The 11-year mood swings of an X-ray binary

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An artist’s impression of a neutron star accreting gas in a binary system. Close to the neutron star, the strong magnetic field funnels material towards the neutron star poles. Image credit: NASA/GSFC/D. Berry. Download Image

During the last week, NuSTAR observed a highly obscured high-mass X-ray binary called IGR J16320−4751. While previous studies of IGR J16320−4751 with lower-energy X-ray telescopes have largely focused on the circumbinary matter surrounding the neutron star, the NuSTAR observation aims to probe the region very close to the neutron star's surface to investigate how its accretion has changed over time. The neutron star in IGR J16320−4751 spins once every ~1,300 seconds, with its spin period slowly changing over the years. Previous observations have suggested that the system’s accretion behavior may change approximately every 11 years. By revisiting the source about 11 years after its last NuSTAR observation, we can test this idea through (i) timing analysis of the neutron star’s beamed X-ray emission, including how the pulse fraction varies with energy, and (ii) spectral analysis to constrain its magnetic field evolution, which plays a key role in channeling matter onto the surface. Together, these measurements will determine whether the accretion flow has changed and explore those changes to the evolution of the neutron star’s magnetic field, which can be trillions of times stronger than that on Earth. For decades, NuSTAR has advanced our understanding of accretion onto neutron stars through its sensitivity to high-energy X-rays. This latest observation is a testament to NuSTAR’s continued contribution towards exploring how matter behaves in the extreme gravity and magnetic fields surrounding neutron stars.

The announcement of opportunity for proposals to NuSTAR General Observer cycle-13 was released last week. In addition to 8.5 Ms of NuSTAR observing time, proposals may include coordinated observations with ESA's XMM-Newton observatory and the JAXA/NASA/ESA mission XRISM. The combination of the high spectral resolution and soft X-ray sensitivity of these missions enhances the scientific return of the NuSTAR observations, and a high oversubscription rate is expected for these joint observations. Proposals to NuSTAR GO cycle-13 are due on January 28th, 2027 with peer reviews planned for March and the first observations for the new observing cycle scheduled for 2027 June.

Authors: Pragati Pradhan, Assistant Professor, Embry-Riddle Aeronautical University (Prescott campus); Karl Forster, NuSTAR Science Operations Lead (Caltech)

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

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Catching the Culprit Behind Globular Clusters’ Disappearing Binaries

The formation of young binary protostars.
Credit: ALMA (ESO / NAOJ / NRAO), F. O. Alves et al.; CC BY 4.0

Roughly one-third of stars in the Milky Way are in binary or multiple systems, but only ~1–10% of stars in globular clusters have a companion. Did globular clusters start with fewer binaries than the solar neighborhood, or have they since been wiped out?

Map of the semi-major axis–primary mass parameter space for binary systems. Solid lines show the boundary between hard (below the line) and soft (above the line) binaries for a variety of models. Models A–K span a variety of cluster masses and virial radii (a proxy for cluster density). Credit: O’Connor et al. 2026

Survival of the Tightest

Globular clusters (GCs) are dense, ancient, gravitationally bound groups of stars. A team led by Christopher O’Connor at Northwestern University explored whether the lack of binary systems could be the result of some process unique to GCs. First, the team developed an analytical formalism to understand how binaries in a GC evolve depending on the binary stars’ masses, distance from each other, and interactions with other stars in the cluster.

It turns out that the fate of a binary system depends on whether it is dynamically “hard” or “soft.” Hard binaries are generally tightly bound, and they tend to get “harder” from stellar flybys, which are common in a crowded cluster environment. Soft binaries are the opposite — they have much shorter lifetimes since encounters with other stars tend to loosen them. The team found that, assuming GCs have the same initial distribution of binaries as the solar neighborhood, the dissolution of soft binaries is sufficient to explain the present-day scarcity of binaries in GCs.

Burning Away the Binaries

What actually tears the soft binaries apart? The answer is a process called “black hole burning.” As some of the most massive objects in a globular cluster, black holes in binary systems can transfer energy when they interact with passing stars. This influx of energy can excite soft binaries to the point of dissolution, the study shows.

Black hole burning can also prevent core collapse in GCs. Left to itself, a cluster’s core gradually loses energy to its outskirts, causing the core to grow hotter and denser with stars. This leads to more dynamical interactions between stars that can then get flung from the core or enter new tight binaries. Black hole burning pumps energy back into the core and prevents this from happening.

The total number of black holes in a cluster (top) and the binary fraction (bottom) as a function of time for three different cluster models. In the densest cluster (blue), binary dissolution starts early on, mainly driven by stellar collisions. For the other two models, binary dissolution mainly occurs after the number of black holes reaches its peak and black hole burning commences. Adapted from O’Connor et al. 2026

Putting the Theory to the Test

To validate their analytical results, the team performed N-body simulations of GC dynamics with the Cluster Monte Carlo code. They found that, in moderate-to-low-density clusters, the decline of binary systems is powered mainly by black hole burning. In more compact clusters, however, stellar collisions also play an important role in the dissolution of binary systems, and at earlier times than the onset of black hole burning.

In general, the final binary fractions of the simulated clusters agree with those predicted by the team’s analytical formalism. This further supports the theory that there is a universal initial binary distribution between galactic GCs and our solar neighborhood. Constraining this distribution is pivotal for refining dynamical models of GCs.

In short, GCs and the solar neighborhood likely started with the same amount of binary systems, and interstellar dynamics handled the rest.

Citation

“A Common Origin for Binary Fractions in the Field and in Dense Clusters,” Christopher E. O’Connor et al 2026 ApJ 1009 L80. doi:10.3847/1538-4357/aea078

Source: American Astronomical Society/AAS-Nova

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ALMA Watches a Massive Binary Assemble in Real Time

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The inset circle shows an ALMA 0.9 mm continuum image of the central binary system of IRAS 07299−1651 with the reconstructed orbital trajectories overlaid. The red- and blue-shifted hydrogen recombination line emission traces the rotation of the ionized circumstellar disks around the two forming stars, while the arrows indicate the directions of the bipolar jets. Background: Mid-infrared image of the region obtained with JWST (red = F470N, green = F405N, blue = F360M). Credit: NASA, ESA, CSA, STScI, J. DePasquale (STScI), ALMA (ESO/NAOJ/NRAO), Y. Zhang

 

An artist’s impression of the formation of a close massive binary system, showing misaligned disks around two young stars.
Credit: Y. Zhangdiv

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Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have captured one of the most detailed three-dimensional views yet of a massive binary star system while it is still being born. By tracking the motions of two young, massive stars over nearly eight years, the team found that the pair follows a highly stretched-out orbit and is surrounded by strongly tilted gas disks, both relative to each other and to the stars' orbit. The findings suggest the two stars didn't form together from a single spinning disk of material, as is often assumed, but instead formed independently and later came together in a close gravitational encounter, revealing a new way close massive binary star systems may form.

