Low Frequency Gravitational Waves Detectable by Radio Telescopes

Summary: Existing Earth-based radio telescopes in Australia, Europe and North America may detect low frequency gravitational waves that take years to reach Earth.

Ripples in space-time, gravitational waves are represented by the green grid and are produced by accelerating bodies such as interacting supermassive black holes. These waves affect the time taken by radio signals from pulsars to arrive at Earth; credit David Champion: "Pulsar Web Could Detect Low-Frequency Gravitational Waves," NASA JPL Stars and Galaxies, Feb. 24, 2016, May be used for any purpose without prior permission, via NASA JPL

Existing radio telescopes appear to be capable of detecting low frequency gravitational waves that affect pulsar pulses, according to a study published online Feb. 23, 2016, in The Astrophysical Journal Letters.

Six co-researchers at the Jet Propulsion Laboratory and the TAPIR Group of California Institute of Technology in Pasadena, California, base the study’s findings upon NANOGrav observations. The acronym NANOGrav comes from the North American Nanohertz Observatory for Gravitational Waves, whose members commit to “observing a set of the fastest-rotating pulsars” since 2007.

Astrophysicists describe pulsars as supermassive stars that explode as supernovae before collapsing into neutron stars whose dense cores rotate a few or many times per second. Pulsars, while rotating, emit beams of radio waves that sweep over Earth as detectable pulses of radio emissions.

Maura McLaughlin, radio astronomer at West Virginia University in Morgantown and team member of NANOGrav, follows the fastest-spinning pulsars that rotate every 1 to 30 milliseconds. That “Millisecond pulsars have extremely predictable arrival times, and our instruments are able to measure them to within a ten-millionth of a second” generates many advantages.

Gravitational waves, as ripples spreading outward from moving masses, have accelerating or delaying effects upon the schedules of pulsar pulses and nudging impacts upon Earth’s orbit. It is “Because of that [predictability], we can use them [millisecond pulsar pulses] to detect incredibly small shifts in Earth’s position” from low frequency gravitational waves.

Maura McLaughlin joins more than 60 other NANOGrav team scientists from 13 institutions in Canada and in the United States.

Data from the National Radio Astronomy Observatory’s telescope in Green Bank, Virginia, and the Arecibo Observatory’s single dish telescope in Puerto Rico keep NANOGrav scientists busy. The National Radio Quiet Zone’s telescope in Green Bank and the world’s largest single-aperture radio telescope in Arecibo let NANOGrav scientists monitor more pulsars and spaces.

Michele Vallisneri, Jet Propulsion Laboratory and TAPIR Group researcher, mentions: “NANOGrav is currently monitoring 54 pulsars, but we can only see some of the southern hemisphere.” He notes that “We will need to work closely with our colleagues in Europe and Australia in order to get the all-sky coverage this search requires.”

NANOGrav operates the International Pulsar Timing Array with the European Pulsar Timing Array and with Australia’s Parkes Pulsar Timing Array.

A five-year, $14.5-million National Science Foundation award permits NANOGrav to organize a Physics Frontiers Center in collaboration with Canada’s McGill University and University of British Columbia. Pedro Marronetti, program director for gravitational wave-related research awards, qualifies the National Science Foundation-funded endeavors as supplements to other technologies for detecting higher frequency gravitational waves. He reveals that “This NSF-funded Physics Frontier Center is poised to complement LIGO [Laser Interferometer Gravitational-Wave Observatory] observations, extending the window” to low frequency gravitational waves.

Co-author Chiara Mingarelli states that LIGO detects black holes when “very close together” while co-author Joseph Lazio specifies that NANOGrav detects pulsars initiating spirals “closer together.”

Lead author Stephen Taylor theorizes: “The smoking gun will be seeing the same pattern of deviations in all of them.”

