Angela Olinto’s cosmic needle in a haystack

MemberCenter website of the American Association for the Advancement of Science 06/12/13

By Delia O’Hara

When Angela Olinto was 20 years old, and the top student at the Pontifícia Universidade Católica in Rio de Janeiro in her native Brazil, she came down with a serious inflammatory disease called polymyositis, which weakens the skeletal muscles, and can be fatal.

How did Olinto spend what she thought could be her last year on Earth? She launched a full-bore effort to get into the physics graduate program at the Massachusetts Institute of Technology.

Consider that a glimpse into the character of Olinto, who chairs the Department of Astronomy and Astrophysics at the University of Chicago, and was named an AAAS Fellow in 2012.

Olinto has had one recurrence of polymyositis since college, and still lives with its threat. “I got a bit lucky,” she says. “I am very impressed when I think about it, though. What was I thinking? If you think you only have a year left to live, are you going to spend it writing essays, doing exams and applying to graduate school, or are you going to go sit on a beach somewhere?”

That ability to focus on the task at hand, no matter what else is going on, serves Olinto well in her specialty, the study of ultra-high-energy cosmic rays, which is a little like looking for a needle in a haystack — if the haystack were as big as all outdoors. These tiny space invaders, nuclei packing energy greater than 1018electron volts (eV), come from outside our galaxy, from hundreds of millions or billions of light years away.

Their exact origin is one of the intriguing mysteries about ultra-high-energy cosmic rays. Supernova explosions of dying stars in our own galaxy are thought to produce less energetic cosmic rays, but “we know supernovae are not the accelerator” for ultra-high-energy particles, Olinto says. She is part of a University of Chicago team that has shown that “baby” pulsars could be the source of ultra-high-energy cosmic rays, but only during the first year of their lives.

Even though cosmic rays break up in the Earth’s atmosphere, the “daughter” (or secondary) particles are still powerful enough to pass through our bodies. Their power to change genetic material may have played a role in evolution.

Why should we care about something we can’t see or feel? For one thing, if we ever want to travel beyond our planet, we will have to know how to protect ourselves against cosmic rays. In outer space, over time, their radiation can cause serious damage to human beings, Olinto says.

The real potential of cosmic rays for science, though, lies in having a chance to study super-energetic ones like the so-called “oh my God particle,” the most powerful cosmic ray ever observed, in Utah in 1991, which registered energy of 3.2 x 1020 eV, tens of millions of times more powerful than anything scientists can now create in a man-made accelerator.

“Nobody expected particles that energetic to exist,” Olinto says. Discovering particles with even higher energies could yield exponential advances in scientists’ understanding of how the universe works, she says.

“The greater the energy, the more interesting the physics becomes. We don’t know if nature can actually reach [even higher] energies [with] an accelerator. We do know ‘the Big Bang’ had that energy. These are questions we can only answer if we have huge volumes [of cosmic rays] to look at.”

Cosmic rays at energy levels of 1019 eV hit the Earth at a rate of only about one-per-square-kilometer per year. For particles with energy above 1020 eV, it’s more like one-per-square-kilometer per century. “The higher the energy, the rarer they are,” Olinto says.

So the greater the area an observatory covers, the better the chance of “capturing” a really interesting particle. In the past, large collectors have been deployed over vast territories to catch “secondary” particles that rain down on Earth, each bearing a portion of the original energy from “primary” cosmic rays that have broken up in our atmosphere.

Olinto has played a key role in the evolution of cosmic ray detectors. She is part of the international collaboration of nearly 500 scientists from 18 countries at the Pierre Auger Observatory in western Argentina.

The Auger Observatory is a hybrid system of 1,600 huge water tanks spread out over an area the size of Rhode Island, and optical fluorescence detectors, which together document the activity of high-energy particles and the “air showers” that fall out from them.

Olinto led the design of Auger North, a similar but much larger collector that was planned in Colorado, but that project fell to funding cuts during the recent recession — a tremendous disappointment, she says now.

Olinto didn’t sit around moping about the loss of Auger North, though, notes Michael Turner, a professor at the University of Chicago and director of the Kavli Institute for Cosmological Physics there. Instead, “she put together plans for the largest cosmic-ray detector ever,” Turner says.

Olinto is part of a group working to put an “extreme universe space observatory” on the Japanese Experiment Module, which is already on the International Space Station.

The new telescope, JEM-EUSO, will point not toward space, but toward the Earth, monitoring the atmosphere from above. “The atmosphere is really the detector,” Olinto says. Lasers fired from the ground will see what the telescope is seeing as the ISS passes overhead.

As the principal investigator for the U.S. team in the collaboration, and a theorist herself, Olinto must engage experimental scientists in defining goals, and “get this guy off the ground” by 2017. “The bigger the telescope, the more events you can see,” she says, but bigger is also more expensive — so goal-setting will be a key part of the effort.

For Olinto, the “wow” part of her job is the fact that actual matter is coming from another galaxy, but the possibility that these extremely energetic cosmic rays might also be carrying new understandings for scientists about how the universe works intrigues her too.

“Scientists are very curious,” she says. “We might be curious about something that looks completely irrelevant, and it turns out to be a really amazing thing. Or it could be irrelevant. We don’t know. If we knew, we wouldn’t be looking at it.”

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