Tessera

Denis Erkal@derkal.bsky.social · last mo.

Come join Surrey and work with the ultimate disequilibrium team!

Interested in working on stellar streams in the UK? I’ll be posting a 3 year postdoc position to work with me and Eugene Vasiliev on measuring dark matter subhalo properties with streams in a few days. Interviews will be in early August with a start date of October 1st. 🧪☄️

The StarXiv ✨ podcast@starxiv.bsky.social · last mo.

Exciting new observations shedding light on what drives the shape of solar flare ribbons.

Payel's second paper discussed the origin of solar flare ribbons. New observations of the lower solar atmosphere where they are actually observed show that its morphology plays an important role in how they look. 🔭 ☄️ arxiv.org/pdf/2606.10505

Solar flare ribbons in bottom right image.

The StarXiv ✨ podcast@starxiv.bsky.social · last mo.

A non-linear data compression that preserves orthogonality - one of the key pluses of the linear PCA.

Nicole's second paper asks how many independent things a galaxy's spectrum can tell you. A neural net built to find independent factors says 5: stellar mass, star formation, dust, and two for the gas's ionization. Notably, age and metallicity aren't among them. arxiv.org/abs/2606.11308 ☄️🔭

Variations in the decoded rest-frame SED when varying one latent eight times with all the others fixed. A different latent is traversed in each panel from top to bottom. The left panel displays the full SED while the right panel zooms into the [O ii], [O iii], H β, and H α regions. The first two and last two columns share a 𝑦-axis range. The different latents are ranked by their relative effect on the spectrum.

The StarXiv ✨ podcast@starxiv.bsky.social · last mo.

This was a very cool paper where JWST literally sees the missing link between large-scale gas flows and gas accretion onto the central black hole of a galaxy.

Payel's first paper discussed how black holes are fed. New JWST observerations track the flow of gas from the kiloparsec-scale filamentary structure to the sub-kiloparsec scale via a circumnuclear disk. 🔭 ☄️ arxiv.org/pdf/2606.06620

The bottom right figure shows the connection across scales.

The StarXiv ✨ podcast@starxiv.bsky.social · last mo.

Nicole told us how simple linear tools can help us to more simply interpret galaxy spectra. I love the everlasting power of PCA!

Nicole's first paper asks how much a galaxy spectrum can tell you - using simple PCA! The dominant axis tracks mainly stellar age and helps partly untangle the age–metallicity degeneracy. Interestingly, the least dominant axis is the one that catches recent starbursts. arxiv.org/abs/2606.13791 ☄️🔭

Correlation of PC6 with recent bursting activity, shown as a function of the age of the most recent burst (log10(Tburst) < 8.4 yr). A density plot is shown, with tracks tracing a running median for cases selected with respect to the burst mass, as labelled.

The StarXiv ✨ podcast@starxiv.bsky.social · last mo.

Tune in for more machine-learning mayhem, solar flares and a JWST view on AGN feedback across the scales.

Episode 39 – data-driven stellar population studies, multi-scale AGN feedback, and solar flare ribbons In this episode, Payel and Nicole discuss machine learning methods to to transform composite galaxy spectra and determine key features of galaxy evolution. They also examine new observations of…

Denis Erkal@derkal.bsky.social · 2mo ago

Want to join Surrey Astro? Get in touch if you want to learn more.

Interested in applying for Astro fellowships in the UK? Come to Surrey! We are a fun group and will help you hone your application. Our deadline for ERF/URF consideration is July 8th. For more details of all the fellowships and how to contact us, see www.surrey.ac.uk/astrophysics... 🔭☄️

Denis Erkal @derkal.bsky.social · 2mo ago

Here’s our press release about Arrakihs! Lots of cool science will hopefully come out of it and I’m especially excited about what can be done with the long streams it will detect. 🔭☄️🧪 www.surrey.ac.uk/news/esa-off...

The StarXiv ✨ podcast@starxiv.bsky.social · 2mo ago

I really enjoyed this paper! Who knew that the craters that formed early on eject material that can reform craters later and cause an asymmetry in crater distribution across the Moon's surface.

Payel's first paper discussed a new theory to explain the difference in the distribution of craters across the moon. Find out more at arxiv.org/pdf/2605.09884 ☄️🔭

Relationship between orbits of lunar ejecta and their initial positions at different initial velocity.

Michelle Collins@runningastronomer.bsky.social · 2mo ago

Fun as ever chatting about papers with Michelle. We happened to say lots of odd things this time too. Like claiming that one of the papers was published in A&E. We'll be saving bloopers for a special episode soon!

