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Title: Protostars at Subsolar Metallicity: First Detection of Large Solid-State Complex Organic Molecules in the Large Magellanic Cloud
Authors: Marta Sewiło et al.
First Author’s Institution: NASA Goddard Space Flight Center
Status: Published in ApJL

Stars and planets form when clouds of molecules collapse in on themselves due to the overwhelming force of gravity (which, relatable). This process is quite mysterious, as these clouds will only live for a couple million years before collapsing, and the newly forming protostars only live for about half a million years before becoming main-sequence stars.

But we are able to find some protostars in the Milky Way and in the Small and Large Magellanic Clouds near us, and observing the molecules around these protostars can help us understand how protostars form.

To look for molecules around protostars, astronomers take spectra of the protostars in the infrared, which is a wavelength region where molecules emit a lot of light. As better instruments are being built, astronomers are more often able to look for what are called complex organic molecules, which are carbon-bearing molecules with at least six atoms.

These complex organic molecules can be detected in different states: most detections have been of gaseous molecules in and around protostars or planet-forming disks, but they can also be found in a solid state on the surfaces of dust grains in the interstellar medium in a galaxy. In this state, they are called complex organic molecule “ices.” These “ices” were rarely found pre-JWST, but since its launch, detections have been more numerous, mainly in the Milky Way. Observing these complex molecules on the surfaces of dust grains tells us more about protostellar dust chemistry, which is an important but still mysterious aspect of star formation.

In this study, researchers look outside of our own galaxy to explore the complex organic molecules in the Large Magellanic Cloud (LMC). The LMC is an interesting place to look for these molecules because it has lower metal content (i.e., elements heavier than hydrogen and helium) than the Milky Way, as well as a harder radiation field. This means photons flying around in the LMC generally have higher energies than photons flying around in the Milky Way, and elements like carbon, oxygen, and nitrogen are less abundant. This is important because these conditions are more similar to what typical galaxies were like in the early universe. Thus the LMC is a better test bed to look at protostars than the Milky Way if we want to understand how stars formed in the early universe.

The authors of this study have found signatures of complex organic molecules in protostars forming in the LMC. They focus on the protostar ST6 in the LMC, shown in the right image in Figure 1. They used JWST’s Mid-Infrared Instrument to take spectra of the region around ST6.

Spectroscopic Signatures of Molecules on Dust Grains

The researchers used the Python tool called dEcompositioN of Infrared Ice features using Genetic Modelling Algorithms (ENIIGMA) to fit the spectroscopy. This code compares the spectra to laboratory data of these complex organic molecules at the temperatures we see in the LMC. The authors fit for complex organic molecules they might expect to see, and they detect methanol (CH₃OH), acetaldehyde (CH₃CHO), ethanol (CH₃CH₂OH), methyl formate (HCOOCH₃), and acetic acid (CH₃COOH); of these, acetaldehyde, ethanol, and methyl formate have never before been detected outside of the Milky Way. Interestingly, this is the first time acetic acid has been definitively detected in any astrophysical environment. The spectral contribution from each molecule is shown in Figure 2; all the individual contributions added together make up the observed spectrum.

These detections provide evidence that these complex organic molecules can be produced on the surfaces of dust grains. Further, their detection in the LMC provides evidence that these molecules can be produced in “harsh” environments like the LMC, with lower metal content and harder radiation fields.

When the authors compared the abundances of these ices to other protostars in the Milky Way galaxy, they found that the abundances are slightly lower around the LMC protostar. This may happen because the dust temperatures are generally higher in the LMC due to the higher-energy photons, which affect the chemistry happening on the dust. Some species they found, however, do have similar abundances to the Milky Way protostars, indicating that the harder radiation field of the LMC does not affect how these species form. Finding more complex organic molecules in the Magellanic Clouds will help us understand further how these compounds form on dust grains and how the galactic environment may affect their formation.

Original astrobite edited by Shalini Kurinchi-Vendhan.

About the author, Caroline von Raesfeld:

I’m a third-year PhD student at Northwestern University. My research explores how we can better understand high-redshift galaxy spectra using observations and modeling. In my free time, I love to read, write, and learn about history.

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Editor’s Note: For the remainder of 2025, 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 January 2nd.

The SOFIA Massive (SOMA) Star Formation Survey. V. Clustered Protostars

Published June 2025

Main takeaway:

A team led by Zoie Telkamp (University of Virginia) used the Stratospheric Observatory for Infrared Astronomy, SOFIA, to study massive protostars and test theories of high-mass star formation. Contrary to the predictions of some star-formation models, the team found no evidence that massive protostars require a certain surface mass density to form. Formation in a cluster environment, however, may limit the formation of the most massive protostars.

Why it’s interesting:

Massive stars are rare, short-lived, and luminous. They influence their environments across a vast range of spatial and temporal scales, from advancing the epoch of reionization in the early universe to impacting the formation of individual planetary systems in the present-day universe. The fundamental question of how high-mass stars form is still unsettled. Theories of high-mass star formation range from scaled-up versions of low-mass star formation to scenarios involving collisions between protostars.

