NASA's Roman Poised to Transform Hunt for Elusive Neutron Stars

Isolated Neutron Star (Artist's Concept)

This artist’s concept shows an isolated neutron star as an ultra-dense stellar remnant, packing more mass than the Sun into a city-sized sphere and radiating energy as it slowly cools in the depths of space.

NASA’s upcoming Nancy Grace Roman Space Telescope will search for, and could measure the mass of, isolated neutron stars using astrometric microlensing. Credits Illustration: NASA, STScI, Ralf Crawford (STScI)

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Astronomers have long known that neutron stars, the crushed cores left behind after massive stars explode, should be scattered throughout the Milky Way galaxy. However, most of them are effectively invisible. A new study published in Astronomy and Astrophysics suggests NASA’s upcoming Nancy Grace Roman Space Telescope could spot them anyway.

Using detailed simulations of the Milky Way and Roman’s future observations, researchers showed the flagship observatory may be able to identify and characterize dozens of isolated neutron stars through a subtle effect called gravitational microlensing.

“Most neutron stars are relatively dim and on their own,” said Zofia Kaczmarek of Heidelberg University in Germany, who led the study. “They are incredibly hard to spot without some sort of help.”

Finding what’s invisible

Neutron stars pack more mass than the Sun into a sphere about the size of a city. Studying them helps us understand how stars live, die, and spread heavy elements throughout the universe. They also provide a chance to study what happens under the most extreme conditions (pressures and densities) imaginable.

Yet, unless they are pulsars that beam in radio wavelengths or glow in X-rays, they can remain hidden from even the most powerful telescopes.

Roman can search for them in a different way. When a massive object like a neutron star moves in front of a distant background star, its intense gravity warps spacetime and deflects the background star’s light. This microlensing effect briefly makes the background star brighter and appear offset from its true position in the sky.

While many telescopes can detect the temporary brightening, Roman can measure both the brightening (photometry) and the tiny positional shift (astrometry) of the lensed star with exceptional precision.

Because neutron stars are relatively massive, they produce a larger astrometric signal than lighter objects, allowing missions like Roman to not only detect them, but also weigh them in some cases, something that is nearly impossible with photometry alone.

“What’s really cool about using microlensing is that you can get direct mass measurements,” said paper co-author Peter McGill of Lawrence Livermore National Laboratory. “Photometry tells us that something passed in front of the star, but it’s the amount the star’s position shifts that tells us how massive that object is. By measuring that tiny deflection on the sky, we can directly weigh something that is otherwise unseen.”

Roman’s measurements could help astronomers determine whether there is a true gap between the masses of neutron stars and black holes and how fast neutron stars are moving.

Scientists are particularly interested in understanding the powerful “kicks” neutron stars receive when they are born in supernova explosions. These kicks can send them racing through the galaxy at hundreds of miles per second.

Huge surveys, high chance of payoff

The research team will utilize Roman’s future Galactic Bulge Time Domain Survey, which will monitor millions of stars at a time in vast images of the sky, taken at a high frequency.

“We’re going to get to work as soon as the data start coming in,” said McGill. “Even in the first months after commissioning, we expect to start identifying promising events.”

Even a relatively small number of confirmed detections could significantly improve models of stellar explosions and extreme matter.

“We don’t know the mass distribution of neutron stars, black holes, or where one ends and the other begins with any certainty,” McGill said. “Roman will really be a breakthrough in that.”

Although only a few thousand neutron stars have been detected so far, mostly as pulsars, scientists estimate there could be tens of millions to hundreds of millions in the Milky Way. Additionally, to date, researchers have only been able to measure the masses of neutron stars in binary pairings.

“We’re seeing a small sample that’s not representative of the big picture,” Kaczmarek said. “Even a single mass measurement would be very powerful. If we found just one isolated neutron star, it would already be incredibly stimulating to our research.”

Looking ahead

The study also highlights a creative use of the mission’s capabilities. While Roman’s survey is designed primarily to find exoplanets using photometric microlensing, its powerful astrometric capabilities open the door to entirely new discoveries with astrometric microlensing.

“This wasn’t part of the original plan,” said McGill. “But it turns out Roman’s astrometric capability is really good at detecting neutron stars and black holes, so we can add a whole new kind of science to Roman’s surveys.”

If the predictions hold true, the mission could provide the first large sample of isolated neutron stars discovered through their gravity alone, revealing a hidden population that has remained out of reach until now. Roman is expected to transform the study of microlensing and the hidden populations of objects in our galaxy, from rogue exoplanets to stellar remnants like neutron stars.

The Nancy Grace Roman Space Telescope is managed at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, with participation by NASA’s Jet Propulsion Laboratory in Southern California; Caltech/IPAC in Pasadena, California; the Space Telescope Science Institute in Baltimore; and a science team comprising scientists from various research institutions. The primary industrial partners are BAE Systems Inc. in Boulder, Colorado; L3Harris Technologies in Rochester, New York; and Teledyne Scientific & Imaging in Thousand Oaks, California.

Source: Space Telescope Science Institute (STScI)/News

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About This Release

Credits:

Media Contact:

Hannah Braun
Space Telescope Science Institute, Baltimore

Christine Pulliam
Space Telescope Science Institute, Baltimore

Permissions: Content Use Policy

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Radio Signals from the Edge of Extreme Stars

The illustration shows a pulsar (red sphere) and its strong magnetic field (yellow lines). As the stellar remnant rotates, narrow beams of radio waves (cones) sweep across the sky and become detectable as regular signals for observers on Earth. The beams originate close to the magnetic poles (yellow cones) but may also arise from a region farther out (blueish cone), as the new study suggests. The proportions and colours are not realistic and are for illustrative purposes only. © MPIfR

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To the point

• Astronomers analysed the radio and gamma-ray emission of nearly 200 extremely fast rotating pulsars.


• One-third of these millisecond pulsars show radio signals coming from two or more separate regions. Some of the isolated radio pulses line up perfectly with the emission of gamma-rays.


• The authors suggest that millisecond pulsars produce radio waves not just close to their surfaces, but also in a region far out, where magnetic fields sweep around at nearly the speed of light to keep up with the star’s rotation.