Start the bank holiday right with our latest episode of @starxiv.bsky.social ! Despite the post below, it's actually an episode with me and @payeldas.bsky.social chatting about the moon, primordial black holes, pre processing in clusters and how spiral galaxies grow 🔭🧪☄️

The StarXiv ✨ podcast@starxiv.bsky.social · 2mo ago

Michelle discussed a very cool possible candidate for a primordial black hole. Tune into this week's @starxiv.bsky.social podcast to find out more!

Michelle discusses the detection of Phoebe, a possible primordial black hole (PBH) in the Milky Way halo. Using DECam and microlensing, this object was found and the paper describes how they come to the conclusion that it is a likely PBH. Tune in to discover more! arxiv.org/abs/2605.19375 🔭 ☄️

The discovery light curve of Phoebe is shown. There is data across 5 nights in December 2019, and in panel 4 (the 4th night) you see brightening in the light curve, typical of what would be expected for a microlensing event

The StarXiv ✨ podcast@starxiv.bsky.social · 2mo ago

Another great use of machine learning for classification in astronomy.

In her second paper, Michelle discusses a machine learning technique to classify groups of galaxies that are falling in to clusters. If we can study these in detail, we can learn about the impact of the cluster on these galaxies before they fall in. Tune in for more! arxiv.org/abs/2605.14930 🔭 ☄️

A diagram showing how well the method can identify the true label for a galaxy (whether it belongs to the main cluster, an infalling group or neither) based on the routine. It does best at identifying the galaxies belonging to the cluster or neither.

The StarXiv ✨ podcast@starxiv.bsky.social · 2mo ago

It's kind of cool that we're starting to get detailed age and metallicity profiles for galaxies at redshift 1!

Payel's second paper uses detailed observations from JWST and HST to derive age and metallicity profiles in redshift-one galaxies and better constrain the balance between evolutionary processes driving disk growth. Find out more at arxiv.org/pdf/2605.15327 ☄️🔭

Age and metallicity profiles in two Milky-Way-like galaxies at redshift one.

Payel Das @payeldas.bsky.social · 3mo ago

GSE possibly happened further back in time than we initially thought!

The StarXiv ✨ podcast@starxiv.bsky.social · 3mo ago

Nicole’s first paper pins down the Milky Way’s last major merger, GSE, to ~11.2 Gyr ago by combining stellar ages, globular clusters, and kinematics. It links the event to a starburst, “Tainá”, and even ties Omega Centauri to the same progenitor. arxiv.org/abs/2604.14502 ☄️🔭

Left panel: Age–metallicity relation for the VandenBerg et al. (2013) GCs. Large hexagons and stars correspond to MW-branch GCs while pentagons highlight the most metal-rich GCs associated with the GSE. White pentagons represent other GSE-related candidate GCs identified in the vicinity of the GSE debris of (Belokurov et al. 2020). Other inner-MW GCs with 𝐸 ≤ −1.5 × 10^5 km^2s^2 are highlighted as large filled grey circles while outer GCs (𝐸 > −1.5 × 10^5 km^2s^2) are represented by smaller filled ones. The cluster sitting at 9 Gyr is Pal 12 which is associated to the Sagittarius dwarf galaxy (Ibata et al. 1994). Age–metallicity relations for the MW and GSE are shown as the thick green and red bands respectively, these are meant to guide the eye on the two sequences. NGC 6121 is highlighted in gold-yellow because its chemistry is consistent with it being in-situ. We will argue that it is most likely a MW-branch GC in section 4. Mean ages of stellar populations of different metallicity bins in the nuclear star cluster 𝜔Centauri (𝜔Cen) from Clontz et al. (2024) are shown as blue stars. Middle panel: Energy versus angular momentum plane. The background density map corresponds to the distribution of subgiants from Xiang & Rix (2022). Despite being a survey in the Northern hemisphere, LAMOST has numerous stars with guiding radii satisfying 0 < 𝑅g < 5, enabling it to probe the formation of the inner MW. MW-branch GCs colour-coded by their ages are mostly confined to the inner MW (𝑅g < 5 kpc), with the exception of NGC104 which has a guiding radius of 𝑅g ∼ 8 kpc. The most metal-rich GSE GCs cluster are not surprisingly in the region where the GSE is most prominent in Gaia DR3 (see Belokurov et al. 2020; Orkney & Laporte 2025). We also highlight the other GSE-related GCs as pentagons. 𝜔Cen’s location is 𝐸 − 𝐿𝑧 is also highlighted. Right panel: Same as the middle panel, except that the GCs are colour-coded according to their metallicity.