Most massive stars are born with stellar companions, and at least 90% are thought to exist in binary or higher-order multiple systems. These massive binaries go on to shape their surroundings dramatically, through supernova explosions and the production of heavy elements. But because most known massive binaries are only studied long after they've finished forming, astronomers have had few opportunities to catch the actual moment of assembly.

An international team led by Yichen Zhang of Shanghai Jiao Tong University set out to change that by studying IRAS 07299−1651, a system containing two massive protostars, stars still growing by pulling in surrounding gas and dust. The team had studied this system before, in 2019, when ALMA observations first provided direct dynamical constraints on the pair. At the time, the results seemed broadly consistent with the standard picture: two stars forming together from the fragmentation of one large disk. But one detail didn't quite fit: the disks around the two stars already looked oddly misaligned.

To dig deeper, the researchers spent nearly eight years measuring extremely subtle shifts in the two stars' positions on the sky, a technique that requires exceptional precision and is well within ALMA's capabilities. "For the first time, we were able to watch two massive stars move around one another while they were still being born," said Yichen Zhang, corresponding author of the study.

The team combined this long-term ALMA monitoring with data from the U.S. National Science Foundation's Very Large Array (VLA), as well as infrared images from the James Webb Space Telescope (JWST) and ESO's Very Large Telescope (VLT), which traced jets of material streaming away from the young stars. Together, these observations let the team reconstruct, for the first time, the system's full three-dimensional architecture, how the stars orbit each other, how their disks are tilted, and how their jets point into space.

"Each telescope revealed a different piece of the puzzle," said Rubén Fedriani, a co-author of the study. "The combination of radio and infrared observations provides the most exquisite detail on the formation of this massive protobinary system."

What they found surprised them. Instead of a neat, roughly circular orbit, the stars are following a highly eccentric trajectory, with the preferred orbital solutions lying close to a parabolic path. And rather than being aligned, as would be expected if the stars formed from the same disk, their surrounding disks are tilted at a sharp angle to each other and to the orbit itself. "It felt like solving a three-dimensional puzzle," said Yao Wang, the study's first author. "Each new observation added another piece, and eventually the orbit, disks, and jets all came together into a single, coherent picture."

This mismatched, chaotic-looking architecture is hard to explain if the two stars grew up together in the same disk — in that scenario, they'd be expected to inherit similar, well-aligned spins. Instead, the evidence points to a different origin story: the two stars likely began forming separately, in their own individual pockets of gas, before a chance close encounter brought them into their present configuration while they were still wrapped in their birth cloud. In representative orbital solutions, the stars passed closest to each other only about 60 years before the observations, practically an instant on cosmic timescales. The compact disks seen today appear to have survived the encounter, retaining well-defined rotational structures.

"This study demonstrates that the early lives of stars can be quite chaotic, with a chance encounter leading to this gravitational dance and stellar coupling," said Jonathan C. Tan, a co-author of the study. It's still not certain whether the two stars will stay gravitationally bound to each other for good — their current motion sits close to the dividing line between a bound orbit and one that could eventually fly apart, and interactions with the surrounding gas may still nudge their fate one way or the other. Future observations will help pin that down.

More broadly, the study opens a new way of investigating how massive binary stars come together. By applying the same long-term monitoring approach to other young massive binaries, astronomers hope to learn how often close encounters like this one—rather than shared birth in a single disk—build the massive binary systems seen across our galaxy.

Source: ALMA (Atacama Large Millimeter/submillimeter Array)/Press Releases

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Additional Information

The results of this research appear in Nature Astronomy as "An eccentric massive protobinary assembled via a core-merger parabolic encounter" by Y. Wang et al.

This article is based on the original press release by the National Astronomical Observatory of Japan (NAOJ), an ALMA partner on behalf of East Asia.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF), and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan, and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning, and operation of ALMA.

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Contacts:

Nicolás Lira
Education and Public Outreach Officer
Joint ALMA Observatory, Santiago - Chile
Phone: +56 2 2467 6519
Cel: +56 9 9445 7726
Email: nicolas.lira@alma.cl

Seiichiro Naito
NAOJ EPO Lead
Email: naito.seiichiro@nao.ac.jp

Jill Malusky
Public Information Officer
NRAO
Email: jmalusky@nrao.edu

Bárbara Ferreira
ESO Media Manager
Garching bei München, Germany
Phone: +49 89 3200 6670
Email: press@eso.org

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Astronomers Determine Brown Dwarf Age Using Tiny Stellar Pulsations

An illustration of a star and a brown dwarf in a binary system.
Generated with ChatGPT by the University of Hawaiʻi .

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Results Test Brown Dwarf Theory challenging astrophysicists

Maunakea, Hawaiʻi – Astronomers using W. M. Keck Observatory on Maunakea, Hawaiʻi Island, have measured one of the most precise ages yet for a Sun-like star hosting a brown dwarf companion. The result offers a powerful new test of how brown dwarfs cool and evolve over time, helping to address a long-standing challenge in astrophysics.

The study focused on the nearby system HR 7672, which includes a Sun-like star and a faint brown dwarf companion. Using Keck Observatory’s Keck Planet Finder (KPF), the team detected subtle oscillations in the star’s surface, ripples that revealed its age to be 2.3 billion years.

Because the brown dwarf formed alongside the star, this precise stellar age serves as a benchmark for the companion’s evolution, offering a rare chance to directly test theoretical models of brown dwarf cooling.

“The 18% age uncertainty establishes the HR7672 system as a valuable benchmark for years to come,” said Yaguang Li, lead author and researcher at the University of Hawaiʻi at Mānoa.

The study, led by the University of Hawaiʻi Institute for Astronomy, is published in The Astrophysical Journal.

A Two-Decade Scientific Arc

The HR 7672 system has played a historic role in the study of substellar objects. The companion, known as HR 7672B, was first discovered by researcher Michael Liu, co-author and professor at the University of Hawaiʻi Institute for Astronomy. HR 7672B was the first directly imaged brown dwarfs orbiting a Sun-like star.

Using Keck Observatory’s Near-Infrared Camera (NIRC2) and the telescope’s Adaptive Optics system to correct for atmospheric blurring, Liu obtained a sharper image of the brown dwarf, which is 2,000 times fainter than its bright host star.

“Pioneering observations with Keck Observatory helped illuminate the so-called “brown dwarf desert,” the scarcity of such companions around Sun-like stars at close separations,” said Liu.