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A team of German and Australian astronomers found evidence that some of the fastest-spinning stars in the Universe broadcast radio waves from far beyond where scientists thought possible.

Pulsars are ultra-dense, rapidly spinning, and highly magnetised remnants of dead stars. They act like cosmic lighthouses, sending out regular pulses of radio waves and sometimes gamma rays in beams that sweep across the sky. A special class called millisecond pulsars spins hundreds of times per second and is among the most precise clocks in the Universe. For decades, astronomers believed that a pulsar’s radio signals are only produced close to the star’s surface, near its magnetic poles. The new study, published in the current issue of Monthly Notices of the Royal Astronomical Society, challenges that long-held idea.

An unexpected discovery

Michael Kramer from the Max Planck Institute for Radio Astronomy (MPIfR) in Germany and Simon Johnston from Australia’s national science agency, CSIRO, analysed radio observations of nearly 200 millisecond pulsars and compared them with gamma-ray data. The duo discovered something striking in this large data set: About one-third of millisecond pulsars show radio signals coming from two or more completely separate regions, with emission free gaps in between. In comparison, this behaviour occurs in only about 3% of slower rotating pulsars. Even more striking, many of these isolated radio pulses line up perfectly with gamma-ray flashes detected by NASA’s Fermi satellite — suggesting that both signals are produced in the same extreme region of space.

A surprising conclusion

To explain these patterns, the authors propose that millisecond pulsars produce radio waves in two very different places: one close to the star’s magnetic poles, as traditionally assumed, and another in a swirling “current sheet” just beyond the so-called light cylinder. Located farther out than the magnetic poles, the light cylinder marks the boundary where magnetic fields sweep around at nearly the speed of light to keep up with the star’s rotation. Depending on the observer's perspective on the pulsar, one sees radio emission from either near the surface, from far out, or from both regions. This gives rise to the unusual, broken-up radio profiles that puzzled astronomers for years. The “current sheet” of charged particles is already thought to be responsible for gamma-ray emission. The alignment of radio waves and gamma-rays can be explained through this shared place of origin.

The animation demonstrates the importance of perspective: Depending on the angle at which an observer sees the pulsar (red sphere), they will detect radio waves (cones) from near the magnetic poles, from a more distant region, or from both. This influences the appearance of the observed radio signals. Credit: Michael Kramer - Video

Exciting prospects and open questions

This discovery has several important consequences: More pulsars may be detectable than previously thought, because radio emission may not be limited to a narrow cone from close to the magnetic poles. Instead, it spreads over a wider range of directions. The finding also helps explain why astronomers often struggle to interpret the polarisation (orientation) of radio waves from millisecond pulsars. Furthermore, it suggests that nearly all gamma-ray millisecond pulsars also emit radio waves, even if those signals may be faint or difficult to detect. This raises new challenges for theory: Scientists now need to explain how stable radio pulses can be generated so far away from the star, in an extreme and turbulent environment.

“Millisecond pulsars are key tools for studying gravity, dense matter, and even gravitational waves. Understanding where their signals come from — and why they look the way they do — is essential for using them as precision instruments”, explains Michael Kramer. Co-author Simon Johnston adds: “This study shows that these tiny, fast-spinning stars are even more complex and surprising than we thought, broadcasting from both their surfaces and from the very edge of their magnetic reach.”

Source: Max Planck for Radio Astronomy/Press Releases

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Contacts:

Prof. Dr. Michael Kramer
Executive Director and Head of “Fundamental Physics in Radio Astronomy“ Research Dept.
Tel: +49 228 525-299
mkramer@mpifr-bonn.mpg.de
Max Planck Institute for Radio Astronomy, Bonn

Dr. Simon Johnston

Senior Principal Research Scientist, Australia Telescope National Facility
Contact via Rachel Rayner, CSIRO communications
Tel: +61 2 9372-4172 rachel.rayner@csiro.au
CSIRO, Australia’s national science agency

Dr. Nina Brinkmann
Press and Public Relations
Tel: +49 228 525-399
brinkmann@mpifr-bonn.mpg.de
Max Planck Institute for Radio Astronomy, Bonn

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Original publication

Michael Kramer and Simon Johnston
Radio emission from beyond the light cylinder in millisecond pulsars
Monthly Notices of the Royal Astronomical Society 547 (2026)

DOI

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Graphics

• pulsar 6.6 MB
• pulsar_annotated 2.46 MB

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NASA’s Hubble Revisits Crab Nebula to Track 25 Years of Expansion

PR Image heic2607a
Crab Nebula (2024 Hubble image)

PR Image heic2607b
Crab Nebula (new image from 1999/2000 data)

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Crab Nebula (2024 Hubble image, annotated)

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Crab Nebula (new image from 1999/2000 data, annotated)

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Videos


PR Video heic2607a
The Crab Nebula


PR Video heic2607b
Pan Video: The Crab Nebula (2024 Hubble image)


PR Video heic2607c
Pan Video: The Crab Nebula (new Hubble image from 1999/2000 data)

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Nearly a millennium ago, astronomers witnessed a brilliant new star blazing in the sky — a supernova so bright it was visible in daylight for weeks. Today, its expanding remnant, the Crab Nebula, continues to evolve 6,500 light-years away. First linked to historical records by Edwin Hubble, the nebula has since been studied in exquisite detail by the NASA/ESA Hubble Space Telescope, which has now revisited this ancient explosion to trace its ongoing expansion and transformation.

A quarter-century after its first observations of the full Crab Nebula, the Hubble Space Telescope has taken a fresh look at the supernova remnant. The Crab Nebula is the aftermath of SN 1054, located 6,500 light-years from Earth in the constellation Taurus.

The result is an unparalleled, detailed look at the aftermath of a supernova and how it has evolved over Hubble’s long lifetime. A paper detailing the new Hubble observation is published in The Astrophysical Journal.

The supernova remnant was discovered in the mid-18th century, and in the 1950s Edwin Hubble was among several astronomers who noted the close correlation between Chinese astronomical records of a supernova and the position of the Crab Nebula. The discovery that the heart of the Crab contained a pulsar — a rapidly rotating neutron star — that was powering the nebula’s expansion finally aligned modern observations and ancient records.

