- 3257 - NEUTRON STARS - collapse from white dwarfs? A nearby White Dwarf star found in 2021 might be about to collapse into a Neutron Star. About 97% of all stars in our Universe are destined to end their lives as “white dwarf stars“, which represents the final stage in their evolution.
-------------- 3257 - NEUTRON STARS - collapse from white dwarfs?
- Like neutron stars, white dwarfs form after stars have exhausted their nuclear fuel and undergo gravitational collapse, shedding their outer layers to become super-compact stellar remnants. This will be the fate of our Sun billions of years from now, which will swell up to become a “red giant star” before losing its outer layers.
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- Unlike neutron stars, which result from the more massive stars, white dwarfs were once about eight times the mass of our Sun or lighter. ( 8 Solar Mass). The density and gravitational force of these objects is an opportunity to study the laws of physics under some of the most extreme conditions imaginable.
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- One such object has been found that is both the smallest and most massive white dwarf ever seen. This white dwarf, known as “ZTF J190132.9+145808.7” is located about 130 light-years from Earth and is estimated to be 1.35 times as massive as our Sun.
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- This white dwarf star has a stellar radius of about 1,125 miles, which is slightly larger than our Moon 1,080 miles, making it the smallest and most massive white dwarf we have ever observed.
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- It may seem counterintuitive, but smaller white dwarfs happen to be more massive. This is due to the fact that white dwarfs lack the nuclear burning that keep up normal stars against their own self gravity, and their size is instead regulated by “quantum mechanics.”
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- This white dwarf also has an extreme magnetic field, ranging from 600 to 900 MegaGauss over its entire surface, or roughly 1 billion times stronger than our Sun’s. This magnetic field has one of the fastest rotational periods ever observed in an isolated white dwarf, whipping around the star’s axis once every 6.94 minutes. That is fast spinning!
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- Spectra obtained by “Keck’s Low-Resolution Imaging Spectrometer” (LRIS) revealed signatures of a powerful magnetic field, ultraviolet data from “Swift observatory” helped constrain the size and mass of the white dwarf.
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- Between its strong magnetic field and seven-minute rotational speed this white dwarf must be the result of two smaller white dwarfs coalescing into one. Roughly 50% of the stars in the observable Universe are binary systems, consisting of two stellar companions that orbit one other. If these stars are less than eight solar masses each, they will evolve into white dwarfs that eventually merge to form a more massive white dwarf star.
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- This process boosts the magnetic field of the resulting white dwarf and speeds up its rotation compared to that of its progenitors. It would also explain how this star manages to concentrate such a considerable mass into a volume slightly more than that of the Moon.
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- It’s possible that this white dwarf is massive enough to further collapse into a neutron star. It is so massive and dense that, in its core, electrons are being captured by protons in nuclei to form neutrons. Because the pressure from electrons pushes against the force of gravity, keeping the star intact, the core collapses when a large enough number of electrons are removed.
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- It may mean that a significant portion of other neutron stars in our galaxy did not start their lives as massive stars, but instead evolved from smaller binary stars. The newfound object’s close proximity to Earth (130 light-years) and the fact that it is relatively young (100 million years old ) are indications that similar objects could be common in our galaxy.
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- Scientists hope to be able to study the population of white dwarfs as a whole and determine how many were the result of massive stars experiencing a supernova, and how many were the result of binary companions merging near the end of their lives.
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- They hope to learn the rate of white dwarf mergers in the galaxy, and is it enough to explain the number of type 1a supernovae?
- How is a magnetic field generated in these powerful events, and why is there such diversity in magnetic field strengths among white dwarfs?
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- Finding a large population of white dwarfs born from mergers will help us answer all these questions and more. The more we learn the more we don’t know!
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- August 23, 2021 NEUTRON STARS - collapse from white dwarfs? 3257
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