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How can I hear (or at least detect) a pulsar at home?

How can I hear (or at least detect) a pulsar at home?


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Scott Manley's video Using Relativistic Raytracing &X-Rays To See Detail on Surface Of Neutron Star talks about X-ray measurements using the NICER X-ray telescope attached to the International Space Station (Wikipedia, in SE: 2 & 3), results which can also be read about in arXiv and these recent papers. Since I'm on Earth I'll need to use radio waves instead.

I understand the signal will be weak and below the noise for a small setup so I'll have to collect a lot of data and do some type of folding analysis. But before I can even make an estimate of signal and noise levels I'll need to choose a few "strong" pulsars and go look up their radio spectral distribution and compare it to thermal and and sky noise spectra.

Also based on frequency I can then know better what kind of antenna can be used; if I can get away with an array of wires like the early days or I'd need a dish.

Is there something like a "Top 10 pulsars of all time" site which has a characterization of some "popular" objects that may have strong signals that would also list their period?

Are there other issues I might not have thought about yet?


Interesting questions - I believe I have answers to them.

You mentioned folding analysis - yes, you will need to do folding analysis to find pulsars - the majority of pulsars are found with what are called prepfold plots - here is some software that is very popular, but you can do this yourself. The general principle is that if you separate a signal at a time interval equal to the period of the pulsar and stack the resulting sections of the signal, you're effectively doing the equivalent of "image stacking" as you would do with images you take in a camera, which will boost the signal to noise ratio of the pulsar you're trying to look at.

The best bet for a small setup would be the Vela pulsar - here is a list of significant pulsars. The Vela is the brightest pulsar in the radio part of the EM spectrum (as per the link, which is from Wikipedia, so take its reliability with a grain of salt), so I would assume that's your best bet in trying to detect a pulsar.

As for antennas or dishes, I would think a dish would work best. You're going to want some decently sensitive equipment to detect a pulsar, so I would recommend a proper dish made for collecting radio waves.

And lastly, you would want to consider which frequencies the target pulsar emits at and check which ones your receiver can collect.

I think you've pretty much covered all the other issues; now you just need supplies and money :).


8 extremely rare 'millisecond pulsars' discovered inside globular clusters

These "cosmic clocks" can help researchers answer big questions in physics.

An international team of astronomers has discovered eight rare millisecond pulsars hiding inside dense clusters of stars surrounding the Milky Way.

A pulsar is a neutron star — city-sized stellar objects packed with a mass of at least 1.4 times the mass of our sun, which emerge from the explosive deaths of their parent stars — that gives off two beams of radio waves at each pole, due to its strong magnetic field, while also rapidly spinning because of its incredibly large mass. From our perspective, they look like flashing stars, visible only when the beams shine directly at us.

"The vast majority of pulsars rotate once every few hundreds of milliseconds or more," or a handful of times a second, lead author Alessandro Ridolfi, a postdoctoral research fellow at the Astronomical Observatory of Cagliari in Italy, told Live Science. "A millisecond pulsar, on the other hand, is a pulsar that spins hundreds of times per second or, equivalently, once every few milliseconds."

In a new study, Ridolfi and his colleagues used the MeerKAT telescope — an array of 64 individual satellite dishes run by the South African Radio Astronomy Observatory (SARAO) — to search specifically for millisecond pulsars, which are much more rare than slower spinning pulsars. To do this, they focused on nine globular clusters — a collection of stars that are bound together by their own gravity and orbit outside the edge of a galaxy — surrounding the Milky Way they found eight millisecond pulsars within five of those clusters, making it one of the biggest millisecond pulsar studies so far.


Listening for Gravitational Waves Using Pulsars

To explore low-frequency gravitational waves, researchers look to a natural experiment in the sky called a pulsar timing array.

One of the most spectacular achievements in physics so far this century has been the observation of gravitational waves, ripples in space-time that result from masses accelerating in space. So far, there have been five detections of gravitational waves, thanks to the Laser Interferometer Gravitational-Wave Observatory (LIGO) and, more recently, the European Virgo gravitational-wave detector. Using these facilities, scientists have been able to pin down the extremely subtle signals from relatively small black holes and, as of October, neutron stars.

But there are merging objects far larger whose gravitational wave signals have not yet been detected: supermassive black holes, more than 100 million times more massive than our Sun. Most large galaxies have a central supermassive black hole. When galaxies collide, their central black holes tend to spiral toward each other, releasing gravitational waves in their cosmic dance. Much as a large animal like a lion produces a deeper roar than a tiny mouse's squeak, merging supermassive black holes create lower-frequency gravitational waves than the relatively small black holes LIGO and similar ground-based experiments can detect.

"Observing low-frequency gravitational waves would be akin to being able to hear bass singers, not just sopranos," said Joseph Lazio, chief scientist for NASA's Deep Space Network, based at NASA's Jet Propulsion Laboratory, Pasadena, California, and co-author of a new study in Nature Astronomy.

To explore this uncharted area of gravitational wave science, researchers look not to human-made machines, but to a natural experiment in the sky called a pulsar timing array. Pulsars are dense remnants of dead stars that regularly emit beams of radio waves, which is why some call them "cosmic lighthouses." Because their rapid pulse of radio emission is so predictable, a large array of well-understood pulsars can be used to measure extremely subtle abnormalities, such as gravitational waves. The North American Nanohertz Observatory for Gravitational Waves (NANOGrav), a Physics Frontier Center of the National Science Foundation, is one of the leading groups of researchers using pulsars to search for gravitational waves.