In its new image of the nebula, Hubble has captured extraordinary details of its filamentary structure, as well as the considerable outward movement of those filaments over 25 years, at a pace of 5.5 million kilometres per hour. Hubble is the only telescope with the combination of longevity and resolution capable of capturing these detailed changes.

For better comparison with the new image, Hubble’s 1999 image of the Crab was re-processed. The variation of colors in both of the Hubble images shows a combination of changes in local temperature and density of the gas as well as its chemical omposition.

The science team has noted that the filaments around the periphery of the nebula appear to have moved more compared to those in the centre and that rather than stretching out over time, they appear to have simply moved outward. This is due to the nature of the Crab as a pulsar wind nebula powered by synchrotron radiation, which is created by the interaction between the pulsar’s magnetic field and the nebula’s material. In other well-known supernova remnants, the expansion is instead driven by shockwaves from the initial explosion, eroding surrounding shells of gas that the dying star previously cast off.

The new, higher-resolution Hubble observations are also providing additional insights into the 3D structure of the Crab Nebula, which can be difficult to determine from a 2D image. Shadows of some of the filaments can be seen cast onto the haze of synchrotron radiation in the nebula’s interior. Counterintuitively, some of the brighter filaments in the latest Hubble images show no shadows, indicating they must be located on the far side of the nebula.

According to the science team, the real value of Hubble’s Crab Nebula observations is still to come. The Hubble data can be paired with recent data from other telescopes that are observing the Crab in different wavelengths of light. The NASA/ESA/CSA James Webb Space Telescope released its infrared-light observations of the Crab Nebula in 2024. Comparison of the Hubble image with other contemporary multiwavelength observations will help scientists put together a more complete picture of the supernova’s continuing aftermath, centuries after astronomers first wondered at a new little star twinkling in the sky.

Source: ESA/Hubble/News

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More information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

Image Credit: NASA, ESA, STScI, W. Blair (JHU). Image Processing: J. DePasquale (STScI)

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Links

• Release on NASA website
• Science paper

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Contacts

Bethany Downer
ESA/Hubble Chief Science Communications Officer
Email: Bethany.Downer@esahubble.org

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NuSTAR Observes a Millisecond Pulsar

An artist's impression of an accreting millisecond pulsar, showing a neutron star accreting matter from a companion star, which speeds it up to a spin period of a fraction of a second. As it rotates, the orientation of its magnetic field spins in and out of the line of sight, causing us to observe pulsations. Image credit: NASA/D. Berry. Download Image

Over the past week, NuSTAR observed the bright Galactic binary SAX J1808.4-3658 as part of an approved joint XMM-Newton and NuSTAR Target-of-Opportunity (ToO) program. SAX J1808 was the first ever discovered accreting millisecond pulsar and has been dormant for around three years before it recently increased in brightness again in a dramatic fashion, when the source was observed by Einstein Probe to have an X-ray flux exceeding the XMM/NuSTAR trigger threshold by more than a factor of 1000. The team has also triggered a 10-day-long ToO observation with IXPE, as well as requesting Director's Discretionary Time (DDT) ToO observations with XRISM, to explore the polarization and high-resolution spectral properties of the source. NuSTAR observations close to the start of IXPE observations will maximize the scientific return, probing the broadband outburst spectra beyond the IXPE, Einstein Probe, and XRISM bands to search for reflection features from the accretion disk as the outburst of this source proceeeds.

Authors: Daniel Stern (NuSTAR Deputy PI)

Source: NASA's Nuclear Spectroscopic Telescope Array (NuSTAR)/Weekly Highlights

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Telescope Tag-Team Discovers Galactic Cluster’s Bizarre Secrets

Terzan 5, located in the constellation Sagittarius, is a crowded globular cluster home to hundreds of thousands of stars.Ten unusual and exotic pulsars were recently discovered by an international team of astronomers from the U.S. National Science Foundation National Radio Astronomy Observatory, the Max Planck Institute for Gravitational Physics (Albert Einstein Institute) (AEI), and the Max Planck Institute for Radio Astronomy.Credit: US NSF, AUI, NSF NRAO, S. Dagnello. Hi-Res File

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U.S. National Science Foundation Green Bank Telescope teams up with South African Radio Astronomy Observatory MeerKAT Telescope, discovers ten strange and exotic pulsars

Towards the center of our Milky Way Galaxy, in the constellation Sagittarius, astronomers have discovered  10 monstrous neutron stars. These particular stars, called pulsars, reside together in globular cluster Terzan 5, a crowded home for hundreds of thousands of different types of stars. Pulsars are millions (or even billions) of times more dense than other stars and rotate rapidly, emitting bright pulses of light from their strong magnetic fields, making them a beacon for astronomers to find. In one of the most jam-packed places in our Milky Way, many pulsars in Terzan 5 have evolved into bizarre and eccentric forms.

Astronomers already knew that 39 pulsars call Terzan 5 home. With the teamwork of the U.S. National Science Foundation Green Bank Telescope (NSF GBT) and the South African Radio Astronomy Observatory’s MeerKAT Telescope, ten more have been added to the count. “It’s very unusual to find exotic new pulsars. But what’s really exciting is the wide variety of such weirdos in a single cluster,” shared Scott Ransom, a scientist with the U.S. National Science Foundation National Radio Astronomy Observatory (NSF NRAO). The discoveries were made by an international team of astronomers from NSF NRAO, the Max Planck Institute for Gravitational Physics (Albert Einstein Institute) (AEI), and the Max Planck Institute for Radio Astronomy.

The Meerkat Telescope was able to determine the rough location of each pulsar by tracking and timing how quickly they rotate, matched against twenty years of Terzan 5 observations taken by the NSF GBT, which revealed the bizarre and eccentric details of these stars. “Without the NSF Green Bank Telescope’s archive, we wouldn’t have been able to characterize these pulsars and understand their astrophysics,” adds Ransom. The archival NSF GBT data allowed astronomers to pinpoint the pulsars’ position on the sky, measure their specific movements, and see how their orbits changed over time.

