Astronomers have received their best look yet at the magnetic fields around the massive black hole in the middle of the Milky Way.
A new picture shows that the huge black hole, called Sagittarius A*, is surrounded by very organized 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*.
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.
