| Mar 24, 2021 |
New images reveal magnetic structures near supermassive black hole
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(Nanowerk News) A new view of the region closest to the supermassive black hole at the center of the galaxy Messier 87 (M87) has shown important details of the magnetic fields close to the black hole and hints about how powerful jets of material can originate in that region.
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A worldwide team of astronomers using the Event Horizon Telescope, a collection of eight telescopes, including the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, measured a signature of magnetic fields -- called polarization -- around the black hole. Polarization is the orientation of the electric fields in light and radio waves and it can indicate the presence and alignment of magnetic fields.
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“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,” said Monika Mo?cibrodzka, Coordinator of the EHT Polarimetry Working Group and Assistant Professor at Radboud University in the Netherlands.
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New images with the EHT and ALMA allowed scientists to map magnetic field lines near the edge of M87's black hole. That same black hole is the first ever to be imaged -- by the EHT in 2019. That image revealed a bright ring-like structure with a dark central region — the black hole’s shadow. The newest images are a key to explaining how M87, 50 million light-years from Earth, can launch energetic jets from its core.
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| View of the M87 supermassive black hole and jet. This composite image shows three radio-telescope views of the central region of the galaxy Messier 87 (M87), where a jet of fast-moving particles is ejected from the galaxy's core. In these images, the lines indicate polarization -- the alignment of the electric fields in the radio waves coming from the object. The polarization is a signature of the magnetic fields. The ALMA image shows the inner 6000 light-years of the jet. The image from the National Science Foundation's Very Long Baseline Array (VLBA) zooms down to show the inner one light-year of the jet, and the EHT image shows the region closest to the supermassive black hole at the galaxy's core. Labels indicate the observing frequency in GigaHertz (GHz) and the distance indicated by the scale bar below the frequency. Combined, these images allow astronomers to study the structure of magnetic fields from very close to the black hole to thousands of light-years outward from it. (Image: EHT Collaboration; Goddi et al., ALMA (ESO/NAOJ/NRAO); Kravchenko et al.; J. C. Algaba, I. Martí-Vidal, NRAO/AUI/NSF) (click on image to enlarge)
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The black hole at M87's center is more than 6 billion times more massive than the Sun. Material drawn inward forms a rotating disk -- called an accretion disk -- closely orbiting the black hole. Most of the material in the disk falls into the black hole, but some surrounding particles escape and are ejected far out into space in jets moving at nearly the speed of light.
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“The newly published polarized images are key to understanding how the magnetic field allows the black hole to 'eat' matter and launch powerful jets,” said Andrew Chael, a NASA Hubble Fellow at the Princeton Center for Theoretical Science and the Princeton Gravity Initiative in the U.S.
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The scientists compared the new images that showed the magnetic field structure just outside the black hole with computer simulations based on different theoretical models. They found that only models featuring strongly magnetized gas can explain what they are seeing at the event horizon.
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“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,” explained Jason Dexter, Assistant Professor at the University of Colorado Boulder and Coordinator of the EHT Theory Working Group.
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To make the new observations, the scientists linked eight telescopes around the world -- including ALMA -- to create a virtual Earth-sized telescope, the EHT. The impressive resolution obtained with the EHT is equivalent to that needed to measure the length of a credit card on the surface of the Moon.
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This resolution allowed the team to directly observe the black hole shadow and the ring of light around it, with the new image clearly showing that the ring is magnetized. The results are published in two papers in the Astrophysical Journal Letters ("First M87 Event Horizon Telescope Results. VIII. Magnetic Field Structure near The Event Horizon") by the EHT collaboration. The research involved more than 300 researchers from multiple organizations and universities worldwide.
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A third paper also was published in the same volume of the Astrophysical Journal Letters ("Polarimetric Properties of Event Horizon Telescope Targets from ALMA"), based on data from ALMA, lead by Ciriaco Goddi, a scientist at Radboud University and Leiden Observatory, the Netherlands.
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"The combined information from the EHT and ALMA allowed scientists to investigate the role of magnetic fields from the vicinity of the event horizon to far beyond the core of the galaxy, along its powerful jets extending thousands of light-years," Goddi said.
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The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
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The EHT collaboration involves more than 300 researchers from Africa, Asia, Europe, North and South America. The international collaboration is working to capture the most detailed black hole images ever obtained by creating a virtual Earth-sized telescope. Supported by considerable international investment, the EHT links existing telescopes using novel systems — creating a fundamentally new instrument with the highest angular resolving power that has yet been achieved.
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The individual telescopes involved are: ALMA, APEX, the Institut de Radioastronomie Millimetrique (IRAM) 30-meter Telescope, the IRAM NOEMA Observatory, the James Clerk Maxwell Telescope (JCMT), the Large Millimeter Telescope (LMT), the Submillimeter Array (SMA), the Submillimeter Telescope (SMT), the South Pole Telescope (SPT), the Kitt Peak Telescope, and the Greenland Telescope (GLT).
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