Among the discoveries, astronomers saw two likely neutron stars pulled into each other’s orbit as a binary system. Out of 3,600 known pulsars in the Galaxy, only 20 have been identified as double neutron-star binaries. When pulsars pair off in binaries, the gravitational pull from one to the other can steal material and energy, causing one to spin even faster, becoming a millisecond pulsar. This pair could be a record breaker, with a new contender for fastest spinning pulsar in a double neutron-star system, and the longest orbit of its kind. The current record holder for fastest spinning pulsar already resides in Terzan 5. Only future observations will reveal the truth.

Astronomers also observed three new rare pulsar “spider” binary systems (in addition to five already known in the cluster) called Redbacks or Black Widows, depending on the types of companion stars that they have. A companion star falls into the orbit of a spider pulsar, where a web of plasma fills the space between the two (caused by outflows from the companion star due to the pulsar’s energy) slowly dissolving the companion over time.

The discovery of these strange pulsars allows scientists to better understand globular clusters, neutron stars, and even test Einstein’s theory of general relativity, along with expanding what is known about pulsar categories. The research team is already making plans to find even more in Terzan 5, with the support of volunteers. Citizen scientists who’d like to share in the excitement of this discovery can help at Einstein@Home. This project, led by scientists at AEI, has already discovered more than 90 new neutron stars.

The Green Bank Observatory, home of the GBT, and the National Radio Astronomy Observatory are major facilities of the U.S. National Science Foundation and are operated by Associated Universities, Inc.

This research was shared in the journal Astronomy & Astrophysics..

Read more at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute.).

Read more at the Max Planck Institute for Radio Astronomy.

Source:National Radio Astronomy Observatory (NRAO)/News

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Media contacts:

Jill Malusky,
NRAO & GBO News & Public Information Manager
jmalusky@nrao.edu

Benjamin Knispel,
Max Planck Institute for Gravitational Physics (Albert Einstein Institute)
benjamin.knispel@aei.mpg.de

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Monthly Roundup: Discovering, Modeling, and Characterizing Pulsars

Composite X-ray, optical, and infrared image of the Crab Nebula, which houses a pulsar at its center
Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA-JPL-Caltech

When a massive star goes supernova, the explosion can leave behind a pulsar: the core of a dead star containing 1–2 times the mass of the Sun in a sphere just 20 kilometers across. Pulsars are almost entirely composed of neutrons and spin extremely quickly — the fastest recorded pulsar spins 716 times every second, meaning that a point on its surface moves at roughly a quarter of the speed of light. Pulsars emit beams of radio waves from their poles, and an observer on Earth sees pulses of radio emission in time with the star’s rotation. The word pulsar comes from pulsating radio source.

Observing pulsars helps us understand the evolution of massive stars, provides a way to study the physics of ultra-dense materials, and gives us a means to search for the background gravitational hum of supermassive black holes in colliding galaxies. Today, we’ll take a look at three recent research articles that explore fundamental questions in pulsar science.

The field surrounding PSR J1032−5804 shown at, from left to right, radio, infrared, and visible wavelengths, as well as a composite of all three. Credit: Wang et al. 2024

How Do We Find Pulsars?

Jocelyn Bell Burnell discovered the first pulsar by chance in 1967, when the characteristic pulses popped up in radio observations taken with a new telescope. Today, researchers design surveys tuned to the particular properties of pulsars to make them stand out from other signals in the sky. Namely, radio surveys can search for sources with steep spectra — in other words, signals that are far brighter at low frequencies than at high frequencies — or strongly polarized light.

Ziteng Wang (Curtin University) and collaborators used the Australian Square Kilometre Array Pathfinder (ASKAP), a 36-dish radio interferometer, to search for circularly polarized signals from pulsars. In addition to known stars and pulsars, the observations pinpointed a strongly circularly polarized source with no known counterpart at other wavelengths. The team followed up on this promising discovery with the 64-meter Murriyang radio telescope at Parkes Observatory and found a pulsar with a rotation period of 78.72 milliseconds. The pulsar, cataloged as PSR J1032−5804, has an estimated age of 34,600 years, making it relatively young and possibly still associated with a visible supernova remnant. The team found a compact region of emission surrounding the pulsar, but they couldn’t rule out the possibility that the material belongs to unrelated nebulae.

PSR J1032−5804 is notable because its pulses are highly scattered by interstellar gas and dust. Highly scattered pulsar signals are hard to detect because scattering broadens and weakens the signal, especially at lower frequencies where pulsars should be at their brightest. Wang’s team has shown that searching at relatively high frequencies — the team’s observations were made at 3 gigahertz — is a viable way to detect scattered pulsars.

Simulation output showing the magnetic field lines (green curves) and plasma density (background color) in a pulsar’s magnetosphere. Credit: Bransgrove et al. 2023

How Do Pulsars Make Their Pulses?

Pulsars may be most famous for their characteristic pulses of radio emission, but the origin of those pulses is still under debate. To understand what powers these radio beacons, researchers use detailed simulations that track the behavior of individual particles to understand how they behave under the exotic conditions present at the surface of a pulsar. To date, localized simulations have been able to produce radio waves from a pulsar’s poles, and global simulations have discerned the source of pulsars’ gamma-ray pulses (10% or so of pulsars produce gamma-ray pulses in addition to radio pulses), but radio pulses have not yet been seen in global simulations.

Ashley Bransgrove (Columbia University and Princeton University) and collaborators carried out high-resolution global simulations of a pulsar’s magnetosphere: the region immediately surrounding a pulsar where its strong magnetic field dominates the motion of charged particles. The simulations show how the rapid rotation of the pulsar lofts charged particles from its surface and accelerates them, filling the magnetosphere with gamma rays and a dense sea of electrons and their positively charged counterparts, positrons. Near the pulsar’s poles and farther out in its magnetosphere, gaps form where the electric current is mismatched, and pairs of electrons and positrons are generated in these gaps. When the gaps discharge — think of a spark, or lightning — they excite waves in the plasma and, subsequently, electromagnetic waves. The emitted radiation is similar in frequency and luminosity to observed pulsars, suggesting that electric discharge may generate the radio waves that pulsars are known for.