Now, more than two decades later, a new generation of Keck Observatory instrumentation continues to advance that legacy. Using ultra-precise measurements of the host star with the Keck Planet Finder (KPF) instrument, astronomers detected tiny stellar pulsations that reveal the star’s internal structure and age with unprecedented precision.

“The unique fast-readout mode of the Keck Planet Finder makes it the only instrument in the Northern Hemisphere capable of sampling oscillations on such short timescales,” added Li.

Testing How Brown Dwarfs Cool Over Time

Brown dwarfs are failed stars that are too small to sustain stable hydrogen fusion, so they gradually cool and fade as they age. Their brightness, therefore, depends sensitively on both their mass and age. However, astronomers have had difficulty testing theoretical models of this cooling, in part because reliable ages are rarely available.

Now, with this new and precise age measurement, combined with HR 7672B’s well-known luminosity and mass, the system becomes an exceptional “benchmark” for testing brown dwarf evolutionary models.

Comparing the observations with six different theoretical cooling models, the team found the best agreement with the most recent models that incorporate updated interior physics. Without the new data, the team would not have been able to distinguish this model from the five other possibilities.

These results demonstrate that high-precision stellar ages are essential for understanding substellar evolution — and show that precision spectroscopy with the next generation of observations will finally provide this information.

“Yaguang’s research has made this object even more valuable for our theoretical understanding of brown dwarfs,” said Liu.

As a next step, the researchers plan to generalize this method to a broader set of benchmark systems and test brown dwarf evolutionary models across different regimes.

Source: W. M. Keck Observatory/News

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Related Links
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• Science Paper.
• University of Hawaiʻi Release

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Media Contact:

Meagan O’Shea
moshea@keck.hawaii.edu

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From Stardust to Stone: Windswept Grains Hold Clues to Planet’s Beginnings

Large dust grains observed surrounding outflows of young protostellar binary system L1551 IRS5.
Credit: B. Saxton U.S. National Science Foundation/NSF National Radio Astronomy Observatory

Astronomers discover that stellar winds help dust grains grow into planet-building pebbles, offering fresh insight into the origins of rocky planets like Earth

The Atacama Large Millimeter/submillimeter Array (ALMA) has uncovered a key piece of the puzzle in how rocky planets, such as Earth, form around young stars. For decades, scientists have struggled to explain how dust grains in the disks around newborn stars grow from tiny dust grains to planet-building “pebbles” without either spiraling into the star or shattering in collisions—a challenge known as the “meter-size barrier.”

A team of more than 50 astronomers and chemists from the world’s leading scientific institutes used ALMA for this large program of research, known as the “Fifty AU STudy of the chemistry in the disk/envelope systems of Solar-like protostars” or FAUST. The team studies the chemistry of the dense molecular gas in the envelopes of a representative sample of Solar-like protostars, and now, for the first time ever, have directly observed millimeter-sized dust grains—about 10,000 times larger than typical interstellar dust—embedded in the walls of a protostellar outflow cavity. These grains appear to have been lifted from the dense inner protostellar disk by winds and then deposited farther out, away from where they can fall back onto the disk, and continue growing. This process gives the grains more time and space to stick together, potentially overcoming a long-standing barrier to planet formation.

Astronomers directly observed these millimeter-sized dust grains in the walls of the protostellar outflow cavity of the young L1551 IRS5 binary system, showing these grains can grow much larger than previously thought in the early stages of planet formation. These findings offer new insight into the processes that may have led to the formation of our own Solar System and highlight a previously underestimated pathway for planet formation.

“This discovery not only provides a new mechanism for building planets but also offers a glimpse into how our own Solar System may have formed,” said Giovanni Sabatini, a scientist with the National Institute for Astrophysics (INAF) at the Arcetri Astrophysical Observatory in Florence, and leader of this research. “The findings open exciting new questions about the diversity of planetary systems in our galaxy and bring us closer to understanding our cosmic origins,” adds Claire Chandler, NSF NRAO scientist and a co-PI of the FAUST collaboration.

Source: National Radio Astronomy Observatory (NRAO)/News

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About NRAO

TThe National Radio Astronomy Observatory (NRAO) is a facility of the U.S. National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

About ALMA

TThe Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

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Einstein Probe Uncovers Rare X-ray Binary System

The figure shows the Nova Outburst which was monitored by Einstein Probe WXT
© C. Maitra, Haonan Yang / MPE

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Einstein Probe satellite, a collaboration of, among others, the Max Planck Institute for Extraterrestrial Physics (MPE) and the Chinese Academy of Sciences (CAS), has captured an extraordinary celestial event: an X-ray outburst from a rare binary system. This discovery sheds new light on the evolution of massive stars and demonstrates the unique capabilities of Einstein Probe in detecting transient X-ray sources.

On 27 May 2024, the satellite’s Wide-field X-ray Telescope (WXT) detected an unusual X-ray source in the Small Magellanic Cloud (SMC). Follow-up observations, including those from NASA’s Swift and NICER telescopes and ESA’s XMM-Newton, confirmed the discovery: a rare pairing of a massive Be-type star and a dense white dwarf. This dynamic duo defies conventional expectations—while the Be star is still burning brightly, its companion has already collapsed into a white dwarf.

"This discovery uncovers an elusive class of object called Be white dwarf binaries (BeWDs). Binary evolution models predict that BeWDs should be about seven times more common than Be-neutron star (BeNS) systems. However, its detection is difficult due to the supersoft nature of the X-ray emission, which can be absorbed by the circumstellar disc of the Be star”, explains MPE scientist Chandreyee Maitra, who contributed to the interpretation of the results.

Haonan Yang, a PhD student at MPE and CAS who led the Einstein Probe data analysis of this object, adds: "The large Field of View of Einstein Probe’s Follow-up X-ray Telescope (EP FXT) allows efficient monitoring of the Magellanic Clouds, where such objects are expected to be detected in plentiful. Moreover, in collaboration with WXT, FXT can turn to a transient source within as little as 3 minutes after a new discovery, with a positioning accuracy better than 10 arcsec. FXT’s large effective area also ensures high sensitivity to low-energy photons, which is critical for probing supersoft sources."

His work highlights FXT’s capabilities in monitoring the nearby galaxies like the Magellanic Clouds, where such objects are expected to be abundant.

“The discovery of this source highlights the importance of soft X-ray surveys with EP FXT and WXT to uncover supersoft X-ray sources and novae. Moreover, the nova outburst from this system indicates the presence of a massive white dwarf close its maximum possible value, i.e., the Chandrasekhar limit. This can be instrumental in solving the debate on the progenitors of Supernova 1a”, says Chandreyee Maitra.

