@8minutesold
Astrophysicist studying cosmic choreographies of dwarf galaxies. Junior Research Group Leader at AIP, Street Photographer (he/him) Autor des Buchs „Von tanzenden Galaxien, Dunkler Materie, und anderen kosmischen Rätseln“ Potsdam, Germany
So shocking and awful. Just a few months ago I had some wonderful conversations with Carl at a conference. He was always such a pleasure to interact with due to his intellect, humor, and openness to ideas and scientific challenges. What a loss.
www.theguardian.com/us-news/2026...
Danke, freut mich! War auch eine tolle Fragerunde im Anschluss, hat Spaß gemacht.
Looking forward to visit the planetarium of the Sternwarte Neanderhöhe Hochdahl tonight, where I will give a public talk about my research on dwarf galaxies and dark matter. If you happen to be near Erkrath: a few seats are still available.
I'd watch a muppet show movie where the muppets infiltrate an academic conference.
Last year I was invited to speak at the "Nicolaus-Copernicus-Symposium" in Nuremberg about limits of modern astronomy and dark matter. 🔭🧪
A recording of the talk is now available (with almost 30k views already, and there's a version dubbed in English, apparently):
www.youtube.com/watch?v=fMt_...
Are you 🤬 kidding me?
Email subject like saying that my research is invisible to AI.
Great, let’s keep it that way.
🌈 Polarlichter über Potsdam – Letzte Nacht löste eine starke Sonneneruption Polarlichter über Potsdam aus. ☀️ 🌌Dieses Naturschauspiel entsteht, wenn energiereiche Teilchen der Sonne mit dem Erdmagnetfeld und der Atmosphäre in Wechselwirkung treten. 🔭 #polarlichter #auroraboreal #potsdam
Green band of polar lights over buildings.
Wow, amazing polar lights over Potsdam right now, visible despite all the light pollution.
Photo of a snowman.
Got some decent snow this morning in Potsdam, perfect consistency for building ☃️.
What I don't understand is why so many politicians remain active on X, given the company's and its owner's reluctance to follow regulations. Even the also sanctioned Thierry Breton, former EU Commissioner who championed the Digital Services Act to regulate online platforms, commented on this on X.
German non-profit HateAid does important work, their founder recently got the Order of Merit of Germany. They support victims of online hate speech and threats – aka "American viewpoints", apparently.
Nobody forces U.S. companies to do business in Europe if they don't want to follow our laws.
The primordial dark matter halo of the Milky Way had a mass distribution nothing like what we expect in LCDM.
tritonstation.com/2025/12/01/t...
Press release by Pengfei, @aippotsdam.bsky.social's former @humboldt-foundation.de Humboldt Fellow, on our new paper about the odd primordial dark matter halo of the Milky Way.
Photo of three copies of the IAU Symposium 379 proceedings titled „Dynamical Masses of Local Group Galaxies“ published by Cambridge University Press.
Look what finally arrived! The proceedings of our International Astronomical Union Symposium 379 „Dynamical Masses of Local Group Galaxies“. 🌌🧪🔭☄️
Which was held in early 2023, with all manuscripts submitted later that same year. So it took CUP only *checks notes* two years to publish.
Please check the great summary of our new paper, inferring the primordial dark matter halos from observations.
Interesting, though doesn't that model predict flat rotation curves, whereas the MW one is declining? So it might have issues explaining the outer, steep slope. This "Scalar/BEC soliton" in Fig. 1 looks interesting in that regard, but I'll have to read this in more detail.
Nanjing Univ. press release: Our Galaxy’s Primordial Dark Matter Halo is a Major Oddity
astronomy.nju.edu.cn/EN/NewsEvent...
Article by Li et al.: www.aanda.org/10.1051/0004...
But those alternative DM models don't explain the steep decline in the outskirts. We don't know what mechanism could cause it. Though it is related to the quickly declining Gaia rotation curve, which remains debated and was in itself unexpected. So better measurements might help resolve this.
6/6
We don't know how a core as large as inferred for the inner part of the primordial MW halo could be formed in the cold dark matter paradigm, also because feedback processes should be compensated by the compression effect. Alternative types of DM, like warm or fuzzy DM may help, but only here.
