The StarXiv ✨ podcast

Payel's second papers uses 16.7 years of Fermi Large Area Telescope (Fermi-LAT) data to establish galaxy mergers as a new class of HE γ-ray sources. Exciting stuff! 🔭☄️ arxiv.org/pdf/2511.13818

The critical mass of a Dark Star at the onset of collapse as a function of the dark matter (WIMP) particle mass for various mass accretion rates. The critical mass of the dark star can be used as an estimate for the mass of the resulting black hole. The critical mass is independent of the accretion rate, except for the case of mχ = 100 TeV

Michelle's second paper discussed whether theoretical dark matter powered stars in the early Universe could act as the seeds for supermassive black holes. The authors study the evolution of these 'dark stars' and determine they could! arxiv.org/abs/2511.08578 🔭 ☄️

Abundances relative to Fe as a function of [Fe/H] for different elements as indicated by the label in the upper right corner of each panel. The figure includes data from two different models in different shades of red and blue, as indicated by the legend in the bottom right panel. For each model, different color shades present different simulations, varying only the random seed for IMF and SNIa sampling. The dashed vertical lines mark the mean value on the corresponding axis for each simulation. Included in the bottom (top) left of the top (bottom) row are colored error bars that show the total dispersion accounting for all stars in the three simulations of the corresponding color.

Nicole’s second paper shows that an ultra-faint dwarf’s chemical fingerprints need to be treated carefully, they shift depending on assumptions about Type Ia supernova timing, massive-star yields, and stochastic sampling. arxiv.org/abs/2511.05695 🔭☄️

Payel's first paper finds compelling evidence for an off-axis merger event in the Coma cluster using high-resolution X-ray spectroscopy of the intracluster medium. 🔭☄️ arxiv.org/abs/2511.10740

How the accreted population was split from the thin- and thick discs using the [Mg/Mn]-[Al/Fe] plane. Left: How the [Mg/Mn]-[Al/Fe] plane was divided into different regions, marked with red lines. Region I is the thick disc, region II is the thin disc, and region III is the halo or accreted stars. Right: Distribution of stars from the selection. The panels show [Mg/Fe]-[Fe/H] in the top row and [Mg/Mn]-[Al/Fe] in the bottom row. Left columns: Region I, the thick disc; Right columns: Region II, the thin disc.

Nicole’s first paper shows the structural parameters of the Milky Way’s thin and thick discs can shift depending on whether stars are split by chemistry, age, or dynamics. Chemically defined discs stay clean, while dynamical cuts can potentially mix populations. arxiv.org/abs/2511.10092 🔭☄️

Predictions for how many planets with mass > 5x the mass of Earth the VOYAGERS survey will find in their focused survey of 10 stars, if planets are distributed in the same way as more metal rich, Galactic stars.

Michelle's first paper focused on finding extragalactic exoplanets! Te VOYAGERS survey looks for planets around stars brought into the Galaxy by the GES merger. Would they be different? Tune in to find out! 🔭 ☄️https://arxiv.org/abs/2511.07632

Episode 25: Extragalactic exoplanets, simulating individual stars, and galaxy mergers as cosmic ray factories In this episode, Michelle and Payel explore various astrophysical topics, including the Solar birth cluster, young stars, the formation of intermediate mass black holes, and the universe's decelerated expansion. They also discuss strong lens detection by Euclid and solar flare predictions.

Episode 25: Extragalactic exoplanets, simulating individual stars, and galaxy mergers as cosmic ray factories

In this episode, Michelle and Payel explore various astrophysical topics, including the Solar birth cluster, young stars, the formation of intermediate mass black holes, and the universe's…

Left: Euclidised 2′×2′RGB image (R= JHE, G= YE, B= IE) of the galaxy cluster Abell 1063, belonging to the test set; the right-most arc is the one injected via SL simulation, while the others are real. Right: single channel 2′×2′Euclidised IE image of the same cluster. The green boxes enclose the gravitational arcs (both real and simulated) present in the field, i.e. the ground truth, while the red dashed boxes are the ‘gravitational arcs’ found by the NN, having an object confidence score greater than 0.996.

Michelle's final paper focuses on machine learning approaches to detect strong gravitational lenses in incredible Euclid space telescope data. Using Masked-R-CNN, the authors are able to detect large lensing arcs in images. Tune in for more! 🔭 ☄️ arxiv.org/abs/2511.03064

Payel's final paper compares how weel state-of-the-art Chat-GPT type models can predict the occurrence of solar flares and coronal mass ejections across high-resolution images, videos, and high-resolution time series data 🔭 ☄️. Find out more at arxiv.org/abs/2510.23400.

Clusters hosting an intermediate mass black hole (IMBH )at z = 0 in Model A (left panel) and Model B (right panel) compared to different classes of IMBH host candidates observations. Note that the masses reported for low-mass AGN refer to the host galaxy mass (up to∼100 times larger than the mass of the galactic nuclei). The gray dashed line shows the theoretical prediction for the initial mass of an IMBH seeded via stellar collisions (Eq. (3) in the left panel and Eq. (5) in the right panel).

