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NASA's Fermi Spots 'Superflares' in The Crab Nebula

For Release: May 11, 2011


Crab Nebula
Credit: NASA/CXC/MSFC/M.Weisskopf et al.
Press Image and Caption

WASHINGTON -- The famous Crab Nebula supernova remnant has erupted in an enormous flare five times more powerful than any flare previously seen from the object. On April 12, NASA's Fermi Gamma-ray Space Telescope first detected the outburst, which lasted six days.

The nebula is the wreckage of an exploded star that emitted light which reached Earth in the year 1054. It is located 6,500 light-years away in the constellation Taurus. At the heart of an expanding gas cloud lies what is left of the original star's core, a superdense 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 (also known as pulsars).

Apart from these pulses, astrophysicists believed the Crab Nebula was a virtually constant source of high-energy radiation. But in January, scientists associated with several orbiting observatories, including NASA's Fermi, Swift and Rossi X-ray Timing Explorer, reported long-term brightness changes 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.

Since 2009, Fermi and the Italian Space Agency's AGILE satellite have detected several short-lived gamma-ray flares at energies greater than 100 million electron volts (eV) -- hundreds of times higher than the nebula's observed X-ray variations. For comparison, visible light has energies between 2 and 3 eV.

On April 12, Fermi's LAT, and later AGILE, detected a flare that grew about 30 times more energetic than the nebula's normal gamma-ray output and about five times more powerful than previous outbursts. On April 16, an even brighter flare erupted, but within a couple of days, the unusual activity completely faded out.

"These superflares are the most intense outbursts we've seen to date, and they are all extremely puzzling events," said Alice Harding at NASA's Goddard Space Flight Center in Greenbelt, Md. "We think they are caused by sudden rearrangements of the magnetic field not far from the neutron star, but exactly where that's happening remains a mystery."

The Crab's high-energy emissions are thought to be the result of physical processes that tap into the neutron star's rapid spin. Theorists generally agree the flares must arise within about one-third of a light-year from the neutron star, but efforts to locate them more precisely have proven unsuccessful so far.

Since September 2010, NASA's Chandra X-ray Observatory routinely has monitored the nebula in an effort to identify X-ray emission associated with the outbursts. When Fermi scientists alerted astronomers to the onset of a new flare, Martin Weisskopf and Allyn Tennant at NASA's Marshall Space Flight Center in Huntsville, Ala., triggered a set of pre-planned observations using Chandra.

"Thanks to the Fermi alert, we were fortunate that our planned observations actually occurred when the flares were brightest in gamma rays," Weisskopf said. "Despite Chandra's excellent resolution, we detected no obvious changes in the X-ray structures in the nebula and surrounding the pulsar that could be clearly associated with the flare."

Scientists think the flares occur as the intense magnetic field near the pulsar undergoes sudden restructuring. Such changes can accelerate particles like electrons to velocities near the speed of light. As these high-speed electrons interact with the magnetic field, they emit gamma rays.

To account for the observed emission, scientists say the electrons must have energies 100 times greater than can be achieved in any particle accelerator on Earth. 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 in size to the solar system.

People Who Read This Also Read...

NASA's Fermi is an astrophysics and particle physics partnership managed by NASA's Goddard Space Flight Center in Greenbelt, Md., and developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

The Marshall Space Flight Center manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

More information, including images and other multimedia, can be found at: and

Media contacts:
Trent Perrotto
Headquarters, Washington

Lynn Chandler
Goddard Space Flight Center, Greenbelt, Md.

Visitor Comments (9)

In the video of the Crab Nebula I noticed a brightening, at a time about in the middle of the detailed slow-motion part. This brightening was in the form of a thick horizontal line that momentarily appeared in a relatively dark area. This area was located to the left of the pulsar, about one-half the way from the pulsar to the left edge of the nebula.

Posted by Joseph E. Molnar on Tuesday, 05.31.16 @ 16:24pm

What would this be classified as?

Posted by Amanda Leitenberger on Thursday, 11.1.12 @ 15:54pm

Reminds me of a famous author of the 19th Century:Mary Baker Eddy, who wrote in Science and Health-"They will no longer look up to the Stars, but down from them upon the Universe"! If one would gaze at it for awhile, even with the help of a magnifying lens, one cuold almost fell BEING THERE! Beautiful color photography: below on this super Cradled Planet Earth! If Terrorist would blow up Earth as the next great target after the Twin Towers, who in the rest of the Universe would give A-DAM about us and these Terrorists: We are not even located in a prominent Galctic area of recognition!

Posted by albert kundrat on Saturday, 07.28.12 @ 23:55pm

Very good.

Posted by narayanaswami.P.S. on Tuesday, 08.16.11 @ 03:58am

There has been a lot discovered about the Crab Nebula. I would very much like it if someone would write a very good book on the Crab telling of what occurs in it and write it for the educated layman. It could be a history of this nebula up to our present day.

Marvin L. S.

Posted by Marvin L. S. on Tuesday, 06.7.11 @ 16:53pm

Outstanding, will follow, the such later.

Posted by Rick Moll on Wednesday, 05.18.11 @ 05:02am

It's difficult to imagine what is a body of "nothing but neutrons" spinning 1800rpm, held together only by gravity. Now, if only I knew what gravity and neutrons really are.

Posted by OJay on Saturday, 05.14.11 @ 07:12am

Amazing, wonderful, no words to express feelings.
Gurudev Observatory, Vadodara

Posted by DDPurohit on Friday, 05.13.11 @ 12:49pm

To watch time-lapse movies of a celestial object such as the Crab Nebula is mind blowing when you think of the scale you are looking at.
Astronomy, the Universe never get boring or mundane. They grab you by the shoulders and demand that you witness their splendor.
A thought comes to mind of a famous saying by a certain Vulcan science officer when viewing the wonders of the Universe "Fascinating".

Posted by JD on Wednesday, 05.11.11 @ 17:26pm