The Event Horizon Telescope (EHT) collaboration has published a new view of the black hole at the center of the M87 galaxy. The EHT published the first-ever image of a black hole in 2019. This time, the image shows the black hole in polarized light, which shows the magnetic field surrounding the black hole. This marks the first time astronomers have been able to measure polarization this close to the edge of a black hole.

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Polarization is a signature of magnetic fields, and being able to observe the magnetic fields provides scientists important new information and helps explain how the M87 galaxy launches energetic jets from its core. Monika Mościbrodzka, Coordinator of the EHT Polarimetry Working Group and Assistant Professor at Radboud Universiteit in the Netherlands, said, 'We are now seeing the next crucial piece of evidence to understand how magnetic fields behave around black holes, and how activity in this very compact region of space can drive powerful jets that extend far beyond the galaxy.'

'A view of the M87 supermassive black hole in polarized light: The Event Horizon Telescope (EHT) collaboration, who produced the first-ever image of a black hole released in 2019, has today a new view of the massive object at the center of the Messier 87 (M87) galaxy: how it looks in polarized light. This is the first time astronomers have been able to measure polarization, a signature of magnetic fields, this close to the edge of a black hole. This image shows the polarized view of the black hole in M87. The lines mark the orientation of polarization, which is related to the magnetic field around the shadow of the black hole.' Image and caption credit: EHT Collaboration. Click to enlarge.

In 2019, when EHT scientists released the first image of a black hole, they had not finished digging through the data collected in 2017 on the supermassive object at the center of the M87 galaxy. Since then, researchers have discovered that a 'significant fraction' of the light around the M87 black hole is polarized. 'This work is a major milestone: the polarization of light carries information that allows us to understand better the physics behind the image we saw in April 2019, which was not possible before,' says Iván Martí-Vidal, also Coordinator of the EHT Polarimetry Working Group and GenT Distinguished Researcher at the Universitat de València, Spain. Martí-Vidal continues, 'Unveiling this new polarized-light image required years of work due to the complex techniques involved in obtaining and analyzing the data.'

Light is polarized when it travels through certain filters, like a circular polarizing filter used on a camera lens to reduce reflections and glare or when light is emitted in hot regions of space that are also magnetized. EHT writes, 'In the same way polarized 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. Specifically, polarization allows astronomers to map the magnetic field lines present at the inner edge of the black hole.' The new polarized images are critical to understanding how the magnetic field surrounding the black hole allows the black hole to consume matter and send out jets of energy.

The energy that emerges from M87's core extends at least 5,000 light-years from its center. Scientists have been working to understand why some matter near the black hole is consumed by it, while other particles escape just before entering the black hole and form the observed jets of energy shooting from the black hole. The new image allows scientists for the first time to look at the region just outside the black hole where there's a mix of matter flowing in and being ejected from the black hole.

An artist's rendition of the black hole at the center of the M87 galaxy. Image credit: ESO/M. Kornmesser

' 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, USA, and coordinator of the EHT Theory Working Group.

If you'd like to learn more about the virtual Earth-sized telescope, the EHT, check out the animated video below.

The European Southern Observatory (ESO) released a neat composite view of the M87 jet in visible and polarized light. There's a lot of information to digest about the image in the caption, which can be found here. You can also click here to download a larger version.

Image credit: EHT Collaboration; ALMA (ESO/NAOJ/NRAO), Goddi et al.; NASA, ESA and the Hubble Heritage Team (STScI/AURA); VLBA (NRAO), Kravchenko et al.; J. C. Algaba, I. Martí-Vidal