FAQ for Astronomers & the General Public

  1. What is NANOGrav?
    • The NANOGrav (North American Nanohertz Observatory for Gravitational Waves) Physics Frontiers Center is a collaboration of scientists working to detect and study very low frequency (about nanohertz) gravitational waves. Using an array of high-precision millisecond pulsars, we seek to measure the influence of gravitational waves on the Earth. At these frequencies, we expect to detect a stochastic background of merging supermassive black holes, individual inspiral and merger events, and possibly cosmic strings and inflationary gravitational waves. NANOGrav consists of astrophysicists at over a dozen institutions throughout the United States and Canada. We count among our ranks senior faculty and researchers, postdoctoral scholars, graduate and undergraduate students, and even high school students through our educational and outreach partnerships.

  2. What telescopes does NANOGrav use?

  3. What kind of science is being performed by NANOGrav?
    • A brief summary of the scientific endevors undertaken by NANOGrav can be found below this section. For more information, you can find a detailed list of all of our publications located here. Should you happen upon a term you are not familiar with while reading our publications, please reference our glossary document.

  4. How many pulsars does NANOGrav observe and how are they chosen?
    • The number grows over time: as of March 2020, 79 pulsars were observed with Arecibo and/or the GBT. We observe millisecond pulsars (generally periods under 10 millisecond) from which we can achieve high timing precision (1 microsecond or better).

  5. How do I get access to the latest timing data?
    • NANOGrav data releases are located at data.nanograv.org. There the public can access published datasets and request access to raw observations. If you would like to access unpublished or under-development datasets, consider joining NANOGrav as an Associate Member.

  6. How does NANOGrav relate to other pulsar timing array efforts?

FAQ for New NANOGrav Members

  1. When are general meetings?
    • There are twice-annual in-person Collaboration meetings, usually in October/November and March/April. Upcoming meetings are listed on our Events page found here. There are also monthly NANOGrav General Telecons hosted via Zoom.

  2. What mailing lists are there? How do I sign up?

  3. How do I get access to the collaboration's wiki?

  4. What are the publication rules?
    • The publication policy for NANOGrav-related papers can be found here.

  5. What are the rules about giving talks?
    • The conference/presentation policy can be found here.

  6. How do I become an Associate Member?
    • Membership in NANOGrav is open to any researcher who is willing to contribute to NANOGrav's goals of detecting and studying gravitational waves via pulsar timing. We welcome applications for Associate Membership from people who have not yet participated in NANOGrav, or who may be working in a related field. After filling out this form, their application will be presented to the full collaboration. If there are no objections by a Full Member, the application is accepted. You can find more information regarding our membership policies here.

  7. How do I become a Full Member?
    • Full membership carries additional responsibilities and duties, including annual reviews of contributions. A researcher must have been an Associate member for at least 12 months prior to application. You can find more information regarding our membership policies here.

  8. Who is on the Management Team?
    • The Management Team is responsible for the on-going management of projects related to NANOGrav's science goals. It consists of the Chair of NANOGrav, four elected Senior Personnel, and the Principal Investigators (PIs) of any large grants that are directly related to NANOGrav's mission and that involve a significant number of NANOGrav members or institutions. The list of current Management Team members can be found here.

  9. What are the Working Groups? How do I join? When are their meetings?
    • The list of active Working Groups and their chairs are listed here. All NANOGrav Associate and Full members are welcome to attend any working group telecon. Meeting times are listed on the NANOGrav Google calendar.

  10. How do I join a telecon?
    • We use Zoom for all NANOGrav telecons. The instructions are sent out with telecon agendas which are sent out prior to each meeting. You may also phone into telecons.

  11. I have a question that isn’t answered here. How can I get it added?

How it Works

Millisecond pulsars rotate with incredible stability, allowing them to be used as precise clocks. The time of arrival (TOA) of a pulse can usually be measured to δ/(S/N), where δ is the pulse width (typically a few hundred microseconds) and S/N is the signal-to-noise. For many millisecond pulsars, this results in TOAs measured with ≲ few μs precision. TOAs are used to construct a timing model that is coherent in pulse phase, i.e. it accounts for every single rotation of the pulsar by modeling the rotational, astrometric, and (when applicable) binary parameters of the system. The residuals in these timing models (the difference between the predicted and measured TOAs) can have an RMS scatter as little as 100 nanoseconds over timescales of many years.