More about this massive-star study and the potential impact of a cluster environment:

Researchers developed the SOFIA Massive Star Formation Survey to investigate the origins of massive stars, targeting roughly 50 high-mass and intermediate-mass protostars in a wide variety of environments in our galaxy. This particular work, the fifth in a series of articles reporting the survey’s findings, described the team’s study of massive protostars forming in cluster environments. Using the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST), Telkamp and collaborators identified 34 protostars in seven star-forming regions and estimated their masses and other physical properties. The team noted a lack of protostars above 30 solar masses in these cluster regions, which might be evidence that competition for gas in dense environments can prevent the formation of more massive protostars. More work is needed to confirm this finding.

Citation

Zoie Telkamp et al 2025 ApJ 986 15. doi:10.3847/1538-4357/adcd79

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There’s been a lot of astronomy in the news lately! Many recent news stories have featured research published in the AAS journals, so today we’re taking a look at four research articles that have recently gotten attention from the media.

New Horizons Navigates by the Stars

Starting closest to home, the first article describes a technological demonstration that took place on the edge of our solar system. In the nearly 20 years since its launch, the New Horizons spacecraft has ventured from Cape Canaveral to its current berth in the Kuiper Belt, roughly 61 au (5.7 billion miles or 9.1 billion kilometers) from Earth. In that time, New Horizons became the first spacecraft to venture close to Pluto and its moons as well as a second Kuiper Belt object called Arrokoth.

New Horizons has also traveled a large enough distance for nearby stars to shift their positions relative to the background of more distant stars, enabling a measurement of the spacecraft’s position in space. Tod Lauer (NSF National Optical Infrared Astronomy Research Laboratory) and collaborators demonstrated this ability using New Horizons Long Range Reconnaissance Imager (LORRI) observations from April 2020, when the spacecraft was 47 au from the Sun. The stars used for the parallax measurements were Proxima Centauri and Wolf 359, two of the nearest stars to Earth. The team measured the stars’ positions relative to the positions of background stars and compared the results to observations made from Earth.

From the apparent shift in position of the two stars, the team determined the location of the spacecraft in space as well as the error in their measurement. They were able to ascertain the position of the spacecraft to within 0.44 au of its true position.

Though this measurement is far less accurate than localization with the Deep Space Network, it’s still an important step toward understanding the future prospects for autonomous spacecraft navigation via the stars. Looking ahead to future interstellar navigation systems, the team showed that measurements of a few nearby stars (Proxima Centauri and Barnard’s Star are the best bets for journeys within tens of thousands of astronomical units of the Sun) are more useful than measurements of a larger number of more distant stars. Basing measurements on a larger number of images to cut down on random scatter in the position of the star would also improve the results, as would simply using newer instruments. Ultimately, other types of navigation systems, such as those based on measurements of pulsars, are more likely to reach the precision necessary for autonomous spacecraft navigation. However, this method remains interesting, given that the straightforward nature of the imaging and analysis is already well within the capabilities of modern spacecraft systems.

First Detection of Semiheavy Water Ice Around a Low-Mass Protostar

Next up is a discovery from 457 light-years away in the Taurus molecular cloud. With a mass of 0.3–0.5 solar mass, a disk spanning 75–125 au, and a surrounding envelope of 0.9 solar mass, the isolated low-mass protostar L1527 is likely to grow into a star of similar mass to the Sun. That makes it an excellent target for investigating how planetary systems like our own acquire critical molecules like water.

Katerina Slavicinska (Leiden Observatory) and coauthors used JWST to search L1527 for semiheavy water (HDO) — a water molecule in which one of the hydrogen atoms is replaced with a deuterium atom. HDO has been detected in many locations throughout our solar system, including in Earth’s oceans, and water in our solar system tends to contain a high abundance of HDO molecules. A high deuterium abundance can be linked to formation in a cold environment, suggesting that our solar system’s water may have formed in the icy clouds out of which the Sun and the planets were born.

Thanks to JWST’s high resolution and sensitivity, Slavicinska’s team was able to detect HDO ice in L1527, where previous, lower-resolution observations had only hinted at the presence of the molecule. They also measured emission from H₂O ice, yielding a ratio of the abundances of the two types of water. The ice HDO/H₂O ratio of L1527 is consistent with the gas HDO/H₂O ratios of other isolated low-mass protostars and 4–7 times higher than the gas HDO/H₂O ratios of clustered low-mass protostars. This difference may be due to differences in the star-forming environments of clustered protostars, or it may signal that the water in these protostars underwent gas-phase processing at some point. If environmental factors are the cause, that would suggest that L1527 should have a higher HDO/H₂O ratio than objects in our solar system, since the Sun likely formed in a cluster environment.

This study demonstrates JWST’s ability to investigate the chemistry of young stars and probe the chemical evolution of protostars and planetary systems. Slavicinska and coauthors identified two important next steps to advance our understanding of the chemistry of star- and planet-forming environments: 1) measuring gas-phase and ice-phase HDO/H₂O ratios in the same object to understand how gas-phase chemistry alters water around protostars and 2) measuring the HDO/H₂O ratios of larger samples of isolated and clustered protostars in order to understand the impact of environmental factors.

