A strong magnetic field around the supermassive black hole at the centre of the Galaxy

TL;DR

This study uses multi-frequency radio observations of a pulsar near the Galactic Centre to reveal a strong, dynamically significant magnetic field around the supermassive black hole, influencing accretion and emission processes.

Contribution

It provides the first direct evidence of a strong magnetic field near the black hole, demonstrating its role in accretion dynamics and emission mechanisms.

Findings

Large Faraday rotation indicates a strong magnetic field

Magnetic flux is sufficient to power observed emissions

Magnetic field influences accretion flow structure

Abstract

The centre of our Milky Way harbours the closest candidate for a supermassive black hole. The source is thought to be powered by radiatively inefficient accretion of gas from its environment. This form of accretion is a standard mode of energy supply for most galactic nuclei. X-ray measurements have already resolved a tenuous hot gas component from which it can be fed. However, the magnetization of the gas, a crucial parameter determining the structure of the accretion flow, remains unknown. Strong magnetic fields can influence the dynamics of the accretion, remove angular momentum from the infalling gas, expel matter through relativistic jets and lead to the observed synchrotron emission. Here we report multi-frequency measurements with several radio telescopes of a newly discovered pulsar close to the Galactic Centre and show that its unusually large Faraday rotation indicates a dynamically relevant magnetic field near the black hole. If this field is accreted down to the event horizon it provides enough magnetic flux to explain the observed emission from the black hole, from radio to X-rays.