SPACE/COSMOS
Detection of phosphine in a brown dwarf atmosphere raises more questions
Astronomers found the elusive gas on Wolf 1130C but wonder why it’s not more prevalent in other brown dwarfs
image:
Schematic of the Wolf 1130ABC triple system, composed of the red dwarf star Wolf 1130A (l), its close and compact white dwarf companion Wolf 1130B (c), and the distant brown dwarf tertiary Wolf 1130C (r). The three components of this system are shown scaled to their relative sizes.
view moreCredit: Adam Burgasser
Phosphorus is one of six key elements necessary for life on Earth. When combined with hydrogen, phosphorus forms the molecule phosphine (PH3), an explosive, highly toxic gas. Found in the atmospheres of the gas giant planets Jupiter and Saturn, phosphine has long been recognized as a possible biosignature for anaerobic life, as there are few natural sources of this gas in the atmospheres of terrestrial planets. On Earth, phosphine is a byproduct of decaying organic swamp matter.
Now a team of researchers, led by University of California San Diego Professor of Astronomy and Astrophysics Adam Burgasser, has reported the detection of phosphine in the atmosphere of a cool, ancient brown dwarf named Wolf 1130C. Their work appears in Science.
Phosphine was detected in Wolf 1130C’s atmosphere using observations obtained with the James Webb Space Telescope (JWST), the first telescope with the sensitivity to look at these celestial objects in detail. The mystery, however, is not why phosphine was found, but why it’s missing in other brown dwarf and gas giant exoplanet atmospheres.
“Our astronomy program, called Arcana of the Ancients, focuses on old, metal-poor brown dwarfs as a means of testing our understanding of atmospheric chemistry,” said lead author Burgasser. “Understanding the problem with phosphine was one of our first goals.”
In the hydrogen-rich atmospheres of gas giant planets like Jupiter and Saturn, phosphine forms naturally. As such, scientists have long predicted that phosphine should be present in the atmospheres of gas giants orbiting other stars, and in their more massive cousins, brown dwarfs — objects sometimes called “failed stars” because they do not fuse hydrogen.
Yet phosphine has largely eluded detection, even in prior JWST observations, suggesting problems with our understanding of phosphorus chemistry. “Prior to JWST, phosphine was expected to be abundant in exoplanet and brown dwarf atmospheres, following theoretical predictions based on the turbulent mixing we know exists in these sources,” said co-author Sam Beiler, who recently graduated from the University of Toledo and is now postdoctoral scholar at Trinity College Dublin.
Beiler, who has led previous work studying the lack of phosphine in brown dwarfs, stated, "Every observation we've obtained with JWST has challenged the theoretical predictions — that is until we observed Wolf 1130C.”
In the star system Wolf 1130ABC, located 54 light-years from the sun in the constellation Cygnus, the brown dwarf Wolf 1130C follows a wide orbit around a tight double star system, composed of a cool red star (Wolf 1130A) and a massive white dwarf (Wolf 1130B). Wolf 1130C has been a favorite source for brown dwarf astronomers due to its low abundance of “metals” – essentially any elements other than hydrogen and helium – compared to the sun.
Unlike other brown dwarfs, the team easily spotted phosphine in JWST’s infrared spectral data of Wolf 1130C. To fully understand the implications of their findings, they needed to quantify the abundance of this gas in Wolf 1130C's atmosphere. This was done by Assistant Professor of Astronomy at San Francisco State University Eileen Gonzales, also a co-author on the study.
“To determine the abundances of molecules in Wolf 1130C, I used a modeling technique known as atmospheric retrievals," explained Gonzales. "This technique uses the JWST data to back out how much of each molecular gas species should be in the atmosphere. It’s like reverse engineering a really delicious cookie when the chef wouldn’t give up the recipe.”
Gonzales’s models showed that abundant phosphine was the secret ingredient in Wolf 1130C. Specifically, she found that phosphine was present at the predicted theoretical abundances of about 100 parts per billion.
While the researchers are delighted by their discovery, it raises an issue: why is phosphine present in the atmosphere of this brown dwarf and not others?
One possibility is the low abundance of metals in Wolf 1130C’s atmosphere, which may change its underlying chemistry. “It may be that in normal conditions phosphorus is bound up in another molecule such as phosphorus trioxide,” explained Beiler. “In the metal-depleted atmosphere of Wolf 1130C, there isn’t enough oxygen to take up the phosphorus, allowing phosphine to form from the abundant hydrogen.”
The team hopes to explore this possibility with new JWST observations that will search for phosphine in the atmospheres of other metal-poor brown dwarfs.
Another possibility is that phosphorus was generated locally in the Wolf 1130ABC system, specifically by its white dwarf, Wolf 1130B.
