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A Cosmic-Ray Hunter Takes to the Sky

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NASA successfully launched its football-stadium-sized, heavy-lift super pressure balloon (SPB) from Wanaka, New Zealand, at 10:50 a.m. Tuesday, April 25 (6:50 p.m. April 24 in U.S. Eastern Time), on a mission designed to run 100 or more days floating at 110,000 feet (33.5 km) about the globe in the southern hemisphere’s mid-latitude band.

While validating the super pressure balloon technology is the main flight objective, the International Extreme Universe Space Observatory on a Super Pressure Balloon (EUSO-SPB) payload is flying as a mission of opportunity.

Natalie Wolchover reports in Quanta:

On April 25, at 10:50 a.m. local time, a white helium balloon ascended from Wanaka, New Zealand, and lifted Angela Olinto’s hopes into the stratosphere. The football stadium-size NASA balloon, now floating 20 miles above the Earth, carries a one-ton detector that Olinto helped design and see off the ground. Every moonless night for the next few months, it will peer out at the dark curve of the Earth, hunting for the fluorescent streaks of mystery particles called “ultrahigh-energy cosmic rays” crashing into the sky. The Extreme Universe Space Observatory Super Pressure Balloon (EUSO-SPB) experiment will be the first ever to record the ultraviolet light from these rare events by looking down at the atmosphere instead of up. The wider field of view will allow it to detect the streaks at a faster rate than previous, ground-based experiments, which Olinto hopes will be the key to finally figuring out the particles’ origin.

Olinto, the leader of the seven-country EUSO-SPB experiment, is a professor of astrophysics at the University of Chicago. She grew up in Brazil and recalls that during her “beach days in Rio” she often wondered about nature. Over the 40 years since she was 16, Olinto said, she has remained captivated by the combined power of mathematics and experiments to explain the universe. “Many people think of physics as hard; I find it so elegant, and so simple compared to literature, which is really amazing, but it’s so varied that it’s infinite,” she said. “We have four forces of nature, and everything can be done mathematically. Nobody’s opinions matter, which I like very much!”

Olinto has spent the last 22 years theorizing about ultrahigh-energy cosmic rays. Composed of single protons or heavier atomic nuclei, they pack within quantum proportions as much energy as baseballs or bowling balls, and hurtle through space many millions of times more energetically than particles at the Large Hadron Collider, the world’s most powerful accelerator. “They’re so energetic that theorists like me have a hard time coming up with something in nature that could reach those energies,” Olinto said. “If we didn’t observe these cosmic rays, we wouldn’t believe they actually would be produced.”

Olinto and her collaborators have proposedthat ultrahigh-energy cosmic rays could be emitted by newly born, rapidly rotating neutron stars, called “pulsars.” She calls these “the little guys,” since their main competitors are “the big guys”: the supermassive black holes that churn at the centers of active galaxies. But no one knows which theory is right, or if it’s something else entirely. Ultrahigh-energy cosmic rays pepper Earth so sparsely and haphazardly — their paths skewed by the galaxy’s magnetic field — that they leave few clues about their origin. In recent years, a hazy “hot spot” of the particles coming from a region in the Northern sky seems to be showing up in data collected by the Telescope Array in Utah. But this potential clue has only compounded the puzzle: Somehow, the alleged hot spot doesn’t spill over at all into the field of view of the much larger and more powerful Pierre Auger Observatory in Argentina.

To find out the origin of ultrahigh-energy cosmic rays, Olinto and her colleagues need enough data to produce a map of where in the sky the particles come from — a map that can be compared with the locations of known cosmological objects. “In the cosmic ray world, the big dream is to point,” she said during an interview at a January meeting of the American Physical Society in Washington, D.C.

She sees the current balloon flight as a necessary next step. If successful, it will serve as a proof of principle for future space-based ultrahigh-energy cosmic-ray experiments, such as her proposed satellite detector, Poemma (Probe of Extreme Multi-Messenger Astrophysics). While in New Zealand in late March preparing for the balloon launch, Olinto received the good news from NASA that Poemma had been selected for further study.

Olinto wants answers, and she has an ambitious timeline for getting them. An edited and condensed version of our conversations in Washington and on a phone call to New Zealand follows.

QUANTA MAGAZINE: What was your path to astrophysics and ultrahigh-energy cosmic rays?

ANGELA OLINTO: I was really interested in the basic workings of nature: Why three families of quarks? What is the unified theory of everything? But I realized how many easier questions we have in astrophysics: that you could actually take a lifetime and go answer them. Graduate school at MIT showed me the way to astrophysics — how it can be an amazing route to many questions, including how the universe looks, how it functions, and even particle physics questions. I didn’t plan to study ultrahigh-energy cosmic rays; but every step it was, “OK, it looks promising.”

How long have you been trying to answer this particular question?

In 1995, we had a study group at Fermilab for ultrahigh-energy cosmic rays, because the AGASA (Akeno Giant Air Shower Array) experiment was seeing these amazing events that were so energetic that the particles broke a predicted energy limit known as the “GZK cutoff.” I was studying magnetic fields at the time, and so Jim Cronin, who just passed away last year in August — he was a brilliant man, charismatic, full of energy, lovely man — he asked that I explain what we know about cosmic magnetic fields. At that time the answer was not very much, but I gave him what we did know. And because he invited me I got to learn what he was up to. And I thought, wow, this is pretty interesting.

Later you helped plan and run Pierre Auger, an array of detectors spread across 3,000 square kilometers of Argentinian grassland. Did you actually go around and persuade farmers to let you put detectors on their land? . . .

Continue reading.

Written by LeisureGuy

29 April 2017 at 12:19 pm

Posted in Science

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