Astronomers have discovered powerful magnetic fields spiralling around the black hole that sits at the centre of the Milky Way, the European Southern Observatory said Wednesday.

A new image from the Event Horizon Telescope (EHT) for the first time showed in polarised light a ring of magnetic fields surrounding the Sagittarius A* black hole.

The fields are similar to those observed around the M87* black hole at the heart of the M87 Galaxy, which the ESO says suggests that strong magnetic fields may be common to all black holes.

"What we're seeing now is that there are strong, twisted, and organised magnetic fields near the black hole at the centre of the Milky Way galaxy," said Sara Issaoun, from Harvard's Center for Astrophysics, and co-lead of the project.

Polarised light images allow the astronomers to isolate the magnetic field lines.

Supermassive black holes, which sit at the centre of galaxies, have masses millions and even billions greater than the Sun. They are believed to have emerged very early in the universe but their creation remains a mystery.

Nothing can escape their gravitational pull, not even light, making them impossible to observe directly.

But with M87* in 2019 and Sagittarius A* in 2022, the EHT captured the halo of light that is produced by the flow of matter and gas that black holes suck in and eject.

"By imaging polarised light from hot glowing gas near black holes, we are directly inferring the structure and strength of the magnetic fields that thread the flow of gas and matter that the black hole feeds on," said Angelo Ricarte, member of the Harvard Black Hole Initiative and a co-lead of the project.

Mariafelicia De Laurentis, deputy scientist at the EHT and professor at the University of Naples Federico II in Italy, said that "since both (black holes) are pointing us toward strong magnetic fields, it suggests that this may be a universal and perhaps fundamental feature of these kinds of systems."