Gamma-ray telescopes are helping unravel the secrets of the universe. See the most important ones in this gallery
MAGIC
Ground-based gamma ray telescopes measure indirectly, as the rays cannot penetrate the Earth’s atmosphere.
An electromagnetic shockwave is created when gamma rays collide with a proton or neutron in the air.
The resultant bluish light, , is picked up by ground-based gamma ray telescopes.
Located on a mountain top on the Canary island of La Palma, the (MAGIC) is a system of imaging atmospheric Cherenkov telescopes, or .
MAGIC-I started routine operation in 2004.
A second telescope has been installed and will be operational later in 2009.
On 30 June 2005, MAGIC spotted a 20-minute outburst of gamma rays from the galaxy Markarian 501 that did not fit with the expected conventions: lower-energy photons outpaced their higher-energy counterparts.
Scientists believe that this phenomenon may be evidence for quantum gravity theories that suggest space is a frothy foam of particles.
(Image: Robert Wagner / MAGIC)
H.E.S.S.
The (H.E.S.S.) is a system of (IACTs) that investigates cosmic gamma rays in the 100 gigaelectronvolts to 100 teraelectronvolts energy range.
H.E.S.S. is located in the Khomas Highland of Namibia, an area renowned for excellent optical quality.
H.E.S.S. scientists recently collaborated with two other gamma-ray telescopes, and , to study the giant radio galaxy .
Observations at the extremes of the electromagnetic spectrum suggested that M87’s nucleus is accelerating elementary particles to very high energies in the vicinity of its central black hole.
(Image: H.E.S.S.)
VERITAS
The (VERITAS) is based at the Fred Lawrence Whipple Observatory, near Amado, Arizona, US.
It is an array of four 12-metre optical reflectors.
Its detectors can spot gamma rays with energies between 100 gigaelectronvolts and 10 teraelectronvolts.
(Image: VERITAS)
Cherenkov Telescope Array
Currently in the advanced design stage, the (CTA) will be the next generation of ground-based gamma ray telescopes.
The idea is that CTA will be spread over two sites: one, in the southern hemisphere, will study a broader range of energies, between 10 GeV and 100 TeV, and will allow the study of the galactic centre. The other, in the northern hemisphere, will focus on lower energies, between 10 GeV and about 1 TeV.
This array would probe energies both lower and higher than currently possible, and would be five to 10 times more sensitive than existing detectors in the energy range between 100 GeV and 10 TeV.
(Image: ASPERA)
Fermi
Launched in 2008, the (previously known as GLAST) is a joint project between NASA and the Department of Energy, as well as government agencies from France, Germany, Italy, Japan, and Sweden.
Because it is in space rather than on the Earth’s surface, Fermi can measure gamma rays directly.
As a result, it operates within a much broader range, from 10 kiloelectronvolts to more than 300 gigaelectronvolts – the broadest energy coverage ever provided by a single spacecraft for gamma-ray studies.
(Image: NASA)
Swift
NASA launched its Swift satellite in November 2004 with the main aim of studying fleeting gamma-ray bursts, volleys of gamma rays that last for just seconds. The bursts are thought to be triggered by the collapse of massive stars or by mergers between massive objects, such as neutron stars.
Swift scans one-sixth of the sky at a time and if it detects a gamma-ray burst, can swivel around in just a minute to observe its afterglow at other wavelengths. The measurements are relayed to observatories automatically over the internet, so they can do quick follow-up observations.
Before Swift, it took about six hours to alert astronomers of GRB detections.
In April 2009, Swift spotted a GRB that detonated more than 13 billion light years away – the most distant object ever confirmed in the universe.
(Illustration: Spectrum/NASA E/PO/Sonoma State University/Aurore Simonnet)
Compton Gamma Ray Observatory
Operational between 1991 and 2000, the (CGRO) was the second of NASA’s .
It was named after , who won the Nobel Prize in physics in 1927 for his discovery that the wavelengths of X-rays change when they collide with, and transfer energy to, electrons.
The telescope covered an energy range of 30 kiloelectronvolts to 30 gigaelectronvolts.
It did so using four main instruments: the (BATSE), the (OSSE), the (COMPTEL), and the (EGRET).
(Image: (JSC / NASA)
Gamma-1
was a Soviet spacecraft.
It launched on 11 July 1990, and was designed to investigate cosmic gamma rays in the energy range from 50 to 5000 megaelectronvolts.
During its 2-year mission, Gamma-1 focused its study on the , the Cygnus binaries, the Heming gamma source in Taurus, and Hercules X-1.
It also gathered information about the high-energy emissions of the Sun during peak solar activity.
(Image: NASA)