The new Nature Astronomy study concerns supermassive black hole binaries -- systems of two of these cosmic monsters. For the first time, researchers surveyed the local universe for galaxies likely to host these binaries, then predicted which black hole pairs are the likeliest to merge and be detected while doing so. The study also estimates how long it will take to detect one of these mergers.

"By expanding our pulsar timing array over the next 10 years or so, there is a high likelihood of detecting gravitational waves from at least one supermassive black hole binary," said Chiara Mingarelli, lead study author, who worked on this research as a Marie Curie postdoctoral fellow at Caltech and JPL, and is now at the Flatiron Institute in New York.

Mingarelli and colleagues used data from the 2 Micron All-Sky Survey (2MASS), which surveyed the sky from 1997 to 2001, and galaxy merger rates from the Illustris simulation project, an endeavor to make large-scale cosmological simulations. In their sample of about 5,000 galaxies, scientists found that about 90 would have supermassive black holes most likely to merge with another black hole.

While LIGO and similar experiments detect objects in the final seconds before they merge, pulsar timing arrays are sensitive to gravitational wave signals from supermassive black holes that are spiraling toward each other and will not combine for millions of years. That's because galaxies merge hundreds of millions of years before the central black holes they host combine to make one giant supermassive black hole.

Researchers also found that while bigger galaxies have bigger black holes and produce stronger gravitational waves when they combine, these mergers also happen fast, shortening the time period for detection. For example, black holes merging in the large galaxy M87 would have a 4-million-year window of detection. By contrast, in the smaller Sombrero Galaxy, black holes mergers typically take about 160 million years, offering more opportunities for pulsar timing arrays to detect gravitational waves from them.

Black hole mergers generate gravitational waves because, as they orbit each other, their gravity distorts the fabric of space-time, sending ripples outward in all directions at the speed of light. These distortions actually shift the position of Earth and the pulsars ever so slightly, resulting in a characteristic and detectable signal from the array of celestial lighthouses.

"A difference between when the pulsar signals should arrive, and when they do arrive, can signal a gravitational wave,"Mingarelli said. "And since the pulsars we study are about 3,000 light-years away, they act as a galactic-scale gravitational-wave detector."

Because all supermassive black holes are so distant, gravitational waves, which travel at the speed of light, take a long time to arrive at Earth. This study looked at supermassive black holes within about 700 million light-years, meaning waves from a merger between any two of them would take up to that long to be detected here by scientists. By comparison, about 650 million years ago, algae flourished and spread rapidly in Earth's oceans -- an event important to the evolution of more complex life.

Many open questions remain about how galaxies merge and what will happen when the Milky Way approaches Andromeda, the nearby galaxy that will collide with ours in about 4 billion years.

"Detecting gravitational waves from billion-solar-mass black hole mergers will help unlock some of the most persistent puzzles in galaxy formation," said Leonidas Moustakas, a JPL research scientist who wrote an accompanying "News and Views" article in the journal.


Students Discover Millisecond Pulsar, Help in the Search for Gravitational Waves

A special project to search for pulsars has bagged the first student discovery of a millisecond pulsar – a super-fast spinning star, and this one rotates about 324 times per second. The Pulsar Search Collaboratory (PSC) has students analyzing real data from the National Radio Astronomy Observatory’s (NRAO) Robert C. Byrd Green Bank Telescope (GBT) to find pulsars. Astronomers involved with the project said the discovery could help detect elusive ripples in spacetime known as gravitational waves.

“Gravitational waves are ripples in the fabric of spacetime predicted by Einstein’s theory of General Relativity,” said Dr. Maura McLaughlin, from West Virginia University. “We have very good proof for their existence but, despite Einstein’s prediction back in the early 1900s, they have never been detected.”

Four other pulsars have been discovered by high school students participating in this project.

Pulsar hunters Sydney Dydiw of Trinity High School, Emily Phan of George C. Marshall High School, Anne Agee of Roanoke Valley Governor's School, and Jessica Pal of Rowan County High School. Not pictured: Max Sterling of Langley High School. Credit: NRAO

“When you discover a pulsar, you feel like you’re walking on air! It is the best experience you can ever have,” said student co-discoverer Jessica Pal of Rowan County High School in Kentucky. “You get to meet astronomers and talk to them about your experience. I still can’t believe I found a pulsar. It is wonderful to know that there is something out there in space that you discovered.”

The other student involved in the discovery was Emily Phan of George C. Marshall High School in Virginia, who along with Pal found the millisecond pulsar on January 17, 2012. It was later confirmed by Max Sterling of Langley High School, Sydney Dydiw of Trinity High School, and Anne Agee of Roanoke Valley Governor’s School, all in Virginia.

“I am considering pursuing astronomy as a career choice,” said Agee. “The Pulsar Search Collaboratory has opened my eyes to how fun astronomy can be!”

Once the pulsar candidate was reported to NRAO, a followup observing session was scheduled on the giant, 17-million-pound telescope. On January 24, 2012, observations confirmed that the pulsar was real.

Pulsars are spinning neutron stars that sling “lighthouse beams” of radio waves around as they rotate. A neutron star is what is left after a massive star explodes at the end of its “normal” life. With no nuclear fuel left to produce energy to offset the stellar remnant’s weight, its material is compressed to extreme densities. The pressure squeezes together most of its protons and electrons to form neutrons hence, the name “neutron star.” One tablespoon of material from a pulsar would weigh 10 million tons.

