Researchers at Michigan Tech are playing a major role in what many have dubbed the largest truly international scientific collaboration in history. More than 250 scientists from 50 institutions representing 19 countries have joined forces in an attempt to solve the mystery and find the source of high-energy cosmic rays that have bombarded the earth since the beginning of time.
The joint effort has been named the Pierre Auger Project after the French scientist who discovered extensive showers of secondary subatomic particles caused by the collision of primary high-energy particles with air molecules in 1938.
The project plans to build two huge observatories at a cost of $50 million each, one in the southern hemisphere at a site near Mendoza, Argentina, and the other in the northern hemisphere in Millard County, Utah. Each observatory will extend over an area 10 times larger than the city of Paris, France, and will combine air fluorescence detectors and an array of detectors located on the ground to measure extensive air showers produced when high-energy cosmic rays strike the earth's atmosphere. The ground array will operate continuously, while the fluorescence detectors will provide additional information on dark moonless nights.
Dr. David Nitz of Michigan Tech's Physics Department directs MTU's portion of the project and has also been designated the spokesperson for the northern hemisphere observatory on which construction is expected to begin in 2003. But what are cosmic rays anyway, and why are scientists so interested in them?
"Cosmic rays are fast-moving particles from space that constantly bombard the earth from all directions," he explains. "Most of the particles, at least those at energies low enough to make identification practical, are either the nuclei of atoms, or electrons. Single protons -- the nuclei of hydrogen atoms -- are the most abundant of the nuclei, but a few are much heavier, ranging in size up to the nuclei of lead atoms."
Nitz says cosmic ray particles travel at nearly the speed of light, which means they have very high energy. In fact, some of them are the most energetic of any particles ever observed in nature. The highest-energy cosmic rays have a hundred million times more energy than the particles produced in the world's most powerful man-made particle accelerator. But the source of such super rays remains a mystery, and scientists love a mystery, because solving a mystery in nature provides the opportunity to learn something new about the universe. Investigating the mystery of high-energy cosmic rays is just such an opportunity.
"Most lower-energy cosmic ray particles that strike the earth come from within our own Milky Way Galaxy," says Nitz. "Many probably come from the exploding stars we call supernovae. But no one knows the source of the highest-energy cosmic ray particles."
Over time, some cosmic ray particles pick up energy from moving magnetic fields they encounter as they wander through space. This process of acceleration is well understood for low-energy cosmic rays accelerated by magnetic fields produced by the sun. In our own galaxy, scientists believe that the strong moving magnetic fields produced by supernovae explosions provide the energy for acceleration. Scientists believe that the highest-energy cosmic ray particles come from sources beyond the Milky Way--but where?
"Wherever they come from, these highest-energy particles could hold secrets to the beginning of the universe," says Nitz. "We know of no source in the cosmos that could produce such energies, not even the power released by the most violent exploding stars. More powerful natural accelerators, therefore, must be responsible for these extraordinary rays, and these accelerators must lie outside our galaxy."
To discover the source of cosmic ray particles, scientists measure their energy and their direction as they arrive from space. To measure cosmic rays directly requires sending detectors to heights above most of the earth's atmosphere -- using high-flying balloons and satellites. These techniques become impractical for the highest-energy cosmic rays, which are extremely rare. However, cosmic rays can also be detected indirectly on the surface of the earth by observing the showers of particles they produce in the air -- which is just what the Pierre Auger observatories are designed to do.
Nitz and his colleagues have received a 3-year $620,000 operating grant from the Department of Energy to fund their participation in the project and will receive an additional $600,000 from the DoE to provide instrumentation for the southern hemisphere observatory, on which construction has already begun. The Michigan Tech team, which includes both graduate and undergraduate students as well as professionals, will develop and supply custom application specific integrated electronic circuits for the surface detector stations which will identify and record in real time the passage of extremely high-energy cosmic rays. They will also oversee the design and implementation of the microwave radio system that provides the link for all information transfer to and from the four fluorescence "eyes" and the 1,600 surface detector stations at each observatory.
"We'll be designing the front-end electronics units for both observatories," says Nitz, "and this includes integrated circuits which take information from detectors and select portions of incoming data that relate to cosmic ray showers." He says the unit will help recognize "significant" cosmic showers and will provide an "enriched sample" that will allow scientists to cast off unwanted information.
"What it does is refine the search process so that we have a 'needle in a bucket' type situation instead of a 'needle in a haystack' situation," he explains.
Nitz and his colleagues are developing about 3,000 integrated chips for each observatory -- 1,600 of which will be in use, while the rest will serve as spares. "When you build a customized unit like this, you have to build enough spare parts because you can't just run down to the store and buy more if you run out," he says.
This year the Michigan Tech team will be working on various iterations of prototypes, with a main production run scheduled for 2002 after field testing at the observatory sites.
One difficulty the team faces is that the units will be running outdoors where they're subject to all the vicissitudes of the weather, including temperatures ranging from 120 degrees Fahrenheit to far below zero. "They have to operate under any and all conditions, and they have to do it while consuming very little power because there aren't many electrical lines running into the sites," says Nitz. "In fact, our power at these remote locations is generated by solar panels, so it's very important that we have sunny sites with few clouds, both from the standpoint of solar energy generation and for the physics we want to be doing."
How will the Pierre Auger Project benefit humankind? Nitz doesn't know for sure, but he's certain there will be benefits.
"A lot of basic science conducted in the 19th century led to impressive developments in the 20th century, and that could happen here," he says. "An immediate benefit is that it allows our students to participate in a large scale project involving scientists from many nations and that experience is bound to be valuable to them during their professional careers. This isn't just a classroom project."