Source: Max Planck Institute for Extraterrestrial Physics (MPE)/News

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About Einstein Probe

MPE played a key role in the development of Einstein Probe’s Follow-up X-ray Telescope (FXT), contributing advanced optics and detector technology. The institute provided one of the FXT’s mirror modules, repurposing a spare from its eROSITA X-ray telescope, and collaborated with ESA and industry partners to supply the second. MPE also developed the state-of-the-art pnCCD detector modules, leveraging its expertise in high-precision X-ray spectroscopy.

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Contact:

Dr. Chandreyee Maitra
Researcher in High-Energy Astrophysics Group
cmaitra@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics

Haonan Yang
PhD-student Highenergy group
tel: +49 89 30000-3347
hnyang@mpe.mpg.de
Max-Planck-Institut für extraterrestrische Physik, Garching

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A. Marino, H. N. Yang, F. Coti Zelati, N. Rea, S. Guillot, G. K. Jaisawal, C. Maitra, et al.
Einstein Probe Discovery of EP J005245.1−722843: A Rare Be–White Dwarf Binary in the Small Magellanic Cloud?

ApJL 980 L36

Source | DOI

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Einstein Probe detects puzzling cosmic explosion

January 23, 2025

Einstein Probe has opened a new window onto the distant X-ray Universe, promising new views of the most faraway explosions in the cosmos. Less than three months after launch, the spacecraft already discovered a puzzling blast of X-rays that could require a change the way we explain the extraordinary explosions known as gamma-ray bursts.

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Jetting into space

HOPS 150 and HOPS 153

An area in the Orion nebula filled with dark, puffy clouds. On the left side a large area of clouds, crossed by a dark bar, is lit up in red and whitish colours by a protostar within. At the other side a large jet of material ejected by the protostar appears, made of thin, wispy, blue and pink clouds. A couple of foreground stars shine brightly in front of the nebula. Credit: ESA/Hubble & NASA, T. Megeath

Today’s NASA/ESA Hubble Space TelescopePicture of the Week peers into the dusty recesses of the nearest massive star-forming region to Earth, the Orion Nebula. Just 1300 light-years away, the Orion Nebula is visible to the naked eye below the three stars that form the ‘belt’ in the constellation Orion. The nebula is home to hundreds of newborn stars including the subject of this image: the protostars HOPS 150 and HOPS 153.

These protostars get their names from the Herschel Orion Protostar Survey, which was carried out with ESA’s Herschel Space Observatory. The object that can be seen in the upper-right corner of this image is HOPS 150: it’s a binary system, two young protostars orbiting each other. Each has a small, dusty disc of material surrounding it that it is feeding from. The dark line that cuts across the bright glow of these protostars is a cloud of gas and dust, over 2 000 times wider than the distance between Earth and the Sun, falling in on the pair of protostars. Based on the amount of infrared versus other wavelengths of light HOPS 150 is emitting, the protostars are mid-way down the path to becoming mature stars.

Extending across the left side of the image is a narrow, colourful outflow called a jet. This jet comes from the nearby protostar HOPS 153, out of frame. HOPS 153 is a significantly younger stellar object than its neighbour, still deeply embedded in its birth nebula and enshrouded by a cloud of cold, dense gas. While Hubble cannot penetrate this gas to see the protostar, the jet HOPS 153 has emitted is brightly visible as it plows into the surrounding gas and dust of the Orion Nebula.

The transition from tightly swaddled protostar to fully fledged star will dramatically affect HOPS 153’s surroundings. As gas falls onto the protostar, its jets spew material and energy into interstellar space, carving out bubbles and heating the gas. By stirring up and warming nearby gas, HOPS 153 may regulate the formation of new stars in its neighbourhood and even slow its own growth.

Source: ESA/Hubble/potw

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Featured Image: The Nova Shells of RX Puppis

RX Puppis, marked with crosshairs in the image above, is a symbiotic star: a binary system containing a puffy red giant and a compact white dwarf or neutron star. As the compact object accretes matter from the red giant, the stolen gas can ignite in a flash of nuclear fusion, powering a nova outburst that brightens the system for anywhere from days to decades. In the 1970s, researchers observed a slowly evolving outburst from RX Puppis. But nova outbursts from symbiotic stars usually recur — is there any evidence of previous outbursts from this sytem? Using the 1-meter Swope telescope in Las Campanas, Chile, and the Southern African Large Telescope, Krystian Iłkiewicz (University of Warsaw, Durham University) and collaborators discovered an arc-like emission feature that appears to be the remnant of a shell of gas ejected during an outburst roughly 1,300 years ago. They also discovered a hint of a second shell that might be from an eruption 7,000 years ago. Given the locations of these two shells and the timing of the 1970s outburst, Iłkiewicz’s team concluded that the rate at which the white dwarf amasses gas from its companion has increased by a factor of three over the past 10,000 years. This is the first time a change in mass transfer rate has been measured in a binary system over such a long timescale. To learn more about this discovery, be sure to check out the full research article linked below.

By Kerry Hensley

Citation

“Ancient Nova Shells of RX Pup Indicate Evolution of Mass Transfer Rate,” Krystian Iłkiewicz et al 2024 ApJL 972 L14. doi:10.3847/2041-8213/ad6e5a

Source: American Astronomical Society/AAS-Nova

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Evaporating Stars, Magnetars, and Bumpy Supernova Light Curves

The Wolf–Rayet star WR 140 as seen by JWST. This image shows the shells of dust created by the interaction of WR 140 with its binary companion. New research shows that the explosion of a Wolf–Rayet star with a binary companion can account for the bumpy light curves of certain supernovae. Credit: NASA, ESA, CSA, STScI, NASA-JPL, Caltech

Artist’s impression of a highly magnetized stellar remnant called a magnetar.
Credit: ESO/L.Calçada; CC BY 4.0

Instead of fading smoothly, some supernova light curves take a bumpy road from brilliance to obscurity. Can unusual binary systems containing a rapidly spinning, wind-emitting magnetar and a stellar companion explain these light curves?

Light Curve Wiggles

When a star explodes, researchers record the light curve from its final moments and attempt to understand its life and death. Certain supernovae show bumps and wiggles in their light curves, the cause of which is not yet agreed upon. Researchers suspect that some of these light-curve bumps crop up when the expanding shock wave of the supernova slams into gas and dust surrounding the star. Other brightness increases might occur when the explosion leaves behind a magnetar — an extremely dense, city-size stellar remnant that spins rapidly and has a strong magnetic field — that injects energy into its surroundings.

In a recent research article, Jin-Ping Zhu (Monash University) and collaborators expanded on the latter possibility, pairing a powerful magnetar with an unlucky companion star to explain bumpy features in the light curves of certain supernovae.