5/6
Structure of the inferred primordial and current Galactic halos, along with predictions for the cold and warm dark matter. The density profiles are scaled so that there is no need to assume or consider the masses or concentrations for these halos. The gray band indicates the range of the current halos derived from the Gaia velocity fits using the 12 baryonic models, and the red band shows their corresponding primordial halos within 1σ. The blue band presents the simulated halos with cold dark matter only (Dutton & Macciò 2014). The purple band shows the warm dark matter halos (normalized to match the primordial Galactic halo) with a core size spanning from 4.56 kpc (WDM5 in Macciò et al. 2012) to 7.0 kpc, corresponding to a particle mass of 0.05 keV and lower.
Halo masses and concentrations of the primordial Galactic halos derived from the Gaia circular velocity fits using 12 baryonic models. The red and blue stars with errors represent the halos with and without adiabatic contraction, respectively. The predicted halo mass-concentration relation within 1σ from simulations (Dutton & Macciò 2014) is shown as the declining band. The vertical band shows the expected range of the MW halo mass according to the abundance-matching relation (Moster et al. 2013). The upper and lower limits are set by the highest stellar mass (model A&S) plus 1σ and the lowest stellar mass (model I) minus 1σ, respectively.
Rather than finding primordial DM halo in line with expectations from simulations, we infer a profile that is odd in two regards: significantly less centrally concentrated (shallow core), but also dropping faster in the outskirts (steep decline). Much less concentrated than DM-only halos, too.
4/6
Example of a circular velocity fit using the McGaugh19 model for baryonic mass distributions. The purple, blue, and green lines represent the contributions of the bar, disk, and gas components, respectively. The solid and dashed black lines show the current and primordial dark matter halos, respectively. The solid red line indicates the total velocity profile. The black points show the latest Gaia measurements (Jiao et al. 2023), and the gray upward triangles and squares show the terminal velocities from (McClure-Griffiths & Dickey 2007, 2016), and Portail et al. (2017), respectively. The data marked with open symbols were not fit because they do not consider the systematic uncertainties. The fits with 12 baryonic models are shown in Fig. A.2.
To test the robustness of the results, a range of plausible baryonic mass distributions (within observational uncertainties) are used. No matter what empirical baryonic mass distribution is adopted, the inferred primordial halo profiles remain very similar. And odd:
3/6
Visualization of the primordial dark matter halo (left) inferred through reverse engineering from the rotation curve of the galaxy in the compressed halo (right).
Cold dark matter only simulations predict a certain halo profile, but once baryons (gas+stars) collapse in the center they pull the DM inward. We invert that baryonic compression process: using the present-day rotation curve and baryonic mass distribution to infer the original DM distribution.
2/6
A (dark matter) Space Oddity:
We have an exciting new paper led by @pengfeili.bsky.social: arxiv.org/abs/2511.17705
He used the best data on the Milky Way rotation curve from Gaia to infer not the current, but the *primordial* dark-matter halo of the Galaxy.
And it is quite odd. 🧪🔭☄️
1/6
One flaw with my analogy (below) regarding the 20 GeV gamma-ray excess as a potential dark matter signal (arxiv.org/abs/2507.072...): For a well regulated lottery, I can at least be sure that the jackpot indeed exists. 🔭
So, I'd say this could be a dark matter signal ... just like I could be a millionaire after buying a lottery ticket:
In principle not ruled out, I really hope for it to happen, but it is unlikely and every time I've tried thus far it didn't work out.
... but I agree with Stacy that the assumed MW halo is too massive/dense to be realistic. And I'd expect that if you reduce the assumed dark matter density, the same amount of DM needs to generate a stronger signal. Which should increase rather than ease the tension with dwarf galaxy constraints.
The paper itself also mentions that the signal is inconsistent with constraints from dwarf galaxies (which I consider as cleaner targets for such studies). It tries to argue that away by saying that the assumed MW dark matter profile has large uncertainties, ...
Calling on my #science network! TeamNDF is #hiring a postdoc to start in 2026!
Are you fascinated by metabolism and the brain? Do you want to dig into life long impacts and the molecular cause?
Learn more about the team and our research here: www.dife.de/en/research/...
Please share! 🧠 🍔 💉
Today’s the day! There are still some tickets if you’re interested to join.