5/06/2013 Peter Durantine

Star Tracker: F&M Professor Searches 'Cosmos Lighthouses' for Gravitational Waves

  • Andrea Lommen, associate professor of astronomy at F&M, is part of a NASA team whose mission is to learn the interior composition of neutron stars and whether future space travelers can use the stars' pulsating light to navigate through the cosmos. (Photo by Marcy Dubroff)

Finding gravitational waves in the universe is a career quest for one Franklin & Marshall College astronomy professor, and she could make this key discovery in a NASA Explorer mission set to launch in 2017.

The research of Andrea Lommen focuses on the detection of gravitational waves, a crucial prediction in Einstein's theory of general relativity, which, once discovered, would revolutionize the field of astrophysics, she said.

"I expect it to be as revolutionary as the telescope," said Lommen, associate professor of astronomy at F&M and director of the College's Grundy Observatory. "We'll be able to see things in the universe that don't give off light."

Information about the universe has always come from light, whether through light waves or radio waves, Lommen said. Gravitational waves would allow scientists to see things without light, such as black holes.

Lommen is among a team of scientists providing expertise on NASA's two-prong mission to learn the interior composition of neutron stars and whether future space travelers can use the stars' pulsating light to navigate through the cosmos.

At a neutron star's two magnetic poles, powerful beams of light, like cosmic lighthouses, sweep around as the star spins. Viewed from Earth, the beams are light flashes, pulsing on and off, from seconds to milliseconds. It's the reason for the stars' other name -- pulsars.

Predictable pulsations make pulsars reliable celestial clocks. Part of NASA's mission is to determine the effectiveness of pulsar-based navigation.        

Sometimes, a pulsar's light arrives a little early, sometimes a little late. This is where Lommen begins her job: determining what causes the deviation that hinders the light's arrival -- ion clouds, gravitational waves, or an error by the Earth clock used to time the light?

"That's the whole game of detecting gravitational waves," she said. "If I can show that it's gravitational waves, then I've detected and confirmed for the first time that gravitational waves actually exist."

A Cross-Cutting Mission

The team Lommen is assigned includes about 80 scientists from the United States, the U.S. Naval Research Laboratory, Canada and Mexico, along with scientists and engineers from NASA, the Massachusetts Institute of Technology and various corporations and foundations.

The multi-purpose mission is known as the Neutron-star Interior Composition Explorer (NICER) and the Station Explorer for X-ray Timing and Navigation Technology, using the acronym SEXTANT, which is also the name of the early seafarer's instrument for charting courses by measuring objects or lights in the celestial skies with the horizon.

NICER/SEXTANT consists of a compact bundle of 56 X-ray telescopes, their associated silicon detectors, and other technologies. The X-ray instrument is roughly the size of a typical college dormitory refrigerator. It will be deployed on the International Space Station in 2017.

"NICER/SEXTANT represents the quintessential cross-cutting mission," said Keith Gendreau, the NASA scientist leading its development, noting the X-ray telescopes technology will establish the viability of spacecraft navigation using neutron stars while also providing a tool to better understand the stars. "It's rare that you get an opportunity to do a cross-cutting experiment like this."

The mission's primary objective is to learn what's inside a neutron star, which is the remnant of a massive star that, after its nuclear fuel is spent, explodes and collapses into a super-dense sphere that can be the size of the City of Lancaster.

"It's a state of matter that exists all over the universe, and there is no way to study it on Earth," Lommen said.

According to NASA scientists, the intense gravity from the star's explosion and collapse crushes an astonishing amount of matter, equaling at least 460,000 Earths, into New York City-sized balls. This creates the densest objects known in the universe.

Just a teaspoonful of the matter in these objects would weigh roughly a billion tons on Earth. So while it's weight makes it impossible to study in a conventional lab, through X-ray telescope observations, scientists expect NICER/SEXTANT to reveal the nature of ultra-dense matter in neutron stars and the physics that govern it.

"We have a laboratory that we couldn't make on Earth," Lommen said.

The laboratory observations of neutron stars begin after their explosive formation, when the stars shine from heat left by the explosion and from the radiation generated by their magnetic fields, which becomes intensely concentrated as the core collapses.  

Scientists believe that observing radiation from the stars through NICER's array of X-ray telescopes should offer the greatest insight into their structure.

Since gravitational waves are very small, Lommen said, NICER will let her determine whether one source causes the deviation in the arrival of the pulsar's light.

"We time pulsars years at a time, and the deviations we're looking for are less than 100 nanoseconds, so we have to be careful to understand all the different processes that can cause small deviations," she said.

NICER's telescopes won't detect whether gravitational waves are the source of the deviation, but they can tell whether the source is an ionized hydrogen cloud or an Earth clock error, Lommen said.

NICER/SEXTANT's payload also will detect X-ray photons within the pulsar's light beams to estimate the arrival times of their pulses. Using these measurements, the system will use special equations to put together an on-board navigation solution. It's similar to how a car's GPS system coordinates a location by triangulating with satellites circling the Earth, Lommen said.

For more information about the NICER/SEXTANT mission, visit Deep Space X-ray Navigation and Communication.

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