A diagram illustrating the stages of the magnetar–star binary engine model.
Credit: Zhu et al. 2024

What Goes Bump in a Supernova Light Curve

The proposed theory starts with an ordinary star and a massive star in a close binary system. As the massive star evolves, it sheds its outer layers through rapid rotation and fierce winds, exposing its super-hot core and becoming a rare Wolf–Rayet star. As the Wolf–Rayet star continues to evolve, tidal interactions between the stars in the binary system spin the Wolf–Rayet star up to high speeds. It eventually explodes in a core-collapse supernova, leaving behind a rapidly spinning magnetar.

Other models have invoked magnetars to explain bumpy supernova light curves, but this theory goes a step further, giving the companion an important role to play. As the newborn magnetar and the companion star swing around each other on their tight orbits, the magnetar’s powerful particle wind collides with the other star, evaporating some of the unlucky companion. The evaporated stellar material is then heated and accelerated by the magnetar wind, producing a bump in the light curve.

Example of multi-band light curves for a supernova that is well fit by the authors’ model.
Adapted from Zhu et al. 2024

A Fitting Theory

That’s the theory — how does it compare to observations? Zhu and collaborators applied their magnetar–star binary engine model to the light curves of supernovae with a single bump after maximum brightness. They found that the model generally fits the observations well, with the best-fitting results implying that a significant chunk — about 25–60% — of the companion star gets evaporated.

Zhu and collaborators suspect that their model may apply to light curves with multiple bumps, as well. If the companion star remains bound to the magnetar after the supernova explosion but is kicked into a new, highly eccentric orbit, a bump could be created each time the stars draw close to one another on their orbits.

The team notes that there isn’t yet firm observational or theoretical evidence that rapidly rotating massive stars leave behind magnetars, and it’s not clear whether a magnetar embedded within a supernova remnant can sustain a magnetar wind, as is required here. Future work may shore up the needed evidence, and in the meantime, this work provides a new way to interpret bumpy light curves.

By Kerry Hensley

Citation

“Bumpy Superluminous Supernovae Powered by a Magnetar–Star Binary Engine,” Jin-Ping Zhu et al 2024 ApJL 970 L42.
doi:10.3847/2041-8213/ad63a8

Source: American Astronomical Society/AAS-Nova

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Orion's Erupting Star System Reveals Its Secrets

Artist's impression of the large-scale view of FU~Ori. The image shows the outflows produced by the interaction between strong stellar winds powered by the outburst and the remnant envelope from which the star formed. The stellar wind drives a strong shock into the envelope, and the CO gas swept up by the shock is what the new ALMA revealed. Image credit: NSF/NRAO/S. Dagnello. Hi-res image

Zoom into the FU Ori binary system and the newly discovered accretion streamer. This artist's impression shows the newly discovered streamer constantly feeding mass from the envelope into the binary system. Image credit: NSF/NRAO/S. Dagnello. Hi-res image

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ALMA sheds light on 88-year-old astronomical mystery

An unusual group of stars in the Orion constellation have revealed their secrets. FU Orionis, a double star system, first caught astronomers' attention in 1936 when the central star suddenly became 1,000 times brighter than usual. This behavior, expected from dying stars, had never been seen in a young star like FU Orionis. The strange phenomenon inspired a new classification of stars sharing the same name (FUor stars). FUor stars flare suddenly, erupting in brightness, before dimming again many years later. It is now understood that this brightening is due to the stars taking in energy from their surroundings via gravitational accretion, the main force that shapes stars and planets. However, how and why this happens remained a mystery—until now, thanks to astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA).

"FU Ori has been devouring material for almost 100 years to keep its eruption going. We have finally found an answer to how these young outbursting stars replenish their mass," explains Antonio Hales, Deputy Manager of the North American ALMA Regional Center, a scientist with the National Radio Astronomy Observatory, and lead author of this research, published today in the Astrophysical Journal, "For the first time we have direct observational evidence of the material fueling the eruptions."

ALMA observations revealed a long, thin stream of carbon monoxide falling onto FU Orionis. This gas didn't appear to have enough fuel to sustain the current outburst. Instead, this accretion streamer is believed to be a leftover from a previous, much more significant feature that fell into this young stellar system. "It is possible that the interaction with a bigger stream of gas in the past caused the system to become unstable and trigger the brightness increase," explains Hales.

Astronomers used several configurations of ALMA antennas to capture the different types of emission coming from FU Orionis and detect the mass flow into the star system. They also combined novel numerical methods to model the mass flow as an accretion streamer and estimate its properties. "We compared the shape and speed of the observed structure to that expected from a trail of infalling gas, and the numbers made sense," says Aashish Gupta, a Ph.D. candidate at European Southern Observatory (ESO) and a co-author of this work, who developed the methods used to model the accretion streamer.

"The range of angular scales we can explore with a single instrument is remarkable. ALMA gives us a comprehensive view of the dynamics of star and planet formation, spanning from large molecular clouds in which hundreds of stars are born, down to the more familiar scales of solar systems," adds Sebastián Pérez of Universidad de Santiago de Chile (USACH), director of the Millennium Nucleus on Young Exoplanets and their Moons (YEMS) in Chile, and co-author of this research.

These observations also revealed an outflow of slow-moving carbon monoxide from FU Orionis. This gas is not associated with the most recent outburst. Instead, it is similar to outflows observed around other protostellar objects. Adds Hales, “By understanding how these peculiar FUor stars are made, we’re confirming what we know about how different stars and planets form. We believe that all stars undergo outburst events. These outbursts are important because they affect the chemical composition of the accretion discs around nascent stars and the planets they eventually form.”

“We have been studying FU Orionis since ALMA's first observations in 2012,” adds Hales. It’s fascinating to finally have answers.”

Source: ALMA (Atacama Large Millimeter/submillimeter Array)/Press Release

Scientific Paper

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Additional Information

This research was published in an article titled "Discovery of an accretion streamer and a slow wide-angle outflow around FU Orionis" by A. Hales et al. in the Astrophysical Journal.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

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ALMA Digs Deeper into the Mystery of Planet Formation

Images of disks around 19 protostars, including 4 binary systems observed with ALMA. For 1 binary system, disks around the primary and secondary are presented independently (2nd line rightmost and 3rd line leftmost). Disks are presented in the order of their evolutionary sequence (the one in the upper-left corner is the youngest while the one at the lower-right corner is the oldest). The two oldest disks show faint ring-gap structures. A scale bar of 20 au (roughly the distance between the Sun and Uranus) is shown for each disk image. (Credit: ALMA (ESO/NAOJ/NRAO), N. Ohashi et al.) Original size (1.0MB)

An international research team used the Atacama Large Millimeter/submillimeter Array (ALMA) to observe disks around 19 protostars with a very high resolution to search for the earliest signs of planet formation. This survey was motivated by the recent findings that planet formation may be well-underway in the more-evolved proto-planetary disks, but until now there had been no systematic study to search for signs of planet formation in younger protostellar systems.