The Hellings-Downs curve, which shows the expected angular correlation in pulsar timing residuals due to gravitational waves.

NANOGrav seeks to detect and study gravitational waves by looking for their influence in timing residuals from an array of ultra-precise millisecond pulsars. Gravitational waves passing through the Solar system will lead to correlations in the timing residuals between pairs of pulsars, even though the influence on the pulsars themselves will not be correlated across the array. This "Earth term" depends only on the baseline between pulsar pairs and is given by the Hellings-Downs curve. We are sensitive to gravitational waves with periods between the cadence of pulsar timing observations (weeks) to the span of our dataset (years), which corresponds to nanohertz frequencies. This allows NANOGrav to probe a unique phase space that is complementary to interferometric gravitational wave detectors. The sensitive of our array increases as we add more pulsars, improve TOA precision and the RMS of our timing residuals (which depend on instrumentation and our understanding of the pulsars and propagation effects through the interstellar medium), and time. The latter factor is thanks to the expected nature of the gravitational wave spectrum, which increases in amplitude as we move to lower frequencies.

Primary Science Goals

Our primary science goal is to directly detect the influence of gravitational waves on space-time within the next decade, thus ushering in a new era of low-frequency gravitational wave astronomy. We are already placing stringent constraints on the stochastic supermassive black hole background, which in turn constrains the black hole merger rate out to redshift z~1. After detection, our increasing sensitivity will allow us to:

  • fully determine the black hole merger rate from 0 < z < 1
  • determine or constrain the solution to the "last parsec problem," thereby bridging the evolutionary gap between dynamical friction and gravitational wave emission
  • map the history of structure formation over cosmic time
  • identify and characterize individual supermassive black hole binaries
  • probe the highly nonlinear regime of strong-field general relativity through the observation of gravitational wave bursts with memory

NANOGrav will also be able to explore large portions of parameter space for cosmic strings. These topological defects are predicted by a large class of cosmological models, from symmetry breaking models to string-theory-inspired models. NANOGrav will either confirm their existence or place severe limits on properties such as the energy scale at which they form. A cosmic string detection would reveal information about high energy physics unattainable via accelerator experiments.

Secondary Science Goals

NANOGrav uses high-precision millisecond pulsars as gravitational wave detectors, observing over two dozen sources at regular intervals. This produces valuable secondary science including a greater understanding of the dynamic interstellar medium, the stability of millisecond pulsar rotation and emission mechanisms, the discovery of new pulsars, and a detailed characterization of individual binary pulsar systems. The latter may include precise neutron star mass measurements that constrain the equation of state of ultra-dense matter and allow us to study general relativity in ever more diverse and extreme environments. Our data set can also be used as an independent check of Solar System ephemerides and universal time standards.

Technical Requirements

NANOGrav uses millisecond pulsars as clocks whose signals respond to the minuscule changes in space-time caused by gravitational waves. This deviation is expected to be less than ~100 nanoseconds, which drives our technical requirements—radio telescopes and backends capable of determining pulse times of arrival to nanosecond precision for an array of dozens of high-precision millisecond pulsars distributed across the sky. NANOGrav's key instruments are the William E. Gordon Telescope at the Arecibo Observatory and the Robert C. Byrd Green Bank Telescope. Both telescopes are absolutely vital; Arecibo because of its unparalleled sensitivity and the GBT because of its own excellent sensitivity and ability to observe over 85% of the sky. NANOGrav members have equipped both telescopes with state-of-the-art GPU-based backends. We currently observe 79 pulsars every two weeks at both telescopes and cooperate closely with two large area pulsar surveys, the PALFA survey at Arecibo and the GBNCC survey at the GBT. The NSF divestment from the GBT is a serious threat to our science goals because there is no other North American telescope that can replace it. NANOGrav is working with our partners to secure the future of the GBT.