North American Nanohertz Observatory for Gravitational Waves (NANOGrav) scientists study pulsars via Robert C. Byrd Green Bank Telescope (GBT) in Green Bank, West Virginia; Sunday, Oct. 18, 2015, 09:33: Carol M. Highsmith, Public Domain, via Wikimedia Commons

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Ripples in space-time, gravitational waves are represented by the green grid and are produced by accelerating bodies such as interacting supermassive black holes. These waves affect the time taken by radio signals from pulsars to arrive at Earth; credit David Champion: "Pulsar Web Could Detect Low-Frequency Gravitational Waves," NASA JPL Stars and Galaxies, Feb. 24, 2016, May be used for any purpose without prior permission, via NASA JPL @ http://www.jpl.nasa.gov/news/news.php?feature=5505

North American Nanohertz Observatory for Gravitational Waves (NANOGrav) scientists study pulsars via Robert C. Byrd Green Bank Telescope (GBT) in Green Bank, Pocahontas County, West Virginia; Sunday, Oct. 18, 2015, 09:33: Carol M. Highsmith, Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Radio_telescope_at_the_National_Radio_Astronomy_Observatory_in_Green_Bank,_West_Virginia_LCCN2015634500.tif

For further information:

“About NANOGrav.” North American Nanohertz Observatory for Gravitational Waves > What?
Available @ http://nanograv.org

Dent, Steve. 25 February 2016. “Astronomers Are Using Pulsars to Spot Gravitational Waves.” Engadget > Science > Space.
Available @ http://www.engadget.com/2016/02/25/pulsars-gravitational-waves-black-holes/

Ferrara, Elizabeth. 24 February 2016. “Pulsar Web Could Detect Low-Frequency Gravitational Waves.” Jet Propulsion Laboratory > NASA > News.
Available @ http://www.jpl.nasa.gov/news/news.php?feature=5505

Mingharelli, Chiara. 24 February 2016. “Searching for the Gravitational Waves LIGO Can’t Hear.” Scientific American > Blogs > Guest Blog.
Available @ http://blogs.scientificamerican.com/guest-blog/searching-for-the-gravitational-waves-ligo-can-t-hear/

The NANOGrav Collaboration. 23 February 2016. “Interpreting the Recent Upper Limit on the Gravitational Wave Background from the Parkes Pulsar Timing Array.” Preprint: arXiv.org/abs/1602.06301v1 [astro-ph.IM].
Available @ http://arxiv.org/pdf/1602.06301v1.pdf

NASA. 24 February 2016. “Pulsar Web Could Detect Low-Frequency Gravitational Waves.” ScienceDaily.
Available @ https://www.sciencedaily.com/releases/2016/02/160224230817.htm

NASA @NASA. 24 February 2016. "Low-frequency gravitational waves could soon be detectable by existing radio telescopes." Twitter.
Available @ https://twitter.com/NASA/status/702583163915255808

Ouellette, Jennifer. 24 February 2016. “We Could Soon Find Even More Gravitational Waves with Pulsar Arrays.” Gizmodo.
Available @ http://gizmodo.com/we-could-find-even-more-gravitational-waves-soon-with-p-1761021828

Taylor, S.R.; M. Vallisneri; J.A. Ellis; C.M.F. Mingarelli; T.J.W. Lazio; and R. van Haasteren. 23 February 2016. “Are We There Yet? Time to Detection of Nanohertz Gravitational Waves Based on Pulsar-Timing Array Limits.” The Astrophysical Journal Letters 819 (1). DOI: http://dx.doi.org/10.3847/2041-8205/819/1/L6.
Available @ http://iopscience.iop.org/article/10.3847/2041-8205/819/1/L6

University of Wisconsin-Milwaukee. 20 March 2015. “New NSF-Funded Physics Frontiers Center Joins the Race to Detect Gravitational Waves.” EurekAlert! > Public Releases.
Available @ http://www.eurekalert.org/pub_releases/2015-03/uow--nnp033015.php