Nonthermal hotspot orbiting the supermassive black hole Sgr A*
Abstract
Recent millimeter wavelength observations at 230 GHz by the Event Horizon Telescope have resolved the innermost structure of the Galactic Center, Sgr A*, revealing a ring-like structure consistent with synchrotron emission from a magnetized torus surrounding a supermassive black hole. These observations reveal two key features: three prominent hotspots near the photon ring and low light-curve variability, with a modulation index of σ̅/μ̅ ≲ 0.1. State-of-the-art general relativistic magnetohydrodynamic and radiative transfer simulations cannot simultaneously reproduce the three hotspots and low light-curve variability observed in Sgr A*. We propose that an orbiting hot blob, formed in the accretion disk, could account for hotspots. We systematically explore its physical properties, including size, emission amplitude, orbital radius, eccentricity, velocity, and orbital plane orientation. The results -- applying two observational constraints--show that the preferred model corresponds to a black hole with dimensionless spin a⋆=0.5, a magnetically arrested disk configuration for the magnetic field, and the presence of a hotspot with size σhs=2 M and intensity amplitude A=10, orbiting circularly at rorb=6 M with Keplerian velocity in the black holes equatorial plane, and an inclination view angle of i∘=20.
Versions
Related
- Wave optical imaging of an oscillating electric dipole orbiting a black hole
- Chaotic accretion can (still) explain early supermassive black hole growth
- Parameter Estimation for Eccentric Supermassive Black Hole Binaries with Pulsar Timing Arrays
- Exploring the faint limit of the ESA Plato space mission. A case study of extragalactic research with the self-lensing supermassive black hole binary candidate, Spikey
- Supermassive Black Hole Winds in X-rays: SUBWAYS. VI. Interplay between the soft X-ray excess and ultrafast outflows
BibTeX
@misc{cruzosorio2026nonthermal,
title = {{Nonthermal hotspot orbiting the supermassive black hole Sgr A*}},
author = {Alejandro Cruz-Osorio and David Barrero-González and Juan J. Zaldívar and Yosuke Mizuno},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.38553},
eprint = {2609.38553},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.38553},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Nonthermal hotspot orbiting the supermassive black hole Sgr A*
AU - Alejandro Cruz-Osorio
AU - David Barrero-González
AU - Juan J. Zaldívar
AU - Yosuke Mizuno
PY - 2026
DA - 2026/09/29
PB - arXiv
DO - 10.48550/arxiv.2609.38553
UR - https://arxiv.org/abs/2609.38553
AB - Recent millimeter wavelength observations at 230 GHz by the Event Horizon Telescope have resolved the innermost structure of the Galactic Center, Sgr A*, revealing a ring-like structure consistent with synchrotron emission from a magnetized torus surrounding a supermassive black hole. These observations reveal two key features: three prominent hotspots near the photon ring and low light-curve variability, with a modulation index of σ̅/μ̅ ≲ 0.1. State-of-the-art general relativistic magnetohydrodynamic and radiative transfer simulations cannot simultaneously reproduce the three hotspots and low light-curve variability observed in Sgr A*. We propose that an orbiting hot blob, formed in the accretion disk, could account for hotspots. We systematically explore its physical properties, including size, emission amplitude, orbital radius, eccentricity, velocity, and orbital plane orientation. The results -- applying two observational constraints--show that the preferred model corresponds to a black hole with dimensionless spin a_⋆=0.5, a magnetically arrested disk configuration for the magnetic field, and the presence of a hotspot with size σ_hs=2 M and intensity amplitude A=10, orbiting circularly at r_orb=6 M with Keplerian velocity in the black holes equatorial plane, and an inclination view angle of i^∘=20.
ER -