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Astronomers show first image of a black hole's magnetic fields

The scientists who gave the world its first true glimpse of a black hole have produced another landmark observation

A view of M87's supermassive black hole in polarized light. The lines mark the orientation of polarization, which is related to the magnetic field around the shadow of the black hole. (Photo by Handout/European Southern Observatory/AFP)

Astronomers working in collaboration between the Smithsonian Astrophysical Observatory and Harvard College Observatory have obtained a new view of the supermassive black hole at the center of galaxy M87 or Messier 87. Images released on 24 March by the Event Horizon Telescope (EHT) collaboration, a network of radio telescopes, show how the black hole, some 55 million light-years away from us, appears in polarized light.

These are the same astronomers who gave the world its first true glimpse of a black hole in 2019. This time they have captured the polarised light swirling around the same anomaly’s magnetic fields. According to an AFP report, never before has it been possible to measure polarisation -- which causes light waves to vibrate in a single plane -- so close to the edge of a black hole.

These new observations, based on data collected by the EHT in 2017, are key to understanding how a galaxy can project streams of energy thousands of lightyears outward from its core, the report added. The new findings were published in two studies in the Astrophysical Journal Letters on 24 March.

“One of the main science drivers of the EHT is distinguishing different magnetic field configurations around the black hole,” Angelo Ricarte, a co-author and researcher at the Center for Astrophysics | Harvard & Smithsonian said in a news release. “Polarization is one of the most direct probes into the magnetic field that nature provides.

The new observations, based on data collected by the Event Horizon Telescope (EHT) in 2017, are key to understanding how a galaxy can project streams of energy thousands of lightyears outward from its core.
The new observations, based on data collected by the Event Horizon Telescope (EHT) in 2017, are key to understanding how a galaxy can project streams of energy thousands of lightyears outward from its core. (AFP)

The EHT collaboration has been studying the supermassive object at the heart of M87 for more than a decade. In April 2019, they revealed the very first image of a black hole. Since then, the scientists have studied the data further, discovering that a significant fraction of the light around the M87 black hole is polarized.

Light becomes polarized when it goes through certain filters -- like, for instance, the lenses of polarized sunglasses, or when it is emitted in hot regions of space that are magnetized. In the same way, the news release explains, polarized sunglasses help us see better by reducing reflections and glare from bright surfaces, astronomers can sharpen their view of the black hole by looking at how light originating from there is polarized. “Specifically, polarization allows astronomers to map the magnetic field lines present around the inner edge of the black hole,” the release adds.

One of the most mysterious features of the M87 galaxy is the bright jet of matter and energy that emerges from its core and extends at least 100,000 light years away, the release explains. Most matter lying close to the edge of a black hole falls in. However, some of the surrounding particles escape moments before capture and are blown far out into space in the form of these jets. Astronomers don't know how these jets of matter larger than the galaxy itself are launched from its core, nor how only certain matter falls into the black hole, the release adds.

With the new image of the black hole in polarized light, the team has looked directly into the region just outside the black hole where this interplay between inflowing and ejected matter occurs. To observe M87’s heart, the EHT collaboration, which involves more than 300 researchers globally, linked eight telescopes around the world, including the Smithsonian Astrophysical Observatory's Submillimeter Array, to create a virtual Earth-sized telescope. The impressive resolution obtained with the EHT is equivalent to that needed to image a credit card on the surface of the Moon, the release explains.

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