By Lauren Gold
When the Arecibo L-Band Feed Array (ALFA) was installed on a misty April morning two years ago, it promised to bring phenomenal new sensitivity to the Arecibo Observatory.
Now, well into an ambitious series of comprehensive sky surveys using the receiver, astronomers say ALFA is delivering spectacularly: both by fulfilling the potential of the observatory’s 1990s Gregorian upgrade and ultimately by changing business as usual for researchers worldwide.
The ALFA system of detectors and associated electronics, jointly built by National Astronomy and Ionosphere Center (NAIC) and Australian engineers, is slightly bigger than a washing machine and has seven feeds — making it essentially a giant seven-pixel radio camera that allows researchers to image large swaths of sky and search for such time-variable phenomena as pulsars seven times more efficiently than in the past.
In just two years, ALFA has provided a wealth of new data, from comets passing near the Earth and giant clouds of gas in our own galaxy, to some of the most distant objects ever detected. It’s a quiet revolution — but Jim Cordes, Cornell professor of astronomy and one of the principal scientists behind ALFA’s conception, says the improvements are unparalleled.
“You could very well say it’s a new phase for Arecibo,” Cordes said. “We’re doing things that are pretty unique to what Arecibo can do — playing on its strengths.”
Cordes uses ALFA to find and observe pulsars, massive rapidly spinning neutron stars that are ejected in stellar explosions, or supernovae. The pulsar search could lead to a deeper understanding of Einstein’s theory of relativity.
“ALFA is going to discover probably 1,000 new pulsars that we haven’t seen yet,” said former ALFA project manager Stephen Torchinsky. “The expectation is that we’re going to find some exotic objects. We could use these systems to test the limits of the theory of relativity — and at the most extreme cases, to find gravitational waves.”
ALFA science is divided into three overarching surveys: the pulsar survey, a survey for sources of neutral hydrogen in the Milky Way and an extragalactic survey. In terms of sheer quantity of data, it is providing an abundance, spurring scientists to come up with new ways of sorting through and managing the constant torrent of information.
“It’s like you have seven fire hoses of data coming at you,” Cordes said. “It’s really a challenge to deal with.”
That challenge is being met in part by scientists at the Cornell Theory Center, who are creating a computer system to manage vast amounts of data from such surveys as the Arecibo Legacy Fast ALFA survey (ALFALFA), a broad extragalactic search for faint cosmic radio signals from hydrogen clouds.
ALFALFA is expected to detect some 20,000 galaxies from as far away as 750 million light years over the next six years. Astronomers hope the survey will lead to the discovery of dark galaxies: never-before-observed galaxies composed largely of dark matter and hydrogen gas that could offer valuable information about the way galaxies form and evolve.
“Without ALFA, a project like this could not have been done,” said Riccardo Giovanelli, Cornell professor of astronomy and ALFALFA project leader. “It would have been too demanding on a few people.”
But part of ALFA’s value, say its users, is in the collaborative style of research it invites. In the receiver’s two years of operation, the number of annual users at Arecibo has jumped by nearly 50 percent — to 335 users in 2005 from 215 users in 2003. (Other factors have been involved, but ALFA is credited with the majority of the increase.) “We’re bringing new users to Arecibo,” said Martha Haynes, Goldwin Smith Professor of Astronomy at Cornell and a member of the ALFALFA team. Many are undergraduates — evidence that the receiver is energizing the next generation of astronomers.
Torchinsky, however, worries that ALFA’s success could overpower other research. “It’s changed the culture a lot,” he said, “but I don’t think it’s entirely for the best. ALFA has begun to dominate astronomy work being done at Arecibo … making it more difficult for individual proposals in general. Some good ideas have not been developed because of this.”
But others say the increase in users — especially young ones — makes it clear that the change is a good one. And they add that the receiver’s science will benefit researchers well beyond those currently involved.
“The goal of the major surveys is to produce archival databases that are accessible to all researchers and will be valuable resources for many decades to come,” said Robert Brown, director of the Cornell-based NAIC, which manages the Arecibo Observatory for the National Science Foundation.
It’s part of a welcome trend, said Haynes.
“ALFA and the big surveys have changed the way science is being done at Arecibo,” she said. “It’s exciting. It’s challenging. This is the modern way of doing astronomy.”
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