Lightnews — Scholar-powered news

Richard Alexander @richardalexander.bsky.social · 3h

Problem is that when it comes to the specific topic of PAHs, you could probably fit *all* the grown-ups who actually understand them in that locked room with you.

1 3

Reposted by Richard Alexander

Prof Anna Watts @profannawatts.bsky.social · 5h

Our annual PhD recruitment process @api.uva.nl is open!! Details of the process and projects are here, deadline November 3! 🔭 #astronomy #astrophysics

werkenbij.uva.nl/en/vacancies...

Vacancy — PhD Positions in Astronomy and Astrophysics

Are you passionate about astronomy and cutting-edge research?Join our dynamic team and explore the universe through multiple PhD positions now open! Work on a range of exciting research topics in a co...

werkenbij.uva.nl

1 11 12

Richard Alexander @richardalexander.bsky.social · 19h

If it’s material I’m familiar with, then that’s about right - roughly one full day per lecture. But if it’s a topic I need to revise first then it’s significantly more. Plus time for problem sets, etc.

Putting it another way: writing 20 lectures from scratch is at least a month’s full-time work.

4

Reposted by Richard Alexander

John Ilee @johnilee.bsky.social · 1d

Great to see our paper on methanol in TW Hya finally come out today (with Catherine Walsh and Jenny Calahan). A quick overview.... 🔭 ☄️ #radioastro

arxiv.org/abs/2510.04106

1 2 6

Richard Alexander @richardalexander.bsky.social · 1d

It's a close call between that and the budget...

dr. evil from the movie dumb and dumber is sitting in a chair .

ALT: dr. evil from the movie dumb and dumber is sitting in a chair .

media.tenor.com

1 2

Richard Alexander @richardalexander.bsky.social · 2d

The proposed budget is my favourite part...

2 10

Richard Alexander @richardalexander.bsky.social · 2d

Don't forget the $380 million in start-up funding, plus an annual budget of $80 million.

1 3

Richard Alexander @richardalexander.bsky.social · 2d

We do sort of know this though (mostly from RV surveys).

How many solar-type stars have a Jupiter analogue between 1-10AU? 5-10% of them.

But how many of those systems also have analogues of the terrestrial planets? No idea...

1

Richard Alexander @richardalexander.bsky.social · 2d

Happy Father Dougal Day to those who celebrate. 🎉

(Admittedly that's basically just my third-year class, but we'll still have some fun with it.)

Richard Alexander @richardalexander.bsky.social · Oct 11

First time on this platform: it's "angular-diameter distances with Father Dougal" day. Looking at my notes, we're also doing luminosity distances with the muppets ("near", "far"...). 🔭

Father Ted and Father Dougal discuss cows.

6

Richard Alexander @richardalexander.bsky.social · 7d

Marvelling at a request for a letter of reference that specifies both a font size and a page limit. I understand the need for guidelines, but who are the people who need to be told that letters of recommendation shouldn't run to more than 3 pages? 🔭

5 9

Richard Alexander @richardalexander.bsky.social · 7d

Reposting for the western time-zones...

👇🏻- thread about @simintong.bsky.social's excellent new paper on understanding turbulence and dust fragility in planet-forming discs. 🔭

Richard Alexander @richardalexander.bsky.social · 8d

New paper, led by @physicsuol.bsky.social PhD student @simintong.bsky.social. Simin looked at the rings we see in planet-forming discs, and combined new models with multi-wavelength ALMA observations to understand the underlying physical properties of the dust and gas. 🔭

arxiv.org/abs/2509.24818

Fig.3 from Tong et al. (2025), showing ALMA observations of the GM Aur protoplanetary disc at 1.3mm (Band 6) and 2.1mm (Band 4). Left panels are the sky-plane images from Huang et al. (2020); right panels show the same observations de-projected.

