Dead stars called white dwarfs can explode in novas or supernovas, but now astronomers have seen much smaller stellar explosions which they call micronovae.
. Three were seen up to 5000 light years from Earth, with the white dwarfs brightening temporarily before dimming again.
The exact mechanism behind the explosions isn’t clear, but it is thought they may be caused by hydrogen accumulating at the poles of the star – perhaps as much as the mass of an asteroid in just 100 days. Eventually, the hydrogen reaches sufficient temperatures and pressures to ignite fusion and cause a localised thermonuclear explosion that releases as much energy as the sun would in a day.
Only very magnetic white dwarfs may be able to accumulate hydrogen at their poles in this way, meaning not all should experience micronovae. Finding and studying more of them could reveal these processes, and perhaps explain how white dwarfs are able to accrete enough mass to explode as supernovae. “It shows how dynamic our universe is,” says Scaringi. “If you’re not looking at the right time, you might miss these things.”
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