Michelle's 2nd paper discusses a semi-analytical approach to modelling the formation of intermediate mass black holes in star clusters. They find different distributions in the cluster mass-black hole mass plane for globular and nuclear star clusters, Tune in for more! 🔭☄️ arxiv.org/abs/2511.00200

Evolution of the deceleration parameter taking different data into account.

Payel's second paper claims a expansion of the universe that is decelerating rather than accelerating after correcting for a correlation between age and magnitude of Type 1a supernovae 🔭 ☄️. Find out more at arxiv.org/abs/2510.13121.

Location of young alpha-enriched stars from APOGEE and GALAH.

Payel's first paper finds bona-fide young alpha-enriched stars in the Milky Way! An unexpected find as alpha enrichment usually happens early in a chemical evolution history 🔭 ☄️. Find out more at arxiv.org/pdf/2510.15654.

Fraction of flyby histories that are compatible with the observed inclination distribution of distant sednoids (initial inclinations are set to zero) as a function of num- ber of flybys with impact parameter <10^4 AU. The result- ing upper limit on χ, if we adopt a KS test threshold of p1 = 0.05 and require at least p2 = 0.05 of all simulations to exceed this threshold in order to remain compatible, is ≲ 5 × 10^3 Myr pc−3. The fraction starts near zero because the initial inclinations are set at zero.

☄️ Michelle's first paper constrains the birth cluster of the Sun. Using N-body simulations and the orbital properties of the Sednoids in the outer Solar system, they can improve constraints on the density of, and time the Sun spent in, the cluster by an order of magnitude! 🔭 arxiv.org/abs/2510.19910

We give a shout out to Benty Fields this episode. It's a great resource for finding and tracking papers. Support them if you can ☄️🔭

Episode 24 of the StarXiv is out! Tune in as Payel and Michelle discuss the latest from the astro-arXiv, including young, high alpha stars, intermediate black holes, solar flares, Euclid lenses and more! Listen below, on Spotify or wherever you get podcasts 🔭 🧪

Episode 24: Strong lenses, Solar Flares and young, high alpha stars In this episode, Michelle and Payel explore various astrophysical topics, including the Solar birth cluster, young stars, the formation of intermediate mass black holes, and the universe's decelerated expansion. They also discuss strong lens detection by Euclid and solar flare predictions.

Episode 24: Strong lenses, Solar Flares and young, high alpha stars

In this episode, Michelle and Payel explore various astrophysical topics, including the Solar birth cluster, young stars, the formation of intermediate mass black holes, and the universe's decelerated expansion. They also discuss…

Sorry to have let you down! We will get you ready for next Tuesdays coffee time 😉

Owing to a technical hiccup, the StarXiv will be arriving a little later this week. Expect to hear Michelle and Payel chat about the latest from astro-ph this Wednesday instead! It'll be worth the wait ☄️ 🔭

These 4 plots show how the simulated failed galaxy progenitors (UDGs) compare to more normal galaxies in the same simulation. They tend to form stars more rapidly (panel 1), have lower metallicities (panel 2), have higher star formation rates (panel 3) and later halo assembly (panel 4) than typical galaxies.

Michelle's final paper discussed the 'failed' galaxies. Thought to be living in massive dark matter halos that have formed fewer stars than expected, this population is poorly undertsood. This paper looks for their progenitors in the MAGNETICUM simulations 🔭 ☄️https://arxiv.org/abs/2510.04416

[Eu/Fe] vs. [La/Fe] ratios for CEMP-r and CEMP-s stars by Masseron et al. (2010), CEMP-s stars by Roederer et al. (2014), Ba stars by Roriz et al. (2021), and the s-rich RRLs DQ Hya and TY Gruis. The dashed line is the 1:1 relationship.

Nicole’s third paper reported two RR Lyrae stars enriched in heavy s-process elements, a rare class previously represented only by TY Gruis. Their chemistry could reveal ancient mass transfer from AGB companions. arxiv.org/abs/2510.15723 🔭☄️

These two plots show the previous work on measuring the velocity dispersion in Ursa Major III/ UNIONS 1 on the left. Including all stars they measure a clear result that would indicate a dark matter halo (orange Gaussian at 3.7 km/s). But these authors noted if one star (a possible binary) was removed, they can no longer resolve this value (dot-dashed curve), making it consistent with no dark matter. Using follow up data, this paper confirms that star is a binary and revises the velocity dispersion (right panel). Now we see it is entirely consistent with no dark matter (gray vertical band). So, *probably* a star cluster!

In Michelle's second paper, she updates us all on the offensively faint Ursa Major III/UNIONS 1 stellar association. Is it a galaxy wtih dark matter or a star cluster? This new paper searches for signs of dark matter and/or binary stars to answer this question! arxiv.org/abs/2510.02431 🔭 ☄️

Panel (a): The universal SFMS of star-forming Au18 as a function of M⋆ and redshift z. The black-solid line indicates the SFMS ridge, while the gray-shaded region denotes a ±0.3 dex scatter of the SFMS (S. Tacchella et al., 2016). The labeled look-back times tlb1, tlb2, tlb3, and tlb4, mark the approximate durations of three compaction events identified in the Au18 evolution, using the same colors as the associated redshifts. Panel (b): The edge-on stellar number-density map of stars formed during the earliest episode of compaction and quenching events, corresponding to ages between tlb2 and tlb1 at z=0. Panels (c) and (d): The same as panel (b), but for the second and third compaction episodes, respectively. The border colors of panels (b)-(d) match the colors of the relevant redshifts. Panel (e): The edge-on stellar number-density distribution at z=0 for all stars formed during the three compaction episodes shown in panel (a). This figure indicates the possible connection between proto-Galaxy formation and multiple high-z (z≳3) compaction episodes.

