It can also detect particles with energy 7 times higher than those produced at the Large Hadron Collider.
The High Altitude Water Cherenkov (HAWC) observatory, which has been operating from the top of a mountain in central Mexico for about a year, has released its first map of the sky (seen above), including measurements of how often black holes flicker on and off.
It has also captured pulsars, supernova remnants, as well as some of the highest-energy photons ever observed, including gamma rays. In fact, the observatory is sensitive to gamma rays between 0.1 and 100 teraelectronvolts (TeV) in energy, which is more than 7 times higher than the energy of particles produced in the Large Hadron Collider. The most energetic photon they’ve picked up so far is 60 TeV.
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“This is our deepest look at two-thirds of the sky, as well as the highest energy photons we’ve ever seen from any source,” Brenda Dingus of Los Alamos National Laboratory, who presented the map at the American Physical Society, told New Scientist. “We’re at the high energy frontier.”
HAWC is not your typical telescope. The detector is made up of 300 water tanks, each filled with 200,000 liters of purified water (seen below). When high-energy particles pass through the water, they emit a blue light called Cherenkov radiation, and physicists then use that light to reconstruct where the particles originated.
Vats of water at the HAWC observatory, Mexico. Photo Credit: HAWC
However, HAWC doesn’t observe these extremely high-energy photons directly. Luckily for us — since they can damage living tissue — they are blocked by our atmosphere. Rather, the detector catches the spray of secondary particles, known as air showers, produced by gamma rays when they strike the atmosphere
“20,000 air shower particles per second hit our detector,” Dingus said. “In fact they’re hitting us right now.”
In just one year, HAWC has detected nearly 40 distinct sources of gamma rays, 10 of which had never been seen before. Researchers are now working to figure out if these were associated with any other known objects that have been spotted in wavelengths, including visible or infrared light.
HAWC can also pick up gamma rays from outside the Milky Way, caused by supermassive black holes found at the center of other galaxies. However, the details of how the photons gain so much energy is still a mystery among astronomers.
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Since HAWC is watching the sky 24 hours a day, 7 days a week, the detector can also detect changes in gamma ray brightness, or black hole flickering. In fact, just 10 days ago, HAWC spotted a flare in a galaxy called Markarian 501.
“On April 5 we didn’t see it, on April 6 it got very bright, and by April 8 it had nearly disappeared again,” said Robert Lauer of the University of New Mexico, to New Scientist.
Previous telescopes capable of detecting such high-energy photons could only look at one part of the sky at once, meaning they could not measure the frequency of these flares. Over the next five years, however, HAWC will be able to make the first measurements of how often they happen. Astronomers currently hypothesize that they occur about 5 to 10 times per year, but it varies from galaxy to galaxy.
The researchers also expect that HAWC will be able to see one of these flares from the supermassive black hole at the center of our own Milky Way galaxy.
“We know these things happen, so we expect them to happen here,” Hui explained. “We just don’t know how often.”
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