New Earth-bound telescopes that will help us understand black holes are being built in Arizona with help from Irish research teams, writes Dick Ahlstrom
When it comes to signals from deep space they don't get much more powerful - or enigmatic - than the gamma rays that pepper our upper atmosphere. Now a €15-million collaboration involving scientists from the US, Ireland and Britain hopes to unlock the secrets to be found in gamma rays.
The project is known as VERITAS for Very Energetic Radiation Imaging Telescope Array System, says Dr John Quinn, a lecturer in experimental physics and head of the very high-energy astrophysics group at University College Dublin.
The collaboration involves building not one but four powerful optical reflector telescopes, each with a mirror measuring 12 metres across. The first prototype telescope is under construction and will be installed by this October, says Dr Quinn.
All four will sit in Horseshoe Canyon, 1,770 metres up along the side of Kitt's Peak in southern Arizona. They won't see any gamma rays which are invisible but will be able to watch the impact they have on Earth's thin atmosphere 10 kilometres up, information that will help scientists understand the rays and where they come from, says Dr Quinn.
"The difficulty in doing gamma ray astronomy is the gamma rays are absorbed by the atmosphere," he explains. They produce a short-lived cascade of light when they smack into the atmosphere however.
They cause an "optical disturbance" known as Cerenkov light, says Dr Quinn. The telescopes pick this up as a very faint but characteristic bluish glow that can be analysed to give information about the source of the rays.
"We don't detect them directly, we detect them through the optical disturbance," he says. "The array gives us much better positional information and information about the energy of the gamma rays."
The real trick is being able to see and record the Cerenkov light, however. "The telescope must be very large to detect this light," he says. It is akin to trying to spot a weak camera flash from 10 kilometres away.
They are also difficult to spot because the cascades happen so fast and come infrequently. A typical optical disturbance lasts only six billionths of a second and existing telescopes only pick up about four rays per minute coming from the Crab Nebula, a super nova remnant that emits gamma rays.
The energy level tells something about the source of the gamma rays, he says. "There are a whole range of scientific targets," including "galactic nuclei" - super massive black holes sitting at the centre of many galaxies-super nova remnants and pulsars.
"The mere detection of this alone is quite important," says Dr Quinn. "It teaches us about the physics of these objects. There is also a lot of indirect information we can learn from this."
The Republic is contributing money and expertise to this effort, with financial support coming originally from Enterprise Ireland and more recently via the basic research grant programme now administered by Science Foundation Ireland. US funding is from the Department of Energy, the National Science Foundation and the Smithsonian Astrophysical Observatory. The collaboration includes the University of Arizona, Harvard and the University of Leeds. Here it includes UCD, NUI Galway and Galway/Mayo and Cork Institutes of Technology.
"The UCD group has developed the data acquisition software for the telescopes," says Dr Quinn. Galway has developed the mirror alignment system and Galway/Mayo is working on a specialised camera system for monitoring weather information during Cerenkov light observations. CIT is also contributing to weather information, developing a specialised pyrometer to measure infrared radiation in cloud cover. "The effect of weather conditions is very important in this," says Dr Quinn.
Find out about the VERITAS project at http://veritas.sao.arizona.edu
