Category: 7. Science

SLAC National Accelerator Laboratory and University of Nevada, Reno scientists have debunked a 40-year-old theory by heating solid gold to 14 times its normal melting point without melting it!

The scientists achieved this feat and rewrote the rules of high-temperature physics using a combination of ultrafast lasers and X-rays.

Understanding Entropy Catastrophe

For nearly 40 years, physicists have believed there is a hard limit to how hot a solid can get without spontaneously breaking apart. 

Known as the “entropy catastrophe,” this theory holds that once a material reaches around three times its melting point, the increased entropy overwhelms its structure, causing it to liquefy.

Hotter Than the Sun

SLAC’s recent experiment, however, challenges this long-standing belief.

The scientists hit a wafer-thin gold film with a 45-femtosecond laser pulse. They followed it up with a flash from SLAC’s 2-mile-long Linac Coherent Light Source X-ray laser that functioned as an atomic thermometer.

While gold’s normal melting point is 1,337 kelvins (1,947°F), the scientists, by observing how the X-rays scattered off the vibrating gold atoms, calculated a mind-boggling 19,000 kelvins (33,740°F) — hotter than even the Sun’s surface (9,900°F)!

And the best part? By heating the material so fast, the atoms didn’t have time to reorganize into a liquid structure. SLAC’s process basically outran the material’s natural melting behavior.

The Future of Thermodynamics

Ask any particle scientist, and they’ll tell you how tough it is to measure and understand extreme states of matter, such as those found in the cores of gas giants like Jupiter or inside fusion reactors on Earth. Even if they do, it would be plagued by large error bars.

By shattering the temperature barrier, the SLAC-Nevada team has now shown it is possible to probe the inner temperatures within ultra-hot systems accurately.

Image credit: artshock/Shutterstock

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Polluted white dwarfs offer a unique way to directly probe the compositions of exoplanetary bodies.

We examine the water content of accreted material using the oxygen abundances of 51 highly polluted white dwarfs. Within this sample, we present new abundances for three H-dominated atmosphere white dwarfs that showed promise for accreting water-rich material.

Throughout, we explore the impact of the observed phase and lifetime of accretion disks on the inferred elemental abundances of the parent bodies that pollute each white dwarf. Our results indicate that white dwarfs sample a range of dry to water-rich material, with median uncertainties in water mass fractions of ≈15%.

Amongst the He-dominated white dwarfs, 35/39 water abundances are consistent with corresponding H abundances. While for any individual white dwarf it may be ambiguous as to whether or not water is present in the accreted parent body, when considered as a population the prevalence of water-rich bodies is statistically robust.

The population as a whole has a median water mass fraction of ≈25%, and enforcing chondritic parent body compositions, we find that 31/51 WDs are likely to have non-zero water concentrations. This conclusion is different from a similar previous analysis of white dwarf pollution and we discuss reasons why this might be the case.

Pollution in H-dominated white dwarfs continues to be more water-poor than in their He-dominated cousins, although the sample size of H-dominated white dwarfs remains small and the two samples still suffer a disjunction in the range of host star temperatures being probed.

Isabella L. Trierweiler, Carl Melis, Érika Le Bourdais, Patrick Dufour, Alycia J. Weinberger, Boris T. Gänsicke, Nicola Gentile-Fusillo, Siyi Xu, Jay Farihi, Andrew Swan, Malena Rice, Edward D. Young

Comments: 30 pages, 14 figures Accepted to ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2508.20172 [astro-ph.EP] (or arXiv:2508.20172v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2508.20172
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Submission history
From: Isabella Trierweiler
[v1] Wed, 27 Aug 2025 18:00:07 UTC (1,655 KB)
https://arxiv.org/abs/2508.20172
Astrobiology

For decades, humans have imagined that the universe might be filled with intelligent life. Yet despite billions of stars and galaxies, we have found no clear evidence of aliens. Now, scientists suggest a possible reason: Earth may be located in an enormous cosmic void—a vast, sparsely populated region of space. If true, our planet could be unusually isolated from the denser regions of the universe, giving the appearance that humanity is alone or even “ostracized” in the cosmic landscape.

