NANOGrav/JPL: Pulsar Web Could Detect Low-Frequency Gravitational Waves

[bystander]

Pulsar Web Could Detect Low-Frequency Gravitational Waves
NASA | JPL-Caltech | NANOGrav | 2016 Feb 24

Gravitational waves are ripples in space-time, represented by the green grid, produced by accelerating bodies such as interacting supermassive black holes. These waves affect the time it takes for radio signals from pulsars to arrive at Earth. (Credit: David Champion)

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The recent detection of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory (LIGO) came from two black holes, each about 30 times the mass of our sun, merging into one. Gravitational waves span a wide range of frequencies that require different technologies to detect. A new study from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has shown that low-frequency gravitational waves could soon be detectable by existing radio telescopes.

"Detecting this signal is possible if we are able to monitor a sufficiently large number of pulsars spread across the sky," said Stephen Taylor, lead author of the paper published this week in The Astrophysical Journal Letters. He is a postdoctoral researcher at NASA's Jet Propulsion Laboratory, Pasadena, California. "The smoking gun will be seeing the same pattern of deviations in all of them." Taylor and colleagues at JPL and the California Institute of Technology in Pasadena have been studying the best way to use pulsars to detect signals from low-frequency gravitational waves. Pulsars are highly magnetized neutron stars, the rapidly rotating cores of stars left behind when a massive star explodes as a supernova.

Einstein's general theory of relativity predicts that gravitational waves -- ripples in spacetime -- emanate from accelerating massive objects. Nanohertz gravitational waves are emitted from pairs of supermassive black holes orbiting each other, each of which contain millions or a billion times more mass than those detected by LIGO. These black holes each originated at the center of separate galaxies that collided. They are slowly drawing closer together and will eventually merge to create a single super-sized black hole.

As they orbit each other, the black holes pull on the fabric of space and create a faint signal that travels outward in all directions, like a vibration in a spider's web. When this vibration passes Earth, it jostles our planet slightly, causing it to shift with respect to distant pulsars. Gravitational waves formed by binary supermassive black holes take months or years to pass Earth and require many years of observations to detect. ...

Are We There Yet? Time to Detection of Nanohertz Gravitational
Waves Based on Pulsar-Timing Array Limits - S. R. Taylor et al

• Astrophysical Journal Letters 819(1):L6 (2016 Mar 01) DOI: 10.3847/2041-8205/819/1/L6
  arXiv.org > astro-ph > arXiv:1511.05564 > 17 Nov 2016

Interpreting the Recent Upper Limit on the Gravitational
Wave Background from the Parkes Pulsar Timing Array - NANOGrav Collaboration

• arXiv.org > astro-ph > arXiv:1602.06301 > 19 feb 2016

[bystander]

Gravitational Wave Search Provides Insights into Galaxy Mergers
National Radio Astronomy Obervatory | NANOGrav | 2016 Apr 05

[c]The Earth is constantly jostled by low-frequency gravitational waves from
supermassive black hole binaries in distant galaxies. Astrophysicists are using
pulsars as a galaxy-sized detector to measure the Earth’s motion from these waves.
Credit: B. Saxton (NRAO/AUI/NSF)[/c][hr][/hr]

Summary: New results from NANOGrav – the North American Nanohertz Observatory for Gravitational Waves – establish astrophysically significant limits in the search for low-frequency gravitational waves. This result provides insight into how often galaxies merge and how those merging galaxies evolve over time. To obtain this result, scientists required an exquisitely precise, nine-year pulsar-monitoring campaign conducted by two of the most sensitive radio telescopes on Earth, the Green Bank Telescope in West Virginia and the Arecibo Observatory in Puerto Rico.

The recent LIGO detection of gravitational waves from merging black holes with tens of solar masses has confirmed that distortions in the fabric of space-time can be observed and measured. Researchers from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) have spent the past decade searching for low-frequency gravitational waves emitted by black hole binaries with masses many millions of times larger than those seen by LIGO.

Analysis of NANOGrav's nine-year dataset provides very constraining limits on the prevalence of such supermassive black hole binaries throughout the Universe. Given scientists’ current understanding of how often galaxies merge, these limits point to fewer detectable supermassive black hole binaries than were previously expected. This result has significant impacts on our understanding of how galaxies and their central black holes co-evolve. ...

The NANOGrav Nine-year Data Set: Limits on the Isotropic Stochastic Gravitational Wave Background - Zaven Arzoumanian et al

• Astrophysical Journal 821(1):13 (2016 Apr 10) DOI: 10.3847/0004-637X/821/1/13
  arXiv.org > astro-ph > arXiv:1508.03024 > 12 Aug 2016

Astrophysicists Help Provide Insights into Galaxy Evolution & Mergers
West Virginia University | 2016 Apr 05