Pōwehi: New research captures a decade of movement  Hawai`i telescopes JCMT and SMA contribute to unravel the mysteries of the black hole Pōwehi in M87

Maunakea, HI (September 23, 2020) — New analysis of data taken between 2009-2013, some of them not published before, by the James Clerk Maxwell Telescope (JCMT) and the Submillimeter Array (SMA) for the Event Horizon Telescope (EHT) collaboration have revealed the how the black hole Pōwehi is moving over decadal timescales. The analysis reveals the persistence of the

crescent-like shadow feature, but also variation of its orientation — the crescent-like shadow

appears to be wobbling. Published today in The Astrophysical Journal , the new result is possible due to scientific advances made by the Maunakea-based telescopes and EHT’s groundbreaking black hole photo  in 2019.

The gas falling onto a black hole heats up to billions of degrees, ionizes and becomes turbulent in the

presence of magnetic fields. This turbulence is what causes the appearance of black holes to vary over time. Modeling prior data with improved techniques revealed that Pōwehi’s shadow was moving from 2009-2013 and has continued to do so ever since. “The most important thing that we have learned is that the shadow of Pōwehi is always there. That means it is real and is caused by the light bending from the black hole,” said Geoff Bower, Hilo resident and EHT Project Scientist at Academia Sinica Institute of Astronomy and Astrophysics (ASIAA). “The wobble tells us about how gas is flowing around the black hole, varying like clouds in the sky or waves on the ocean. What’s next is to use our improved array and make images over years to come and learn from those changes to answer questions like, ‘How does Pōwehi feed itself?’ ”

Prior experiments were critical to learning more about the famed black hole. Relying on theory, scientists already believed that the shadow was changing over time, but the 2019 image alone provided just a week-long snapshot into its life, too short a time to see those changes or understand them. “ This is a little bit like going back to old family photographs and seeing a child’s resemblance to their ancestors,” said Bower. “The more we learn in the future, the more interesting information we can extract from the past. Black holes change on time scales as short as hours and as long as billions of years, so we have a lot to learn.”

Very Long Baseline Interferometry (VLBI)—the technique used to power EHT—collects signals from

astronomical radio sources, like black holes, at multiple radio telescopes around the world and combines the data to create complete results. “Hawai`i telescopes were crucial to the success of early EHT experiments over the past decade that pioneered the development of VLBI at very short wavelengths,” said Simon Radford, Operations Director of SMA at the Smithsonian Astrophysical Observatory (SAO). “The early experiments required the development and refinement of specialized signal processing electronics, observing techniques, and data analysis methods, setting the stage for the later observations that revealed the image of Pōwehi.”

The Maunakea team is already working on preparing for the next EHT observations of Pōwehi in 2021. At JCMT in Hawaii the work is focused on ensuring a new more sensitive instrument Nāmakanui (“Big Eyes”) is ready. This new instrument, Nāmakanui — is funded by ASIAA and named for a type of fish found in and around the islands. “It is rewarding for our Hawai`i staff to see the depth and breadth of new science being mined from a decade of observations, ” said Jessica Dempsey, Deputy Director of the East Asian Observatory (EAO) and JCMT. “It’s like we started the sketch ten years ago, and now with new tools and experience, our science teams are going back and able to not just fill in the color in the image,but make that image come to life.”