Astronomers have discovered evidence of a rare type of thermonuclear explosion, called a ‘hyper burst’, which occurred within a neutron star on the edge of the Milky Way, releasing as much energy in three minutes as the sun does in 800 years. This explosion appears to have happened after hundreds or possibly thousands of years of heat and pressure building up, and its occurrence may only happen once every 1,000 years.
If confirmed, this would be the most powerful explosion ever detected in a neutron star and possibly the rarest explosion detected anywhere.
The neutron star that exhibited the hyper burst, MAXI J0556-332, is located about 140,000 light-years from Earth in the Milky Way’s halo. Neutron stars that are part of a binary star system, which share a common centre of gravity with another nearby star, commonly have X-ray outbursts. The outbursts occur when a neutron star’s gravity draws in gas from its companion star, causing the gas to explode upon impact with the neutron star’s surface.
What made the MAXI J0556-332 outburst unique was the extreme heat observed during the first week after the outburst ended. This extreme heat could not result from matter slamming into the neutron star’s surface, as other large X-ray outbursts did not leave the star as hot.
Instead, the researchers believe a massive thermonuclear explosion within the neutron star caused the extreme heating observed in 2011. This explosion may have been building up for hundreds or more than a thousand years as matter from the partner star fell onto the neutron star’s surface every few years, steadily increasing the heat and pressure within the star.
The explosion likely resulted from the nuclear fusion of oxygen or neon, making this the first observation of a hyper burst. Observing another hyper burst in this lifetime may be near impossible since they are a vanishingly rare phenomenon that occurs under extremely specific circumstances. Future research will focus on MAXI J0556-332’s mysterious companion star to determine what makes this distant star system more prone to hyper bursts.
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