Planets form in a disk around a newborn star. These ‘proto-planetary’ disks only last a few million years, meaning that a forming planetary system only has this amount of time to finish its formation. However, it is still not clear just how rapidly planet formation begins within these disks. Recent ALMA observations have revealed that many proto-planetary disks have substructures such as gaps and rings, indicating that planets are already forming from the disk. “These previous results motivated us to examine even younger disks around protostars to answer the question, at what stage of star formation do planet forms,” says Nagayoshi Ohashi at Academia Sinica Institute of Astronomy and Astrophysics (ASIAA, Taiwan), who led the team.

The team observed disks around 19 protostars located within about 650 light-years from the Earth. This is the first systematic study to investigate the detailed structure of disks around a large sample of protostars with high angular resolution. The observations clearly show that the disks around protostars are different from more-evolved proto-planetary disks. Among the 19 protostars, rings, and gaps, which are signs of planet formation, were observed only in a few disks. Moreover, the ring structures are less distinct than those seen in the proto-planetary disks.

“We did not expect to see such clear differences between disks around protostars and more-evolved disks,” says Ohashi. John Tobin, a Co-PI of the program at the National Radio Astronomical Observatory (USA) adds “Our results suggest that disks around protostars are not fully ready for planet formation. We believe that the actual formation of the planetary system progresses rapidly in the 100,000 years to 1,000,000 years after star formation begins.”

This research was detailed in Nagayoshi Ohashi et al. “Early Planet Formation in Embedded Disks (eDisk). I. Overview of the Program and First Results” and 3 other papers (Lin et al., van 't Hoff et al., Yamato et al.) published on June 28, 2023 in the Astrophysical Journal, and one paper accepted for later publication in the same journal (Kido et al.).

Related Links

• ALMA Digs Deeper into the Mystery of Planet Formation (ALMA)
• ALMA Digs Deeper into the Mystery of Planet Formation (The University of Tokyo)

Source: National Astronomical Observatory of Japan (NAOJ)/Science

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Knock, Knock. Who’s There? A Free-Floating Planet! Knock, Knock. Who’s There?

An illustration of a free-floating planet
Credit: NASA’s Goddard Space Flight Center Conceptual Image Lab

Title: Formation History of HD106906 and the Vertical Warping of Debris Disks by an External Inclined Companion
Authors: Nathaniel Moore et al.
First Author’s Institution: Georgia Institute of Technology
Status: Accepted to ApJ

When early astronomers theorized how planets formed, they often used the solar system as a model, mainly because that was all we had observationally available at the time. The thing is, the solar system is pretty “well behaved” — the planets are more or less in the same orbital plane, and their orbits are not too eccentric (i.e., they are closer to being circles than ellipses). However, as more exoplanets are found, astronomers begin to question their ideas for how planets formed. The binary system HD 106906, for example, has an asymmetrical debris disk and a planet that is not in the same plane as the disk and is separated from the stars by 730 astronomical units (au; for reference, Earth is 1 au away from the Sun). This system has an unusual architecture, and the authors of today’s article try to theorize how this system formed. Understanding the formation of an usual system like this one allows us to expand our knowledge of planet formation beyond the simplicity of such well-behaved systems such as our own!

There are two main theories for the formation of planets: core accretion and gravitational instability (also called the gas-collapse model). Figure 1 shows the two different scenarios. In both cases, the planets form in a protoplanetary disk, which means that the planets initially start in the same orbital plane. A system like HD 106906 challenges this notion, since it has a very massive planet far away from the disk and in a different orbital plane. The authors of this article explore the idea that the planet HD 106906 b actually formed from the disk, but a recent (about 1–5 million years ago) close encounter with a free-floating planet knocked the planet away from the disk into an eccentric orbit, and the interactions from this close encounter actually caused the disk to become more eccentric as well. The authors explore this idea using N-body simulations (a simulation of how bodies interact over a period of time) of the system combined with simulations of how the observational data would look for this scenario. They then compare the simulations to real observations.

Figure 1. The two possible scenarios for planet formation: accretion model (“bottom-up”) and gravitational instability (“top-down”). Click to enlarge. Credit: NASA and A. Feild (STScI); CC BY 4.0

Companion and Disk Interactions

The authors first try to determine whether the HD 106906 system has been like this for a long time or if its current configuration is the result of a recent event. To do this, they simulate different variations of the planet’s eccentricity, inclination, and semi-major axis. For the simulations, they include the effects of radiation pressure. They also use two different central body configurations: one with a binary star system and another with a single central body and an extra J2 potential term, which emulates the binary system but is more computationally efficient. The main results from these simulations are shown in Figure 2.

Figure 2: The simulations at 1 million years (top left), 5 million years, (bottom left) and 10 million years (bottom right) compared to the Crotts et al. 2021 original observations. After a million years, the simulated disk is very similar to the real image. By 5 and 10 million years, the appearance (size and brightness) of the disk exceeds the observational constraints. Credit: Moore et al. 2023

The simulations lead the authors to conclude that the disk and planet have likely been in this configuration for only 1–5 Myr, which for the system’s age of 13 Myr is quite recent. If it had been there for longer than that, the simulations for 5 and 10 Myr would have been within the observational constraints from the real data.

Figure 3: The free-floating planet, represented in red, can simply “fly by” the system, leaving the original configuration mostly unchanged; be exchanged with the original planet (blue), which then gets ejected; or be captured into the system. Credit: Moore et al. 2023

Knock, Knock. Who’s There?

Next, the authors simulate a close encounter between a 11±1 Jupiter-mass free-floating planet and the native planet of the HD 106906 system to see if this can cause the system’s current arrangement. Figure 3 shows the possible outcomes of simulations of this (un)expected visit. The authors simulate 100,000 initial conditions and see their outcomes. These 100,000 conditions are obtained such that the closest approach distance of the planets is less than 50 au (if it winds up being more than that, the initial condition is rejected).

The team’s final results are shown in Figure 4. From the figure, we can see that a few outcomes in which either the free-floating planet stays in the system or the native planet stays in the system agree with observations. The authors conclude that an encounter with a free-floating planet is a possible explanation for the current architecture of this system. The close encounter only reproduces observational results 0.2% of the time, but this system is quite unusual — so a low probability of a system forming like this is expected!