On January 24, 2012, observations with the Green Bank Telescope at 800 MHz confirmed that the signal was astronomical and zeroed in on its position. Pulsars are brighter at lower frequencies (like 350 MHz, above) than at higher frequencies, and so the confirmation plot is noisier than the original data. Since this pulsar spins so fast, it may be used as part of the pulsar timing array used to detect gravitational waves. Courtesy NRAO.

The object that the students discovered is a special class of pulsars called millisecond pulsars, which are the fastest-spinning neutron stars. They are highly stable and keep time more accurately than atomic clocks.

Astronomers don’t know much about them, however. But because of their stability, these pulsars may someday allow astronomers to detect gravitational waves.

Millisecond pulsars, however, could hold the key to that discovery. Like buoys bobbing on the ocean, pulsars can be perturbed by gravitational waves.

“Gravitational waves are invisible,” said McLaughlin. “But by timing pulsars distributed across the sky, we may be able to detect very small changes in pulse arrival times due to the influence of these waves.”

Millisecond pulsars are generally older pulsars that have been “spun up” by stealing mass from companion stars, but much is left to discover about their formation.

“This latest discovery will help us understand the genesis of millisecond pulsars,” said Dr. Duncan Lorimer, who is also part of the project. “It’s a very exciting time to be finding pulsars!”

Robert C. Byrd Green Bank Telescope CREDIT: NRAO/AUI/NSF

The PSC is a joint project of the National Radio Astronomy Observatory and West Virginia University, funded by a grant from the National Science Foundation. The PSC includes training for teachers and student leaders, and provides parcels of data from the GBT to student teams. The project involves teachers and students in helping astronomers analyze data from the GBT.

Approximately 300 hours of the observing data were reserved for analysis by student teams. These students have been working with about 500 other students across the country. The responsibility for the work, and for the discoveries, is theirs. They are trained by astronomers and by their teachers to distinguish between pulsars and noise.

The PSC will continue through the 2012-2013 school year. Teachers interested in participating in the program can learn more at this link. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.


Fermi Discovers Unusual Gamma-Ray Pulsar

A gamma-ray pulsar is a compact neutron star that accelerates charged particles to relativistic speeds in its extremely strong magnetic field. This process produces gamma radiation, violet, far above the surface of the compact remains of the star, while radio waves, green, are emitted over the magnetic poles in the form of a cone. The rotation sweeps the emission regions across the terrestrial line of sight, making the pulsar light up periodically in the sky (NASA / Fermi / Cruz de Wilde)

The newly discovered pulsar J1838-0537 is radio-quiet, very young, and, during the observation period, experienced the strongest rotation glitch ever observed for a gamma-ray-only pulsar.

Pulsars are superlative cosmic beacons. These compact neutron stars rotate about their axes many times per second, emitting radio waves and gamma radiation into space. Pure gamma-ray pulsars are difficult to identify because their characteristics, such as its sky position, the period of rotation and its change in time, are unknown. And astronomers can only determine their approximate position in the sky from the original Fermi observations. They must therefore check many combinations of these characteristics in a blind search, which requires a great deal of computing time.

The team used algorithms originally developed for the analysis of gravitational-wave data to conduct a particularly efficient hunt through the Fermi data.

“By employing new optimal algorithms on our ATLAS computer cluster, we were able to identify many previously-missed signals,” said Dr Bruce Allen, Director of the Albert Einstein Institute (AEI) in Hannover, Germany, and co-author of the study that will be published in the Astrophysical Journal Letters.

The gamma-ray pulsar J1838-0537 is located towards the Scutum constellation, which is above the southern horizon in the summer sky. This detailed map shows the position of the pulsar, yellow, which is invisible to terrestrial telescopes, in a simulated view of the sky (Stellarium / AEI / Knispel)

The name of the new pulsar comes from its celestial coordinates. “The pulsar is, at 5,000 years of age, very young. It rotates about its own axis roughly seven times per second and its position in the sky is towards the Scutum constellation,” said lead author Dr Holger Pletsch of the AEI. “After the discovery we were very surprised that the pulsar was initially only visible until September 2009. Then it seemed to suddenly disappear.”

Only a complex follow-up analysis enabled the team to solve the mystery of pulsar J1838-0537: it did not disappear, but experienced a sudden glitch after which it rotated 38 millions of a Hertz faster than before. “This difference may appear negligibly small, but it’s the largest glitch ever measured for a pure gamma-ray pulsar,” Dr Allen said. And this behavior has consequences.

“If the sudden frequency change is neglected, then after only eight hours, a complete rotation of the pulsar is lost in our counting, and we can no longer determine at which rotational phase the gamma-ray photons reach the detector aboard Fermi,” Dr Pletsch explained. The ‘flashing’ of the neutron star then disappears. If the researchers take the glitch into account and correct the change in rotation, the pulsar shows up again in the observational data.

The precise cause of the glitches observed in many young pulsars is unknown. Astronomers consider ‘star quakes’ of the neutron star crust or interactions between the superfluid stellar interior and the crust to be possible explanations.

“Detecting a large number of strong pulsar glitches makes it possible to learn more about the inner structure of these compact celestial bodies,” said Dr Lucas Guillemot of the Max Planck Institute for Radio Astronomy in Bonn, the second author of the study.

After the discovery in data from the Fermi satellite, the researchers pointed the radio telescope in Green Bank at the celestial position of the gamma-ray pulsar. In an observation of almost two hours and by analyzing a further, older, one-hour observation of the source they found no indications of pulsations in the radio range, indicating that J1838-0537 is a rare gamma-ray-only pulsar.