The team notes that it’s too soon to apply their simulations to observations of individual pulsars, and more work is needed to understand the role of gamma-ray emission, explore the details of electron–positron pair production, and extend the work to pulsars whose spin axes and magnetic axes are misaligned.

The location of the Boomerang within the supernova remnant surrounding the pulsar PSR J2229+6114
Credit: Pope et al. 2024

How Do Pulsars Interact with Their Surroundings?

When pulsars are young, they’re swaddled in the gas and dust of their surrounding supernova remnants. This leads young pulsars to create a pulsar wind nebula: a glowing cloud of gas energized by winds of relativistic charged particles streaming off the pulsar. A recent article authored by the Nuclear Spectroscopic Telescope Array (NuSTAR) and Very Energetic Radiation Imaging Telescope Array System (VERITAS) collaborations presents multiwavelength observations of the Boomerang, a 10,000-year-old pulsar wind nebula well known for its complex structure.

The teams combined archival data from radio telescopes and the Chandra X-ray Observatory with newly collected data from NuSTAR, VERITAS, and the Fermi Gamma-ray Space Telescope to probe the nebula’s multiwavelength behavior. These observations revealed that the nebula appears far larger at radio wavelengths than at X-ray wavelengths, a common feature of pulsar wind nebulae due to the difference sources of emission: the nebula’s size at radio wavelengths is set by outflowing particles, while its size at X-ray wavelengths comes from the rate at which electrons lose energy as they spiral around magnetic field lines and emit X-rays. The nebula’s size even varies across X-ray wavelengths, appearing smaller at shorter wavelengths.

Judging from how the nebula’s size changes with wavelength, its overall energy output, and its X-ray emission over the past two decades, the authors provide a new estimate on its distance and magnetic field strength, finding it to be more distant and with a far weaker magnetic field than previously thought. By modeling how the nebula’s energy output may have evolved over time, the team also found that the Boomerang is, well, boomeranging! Roughly 1,000 years ago, a backwards-moving supernova shock wave crashed into the expanding nebula, crushing the nebula and temporarily reversing its expansion. Today, the nebula is re-expanding in the wake of the shock wave, showcasing how pulsars dynamically interact with their surroundings.

By Kerry Hensley

Source: American Astronomical Society/AAS-Nova

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Citation

“Discovery of a Young, Highly Scattered Pulsar PSR J1032-5804 with the Australian Square Kilometre Array Pathfinder,” Ziteng Wang et al 2024 ApJ 961 175. doi:10.3847/1538-4357/ad0fe8

“Radio Emission and Electric Gaps in Pulsar Magnetospheres,” Ashley Bransgrove et al 2023 ApJL 958 L9. doi:10.3847/2041-8213/ad0556

“A Multiwavelength Investigation of PSR J2229+6114 and Its Pulsar Wind Nebula in the Radio, X-ray, and Gamma-ray Bands,” I. Pope et al 2024 ApJ 960 75. doi:10.3847/1538-4357/ad0120

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Four Pulsars Discovered in New Survey

The supernova remnant 30 Doradus B encloses a pulsar at its center.
X-ray: NASA/CXC/Penn State Univ./L. Townsley et al.;
Optical: NASA/STScI/HST; Infrared: NASA/JPL/CalTech/SST;
Image Processing: NASA/CXC/SAO/J. Schmidt, N. Wolk, K. Arcand

A pilot survey using the world’s largest radio dish has led to the discovery of four pulsars, two of which are ultra-precise millisecond pulsars. This survey highlights the wealth of pulsars that await discovery at intermediate galactic latitudes.

An artist’s impression of a pair of pulsars.
Credit: Michael Kramer (Jodrell Bank Observatory, University of Manchester)

Small Stars with a Big Impact

When massive stars explode as supernovae, they can leave behind their extremely dense, collapsed cores in the form of neutron stars. Neutron stars spin rapidly and have strong magnetic fields, leading many of them to produce beams of radio emission along their poles. When these beams sweep across our field of view, we see brief, regular pulses of emission and call the objects pulsars.

Several thousand pulsars have been discovered in our galaxy, but there’s a need to find even more: pulsars provide a path to studying stellar evolution, the interiors of neutron stars, and even gravitational waves. Millisecond pulsars — those with the shortest rotation periods, around 10 milliseconds or less — are especially precious, as their pulses are exceptionally regular. By monitoring the arrival times of the pulses from many millisecond pulsars at once, researchers have found evidence for the gravitational wave background, which is thought to be the combined signals of millions of distant supermassive black hole binaries.

Pulse profiles of the four newly discovered pulsars.

Click to enlarge. Credit: Zhi et al. 2024

A Small FAST Survey

Where and how do we find pulsars? The word pulsar is short for pulsating radio source, and most pulsars are identified in surveys by their characteristic pulses of radio emission. Like most stars, pulsars are concentrated in the thin disk of our galaxy, but interstellar clouds of gas and dust in this region can scatter pulsar signals. Searching the area just above the galactic plane makes for easier pulsar discovery, and current evidence suggests that millisecond pulsars may be more common in these higher-latitude regions.

Using the Five-hundred Aperture Spherical Telescope (FAST) — the world’s largest radio dish — Qijun Zhi (Guizhou Normal University) and collaborators searched for pulsars in a small area of the sky about 5 degrees above the galactic midplane. The survey discovered four new pulsars and recovered all seven of the known pulsars in the search area. Of the four newly discovered pulsars, two are of the coveted millisecond variety, with rotation periods of 3.9 and 4.6 milliseconds. One of these two millisecond pulsars especially warrants further study, since it is bright enough to possibly be included in pulsar timing arrays in the future.

llustration of how galactic latitude is measured.
Credit: AAS Nova/Kerry Hensley

More Pulsars to Come

The pilot survey described in this study complements the efforts of other pulsar surveys. FAST is currently at work on the Commensal Radio Astronomy FAST Survey and the Galactic Plane Pulsar Survey, both of which aim to find pulsars at galactic latitudes below 10 degrees. These surveys have led to the discovery of roughly 800 pulsars so far, about 200 of which are millisecond pulsars.

Zhi and collaborators expect that many more pulsars await discovery at intermediate galactic latitudes, 5 to 15 degrees above the midplane of the Milky Way. Considering the success of their limited pilot study, the team expects that roughly 900 millisecond pulsars could be found in that region.