Figure 4: The final results of the close encounter simulations of the free-floating planet and the HD 106906 system. The dots within the dashed square fall within the expected observational constraints of the companion (i.e., that agree with current estimates for the orbital eccentricity, semi-major axis, and inclination of the companion). The blue dots represent the outcomes that agree with observations where the native planet remains bound to the system. The red dots represent the outcomes where the free-floating planet remains bound to the system. The gray dots represent the other parameters of the 100,000 simulations. Credit: Moore et al. 2022

By Astrobites

Original astrobite edited by H Perry Hatchfield.

Source: American Astronomical Society - AAS Nova

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About the author, Clarissa Do O:

I am a third-year physics graduate student at UC San Diego. I study exoplanet orbital dynamics and also work on exoplanet instrumentation. My current work is on the adaptive optics upgrade of the Gemini Planet Imager 2.0, an instrument that aims to directly image and characterize exoplanets.

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Insights from Misaligned Black Hole Pairs

This visualization shows the light-bending capabilities of two black holes locked in a binary system.
Credit: NASA’s Goddard Space Flight Center/Jeremy Schnittman and Brian P. Powell

Astronomers study gravitationally linked pairs of black holes to understand how stellar-mass black holes form. What can we learn from black holes that are off kilter from the binaries they belong to?

Top: The black hole spins are aligned with the system’s orbital angular momentum (positive χeff). Bottom: The black hole spins are misaligned with the system’s orbital angular momentum (negative χeff). Credit: Kerry Hensley

You Spin Your Way, and I’ll Spin Mine

Collecting the gravitational waves from merging stellar-mass black holes allows us get at one of the fundamental questions in high-energy astrophysics: how did the black holes that exist in the universe today come to be? A black hole’s mass and spin hint at whether it formed directly from the collapse of a massive star or through a process called hierarchical merging — the formation of large black holes through successive mergers of smaller ones.

One property we can use to probe the origins of black holes in merging binary systems is the effective inspiral spin parameter, denoted χeff, which is a measure of how aligned the spins of the black holes are with the orbit of the binary pair. In some systems, the black holes spin in the same direction as they orbit, giving the system positive χeff. In others, one or both black holes are tilted, and they spin in directions that are at odds with their orbital motion, giving the system negative χeff. A recent publication searches for the most misaligned black hole binaries to understand the origins of the black holes in the universe today.

Theoretical probability distribution functions (top) and cumulative distribution functions (bottom) for the effective inspiral spin parameters (χeff) of binary systems containing one (orange) or two (blue) black holes formed through hierarchical merging. The different lines in the top panel show the effect of different initial black hole spins. Credit: Fishbach et al. 2022

Monitoring Misalignment

Maya Fishbach (Northwestern University) and collaborators began their investigation by predicting the spins of black holes in binaries in which at least one member formed through hierarchical merging. The team’s calculations showed that hierarchical merging results in a substantial number of black holes with spins misaligned from their direction of orbital motion. Specifically, the team predicted that 16% of black hole binaries would have χeff less than −0.3, regardless of whether one or both members of the binary system arose through hierarchical merging.

With this prediction in hand, Fishbach and coauthors turned to the data, assessing the χeff values of 69 merging black hole pairs in the third Gravitational-wave Transient Catalog (GWTC-3), which is the most recent catalog of gravitational wave events detected by LIGO and Virgo. Depending on the model used to analyze the data, the team found that the maximum proportion of binary systems with χeff less than −0.3 is 4.2%.

The expected number of gravitational wave events for systems with χeff less than −0.3 that we expect to observe as a function of the hierarchical merger (HM) fraction and the total number of events observed. Credit: Fishbach et al. 2022

Evidence for Meager Mergers

Given the small fraction of strongly misaligned black hole systems, the team found that hierarchical mergers likely populate no more than 26% of black hole binaries. Intriguingly, only 69% of massive black holes (60 solar masses) are expected to be products of hierarchical merging, meaning that some of these high-mass black holes most likely result from enormous collapsing stars — a finding that has implications for our understanding of stellar interiors and nuclear physics.

Fishbach and collaborators note that if black hole binaries with χeff less than −0.3 aren’t detected in the future, that would point to hierarchical merging being even less common. If the LIGO, Virgo, and KAGRA gravitational wave detectors find no such systems during their next observing runs, the team limits the percentage of black holes formed through hierarchical merging to no more than 2.5%.

Citation

“Limits on Hierarchical Black Hole Mergers from the Most Negative χeff Systems,” Maya Fishbach et al 2022 ApJL 935 L26. doi:10.3847/2041-8213/ac86c4

By Kerry Hensley

Source: American Astronomical Society - AAS-Nova

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Huge Rings Around a Black Hole

V404 Cygni
Image Credit X-ray: NASA/CXC/U.Wisc-Madison/S. Heinz et al.; Optical/IR: Pan-STARR

This image features a spectacular set of rings around a black hole, captured using NASA's Chandra X-ray Observatory and Neil Gehrels Swift Observatory. The X-ray images of the giant rings reveal information about dust located in our galaxy, using a similar principle to the X-rays performed in doctor's offices and airports.

The black hole is part of a binary system called V404 Cygni, located about 7,800 light years away from Earth. The black hole is actively pulling material away from a companion star — with about half the mass of the Sun — into a disk around the invisible object. This material glows in X-rays, so astronomers refer to these systems as "X-ray binaries."

Editor: Yvette Smith

Source: NASA/Black Holes

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The origin of Type Ia supernovae revealed by manganese abundances

Image caption 1: (a) Near-Chandrasekhar mass explosions: In a binary system of one white dwarf that is made of carbon and oxygen, mass accretion from the companion star (a main se-quence star or red giant) causes winds of material from the white dwarf, which regu-lates the mass accretion onto the white dwarf, and increases the white dwarf mass. Subsonic waves from the explosion at the centre of near-Chandrasekhar mass white dwarf trigger a detonation in the outskirts. This explosion can produce a lot of manga-nese (Mn) and nickel (Ni) as well as iron (Fe). (b) An example of sub-Chandrasekhar mass explosions: In a binary system of two white dwarfs (at least one white dwarf consists of carbon and oxygen), the smaller one is dis-rupted by tidal forces and merges with the larger one. A detonation in a thin helium enve-lope around the white dwarf triggers a carbon detonation at the centre. This explosion can produce more silicon (Si) and sulphur (S), as well as iron (Fe), and unburnt carbon and oxygen.

