June 19, 2019

Crab Nebula unleashes huge gamma ray flares

The Crab Nebula

The Crab Nebula has surprised astronomers by emitting an unprecedented blast of gamma rays, in early April.

Gamma rays are the highest energy light in the solar system, and the cause of the massive 12th April gamma-ray flare, is a mystery.

The event has been detailed at the Third Fermi Symposium in Rome, and is a total mystery. The Fermi space telescope was launched in 2008, and is managed by NASA.

The gamma rays seem to have come from a small area of the Crab Nebula, which is the wreckage from an exploded star.

The object has long been considered a steady source of light, but the Fermi telescope hints at greater activity.

The gamma-ray emission lasted for six days, hitting levels 30 times higher than normal and varying at times from hour to hour.

The Crab Nebula is composed mainly of the remnant of a supernova, which was seen on Earth to rip itself apart in the year 1054.

The Fermi telescope is set up to measure only the highest sources of energy – gamma rays. At this stage, astronomers have identified all the objects they can see within the Crab Nebula, but none of them are capable of generating the level of gamma rays that Fermi is detecting.

So the conclusion is that there is something yet unseen within the nebula that is the source of the gamma rays.

To make it extra fascinating, the area of the nebula where the rays are coming from is extremely compact compared to the nebula as a whole.

Since its launch nearly three years ago, Fermi has spotted three such outbursts, with the first two reported earlier this year at the American Astronomical Society meeting.

These events are unleashing gamma rays with energies of more than 100 million electron-volts – that is, each packet of light, or photon, carries tens of millions of times more energy than the light we can see.

But the Crab’s recent outburst is more than five times more intense than any yet observed.

Professor Rolf Buehler from the Kavli Institute says that understanding the flare may take some time. “To have something that puts almost all of its energy into gamma rays is an unusual thing,” he said.

“We’re looking at a big puzzle and are probably going to need a couple of years to understand it.”

The best guess so far is that in a region near the neutron star, intense magnetic fields become opposed in direction, suddenly re-organising themselves and accelerating close-by particles to near the speed of light.

As they move in curved paths, the particles emit the gamma rays seen by Fermi.