7

Richard Alexander @richardalexander.bsky.social · 8d

Yes, and we do 😀, but the derived fragmentation velocities are slightly degenerate with the strength of disc turbulence. We didn't do the comparison with solar system bodies directly, but it would be interesting to look at. 👍🏻

1

Richard Alexander @richardalexander.bsky.social · 8d

There is a *lot* more detail and nuance in the paper than I can cover in a thread like this (including spectral index measurements, the effects of bouncing collisions, etc.), so if you'd like to know more, please read the paper. 😀 🔭

arxiv.org/abs/2509.24818

Turbulence and dust fragility in protoplanetary discs

Dust growth from micron- to planet-size in protoplanetary discs involves multiple physical processes, including dust growth and fragmentation, the streaming instability, and pebble accretion. Disc tur...

arxiv.org

5

Richard Alexander @richardalexander.bsky.social · 8d

- reproducing the observed fluxes is only possible if the rings are optically thick at mm wavelengths.
- in time-dependent models, the inner dust ring has to form before the outer ring (otherwise it is never bright enough).
- these results don't change significantly with different opacity models. 🔭

1 1

Richard Alexander @richardalexander.bsky.social · 8d

These are steady-state models, but real discs evolve. Simin therefore extended her analysis to time-dependent calculations, and explored a wide range of models to understand what multi-wavelength observations of these rings tell us. She was able to draw several interesting new conclusions... 🔭

Fig.5 from Tong et al. (2025), showing the successful numerical models from the simulation suite. The first column shows the dust size distribution in the disc, at t=1Myr, as a function of radius; the second and third columns show synthetic ALMA observations of these models. Columns 4-6 show the same results at t=3Myr.

1

Richard Alexander @richardalexander.bsky.social · 8d

Simin first used an analytic model to show that the dust and gas properties are correlated. If the dust is fragile (with a low fragmentation threshold), then seeing rings implies the turbulence is very weak; while stronger turbulence requires much more resilient dust aggregates. 🔭

Fig.1 from Tong et al. (2025). The figure shows the results from analytic modelling of multiple rings observed in three well-known discs from the MAPS survey. Reproducing the observations at multiple wavelengths is only possible for specific combinations of dust material strength (fragmentation velocity) and gas turbulence.

2 1

Richard Alexander @richardalexander.bsky.social · 8d

Rings in ALMA continuum emission arise when mm-size dust becomes trapped in structures in the gas disc. However, if grains collide too energetically they fragment, so seeing rings tells us about the local physics: how fragile (or not) the dust is, and how turbulent the gas is. 🔭

1

Richard Alexander @richardalexander.bsky.social · 8d

New paper, led by @physicsuol.bsky.social PhD student @simintong.bsky.social. Simin looked at the rings we see in planet-forming discs, and combined new models with multi-wavelength ALMA observations to understand the underlying physical properties of the dust and gas. 🔭

arxiv.org/abs/2509.24818

1 2 23

Richard Alexander @richardalexander.bsky.social · 12d

Very sad news. Ming Campbell was my MP when I was a kid, and he was a lovely man. I remember going to his surgery as part of a school project, and he talked with us - a pair of 12-year-olds - for half an hour, with the same earnestness as when he spoke in parliament.

www.bbc.co.uk/news/article...

Former Lib Dem leader Sir Menzies Campbell dies aged 84

Sir Menzies led the Liberal Democrats from 2006 to 2007 and was the MP for North East Fife at Westminster for 28 years.

www.bbc.co.uk

2 1 5

Richard Alexander @richardalexander.bsky.social · 13d

a man with red hair and a beard is standing in the woods

ALT: a man with red hair and a beard is standing in the woods

media.tenor.com

1

Richard Alexander @richardalexander.bsky.social · 14d

Friedmann, Lemaître, Robertson, Walker, Cuthbert, Dibble, and Grubb?

4

Reposted by Richard Alexander

Michael Merrifield @astromikemerri.bsky.social · 15d

Academic family tree of descendants, beautifully calligraphed by a colleague, hung in a place of honour.

1 1 11

Richard Alexander @richardalexander.bsky.social · 21d

You can get thermos mugs designed to fit in a bottle cage. 👌🏻

1 2

Reposted by Richard Alexander

Matthew Kenworthy @mattkenworthy.bsky.social · 26d

My periodic reminder for #astrosci #astrodon #exoplanets Early Career Researchers to please, please, please have a simple web site with your current email address on it - rationale here: kenworthy.space/advice/

A pen sketch of a web page for an astronomer, showing name, email, optional phone number, and professional contact details, with a one sentence summary of their research and an ADS link.

1 31 72

Richard Alexander @richardalexander.bsky.social · Sep 4

This is dangling modifier art. 👏🏻👏🏻👏🏻 😂

5