White dwarf stars have been doing some weird things lately. There was that one which got flung across the Milky Way half-burnt, and now a white dwarf that went supernova was found to have emitted a monstrous and mysterious UV flash.
This is not your typical supernova. Whatever it is, since it doesn't yet have a name, the phenomenon of a white dwarf exploding into UV light is so rare that this is just the second time it has ever been observed. Nobody knows exactly how or why it happens yet. Finding out what sets off such a flash could help reveal even more dark secrets, from how the universe creates heavy metals to the cosmic acceleration believed to be caused by dark energy. Astrophysicist Adam Miller of Northwestern University and his team of researchers might be able to find out.
“These are some of the most common explosions in the universe,” Miller, who recently published a study in The Astrophysical Journal, said in a press release. “But what’s special is this UV flash. Astronomers have searched for this for years and never found it.”
There is definitely something abnormal about this cosmic outburst (now known as SN2019yvq). Type Ia (one-A) supernovae are the typical way binary white dwarf systems enter their death throes, though they don’t always finish what they started. Many are also superluminous and the brightest supernovae known to occur. White dwarfs made of carbon and oxygen keep accreting star stuff until they reach a limit at which they end up exploding — the Chandrasekhar Limit of 1.4 solar masses. It is thought to be the maximum mass a white dwarf can reach without collapsing into a neutron star or black hole.
Human eyes first caught sight of the strange supernova the day after it exploded. Using the Zwicky Transient Facility in California, researchers were able to tell it happened right next to the Draco constellation, and astrophysicists then took a closer look at the X-ray and UV wavelengths at NASA’s Neil Gehrels Swift Observatory. SN2019yvq was initially classified as a type Ia. It almost passed for one, but the intense UV emission could not be ignored. This wasn’t a flash that was gone in a blink. It lasted several days, meaning something unfathomably hot must have been in or at least close to the dying star. Except white dwarfs cool down as they decline.
UV light this intense needs something at least three or four times hotter than the sun to generate it. It is invisible to us because UV wavelengths are too short for our eyes to process, and X-rays have even shorter wavelengths. Previously, another team of researchers had found ways to determine characteristics of superluminous supernovae using this kind of light. Computer simulations that showed the event at UV wavelengths is how the explosion mechanism behind it was determined, and that method could be used to identify explosion mechanisms in other supernovae. This goes way beyond that.
“Most supernovae are not that hot, so you don’t get the very intense UV radiation. Something unusual happened with this supernova to create a very hot phenomenon,” Miller said.
Miller has four hypotheses on how this could have happened. The dying white dwarf might have accreted gas and dust the Ia supernova way, exploding when it exceeded the limit, and the exploded star colliding with the other star in its binary system caused the UV flash. Maybe there was superhot radioactive material in its core that heated up tis outer shell past the point of no return. There is a chance helium was what drastically raised star’s temperature so high that the double explosion which ensued also released the UV flash. Finally, it is possible the immense amount of UV radiation lit up the cosmos when the two white dwarfs in the star system merged and the remnants of the explosion collided.
What actually caused these real-life movie special effects could reveal itself in about a year, according to Miller. Ejecta will travel further and further from the source until the core of the explosion is exposed. Activate suspense.
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July 28, 2020 at 08:33PM
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Grab your sunscreen, because the intense UV flash from an exploded star could light up a cosmic mystery - SYFY WIRE
"Flash" - Google News
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