Astronomers Iván Martí-Vidal and Alejandro Mus, from the University of Valencia are among the specialists from different countries who have contributed to this work.

‘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,’ said Monika Mościbrodzka, coordinator of the EHT Polarimetry Working Group and a professor at Radboud Universiteit in the Netherlands.

On 10 of April 2019 scientists released the first image of a black hole, which showed a dark central region outlined by a bright ring-like structure. Since then, the EHT collaboration has delved deeper in data on the supermassive object at the heart of galaxy M87 that were gathered in 2017. They have discovered that the light originating from a region around the M87 back hole is polarized.

‘This work is a major milestone: the polarisation of light carries information that allows us to better understand the physics behind the image we saw in April 2019, which was not possible before,’ said Iván Martí-Vidal, coordinator of the EHT Polarimetry Working Group and GenT Distinguished Researcher at the University of Valencia, ‘revealing this new image in polarised light has taken years of work, due to the complex techniques involved in obtaining analysing data’, added the researcher.

The light polarises when it passes through certain filters, as happens with the lenses of polarized sunglasses, or when it is emitted in hot, magnetised regions of the space. Just as polarized sunglasses only let light through with the electric field pointing in a particular direction, astronomers can detect the polarization of light coming from space using polarisers fitted in telescopies. In the case of EHT, studying the polarisation of light allows astronomers to map the lines of the magnetic field around the event horizon of the M87 black hole.

The newly published polarised images are key to understanding how the magnetic field allows the black hole to ‘eat’ matter and launch powerful jets, noted Andrew Chael, member of the EHT collaboration and researcher at the Princeton Center for Theoretical Science (USA).

Bright jets of energy and matter emerge from M87's core and extend at least 5,000 light-years from its centre are one of the galaxy’s most mysterious and energetic features. Most of the matter lying close to the black hole's edge falls in, but some of the surrounding particles manage to escape and get blasted far into space in the form of jets.

To better understand this process, the research team has relied on different models on how matter behaves near the black hole. But they still do not know exactly how jets larger than the galaxy itself are launched from the black hole within it (as small as the Solar System), nor exactly how matter falls into the black hole. With this EHT new image, astronomers have for the first time been able to glimpse the boundary region of the black hole where this interaction between inward-flowing and ejected matter takes place.

The observations will enable researchers to find out new information about the magnetic field structure surrounding the edge of the black hole. The team discovered that only theoretical models with strongly-magnetised gas can explain what the event horizon is seeing. ‘The new observations indicate that the magnetic fields at the edge of the black hole 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, coordinator of the EHT Theory Working Group and a professor at the University of Colorado Boulde.

To observe the heart of M87 galaxy, the collaboration linked eight telescopes together around the world to create the virtual Earth-sized telescope EHT. The impressive obtained resolution with the EHT is equivalent to that needed to measure the length of a credit card on the surface of the Moon.

This allowed the team to directly observe the shadow of the black hole and the surrounding ring of polarised light, which clearly shows that the material surrounding the black hole is magnetised. The results are published today in two separated papers in The Astrophysical Journal Letters by the EHT collaboration, which involves more than 300 researchers of multiple organisations and universities around the world.

‘The EHT is making rapid progress, with technology upgrades to the network and the addition of new observatories. We expect that future EHT observations will reveal more precisely the structure of the magnetic field around the black hole and tell us more about the physics of hot gas in this region’, concluded Jogho Park, member of the EHT collaboration and researcher of the Academia Sinica (Institute of Astronomy and Astrophysics of Taipei).

Alejandro Mus, trainee researcher attached to the GenT project at the University of Valencia stresses: ‘In addition to the coordination work co-led by Iván Martín-Vidal, at the University we have also contributed to the development of several algorithms to overcome the instrumental limitations of EHT, as well as to guarantee the reproducibility of our analyses by any other researcher.'  

Iván Martí-Vidal also highlights the efficiency of the Valencian group dedicated to the analysis of polarisation in M87. 'Despite being a small group, with only two people, our contribution has reached the same level as those of much larger groups within the EHT Collaboration', the researcher emphasises.

In parallel to these results, Iván Martí Vidal also co-leads another official EHT paper, which contains a detailed study on the polarised emission of several black holes observed with the ALMA telescope. According to Martí-Vidal, 'this is an example of how programmes like GenT (Valencian programme for the support of talented researchers) are helping to put Valencian science and innovation on the world map'.

Other Valencian members of the EHT Collaboration are Juan Carlos Algaba (University of Malaya), Rebecca Azulay and Eduardo Ros (both from the University of Valencia and the Max Planck Institute for Radioastronomy, Germany).

