The world’s first observatory to detect cosmic rays by radar has begun experimental transmissions in Delta.
WF2XHR, the callsign provided by the Federal Communications Commission, is broadcasting at only 2 kilowatts now, but scientists plan to step up the transmitter to 20 kW when more funding is available.
About a dozen researchers from the University of Utah Department of Physics & Astronomy, the U. Department of Electrical Engineering, Brookhaven National Laboratory and the universities of Kansas and Nebraska are involved in the project, led by the U.’s Prof. John Belz.
He and graduate student Isaac Myers described the advances last week during a meeting of the Salt Lake Astronomical Society, in a follow-up to a public lecture Belz gave last November.
Since then, one of the two transmitters donated to the project by Salt Lake TV station KUTV, Ch. 2, has been working at cosmic ray headquarters in Delta.
“Within the past several weeks we’ve started to set up a receiver,” he said. It is at Long Ridge, about 30 miles away from the transmitter. If it works, “we’re going to have to start to put remote detection sites out in the field.”
[University of Utah Prof. John Belz at his appearance before the Salt Lake Astronomical Society during the group’s recent monthly meeting, U. of U. Engineering and Mining Building. Photo by Cory Bauman]
The radar system is “still under construction and hopefully we’ll have results soon.” Altogether, four receivers are planned.
Delta is also the base for two other systems that record cosmic rays, one using 507 ground detectors and the other a set of telescopic units that can pick up extremely faint air flashes called scintillation when the mysterious energetic particles crash into the atmosphere.
Both of these techniques have been used before, but WF2XHR’s carrier signal is pioneering a new method that may turn out to be less expensive than a ground array and able to operate during the daytime and moonlit nights, unlike scintillation detectors.
[U. graduate student Isaac Myers helped Belz explain the workings of the radar-based detectors. Photo by Cory Bauman]
Cosmic rays aren’t rays in the sense of a sc-fi beam of energy; they’re subatomic particles such as protons. Depending on how fast it was accelerated, one can wallop our atmosphere at a force of around 10 to the 20th electron-Volts.
With his cooperation, Belz dropped a full soft-drink can into the palm of SLAS board member Steve Fisher from a distance of about four inches. The impact on Fisher was around 10 to the 18th eV, Belz said. “Remember, that’s concentrated in a single cosmic ray particle.”
The amount of energy one of these subatomic particles can pack is limited, but it’s big. “If I drop a bowling ball in his hand, that’s about 10 to the 20th eV of energy, about where we expect the (cosmic ray) energy spectrum to peter out,” he added.
Radar detection works like a police officer’s radar gun: a beam of radio energy from the unit reflects from a vehicle, and the Doppler shift that is recorded when the beam returns to a detector tells how fast the vehicle is moving. The new observatory will broadcast a radio carrier wave from which evidence of cosmic rays will be reflected.
Bob Moore, the club’s vice president, asked what new information can be learned through radar detection. Belz answered that the observatory might help gather enough data to find sources of high-energy rays.
“Theory still has a hard time” explaining the sources, he said. If they don’t come from supernovas as stars are blown apart, “then what is it?” Other possible origins are active nuclei in galaxies or black hole hurling material from their accretion disks. But so far these things have not been shown to be the sources.
“Of course, there are as many theories as there are theorists,” Belz said. “People talk about colliding cosmic strings and tears in space-time, any Star-Trekky thing.”
Receiver stations spaced miles apart might be able to triangulate on the same entering particle, to pinpoint its direction. Perhaps that would point to the cosmic ray’s source.
Micrometeor strikes are easy to hear by the radar method, when the sand-grain-size bits of rock and ice from space create ionization trails in the atmosphere. Listening to the reflected radio waves, they sound like pings, high- or low-pitched depending on their direction.
But signals reflected from cosmic rays will be “very compressed in time,” said Belz. They would last only 10 or 15 microseconds. A microsecond is one-millionth of a second.
Additional information beyond direction of travel may be hidden in the signal, if it can be ferreted out from something lasting only 15-millionth of a second. If a high-speed recording can capture the blip of a cosmic ray reflection, playing it back at a much slower rate may tell something about its structure.
However, “you can’t record a really high sample rate all the time,” said Myers. That would fill up computer hard drives rapidly.
Belz said one of the biggest problems the scientists are working on is how to record the occasional cosmic ray click at high speed.
Eventually the 20 kW transmitter will begin broadcasting, but its power consumption makes it more expensive to use than the 2 kW device. Belz added, “We need to get some additional funding for that.”
The observatory could begin detecting cosmic rays sometime this summer.
For information about the Salt Lake Astronomical Society, including the location and time of the club’s monthly meetings, CLICK HERE. Visitors are welcome at the scintillating meetings and public star parties.