Leonard E Parker

Center for Gravitation, Cosmology & Astrophysics

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Leonard E Parker Center for Gravitation, Cosmology and Astrophysics

Physics undergrads use radio waves to search for elusive gravitational waves

Posted by on 1 May 2009

After class, while many undergraduates are kicking back and reaching for the TV remote control, three students at the University of Wisconsin–Milwaukee (UWM) are taking remote control of the world’s largest radio telescope – from their computers in the Physics Building.

Ryan Falk, Anne Wierzbinski and Mike Blemberg are on a hunt for radio-wave-emitting pulsars in space. Using data from the Arecibo Observatory in Puerto Rico, the three are part of a diverse group of students who are scanning the skies from UWM’s Remote Command Center for Arecibo (ARCC@UWM). Then they rate the thousands of radio-wave patterns the observatory’s data produces.

To find a pulsar, all they have to do is find the right radio-wave pattern – from among nearly a million.

“We are sorting up to 1,500 a week, so at 10 hours a week, we’re each rating about 150 images an hour,” says Wierzbinski. “It can be mind-numbing.”

A pulsar is a spinning neutron star that emits radio waves (energy) in a two-pronged form that resembles a lighthouse beam. If one of the beams is along the telescope’s line of sight, a pulse is recorded in every rotation. Just over 1,000 of them have been found since 1967, when the first one was identified.

Locating these massive dying stars is important to ARCC@UWM because where there are pulsars, there may be a chance at finding evidence of Albert Einstein’s most elusive prediction: gravitational waves.

Gravitational waves are produced when massive objects in space move violently. These invisible ripples in space and time carry so much information about space and the beginnings of the universe that an international effort is under way to detect them.

The research life

For Falk, Wierzbinski and Blemberg, ARCC@UWM is the chance to apply their knowledge to a real-life problem.

They are three of the 500 UWM students who are embedded in the university’s research life each year through the Office of Undergraduate Research (OUR). Although most undergraduate researchers work for credit, Falk, Wierzbinski and Blemberg are funded as “fellows” by OUR, which means they earn a stipend for their work. (See samples of other OUR projects in the slide show.)

There are about 15 undergrads from several majors involved in ARCC@UWM, but the group also includes faculty, postdoctoral students and even local high school students and teachers. UWM’s team works with a similar group at the University of Texas at Brownsville (UTB), where the ARCC project began.

The undergraduates and high school students at each location compare notes while operating the telescope, and each team analyzes the same wave patterns as a cross-check.

“It takes about four weeks to look at all the data that is collected by the telescope in only three or four hours,” says Falk. “It’s very math-intensive to give us data that we are going to look at for 30 seconds.”

The information from the telescope is processed by several supercomputer clusters which translate the data into a variety of radio-wave patterns.

Super sorting

The peaks in each pattern represent pulses, but that doesn’t mean that every signal is a pulsar. In fact, very few are.

Radio-wave signals are generated by other sources, too, and the telescope picks up all data that fall in the radio-wave band. It is up to the students to pick out the pulsars. To find a wave pattern that is a strong “candidate,” the students look at each one individually.

Over the last year, Falk has analyzed 17,000 images and only “a handful” turned out to be promising.

While Falk and Wierzbinski are immersed in analysis, Blemberg, an electrical engineering major, is working on a method that would streamline the wave-pattern rating process.

He and others are using a computer simulation of a “brainlike” system called a neural network. With a million samples of wave patterns to evaluate, the students hope the neural network can cut their viewing time.

View a sampling of other undergraduate research projects “First we teach the computer the wave signature of a pulsar,” says Blemberg, “and then we can have a computer go through all of the wave patterns and rank them before we ever look at them.”

The reward

The arduous task of pulsar-searching could pay off handsomely in the effort to detect gravitational waves, says Xavier Siemens, assistant professor of physics and leader of ARCC@UWM.The tremendous mass of the pulsar makes the pulses extremely regular.

If present, gravitational waves would cause the individual pulses to arrive sooner or later than we expect, he says.

“We look for gravitational waves in the differences between predicted and actual arrival times of radio pulses at our radio telescope,” says Siemens.

In addition to the undergraduates and Siemens, the research group of ARCC@UWM includes postdoctoral researchers Jessica Clayton and Larry Price, graduate student Melissa Anholm and Jean Creighton, director of the UWM Manfred Olson Planetarium.

Further Reading

Photo by Alan Magayne-Roshak. Anne Wierzbinski, Ryan Falk and Mike Blemberg (from left) are undergraduate fellows on a physics project to identify pulsars in space by sifting through thousands of radio wave patterns.

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