Astronomy

Can't pulsars and stars be used for gravitational wave measurement?

Can't pulsars and stars be used for gravitational wave measurement?


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Suppose that we collected photons from a distant star, and they arrive regularly at 15 photons every microsecond onto a CCD, when a gravity wave bends space time, wouldn't the regular 15 photons graph wobble as a result of the gravitational wave?

Why does the LISA observatory have to compare laser timings, if pulsars can be as precise as atomic clocks, can't it just compare a bunch of pulsar signals? A single satellite that records 50 pulsars would move compared the the pulsars and would have a frequency of 50Hz ticks with pulses which can be graphed at kHz frequencies.


Can't pulsars and stars be used for gravitational wave measurement?

In theory, yes. See the 2017 NASA article Listening for Gravitational Waves Using Pulsars.

Suppose that we collected photons from a distant star, and they arrive regularly at 15 photons every microsecond onto a CCD, when a gravity wave bends space time, wouldn't the regular 15 photons graph wobble as a result of the gravitational wave?

Kind of. When the gravitational wave is passing by, we'll be subject to a slight time dilation. So it would look as if the pulsar had speeded up.

Why does the LISA observatory have to compare laser timings, if pulsars can be as precise as atomic clocks, can't it just compare a bunch of pulsar signals? A single satellite that records 50 pulsars would move compared the pulsars and would have a frequency of 50Hz ticks with pulses which can be graphed at kHz frequencies.

Sorry, I don't know the answer to that. But see the Wikipedia article on LISA and note that it's scheduled for the 2030s. A lot can happen between now and then. Maybe it won't go ahead.


How LIGO, LISA, etc. Detect Gravitational Waves

The point of instruments like LIGO and LISA is to measure time-varying changes in the distance within different arms of the instrument. In the case of an arm oriented in the direction of an incoming gravitational wave (GW), the length of the arm will increase and decrease, while an arm oriented perpendicular will remain unchanged.

The method for measuring this is to split a laser beam, send each half down the different arms, and then recombine them and look at the interference pattern. If the arms have identical lengths, then the beams will destructively interfere. If, however, one of the arms becomes longer (or shorter), the recombined beams will be out of phase, and you will no longer have perfect destructive interference.

The key to being able to measure this sort of thing accurately is two things:

  1. Arm length, so the beam traveling down the altered-length path has time to accumulate a large enough phase shift for the interference pattern to change enough to be measured. Longer arms lead to larger phase shifts, which is why LISA aims to have arms that are 2.5 million km in length.

  2. The wavelength of the light: the shorter the wavelength, the smaller the actual shift in arm length needs to be to make the beam shift appreciably in phase. If the recombined beams differ in phase by 0.001%, then the change in the interference pattern will be very hard to detect and measure. But if they differ in phase by 50%, then the difference will be obvious. Shorter wavelengths make for larger phase shifts.

If you want think of the interferometric measurement as a kind of timing measurement (that is, we are, in a sense, measuring the difference in time it takes light to travel down the two arms), then optical light is vastly better than radio for "timing" measurements.

Pulsar Timing

As you pointed out, there are projects that use pulsars to try to detect gravitational waves (e.g., pulsar timing arrays).

These work by measuring time delays in the arrival of radio pulses from millisecond pulsars. However, it's important to note the limitations: in order to measure the arrival time accurately, you have to observe a pulsar over a period of several minutes (or more) and add up all the pulse arrivals to get a single, accurate value. (You are not measuring changes between the arrival of one single pulse and the next.) You then repeat this measurement several weeks or months later to get another arrival time. Since you're taking measurements weeks or months apart, you can only detect variations on that same time scale, which is why pulsar timing arrays are hoping to detect GWs with periods of months to years (e.g., from binary supermassive black holes). The kinds of GWs that LIGO detects -- with periods of fractions of a second -- are completely beyond what pulsar timing arrays can do.

We cannot use optical light from stars, because we know of no star that produces the exquisitely regular periodicity of a millisecond pulsar.

As a final comment, your scenario of photons that "arrive regularly at 15 photons every microsecond onto a CCD" has the problem that Poisson noise (a.k.a. "shot noise") means that you wouldn't actually get 15 photons every microsecond; you'd get around 15 every microsecond (a typical sequence might look like this: 16, 15, 18, 15, 14, 14, 15, 23, 16, 12,… ). With that much variation, it's really hard to detect subtle variations in intrinsic signal strength.


The other point to raise, is the expected frequency of the gravitational waves you detect varies between Lisa and pulsar timing systems. This then alters the types of systems you will detect. Pulsar timing arrays should find massive black hole mergers, while Lisa should find; stellar mass black holes years before they merge, white dwarf binaries in the galaxy (also not merging), as well as intermediate mass black holes (merging). So the different detectors have different uses, even if one could be made more accurate than the other.


Have pulsars provided a glimpse of gravitational waves from merging supermassive black holes?

The observation of tiny deviations in the arrival times of radio pulses from neutron stars could be our first glimpse at gravitational waves from merging supermassive black holes – according to astronomers working on the NANOGrav pulsar timing array. The team has scoured 12.5 years of data from two radio telescopes for evidence of gravitational waves created by the mergers of large numbers of pairs of supermassive black holes throughout the history of the universe. Although this preliminary observation is far from conclusive, the astronomers are encouraged by the result and believe that the existence of a cosmic gravitational-wave background could soon be confirmed by observing more pulsars over longer periods of time.

Supermassive black holes are found at the centres of most galaxies – including the Milky Way – and have masses that are millions or even billions times that of the Sun. As galaxies evolve and merge, supermassive black holes can orbit each other and eventually merge – broadcasting gravitational waves. These mergers contribute to the cosmic gravitational-wave background, which is believed to be a noise-like cacophony of waves that permeates the universe.

Measuring this background would provide astronomers with a wealth of information about how galaxies form and evolve. However, the very low frequency gravitational waves from supermassive mergers cannot be detected with the existing LIGO–Virgo gravitational wave observatories.

Celestial clocks

Fortunately, millisecond pulsars offer a way of probing these gravitational waves. Pulsars are rapidly rotating neutron stars that beam pulses of radiation towards Earth. Their pulse frequencies are extremely stable – indeed, they act as “celestial clocks” with stabilities that rival that of atomic clocks.