Bibliographic information: Pletsch HJ et al. 2012. PSR J1838-0537: Discovery of a young, energetic gamma-ray pulsar. Accepted for publication in the Astrophysical Journal Letters arXiv: 1207.5333v1


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Detecting Pulsars (Rotating Neutron Stars) with an RTL-SDR

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  • A pulsar is a rotating neutron star that emits a beam of electromagnetic radiation
  • If this beam points towards the earth, it can then be observed with a large dish antenna and a radio, like the RTL-SDR
  • The abstract of the paper reads:

Quick Answer: How Are Pulsars Detected

  • Neutron stars are detected from their electromagnetic radiation
  • Neutron stars are usually observed to pulse radio waves and other electromagnetic radiation, and neutron stars observed with pulses are called pulsars. Therefore, periodic pulses are …

How can I hear (or at least detect) a pulsar at home

The general principle is that if you separate a signal at a time interval equal to the period of the pulsar and stack the resulting sections of the signal, you're effectively doing the equivalent of "image stacking" as you would do with images you take in a camera, which will boost the signal to noise ratio of the pulsar you're trying to look at.

Pulsars: The Universe's Gift to Physics

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  • Pulsars are neutron stars that emit beams of radio waves outward from the poles of their magnetic fields
  • When their rotation spins a beam across the Earth, radio telescopes detect that as a "pulse" of radio waves
  • By precisely measuring the timing of such pulses, astronomers can use pulsars for unique "experiments" at the frontiers of modern

Listening for Gravitational Waves Using Pulsars NASA

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Pulsars are dense remnants of dead stars that regularly emit beams of radio waves, which is why some call them "cosmic lighthouses." Because their rapid pulse of radio emission is so predictable, a large array of well-understood pulsars can be used to measure extremely subtle abnormalities, such as gravitational waves.

Pulsars Astronomy – National Radio Astronomy Observatory

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  • Artist’s depiction of a pulsar with the central, spinning neutron star and its powerful magnetic field (blue)
  • Coming out of the poles are jets of charged particles escaping the star (yellow)
  • As the star spins, the beam swings past, and we detect a pulse of radio waves.

Neutron Stars and Pulsars Astronomy 801: Planets, Stars

  • The first neutron stars to be detected were observed by radio telescopes as regularly repeating pulses of radio light with periods of about 1 second
  • These objects are called pulsars, and they happen to be the neutron stars oriented such that the Earth lies in the path of their lighthouse beam.

Detecting Gravitational Waves With Pulsars

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  • We've talked about gravitational waves and we've talked about pulsars now we can learn how pulsars can help us "see" gravitational waves

Pulsar Timing Method Las Cumbres Observatory

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  • Pulsar Timing is the method that was used in 1992 by Aleksander Wolszczan and Dale Frail to detect the first confirmed exoplanets
  • These exoplanets orbit a pulsar, which is a rapidly rotating neutron star.A neutron star is the extremely dense remnant of a star that exploded as a supernova
  • As they rotate, pulsars emit intense electromagnetic radiation that is detected on Earth as regular and

Neutron Stars, Pulsars, and Magnetars

  • Designed by Antony Hewish and used by Jocelyn Bell to detect pulsars
  • Consists of two wooden vertical supports, one wooden cross support, and a section of copper wire and cables
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How to detect the shortest-period binary pulsars in the

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  • Download PDF Abstract: We discuss a multimessenger strategy to detect radio pulses from Galactic binary neutron stars in a very tight orbit with the period shorter than 10 min
  • On one hand, all-sky surveys by radio instruments are inefficient for detecting faint pulsars in very tight binaries due partly to the rarity of targets and primarily to the need of correction for severe Doppler smearing.

How to build a radio telescope in your garage that can

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  • There's no special requirement for a radio telescope to observe a pulsar
  • In fact, you can observe it with regular optical telescope if you know where to look
  • The only thing needed is for the beam from the pulsar to point our way
  • If not, then it will be almost impossible to detect, even with the best radio telescope.

A Lab to Detect Radio Pulsars Using a Remotely Accessed 18

"A Lab to Detect Radio Pulsars Using a Remotely Accessed 18-Meter Radiotelescope." Paper presented at the 2018 Conference on Laboratory Instruction Beyond …

How to detect the shortest period binary pulsars in the

  • We discuss a multimessenger strategy to detect radio pulses from Galactic binary neutron stars in a very tight orbit with the period shorter than 10 min
  • On one hand, all-sky surveys by radio instruments are inefficient for detecting faint pulsars in very tight binaries due partly to the rarity of targets and primarily to the need of correction for severe Doppler smearing.

Pulsars at 50: Still going strong Astronomy Magazine

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  • The objects revealed by the scruff — dubbed “pulsars” — turned out to be smaller than a city but more powerful than the Sun
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North American Nanohertz Observatory for Gravitational Waves

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  • NANOGrav uses the Galaxy itself to detect gravitational waves with the help of objects called pulsars — exotic, dead stars that send out pulses of radio waves with extraordinary regularity
  • This is known as a Pulsar Timing Array, or PTA.

Pulsar Web Could Detect Low-Frequency Gravitational Waves

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  • In 2007, NANOGrav began observing a set of the fastest-rotating pulsars to try to detect tiny shifts caused by gravitational waves
  • Pulsars emit beams of radio waves, some of which sweep across Earth once every rotation
  • Astronomers detect this as a rapid pulse of radio emission
  • Most pulsars rotate several times a second.

