For the first time ever, astronomers watch a sleeping white dwarf go nova


#Astronomers #NasaFor the first time ever, astronomers watch a sleeping white dwarf go nova : Maybe Sleepy Dwarf was the star of the story all along. After years of careful observations, a team of Polish scientists have watched a white dwarf emerge from hibernation, steal enough mass from its companion star to go nova, and then return to sleep.

Astronomers at the Optical Gravitational Lensing Experiment (OGLE) – a long-term surveying project using microlensing to search for dark matter – have now witnessed, for the first time in recorded history, a white dwarf going from its pre- to post-nova phases, thus providing the first-ever visual record of the steps of the cataclysm that gives cataclysmic variable stars their name.

They detailed their findings in an article published Wednesday in the journal Nature. A white dwarf is the remnant core of a star that used up all its nuclear fuel. After its collapse, this one settled into a binary system with a companion star whose mass it slowly steals.

The stolen mass (primarily hydrogen) orbits around the white dwarf in a loose disk. Because of the slow rate of theft, which scientists refer to as “mass transfer,” the star-stuff occasionally becomes unstable and explodes in small “dwarf novas.” (Like a spinning top, mass transfer is more stable at higher speeds.)

Dwarf novas fling the hydrogen down onto the surface of the white dwarf, where it builds up until it erupts in a thermonuclear explosion known as a classical nova.

Starting in 2003, the research team tracked several dwarf novas, and then in 2009, enough mass had gathered on the surface of the white dwarf to begin fusing into a full classical nova.

According to the hibernation hypothesis, white dwarfs emerge from hibernation, start stealing hydrogen at a low, unstable rate, go nova, then have several centuries of high-rate mass transfer before settling into another long hibernation period, anywhere between 1,000 and one million years long.