The StarXiv ✨ podcast@starxiv.bsky.social · 4mo ago

I mean it’s a few billion years in the future, but can’t help but think about the possibility of a collision between the Milky Way and Andromeda: spoilers - LMC gets engulfed but M33 stays intact!

Michelle's final paper reopened the debate on whether and how the Milky Way and Andromeda will merge. With updated proper motions for the main players (M31, M33 and the LMC), they found that these two spirals will likely collide in ~6 Gyr time. ☄️ 🔭 arxiv.org/abs/2603.22863

Predicted orbital evolution of the local group (LG) galaxies. Panels (a) and (b) show 100 randomly selected tracks
from 10,000 MC realizations for the two-body configuration (MW-M31), and panels (c) and (d) show the same for the four-body
configuration (MW, M31, M33 and LMC). In each case,in face-on projection and
edge-on projection with respect to the MW–M31 orbital plane. The green and red lines trace the orbits of the MW and M31, while the pink and silver lines trace the LMC
and M33, respectively. Line brightness indicates the relative probability density at any position. If a MW–M31 merger is flagged, a
white point marks the merger location and the corresponding track terminates; otherwise, tracks are integrated to 10 Gyr.

The StarXiv ✨ podcast@starxiv.bsky.social · 4mo ago

Pulsars can measure the gravitational force directly! So the more we find, the better we can understand whether an intermediate mass black hole exists at the heart of Omega Centauri.

Michelle also discussed a new hunt for pulsars in Omega Centauri, the unique Milky Way star cluster that is likely the nucleus of a galaxy that has been stripped away. This search found one new pulsar and investigated the pulsar population. Check it out! arxiv.org/abs/2603.21845 ☄️ 🔭

A localisation map of the newly discovered pulsar S!

The StarXiv ✨ podcast@starxiv.bsky.social · 4mo ago

We learned a lot of things here. Apparently galaxies can be banana shaped and UV emission can be dominated by nebulae emission rather than star formation.

Michelle discussed the banana and the blueberry: a UV bright, banana shaped galaxy at redshift ~ 5 that seems dominated by nebulae emission. And, it's compact, blue companion that may be a Population III source! Find out more in the episode. arxiv.org/abs/2603.13471 ☄️ 🔭

(Left:) JWST/NIRcam false-color red-green-blue (RGB) thumbnail image, showing a 2′′×2′′cutouts centred on the main
target (the “banana”) from the Primer survey (Donnan et al. 2024). (Right:) The top shows the 2D spectrum extracted from
the shutter, where the bottom shows the 1D spectrum extracted using a global-average background subtraction to remove potential
contamination from the nearby neighbor (the “blueberry”, see text for details). The most prominent emission-line features identified
at the spectroscopic redshift z = 5.124 are marked.

The StarXiv ✨ podcast@starxiv.bsky.social · 4mo ago

Check out our latest episode! At the end of a tiring week, definitely one of my favourite things is to curl up with the coolest research from the last few weeks!

New episode incoming! Tune in now to hear Michelle and Payel discuss planet eating stars, UV bright galaxies at high redshift, binary black holes, pulsars in Omega Centauri and the fate of the Galaxy. Link is below, and its available wherever you get your podcasts. ☄️ 🔭 starxiv.com/2026/03/30/b...

The StarXiv ✨ podcast@starxiv.bsky.social · 5mo ago

The elusive BH seed! Could this be the answer?

Michelle's second paper also focused on how to grow a massive black hole. This one simulates how big you can get when starting from a very massive star in a giant molecular cloud. They find that growth is tough, but some is possible under the right conditions. arxiv.org/abs/2603.10581 🔭 ☄️

A schematic showing how the authors use a hybrid approach to modelling very massive stars (tracking them individually) and other stars (using single stellar population particles) in their modified FIRE simulation. The evolution of the star from main sequence through to the formation of a black hole and its subsequent growth is all tracked.

The StarXiv ✨ podcast@starxiv.bsky.social · 5mo ago

Cool that you can do this at all.

Nicole’s final paper traces nitrogen-rich field stars using chemistry and Gaia orbits, revealing two origins: some escaped globular clusters formed in the Milky Way, others from clusters accreted with dwarf galaxies. Orbital modeling even links one star to NGC 6235. arxiv.org/abs/2603.02564 🔭☄️

The [α/Fe] – [Fe/H] planes, where α elements include Mg, Si, Ca, and Ti. Violin shaped symbols indicate GC stars from APOGEE (Meszaros et al. 2020), including the average [Fe/H], maximum and minimum [α/Fe] of each GC. In-situ GCs are colored light green, while accreted GCs are light red. Orange circles correspond to Sagittarius (Hasselquist et al. 2017; Hayes et al. 2020). Blue circles represent stars from Sculptor (Hill et al. 2019).