A Lab to Detect Radio Pulsars Using a Remotely Accessed 18

A Lab to Detect Radio Pulsars Using a Remotely Accessed 18-Meter Radiotelescope Norman Jarosik and Daniel Marlowy Joseph Henry Laboratories of Physics, Princeton University, New Jersey 08544, USA yPresenting author An undergraduate laboratory experiment where students use an 18-m radio telescope to observe radio pulsars is described.

A New Search Technique for Short Orbital Period Binary Pulsars

  • We describe a new and efficient technique, which we call sideband or phase-modulation searching, that allows one to detect short-period binary pulsars in observations longer than the orbital period
  • The orbital motion of the pulsar during long observations effectively modulates the phase of the pulsar signal, causing sidebands to

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Astronomers Use Pulsars to Listen for Gravitational Waves

  • Astronomers Use Pulsars to Listen for Gravitational Waves
  • This computer simulation shows the collision of two black holes, which produces gravitational waves
  • “By expanding our pulsar timing array over the next 10 years or so, there is a high likelihood of detecting gravitational waves from at least one supermassive black hole

The World's Largest Telescope Has Detected Pulsars, Can

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New FAST discoveries shed light on pulsars

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Such a survey can detect pulsars with a flux density down to 5 microJy, about a magnitude weaker than previous surveys by other radio telescopes over the world.

Pulsar web could detect low-frequency gravitational waves

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  • Pulsars emit beams of radio waves, some of which sweep across Earth once every rotation
  • Astronomers detect this as a rapid pulse of radio emission

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NANOGrav Finds Possible ‘First Hints’ of Low-frequency Gravitational Waves

In data gathered and analyzed over 13 years, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) found an intriguing low-frequency signal that may be attributable to gravitational waves. Caused by the movements of incredibly massive objects, such as black holes orbiting each other or neutron stars colliding, gravitational waves are ripples in space-time that cannot be observed by traditional telescopes.

NANOGrav researchers studying the signals from distant pulsars—small, dense stars that rapidly rotate, emitting beamed radio waves, much like a lighthouse—used radio telescopes to collect data that may indicate the effects of gravitational waves. Their research was presented in two studies published in the January 2021 issue of Astrophysical Journal Supplements .

“This announcement brings together a collection of recent papers and is the first demonstration that the detection of a signal in the dataset that may be attributable to gravitational waves,” said Elizabeth Ferrara, an associate research scientist in the Department of Astronomy at the University of Maryland and a NASA research scientist who is a co-author of the study. “At the moment, the signal is significant, but NANOGrav is not yet able to pin the source to gravitational waves. However, this is a necessary first step in the process of opening the next window on the gravitational universe.”

Further studies will help the researchers confirm whether they have detected gravitational waves and where they came from.

“It is incredibly exciting to see such a strong signal emerge from the data,” said Joseph Simon, lead researcher on the research papers. “However, because the gravitational-wave signal we are searching for spans the entire duration of our observations, we need to carefully understand our noise. This leaves us in a very interesting place, where we can strongly rule out some known noise sources, but we cannot yet say whether the signal is indeed from gravitational waves. For that, we will need more data.”

NANOGrav has been able to rule out some effects caused by things 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.

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.

“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, National Science Foundation (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 is an NSF Physics Frontiers Center (PFC). Maura McLaughlin, 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 data analysis over the past six years.”

NANOGrav created its pulsar timing array by studying 47 of the most stably rotating “millisecond pulsars,” as reported in the 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 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 isn’t apparent when studying any individual pulsar, but in aggregate, they add up to a significant signature.

Potential Next Steps

In order 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 signal is too weak 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.

At the same time, NANOGrav is developing techniques to ensure the detected signal could not be from another source. NanoGrav researchers 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.

“Trying to detect gravitational waves with a pulsar timing array requires patience,” said Scott Ransom, from the National Radio Astronomy Observatory, and the current chair of NANOGrav. “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.”

Like light from distant objects, gravitational waves are a cosmic messenger signal—one that holds great potential for understanding “dark” objects, like black holes. In 2015, NSF’s Laser Interferometer Gravitational-Wave Observatory (LIGO) made the first direct observation of gravitational waves.

LIGO and its counterparts, Virgo in Europe and Kagra in Japan, use purpose-built interferometry facilities to detect high-frequency gravitational waves. However, unlike the transient signals detected by LIGO, Virgo and Kagra, low-frequency gravitational waves are persistent, requiring many years of data to detect. Over the past decade, NANOGrav used existing radio telescopes to search for evidence of these low-frequency gravitational waves, which have the potential to help answer longstanding questions in astrophysics, including how massive black holes form and how galaxies merge.

This story was adapted from text provided by NANOGrav.

This work is supported by the National Science Foundation (NSF) Physics Frontiers Center (Award No. 1430284). NANOGrav uses data from two NSF-supported instruments: the Green Bank Telescope a facility of the National Science Foundation operated in West Virginia under cooperative agreement by Associated Universities, Inc. and Arecibo Observatory, a facility of the National Science Foundation operated in Puerto Ricounder cooperative agreement (#AST-1744119) by the University of Central Florida (UCF) in alliance with Universidad Ana G. Méndez (UAGM) and Yang Enterprises (YEI), Inc.