This theory, presented at the Royal Astronomical Society’s National Astronomy Meeting, has been led by Dr. Indranil Banik of the University of Portsmouth. The discovery could have far-reaching implications for our understanding of the universe’s structure and expansion.

Dr. Banik’s team explained that the local void, also referred to as an underdensity, could be roughly one billion light-years wide and about 20% less dense than the average universe. This sparsity of matter would affect how we perceive galaxy movements, potentially making it appear that the universe is expanding faster than it actually is.

Possible Solution to the Hubble Tension

The idea of a local cosmic void provides a potential explanation for the long-standing Hubble Tension, which arises from discrepancies in measuring the universe’s expansion rate. Observations of distant galaxies suggest a slower expansion, while local measurements indicate a faster rate. According to Dr. Banik, if the Milky Way is located inside a vast void, gravitational effects from denser surrounding regions would pull matter outward, making local velocities seem larger.

“This model, based on two decades of baryon acoustic oscillation data, is significantly more likely than a void-free model,” Dr. Banik said, highlighting the consistency of his team’s findings with patterns left from the Big Bang.

Implications for Cosmology

If confirmed, the local void theory challenges the assumption that the universe is uniform on large scales. It would also have consequences for predictions about the universe’s future, including the timing of the so-called “heat death,” when energy is evenly distributed and no significant cosmic activity occurs.While the idea of humans living in a cosmic void is still debated, Banik’s research strengthens the possibility that our region of the universe may be lonelier than previously thought. By analyzing oscillations caused by the early universe, his team has provided evidence that supports the existence of this massive void.

Life in the Void

Living in a cosmic void could have indirect implications for humanity, as it affects how we perceive the universe around us. Although the void does not directly indicate alien activity or ostracization, it does suggest that our cosmic neighborhood is isolated compared to denser regions of the universe.

Further research, including comparisons with supernova data, will be necessary to fully validate this theory and understand its consequences for cosmology. For now, Earth’s place in a giant cosmic void remains a compelling possibility that may reshape how scientists view the universe.

An increasing number of applications in exoplanetary science require spectrographs with high resolution and high throughput without the need for a broad spectral range.

Examples include the search for biosignatures through the detection of the oxygen A-band at 760 nm, and the study of atmospheric escape through the helium 1083 nm triplet. These applications align well with the capabilities of a spectrograph based on a Virtually Imaged Phased Array (VIPA), a high-throughput dispersive element that is essentially a modified Fabry-Perot etalon.

We are developing VIPER, a high-resolution, narrowband, multimode fiber-fed VIPA spectrograph specifically designed to observe the helium 1083 nm triplet absorption line in the atmospheres of gaseous exoplanets. VIPER will achieve a resolving power of 300,000 over a wavelength range of 25 nm, and will be cross-dispersed by an echelle grating. VIPER is intended for operation on the 1.5 m Tillinghast Telescope and potentially on the 6.5 m MMT, both located at the Fred Lawrence Whipple Observatory (FLWO) on Mount Hopkins, Arizona, USA.

In this paper, we present VIPER’s instrument requirements, derived from the primary science goal of detecting anisotropic atmospheric escape from exoplanets. We discuss the design methodology for VIPA-based spectrographs aimed at maximizing throughput and diffraction efficiency, and we derive a wave-optics-based end-to-end model of the spectrograph to simulate the intensity distribution at the detector.

We present an optical design for VIPER and highlight the potential of VIPA-based spectrographs for advancing exoplanetary science.

