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#astro

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Rxiv mechanobio

📰 "Gas Pressure Driven Screening Forces and Pebble Aggregation: A Pathway for Growth in Planet Formation"
arxiv.org/abs/2507.02570 #Physics.Class-Ph #Astro-Ph.Ep #Astro-Ph.He #Adhesion #Force

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arXiv.orgGas Pressure Driven Screening Forces and Pebble Aggregation: A Pathway for Growth in Planet FormationThe formation of planetesimals from cm-sized pebbles in protoplanetary disks faces significant barriers, including fragmentation and radial drift. We identify a previously unaccounted screening force, arising from mutual shielding of thermal gas particles between pebbles when their separation falls below the gas mean free path. This force facilitates pebble binding, overcoming key growth barriers under turbulent disk conditions. Unlike conventional mechanisms, screening forces operate independently of surface adhesion and complement streaming instability and pressure traps by enhancing aggregation in high-density regions. Our analysis predicts that screening interactions are most effective in the {middle disk regions ($ \sim 0.3$ to few AU),} consistent with ALMA observations (e.g., TW Hya) of enhanced dust concentrations. {Furthermore, we find that screening-induced pebble growth from centimeter to kilometer scales can occur on timescales significantly shorter than the disk lifetime ($\sim 10^5$ years). Importantly, this growth naturally terminates when particles smaller than the local gas mean free path are depleted, thereby avoiding runaway accretion.} Beyond planetary science, the screening forces have {potential} implications for high-energy astrophysics, dusty plasmas, confined particle suspensions and other relevant areas, suggesting a broader fundamental significance.
Micah Ilbery :sloth_coffee:

If I want to write a site with vanilla #HTML / #CSS / #JS using #Astro as my #SSG are there any doc sources, projects, general setups, or tips I should know / look to for good reference? Seems like most of the things I see are about incorporating all the various frameworks that I have no interest in. I want to build a fairly simple blog and personal site. With minimal client side js. But I also want the benefits of an SSG especially when it comes to writing blog posts. Do you use or have you used Astro for a similar workflow? How do you like to set everything up?

Ethan Siegel

Busting the top 5 myths about the Big Bang There are lots of arguments against the Big Bang, and many proclamations that it's already been disproven. But those are mostly based on an incorrect depiction of what the Big Bang even is. bigthink.com/starts-with-... #space #astro #physics #bigbang

Busting the top 5 myths about ...

Big ThinkBusting the top 5 myths about the Big BangFor over 50 years, it’s been the scientifically accepted theory describing the origin of the Universe. It’s time we all learned its truths.
Ethan Siegel

Is the Hubble tension a real problem? #AskEthan Famed astronomer Wendy Freedman claims (including in an interview with me) that the Hubble tension may not be real. A large suite of evidence, rebutting many of her claims, suggests otherwise. bigthink.com/starts-with-... #space #astronomy #astro

Ask Ethan: Is the Hubble tensi...

Big ThinkAsk Ethan: Is the Hubble tension a real problem?Is the Universe's expansion rate 67 km/s/Mpc, 73 km/s/Mpc, or somewhere in between? The Hubble tension is real, and not so easy to resolve.
Deutscher Wetterdienst (DWD)

Da das Wetter heute nicht viel Spannendes hergibt, zeigen wir heute mal ein Astrobild, dass unser Kollege in den klaren Frühlingsnächten in Klingenthal im dunklen oberen Vogtland mit 12 Stunden Belichtungszeit gemacht hat. Das Bild zeigt #M51, die "Whirlpoolgalaxie". Zu sehen sind 2 kollidierende #Galaxien dabei wird die kleinere Galaxie von der größeren Spiralgalaxie "verschlungen". Das ganze geschah in einer Entfernung von etwa 24 Mio. Lichtjahren. #astro

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insomniac

Strawberry moon in Turin, Italy. The moon is rising over the hills east of the city, along the lines of the Colle della Maddalena.

The yellow-ish colour is due to higher light refraction when traversing thicker and more angled layers of atmosphere at such a low height over the horizon. The result is that the blue tones leave more room for the yellow-red ones.