Media Relations Contact: Kimbra Cutlip, 301-405-9463, [email protected]

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September 18th: Pulsar Search Collaboratory

Date: September 18, 2009

Title: Pulsar Search Collaboratory

Podcaster: Sue Ann Heatherly from NRAO

Description: Join Lucas Bolyard, a sophomore at a small high school in West Virginia, and Rachel Rosen, an astronomer at the National Radio Astronomy Observatory to learn about the Pulsar Search Collaboratory, an NSF funded program that enables high school students to get interested in science and technology careers while they search their own data for new pulsars. Tune in. We have an announcement to make!

Bio: Sue Ann Heatherly is the Education Officer at the NRAO Green Bank WV site. She comes to astronomy by way of biology (BA in 1981), and science education (MA in 1985) She visited the Observatory as a teacher in 1987 and knew she’d found Camelot. She has been employed with the NRAO since 1989.

Today’s sponsor: This episode of � Days of Astronomy” is sponsored by the National Radio Astronomy Observatory, celebrating Five Decades of Training Young Scientists through summer programs. Explore the hidden universe in radio at www.nrao.edu.

Pulsar Search Collaboratory
Dr. Rachel Rosen
Lucas Bolyard

SUE ANN HEATHERLY: Welcome to this edition of 365 Days of Astronomy podcasts. My name is Sue Ann Heatherly. I work for the National Radio Astronomy Observatory in Green Bank, West Virginia, and I’m going to be your host for this edition.

Today’s podcast is all about pulsars, and a program called the Pulsar Search Collaboratory. As you may already know from tuning into some of the previous 365 Days of Astronomy podcasts, pulsars are stellar corpses. When stars more massive than our Sun go supernova, a super dense core is created, composed mostly of neutrons. These objects have super strong magnetic fields, too, and rotate. Some can rotate about once per second, while others can rotate nearly a thousand times per second. Radio telescopes have discovered the most pulsars, because they emit lighthouse-like beams of radio waves. As the neutron stars spin, we observe these beams as they sweep by the Earth. Because the spin rates of pulsars are incredibly predictable, astronomers can use pulsars to study things like Einstein’s Theory of Relativity.

Pulsars have been used indirectly to detect gravitational radiation. And, one day, astronomers hope to directly detect gravitational waves using pulsars. This is one of the many reasons we need to find more of them. The Pulsar Search Collaboratory is a program that does just that.

Joining us today is Dr. Rachel Rosen. Dr. Rosen is the project director for an NSF-funded project called the Pulsar Search Collaboratory. So, welcome to the program, Rachel. Thanks for joining us today.

DR. RACHEL ROSEN: Thank you.

SUE ANN HEATHERLY: So, tell us, first of all, what the Pulsar Search Collaboratory is. That’s a mouth full.

DR. RACHEL ROSEN: The Pulsar Search Collaboratory is a program funded by the National Science Foundation that is designed to engage students in actual scientific astronomical research. Uh, we’re working with kids in West Virginia and in other states. They get to actually look through data that has never been looked through before to look for new pulsars.

SUE ANN HEATHERLY: So, how is it that this data happened to be that these students get a chance to look through it for new pulsars? Tell us that story.

DR. RACHEL ROSEN: In 2007 the Green Bank Telescope, which is the world’s largest fully steerable radio telescope, had to go under repairs for a track replacement, and during this time the telescope wasn’t able to move in any direction and which is usually bad for most astronomers, but for us it turned out to be a good thing. Because we kept the telescope immobilized, and as the sky drifted overhead, we just collected a lot of data. And some of this data went to the astronomical community to look for new pulsars. And we, in addition, got some data for high school students.

SUE ANN HEATHERLY: This data that was collected over the summer, while the GBT track was being replaced, how much of it is there?

DR. RACHEL ROSEN: We got about three hundred hours worth of data, which translates to about thirty terabytes worth of data. Uh, and then, in addition, we are collecting more data as well. So, this is an active project, and so we’re continually adding more data that students can look through.

SUE ANN HEATHERLY: Well, tell us about your role as the project director. What do you do to make the Pulsar Search Collaboratory happen?

DR. RACHEL ROSEN: Most of what I do is, I interact with the students and the teachers on a regular basis. Uh, these . . . we . . . the teachers and the students come to Green Bank for the summer. The teachers come for two weeks, and then an additional third week with their students, and we teach them all about pulsars and why we think they’re fun and interesting things to study, and then they go back to their schools and they form teams to look through this data to look for new pulsars. As the program director, I interact with the teachers and the students, and anytime the students find anything interesting, we talk about it, we have discussions, we have online classes, uh, we do follow-up observations of any potentially interesting things that students find.

SUE ANN HEATHERLY: So, you are their ask-an-astronomer astronomer is that right?

DR. RACHEL ROSEN: I am.

SUE ANN HEATHERLY: What kinds of questions do you get?

DR. RACHEL ROSEN: Uh, I get lots of questions about, uh, RFI, which is radio frequency interference, and how it affects our data. Uh, I get questions about how the telescope works and how we collect the data, and how we, uh, turn this, the signals that we receive from space, into something the students can analyze.

SUE ANN HEATHERLY: Do you find that these students are actually capable of analyzing this data and, uh, finding new pulsars?

DR. RACHEL ROSEN: Absolutely. They come to Green Bank and we go and visit the schools, and the students just get a wonderful grasp of what they’re looking at, and they are understanding the science behind the plots that they’re looking at.

SUE ANN HEATHERLY: How many students are involved, and have any of them found a pulsar yet?

