Superflare From Crab Nebula Has Astronomers Mystified
The Crab Nebula, the dusty remains of an exploded star, has unleashed a surprisingly massive flare that is five times more powerful than any eruption previously seen from the celestial object, leaving scientists struggling to explain the event, NASA says.
The so-called “superflare” was detected on April 12 by NASA’s Fermi Gamma-ray Space Telescope, which is continuously mapping the sky in gamma ray wavelengths in search of gamma-ray bursts, the brightest explosions in the universe.
The Crab Nebula’s strong outburst lasted six days, and its exact cause has scientists scratching their heads, especially since the superflare followed an earlier gamma-ray flare from the nebula in January.
The outburst observed by Fermi was likely triggered by electrons with energies 100 times greater than can be achieved in any particle accelerator on Earth, scientists said.
This makes them the highest-energy electrons known to be associated with any galactic source.
Based on the rise and fall of gamma rays during the April outbursts, scientists estimate that the size of the emitting region must be comparable to our entire solar system.
The Crab Nebula’s legacy
The spectacular and colorful Crab Nebula is the wreckage of a dying star that emitted an explosion of light that reached Earth in the year 1054.
The former star was located 6,500 light-years away from Earth in the constellation Taurus when it erupted in a brilliant supernova explosion.
At the heart of an expanding gas cloud lies what is left of the original star’s core, a super-dense neutron star that spins 30 times a second.
With each rotation, the star swings intense beams of radiation toward Earth, creating the pulsed emission characteristic of spinning neutron stars, which are also known as pulsars.
Apart from these pulses, astrophysicists thought the Crab Nebula was a virtually constant source of high-energy radiation.
But, in January, scientists representing a variety of space-based observatories, including NASA’s Fermi, Swift and Rossi X-ray Timing Explorer, reported long-term changes in brightness at X-ray energies.
“The Crab Nebula hosts high-energy variability that we’re only now fully appreciating,” said Rolf Buehler, a member of the Fermi Large Area Telescope (LAT) team at the Kavli Institute for Particle Astrophysics and Cosmology, a facility jointly located at the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University in California.
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