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Something we have never seen before is shooting out of a rare exploding star in our own galaxy, astronomers have said.
The material – likened to “bullets” by the scientists who first spotted them – appear to be clumps of gas that are being sent out at up to 20 million miles per hour. They are coming from an exploding star that is the rarest object of its kind in our galaxy.
Astronomers do not know exactly what the bullets are, or where they are coming from. Nothing like them has ever been seen in other exploding stars anywhere in the universe.
They were seen after a a cloud of dust that surrounds the Milky Way’s only known helium nova cleared, more than 20 years since astronomers started watching it. That revealed the rare stellar explosion behind them, which is made up of a white dwarf feeding on a rare helium star.
Scientists from the University of Warwick were able to confirm the real nature of the stellar explosion, known as V445 Puppis. It is our galaxy’s only known helium nova of this kind, and so allows researchers to study that rare stellar explosion in a way they have never before.
Novae are sudden, explosive bursts of energy in binary star systems. They happen when Sun-like star dies and leaves behind a remnant known as a white dwarf, which then pulls gas from its companion star.
The material that is pulled off the companion star then gathers on the white dwarf’s surface. That forces the temperature and pressure to rise – which then triggers a thermonuclear explosion.
When this happened to V445 Puppis, in late 2000, it launched a huge outflow that could spread more than a trillion miles across space. But the eruption also obscured the star system in a thick disc of dust that meant that astronomers could only see the debris, and not the stars that had produced it.
"The explosion's outflow has now faded sufficiently for us to probe its origin, and so we can confirm that the star system does indeed consist of a white dwarf grabbing material off an extremely rare type of star called a helium star," said John Mills, a researcher and PhD student at the University of Warwick.
The new visibility meant that astronomers could properly see the “bullets”, which are thought to be made up of oxygen-rich gas.
"The origin of these 'bullets' is a mystery. We suspect that these originated post-outburst, but 'bullets' of this kind have not been observed in any other nova," said Mills.
Astronomers hope that the discovery of the new stellar system, and the helium nova, mean that they can better understand these kinds of eruptions. Among other things, they are thought to be one thing that leads to a Type Ia supernovae, which is one of the brightest kinds of explosions in the universe.
Those explosions are useful in a variety of ways. Their intense and consistent brightness mean that they can be used as “standard candles”, to measure the distance across galaxies – but astronomers are still not sure exactly where they come from.
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