the background star was so faint, the main challenge for astronomers
was extracting its image from the glare of the white dwarf, which is 400 times
brighter than the background star. Only Hubble can make these kinds of
high-contrast observations in visible light.
-
- The
precision of LAWD 37’s mass measurement allows us to test the mass-radius
relationship for white dwarfs. This
means testing the theory of degenerate matter (a gas so super-compressed under
gravity it behaves more like solid matter) under the extreme conditions inside
this dead star.
-
- These
alignments can now be detected with NASA’s James Webb Space Telescope. Because Webb works at infrared wavelengths,
the blue glow of a foreground white dwarf looks dimmer in infrared light, and
the background star looks brighter.
-
- Based on
Gaia’s predictive powers observing another white dwarf, LAWD 66, with NASA’s
James Webb Space Telescope. The first observation was done in 2022. More
observations will be taken as the deflection peaks in 2024 and then subsides.
-
- In his 1915
theory of general relativity, Einstein predicted that when a massive compact
object passes in front of a background star, the light from the star would bend
around the foreground object due to the warping of space by its gravitational
field.
-
- Exactly a
century before this latest Hubble observation, in 1919, two British-organized
expeditions to the southern hemisphere first detected this lensing effect
during a solar eclipse on May 19th.
-
- It was
hailed as the first experimental proof of general relativity that gravity warps
space. However, Einstein was pessimistic that the effect could ever be detected
for stars outside our solar system because of the precision involved. These measurements were 625 times smaller
than the effect measured at the 1919 solar eclipse.
-
March 19, 2023 WHITE DWARF
STAR - measuring its mass. 3924
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--- Sunday, March 19, 2023 ---------------------------
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