The NANOGrav pulsar timing array monitors signals from 45 different pulsars in different locations in the sky. If a gravitational wave travels between Earth and a pulsar (or vice versa), the distance between us and the pulsar will expand and contract slightly. Pulses travel at the speed of light, so during the contraction pulses will arrive on Earth sooner than expected, whereas during the expansion pulses will arrive later.

This arrival-time deviation is dependent upon the angle between the direction to the pulsar and the direction of travel of the gravitational wave. So, a comparison of arrival times from an array of different pulsars should reveal the effect of gravitational waves. Measuring this effect, however, is very difficult because the deviations are on the order of a few hundred nanoseconds and occur over timescales of years.

On the curve

A powerful way of searching for this effect is to measure correlations between the arrival times of pulses from pairs of pulsars. When plotted as a function of the angle between the pulsars, the result is the “Hellings–Downs curve”. This curve is independent of the direction of the gravitational waves so it can be used to look for evidence for the cosmic gravitational-wave background – which should include waves travelling in all directions.

Radio signals from the 45 pulsars were observed for 12.5 years using the Arecibo Observatory in Puerto Rico (which has since shutdown) and the Green Bank Telescope in West Virginia. After doing an extensive statistical analysis of the data, the NANOGrav team found tantalizing preliminary evidence something is affecting the arrival times from different pulsars.

“These enticing first hints of a gravitational-wave background suggest that supermassive black holes likely do merge and that we are bobbing in a sea of gravitational waves rippling from supermassive black hole mergers in galaxies across the universe,” says NANOGrav member Julie Comerford at the University of Colorado Boulder.

Hunting gravitational waves using pulsars

However, the team is not yet able to conclude that the observed effect is the result of the cosmic gravitational-wave background. In particular, the team was unable to establish correlations between pairs of pulsars.

“We’ve found a strong signal in our dataset, but we can’t say yet that this is the gravitational wave background,” says NANOGrav’s Joseph Simon, who is also in at Boulder.

Scott Ransom at the US’s National Radio Astronomy Observatory adds, “Trying to detect gravitational waves with a pulsar timing array requires patience. We’re currently analyzing over a dozen years of data, but a definitive detection will likely take a couple more. It’s great that these new results are exactly what we would expect to see as we creep closer to a detection.”


NANOGrav finds possible ‘first hints’ of low-frequency gravitational wave background

In data gathered and analyzed over 13 years, the North American Nanohertz Observatory for Gravitational Waves Physics Frontiers Center has found an intriguing low-frequency signal that may be attributable to gravitational waves.

NANOGrav researchers – including several from West Virginia University’s Department of Physics and Astronomy and the Center for Gravitational Waves and Cosmology – measure the times of arrival of radio pulses from exotic stars called pulsars with large radio telescopes, including the Green Bank Telescope in Pocahontas County, West Virginia. Pulsars are small, dense stars that rapidly rotate, emitting beamed radio waves, much like a lighthouse. The results from this most recent dataset show perturbations in the arrival times from these pulsars that may indicate the effects of gravitational waves, as reported recently in The Astrophysical Journal Letters. The most likely source of these gravitational waves is the combined signal from all the supermassive black hole pairs at the cores of merged, distant galaxies.

NANOGrav has ruled out some effects other than gravitational waves, such as interference from the matter in our own solar system or certain errors in the data collection. These newest findings set up direct detection of gravitational waves as the possible next major step for NANOGrav and other members of the International Pulsar Timing Array, a collaboration of researchers using the world’s largest radio telescopes.

“We can't yet say with confidence that what we're seeing is gravitational waves, but if it is, the ‘signal’ makes a lot of sense given what we think we know about supermassive black holes,” said Dustin Madison, a postdoctoral researcher at WVU. “This was always how this was going to play out – enticing hints of a signal before we would be able to definitively claim a detection. We're on the right track to make that definitive assessment in just a couple of years.”

Looking to the future, he thinks researchers will then be able to characterize the signal and learn more from it for years and years to come.

Gravitational waves are ripples in space-time caused by the movements of incredibly massive objects, such as black holes orbiting each other or neutron stars colliding. Astronomers cannot observe these waves with a telescope like they do stars and galaxies. Instead, they measure the effects passing gravitational waves have, namely tiny changes to the precise position of objects – including the position of the Earth itself. Gravitational waves were first detected in 2015 by NSF’s Laser Interferometer Gravitational-Wave Observatory by a team including other researchers at WVU. Like light from distant objects, gravitational waves are a cosmic messenger signal – one that holds great potential for understanding “dark” objects, like black holes.

NANOGrav chose to study the signals from pulsars because they serve as detectable, dependable Galactic clocks. These small, dense stars spin rapidly, sending pulses of radio waves at precise intervals toward Earth. Pulsars are in fact commonly referred to as the universe’s timekeepers, and this unique trait has made them useful for astronomical study.

But gravitational waves can interrupt this observed regularity, as the ripples cause space-time to undergo tiny amounts of stretching and shrinking. Those ripples result in extremely small deviations in the expected times for pulsar signals arriving on Earth. Such deviations indicate that the position of the Earth has shifted slightly. By studying the timing of the regular signals from many pulsars scattered over the sky at the same time, known as a “pulsar timing array,” NANOGrav works to detect minute changes in the Earth’s position due to gravitational waves stretching and shrinking space-time.

“This signal is incredibly enticing. It could be that our orchestra is tuning up, hinting that we're about to hear the grand symphony of waves from supermassive black holes that we expect pervades the universe,” said Sarah Burke-Spolaor, WVU assistant professor and NANOGrav member. “If this signal is indeed gravitational waves, future study will offer unique insights into how the biggest black holes and galaxies in our universe form and evolve.”

“NANOGrav has been building to the first detection of low frequency gravitational waves for over a decade and today’s announcement shows that they are on track to achieving this goal,” said Pedro Marronetti, NSF program director for gravitational physics. “The insights that we will gain on cosmology and galaxy formation are truly unparalleled.”

NANOGrav is a collaboration of U.S. and Canadian astrophysicists and a National Science Foundation Physics Frontiers Center.

"We are so grateful for the support of the NANOGrav PFC,” said Maura McLaughlin, Eberly Distinguished Professor of Physics and Astronomy at WVU and co-director of the NANOGrav PFC. “That's allowed us to dramatically increase both the number of pulsars being timed and the number of participants working on NANOGrav research over the past six years."

