Pōwehi: New research captures a decade of movement

MAUNAKEA, HAWAIʻI – 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 orientationthe 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?’

Top: Snapshots of the Pōwehi (M87*) black hole obtained through imaging / geometric modeling. The diameter of all rings is similar, but the location of the bright side varies. Bottom: the EHT array of telescopes in 2009-2017. The JCMT and SMA in Hawai`i have continually provided the critical western baseline of the telescope array. Credit: M. Wielgus, D. Pesce & the EHT Collaboration.

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.

Supplemental information

The James Clerk Maxwell Telescope

With a diameter of 15m (50 feet) the James Clerk Maxwell Telescope (JCMT) is the largest single dish astronomical telescope in the world designed specifically to operate in the submillimetre wavelength region of the electromagnetic spectrum. The JCMT is used to study our Solar System, interstellar and circumstellar dust and gas, evolved stars, and distant galaxies. It is situated in the science reserve of Maunakea, Hawai`i, at an altitude of 4092m (13,425 feet).

The JCMT is operated by the East Asian Observatory on behalf of CAMS (NAOC, PMO, and SHAO); NAOJ; ASIAA; KASI; as well as the National Key R&D Program of China. Additional funding support is provided by the STFC and participating universities in the UK and Canada.

Nāmakanui was constructed and funded by ASIAA, with funding for the mixers provided by ASIAA and at 230GHz by EAO. The Nāmakanui instrument is a backup receiver for the GLT.

The Event Horizon Telescope

The international collaboration of the Event Horizon Telescope announced the first-ever image of a black hole at the heart of the radio galaxy Messier 87 on April 10, 2019 by creating a virtual Earth-sized telescope. Supported by considerable international investment, the EHT links existing telescopes using novel systems — creating a new instrument with the highest angular resolving power that has yet been achieved.

The individual telescopes involved in the EHT collaboration are: the Atacama Large Millimeter/submillimeter Array (ALMA), the Atacama Pathfinder EXplorer (APEX), the Greenland Telescope (since 2018), the IRAM 30-meter Telescope, the IRAM NOEMA Observatory (expected 2021), the Kitt Peak Telescope (expected 2021), the James Clerk Maxwell Telescope (JCMT), the Large Millimeter Telescope (LMT), the Submillimeter Array (SMA), the Submillimeter Telescope (SMT), and the South Pole Telescope (SPT).

The EHT consortium consists of 13 stakeholder institutes; the Academia Sinica Institute of Astronomy and Astrophysics, the University of Arizona, the University of Chicago, the East Asian Observatory, the Harvard-Smithsonian Center for Astrophysics, the Goethe- Universität Frankfurt, the Institut de Radioastronomie Millimétrique, the Large Millimeter Telescope, the Max-Planck-Institut für Radioastronomie, the MIT Haystack Observatory, the National Astronomical Observatory of Japan, the Perimeter Institute for Theoretical Physics, and the Radboud University.


Astronomers collaborated with renowned Hawaiian language and cultural practitioner Dr. Larry Kimura for the Hawaiian naming of the supermassive black hole at the centre of the galaxy M87. Pōwehi, meaning embellished dark source of unending creation, is a name sourced from the Kumulipo, the primordial chant describing the creation of the Hawaiian universe. Pō, profound dark source of unending creation, is a concept emphasized and repeated in the Kumulipo, while wehi, or wehiwehi, honored with embellishments, is one of many descriptions of pō in the chant. Dr. Kimura is an associate professor at University of Hawai‘i at Hilo Ka Haka ‘Ula o Ke‘elikolani College of Hawaiian Language.

Media Contacts

Geoff Bower
Chief Scientist for Hawaii Operations, ASIAA
Project Scientist, Event Horizon Telescope
Affiliate Graduate Faculty, UH Manoa Physics and Astronomy

Jessica Dempsey
Deputy Director of the East Asian Observatory (EAO) and JCMT

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