DR. RACHEL ROSEN: The program has been going on for one year, and we have, uh, over a hundred active students involved. Uh, we’re about to start a second year, and more students would become involved then, as well. And one student has found a astronomical detection . . . uh . . . of some kind of transient signal coming from outer space. We’re very excited about that.

SUE ANN HEATHERLY: Looming on the horizon, how many detections do you expect students to make? How many discoveries could they make?

DR. RACHEL ROSEN: Uh. . .we expect in, uh, the data, the . . .the original data that was taken – to find at least ten pulsars. We have no idea how many transient objects they could find. There could be many more than that. And there could be potentially more pulsars in the new data that we’re collecting as well.

SUE ANN HEATHERLY: Very, very cool. Thanks so much for joining us today, Rachel.

DR. RACHEL ROSEN: Absolutely. I’m glad to be here.

SUE ANN HEATHERLY: We take a break here and travel to South Harrison High School to talk with Lucas Bolyard, a sophomore, who made this discovery. I asked him to tell the story of how he discovered an astronomical object in the Pulsar Search Collaboratory data and how it made him feel.

LUCAS BOLYARD: We go to Pulsar Search Collaboratory dot com and, uh, we look at the different, uh, data plots that the GBT took while it was down for maintenance. I’ve looked at, roughly, about sixty or seventy plots. It was in March. And I was at home, actually. It was on the weekend. And. . .I. . .I didn’t really have anything to do, so I thought, “Hey, I’ll just get online and see if I can’t find a pulsar. I got on, looked through a data set didn’t really see anything. But then I got to the single pulse plots and saw a plot that looked like it might be a pulsar, but it had a lot of RFI. So, I reported it to Rachel and Dr. McLaughlin. It, it almost got dismissed as, as just RFI, but, uh, then, Maura thought it looked pretty good, and there was a pulsar in with the RFI.

We waited a few months, and uh. . .and we finally got time on the GBT, and we did follow-up observations, which didn’t show anything. So, at that time, I was getting kind of worried. But then I learned about something called an “RRAT,” which is basically a pulsar that turns kind of on and off for short periods of time. Dr. McLaughlin said that that would explain why we haven’t been seeing it.

And in July I was actually on site at the GBT for a Pulsar Collaboratory workshop, and I think it was on Wednesday morning. Duncan came into the room and, uh, asked me if this plot reminded me of something. And he held up my plot and, uh, I said, “Yeah, that’s the pl. . .that’s the plot I found in, uh. . .in March.” And he said, “Well, here’s” – well, we went back and looked at the raw data – “and here’s the raw data.” And you could see that there was something in the raw data which confirmed that it definitely was something. I was excited, and I was really tired, because the night before we got time on the GBT. But that just kind of made me get full of energy and. . .uh, well, my, my family was really excited for me. I tried to explain it to them, but they didn’t understand what it is that they’re excited for me anyway. My friends were really excited, because they think I’m going to be famous and everything.

As of a year ago, I wouldn’t have even thought about wanting to become an astronomer, but this has kind of given me second thoughts. Making this discovery has made me very excited to get into a scientific field. It’s a lot of hard work, but it’s worth it.

Getting to use the world’s largest, uh, fully movable telescope was really exciting. We had to wake up at about two o’clock in the morning to use the. . .to use the Green Bank Telescope, because that was when our time was. And by the time we were finished, it was probably about 3:30. So, we went to sleep and got up at seven o’clock in the morning. And that was the morning before I figured out that I had discovered the pulsar. It made me feel really good about myself, because I thought, “Hey, I discovered something this big it’s. . .it’s a big deal.”

SUE ANN HEATHERLY: I think we’d all agree with that. It is a big deal. That was Lucas Bolyard, a sophomore at South Harrison High School in Harrison County, West Virginia. You can learn more about his discovery later this month when the official press release comes out, but, for now, let it be known that you all are the first to hear of Lucas Bolyard’s discovery of a rotating radio transient object in the Pulsar Search Collaboratory data.


Milky Way’s Youngest Pulsar Confirmed

In this composite image of Kes 75, high-energy X-rays observed by Chandra are colored blue and highlight the pulsar wind nebula surrounding the pulsar, while lower-energy X-rays appear purple and show the debris from the explosion. Image credit: X-rays – NASA / CXC / NCSU / S. Reynolds optical – PanSTARRS.

After some massive stars run out of nuclear fuel, then collapse and explode as supernovas, they leave behind dense stellar nuggets called ‘neutron stars.’

Rapidly rotating and highly magnetized neutron stars produce a lighthouse-like beam of radiation that astronomers detect as pulses as the pulsar’s rotation sweeps the beam across the sky.

The rapid rotation and strong magnetic field of the Kes 75 pulsar, which is located about 19,000 light-years from Earth, have generated a wind of energetic matter and antimatter particles that flow away from the pulsar at near the speed of light.

This pulsar wind has created a large, magnetized bubble of high-energy particles called a pulsar wind nebula, seen as the blue region surrounding the pulsar.

The Chandra data taken in 2000, 2006, 2009, and 2016 show changes in Kes 75’s pulsar wind nebula with time.

Between 2000 and 2016, the Chandra observations reveal that the outer edge of the pulsar wind nebula is expanding at a remarkable 2 million mph (894 km per second).

This high speed may be due to the pulsar wind nebula expanding into a relatively low-density environment.

“It is expanding into a gaseous bubble blown by radioactive nickel formed in the explosion and ejected as the star exploded,” said Dr. Stephen Reynolds and his colleagues from North Carolina State University.

