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Alex Ji

@alexji.bsky.social
1K followers 333 following 483 posts

Near-field Cosmologist and Assistant Professor of Astronomy and Astrophysics at University of Chicago. he/him

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Reposted by Alex Ji
Nobel Prize @nobelprize.org · 06/10/2026
BREAKING NEWS The Royal Swedish Academy of Sciences has decided to award the 2026 #NobelPrize in Physics to Francis Halzen “for decisive contributions to the IceCube Neutrino Observatory and the discovery of high-energy neutrinos of astrophysical origin.”
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Reposted by Alex Ji
Jacob Aron @jjaron.bsky.social · 06/10/2026
I claim best quote from Nobel prize winner Francis Halzen in this 2015 story: “We are in the happy situation that there are not enough Muppets,” he says. “We’ve run out of Muppets." www.newscientist.com/article/2053...
newscientist.com
Neutrinos from inside Earth and deep space illuminate the cosmos | New Scientist
A batch of ghostly, chargeless particles have been caught coming from inside Earth and from deep space
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Reposted by Alex Ji
Laura Lopez @ohdearz.bsky.social · 03/10/2026
@aussiastronomer.bsky.social! Here's the other stuff Chris Smith said that may be helpful to astronomers! Will have office hours on Wed, Oct 7 at 2pm ET and Thurs, Oct 15 at 3pm ET. 🔭
FY27 Core Astronomical Sciences
• Astro-Core is expected to be especially competitive.
o Multiple proposals by the same PI are strongly discouraged.
o PIs who already have an active AST award should contact their cognizant
Program Officer before considering submitting a proposal for another
concurrent award.
o Resubmissions of previously declined proposals that have not been sufficiently
revised to account for reviewer feedback may be returned without review.
o Projects that request more than the typical 3 years in order to deliver
transformative outcomes should include strong justification.
o Collaborative projects should be well-justified.
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Reposted by Alex Ji
hammancheez but spooky @hammancheez.bsky.social · 01/10/2026
Yall wanna see a 2 hour old highland cow
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Reposted by Alex Ji
The Open Journal of Astrophysics @ojastro.bsky.social · 25/09/2026
If anyone thinks it matters, as of last year (2025), the Open Journal of Astrophysics is a Q1 Journal. It is the only Diamond Open Access Journal with that status in Astronomy and Astrophysics. www.scimagojr.com/journalrank....
scimagojr.com
Journal Rankings on Astronomy and Astrophysics
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Alex Ji @alexji.bsky.social · 25/09/2026
I stayed up for this
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Alex Ji @alexji.bsky.social · 24/09/2026
I once made a joke about Pluto in an outreach talk to a younger audience and the blank stares I received were absolutely crushing.
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Alex Ji @alexji.bsky.social · 23/09/2026
Astronomy can wait, I must know the conclusion to this journey
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Reposted by Alex Ji
John Timmer @jtimmer.bsky.social · 22/09/2026
Ok, this "there are two separate brains" thing appears to be making the rounds, and I want to be absolutely clear: this is a press office overhyping some perfectly reasonable science that won't come as a surprise to most developmental biologists.
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Reposted by Alex Ji
jad, unusually spooky 📸👻 @aerojad.bsky.social · 20/09/2026
📝 This Wednesday is the autumn equinox (already) which means it's time for the twice-annual show that is Chicagohenge. I wrote a bit about it, suggestions on where to shoot, and in general trying to answer the question "how do I know if I'm gonna have good weather for a sunset" #photography #Chicago
dust.aerojad.com
Chicagohenge & Shooting A Sunset - dust
Coming up soon, at time of writing, is the second edition of the bi-yearly phenomenon known as “Chicagohenge.” To make a long story short, Chicago’s layout sits on a due north/south/east/west sort of ...
