- 2922 - WHITE DWARFS - the core of supernovae? An exploding white dwarf star blasted itself out of its orbit with another star in a ‘partial supernova’ and is now hurtling across our galaxy. This opens up the possibility of many more survivors of supernovae traveling undiscovered through the Milky Way, as well as other types of supernovae occurring in other galaxies that astronomers have never seen before.
--------------------------- 2922 - WHITE DWARFS - the core of supernovae?
- The material ejected by the supernova explosions will initially expand very rapidly, but then gradually slow down, forming an intricate giant bubble of hot glowing gas. Eventually, the charred remains of the “white dwarf” that exploded will overtake these gaseous layers, and speed out onto its journey across the galaxy.
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- Reported July 15, 2020 by the Trust and Science and Technology Facilities Council, that analyzed a white dwarf that was previously found to have an unusual atmospheric composition. It reveals that the star was most likely a binary star that survived its supernova explosion, which sent it and its companion flying through the Milky Way in opposite directions.
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- White dwarfs are the remaining cores of red giant stars after these huge stars have died and shed their outer layers, cooling over the course of billions of years. The majority of white dwarfs have atmospheres composed almost entirely of hydrogen or helium, with occasional evidence of carbon or oxygen dredged up from the star’s core.
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- The white dwarf star, designated “SDSS J1240+6710” was discovered in 2015. It seemed to contain neither hydrogen nor helium, composed instead of an unusual mix of oxygen, neon, magnesium, and silicon. Using the Hubble Space Telescope, the scientists also identified carbon, sodium, and aluminum in the star’s atmosphere, all of which are produced in the first thermonuclear reactions of a supernova.
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- However, there is a clear absence of what is known as the ‘iron group’ of elements, iron, nickel, chromium, and manganese. These heavier elements are normally cooked up from the lighter ones, and make up the defining features of thermonuclear supernovae. The lack of iron group elements suggests that the star only went through a partial supernova before the nuclear burning died out.
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- The scientists were able to measure the white dwarf’s velocity and found that it is traveling at 900,000 kilometers per hour. It also has a particularly low mass for a white dwarf, only 40% the mass of our Sun, which would be consistent with the loss of mass from a partial supernova.
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- This star is unique because it has all the key features of a white dwarf but it has this very high velocity and unusual abundances that make no sense when combined with its low mass.
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- It has a chemical composition which is the fingerprint of nuclear burning, a low mass and a very high velocity. All of these facts imply that it must have come from some kind of close binary system and it must have undergone thermonuclear ignition. It would have been a type of supernova, but of a kind that we haven’t seen before.
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- The scientists theorize that the supernova disrupted the white dwarf’s orbit with its partner star when it very abruptly ejected a large proportion of its mass. Both stars would have been carried off in opposite directions at their orbital velocities in a kind of slingshot maneuver. That would account for the star’s high velocity. It is called the conservation of energy, momentum energy.
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- If it was a tight binary and it underwent thermonuclear ignition, ejecting quite a lot of its mass, you have the conditions to produce a low mass white dwarf and have it fly away with its orbital velocity.
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- The best-studied thermonuclear supernovae are the “Type Ia,” which led to the discovery of dark energy, and are now routinely used to map the structure of the Universe. But there is growing evidence that thermonuclear supernovae can happen under very different conditions.
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- SDSSJ1240+6710 may be the survivor of a type of supernova that hasn’t yet been “caught in the act”. Without the radioactive nickel that powers the long-lasting afterglow of the Type Ia supernovae, the explosion that sent SDSS1240+6710 hurtling across our Galaxy would have been a brief flash of light that would have been difficult to discover.
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- The study of thermonuclear supernovae is a huge field and there’s a vast amount of observational effort into finding supernovae in other galaxies. The difficulty is that you see the star when it explodes but it’s very difficult to know the properties of the star before it exploded.
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- We are now discovering that there are different types of white dwarf that survive supernovae under different conditions and using the compositions, masses and velocities that they have, we can figure out what type of supernova they have undergone. Studying the survivors of supernovae in our Milky Way will help us to understand the myriads of supernovae that we see going off in other galaxies.”
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- The fact that such a low mass white dwarf went through carbon burning is a testimony of the effects of interacting binary evolution and its effect on the chemical evolution of the Universe.
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- 2851 - FUSION - how does it work in the stars? - The fusion in the core of stars can be analyzed as simple hydrogen nuclei, which are protons, fusing together to create heavier elements. Each fusion process up to the element Iron releases some amount of energy. Knowing how much energy our Sun puts out we can estimate the lifetime of our star, how long it will take to “burn up” all of this proton fuel.
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- 2815 - WHITE DWARF - spinning neutron star? A White Dwarf star is the left over core of a star that has exploded in a supernova. It has the mass of the Sun and has the volume of the Earth. Therefore it is a very dense material made of neutrons, or electron - degenerate matter. No fusion takes place anymore so it is a “dead star” continuously loosing its thermal energy.
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- 2805 - WHITE DWARF - stars. The stars in the sky may seem ageless and unchanging, but eventually most of them will turn into White Dwarf Stars. This is the last observable stage of evolution for low- and medium-mass stars. These dim stellar corpses dot the galaxy, leftovers of stars that once burned bright.
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- 21 - 381 stars grow old and become white dwarfs, neutron stars, or blackholes.
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- November 29, 2020 - 2922 - WHITE DWARFS - the core of supernovae?
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