-----------------------------------------------
Vídeo realitzat per Iván Martí-Vidal : https://www.dropbox.com/s/b4bvkmltc4dtrx1/EHT_POL_ANIM_SPA.m4v?dl=0

- Image: Composite Visual of the M 87 jet and ring in polarisation - Caption: View of the M 87 supermassive black hole and jet in polarized light This composite image shows three views of the central region of the Messier 87 (M87) galaxy in polarised light, namely, from top to bottom, with the Chile-based Atacama Large Millimeter/submillimeter Array (ALMA), the National Radio Astronomy Observatory’s Very Long Baseline Array (VLBA) in the US, and with the Earth-sized telescope synthesized by the Event Horizon Telescope.

Credit: © EHT Collaboration; ALMA (ESO/NAOJ/NRAO), Goddi et al.; VLBA

(NRAO), Kravchenko et al.; J.C. Algaba, I. Martí-Vidal

Portrait PDF [11.3 MB]

https://tinyurl.com/nynjad82

Landscape PDF [8.6 MB]

https://tinyurl.com/hj63e7rp

- Paper VII (The Astrophysical Journal Letters, Vol. 910, L12):

http://doi.org/10.3847/2041-8213/abe71e

- Paper VIII (The Astrophysical Journal Letters, Vol. 910, L13):

http://doi.org/10.3847/2041-8213/abe4de

<http://doi.org/10.3847/2041-8213/abe4de>

- Related Paper, Goddi et al. (//The Astrophysical Journal Letters, Vol.

910, in press):

http://doi.org/10.3847/2041-8213/abee6a

- EHT Press Release page:

https://eventhorizontelescope.org/blog/astronomers-image-magnetic-fields-edge-m87%E2%80%99s-black-hole

https://tinyurl.com/prsrubvf

-Official EHT Press Release as PDF:

https://owncloud.mpifr-bonn.mpg.de/index.php/s/jFFYCaqfJCtrkaX

https://tinyurl.com/2mwbynry

- Main image:

- Caption: A view of the M87 supermassive black hole in polarised 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 centre of the Messier 87 (M87) galaxy: how it looks in polarised light. This is the first time astronomers have been able to measure polarisation, a signature of magnetic fields, this close to the edge of a black hole. This image shows the polarised view of the black hole in M87. The lines mark the orientation of polarisation, which is related to the magnetic field around the shadow of the black hole.

/Credit: EHT Collaboration/

/https://tinyurl.com/av3ys389

-Video: Zoom into M87 including the polarized emission of the ring (47s)

Caption: Zooming-in to the heart of M87 to see a new view of its black hole This zoom video starts with a view of ALMA, a telescope in which ESO is a partner and that is part of the Event Horizon Telescope, and zooms-in on the heart of M87, showing successively more detailed observations. At the end of the video, we see the first ever image of a black hole –first released in 2019– followed by a new image released in 2021: how this supermassive object looks in polarised light. This is the first time astronomers have been able to measure polarisation, a signature of magnetic fields, this close to the edge of a black hole.

Credit: /© ESO/L. Calçada, Digitized Sky Survey 2, ESA/Hubble, RadioAstron, De Gasperin et al., Kim et al., EHT Collaboration. Music:

Niklas Falcke/

https://cdn.eso.org/videos/hd_1080p25_screen/eso2105b.mp4/

- Video: The M 87 image as seen through a light polarizer

  -Caption: The M 87 image as seen with a polarizer.Representation of the effect of a polarizer and how the polarization vectors in the M 87 ring image are produced from the combination of different linearly polarized components.

Credit: ©Iván Martí-Vidal (Universitat de València), EHT Collaboration

//https://tinyurl.com/58r3y7nk

- Video: What Is Polarization

- Caption: What Is Polarization | Event Horizon Telescope Light is an oscillating electromagnetic wave. If the waves have a preferred direction of oscillation, they are polarized. In space, moving hot gas, or ‘plasma’, threaded by a magnetic field emits polarized light. The polarized light rays that manage to escape the pull of the black hole travel to a distant camera. The intensity of the light rays and their direction are what we observe with the Event Horizon Telescope.

Credit: /© EHT Collaboration and Fiks Film/

/https://tinyurl.com/24ufxd3y/

Video: Magnetic fields and black hole images /

Caption: How Magnetic Fields Affect Black Hole Images | Event Horizon Telescope Black holes are enveloped in plasma. This plasma has magnetic fields –areas where magnetism affects how matter moves– threaded throughout. As the magnetic field grows stronger, it changes shape and the polarized light we measure exhibits different patterns.

Credit: © EHT Collaboration and Crazybridge Studios

https://www.youtube.com/watch?v=6xrJoPjfJGQ

- Animated image: Transition between the observed polarization image and a best-fit theory image Caption: Transition between the observed polarization image and a best-fit theory image /Credit: © Monika Mościbrodzka & Sara Issaoun, Radboud Universiteit Nijmegen, EHT Collaboration/

https://tinyurl.com/3t5rfptz