Year: 2026
Type: article
Abstract: Of the two black holes, M87* and Sgr A*, for which event-horizon-scale imaging is currently achievable, only Sgr A* at our Galactic center exhibits sub-hour variability, making light-curve observations of the inner accretion flow especially valuable for time-domain studies of the spacetime and the surrounding plasma. Observed light curves are often sampled with variable cadence, so a structure function is often used to quantify their variability properties. In this work, we assemble a heterogeneous Sgr A* light-curve dataset from discrete observations acquired over ∼12 yr at 230 GHz, with different instruments, durations, and cadences, and study its structure function in three frameworks. First, we consider analytic predictions for the features of structure functions of stationary random processes with Fourier spectra dictated by the Matérn covariance. We then study the structure functions resulting from lensed movies of synthetic optically thin accretion flows approximated with Matérn covariance in both space and time and identify which features in the structure function can be attributed to the black-hole geometry. Lastly, we examine the structure functions of a library of 72 general relativistic magnetohydrodynamic simulations. We find that, in general, magnetically arrested disk (MAD) models produce smoother structure functions with steeper slopes than standard and normal evolution (SANE) counterparts. On time scales of 5–15 minutes, the observed structure function slope of Sgr A* more closely aligns with the MAD trend, while both simulation types are generally more variable than the data on all sub-hour timescales.
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,400
Funders: National Science Foundation, U.S. Department of Energy, John Templeton Foundation, Gordon and Betty Moore Foundation, Northwestern University, National Centre for Supercomputing Applications, National Radio Astronomy Observatory, Korea Astronomy and Space Science Institute, National Astronomical Observatory of Japan, University of Illinois at Urbana-Champaign, Office of Science, Smithsonian Astrophysical Observatory, Quest High Performance Computing, National Institutes of Natural Sciences, Office of Advanced Cyberinfrastructure, Oak Ridge National Laboratory
Awards: G1018711323, G121915436, G1353381076, G1453181110, G1503004319, G1645119126, Track 4: Advanced CI Coordination Ecosystem: Monitoring and Measurement Services, G203625172, G2154383771, G2411683797, G2598886323, G2848635288, G298330452, Partnership to Advance Throughput Computing (PATh), G3562386289, Track 1: ACCESS Resource Allocations Marketplace and Platform Services (RAMPS), G4010157413, G4263569045, G4403015908, G4423657506, ACO: An Open CI Ecosystem to Advance Scientific Discovery (OpenCI), Category I: Crossing the Divide Between Today's Practice and Tomorrow's Science, Collaborative Research: Experimental General Relativity using Radio Interferometry of a Black Hole Photon Ring, Track 3: COre National Ecosystem for CyberinfrasTructure (CONECT), G5214277425, G5367127336, Institute for Research and Innovation in Software for High Energy Physics (IRIS-HEP), G5464919783, G6551648957, G6709186444, G675320460, G6754955425, Black Hole Initiative Phase 3, G8108599699, G8269158468, G829097948, Track 2: Customized Multi-tier Assistance, Training, and Computational Help (MATCH) for End User ACCESS to CI, G8562358136, G8851268641
OpenAlex ID: W7220393288