WVU has played a significant role in the PFC. Twelve of the 63 authors on this paper are WVU faculty, postdocs and students. Low-frequency gravitational wave detection is one of the main aims of the Center for Gravitational Waves and Cosmology, formed in 2015 along with the award of the PFC.

“The long-term institutional support provided by the Eberly College and University has played a critical role in NANOGrav’s success since its inception in 2007,” said Duncan Lorimer, WVU professor and Eberly College associate dean for research.

NANOGrav created its pulsar timing array by studying 47 of the most stably rotating “millisecond pulsars” with both the GBT and the Arecibo Observatory in Puerto Rico as reported in the January 2021 Astrophysical Journal Supplements. Not all pulsars can be used to detect the signals that NANOGrav seeks – only the most stably rotating and longest-studied pulsars will. These pulsars spin hundreds of times per second with incredible stability, which is necessary to obtain the precision required to detect and study gravitational waves.

Of the 47 pulsars studied, 45 had sufficiently long datasets of at least three years to use for the analysis. Researchers studying the data uncovered a spectral signature, a low-frequency noise feature that is the same across multiple pulsars. The timing changes NANOGrav studies are so small that the evidence is not apparent when studying any individual pulsar, but in aggregate, they add up to a significant signature.

To confirm direct detection of a signature from gravitational waves, NANOGrav’s researchers will have to find a distinctive pattern in the signals between individual pulsars.

At this point, the sensitivity of the experiment is not currently good enough for such a pattern to be distinguishable. Boosting the signal requires NANOGrav to expand its dataset to include more pulsars studied for even longer lengths of time, which will increase the array’s sensitivity. In addition, by pooling NANOGrav's data together with those from other pulsar timing array experiments, a joint effort by the IPTA may reveal such a pattern.

Students and faculty at WVU are important contributors to this effort, and 24 WVU students have traveled to IPTA partner countries to undertake research abroad as part of NSF-funded programs led by WVU.

At the same time, NANOGrav is developing techniques to ensure the detected signal could not be from another source. They are producing computer simulations that help test whether the detected noise could be caused by effects other than gravitational waves, in order to avoid a false detection.

While the next several years hold a great deal of scientific promise, they are not without challenges. With the recent collapse of the Arecibo Observatory’s 305-meter telescope, NANOGrav will seek alternate sources of data and working even more closely with their international colleagues. Although significant delays in detection are not expected due to years of very sensitive Arecibo data already contributing to its datasets, the loss of Arecibo is a terrible blow to science in general. For NANOGrav, it may impact the ability to characterize the background and detect other types of gravitational-wave sources in the future in the absence of another instrument. The loss of the telescope also directly impacts the graduate studies of several WVU PhD students. NANOGrav members are deeply saddened by the collapse and its impact on the staff and the island of Puerto Rico.

For more information about NANOGrav, visit http://nanograv.org.

NANOGrav research at WVU is supported through NSF PFC award no. 1430284 and NSF OIA award no. 1458952. The Arecibo Observatory is a facility of the National Science Foundation operated under cooperative agreement (no. AST-1744119) by the University of Central Florida in alliance with Universidad Ana G. Méndez and Yang Enterprises, Inc. The Green Bank Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.


NANOGrav finds possible ‘first hints’ of low-frequency gravitational wave background

In data gathered and analyzed over 13 years, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) Physics Frontiers Center (PFC) has found an intriguing low-frequency signal that may be attributable to gravitational waves.

NANOGrav researchers – including a number from West Virginia University’s (WVU’s) Department of Physics and Astronomy and the Center for Gravitational Waves and Cosmology – measure the times of arrival of radio pulses from exotic stars called pulsars with large radio telescopes, including the Green Bank Telescope (GBT) in Pocahontas County, West Virginia. Pulsars are small, dense stars that rapidly rotate, emitting beamed radio waves, much like a lighthouse. The results from this most recent dataset show perturbations in the arrival times from these pulsars that may indicate the effects of gravitational waves, as reported recently in The Astrophysical Journal Letters. The most likely source of these gravitational waves is the combined signal from all the supermassive black hole pairs at the cores of merged, distant galaxies.

Representative illustration of the Earth embedded in space-time which is deformed by the background gravitational waves and its effects on radio signals coming from observed pulsars. Image courtesy of Tonia Klein/NANOGrav.

NANOGrav has been able to rule out some effects other than gravitational waves, such as interference from the matter in our own solar system or certain errors in the data collection. These newest findings set up direct detection of gravitational waves as the possible next major step for NANOGrav and other members of the International Pulsar Timing Array (IPTA), a collaboration of researchers using the world’s largest radio telescopes.

Dustin Madison, a postdoctoral researcher at WVU, comments “We can't yet say with confidence that what we're seeing is gravitational waves, but if it is, the "signal" makes a lot of sense given what we think we know about supermassive black holes. This was always how this was going to play out. enticing hints of a signal before we would be able to definitively claim a detection. We're on the right track to make that definitive assessment in just a couple of years.” Looking to the future, he thinks researchers will then be able to characterize the signal and learn more from it for years and years to come.

Gravitational waves are ripples in space-time caused by the movements of incredibly massive objects, such as black holes orbiting each other or neutron stars colliding. Astronomers cannot observe these waves with a telescope like they do stars and galaxies. Instead, they measure the effects passing gravitational waves have, namely tiny changes to the precise position of objects - including the position of the Earth itself. Gravitational waves were first detected in 2015 by NSF’s Laser Interferometer Gravitational-Wave Observatory (LIGO) by a team including other researchers at WVU. Like light from distant objects, gravitational waves are a cosmic messenger signal – one that holds great potential for understanding “dark” objects, like black holes.

NANOGrav chose to study the signals from pulsars because they serve as detectable, dependable Galactic clocks. These small, dense stars spin rapidly, sending pulses of radio waves at precise intervals toward Earth. Pulsars are in fact commonly referred to as the universe’s timekeepers, and this unique trait has made them useful for astronomical study.

But gravitational waves can interrupt this observed regularity, as the ripples cause space-time to undergo tiny amounts of stretching and shrinking. Those ripples result in extremely small deviations in the expected times for pulsar signals arriving on Earth. Such deviations indicate that the position of the Earth has shifted slightly. By studying the timing of the regular signals from many pulsars scattered over the sky at the same time, known as a “pulsar timing array,” NANOGrav works to detect minute changes in the Earth’s position due to gravitational waves stretching and shrinking space-time.