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Alex Ji @alexji.bsky.social · 18/09/2026
I appreciate this and also no one has found Pop III stars, they are actually quite metal rich stars
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Reposted by Alex Ji
Michelle Collins @runningastronomer.bsky.social · 18/09/2026
ALMOST DARK GALAXIES ARE JUST CLASSICAL DWARF SPHEROIDAL GALAXIES. WE EXPECT TO FIND THEM EVERYWHERE. THEY DON'T NEED A NEW NAME. ALSO THEY'RE ACTUALLY QUITE BRIGHT. This has been a public service announcement. 🔭🧪☄️
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Reposted by Alex Ji
Stand Up for Science! @standupforscience.net · 17/09/2026
The Trump admin has decimated American science budgets, taking away life saving opportunities, and the potential for groundbreaking discoveries. This is how you destroy American innovation. apnews.com/article/trum...
apnews.com
Trump administration has cut or frozen $177 billion in grants across every state, analysis shows
An analysis finds that the Trump administration has cut or frozen up to $177 billion in federal grants since the president took office for his second term.
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Alex Ji @alexji.bsky.social · 17/09/2026
OK people need to stop finding objects “more metal poor than a few percent solar” and calling them Population III star candidates. This is getting absurd.
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Reposted by Alex Ji
David Ho @davidho.bsky.social · 15/09/2026
The US National Science Foundation Directorate for Geosciences, which has funded most of my research over the past three decades, has been enshitified by Trump and his lackeys.
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Reposted by Alex Ji
Brandon Bishop @brandontbishop.bsky.social · 15/09/2026
Note this contradicts the FAQ answer.
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Jake Grumbach @jakemgrumbach.bsky.social · 09/09/2026
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Zach Weinersmith @zachweinersmith.bsky.social · 08/09/2026
For anyone not following the drama, there's been apparently a big development in ai math, along with some accusations of very bad behavior by OpenAI. But we don't have details yet. If I understand it, Buckmaster and Levent Alpoge made a big discovery on Navier-Stokes. Events go something like this:
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Alex Ji @alexji.bsky.social · 08/09/2026
astrobites.org/2026/09/08/r... We (ie @wcerny.bsky.social ) found a (candidate) dwarf galaxy!
astrobites.org
An Early Discovery by Rubin Observatory!
The Vera C. Rubin Observatory has found a new ultra-faint dwarf galaxy in our galactic backyard just by using preview data, taken before its 10-year survey!
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Reposted by Alex Ji
Mineral Cup & Ore Cup @mineralcup.bsky.social · 29/08/2026
Oooh, a bracket! www.mineralcup.org/2026/bracket
A sports-style elimination bracket of 32 minerals labeled "Mineral Cup 2026". Text below reads, "Daily voting takes place on www.MineralCup.org in September. Campaign on your favourite social media using #MinCup26."

The starting matches are, in chronological order in pairs from top to bottom alternating from left to right each match:
Azurite vs Smithsonite
Erythrite vs Skutterudite
Sphalerite vs Anorthite
Bournonite vs Vesuvianite
Cuprite vs Orpiment
Quartz vs Asagiite
Monazite-(Ce) vs Andalusite
Stichtite vs Talc
Hafnon vs Putnisite
Pyromorphite vs Gypsum
Calcite vs Julienite
Pyrrhotite vs Cylindrite
Arsenopyrite vs Halite
Riebeckite vs Gadolinite-(Y)
Chrysocolla vs Xocolatlite
Cassiterite vs Graphite
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Alex Ji @alexji.bsky.social · 04/09/2026
Brooks: with CDM only, see correlation with surface brightness. If you add SIDM in this model, you *lose* diversity because it cores everything...SIDM changes galaxy gas disk sizes, masses, and symmetry. In this mass range can probe halo shape. Mock observations add even more scatter #KICPDM
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Alex Ji @alexji.bsky.social · 04/09/2026
Alyson Brooks: LMC/SMC mass galaxies have a diversity of rotation curves, some steeply rising some slowly rising. LCDM can do one or the other, but seemed hard to do both. However, Marvelous Massive Dwarf Zoom simulations can make things spanning the full range of diversity #KICPDM