Sony Alpha1 II + Sony 200-600mm + TC 2x @ 1200mm with tight crop

#moon#strawberry#astro
Rxiv mechanobio

📰 "Particle collisionality in scaled kinetic plasma simulations"
arxiv.org/abs/2506.08495 #Physics.Plasm-Ph #Astro-Ph.He #Dynamics #Cell

arXiv.orgParticle collisionality in scaled kinetic plasma simulationsKinetic plasma processes, such as magnetic reconnection, collisionless shocks, and turbulence, are fundamental to the dynamics of astrophysical and laboratory plasmas. Simulating these processes often requires particle-in-cell (PIC) methods, but the computational cost of fully kinetic simulations can necessitate the use of artificial parameters, such as a reduced speed of light and ion-to-electron mass ratio, to decrease expense. While these approximations can preserve overall dynamics under specific conditions, they introduce nontrivial impacts on particle collisionality that are not yet well understood. In this work, we develop a method to scale particle collisionality in simulations employing such approximations. By introducing species-dependent scaling factors, we independently adjust inter- and intra-species collision rates to better replicate the collisional properties of the physical system. Our approach maintains the fidelity of electron and ion transport properties while preserving critical relaxation rates, such as energy exchange timescales, within the limits of weakly collisional plasma theory. We demonstrate the accuracy of this scaling method through benchmarking tests against theoretical relaxation rates and connecting to fluid theory, highlighting its ability to retain key transport properties. Existing collisional PIC implementations can be easily modified to include this scaling, which will enable deeper insights into the behavior of marginally collisional plasmas across various contexts.
Rxiv mechanobio

📰 "Density jump as a function of the field for parallel relativistic collisionless shocks"
arxiv.org/abs/2506.07973 #Physics.Plasm-Ph #Astro-Ph.Sr #Astro-Ph.He #Pressure #Cell

arXiv.orgDensity jump as a function of the field for parallel relativistic collisionless shocksCollisionless shocks are frequently analyzed using the magnetohydrodynamic formalism (MHD), even though the required collisionality hypothesis is not fulfilled. In a previous work \citep{BretJPP2018}, we presented a model of collisionless shock displaying an important departure from the expected MHD behavior, in the case of a strong flow aligned magnetic field. This model was non-relativistic. Here, it is extended to the relativistic regime, considering zero upstream pressure and upstream Lorentz factor $\gg 1$. The result agrees satisfactorily with Particle-in-Cell simulations and shows a similar, and important, departure from the MHD prediction. In the strong field regime, the density jump $r$, seen in the downstream frame, behaves like $r \sim 2 + 1/γ_{\mathrm{up}}$ while MHD predicts 4 ($γ_{\mathrm{up}}$ is the Lorentz factor of the upstream measured in the downstream frame). Only pair plasmas are considered.
Ethan Siegel

780,000 galaxies revealed in JWST's largest science operation With 255 hours of dedicated observing time and a full 0.54 square degrees of sky coverage, COSMOS-Web is JWST's largest deep observing program. Now released, in full, to everyone. bigthink.com/starts-with-... #space #astro #science

780,000 galaxies revealed in J...

Big Think780,000 galaxies revealed in JWST's largest science operationThe COSMOS-Web has just finalized their release of their full field: larger and deeper than any other JWST program. Here's what's inside.
Angelika Cathor

My team is still looking to hire two mid or senior frontend developers, fully remotely from Europe.

We're looking for like-minded individuals that share our love of artisanal #CSS #A11y, web standards, and #Astro

On the website team at Storyblok, we build marketing websites *for* Storyblok *using* Storyblok 🙂 (but we don't build the product itself)

storyblok.com/job?gh_jid=45196

www.storyblok.comFrontend Engineer II | Storyblok CareersApply for a Frontend Engineer II career at Storyblok. Our team is made up of smart, passionate individuals who excel in their work. With a dynamic team spanning 45+ countries, we're not just breaking boundaries; we're redefining them!
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