WVU Professor and NANOGrav member Sarah Burke-Spolaor explains “This signal is incredibly enticing. It could be that our orchestra is tuning up, hinting that we're about to hear the grand symphony of waves from supermassive black holes that we expect pervades the Universe,” Burke-Spolaor reflects. She adds, “If this signal is indeed gravitational waves, future study will offer unique insights into how the biggest black holes and galaxies in our universe form and evolve”.

“NANOGrav has been building to the first detection of low frequency gravitational waves for over a decade and today’s announcement shows that they are on track to achieving this goal,” said Pedro Marronetti, NSF Program Director for gravitational physics. “The insights that we will gain on cosmology and galaxy formation are truly unparalleled.”

NANOGrav is a collaboration of U.S. and Canadian astrophysicists and a National Science Foundation Physics Frontiers Center (PFC). Maura McLaughlin, WVU Professor and Co-Director of the NANOGrav PFC, added "We are so grateful for the support of the NANOGrav PFC, that's allowed us to dramatically increase both the number of pulsars being timed and the number of participants working on NANOGrav research over the past six years". WVU has played a significant role in the PFC 12 of the 63 authors on this paper are WVU faculty, postdocs, and students. And low-frequency gravitational wave detection is one of the main aims of the Center for Gravitational Waves and Cosmology, formed in 2015 along with the award of the PFC. As, Duncan Lorimer, WVU Professor and Eberly College Associate Dean for Research, notes “The long-term institutional support provided by the College and University has played a critical role in NANOGrav’s success since its inception in 2007”.

NANOGrav created their pulsar timing array by studying 47 of the most stably rotating “millisecond pulsars” with both the GBT and the Arecibo Observatory in Puerto Rico as reported in the January 2021 Astrophysical Journal Supplements. Not all pulsars can be used to detect the signals that NANOGrav seeks – only the most stably rotating and longest-studied pulsars will do. These pulsars spin hundreds of times a second, with incredible stability, which is necessary to obtain the precision required to detect and study gravitational waves.

Of the 47 pulsars studied, 45 had sufficiently long datasets of at least three years to use for the analysis. Researchers studying the data uncovered a spectral signature, a low-frequency noise feature, that is the same across multiple pulsars. The timing changes NANOGrav studies are so small that the evidence is not apparent when studying any individual pulsar, but in aggregate, they add up to a significant signature.

To confirm direct detection of a signature from gravitational waves, NANOGrav’s researchers will have to find a distinctive pattern in the signals between individual pulsars. At this point, the sensitivity of the experiment is not currently good enough for such a pattern to be distinguishable. Boosting the signal requires NANOGrav to expand its dataset to include more pulsars studied for even longer lengths of time, which will increase the array’s sensitivity. In addition, by pooling NANOGrav's data together with those from other pulsar timing array experiments, a joint effort by the IPTA may reveal such a pattern. Students and faculty at WVU are important contributors to this effort, and in fact 24 WVU students have traveled to IPTA partner countries to undertake research abroad as part of NSF-funded programs led by WVU.

At the same time, NANOGrav is developing techniques to ensure the detected signal could not be from another source. They are producing computer simulations that help test whether the detected noise could be caused by effects other than gravitational waves, in order to avoid a false detection.

Publications referenced in this article

For more information about NANOGrav, please visit the website at http://nanograv.org.

NANOGrav research at WVU is supported through NSF PFC award #1430284 and NSF OIA award #1458952. The Arecibo Observatory is a facility of the National Science Foundation operated under cooperative agreement (#AST-1744119) by the University of Central Florida (UCF) in alliance with Universidad Ana G. Méndez (UAGM) and Yang Enterprises (YEI), Inc. The Green Bank Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.


Pulsars and Gravitational Wave Astronomy

We're investigating some of the most extreme and amazing objects of the universe, and we are at the forefront of Australian research into gravitational waves.

Pulsars are spinning dead stars that have long since consumed all their nuclear fuel and collapsed into super-dense remnants. Astronomers have discovered over 3,000 of these objects including a remarkable binary pulsar that provided the first experimental evidence for the emission of gravitational waves leading to the 1993 Nobel Prize. Pulses of radiation from the spin can be used as extremely precise clocks with which to measure extreme gravity and test the limits of general relativity.

Gravitational waves can also be measured directly here on Earth, as they cause space and time to squeeze and stretch as they pass through the world's most precise interferometers. Over 100 years ago, Albert Einstein predicted that these ripples in space-time would be created by accelerating masses and objects orbiting each other. Recent advances in detector sensitivity led to the first direct detection of gravitational waves in 2015.

This was a landmark achievement in human discovery, heralding the birth of the new field of gravitational wave astronomy and receiving the 2017 Nobel Prize in Physics. This was followed in 2017 by the first observations of the collision of two neutron-stars. The accompanying explosion was subsequently seen in follow-up observations by telescopes across the globe and ushered in a new era of multi-messenger astronomy.

"OzGrav's mission is to capitalise on the historic first detections of gravitational waves to understand the extreme physics of black holes and warped spacetime, and to inspire the next generation of scientists and engineers through this new window on the universe."

Professor Matthew Bailes , Centre of Astrophysics and Supercomputing

The Centre for Astrophysics and Supercomputing (CAS) is home to the headquarters of the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), which involves over 200 members around Australia and overseas, and is part of the international LIGO-Virgo-Kagra collaboration. Swinburne's Professor Matthew Bailes leads OzGrav and is a pioneer in the discovery of pulsars, having led several pulsar survey and timing arrays, including MeerTIME that uses the power of the new MeerKAT telescope to explore fundamental physics and astrophysics via radio pulsar timing.

Swinburne is also one of the founding members of the Parkes Pulsar Timing Array that regularly times over 20 millisecond pulsars to microsecond precision with the aim of detecting gravitational waves from supermassive black hole binaries in distant galaxies. We also develop models of gravitational wave emission from supernovae and the binaries that produce gravitational wave sources and binary pulsars.

CAS is also a world leader in the electromagnetic follow-up of gravitational waves and other transient sources, through the Deeper, Wider, Faster program led by Associate Professor Jeff Cooke. We are also home to the GW Data Centre, which is one of the largest dedicated gravitational wave supercomputing groups in the world, led by Professor Jarrod Hurley.