Citation

“Discovery of Four Pulsars in a Pilot Survey at Intermediate Galactic Latitudes with FAST,” Q. J. Zhi et al 2024 ApJ 960 79. doi:10.3847/1538-4357/ad0eca

By Kerry Hensley

Source: American Astronomical Society/AAS-Nova

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The Crab Nebula Seen in New Light by NASA's Webb

Crab Nebula (NIRCam and MIRI Image)
Credits> Image: NASA, ESA, CSA, STScI, Tea Temim (Princeton University)

Crab Nebula (Webb and Hubble Comparison)
Credits: Image: NASA, ESA, CSA, STScI, Jeff Hester (ASU), Allison Loll (ASU), Tea Temim (Princeton University)

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NASA’s James Webb Space Telescope has gazed at the Crab Nebula, a supernova remnant located 6,500 light-years away in the constellation Taurus. Since the recording of this energetic event in 1054 CE by 11th-century astronomers, the Crab Nebula has continued to draw attention and additional study as scientists seek to understand the conditions, behavior, and after-effects of supernovae through thorough study of the Crab, a relatively nearby example.

Using Webb’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument), a team led by Tea Temim at Princeton University is searching for answers about the Crab Nebula’s origins.

“Webb’s sensitivity and spatial resolution allow us to accurately determine the composition of the ejected material, particularly the content of iron and nickel, which may reveal what type of explosion produced the Crab Nebula,” explained Temim.

At first glance, the general shape of the supernova remnant is similar to the optical wavelength image released in 2005 from NASA’s Hubble Space Telescope : In Webb’s infrared observation, a crisp, cage-like structure of fluffy gaseous filaments are shown in red-orange. However, in the central regions, emission from dust grains (yellow-white and green) is mapped out by Webb for the first time.

Additional aspects of the inner workings of the Crab Nebula become more prominent and are seen in greater detail in the infrared light captured by Webb. In particular, Webb highlights what is known as synchrotron radiation: emission produced from charged particles, like electrons, moving around magnetic field lines at relativistic speeds. The radiation appears here as milky smoke-like material throughout the majority of the Crab Nebula’s interior.

This feature is a product of the nebula’s pulsar, a rapidly rotating neutron star. The pulsar’s strong magnetic field accelerates particles to extremely high speeds and causes them to emit radiation as they wind around magnetic field lines. Though emitted across the electromagnetic spectrum, the synchrotron radiation is seen in unprecedented detail with Webb’s NIRCam instrument.

To locate the Crab Nebula’s pulsar heart, trace the wisps that follow a circular ripple-like pattern in the middle to the bright white dot in the center. Farther out from the core, follow the thin white ribbons of the radiation. The curvy wisps are closely grouped together, outlining the structure of the pulsar’s magnetic field, which sculpts and shapes the nebula.

At center left and right, the white material curves sharply inward from the filamentary dust cage’s edges and goes toward the neutron star’s location, as if the waist of the nebula is pinched. This abrupt slimming may be caused by the confinement of the supernova wind’s expansion by a belt of dense gas.

The wind produced by the pulsar heart continues to push the shell of gas and dust outward at a rapid pace. Among the remnant’s interior, yellow-white and green mottled filaments form large-scale loop-like structures, which represent areas where dust grains reside.

The search for answers about the Crab Nebula’s past continues as astronomers further analyze the Webb data and consult previous observations of the remnant taken by other telescopes . Scientists will have newer Hubble data to review within the next year or so from the telescope’s reimaging of the supernova remnant. This will mark Hubble’s first look at emission lines from the Crab Nebula in over 20 years, and will enable astronomers to more accurately compare Webb and Hubble’s findings.

Want to learn more? Through NASA’s Universe of Learning, part of NASA’s Science Activation program, explore images of the Crab Nebula from other telescopes, a 3D visualization, data sonification, and hands-on activities. These resources and more information about supernova remnants and star lifecycles can be found at NASA’s Universe of Learning.

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency. NASA’s Universe of Learning materials are based upon work supported by NASA under cooperative agreement award number NNX16AC65A to the Space Telescope Science Institute, working in partnership with Caltech/IPAC, Center for Astrophysics | Harvard & Smithsonian, and Jet Propulsion Laboratory.

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About This Release

Credits:

Media Contact:

Abigail Major
Space Telescope Science Institute, Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Science: Tea Temim (Princeton University)

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

Source: NASA's James Webb Space Telescope/News

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Looking for a Dragonfly in the Sky

Composite radio and X-ray image of the Dragonfly pulsar wind nebula.
Adapted from Jin et al. 2023

Title: Hard X-ray Observation and Multiwavelength Study of the PeVatron Candidate Pulsar Wind Nebula “Dragonfly”
Authors: Jooyun Woo et al.
First Author’s Institution: Columbia Astrophysics Laboratory
Status: Published in ApJ

Figure 1: A multi-wavelength view of the Crab Nebula that shows the X-rays from the pulsar wind nebula (pinkish-white region at the center)
Credit: NASA, ESA, NRAO/AUI/NSF and G. Dubner (University of Buenos Aires)

Pulsar Wind Nebulae: Little Space Animals

Pulsar wind nebulae are cosmic particle accelerators found all over the Milky Way (and in other galaxies too!). They’re made by the winds of pulsars — rapidly rotating and highly magnetized neutron stars, which are remnants of massive stars — pushing out winds of particles into the environments around them. The most famous example of a pulsar wind nebula is the Crab Nebula, which can be seen in Figure 1 as the small, pinkish-white, tornado-esque structure located in the larger multicolored supernova remnant left over from the original star’s explosion around a thousand years ago.

The Crab Nebula isn’t the only pulsar wind nebula with a fun nickname; in fact, most of these nebulae and their associated supernova remnants are named after animals that they (very) vaguely resemble. There’s the Mouse, the Goose, and the Kookaburra, just to name a few — and of course, the topic of today’s article, the Dragonfly (see Figure 2). Besides slightly resembling animals, pulsar wind nebulae are also thought to produce the highest-energy particles we detect on Earth. A new catalog of the highest-energy gamma-rays ever seen (see this bite) either links or tentatively associates many of these energetic systems with pulsars or pulsar wind nebulae.

