New images from the Event Horizon Telescope (EHT), an international collaboration involving several University of Toronto astronomers and astrophysicists, have shown a reversal in the magnetic fields of the supermassive black hole at the centre of the galaxy M87.
Scientists also found the first signatures of emission associated with a jet of energetic particles blasting out from M87's black hole at nearly the speed of light.
The observations, published in the journal Astronomy & Astrophysics , offer insight into how matter and energy behave in the extreme environments surrounding black holes.
The EHT, a global network of radio telescopes acting as an Earth-sized observatory, first captured the iconic image of M87's black hole shadow in 2019 . Located about 55 million light-years away from Earth, M87 harbors a supermassive black hole more than six billion times the mass of the sun.
In 2021, the collaboration began observing polarized light from M87. Polarized light vibrates in an aligned manner due to its passing through a magnetic field - unlike most light we experience around us, which is not polarized and comprises waves that vibrate in random directions.
Now, by comparing observations from 2017, 2018 and 2021, scientists have taken the next step towards uncovering how the magnetic fields near the black hole change over time.
The latest publication featured key contributions from Sebastiano von Fellenberg, a postdoctoral researcher at the Canadian Institute for Theoretical Astrophysics (CITA) , hosted at U of T, and the Max Planck Institute for Radio Astronomy in Germany.
Leading the calibration of the new 2021 observations, von Fellenberg corrected for atmospheric interferences and slight differences between the telescopes that comprise the EHT.
The most recent observations included two new telescopes - Kitt Peak in Arizona and NOEMA in France - that enhanced the array's sensitivity and image clarity, enabling scientists to constrain the emission direction of the base of M87's relativist jet (a stream of plasma and radiation). Upgrades at the Greenland Telescope and James Clerk Maxwell Telescope have further improved the quality of data.
"What is genuinely new here is that we can now place constraints on emission originating from the very base of the jet, rather than emission coming from the bright 'ring' structure," says von Fellenberg, who is a Humboldt Feodor Lynen Fellow.
"This is exciting because it provides new information on how enormous, kiloparsec-scale jets are launched - one of the main outstanding questions in jet physics.
"With just two sensitive baselines, our current EHT observations cannot yet form a detailed image of this region. However, we can now detect its presence, and that's a significant step forward. It leaves us eager to see what upcoming data will reveal."
The flipping of M87's polarization pattern between 2017 and 2021 was not expected by astronomers.
The fields appeared to spiral one way in 2017, before settling in 2018 and reversing and spiraling in the opposite direction in 2021.
The changes - which could be due to a combination of internal magnetic structure and external factors - suggest an evolving, turbulent environment in which magnetic fields play a vital role in governing how matter falls into the black hole and how energy is launched outward.
Jets like M87's play a crucial role in galaxy evolution by regulating star formation and distributing energy on vast scales. Emitting across the electromagnetic spectrum - including gamma rays and neutrinos - M87's jet provides a unique laboratory to study how these cosmic phenomena form and are launched.
Other members of the EHT collaboration at U of T and CITA include Professor Ue-Li Pen and Assistant Professor Bart Ripperda of the David A. Dunlap department of astronomy and astrophysics in the Faculty of Arts & Science; CITA postdoctoral fellows Gibwa Musoke and Rohan Dahale; and Aviad Levis, an assistant professor of computer science.
The researchers say they're excited by the improvement in data quality and look forward to even greater resolution in future EHT observations.
"M87 is really massive, so it takes months to years for changes in the accretion flow to occur. Due to this timescale, we really need to have multi-year observations," says Ripperda. "In essence, we need a long-time-scale video of the black hole.
"The black hole flares about every few years, when it gets brighter and emits at very high, gamma-ray energies. Those flares come from near the horizon in some cases, so if we want to monitor what is happening close to the event horizon we need to capture those flares."
The new results illuminate the dynamic environment surrounding M87 and deepen scientists' understanding of black hole physics.
"What's remarkable is that while the ring size has remained consistent over the years - confirming the black hole's shadow predicted by Einstein's theory - the polarization pattern changes significantly," said the study's co-lead Paul Tiede, an astronomer at the Center for Astrophysics, Harvard & Smithsonian.
"This tells us that the magnetized plasma swirling near the event horizon is far from static; it's dynamic and complex, pushing our theoretical models to the limit."