Our projects

MeerTime

The MeerTime project is a five-year program on the MeerKAT array, led by Swinburne, which will regularly time over 1000 radio pulsars to perform tests of relativistic gravity, search for the gravitational-wave signature induced by supermassive black hole binaries in the timing residuals of millisecond pulsars, explore the interior of neutron stars through a pulsar glitch monitoring programme, explore the origin and evolution of binary pulsars, monitor the swarms of pulsars that inhabit globular clusters, and monitor radio magnetars.

Parkes Pulsar Timing Array

Swinburne is a foundation partner in the Parkes Pulsar Timing Array project, which monitors 24 millisecond pulsars with the iconic 64-metre Parkes radio telescope for the primary goal of studying the low-frequency gravitational wave universe.

Zooming in on cosmic fireballs

When the dense, massive stellar remnants called neutron stars collide, the result is a fiery, radioactive train wreck that can be seen from hundreds of millions of light years away. This project uses radio telescopes spread across the earth working in unison to sift through the glowing wreckage to determine the nature of the collision.

UTMOST studies of FRBs and pulsars

The UTMOST telescope is a wide-field radio telescope with a powerful digital backend jointly operated by Swinburne and used to find and study radio pulsars and fast radio bursts.


Zero Genie

Since the beginning of time, humans have hoped to one day unlock the secrets of the universe. With ongoing research funding from the National Science Foundation (NSF) and the expertise of people like Texas Tech’s Joseph D. Romano, they are now closer than ever.

Romano, a professor in the Department of Physics & Astronomy, conducts research in gravitational-wave data analysis, specializing in searches for weak gravitational-wave signals coming from the very early universe. As such, his work fits in perfectly with that of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav).

The NSF announced recently that it has renewed its support of NANOGrav with a $17 million grant over five years to operate the NANOGrav Physics Frontiers Center (PFC). The NANOGrav PFC will address a transformational challenge in astrophysics: the detection and characterization of low-frequency gravitational waves. The most promising sources of low-frequency gravitational waves are supermassive binary black holes that form via the mergers of massive galaxies. Additional low-frequency gravitational-wave sources include cosmic strings, inflation and other early universe processes.

Astrophysicists now detect low-frequency gravitational waves using millisecond pulsars – rapidly spinning, superdense remains of massive stars that have exploded as supernovas. These ultra-stable stars are nature’s most precise celestial clocks, appearing to “tick” every time their beamed emissions sweep past the Earth, like the beacon on a lighthouse. Gravitational waves may be detected in the small but perceptible fluctuations – a few dozen nanoseconds over 10 or more years – they cause in the measured arrival times at Earth of radio pulses from these millisecond pulsars.

“The goal is to detect the presence of low-frequency gravitational waves in an effort to better understand how supermassive black holes and galaxies form,” Romano said.

The precision required in these measurements makes Romano’s work especially important. You see, he helps develop the data analysis algorithms that identify the presence of gravitational waves. For his role in the NANOGrav PFC collaboration, Romano will receive $298,366 over the next five years.

When it was founded in 2007, NANOGrav consisted of 17 members in the U.S. and Canada. With support from the NSF in the form of a Partnerships for International Research and Education (PIRE) award in 2010 and a PFC in 2015, NANOGrav has grown tremendously. It is now a truly global collaboration with around 200 students and scientists at about 40 institutions around the world. Over the past few years, NANOGrav PFC students, postdoctoral researchers and senior personnel have pushed the frontiers of multi-messenger astrophysics, achieved an unprecedented sensitivity to low-frequency gravitational waves and enabled a transition into an astrophysically interesting territory: NANOGrav is now poised to detect low-frequency gravitational waves and use them to study the universe in a completely new way.

NANOGrav’s five-year program will make use of the unique capabilities and sensitivity of the Green Bank Telescope (GBT) in Green Bank, West Virginia. The GBT is located in the National Radio Quiet Zone, which protects the incredibly sensitive telescope from unwanted radio interference, enabling it to study pulsars and other astronomical objects. The program also uses data from the Very Large Array (VLA) in New Mexico and the Canadian Hydrogen Intensity Mapping Experiment (CHIME) in Canada. In addition, NANOGrav will use legacy Arecibo Observatory data, which will anchor combined future data sets and greatly increase sensitivity.

“The NANOGrav PFC has made significant progress over the last five years, remaining at the frontier of fundamental physics research,” said Jim Shank, the program director for NSF’s PFC program. “The center now seems close to making a breakthrough discovery in gravitational waves and the way we perceive the universe.”

Xavier Siemens, a physicist at Oregon State University, is the principal investigator (PI) for the project and will serve as co-director of the center. Maura McLaughlin, an astronomer at West Virginia University and co-investigator of the project, will serve as co-director.

NSF currently supports 10 other PFCs, which range in research areas from theoretical biological physics and the physics of living cells to quantum information and nuclear astrophysics. By bringing together astronomers and physicists from across the U.S. and Canada to search for the telltale signature of gravitational waves buried in the incredibly steady ticking of distant pulsars, the NANOGrav PFC will advance the mission to “foster research at the intellectual frontiers of physics” and to “enable transformational advances in the most promising research areas.”

In addition to his membership in the NANOGrav collaboration, Romano is a member of the Laser Interferometer Gravitational-Wave Observatory (LIGO) Scientific Collaboration and the Laser Interferometer Space Antenna (LISA) Consortium, both of which are international collaborations of scientists searching for gravitational waves. Romano’s prior research experience involved investigations into the relationship between gravitational physics and quantum mechanics.

Romano was co-chair of the LIGO Scientific Collaboration Stochastic Sources Analysis Group from 2000-2006 and 2018-2020. He is a member of Texas Tech’s STEM Center for Outreach, Research & Education, a member of the American Physical Society and was associate editor of the American Journal of Physics.


The gravitational background

Researchers at the premiere astronomy conference also reported finding the first possible hints of a mysterious new kind of gravitational wave, cosmic ripples that warp the fabric of space and time itself.

Scientists reported the first-ever direct detection of gravitational waves in 2016 using the Laser Interferometer Gravitational-Wave Observatory (LIGO), a discovery that earned the 2017 Nobel Prize in Physics. The space-time distortions those researchers saw were created when two black holes collided with each other about 130 million light-years from Earth. Since then, LIGO has observed dozens more such signals.

