GRAPPA Centre

One more paper from the group out arxiv.org/abs/2508.00062 🎉 Led by Lieke Sippens Groenewegen, who finished her MSc in my group @grappainstitute.bsky.social in February, and with @sanjanacurtis.bsky.social we developed an end-to-end pipeline for kilonova lightcurves and spectra #highenergyastro 🔭🧪

Moreover, thanks to simulation reuse enabled by SBI, they could perform the combined analysis using *zero* calls to a Boltzmann solver

To illustrate their method, they combine the full Planck CMB likelihoods with a 3x2pt simulator for a Stage IV galaxy survey (e.g. Euclid), and test evolving dark energy. They find that future 3x2pt data *alone* could detect dynamical dark energy preferred by DESI at the *5sigma* level

This is particularly relevant for legacy cosmology likelihoods such as Planck, which can't easily be reformulated as forward simulators, complicating its integration into simulation-based combined analyses

Looking for a summer read? Check out this new GRAPPA paper! arxiv.org/abs/2507.22990 The authors introduce a simple method to construct an effective simulator for *any* explicit likelihood, using samples from a previous MCMC

3D full-GR simulations of magnetorotational core-collapse supernovae on GPUs: A systematic study of rotation rates and magnetic fields We present a series of fully three-dimensional, dynamical-spacetime general relativistic magnetohydrodynamics (GRMHD) simulations of core-collapse supernovae (CCSNe) for a progenitor of zero-age-main-...

To kick off here on bluesky I wanted to share some recent work from the group. First off arxiv.org/abs/2504.11537, the first science paper produced with our new GPU-accelerated GRMHD code GRaM-X.

Huge congratulations to Dr. Uddipta Bhardwaj, who successfully defended his PhD thesis "Sequentially learning Gravity" on the 19th of May 2025 🥳

Applying it to the case of dark matter (DM) spikes around massive black holes (BHs), they show that a fully relativistic treatment is needed to accurately model the environmental dephasing of gravitational wave (GW) signals from EMRIs

New GRAPPA paper! arxiv.org/abs/2505.097...
The authors (Rodrigo Vicente, Theophanes Karydas, @gfbertone.bsky.social) introduce a relativistic framework to model environmental effects on extreme mass-ratio inspirals (EMRIs) in collisionless media

Map of the "blue component" of the Doppler velocities (left) and the "red component" of the Doppler velocities. Note that the "red component" in the southeast is still blueshifted, and the "blue component" in the NW is mostly redshifted.

I like to bring your attention to a recently accepted paper by me, my student Manan Agarwal and several members of the XRISM science on the magnificent supernova remnant Cassiopeia A: arxiv.org/abs/2505.04691.

Today we had a fantastic Colloquium by Dr. Malcolm Fairbairn (@KingsCollegeLon) to tell us about "Galaxies, Axions, Gravitational Waves, Black Holes and More Galaxies"

It's a real pleasure to have Dr. Jonathan Gair (@mpi_grav) giving the GRAPPA Colloquium today, to tell us about "Opportunities and challenges in SBI for future gravitational wave detectors"

Congrats to the KM3NET collaboration for this fantastic discovery!

Celebrating the start of the year with our fantastic GRAPPA members 🥂🥳🎉

He will use it to conduct six months of research at DESY, the German laboratory for high-energy physics in Berlin.

Jacco Vink (UvA) ontvangt Humboldt-prijs

Huge congrats to @jaccovink.bsky.social for receiving the prestigious German Humboldt Prize for research!
www.astronomie.nl/nieuws/jacco...

Inspiring and wonderful article about former GRAPPA PhD student Gimmy Tomaselli on dutch newspaper NRC. Congratulations!
www.pressreader.com/netherlands/...

Huge congratulations to Dr Ben Miller @bkmi.bsky.social on a fabulous PhD defence and thesis on “Machine Learning for Scientific Simulation: Inference and Generative Models.” The thesis is such a great reference for simulation based reference & a real tour de force! Proud of you & to have been your

Congrats to all the authors!
Oleg Savchenko, Florian List, Guillermo Franco Abellán, Noemi Anau Montel, Christoph Weniger

Owing to its simplicity, the method is significantly faster than other proposed algorithms (training only takes ~1h on a GPU, and sampling just ~3s for 1000 samples), while still being highly precise and interpretable

The method relies on the assumption that the multi-million dimensional posterior of cosmic ICs can be described by a simple Gaussian, where the mean and covariance have been trained on the Quijote N-body simulations suite

Paper alert!
The authors introduce a fast and accurate method to reconstruct the cosmological initial conditions from present-day dark matter density fields, including uncertainty quantification!
arxiv.org/abs/2410.15808
Led by GRAPPA PhD Oleg Savchenko

As an application to non-gaussian posteriors, the authors also test a model of 2-body decaying dark matter, finding that Stage IV surveys can improve current bounds by up to 1 order of magnitude!

They are able to recover the posterior distribution of all parameters with a speedup factor of ~40-60 compared to MCMC!

New GRAPPA paper!
arxiv.org/abs/2403.14750
The authors show the first application of Marginal Neural Ratio Estimation (MNRE) to accelerate parameter inference from upcoming Stage IV photometric surveys (like Euclid or LSST)

Thrilled that the @_nikhef bachelors gravitational wave workshop that I am teaching @IoP_UvA @UvA_Science got to hang out with Dave Reitze director of @LIGO , Albert Lazzarini, Stuart Anderson & Jess McIver deputy spokesperson

Many many congratulations @samayanissanke.bsky.social ! We are so proud of you

Celebrating and sharing the New Year with our fantastic GRAPPA members 🎉🎉🎉

Samengestelde afbeelding in valse kleuren van Cassiopeia A met daarbij groene slierten: het groene monster. De slierten bevinden zich in het midden. Verder naar buiten is de nevel blauw. En weer verder rood. Credit: NASA, ESA, CSA, Milisavljevic et al & Vink et al.

'Groen monster' was er al voordat Cassiopeia A ontplofte.

Onderzoekers (o.a. Jacco Vink) presenteren analyse tijdens congres van de American Astronomical Society.

📡 www.astronomie.nl/ni...

#astrodon #astronomie #astronomy

Huge congratulations to Prof. Daniel Baumann for receiving prestigious Humboldt Research Award! 🥳🥳🥳
iop.uva.nl/content/news...