Black hole breakthrough: New images show magnetic fields around M87*

Thursday, March 25, 2021

The black hole at the centre of the M87 galaxy is like a giant fire-breathing dragon that spews enormous jets of energetic particles at near light speeds across some 5,000 light years of space.

A new view of this black hole in polarized light, released today by the Event Horizon Telescope (EHT) collaboration, will help astrophysicists understand just how those jets are launched by this monstrous black hole.

M87* image, showing lines of bright light spiralling around the black hole

A team led by Avery Broderick, a member of the EHT collaboration who is an astrophysicist at the University of Waterloo's Department of Physics and Astronomy, and Perimeter Institute for Theoretical Physics in Waterloo, contributed to making this new view in polarized light possible.

“It is a breakthrough in radio astronomy to see the polarization structure on horizon scales around the black hole,” Broderick said.

The black hole known as M87* (for Messier 87 star) became famous in 2019 as the subject of the historic first-ever picture of a black hole ever taken.  

This is yet another first. It is the first time that astronomers have been able to measure polarization this close to the edge of a black hole. It enables scientists to trace the structure of the magnetic fields that drive the powerful jets extending far beyond the galaxy.

In the same way polarised sunglasses help us see better by reducing reflections and glare from bright surfaces, astronomers can sharpen their vision of the region around the black hole by looking at how the light originating from there is polarized.

“The observations suggest that the magnetic fields at the black hole’s edge are strong enough to push back on the hot gas and help it resist gravity’s pull. Only the gas that slips through the field can spiral inwards to the event horizon,” said Jason Dexter, Assistant Professor at the University of Colorado Boulder, US, and one of the co-ordinators of the EHT Theory Working Group, in a press release.

But getting accurate polarization data has been a long-standing challenge in radio astronomy. Broderick and his team played a part in finding solutions to those problems.

“Misaligned antennas, imperfect polarization signal separation, and wavelength-dependent optical elements all result in mixing polarized and unpolarized emission — this mixing has the unfortunate effect of creating false polarization signals and corrupting real ones,” Broderick said.

Learn more about how Broderick and his team contributed to this image in the full article, on Waterloo News.

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