But the gravitational waves that LIGO are best at detecting are the most powerful ones, loud outbursts released when extraordinarily massive objects collide with one another. Researchers now also want to detect gravitational waves that are more like the background noise of small talk at a crowded party.

In theory, merging galaxies and other cosmic events should generate such a "gravitational wave background." Detecting this steady hum could shed light on mysteries such as how galaxies have grown over time.

However, these waves are huge, posing a major challenge for detecting this gravitational wave background. Whereas existing gravitational-wave observatories on Earth are designed to search for gravitational waves on the order of seconds long, ripples from the gravitational wave background are years or even decades long.

Now researchers say they may have detected a strong signal of the gravitational wave background using a U.S. and Canadian project called the North American Nanohertz Observatory for Gravitational Waves (NANOGrav).

"We're seeing incredibly significant evidence for this signal," study lead author Joseph Simon, an astrophysicist at the University of Colorado Boulder, said during the AAS press conference. "Unfortunately, we can't quite say what it is yet."

NANOGrav uses telescopes on the ground to monitor dozens of pulsars. Gravitational waves can alter the steady blinking pattern of light from pulsars, squeezing and expanding the distances these rays travel through space.

"As these waves pass us, the Earth gets pushed around very slightly," Simon said. "As Earth is pushed closer to pulsars in one part of the sky, those pulsars' pulses will appear a little bit sooner than expected, and pulses from pulsars in the other part of the sky appear to come a bit later."

Analyzing this pulsar light could therefore help scientists detect signs of the gravitational wave background.

"By monitoring signals from a large number of these pulsars, we created a galaxy-size gravitational-wave detector within our own Milky Way," Simon said.

To find these subtle hints, NANOGrav scientists have attempted to observe as many pulsars as they can for as long as possible. So far, they have observed 45 pulsars for at least three years, and in some cases, for more than a dozen years.

"These pulsars are spinning about as fast as your kitchen blender," Simon said in a statement. "And we're looking at deviations in their timing of just a few hundred nanoseconds."

Now the researchers said they have detected potential evidence of a common process distorting the light from many of the pulsars. As of yet, they cannot verify whether this signal is evidence for the gravitational wave background, "but we also don't have evidence against it," Simon said.

The scientists caution they still need to look at more pulsars and monitor them for longer time periods to confirm whether the gravitational background is the cause.

If the researchers can verify they have detected the gravitational wave background, they next want to pinpoint what causes these waves and what such signals can tell scientists about the universe.

The scientists detailed their findings Jan. 11 at an online meeting of the American Astronomical Society. Chakrabarti and her colleagues detailed their findings in a study accepted in the journal Astrophysical Journal Letters. Simon and his colleagues detailed their NANOGrav findings online Dec. 24 in the journal The Astrophysical Journal Letters.


To find giant black holes, start with our solar system’s center

Artist’s concept of an array of pulsars, used in a system to find black holes with billions of times our sun’s mass. The best place to start? One idea is to use the gravitational center of our solar system. Image via David Champion/ Vanderbilt University.

Black holes are places where gravity is so immense that light cannot escape. The spacetime surrounding black holes is warped. In recent decades, astronomers have come to believe that largest black holes – supermassive black holes – reside in the hearts of most galaxies. Each is millions or billions of times the mass of our sun. But many supermassive black holes remain undetected. How can scientists find them? Enter gravitational waves, ripples in spacetime, theorized as far back as Albert Einstein, but observed only since 2015. Astronomers now say we can find supermassive black holes by observing the effect of their gravitational waves on the timing of light flashes from pulsars. While conducting this research, these scientists say they’ve also refined our knowledge of the gravitational center – or barycenter – of our solar system.

The new research comes from Stephen Taylor, assistant professor of physics at Vanderbilt University and the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration. Taylor explained in a statement:

Using the pulsars we observe across the Milky Way galaxy, we are trying to be like a spider sitting in stillness in the middle of her web. How well we understand the solar system’s barycenter is critical as we attempt to sense even the smallest tingle to the web.

This new technique for finding supermassive black holes was announced on June 30, 2020 by Vanderbilt University.

The peer-reviewed paper detailing their findings was published in The Astrophysical Journal last April 21.

Gravitational waves – ripples in space-time – can be generated by pairs of black holes orbiting each other. To find these ripples, Taylor and his colleagues measure the regular flashes of light from pulsars, which are neutron stars that spin extremely fast and blast out beams of light, much like a cosmic lighthouse. The researchers are looking for changes in the arrival rate of these flashes, using NANOGrav data. Like clocks keeping time perfectly, pulsars are known to emit their flashes in a way that’s extremely regular (which is why, when first discovered, it was thought they might be artificial signals from aliens). So slight deviations from the otherwise regular flashing of a pulsar could indicate the passing of gravitational waves.

It turns out that the exact gravitational center – the barycenter – of the solar system is not in the middle of the sun, but rather about 330 feet (100 meters) above the sun’s surface, according to the new study. Image via Tonia Klein/ NANOGrav Physics Frontier Center/ Vanderbilt University.

In the statement from these scientists, Taylor said that understanding the exact location of the barycenter of the solar system helps in the search for gravitational waves from supermassive black holes. What is the barycenter, exactly? Perhaps you know that – as in the Earth-moon system, for example – the moon doesn’t orbit the center of Earth. Instead, both Earth and moon orbit around the barycenter, or common center of gravity in the system. In the Earth-moon system, the center of gravity, or barycenter, is inside Earth, but not at the center of Earth. It’s about 2,902 miles (4,671 km) from Earth’s center, or about 75% of the way from Earth’s center to its surface.

Likewise, the barycenter – or center of mass – in our solar system isn’t in the middle of the sun. It’s near the sun’s surface, about 330 feet (100 meters) above the sun’s surface, according to the new study. These scientists’ statement called this point “the location of absolute stillness in our solar system.”

So understanding the location of the exact gravitational center of the solar system helps scientists measure the very slight but detectable changes in pulsar flashes caused by passing gravitational waves. That location has been estimated before, using data from Doppler tracking. This provides the locations and trajectories of objects as they orbit the sun. But that can lead to errors and inconsistent results, showing evidence of gravitational waves that aren’t really there. Co-author Joe Simon said:

The catch is that errors in the masses and orbits will translate to pulsar-timing artifacts that may well look like gravitational waves.