Nicole’s second paper showed our Galaxy’s oldest stars mark a dense proto-Galaxy at its center, mirroring compaction-driven starbursts seen in Milky Way–like Auriga simulations that shaped the early, central galaxy. arxiv.org/abs/2510.17693 🔭☄️

Two plots from the paper, the one on the left shows the average iron abundance of their simulated galaxies using different Population II star formation and feedback models. Then, on the right they show the averages of these per magnitude bin and show that not only do they capture the mass metallicity relation, but they reproduce the metallicity plateau!

Michelle's first paper discussed MEGATRON! No, it's not some sort of transformer, but a neat suite of simulations that can help us understand what sets the metallicity of the faintest galaxies. Tune in for more! 🔭 ☄️ arxiv.org/abs/2510.05232

Episode 23 – Failed galaxies, faint galaxies, and the proto-Galaxy In this episode, Michelle and Nicole explore the chemistry of faint galaxies and RR-Lyrae stars, tracing the proto-Galaxy, discussing the failure of some galaxies, examining quasi-stars in relation…

Episode 23 has dropped! Tune in to hear about faint galaxies, failed galaxies and how binaries are always causing trouble. 🔭☄️ starxiv.com/2025/10/27/e...

Predicted SEDs of a 10^6 M⊙ total mass, late-stage quasi-star both on its own (black dashed line) and embedded in a host galaxy (solid blue line) compared with JWST observations of LRDs (red) that includes the emission from the host stellar component with masses ∼10^9.5 M⊙. The top row shows comparisons with UNCOVER-45924 (I. Labbe et al., 2024) and the bottom row with MoM-BH*-1 (R. P. Naidu et al., 2025). We show models with (left) and without (right) dust. Semi-synthetic models of quasi-stars embedded in a host galaxy are shown in blue, using hosts properties inferred for UNCOVER-24996 and MoM-UDS-948311 respectively. The faded colors surrounding the lines represent 1​σ uncertainties in JWST measurements. Gray dashed lines indicate key wavelengths: the Balmer break (H∞), Hγ, Hβ, [OIII], and both CaII lines. Discrepancies in emission lines likely arise from the use of LTE atmospheres at nonzero metallicity, particularly in the Hβ emission and CaII absorption lines - these are discussed in Sec. 2.2. Shaded regions indicate the far-UV and NIR approach, highlighting a few of the well fit continuum regions discussed in Sec. 3. The stellar parameters of the quasi-star model at this point are Teff=6241 K, log​(g)=−0.003, and Z=0.

Nicole’s first paper showed that quasi-stars, black holes cocooned in stellar envelopes, can reproduce JWST’s “Little Red Dots,” matching their red colours and Balmer breaks. These could be SMBHs in formation. arxiv.org/abs/2510.17952 🔭☄️

Ha! Yes, we need to up our frequency so that you always have a StarXiv to listen too. If only there were more hours (/less admin) in the day. We would also love music! Music is on our to-do list :) One day...

Episode 23 – Failed galaxies, faint galaxies, and the proto-Galaxy

In this episode, Michelle and Nicole explore the chemistry of faint galaxies and RR-Lyrae stars, tracing the proto-Galaxy, discussing the failure of some galaxies, examining quasi-stars in relation to Little Red Dots, and…

Integrated stellar age distribution of the stars within 0.6 kpc of the plane of the disc (|z|<0.6 kpc). We divide it into total (including all stars, shaded black area); metal-rich (considering only stars with [M/H] ≥0.3, red); and rest (stars with [M/H] < 0.3, blue).

Nicole’s last paper traced the inner Milky Way’s past using super-metal-rich stars in the solar neighbourhood. Their age distribution reveals six starburst episodes, a bursty formation history likely driven by bars, mergers, and interactions. arxiv.org/abs/2510.02238 🔭☄️

In Payel's second paper, she discusses a new approach for finding Einstein rings using spectra and images. The authors find 2164 new lens candidates in DESI DR1, and a new category of 318 “dimple-lens” candidates that may represent dwarf galaxy lensing.
arxiv.org/pdf/2509.16033

An optical radio map with LoTSS 6′′ resolution contours overlaid on optical at is shown, where green circles have been drawn to guide the eye to the double-ring structure. Mild brightness enhancements are visible at the ring intersections.

Nicole’s next paper looked at rare radio objects found by the RAD@home citizen-science collaboratory. One of these is an Odd Radio Circle (ORC) with intersecting ~300 kpc rings, pointing to a relic synchrotron origin. arxiv.org/abs/2510.01999 🔭☄️