Matthew C. H. Leung, David Charbonneau, Andrew Szentgyorgyi, Colby Jurgenson, Morgan MacLeod, Surangkhana Rukdee, Shreyas Vissapragada, Fabienne Nail, Joseph Zajac, Andrea K. Dupree

Comments: 39 pages, 27 figures, SPIE Optics + Photonics 2025
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2508.20169 [astro-ph.IM](or arXiv:2508.20169v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2508.20169
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From: Matthew Leung
[v1] Wed, 27 Aug 2025 18:00:04 UTC (4,856 KB)
https://arxiv.org/abs/2508.20169
Astrobiology

A groundbreaking study by researchers from Wuhan University, York University (UK), and Peking University has uncovered how Escherichia coli (E. coli) persister bacteria survive antibiotics by protecting their genetic instructions. The work, published in Nature Microbiology, offers new hope for tackling chronic, recurring infections.

Persister bacteria, which enter a dormant state to survive antibiotics that target active cells, are linked to over 20% of chronic infections and resist current treatments. Understanding their survival mechanisms could lead to new ways to combat recurring infections. This study utilized E. coli bacteria as a model and found that prolonged stress leads to the increased formation of aggresomes (membraneless droplets) and the enrichment of mRNA (molecules that carry instructions for making proteins) within them, which enhances the ability of E. coli to survive and recover from stress.

Key findings

They used multiple approaches, including imaging, modeling, and transcriptomics, to show that prolonged stress leading to ATP(fuel for all living cells) depletion in Escherichia coli results in increased aggresome formation, their compaction, and enrichment of mRNA within aggresomes compared to the cytosol(the liquid inside of cells). Transcript length was longer in aggresomes compared to the cytosol. Mass spectrometry showed exclusion of mRNA ribonuclease(an enzyme that breaks down RNA) from aggresomes, which was due to negative charge repulsion. Experiments with fluorescent reporters and disruption of aggresome formation showed that mRNA storage within aggresomes promoted translation and was associated with reduced lag phases during growth after stress removal. These findings suggest that mRNA storage within aggresomes confers an advantage for bacterial survival and recovery from stress.

Future implications

This breakthrough illuminates how persister cells survive and revive after antibiotic treatment. By targeting aggresomes, new drugs could disrupt this protective mechanism, preventing bacteria from storing mRNA and making them more vulnerable to elimination, thus reducing the risk of infection relapse.

This white paper is a summary of the Uranus Flagship Workshop that took place 21 to 23 May 2024 at NASA’s Goddard Space Flight Center. Co-led by Goddard and Johns Hopkins Applied Physics Lab conveners, we had a broad, international, Science Organizing Committee, and a largely early career Local Organizing Committee from APL and GSFC.

From prior workshops, it was apparent that the community was wildly enthusiastic about starting a mission, but lacked focus on what was possible or where to begin. Thus, the purpose of our workshop was to discuss practical aspects of the next planetary flagship and how we can employ new paradigms to better enable robust outer planet exploration.

To enable this goal, we introduced the community to the best practices and lessons learned from previous missions and NASA-commissioned studies, and discussed the challenges involved with a mission so far from the Earth/Sun.

The underlying workshop purpose was to steward the community towards a more practical mission design approach that will enable the development of this mission, as well as future missions, on a shorter cadence by setting expectations and having difficult discussions early in development. Because of the time scales involved in this mission, special effort was made towards early career inclusion and participation.

Amy Simon, Louise Prockter, Ian Cohen, Kathleen Mandt, Lynnae Quick

Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2508.21074 [astro-ph.IM] (or arXiv:2508.21074v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2508.21074
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From: Amy Simon
[v1] Mon, 11 Aug 2025 12:57:46 UTC (2,876 KB)
https://arxiv.org/abs/2508.21074
Astrobiology,

The occurrence rate of close-in super-Earths is higher around M-dwarfs compared to stars of higher masses.

In this work we aim to understand how the super-Earth population is affected by both the stellar mass, the size of the protoplanetary disc, and viscous heating. We utilise a standard protoplanetary disc model with both irradiated and viscous heating together with a pebble accretion model to simulate the formation and migration of planets.

We find that if the disc is heated purely through stellar irradiation, inwards migration of super-Earths is very efficient, resulting in the close-in super-Earth fraction increasing with increasing stellar mass.

