Probing within the Bondi radius of the ultramassive black hole in NGC 1600

TL;DR

This study uses deep Chandra X-ray observations to analyze the hot gas around the ultramassive black hole in NGC 1600, revealing flat temperature profiles and shallow density gradients that challenge classical accretion models.

Contribution

First detailed spatially resolved temperature and density profiles within the Bondi radius of an ultramassive black hole in NGC 1600 using high-resolution Chandra data.

Findings

Temperature profile is flat near the center, contrary to Bondi accretion expectations.

Density profile follows a shallow power-law, implying lower accretion rates.

Gas dynamics are not dominated by the black hole within the Bondi radius.

Abstract

We present deep (250 ks) Chandra observations of the nearby galaxy group NGC 1600, which has at its centre an ultramassive black hole (17$\pm$1.5 billion M$_{\odot}$). The exceptionally large mass of the black hole coupled with its low redshift makes it one of only a handful of black holes for which spatially resolved temperature and density profiles can be obtained within the Bondi radius with the high spatial resolution of Chandra. We analyzed the hot gas properties within the Bondi accretion radius R$_B$=1.2" - 1.7"= 0.38 - 0.54 kpc. Within a $\sim\!3$ kpc radius, we find two temperature components with statistical significance. Both the single temperature and two temperature models show only a very slight rise in temperature towards the centre, and are consistent with being flat. This is in contrast with the expectation from Bondi accretion for a temperature profile which increases towards the centre, and appears to indicate that the dynamics of the gas are not being determined by the central black hole. The density profile follows a relatively shallow $\rho\propto~r^{-[0.61\pm0.13]}$ relationship within the Bondi radius, which suggests that the true accretion rate on to the black hole may be lower than the classical Bondi accretion rate.