Image caption 2: Evolution of oxygen (left) and manganese (right) in the solar neighborhood of the Milky Way Galaxy. The x-axis shows the metallicity (iron abundance relative to hydrogen), which is a proxy of time increasing from the left to right. The y-axis shows the oxygen and manganese abundances, relative to iron. The points are for the elemental abundances observed in nearby stars with high-resolution spectroscopy. From the comparison, it is found that at least 75 percent of Type Ia supernovae are near-Chandrasekhar mass ex-plosions.

A research team at the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) consisting of Visiting Scientist Chiaki Kobayashi, Project Researcher at the time Shing-Chi Leung (currently at the California Institute of Technology), and Senior Scientist Ken’ichi Nomoto have used computer simulations to follow the explosion, nuclear reaction, production of elements, and evolution of elemental abundances in galaxies. As a result, they placed stringent constraints on the origin of Type Ia supernovae. 

A Type Ia supernova is a type of supernova that is not related to the death of a massive star. Instead, a Type Ia supernova is a luminous explosion of a star that occurs in a binary system, where two relatively low-mass stars are evolving together. Because of their relatively constant luminosity, Type Ia supernovae have been used as a standard “candle” to measure the expansion of the universe, a result for which the 2011 Nobel Prize in Physics was awarded. However, the progenitor star of a Type Ia supernova is unknown, and has been the topic of debate for around a half century. 

“As usual for normal supernovae, Type Ia supernovae produce “metals”—or, in astronomical terms, chemical elements heavier than hydrogen and helium, the latter pair tracing their origin to the Big Bang—but Type Ia supernovae produce different elements, such as manganese (Mn), nickel (Ni), and iron (Fe). These elemental abundances can be measured in spectral features of nearby stars, which keep a “record” of supernovae from the past, like fossils do in archaeology,’’ Kobayashi, who is also an associate professor at the University of Hertfordshire in the United Kingdom, said. Therefore, the evolution of elemental abundances in galaxies can provide a stringent constraint on the true origin of Type Ia supernovae.

The progenitor stars of Type Ia supernovae are a type of white dwarf that are made of carbon and oxygen. White dwarfs form after the deaths of intermediate-mass stars, where electron degeneracy pressure supports the star against collapsing under its own gravity. However, if a white dwarf exceeds its upper mass limit—also called the Chandrasekhar mass limit (named after physicist Subrahmanyan Chandrasekhar)—this leads to nuclear reactions that cause it to explode.

Therefore, in a binary system containing a near-Chandrasekhar-mass white dwarf, mass accretion from a companion star can cause an explosion, which is one of the two proposed scenarios (the “single degenerate scenario”) for Type Ia supernovae (Figure 1a). In the other scenario, two white dwarfs are formed in a binary system (the “double degenerate scenario”), which merge together to cause an explosion—namely, a sub-Chandrasekhar-mass explosion (Figure 1b).  

Click here for Figure 1 (with a white background).

 To investigate both cases, the research team run detailed calculations (2-dimensional hydrodynamical simulations and nucleosynthesis) of both near-Chandrasekhar-mass and sub-Chandrasekhar-mass explosions, and calculated the evolution of the Milky Way Galaxy, something that had not been done in previous research. 

“Between these two cases, we find a critical difference in the evolution of elemental abundances, in particular for the element manganese,’’ Kobayashi explained. In the first simulation, the explosion provided high-temperature and high-density matter where a lot of manganese was produced, while in the second simulation, there was no such matter and hence not enough manganese was produced.

The research team then incorporated the production amount of each chemical element into their galaxy model to predict the evolution of elements in the Milky Way. Compared to observational data, namely, elemental abundances measured in nearby stars with high-resolution spectroscopy, they found that at least 75 percent of Type Ia supernovae are near-Chandrasekhar mass explosions (Figure 2). In both cases, the research found, the produced iron mass is roughly the same—that is, 60 percent of the mass of the Sun—which is about 10 times larger than in normal supernovae from massive stars.

“The chemical evolution of galaxies is powerful for solving long-standing problems in nuclear astrophysics. Not only manganese but also nickel abundances are updated in our calculations with the latest nuclear reactions. Nickel was overproduced in previous calculations, but now the predicted abundance is consistent with observations,’’ Kobayashi added. As a result of their findings, the nickel overproduction problem is finally solved, after two decades of studies.

More interestingly, the research team also showed that a larger contribution from sub-Chandrasekhar-mass explosions is preferred to near-Chandrasekhar-mass explosions  from the available observations in different galaxies—dwarf spheroidal galaxies around the Milky Way, for example. 

Kobayashi and her team noted that the elemental abundances of millions of stars will be obtained with ongoing and future international projects, such as APOGEE (Apache Point Observatory Galactic Evolution Experiment), HERMES-GALAH (GALactic Archeology with HERMES), WEAVE (WHT Enhanced Area Velocity Explorer), 4MOST (4-metre Multi-Object Spectroscopic Telescope), MSE (The Maunakea Spectroscopic Explorer), in the new research area of “Galactic Archaeology,” or the study of the history of the Milky Way Galaxy, and their findings will be tested further in future research.

Paper details:

Journal: The Astrophysical Journal

Title: New Type Ia Supernova Yields and the Manganese and Nickel Problems in the Milky Way and Dwarf Spheroidal Galaxies

Authors: Chiaki Kobayashi (1,2), Shing-Chi Leung (2,3), Ken'ichi Nomoto (2)

Author affiliation:

1. Center for Astrophysics Research, Department of Physics, Astronomy and Mathemat-ics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
2. Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
3. TAPIR, Walter Burke Institute for Theoretical Physics, Mailcode 350-17, Caltech, Pasa-dena, CA 91125, USA

DOI: https://doi.org/10.3847/1538-4357/ab8e44 (Posted on June 4, 2020)

Paper abstract: (Astrophysical Journal page): https://iopscience.iop.org/article/10.3847/1538-4357/ab8e44 

Preprint (arXiv.org page): https://arxiv.org/abs/1906.09980 

Research contact: 

Ken’ichi Nomoto 
Senior Scientist
Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo
E-mail: nomoto@astron.s.u-tokyo.ac.jp
TEL: +81-4-7136-5940

Chiaki Kobayashi
Associate Professor
University of Hertfordshire
Visiting Scientist
Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo
E-mail: c.kobayashi@herts.ac.uk

Media contact:

John Amari
Press officer 
Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo
E-mail: press@ipmu.jp
TEL: 080-4056-2767 

Related links:

Gold in the cosmos is an astronomical mystery (University of Hertfordshire press release, English)*
https://www.herts.ac.uk/about-us/media-centre/news/2020/gold-in-the-cosmos-is-an-astronomical-mystery 

*Contents related to the research results, by Kavli IPMU Visiting Scientist Chiaki Koba-yashi, published in the Astrophysical Journal on September 16, 2020

Source: Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)

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