Space

A new image reveals magnetic fields around our galaxy’s central black hole

Event Horizon Telescope observations show the orientation of light around Sagittarius A*

Whirling magnetic field lines seen in polarized light surround the Milky Way’s central supermassive black hole in this new image from the Event Horizon Telescope.

EHT Collaboration

By Adam Mann

March 27, 2024 at 9:00 am

Astronomers have gotten their best view yet of the magnetic fields around the gargantuan black hole at the center of the Milky Way.

A new image reveals that the behemoth, named Sagittarius A*, is encircled by highly-ordered magnetic structures, researchers report in two papers published March 27 in the Astrophysical Journal Letters. The features are similar to ones previously seen surrounding the galaxy M87’s supermassive black hole (SN: 3/24/21).

Using the Event Horizon Telescope, a global collection of radio telescopes working in tandem, scientists captured polarized light coming from around Sagittarius A*, which lies about 27,000 light-years from Earth (SN: 4/10/19). Polarized light has waves that wiggle in the same direction, such as up and down or left and right. Mapping such light often gives astronomers insights into underlying magnetic phenomena.

The magnetic field closest to the black hole is relatively strong, about 30 times that of Earth’s, though still only about as powerful as a fridge magnet, says astronomer Sara Issaoun of the Harvard and Smithsonian Center for Astrophysics in Cambridge, Mass. It’s produced by charged particles in the hot dense plasma surrounding the black hole’s accretion disk, a collection of gas and dust spiraling into Sagittarius A*.

Comparison of magnetic field lines around galaxy M87's central supermassive black hole and the one in the Milky Way — Magnetic structures previously spied encircling the supermassive black hole in the galaxy M87 (left) look remarkably like those now seen around the much smaller and less active black hole in the center of our galaxy (right). For comparison, 120 billion kilometers is roughly 25 times the distance between Neptune and the sun, and 60 million kilometers is approximately the distance between Mercury and the sun.EHT CollaborationMagnetic structures previously spied encircling the supermassive black hole in the galaxy M87 (left) look remarkably like those now seen around the much smaller and less active black hole in the center of our galaxy (right). For comparison, 120 billion kilometers is roughly 25 times the distance between Neptune and the sun, and 60 million kilometers is approximately the distance between Mercury and the sun.EHT Collaboration

The Milky Way’s central black hole is very different from the one in M87. The latter weighs as much as 6 billion suns, lives in a giant elliptical galaxy, and ejects a powerful jet of plasma visible at all wavelengths. Sagittarius A* weighs a mere 4 million suns, lives in a smaller spiral galaxy, and appears to have no jet at all.

Given such dissimilarities, “we expected to see different properties of their magnetic fields,” Issaoun says. The fact that both are highly structured suggests such fields are ubiquitous around black holes and affect how these cosmic vacuum cleaners grow and evolve.