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The supermassive black hole at the centre of the galaxy M87 reveals a delicate spiral pattern in this image, based on a re-analysis of observations made in 2018. The pattern is caused by the influence of powerful magnetic fields on the radio waves that are emitted by the hot gas circling around the black hole.
EHT Collaboration
Astronomers have added a twist to their first-ever picture of a black hole.
A new take of the historic image, released on Wednesday, shows that in addition to a fearsome gravitational pull, the black hole also emanates a powerful magnetic field that threads through the hot gas orbiting around it, giving the picture a van Gogh-esque swirl.
While the presence of magnetic forces near the black hole has long been suspected, it has never been observed until now.
Avery Broderick, a researcher at the Perimeter Institute for Theoretical Physics in Waterloo, Ont., was part of the team that spent two years carefully teasing the magnetic signal out of the image – an achievement he compared to being able to watch a play in its entirety after previously only hearing snatches of dialogue at the stage door.
“Now we can watch the drama unfold,” said Dr. Broderick, who is also an associate professor at the University of Waterloo.
The picture is the work of the Event Horizon Telescope, a project that combines data gathered simultaneously by several radio dishes located around the globe to produce an image that is as sharp as would be seen by a single radio telescope the size of Earth. When the original version of the image was published in 2018, it was hailed as the first direct view of the environment around a black hole, one of the most extraordinary classes of objects in the universe.
The black hole resides at the heart of a distant galaxy known as M87 and is estimated to contain a mass equivalent to six and and a half billion suns. By definition, it gives off no light. In the image it is seen in silhouette, occupying the dark area at the centre. The glowing ring around it is made up of ionized gas circling the black hole at high speed.
For their updated version of the image, Dr. Broderick and his colleagues used the original data to extract additional information. By measuring how the the radio waves emanating from around the black hole are aligned – an effect that is analogous to looking at the object through polarized sunglasses – they could map the influence of the black hole’s magnetic field on the gas.
The resulting swirl is not a physical depiction of the gas; in reality, the brush-like grooves are merely a representation that indicates the strength and direction of the polarizing effect. However, it amounts to proof that the gas is highly magnetized. Dr. Broderick said the effect can now be studied in more detail to reveal how the black hole’s immense gravitational and rotational energy is transferred to its surroundings via magnetic forces.
Jayanne English, an astronomer at the University of Manitoba who has mapped the magnetism around galaxies but is not part of the Event Horizon Telescope project, called the new image “evocative” and reminiscent of the way a sprinkle of iron filings can be used to reveal the invisible field around a household magnet.
“This rendition of the data helps build bridges between the public and the astrophysicists who want to share their ongoing investigations,” she said.
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2021-03-24 14:00:00Z
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