Graphic depiction of gravitational waves generated by two black holes orbiting each other. Image via LIGO/ T. Pyle/ Science.

Artist’s concept of a peculiar black hole system, in which 2 small black holes are merging in the disk surrounding a 3rd, supermassive black hole. To find the most massive black holes, researchers are measuring the timing of light flashes coming from pulsars, as affected by gravitational waves. Image via Caltech/ R. Hurt (IPAC).

We weren’t detecting anything significant in our gravitational wave searches between solar system models, but we were getting large systematic differences in our calculations. Typically, more data delivers a more precise result, but there was always an offset in our calculations.

So how do the researchers account for the previous errors and inconsistencies, and improve the accuracy of detecting the gravitational waves? They decided to try a different approach, searching for the gravity waves and the exact gravitational center of the solar system at the same time. And it worked. They were even able to specifically pinpoint the center of gravity in the solar system to within 100 meters! The precise gravitational center of the solar system is not in the center of the sun, as might be presumed. It is actually only about 330 feet above the surface of the sun, according to the paper. This discrepancy is due to the affect of the huge mass of the largest planet, Jupiter. Taylor said:

Our precise observation of pulsars scattered across the galaxy has localized ourselves in the cosmos better than we ever could before. By finding gravitational waves this way, in addition to other experiments, we gain a more holistic overview of all different kinds of black holes in the universe.

Stephen Taylor at Vanderbilt University, co-author of the new study. Image via Vanderbilt University.

Just a few days ago, it was reported that, for the first time, astronomers had observed visible light from a black hole merger. In this system, two smaller black holes are merging together within a disk of material surrounding a supermassive black hole 12.8 billion light-years away. Such mergers have been detected before by the gravitational waves they create, but this was the first time that a flare-like visible light phenomenon had also been seen. The light comes from the gaseous disk of material surrounding the larger black hole, not from within the black holes themselves.

NANOGrav will continue to collect additional pulsar timing data, and astronomers are confident that this will lead to the unequivocal discovery of more supermassive black holes.

Bottom line: New study says that the best way to find the most massive black holes is to measure gravitational waves at the precise gravitational center of the solar system.


Astronomers find possible hints of gravitational waves

An international team of astronomers – including 17 Cornellians – report they have found the first faint, low-frequency whispers that may be gravitational waves from gigantic, colliding black holes in distant galaxies.

A group of international astronomers have found the first faint evidence of gravitational waves from merging, supermassive black holes.

The findings were obtained from more than 12.5 years of data collected from the national radio telescopes at Green Bank, West Virginia, and the recently collapsed dish at the Arecibo Observatory, in Arecibo, Puerto Rico.

The research was announced Jan. 11 at a press conference at the American Astronomical Society’s national meeting, held online due to the COVID-19 pandemic. The press conference highlighted the research, “The NANOGrav 12.5-year Data Set: Search for an Isotropic Stochastic Gravitational-wave Background,” published Dec. 24 in The Astrophysical Journal Letters.

The astronomers are all participants in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project, which uses pulsars – rapidly spinning dense stars – that act as wave detectors and cosmic timekeepers.

Merging gargantuan black holes create gravitational waves that can send ripples through space-time and affect a pulsar’s timekeeping regularity – ultimately indicating that Earth’s position in the universe may have slightly shifted.

“We must be clear: We are not yet claiming to have detected gravitational waves,” said Shami Chatterjee, Ph.D. ’03, a Cornell principal research scientist in the College of Arts and Sciences’ (A&S) Department of Astronomy. “We have detected a signal that is consistent with the existence of gravitational waves, but we can’t prove that quite yet. We think this is the tip of the iceberg, but we have to actually demonstrate it to our own satisfaction.”

To get a sense of the size of these gravitational waves, recall the wave detection by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in early 2016, when scientists caught two black holes merging.

The merger set off kilohertz waves that were hundreds of kilometers in length, small enough to allow Earth-based detectors to capture them from kilometer-wide, land-based sensors. That finding confirmed a major prediction of Albert Einstein’s 1915 general theory of relativity.

In the NANOGrav case, gigantic black holes are in the process of merging.

“The masses we’re talking about are the giant black holes that are in the centers of galaxies,” said James Cordes, the George Feldstein Professor of Astronomy (A&S). “They are a billion times the mass of the sun. They’re monsters.”

And these monsters are generating nanohertz-scale gravitational quavers that are light-years in length, said Cordes. Thus, astronomers enlist pulsars to help detect these waves.

The paper notes that 47 pulsars were studied to gather this data currently the astronomers are using 80 pulsars. Cordes said the plan is for the project’s astronomers to use about 200 pulsars, once they secure telescope time on other radio telescopes – to replace the time lost at the Arecibo Observatory, which recently collapsed.

In addition to Cordes and Chatterjee, the other Cornellians who work on this project include:

  • Ross Jennings, doctoral candidate
  • H. Thankful Cromartie, NASA Einstein Postdoctoral Fellow
  • Adam Brazier, computational scientist, Cornell Center for Advanced Computing
  • Maura A. McLaughlin, Ph.D. ‘01, professor, West Virginia University, a member of NANOgrav and co-director of the Physics Frontier Center
  • Michael T. Lam, Ph.D. ’16, assistant professor, Rochester Institute of Technology
  • T. Joseph W. Lazio, Ph.D. ’97, chief scientist of the Interplanetary Network Directorate, Jet Propulsion Laboratory, California Institute of Technology
  • Dustin R. Madison, Ph.D. ’15, postdoctoral fellow, University of West Virginia
  • David L. Kaplan ’98, visiting associate professor, University of Wisconsin, Madison
  • Dan Stinebring M.S. ’78, Ph.D. ’82, emeritus professor of physics, Oberlin College
  • Caitlin A. Witt ’16, Brent J. Shapiro-Albert (former summer student), and Jacob E. Turner (former summer student), doctoral students at the University of West Virginia
  • Duncan Lorimer, professor and associate dean for research, University of West Virginia, former astronomer at the Arecibo Observatory
  • Zaven Arzoumanian, deputy principal investigator and science lead, NASA Goddard Spaceflight Center, former postdoctoral researcher at Cornell and
  • Timothy Dolch, assistant professor, Hillsdale College, former postdoctoral researcher at Cornell.