Figure 2: Radio (colour) and X-ray (contours) image of the Dragonfly pulsar wind nebula. Doesn’t it sort of look like a dragonfly? Credit:

Jin et al. 2023

Looking for the Dragonfly with All Sorts of Different (Wavelength) Eyes!

The authors of today’s article investigate the Dragonfly with multiple different telescopes that detect light across the electromagnetic spectrum to get a full picture of what’s going on with the particles accelerated in and around the nebula. The authors model the multi-wavelength emission to try to figure out if the Dragonfly is capable of accelerating particles (electrons, protons, and other things) up to petaelectronvolt (PeV; that’s a quadrillion electronvolts!) energies that then interact to make gamma rays, which would classify it as a PeVatron (a name that aptly describes any astronomical source that can accelerate particles up to PeV energies). We detect the highest-energy charged cosmic rays up to PeV energies, but we haven’t seen too many sources that emit gamma rays at these energies due to instrumental limitations and other things like photon absorption. Since cosmic rays (usually protons) get deviated in their travels to Earth by the swirling magnetic fields of the Milky Way, we need to search for neutral particles of similar energies, like photons (i.e., gamma rays) to find PeVatrons, since they trace a straight line back from the particle to its source.

Using model fitting, the authors can create and evolve a pulsar and pulsar wind nebula to match the observed data, which gives them information like the nebular age, the expected shape of the nebula’s emission, and whether or not it can be a PeVatron, among many other interesting clues that help narrow down what’s going on with the particles and material in this system.

In particular, one interesting thing the authors notice is that the shape of the Dragonfly is long and asymmetric in soft X-ray wavelengths (and potentially in other wavelengths, but it’s hard to say due to much coarser angular resolution; see Figure 3b). Usually we’d expect to see a more spherical shape, so the explanation for this could be that the pulsar that’s powering the nebula is zooming through space at an unusually high speed or, more likely, that the nebula lives within a supernova remnant that hasn’t been seen yet. The interaction of particles from the pulsar wind nebula with the supernova remnant can cause some funky shapes to appear in the surrounding material. The authors suggest that looking at the Dragonfly with a long exposure in radio wavelengths might be able to pick up signs of a supernova remnant that are overwhelmed in other wavelengths by the bright pulsar wind nebula to confirm this scenario.

By looking at the full multi-wavelength picture (see Figure 3), the authors note that the size of the pulsar wind nebula decreases with increasing energy in X-ray wavelengths (this isn’t apparent in Figure 3d, because the instrument isn’t able to resolve small structure and blurs everything out to look bigger than it is), meaning that the the nebula becomes a less efficient particle accelerator as we move to higher energies. By modelling this behaviour, the authors find a maximum particle energy of 1.4 PeV, meaning that the Dragonfly really can be a PeVatron.

Figure 3: The observed shape of the Dragonfly in a) radio, b) soft X-ray, c) hard X-ray, and d) very-high-energy gamma rays with X-ray contours in blue. The star or X in each figure marks the pulsar location. Adapted from Woo et al. 2023

Maybe a PeVatron? We’ll Have to Wait and See!

There’s still more work to do to figure out if we can actually see gamma rays at energies beyond a PeV from the Dragonfly and to figure out how particles are being transported around the nebula to get the weird asymmetric shape that today’s authors observed. More observations using existing radio, X-ray, and other instruments as well as future ultra-high-energy gamma-ray telescopes (like SWGO and CTAO-South) can help answer these questions and help us get an even more full picture of the Dragonfly.

Original astrobite edited by Lucie Rowland

Source: American Astronomical Society/AAS-Nova

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About the author, Samantha Wong:

I’m a graduate student at McGill University, where I study high energy astrophysics. This includes studying all sorts of extreme environments in the universe like active galactic nuclei, pulsars, and supernova remnants with the VERITAS gamma-ray telescope.

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

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Selections from 2022: A Pulsar in the Large Magellanic Cloud

A view of the Large Magellanic Cloud taken with the Visible and Infrared Survey Telescope for Astronomy
Credit: ESO/VMC Survey; CC BY 4.0

Editor’s Note: In these last two weeks of 2022, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume in January.

Total intensity (left) and circularly polarized intensity (right) images of part of the Large Magellanic Cloud at 888 megahertz, as seen by ASKAP. The zoomed-in images show the location of the newly discovered pulsar. Click to enlarge. Credit: Wang et al. 2022

Discovery of PSR J0523-7125 as a Circularly Polarized Variable Radio Source in the Large Magellanic Cloud

Main takeaway:

A team led by Yuanming Wang (The University of Sydney, Australia) reported the discovery of a pulsar — the dense, rapidly spinning remnant of a massive star’s core — using radio continuum data from the Australian Square Kilometre Array Pathfinder (ASKAP). The newfound pulsar is located in the Large Magellanic Cloud, a satellite galaxy of the Milky Way, and its discovery may pave the way for astronomers to find other extragalactic pulsars with unusual properties.

Why it’s interesting:

The newly discovered pulsar, PSR J0523−7125, is one of the most luminous known radio pulsars, but several aspects of its radio signal made it difficult to find: while most pulsars are identified via their brief flashes of radio emission, PSR J0523−7125’s pulses are uncharacteristically broad, and its radio emission falls off sharply at higher frequencies. Wang and collaborators observed the new pulsar as part of the Variables and Slow Transients (VAST) survey and identified it based on its high degree of circular polarization and lack of a multiwavelength counterpart.

Prospects for finding further pulsars:

This work by Wang and collaborators shows that radio surveys are a viable means of discovering pulsars with unusual pulse properties. The combination of circular polarization data with multiwavelength images is especially useful, allowing researchers to identify sources that emit circularly polarized light but are absent in optical images. The authors also posit that future searches with the Next Generation Very Large Array — a network of 263 radio dishes scheduled to begin construction in 2026 — could lead to the first discovery of a pulsar in another neighboring galaxy, Andromeda.

