Probe studies 'extreme physics'


Jan 11, 2007

Glast will examine supernova remnants

A pioneering US space agency spacecraft is set to launch on a mission to explore the most energetic phenomena in the Universe.

The Gamma-ray Large Area Space Telescope (Glast) has been described as an "extreme physics" laboratory.

The probe is due to launch from Florida's Cape Canaveral base in November on a Boeing Delta II rocket.

The team presented details of the mission at the meeting of the American Astronomical Society in Seattle.

As its name suggests, Glast will detect the emissions of gamma rays in space. Gamma rays are the most energetic form of radiation known to science.

Examples of energetic phenomena to be probed by Glast include active galaxies, which spew massive amounts of energy from their centres.

This explosive outpouring is thought to be powered by supermassive black holes.

Other targets for Glast include pulsars - rotating neutron stars which emit radio waves - as well as the remnants of exploded stars, and galaxy clusters.

Uncharted territory

"The objects that we tend to study are extreme examples of their type," Julie McEnery, Glast's deputy project scientist, told BBC News.

"We're looking at active galaxies where the jets [of their black holes] are pointing directly at us and you are seeing the relativistic particles.

"We're looking at pulsars, we're exploring the Universe in regions of very high magnetic fields."

Glast will examine supernova remnants

Dr McEnery, from Nasa's Goddard Space Flight Center (GSFC) in Maryland, said that Glast was likely to make many important discoveries because it would study a region of the electromagnetic spectrum that had hardly been explored.

To be precise, this energy-range runs from 10 kiloelectron volts (keV) to 300 gigaelectron volts GeV.

"We've got lots of theoretical ideas on what we expect to find and some observational hints there are exciting things there," she explained.

"But we really don't know what the sky is going to look like."

With Glast, mission scientists hope to address several unanswered questions about the high energy Universe.

One question central to the mission is where in the Universe cosmic rays are accelerated to tremendous energies.

Energetic particles

Cosmic rays are composed of atomic nuclei that can move at close to the speed of light.

They can be about one billion times more energetic than the high energy particles created on Earth in the most powerful particle accelerators.

"Almost all of the astrophysical scenarios where you expect to accelerate cosmic rays, you also expect to produce gamma rays," said Dr McEnery.

"The efficiency of an object to accelerate particles is a function of its size and the strength of its magnetic field.

"You can have a supernova remnant, with a relatively strong magnetic field but relatively small size. Or you can look at a galaxy cluster, which has a relatively small magnetic field but is gigantic.

"A particle running around in a galaxy cluster can spend a long time getting up to a high energy."

Most of the sources Glast will look at are thought to play important roles in the acceleration of cosmic rays, the deputy project scientist said.

The spacecraft will carry two instruments: the Large Area Telescope (Lat) and the Glast Burst Monitor (GBM).

Lat has a large field of view which can see about 20% of the sky at any one time. In its primary observing mode, the telescope can cover the entire sky every three hours.

Glast is due to be launched in the middle of November this year.