“This nickel also powered the supernova light, as it decayed into diffuse iron gas that filled the bubble.”

If so, this gives the astronomers an insight into the very heart of the exploding star and the elements it created.

The expansion rate also tells the scientists that Kes 75 exploded about 500 years ago as seen from Earth.

Unlike other supernova remnants from this era such as Tycho and Kepler, there is no known evidence from historical records that the explosion that created Kes 75 was observed.

The findings were published in the Astrophysical Journal (arXiv.org preprint).

Stephen P. Reynolds et al. 2018. Expansion and Brightness Changes in the Pulsar-wind Nebula in the Composite Supernova Remnant Kes 75. ApJ 856, 133 doi: 10.3847/1538-4357/aab3d3


Listening for Gravitational Waves Using Pulsars

One of the most spectacular achievements in physics so far this century has been the observation of gravitational waves, ripples in space-time that result from masses accelerating in space.

So far, there have been five detections of gravitational waves, thanks to the Laser Interferometer Gravitational-Wave Observatory (LIGO) and, more recently, the European Virgo gravitational-wave detector. Using these facilities, scientists have been able to pin down the extremely subtle signals from relatively small black holes and, as of October, neutron stars.

But there are merging objects far larger whose gravitational wave signals have not yet been detected: supermassive black holes, more than 100 million times more massive than our Sun. Most large galaxies have a central supermassive black hole. When galaxies collide, their central black holes tend to spiral toward each other, releasing gravitational waves in their cosmic dance. Much as a large animal like a lion produces a deeper roar than a tiny mouse's squeak, merging supermassive black holes create lower-frequency gravitational waves than the relatively small black holes LIGO and similar ground-based experiments can detect.

"Observing low-frequency gravitational waves would be akin to being able to hear bass singers, not just sopranos," said Joseph Lazio, chief scientist for NASA's Deep Space Network, based at NASA's Jet Propulsion Laboratory, Pasadena, California, and co-author of a new study in Nature Astronomy.

To explore this uncharted area of gravitational wave science, researchers look not to human-made machines, but to a natural experiment in the sky called a pulsar timing array. Pulsars are dense remnants of dead stars that regularly emit beams of radio waves, which is why some call them "cosmic lighthouses." Because their rapid pulse of radio emission is so predictable, a large array of well-understood pulsars can be used to measure extremely subtle abnormalities, such as gravitational waves. The North American Nanohertz Observatory for Gravitational Waves (NANOGrav), a Physics Frontier Center of the National Science Foundation, is one of the leading groups of researchers using pulsars to search for gravitational waves.

The new Nature Astronomy study concerns supermassive black hole binaries -- systems of two of these cosmic monsters. For the first time, researchers surveyed the local universe for galaxies likely to host these binaries, then predicted which black hole pairs are the likeliest to merge and be detected while doing so. The study also estimates how long it will take to detect one of these mergers.

"By expanding our pulsar timing array over the next 10 years or so, there is a high likelihood of detecting gravitational waves from at least one supermassive black hole binary," said Chiara Mingarelli, lead study author, who worked on this research as a Marie Curie postdoctoral fellow at Caltech and JPL, and is now at the Flatiron Institute in New York.

Mingarelli and colleagues used data from the 2 Micron All-Sky Survey (2MASS), which surveyed the sky from 1997 to 2001, and galaxy merger rates from the Illustris simulation project, an endeavor to make large-scale cosmological simulations. In their sample of about 5,000 galaxies, scientists found that about 90 would have supermassive black holes most likely to merge with another black hole.

While LIGO and similar experiments detect objects in the final seconds before they merge, pulsar timing arrays are sensitive to gravitational wave signals from supermassive black holes that are spiraling toward each other and will not combine for millions of years. That's because galaxies merge hundreds of millions of years before the central black holes they host combine to make one giant supermassive black hole.

Researchers also found that while bigger galaxies have bigger black holes and produce stronger gravitational waves when they combine, these mergers also happen fast, shortening the time period for detection. For example, black holes merging in the large galaxy M87 would have a 4-million-year window of detection. By contrast, in the smaller Sombrero Galaxy, black holes mergers typically take about 160 million years, offering more opportunities for pulsar timing arrays to detect gravitational waves from them.

Black hole mergers generate gravitational waves because, as they orbit each other, their gravity distorts the fabric of space-time, sending ripples outward in all directions at the speed of light. These distortions actually shift the position of Earth and the pulsars ever so slightly, resulting in a characteristic and detectable signal from the array of celestial lighthouses.

"A difference between when the pulsar signals should arrive, and when they do arrive, can signal a gravitational wave," Mingarelli said. "And since the pulsars we study are about 3,000 light-years away, they act as a galactic-scale gravitational-wave detector."

Because all supermassive black holes are so distant, gravitational waves, which travel at the speed of light, take a long time to arrive at Earth. This study looked at supermassive black holes within about 700 million light-years, meaning waves from a merger between any two of them would take up to that long to be detected here by scientists. By comparison, about 650 million years ago, algae flourished and spread rapidly in Earth's oceans -- an event important to the evolution of more complex life.

Many open questions remain about how galaxies merge and what will happen when the Milky Way approaches Andromeda, the nearby galaxy that will collide with ours in about 4 billion years.

"Detecting gravitational waves from billion-solar-mass black hole mergers will help unlock some of the most persistent puzzles in galaxy formation," said Leonidas Moustakas, a JPL research scientist who wrote an accompanying "News and Views" article in the journal.