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Alex Ji @alexji.bsky.social · 04/09/2026
Atzberger: major challenge is models are giving different predictions for what cored and cusped halos predict for stream width :( however cosmological simulations predict we should get more of these if we could go fainter. Now looking at total mass loss as a constraint. #KICPDM
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Alex Ji @alexji.bsky.social · 04/09/2026
Kaia Atzberger: Crater II has large size and low sigma_v, hard to make form an NFW halo, but can do it with cored profile. Need to understand how much mass is lost and in tidal tails. Using CaHK metallicity filter to remove contamination (36 mag/sq arcsec), >25% stellar mass loss. #KICPDM
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Alex Ji @alexji.bsky.social · 04/09/2026
Pace: velocity dispersion profile is flat, can measure kurtosis with 100 stars per bin, difference dynamics between metallicity bins. New surveys are finally coming, but the future is here too :) #KICPDM
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Alex Ji @alexji.bsky.social · 04/09/2026
Andrew Pace: infer density profiles with 400-2000 stars hard to distinguish core-to-cusp. Chang+Necib: need at least 10k stars to do it. No one did it for a while, so he decided to do it himself :) crazy campaign now has ~7600 new unique stars -> 8300 total numbers #KICPDM
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Alex Ji @alexji.bsky.social · 04/09/2026
Li: ELVES-dwarf from Mstar 1e7-8 have low quenched fraction #KICPDM
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Alex Ji @alexji.bsky.social · 04/09/2026
Li: ELVES-dwarf is out, 39 satellites of 39 isolated NGC dwarf hosts (4-12Mpc), confirming with surface brightness fluctuations. But DDO161 has 4 satellites, <1% chance given current SMHM arxiv.org/abs/2609.00283 #KICPDM
arxiv.org
ELVES-Dwarf. II. A Systematic Search for Satellite Systems of Dwarf Galaxies in the Local Volume
We present the Exploration of Local VolumE Satellites of Dwarf Galaxies (ELVES-Dwarf) survey, a systematic census of satellite systems around dwarf hosts in the Local Volume. Our final sample comprise...
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Alex Ji @alexji.bsky.social · 04/09/2026
Jiaxuan Li: host-to-host scatter and different environment may affect SMHM inference. No one would say galaxy formation does not depend on environment :) a promising environment is around dwarfs #KICPDM
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Alex Ji @alexji.bsky.social · 04/09/2026
Jiaxian Li went to the Roman launch!! Some cool pictures :) #KICPDM
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Alex Ji @alexji.bsky.social · 04/09/2026
Li: ex with Boo3, need to throw in an NFW halo with Mhalo ~ 1e6 Msun in order to explain low velocity dispersion. Same with Crater II. #KICPDM
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Alex Ji @alexji.bsky.social · 04/09/2026
Ting Li: Sgr Ant2, Boo3, Cra2, and Tuc3 are the 5 MW satellites with unusually large sizes and small velocity dispersions (low density, below MW density). All of them have clear tidal features. Ting got impatient with the theorists to model these so she has done it herself :) #KICPDM
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Alex Ji @alexji.bsky.social · 04/09/2026
Last day of #KICPDM is the best day, dwarf galaxies! :D This thread is Ting Li, Jiaxuan Li, Andrew Pace, Kaia Atzberger, and Alyson Brooks. I am chairing so let’s see how I do with the skeeting..
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Alex Ji @alexji.bsky.social · 04/09/2026
I feel like your life is headed in a bad direction when you start thinking “maybe I should do some work on the Galactic bar” 😵‍💫
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Alex Ji @alexji.bsky.social · 03/09/2026
Wheeeeee aas.org/posts/news/2...
aas.org
NSF Astronomical Sciences Grants Reduced by Over 50% in Fiscal Year 2026
An analysis of new awards suggests that as of 26 August 2026, the National Science Foundation (NSF) has issued 57% fewer awards in the astronomical sciences in the current fiscal year compared to the ...
