Swirling Magnetic Fields Visible in New Black Hole Images

It’s been about five years since scientists captured the first blurry image of a black hole. Using what they learned from that experience, they’ve teased out some more detailed images of the black holes at the centers of the Milky Way galaxy (top) and the M87 galaxy (bottom). The process of collecting the data for these images is interesting:

The only way to “see” a black hole is to image the shadow created by light as it bends in response to the object’s powerful gravitational field. As Ars Science Editor John Timmer reported in 2019, the EHT isn’t a telescope in the traditional sense. Instead, it’s a collection of telescopes scattered around the globe. The EHT is created by interferometry, which uses light in the microwave regime of the electromagnetic spectrum captured at different locations. These recorded images are combined and processed to build an image with a resolution similar to that of a telescope the size of the most distant locations. Interferometry has been used at facilities like ALMA (the Atacama Large Millimeter/submillimeter Array) in northern Chile, where telescopes can be spread across 16 km of desert.

In theory, there’s no upper limit on the size of the array, but to determine which photons originated simultaneously at the source, you need very precise location and timing information on each of the sites. And you still have to gather sufficient photons to see anything at all. So atomic clocks were installed at many of the locations, and exact GPS measurements were built up over time. For the EHT, the large collecting area of ALMA-combined with choosing a wavelength in which supermassive black holes are very bright-ensured sufficient photons.

The images of the two black holes look similar, which was somewhat unexpected:

While this idea may initially sound somewhat mundane, it is anything but. The result is surprising because Sgr A*’s mass is about 4.3 million times that of the Sun, while M87*’s is about 6.5 billion times that of the Sun. Despite the significant difference in mass between the two supermassive black holes, the fact that their magnetic fields behave similarly and are both well-organized is an incredible discovery.

• astronomy
• black holes
• photography
• science
• space