Free Astronomy Magazine May-June 2021

15 MAY-JUNE 2021 ASTRO PUBLISHING the magnetic field lines present at the inner edge of the black hole. “The newly published polarised images are key to understanding how the magnetic field al- lows the black hole to 'eat' matter and launch powerful jets,” says EHT collaboration member Andrew Chael, a NASA Hubble Fellow at the Princeton Center for Theoretical Science and the Princeton Gravity Initiative in the US. The bright jets of en- ergy and matter that emerge from M87’s core and extend at least 5000 light-years from its centre are one of the galaxy’s most mysterious and energetic features. 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 jets. Astronomers have relied on differ- ent models of how matter behaves near the black hole to better under- stand this process. But they still don’t know exactly how jets larger than the galaxy are launched from its central region, which is compara- ble in size to the Solar System, nor how exactly matter falls into the black hole. With the new EHT image of the black hole and its shadow in polarised light, astronomers man- aged for the first time to look into the region just outside the black hole where this interplay between matter flowing in and being ejected out is happening. The observations provide new infor- mation about the structure of the magnetic fields just outside the black hole. The team found that only theoretical models featuring strongly magnetised gas can explain search,” says Ciska Kem- per, European ALMA Programme Scientist at ESO. “With its 66 anten- nas, ALMA dominates the overall signal collec- tion in polarised light, while APEX has been es- sential for the calibra- tion of the image.” “ALMA data were also crucial to calibrate, im- age and interpret the EHT observations, pro- viding tight constraints on the theoretical mod- els that explain how matter behaves near the black hole event hori- zon,” adds Ciriaco Goddi, a scientist at Radboud University and Leiden Observatory, the Netherlands, who led an accompanying study that re- lied only on ALMA observations. The EHT setup allowed the team to directly observe the black hole shadow and the ring of light around it, with the new polarised- light image clearly showing that the ring is magnetised. The results have been published in two separate papers in The Astro- physical Journal Letters by the EHT collaboration. The research involved over 300 researchers from multiple organisations and universities world- wide. “The EHT is making rapid advance- ments, with technological upgrades being done to the network and new observatories being added. We expect future EHT observations to reveal more accurately the mag- netic field structure around the black hole and to tell us more about the physics of the hot gas in this re- gion,” concludes EHT collaboration member Jongho Park, an East Asian Core Observatories Association Fel- low at the Academia Sinica Institute of Astronomy and Astrophysics in Taipei. T his video summarises the discovery made by the Event Horizon Telescope (EHT) collaboration. [ESO] what they are seeing at the event horizon. “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 spi- ral inwards to the event horizon,” explains Jason Dexter, Assistant Pro- fessor at the University of Colorado Boulder, US, and Coordinator of the EHT Theory Working Group. To observe the heart of the M87 galaxy, the collaboration linked eight telescopes around the world — including the northern Chile- based Atacama Large Millimeter/ submillimeter Array (ALMA) and the Atacama Pathfinder EXperiment (APEX), in which the European Southern Observatory (ESO) is a partner — to create a virtual Earth- sized telescope, the EHT. The im- pressive resolution obtained with the EHT is equivalent to that needed to measure the length of a credit card on the surface of the Moon. “With ALMA and APEX, which through their southern location en- hance the image quality by adding geographical spread to the EHT net- work, European scientists were able to play a central role in the re- !