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Alex Ji @alexji.bsky.social · 03/09/2026
Derek Perera: measure the critical curve with counter-image pairs. If they're not perfectly symmetric, deviations in the image pairs imply substructure. Can simulate the distribution of expected deviations for different subhalo pops and compare to observed. More to come with VENUS! #KICPDM
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Alex Ji @alexji.bsky.social · 03/09/2026
Hadrian Paugnat: IFU spectroscopy can look at flux ratios in quasar nuclear narrow line region. Showed results with JWST/NIRSPEC IFS (flux ratios are not consistent with warm dust) and Keck AO new instrument KAPA with multiple laser guide stars that's just commissioned #KICPDM
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Alex Ji @alexji.bsky.social · 03/09/2026
Ollie Jackson: use cosmological simulations to test flux ratio constraints, three main sources of scatter: Poisson scatter, host-to-host scatter, dominated by projection angle scatter. Most subhalos if going along host major axis. Clumpiness (sub/subsubhalos) matters too. #KICPDM
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Alex Ji @alexji.bsky.social · 03/09/2026
Projections for the future: with 200 lenses in the coming surveys, can reach half mode mass to 10^7 Msun arxiv.org/abs/2604.05237 #KICPDM
arxiv.org
Measurement of the minimum cold dark matter halo mass with strong gravitational lensing
We explore the lowest mass limit that can be placed on the halo mass function in CDM using 28 strong gravitational lenses. For this purpose, we study an extreme model in which the halo mass function a...
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Alex Ji @alexji.bsky.social · 03/09/2026
Nierenberg: Euclid/LSST/Roman will get 100k's of new galaxy-galaxy lenses! Overall hints of very dense perturbers relative to CDM, interesting to see similar to streams #KICPDM
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Alex Ji @alexji.bsky.social · 03/09/2026
Nierenberg: If the source is not resolved (e.g. quasars), it causes magnification (at the observed image resolution). Multiple images can give flux ratios, forward model realizations of all the subhalos in foreground. With JWST, constrain m_wdm > 10 keV, M_halo_min < 10^8 Msun #KICPDM
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Alex Ji @alexji.bsky.social · 03/09/2026
Nierenberg: The single subhalo detections so far all seem to be very concentrated (e.g. arxiv.org/abs/2601.02466 most recently). #KICPDM
arxiv.org
A possible challenge for Cold and Warm Dark Matter
Measuring the density profile and mass concentration of dark-matter haloes is a key test of the standard cold dark matter paradigm. Such objects are dark and thus challenging to characterise, but they...
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Alex Ji @alexji.bsky.social · 03/09/2026
Anna Nierenberg: strong lensing images affected by low mass halos in the lens, either deflection or magnification. Can do resolved source, single extreme subhalo detection; and resolved/unresolved source with multiple subhalos #KICPDM
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Alex Ji @alexji.bsky.social · 03/09/2026
Tyler Smith simulates SIDM at z>6, can see its effect even at z~15. SIDM makes subhalos disrupt 4-5x more (maybe can feed gas to host halo for starburst). SIDM core-collapse has been proposed for LRD formation but is prevented by lots of mergers stopping collapse. #KICPDM
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Alex Ji @alexji.bsky.social · 03/09/2026
Jared Barron: can constrain atomic-like dark matter (transfer function cutoff with oscillations) with CMB, high-z UVLF, LyA, and CMB spectral distortions. #KICPDM
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Alex Ji @alexji.bsky.social · 03/09/2026
Munoz: in the far future can do this with intensity mapping, mix resolved systems and look at residual light integrated to measure further down possibly to k ~ 100 #KICPDM
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Alex Ji @alexji.bsky.social · 03/09/2026
Julian Munoz: the UV luminosity function of high-z galaxies also constrains power spectrum (lots of degeneracies as M_UV closer to SFR the Mstar, can partially break with clustering). With JWST/GLIMPSE can reach k~30 #KICPDM
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Alex Ji @alexji.bsky.social · 03/09/2026
Chandra: Via can cover velocity dispersions for all >3000 Msun dwarf galaxies out to 300 kpc (e.g. 40 Segue 1 stars in one hour), and it will get ~1000 QSOs for the LyA forest from z=3.2-4.1 that can constrain the IGM thermal history #KICPDM
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Alex Ji @alexji.bsky.social · 03/09/2026
Vedant Chandra: the Via project will get 0.1 km/s stable velocity precision for streams. If v precision of only 1 km/s, can only see a few very large impacts; but 0.1 km/s resolves 20-30x more impacts reaching to 1e8 Msun halos at infall #KICPDM
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Alex Ji @alexji.bsky.social · 03/09/2026
Silverman: SIDM can change stellar stream properties on average: doesn't affect the earliest disruption, but by the end about 80% of SIDM vs 55% of CDM dwarf galaxies are completely disrupted #KICPDM
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