By Kerry Hensley  

 

Citation

Yuanming Wang et al 2022 ApJ 930 38. doi:10.3847/1538-4357/ac61dc

Source: American Astronomical Society/AAS - Nova

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Four Perspectives on Neutron Stars, Pulsars, and Magnetars By Kerry Hensley

Illustration of a neutron star emitting a jet.
Credit: ICRAR/University of Amsterdam

When a massive star explodes as a supernova, its core collapses into a city-sized sphere of neutrons called a neutron star. These extraordinarily dense stars — just one teaspoon of a neutron star would weigh billions of tons in Earth’s gravity — exhibit some of the most intriguing behavior in the universe: rapid rotation, beams of radio emission, and extremely strong magnetic fields. Today, we’ll introduce four recent research articles that explore different aspects of these stars.

Simulated light curves during an X-ray burst, showing the effects of incorporating different physics. A model without neutrino cooling (labeled “No DU” in reference to the neutrino cooling pathway called direct Urca), peaks at a lower luminosity than models incorporating neutrino cooling. Credit: Adapted from Dohi et al. 2022

Bursting, Cooling, and Bursting Again

Sometimes, neutron stars reveal themselves by interacting with other stars. When a neutron star gathers gas from a stellar companion, the gas can ignite on the star’s scorching surface, resulting in a sudden burst of X-rays. After this sudden influx of heat, how does the neutron star cool, and how is the cooling reflected in the star’s light curve? While this may seem like a simple question, the answer hinges on our understanding of the conditions within the neutron star’s interior as well as the characteristics of the gas being accreted.

In a recent publication, a team led by Akira Dohi (土肥明; Kyushu University, Japan) explored the issue of neutron star cooling with general relativistic stellar evolution models. Specifically, the team investigated the effects of cooling by emitting neutrinos — chargeless, nearly massless particles that scarcely interact with matter — which is expected to speed up the cooling rate. The authors found that neutrino cooling increases the time between outbursts but makes them brighter at their peak, though additional physics to be included in future modeling might suppress this effect.

Simulated pulses showing a change in the phase of the pulse due to the shifting motion of the sparks.
Credit: Adapted from Basu et al. 2022

Simulating Pulsar Sparks

Rahul Basu (University of Zielona Góra, Poland) and collaborators reported on simulations of conditions very close to the surface of a neutron star that emits beams of radio emission. Neutron stars that emit beamed radio waves are called pulsars for the way the beams sweep across our field of view, generating what we see as pulses of emission. Near a pulsar’s surface, extremely high temperatures and strong magnetic and electric fields combine forces to summon a sea of charged particles that are then accelerated to relativistic speeds.

Basu and collaborators focused on a phenomenon called sparking, in which charged particles jump the gap between the pulsar’s surface at its poles and its plasma-rich magnetosphere. The team’s modeling demonstrated that a pulsar’s poles are tightly filled with constant sparks, and the arrangement of these sparks slowly shifts over time. By modeling the emission associated with the simulated sparks, the team showed that the shifting motion of the sparks appears to be responsible for the observed periodic variations in the phases and amplitudes of some pulsars’ pulses.

Example of a pulse observed with the Giant Metrewave Radio Telescope.
Credit: Adapted from Sharma et al. 2022

Pulsars Probing Gravitational Waves

By studying large groups of pulsars, astronomers hope to learn about something seemingly unrelated: gravitational waves. Pulsars provide a method to detect gravitational waves by way of these stars’ impeccable timekeeping abilities — because a pulsar’s radio beat is so reliable, the slight distortion of space caused by a passing gravitational wave should impact the arrival times of a pulsar’s pulses.

However, there’s a complication to this technique: spatial and temporal changes in the interstellar medium plasma can also affect when a pulsar’s radio pulses arrive at Earth. In order to compensate for the effect of the interstellar medium, we need to be able to make precise observations of pulsars across a range of radio frequencies. In a recent research article, Shyam Sharma (Tata Institute of Fundamental Research, India) and collaborators tested a pulsar-timing measurement technique using the Giant Metrewave Radio Telescope, which is highly sensitive to low-frequency radio waves. Sharma and coauthors showed that observing using a wide frequency band yields results comparable to typical narrowband observations, indicating that this technique could be used to disentangle the effects of the interstellar medium and more accurately time the pulses of arrays of pulsars, opening a new window onto gravitational waves.

Temperature maps of the top of a magnetar’s crust (top) and the magnetar’s surface (bottom) after a hotspot is injected.
Credit: De Grandis et al. 2022

Magnetic Outbursts

As if neutron stars could get any wilder: some neutron stars, dubbed magnetars, have extremely strong magnetic fields and exhibit frequent X-ray flares. While the cause of these X-ray outbursts is still unknown, some researchers have suggested that they arise from a sudden upwelling of magnetic energy beneath the magnetar’s crust, creating a hot spot that cools gradually over days or months.

To understand how the injection of heat into a magnetar’s crust might create the spectral features seen during X-ray outbursts, Davide De Grandis (University of Padova, Italy) and coauthors employed a three-dimensional magnetothermal model of hotspot formation and cooling. This model allowed the team to study the effects of asymmetrical hot spots under a magnetar’s crust for the first time. The team was able to confirm that these hot spots can be responsible for outbursts, though we’ll have to wait for future research to fully explore the evolution of the spectral features generated during these events.

By Kerry Hensley

Citation

“Impacts of the Direct Urca and Superfluidity inside a Neutron Star on Type I X-Ray Bursts and X-Ray Superbursts,” A. Dohi et al 2022 ApJ 937 124. doi:10.3847/1538-4357/ac8dfe

“Two-dimensional Configuration and Temporal Evolution of Spark Discharges in Pulsars,” Rahul Basu et al 2022 ApJ 936 35. doi:10.3847/1538-4357/ac8479

“Wide-band Timing of GMRT-discovered Millisecond Pulsars,” Shyam S. Sharma et al 2022 ApJ 936 86. doi:10.3847/1538-4357/ac86d8

“Three-dimensional Magnetothermal Simulations of Magnetar Outbursts,” Davide De Grandis et al 2022 ApJ 936 99. doi:10.3847/1538-4357/ac8797

Source: American Astronomical Society - AAS Nova

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