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Astronomers have just stumbled across one of the biggest explosions in the universe, confirming a theory about how dead stars can temporarily and dramatically come back to life.
Astronomers using the space-based Erosita X-ray Telescope observed a single bright flash of X-rays on July 7, 2020, which has never been seen before or since. In a new article published in the journal Naturethe researchers detail how they paired this X-ray flash with the classic Nova YZ Reticuli, a white dwarf star that explodes some 8,000 light-years away, observing the predicted “fireball phase” of a nova for the first time.
A white dwarf star is a dark, cold, but very dense remnant of a larger star that has exhausted its nuclear fuel – a dead star that can no longer generate the thermonuclear reactions that sustain living stars. But as a very dense object with powerful gravity, white dwarfs with a larger, still-living companion star sometimes siphon hydrogen from their companion’s outer shell.
When enough hydrogen builds up on the surface of a white dwarf, the pressure and heat build up to the point that a runaway thermonuclear reaction occurs – the hydrogen is fused into helium and a colossal explosion, a classic nova, results. It is a type of stellar explosion different from a supernova, which results from the agony of a star that is still alive and very massive.
As described by the Stony Brook University astronomer and author of a commentary in the same issue of Nature, Frederick Walter, a 1990 prediction claimed that a classic nova would shine brightest the moment the explosion reached the outer layer of the white dwarf, the photosphere – a “fireball” nova. This fireball would be so hot and bright, it was thought, that it would not be visible in X-rays until hours or days later, when the material ejected from the white dwarf during the nova had cooled sufficiently. to shine in the visible part of the spectrum.
The erosita researchers were able to reconstruct the X-ray burst they observed and the visible explosion of the YZ Reticule Nova seen on July 15, and realize that they had managed to capture both the fireball and Nova, confirming the 1990 prediction.
As Dr. Walter wrote in his commentary, this was a chance finding.
The erosita instrument flies on the Spektr-RG space telescope, a partnership between Germany and Russia. It takes erosita six months to perform a scan of the sky, and it only performed four such scans before the Russian invasion of Ukraine interrupted the mission. Luckily, one of those scans captured the YZ Reticuli nova’s fireball.