In contrast, when viscous heating is included, planets can undergo outwards migration, delaying migration to the inner edge of the protoplanetary disc, which causes a fraction of super-Earth planets to grow to become giant planets instead.

This results in a significant reduction of inner super-Earths around high-mass stars and an increase in the number of giant planets, both of which mirror observed features of the planet population around high-mass stars. This effect is most pronounced when the protoplanetary disc is large, since such discs evolve over a longer time-scale. We also test a model when we inject protoplanets at a fixed time early on in the disc lifetime.

In this case, the fraction of close-in super-Earths decreases with increasing stellar mass in both the irradiated case and viscous case, since longer disc lifetimes around high-mass stars allows for planets to grow into giants instead of super-Earths for most injection locations.

Jesper Nielsen, Anders Johansen

Comments: 19 Pages, 16 figures, accepted for publication in A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2508.21627 [astro-ph.EP] (or arXiv:2508.21627v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2508.21627
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From: Jesper Nielsen
[v1] Fri, 29 Aug 2025 13:39:28 UTC (3,995 KB)
https://arxiv.org/abs/2508.21627
Astrobiology,

Identifying Earth-like planets outside out solar system is a leading research goal in astronomy, but determining if candidate planets have atmospheres, and more importantly if they can retain atmospheres, is still out of reach.

In this paper, we present our study on the impact of enhanced EUV flux on the stability and escape of the upper atmosphere of an Earth-like exoplanet using the Global Ionosphere and Thermosphere Model (GITM). We also investigate the differences between one- and three-dimensional solutions.

We use a baseline case of EUV flux experienced at the Earth, and multiplying this flux by a constant factor going up to 50. Our results show a clear evidence of an inflated and elevated ionosphere due to enhanced EUV flux, and they provide a detailed picture of how different heating and cooling rates, as well as the conductivity are changing at each EUV flux level.

Our results also demonstrate that one-dimensional solutions are limited in their ability to capture a global atmosphere that are not uniform. We find that a threshold EUV flux level for a stable atmosphere occurs around a factor of 10 times the baseline level, where EUV fluxes above this level indicate a rapidly escaping atmosphere. This threshold EUV flux translates to about 0.3AU for a planet orbiting the Sun.

Thus, our findings indicate that an Earth-like exoplanet orbiting its host star in a close-in orbit is likely to lose its atmosphere quickly.

Lukas Hanson, Ofer Cohen, Aaron Ridley, Alex Glocer

Comments: 13 pages, 9 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2508.21745 [astro-ph.EP] (or arXiv:2508.21745v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2508.21745
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Related DOI:
https://doi.org/10.3847/1538-4357/adff7f
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Submission history
From: Lukas Hanson
[v1] Fri, 29 Aug 2025 16:19:14 UTC (2,268 KB)
https://arxiv.org/abs/2508.21745
Astrobiology,

Archaea, a domain of microorganisms found in diverse environments including the human microbiome, represent the closest known prokaryotic relatives of eukaryotes.

This phylogenetic proximity positions them as a relevant model for investigating the evolutionary origins of nucleic acid secondary structures such as G-quadruplexes (G4s), which play regulatory roles in transcription and replication. Although G4s have been extensively studied in eukaryotes, their presence and function in archaea remain poorly characterized.

In this study, a genome-wide analysis of the halophilic archaeon Haloferax volcanii identified over 5, 800 potential G4-forming sequences. Biophysical validation confirmed that many of these sequences adopt stable G4 conformations in vitro. Using G4-specific detection tools and super-resolution microscopy, G4 structures were visualized in vivo in both DNA and RNA across multiple growth phases.

Comparable findings were observed in the thermophilic archaeon Thermococcus barophilus. Functional analysis using helicase-deficient H. volcanii strains further identified candidate enzymes involved in G4 resolution. These results establish H. volcanii as a tractable archaeal model for G4 biology.

Archaeal G-Quadruplexes: A Novel Model for Understanding Unusual DNA/RNA Structures Across the Tree of Life

Astrobiology, Genomics,