Mexico Observatory To Hunt For Gamma Rays In Known Universe
August 22, 2013

Mexico Observatory To Hunt For Gamma Rays In Known Universe

April Flowers for - Your Universe Online

A new observatory has begun formal operations in Mexico. The High-Altitude Water Cherenkov (HAWC) Gamma Ray Observatory is designed to study the origins of very high-energy cosmic rays and observe the most energetic objects in the known universe.

The HAWC uses a unique detection technique that is different from the classical astronomical design of mirrors, lenses, and antennae, making the extraordinary observatory a significant boost to international scientific and technical knowledge.

“The HAWC observatory will search for signals from dark matter and to study some of the most extreme objects in the universe, such as supermassive black holes and exploding stars,” said Brenda Dingus, principal investigator and a research fellow at Los Alamos National Laboratory. Dingus is also a Fellow of the American Physical Society, and was a recipient of the Presidential Early Career Award for Scientists and Engineers in 2000.

The new observatory is located at an altitude of 13,451 feet on the slope of the volcanoes Sierra Negra and Pico de Orizaba at the border between the states of Puebla and Veracruz. An array of Cherenkov detectors will be used by the observatory, which is still under construction, to observe high-energy cosmic rays and gamma rays. Currently, 100 of the 300 projected Cherenkov detectors are online and taking data. Almost 5,000 gallons of extra-pure water is stored inside an enormous tank -- 16 feet high and 23 feet deep -- in each detector. Four highly sensitive light sensors are fixed to the bottom of each tank.

“Los Alamos has a long history of working in this field and built the predecessor to the HAWC observatory, called Milagro, located at the Los Alamos site in New Mexico,” Dingus said.

“HAWC will be more than 15 times more sensitive than Milagro was, and it will detect many new sources of high-energy photons. Los Alamos also studies these high-energy phenomena through complex computer simulations to understand the physical mechanisms that accelerate particles to energies millions of times greater than man-made accelerators,” Dingus said.

The array of 100 Cherenkov detectors has been online since August 1, and is growing each week. It will be sensitive to high-energy particles and radiation between 100 GeV and 100 TeV, energy equivalent to a billion times the energy of visible light.

HAWC was identified in 2009 as the Mexican astronomical project with the highest expected impact on high-energy astrophysics. Three Cherenkov detectors were installed at the volcano Sierra Negra shortly afterwards and the array began successfully observing cosmic rays and gamma rays. Later that same year, a seven detector array was built to test the tank design, simulate real data-taking, and study the logistics of deploying a large-scale observatory in this remote location. The first 30 detectors of the eventual 300 were deployed in 2012 and have operated continuously since. This 30 detector stage allowed calibration of the observatory via the observation of the shadow of the moon as it blocked cosmic rays.

With the formal opening, the scientists of HAWC will begin observations of the most violent phenomena in the known universe, such as supernovae explosions and the evolution of supermassive black holes.

The most energetic and cataclysmic events in the known universe produce gamma rays - electromagnetic radiation of very high frequency – and cosmic rays - subatomic particles of very high energy. These events include the collisions of two neutron stars, the explosions of supernovae, and binary systems of stars with stellar accretion, and active galactic nuclei that host black holes millions of times more massive than the sun.

As they reach Earth, the high-energy cosmic rays and gamma rays interact with air molecules in the upper atmosphere. For example, gamma rays are converted into pairs of charged matter and anti-matter particles – mainly electrons and positrons. Other air molecules rapidly react with these, creating further charged particle pairs, which result in a continuing chain reaction. The reaction continues until a large cascade of particles and radiation reaches ground level, where it can be recorded in the HAWC detectors.

When a Cherenkov detector captures a charged particle cascade from an extra-terrestrial gamma ray, its particles are traveling faster than the speed of light in water. This results in an effect that is similar to the shock wave produced in the atmosphere by a supersonic airplane, known as a sonic boom. Instead of producing sound, the particles in the detector produce a visible cone of light, called the Cherenkov radiation.

The Cherenkov radiation is measured by the light sensor fixed to the bottom of each detector in HAWC. Scientists are able to determine the time of arrival, energy, and direction of the original extraterrestrial gamma ray or cosmic ray by combining the light signal observed in many tanks with fast electronics and high precision computing equipment.