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- Like a little stellar mosquito, the white dwarf continually sucks hydrogen from its partner, forming an ocean on its surface. After drawing about as much mass as the entire planet Saturn, the pressure reaches a critical point, then boom!
- Like a little stellar mosquito, the white dwarf continually sucks hydrogen from its partner, forming an ocean on its surface. After drawing about as much mass as the entire planet Saturn, the pressure reaches a critical point, then boom!
Astronomers have captured the first timelapse images of a thermonuclear fireball exploding out of a nova star, allowing them to track the event as it happened.
An international team of researchers worked together to map the nova eruption, a baby brother to a supernova explosion, and publish the results in Nature.
"Although novae often play second fiddle in the popular imagination to their more famous big cousins - the supernovae - they are a truly remarkable celestial phenomenon," said Professor Peter Tuthill of the University of Sydney’s Institute for Astronomy.
Novae happen when an exotic, compact star called a white dwarf strips the matter from a nearby companion star with its intense gravitational field.
This is an artist's conception of a star system responsible for a nova. A stream of matter is being... [+]
“The stellar surface turns into one titanic hydrogen bomb hurling a fireball out into space and propelling a formerly dim, obscure star system into prominence as a nova in our night skies," Professor Tuthill explained.
"The ferocity of the expansion is breathtaking, engulfing a region the size of the Earth's orbit within a day, and passing Jupiter's orbit in less than two weeks. Despite the enormous size of the fireball, at the remote distance to this star of fifteen thousand light years, it took very special technology to be able to image it at all."
The team collaborated with the Georgia State University scientists running the Centre for High Angular
"The technical challenge posed requires magnification equivalent to watching a flower in my Spanish hometown of Algeciras unfold from here in Sydney, a distance of 12,000 kilometres away," Dr Vicente Maestro, also of the University of Sydney, said.
The array was able to produce the first pictures of a nova at the early fireball stage from one that erupted in the Delphinus constellation last year, from Earth’s point of view. In actual fact, the star went nova 15,000 years ago, but the star is 14,800 light years from our Sun so we only spotted it last August.
The observations were clearer than any before and showed how the structure of the ejected material evolves as the gas expands and then cools. From this study, it now appears that this expansion is more complicated than the simple models previously predicted.
During the first observation, the fireball was roughly the size of Earth’s orbit. When last measured, 43 days after detonation, it had expanded nearly 20-fold at a velocity of more than 600 kilometres per second to nearly the size of Neptune’s orbit, the outermost planet of our Solar System.
However, the explosion was not precisely spherical, instead the fireball had a slightly elliptical shape. The researchers also found that the outer layers of the eruption became more diffuse and transparent as the fireball expanded. After around a month, the team say a brightening in the cooler, outer layers, potentially caused by the formation of dust grains that emit light at infrared wavelengths.
"These new data allow us to study in detail exactly how the fireball evolves as the gas expands and cools. It seems like the ride is a lot more complicated and bumpy for the gas than the simple models used previously would have predicted," said Dr Theo ten Brummelaar of Georgia State University.
Perhaps most surprisingly, the astronomers found that despite the ferocity of the detonation on the white dwarf’s surface, the star itself emerges almost unscathed – leaving it free to start the whole process all over again.
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