"A white dwarf is the leftover husk of a star that has finished fusing its hydrogen," explained Burgasser. "They are so dense that when they accrete material on their surface they can undergo runaway nuclear reactions, which we detect as novae.”
While astronomers haven't seen evidence of such events in the Wolf 1130ABC system in recent history, novae typically have outburst cycles of thousands to tens of thousands of years. This system has been known for just over a century, and early, unseen outbursts could have left a legacy of phosphorus pollution. Earlier research studies have proposed that a significant fraction of phosphorus in the Milky Way could have been synthesized by this process.
Understanding why this one brown dwarf shows a clear signature of phosphine may lead to new insights into the synthesis of phosphorus in the Milky Way and its chemistry in planetary atmospheres. Explained Burgasser, “Understanding phosphine chemistry in the atmospheres of brown dwarfs where we don’t expect life is crucial if we hope to use this molecule in the search for life on terrestrial worlds beyond our solar system.”
This study was funded in part by NASA/STScI (NAS 5-03127 and AR-2232) and the Heising-Simons Foundation.
Journal
Science
Method of Research
Observational study
Article Title
Observation of undepleted phosphine in the atmosphere of a low-temperature brown dwarf
Article Publication Date
2-Oct-2025
New approach to gravitational wave detection opens the Milli-Hz Frontier
University of Birmingham
image:
Gravitational waves from merging black holes. 3D illustration
view moreCredit: Peter Jurik/Alamy
Scientists have unveiled a new approach to detecting gravitational waves in the milli-Hertz frequency range, providing access to astrophysical and cosmological phenomena that are not detectable with current instruments.
Gravitational waves—ripples in spacetime predicted by Einstein—have been observed at high frequencies by ground-based interferometers such as LIGO and Virgo, and at ultra-low frequencies by pulsar timing arrays. However, the mid-band range has remained a scientific blind spot.
Developed by researchers at the Universities of Birmingham and Sussex, the new detector concept uses cutting-edge optical cavity and atomic clock technologies to sense gravitational waves in the elusive milli-Hertz frequency band (10⁻⁵ – 1 Hz).
Publishing their proposal today (3 Oct) in Classical and Quantum Gravity, the scientist reveal a detector that uses advances in optical resonator technology, originally developed for optical atomic clocks, to measure tiny phase shifts in laser light caused by passing gravitational waves. Unlike large-scale interferometers, these detectors are compact, relatively immune to seismic and Newtonian noise.
Co-author Dr Vera Guarrera, from the University of Birmingham, commented: “By using technology matured in the context of optical atomic clocks, we can extend the reach of gravitational wave detection into a completely new frequency range with instruments that fit on a laboratory table. This opens the exciting possibility of building a global network of such detectors and searching for signals that would otherwise remain hidden for at least another decade.”
The milli-Hertz frequency band - sometimes called the ‘mid-band’ - is expected to host signals from a variety of astrophysical and cosmological sources, including compact binaries of white dwarfs and black hole mergers. Ambitious space missions such as LISA also target this frequency band, but they are scheduled for launch in the 2030s. The proposed optical resonator detectors could begin exploring this territory now.
Co-author Professor Xavier Calmet, from the University of Sussex, commented: “This detector allows us to test astrophysical models of binary systems in our galaxy, explore the mergers of massive black holes, and even search for stochastic backgrounds from the early universe. With this method, we have the tools to start probing these signals from the ground, opening the path for future space missions.”
While future space-based missions like LISA will offer superior sensitivity, their operation is over a decade away. The proposed optical cavity detectors provide an immediate, cost-effective means to explore the milli-Hz band.
The study also suggests that integrating these detectors with existing clock networks could extend gravitational wave detection to even lower frequencies, complementing high-frequency observatories like LIGO.
Each unit consists of two orthogonal ultrastable optical cavities and an atomic frequency reference, enabling multi-channel detection of gravitational wave signals. This configuration not only enhances sensitivity but also allows for the identification of wave polarisation and source direction.
ENDS .
Image Caption – please credit Peter Jurik/Alamy:
Gravitational waves from merging black holes. 3D illustration
Notes to Editors
The University of Birmingham is ranked amongst the world’s top 100 institutions, its work brings people from across the world to Birmingham, including researchers and teachers and more than 8,000 international students from over 150 countries.
‘Detecting milli-Hz gravitational waves with optical resonators’ - Giovanni Barontini, Xavier Calmet, Vera Guarrera, Aaron Smith, and Alberto Vecchio is published in Classical and Quantum Gravity.
Journal
Classical and Quantum Gravity
Method of Research
Computational simulation/modeling
Subject of Research
Not applicable
Article Title
Detecting milli-Hz gravitational waves with optical resonators
Article Publication Date
3-Oct-2025
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