The StarXiv ✨ podcast@starxiv.bsky.social · 5mo ago

Interesting paper about the mischief binary stars can cause for Galactic archaeology studies.

Nicole’s first paper tests the idea that nitrogen-rich field stars are escaped globular-cluster members. APOGEE chemistry and Kepler ages show many are too young for a GC origin, suggesting binary interactions can mimic GC-like chemistry. arxiv.org/abs/2603.02327 🔭☄️

The primordial (blue) and enriched (red) field stars in the Kepler sample, with the sample of GC stars identified by Schiavon et al. (2024) (green), both using APOGEE DR17 abundances. Stars in the Kepler sample with ages determined through asteroseismology are shown with black borders. Upper left: [N/Fe] vs. [C/Fe] anticorrelation, lower left: [N/Fe] vs. [O/Fe] anticorrelation, upper middle: Toomre diagram, lower middle: integral of motion plot, upper right: histogram of ages estimated from asteroseismology against GC ages from Forbes & Bridges (2010) (grey histogram), lower right: histogram of masses derived from asteroseismology.

The StarXiv ✨ podcast@starxiv.bsky.social · 5mo ago

Dwarf galaxies aren't much good at retaining gas so it will be interesting to find out how big that central black holes can get!

Michelle's first paper discussed a novel method for studying accretion onto a black hole seed in a dwarf galaxy. Dwarf galaxies can easily provide gas to grow a central black hole, but how massive can it get? This paper goes into detail arxiv.org/abs/2603.00241 ☄️ 🔭

3 images showing the dwarf galaxy being simulated. The first shows the dark matter distribution of the simulation. The central paenal shows the gas, and the final panel zooms into the centre where the black hole seed is placed.

The StarXiv ✨ podcast@starxiv.bsky.social · 5mo ago

If you want to never miss another Starxiv podcast, you can subscribe on the website starxiv.com.

You can listen on our website, Spotify, Apple or wherever you get your podcasts. Don't forget to subscribe so we can keep you up to date on astro-ph! 🔭 ☄️

The StarXiv ✨ podcast@starxiv.bsky.social · 5mo ago

Ancient stars and black holes - what more could you want!

Episode 32 – Ancient star clusters and growing black holes In this episode, Michelle and Nicole discuss the role of stars from ancient globular clusters in the Milky Way's stellar halo. They also explore research on forming massive black hole seeds within small dwarf galaxies. Listen on Spotify,…

The StarXiv ✨ podcast @starxiv.bsky.social · 5mo ago

Went to a fun workshop today ran by @niftyfoxcreative.bsky.social about how to optimise using AI for creative tasks. We put together a design brief for creating an infographic for a research paper and I eventually got this. I like it! You can find out more at academic.oup.com/mnras/articl....

Episode 31 – Near Earth Objects, Little Red Dots, bursty star formation and life around massive stars In this podcast episode, Michelle and Payel discuss theories on little red dot formation, bursty star formation, and the origins of asteroids like Apophis. They also discuss the potential for life…

Episode 31 – Near Earth Objects, Little Red Dots, bursty star formation and life around massive stars

In this podcast episode, Michelle and Payel discuss theories on little red dot formation, bursty star formation, and the origins of asteroids like Apophis. They also discuss the potential for life around massive stars and unusual triple-double radio galaxies.

starxiv.com

The StarXiv ✨ podcast @starxiv.bsky.social · 5mo ago

Our latest episode is live! Tune in to hear about where the Apophis asteroid came from, bursty star formation at high redshift, truple-double radio galaxies and more! Available below and wherever you get your podcasts 🔭 ☄️

starxiv.com

The StarXiv ✨ podcast@starxiv.bsky.social · 5mo ago

This is why we love doing Starxiv! Definitely one of the coolest objects that I had never heard about.

Michelle's first paper discussed an object she'd never heard about before: triple-double radio galaxies.While very rare, they have the potential to teach us about the duty cycle of active galactic nuclei ☄️ 🔭 arxiv.org/abs/2602.19729

An image of the 7th known triple-double radio galaxy detected with MIGHTEE. Its three lobes tell us about different epochs of AGN activity, and are shown as contours. The oldest are the outer most and the youngest are the inner most.

The StarXiv ✨ podcast@starxiv.bsky.social · 5mo ago

Can help but love such a simple model to explain the MUV-M* observations.

Payel's first paper introduces a very simple model for bursty star formation that is able to replicate recent observations of where galaxies lie in the plane of UV magnitude and stellar mass. ☄️ 🔭 arxiv.org/pdf/2602.16706