One of the most well-known celestial objects still has some tricks up its sleeve, according to a new discovery of surprising gamma-ray flares coming from the famous Crab Nebula.
The Crab, long-considered such a steady celestial light that it was used to calibrate other sources, has now had three flare-ups where it brightened significantly in the gamma-ray range for a few days, astronomers report. [Hubble photo of the Crab nebula]
"Our belief of a stable Crab got smashed completely — now we have to think again," said Marco Tavani, an astronomer at the INAF-IASF (Istituto Nazionale di Astrofisica-Istituto di Astrofisica Spaziale e Fisica Cosmica) in Rome. Tavani was lead author of one of two papers announcing the discovery of the flares in the Jan. 7 issue of the journal Science.
The Astronomical Research Center (A.R.C) mentioned that Tavani's team used the Italian Space Agency's AGILE satellite to observe flares in October 2007 and September 2010. Another team, led by Stefan Funk and Rolf Buehler at the SLAC National Accelerator Laboratory at Stanford University, observed the September 2010 flare as well, along with one in February 2009, using NASA's Fermi Gamma-ray Space Telescope.
"We had always thought we understand essentially what is going on in the Crab Nebula, but obviously these flares we didn't expect," Funk told SPACE.com.
The Crab Nebula is actually the burial ground of a long-dead star. Its photogenic layers of colorful gas are the sloughed-off remains of the star's body, ejected before it collapsed in on itself to create a dense hulk called a neutron star.
The particular neutron star at the heart of the Crab Nebula is called a pulsar, because it emits a continuous beam of radiation like a lighthouse that appears to pulse when it crosses Earth's line of sight.
Yet why this nebula is emitting these strange flares is not known. These flares, which each lasted a few days, are different from gamma-ray bursts, which are much shorter explosions of light sometimes created when a massive star dies.
"It's still a real mystery what is the ultimate cause," Tavani said.