A Massive Planet Approaches Its Doom

TOI-2109b is an ultra-hot Jupiter exoplanet that orbits its host star every 16 hours, giving it the shortest period of any known hot Jupiter. Orbiting its host star so closely, TOI-2109b is susceptible to powerful tidal forces that can lead to an exchange of angular momentum between the planet and its home star, potentially causing the planet to spiral inward and be engulfed by its star.

Jaime Alvarado-Montes (Macquarie University) and collaborators investigated how and when TOI-2109b’s doom might come about. Critical to the discussion is the uncertain age of TOI-2109, which likely lies in the range of 1.09–2.65 billion years. If the star’s age is on the lower end of the range, TOI-2109b’s orbit would decay slowly (~4 milliseconds per year); if the star’s age is on the higher end of the range, the planet’s orbit would decay quickly (~1,100 milliseconds per year). The decay rate depends on the star’s age because planets lose their kinetic energy due to friction inside their host stars, and the efficiency of this process depends upon the interior structure of the star, which changes with age.

Alvarado-Montes and coauthors used data from the Transiting Exoplanet Survey Satellite (TESS), the CHaracterising ExOPlanet Satellite (CHEOPS), and multiple ground-based telescopes to constrain the rate of change of TOI-2109b’s orbital period. Taking into account changes in transit timing due to an outer planet candidate in the system, deviations from spherical symmetry, and other factors, the authors find a likely orbital decay rate of just 2.6 milliseconds per year. This is consistent with the rate predicted for a “young” host star, and it’s expected to shift TOI-2109b’s mid-transit time by a few seconds over a three-year period. This change is potentially detectable with high-cadence observations, helping to understand not just the fate of TOI-2109b, but of ultra-short-period planets as a whole.

Discovery of a Mysterious Long-Period Transient

Finally, Fengqiu Adam Dong (National Radio Astronomy Observatory; Green Bank Observatory) and coauthors recently described their discovery of an unusual long-period transient radio signal. Long-period radio transients exhibit signals that repeat with periods ranging from 10 seconds to multiple hours. While the exact origin of these signals remains unknown, researchers suspect that magnetic white dwarfs and neutron stars are the cause, with the two sources perhaps representing different classes under the long-period radio transient umbrella.

The signal was detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope, which was searching for bursts of radio emission from pulsars within our galaxy. The newly discovered radio signal, which comes from a source named CHIME J1634+44, has a primary period of 841 seconds and a secondary period of 4,206 seconds, making it decidedly un-pulsar-like. Dong’s team performed follow-up observations of CHIME J1634+44 with the Very Large Array, the Neil Gehrels Swift Observatory, and the Green Bank Telescope. The Very Large Array and the Green Bank Telescope each detected two bursts from the source, bringing the total number of bursts reported in this study to 89.

CHIME J1634+44 is unusual in a number of ways. Its emission is almost entirely circularly polarized, meaning that the plane in which the electric and magnetic waves of the radio signal oscillates rotates in a circle as the signal travels through space. The time between pulses is also decreasing, slowly but steadily. If the pulsation period coincides with an object’s spin period, this means that the object is spinning faster as time goes on; this could occur if the source of the bursts is accreting material from a companion. If instead the pulsation period is linked to the orbital period of an object in a binary system, emission of gravitational waves could be causing the orbit to shrink.

What kind of object could produce this signal? Dong and coauthors considered binary systems containing either a white dwarf or a neutron star. Neither scenario perfectly fits the available evidence, but the team concluded that a binary system containing a neutron star is the likeliest source of the long-period, highly polarized, steadily accelerating pulses of CHIME J1634+44. The strongest evidence in favor of this scenario is that neutron stars are known to exhibit strongly polarized pulses of similar luminosity to those from CHIME J1634+44. Dong’s team expects that CHIME J1634+44 will remain an important test of theories of long-period radio transients — and as new information emerges about its identity, CHIME J1634+44 might just find its way into the news again!

Citation

“A Demonstration of Interstellar Navigation Using New Horizons,” Tod R. Lauer et al 2025 AJ 170 22. doi:10.3847/1538-3881/addabe

“HDO Ice Detected Toward an Isolated Low-Mass Protostar with JWST,” Katerina Slavicinska et al 2025 ApJL 986 L19. doi:10.3847/2041-8213/addb45

“Orbital Decay of the Ultra-Hot Jupiter TOI-2109b: Tidal Constraints and Transit-Timing Analysis,” Jaime A. Alvarado-Montes et al 2025 ApJ 988 66. doi:10.3847/1538-4357/ade057

“CHIME/Fast Radio Burst Discovery of an Unusual Circularly Polarized Long-Period Radio Transient with an Accelerating Spin Period,” Fengqiu Adam Dong et al 2025 ApJL 988 L29. doi:10.3847/2041-8213/adeaab

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