A team of international scientists that includes a Canadian researcher said it has mapped, for the first time, the magnetic fields surrounding a black hole.
The Event Horizon Telescope Collaboration team produced an image that shows electromagnetic fields that look like a "crisp swirl" of light around the black hole as it appears in polarized light.
The discovery will help astrophysicists better understand black holes and their profound effects on galaxies, said Avery Broderick, one of the team's researchers who works at Perimeter Institute for Theoretical Physics in Waterloo, Ont.
"We’re watching this astrophysical drama, this twisting up of magnetic fields, building that spring at the bottom that’s going to launch this jet out into this large universe and rule the fates of galaxies," Broderick said in an interview.
The polarized image allows researchers to learn more about the magnetic fields surrounding the black hole in the M87 galaxy, he said.
They believe the research helps its understanding of how magnetic fields allow the black hole to "eat" matter and eject powerful energetic jets.
Two years ago the same team released the first-ever image of a black hole.
The international collaboration is composed of more than 300 researchers who compiled the image from eight Earth-based telescopes positioned around the world.
The new image is part of two related papers published Wednesday in The Astrophysical Journal.
The scientists have been working on the new project the past two years, Broderick said, ensuring what they were seeing was, in fact, real.
He said he and his team devised a new radioimaging method that helped show the electromagnetic fields.
There were five other teams that were using different methods to show the polarization, some tried and true, others novel.
"All six of these achieved very similar results," he said.
"Only when we have this kind of replication across this many teams that we feel confident we’re seeing something that’s really in the sky and not an artifact of our analysis."
What the team produced is comparable, in a sense, to the old high school experiment where students drop iron filings around a magnet bar, he explained.
The filings will line up in a unique fashion around the poles and illustrate the invisible magnetic field.
"What we have shown is those magnetic fields are not random, not just angled up in random directions, but very much like that bar magnet," said Broderick, who is also a professor at the University of Waterloo.
He said the teams produced four images between on April 5 and 11 in 2017.
"In some sense we have a polarized movie," he said. "But the movie only has four frames."
There is a difference between the first two images and the last two, he said.
"From the beginning of the week to the end of the week, the high polarization moves a bit," Broderick said.
"That’s interesting — we don’t have a lot to say about it other than that’s interesting."
The image researchers captured is not of the black hole closest to Earth, however, but of one at the centre of neighbouring galaxy Messier 87 that was easier to observe by telescope. It is about six billion times the mass of our sun and located about 53 million light years from Earth. One light-year is equal to 9.5 trillion kilometres.
"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, part of the team and a NASA Hubble Fellow at the Princeton Centre for Theoretical Science.
For Broderick, it’s not that different than building a fence.
"It’s a lot of work, a lot of sweat and frustration digging the post holes and screwing the whole thing together and making sure everything is plum, and while you’re doing that you’re focused on the mundane and onerous tasks," he said.
"But then you get to step back when you’re finished and you have a nice looking fence that’s not too crooked and you feel an immense measure of pride and that's where we are today."
This report by The Canadian Press was first published March 24, 2021.
Liam Casey, The Canadian Press
Black hole shows magnetic fields surrounding it are strong enough to resist gravity
Wits University astrophysicists are the only two scientists on African continent that contributed to the study.
IMAGE: 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. view more
CREDIT: CREDIT: © EHT COLLABORATION
The Event Horizon Telescope (EHT) collaboration, a multinational team of over 300 scientists including two astrophysicists from the University of the Witwatersrand (Wits University), has revealed today a new view of the massive object at the centre of the 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. The observations are key to explaining how the M87 galaxy, located 55 million light-years away, is able to launch energetic jets from its core.
"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," says Monika Mo?cibrodzka, Coordinator of the EHT Polarimetry Working Group and Assistant Professor at Radboud Universiteit in the Netherlands.
"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," explains Iván Martí-Vidal, also Coordinator of the EHT Polarimetry Working Group and GenT Distinguished Researcher at the Universitat de València, Spain. He adds that "unveiling this new polarised-light image required years of work due to the complex techniques involved in obtaining and analysing the data."
Professor Roger Deane, SARAO/NRF Chair in Radio Astronomy at Wits and his postdoctoral researcher, Dr Iniyan Natarajan, are the only two scientists in the EHT collaboration that are based on the African continent. On 10 April 2019, the collaboration released the first ever image of a black hole, revealing a bright ring-like structure with a dark central region -- the black hole's shadow. Today's results reveal that a significant fraction of the light around the M87 black hole is polarised.
"When unpolarised, the oscillations of the electromagnetic fields have no preferred direction. Filters such as polarised sunglasses or magnetic fields in space, preferentially let the oscillations in one direction pass through, thereby polarising the light. Thus, the polarised-light image illuminates the structure of the magnetic fields at the edge of the black hole," says Natarajan, who was part of the EHT Polarimetry Working Group.
Black holes have long been known to launch powerful jets of energy and matter far out into space. Astronomers have relied on different physical models of how matter behaves near the black hole to better understand this process. The jet emerging from M87's core extends at least 5000 light-years from its centre, the process behind which is still unexplained.
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.
To observe the heart of the M87 galaxy, the collaboration linked eight telescopes around the world to create a virtual Earth-sized telescope, the EHT. The impressive resolution obtained with the EHT is equivalent to that needed to measure the size of a cricket ball on the surface of the Moon.
This 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 are published today in two separate papers in The Astrophysical Journal Letters by the EHT collaboration.
"Peering as close as we can to the edge of black holes using cutting-edge techniques is precisely the sort of challenge we relish here at Wits," says Deane, Founding Director of the newly approved Wits Centre for Astrophysics. "We are in a golden era for radio astronomy, and our involvement in projects like the Event Horizon Telescope and the Square Kilometre Array is at the centre of our plan to carry out fundamental research, and train world-class postgraduate students who will become the leading African scientists of tomorrow."
Natarajan was involved in simulating the black hole polarisation observations and was also part of the efforts to calibrate and generate the polarised image. Deane and Natarajan have also written one of the software packages that is being used to simulate black hole observations within the EHT collaboration.
"Our collaboration developed new techniques for analysing the polarisation data, which were validated on simulations before being applied to real observations," says Natarajan.
"Such challenging projects provide the opportunity to develop techniques which later find wider applicability in the community in ways which can pleasantly surprise us."
CAPTION
Group picture of the workshop which triggered the imaging the magnetic fields at the Max-Planck-Institut für Radioastronomie in Bonn, Germany, on July 15-19, 2019.
CREDIT
Credit: © E. Traianou/MPIfR
No comments:
Post a Comment