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John Tonry headshot

John Tonry

University of Hawaiʻi at Mānoa Astronomer John Tonry, a camera designed and built at the Institute for Astronomy and an observatory on Mauna Kea all played a role in the work awarded the 2011 Nobel Prize in Physics this month.

Tonry was a member of one of the two large groups of astronomers whose leaders received the prize for discovering that the Universe is expanding at an ever-increasing rate and will therefore last forever.

The discovery, first announced in 1998, grew out of scientists’ efforts to compare how fast the Universe is expanding now compared with its expansion billions of years ago. They expected to find that the expansion was slowing down, suggesting the possibility that the Universe would eventually stop expanding and then collapse in a “big crunch.”

To study the problem, astronomers searched for exploding stars called type 1a supernovae in very distant galaxies, which could be used to measure how far away other galaxies are.

In 1996, when the project began, the most sensitive system for doing this kind of research was a giant digital camera designed and built at IfA and mounted on the Canada-France-Hawaiʻi Telescope. The telescope had superb optics and was located on Mauna Kea, where the skies are uniquely clear and dark, an improvement over conditions in Chile, where the work had begun.

Canada-France-Hawaii Telescope against pink-tinged sky

Canada-France-Hawaiʻi Telescope on Mauna Kea; photo by Roy Gal

Tonry spent his nights observing on the telescope and his days analyzing the data. There was no time to waste because supernovae explode brightly and fade fast. He needed to relay the locations of such explosions quickly so other members of his team could observe them using a spectrometer mounted on one of the two 10-meter-diameter telescopes of the neighboring W. M. Keck Observatory. Their job was to measure the speed at which the galaxies were moving away from us as well as to confirm the nature of the exploding stars.

Because these faint, distant galaxies are so far away, their light must travel for billions of years to reach Earth, thus providing a glimpse of our Universe at a time when it was much younger than it is now.

What they discovered was considered surprising, even shocking: the distant galaxies were moving apart from each other more slowly than were the nearby galaxies. In other words, the Universe must be expanding faster now than it did in the past.

Team members were amazed. Their reaction was: “It couldn’t be. We had better recheck our calculations.” But it was, and it has since been confirmed by other observations.

What could cause the expansion to speed up? It couldn’t be gravity because gravity always pulls things together. It had to be a new kind of pressure, since named “dark energy.”

Interestingly, when Albert Einstein formulated his theory of general relativity in 1915, one of his equations hinted at the existence of such a pressure, but it took nearly 100 years for its significance to be realized.

What is dark energy? No one knows. But UH scientists are involved in the search for the answer—both through particle physics experiments at giant collider laboratories abroad, and ongoing observations at large telescopes like as those on Mauna Kea.

—by Louise Good, Institute for Astronomy publications editor
A similar version of this article was published in the Honolulu Star-Advertiser Oct. 16, 2011, and on the IfA website.

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