Earlier this week, NASA's Fermi Gamma-ray Space Telescope picked up a flash of high-energy gamma radiation from what may seem like an unlikely source, the Earth. This radiation, traditionally seen emitting from powerful neutron stars and supernovas, was seen in a temporary flash at the center of Hurricane Julio as it continues to make its way towards the Hawaiian Islands - a testament to the power of the right storm conditions.
According to NASA, this type of unique gamma-ray outburst is called a terrestrial gamma-ray flash (TGF) and is the only kind of natural gamma-ray emission seen on earth. That's because gamma rays are only seen in phenomena that boast exceptionally high-energy, such as a supernovae. Researchers have recently discovered that novae, explosions occurring on the surface of white dwarf stars, also emit blips of gamma radiation. Even though these explosions release more energy than 100,000 times the annual energy output of the Sun, it these gamma emissions actually came as a surprise to astronomers, who thought the energy in novae was too small.
So how is it that Julio flashed some gamma, even if extremely briefly? The storm certainly hasn't formed a neutron star the last time we checked.
According to NASA's Fermi team, it's all about proportion. The Fermi is equipped with a short-range (relatively) Gamma-ray Burst Monitor (GBM). This equipment is extremely sensitive to even the tiniest of gamma bursts, but unfortunately can only monitor space within 500 miles of the orbiting spacecraft. It is very likely there are small bursts of gamma radiation occurring all the time in space in less-than cataclysmic events, but they are so insignificant compared to some gamma bursts that Fermi's long range tech cannot pick them up.
Still, the fact that Julio produced any radiation of all is still testament to the storm's growing power.
"As far as I know, a TGF from a tropical storm has never been reported before," said Michael Briggs, a member of the GBM team at the University of Alabama in Huntsville.
The team reports that the TGF was emitted from excessively high energy interaction between clashing lighting storms, just before they drew closer together to form a full-fledged hurricane.
According to NASA, as of Saturday, Julio's maximum sustained winds are near 100 mph, extending hurricane force winds for 35 miles, and weaker storm winds for 175 miles from the center of the storm.
The current forecast shows Julio passing a couple of hundred miles northeast of the Big Island on Sunday, leaving heavy rain and lightning storms in its wake.