Cordes and Chatterjee are members of Cornell’s Carl Sagan Institute.

NANOGrav – of which Cornell is a founding member – is joint venture between the National Science Foundation and the Natural Sciences and Engineering Research Council of Canada. Both organizations provided funding.


Gravitational wave astronomy of single sources with a pulsar timing array

The stability of radio millisecond pulsars as celestial clocks allows for the possibility to detect and study the properties of gravitational waves (GWs) when the received pulses are timed jointly in a ‘Pulsar Timing Array’ (PTA) experiment. Here, we investigate the potential of detecting the GW from individual binary black hole systems using PTAs and calculate the accuracy for determining the GW properties. This is done in a consistent analysis, which at the same time accounts for the measurement of the pulsar distances via the timing parallax.

We find that, at low redshift, a PTA is able to detect the nano-hertz GW from super-massive black hole binary systems with masses of ∼10 8 –10 10 M less than ∼10 5 yrs before the final merger. Binaries with more than ∼10 3 –10 4 yr before merger are effectively monochromatic GW, and those with less than ∼10 3 –10 4 yr before merger may allow us to detect the evolution of binaries.

For our findings, we derive an analytical expression to describe the accuracy of a pulsar distance measurement via timing parallax. We consider 5 yr of bi-weekly observations at a precision of 15 ns for close-by (∼0.5–1 kpc) pulsars. Timing 20 pulsars would allow us to detect a GW source with an amplitude larger than 5 × 10 −17 . We calculate the corresponding GW and binary orbital parameters and their measurement precision. The accuracy of measuring the binary orbital inclination angle, the sky position and the GW frequency is calculated as functions of the GW amplitude. We note that the ‘pulsar term’, which is commonly regarded as noise, is essential for obtaining an accurate measurement for the GW source location.

We also show that utilizing the information encoded in the GW signal passing the Earth also increases the accuracy of pulsar distance measurements. If the GW is strong enough, one can achieve sub-parsec distance measurements for nearby pulsars with distance less than ∼0.5–1 kpc.


Astronomers find possible hints of gravitational waves

An international team of astronomers – including 17 Cornellians – report they have found the first faint, low-frequency whispers that may be gravitational waves from gigantic, colliding black holes in distant galaxies.

The findings were obtained from more than 12.5 years of data collected from the national radio telescopes at Green Bank, West Virginia, and the recently collapsed dish at the Arecibo Observatory, in Arecibo, Puerto Rico.

The research was announced Jan. 11 at a press conference at the American Astronomical Society’s national meeting, held online due to the COVID-19 pandemic. The press conference highlighted the research, “The NANOGrav 12.5-year Data Set: Search for an Isotropic Stochastic Gravitational-wave Background,” published Dec. 24 in The Astrophysical Journal Letters.

The astronomers are all participants in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project, which uses pulsars – rapidly spinning dense stars – that act as wave detectors and cosmic timekeepers.

Merging gargantuan black holes create gravitational waves that can send ripples through space-time and affect a pulsar’s timekeeping regularity – ultimately indicating that Earth’s position in the universe may have slightly shifted.

“We must be clear: We are not yet claiming to have detected gravitational waves,” said Shami Chatterjee, Ph.D. ’03, a Cornell principal research scientist in the College of Arts and Sciences’ (A&S) Department of Astronomy. “We have detected a signal that is consistent with the existence of gravitational waves, but we can’t prove that quite yet. We think this is the tip of the iceberg, but we have to actually demonstrate it to our own satisfaction.”

To get a sense of the size of these gravitational waves, recall the wave detection by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in early 2016, when scientists caught two black holes merging.

The merger set off kilohertz waves that were hundreds of kilometers in length, small enough to allow Earth-based detectors to capture them from kilometer-wide, land-based sensors. That finding confirmed a major prediction of Albert Einstein’s 1915 general theory of relativity.

In the NANOGrav case, gigantic black holes are in the process of merging.

“The masses we’re talking about are the giant black holes that are in the centers of galaxies,” said James Cordes, the George Feldstein Professor of Astronomy (A&S). “They are a billion times the mass of the sun. They’re monsters.”

And these monsters are generating nanohertz-scale gravitational quavers that are light-years in length, said Cordes. Thus, astronomers enlist pulsars to help detect these waves.

The paper notes that 47 pulsars were studied to gather this data currently the astronomers are using 80 pulsars. Cordes said the plan is for the project’s astronomers to use about 200 pulsars, once they secure telescope time on other radio telescopes – to replace the time lost at the Arecibo Observatory, which recently collapsed.

In addition to Cordes and Chatterjee, the other Cornellians who work on this project include:

  • Ross Jennings, doctoral candidate
  • H. Thankful Cromartie, NASA Einstein Postdoctoral Fellow
  • Adam Brazier, computational scientist, Cornell Center for Advanced Computing
  • Maura A. McLaughlin, Ph.D. ‘01, professor, West Virginia University, a member of NANOgrav and co-director of the Physics Frontier Center
  • Michael T. Lam, Ph.D. ’16, assistant professor, Rochester Institute of Technology
  • T. Joseph W. Lazio, Ph.D. ’97, chief scientist of the Interplanetary Network Directorate, Jet Propulsion Laboratory, California Institute of Technology
  • Dustin R. Madison, Ph.D. ’15, postdoctoral fellow, University of West Virginia
  • David L. Kaplan ’98, visiting associate professor, University of Wisconsin, Madison
  • Dan Stinebring M.S. ’78, Ph.D. ’82, emeritus professor of physics, Oberlin College
  • Caitlin A. Witt ’16, Brent J. Shapiro-Albert (former summer student), and Jacob E. Turner (former summer student), doctoral students at the University of West Virginia
  • Duncan Lorimer, professor and associate dean for research, University of West Virginia, former astronomer at the Arecibo Observatory
  • Zaven Arzoumanian, deputy principal investigator and science lead, NASA Goddard Spaceflight Center, former postdoctoral researcher at Cornell and
  • Timothy Dolch, assistant professor, Hillsdale College, former postdoctoral researcher at Cornell.

Cordes and Chatterjee are members of Cornell’s Carl Sagan Institute.

NANOGrav – of which Cornell is a founding member – is joint venture between the National Science Foundation and the Natural Sciences and Engineering Research Council of Canada. Both organizations provided funding.