In April 2019, scientists released the first image of a black hole in the galaxy M87 using the Event Horizon Telescope (EHT). However, that remarkable achievement was just the beginning of the science story to be told. Data from nineteen observatories are being released that promise to give unparalleled insight into this black hole and the system it powers, and to improve tests of Einstein’s General Theory of Relativity.
The immense gravitational pull of a supermassive black hole can power jets of particles that travel at almost the speed of light across vast distances. M87’s jets produce light spanning the entire electromagnetic spectrum, from radio waves to visible light to gamma rays. This pattern is different for each black hole. Identifying this pattern gives crucial insight into a black hole’s properties (for example, its spin and energy output), but this is a challenge because the pattern changes with time.
Scientists compensated for this variability by coordinating observations with many of the world’s most powerful telescopes on the ground and in space, collecting light from across the spectrum. This is the largest simultaneous observing campaign ever undertaken on a supermassive black hole with jets. Each telescope delivers different information about the behaviour and impact of the 6.5-billion-solar-mass black hole at the center of M87, which is located about 55 million light-years from Earth. The data were collected by a team of 760 scientists and engineers from nearly 200 institutions, spanning thirty-two countries or regions, and using observatories funded by agencies and institutions around the globe. The observations were concentrated from the end of March to the middle of April 2017.
The combination of data from these telescopes, and current (and future) EHT observations, will allow scientists to conduct important lines of investigation into some of astrophysics’ most significant and challenging fields of study. For example, scientists plan to use these data to improve tests of Einstein’s Theory of General Relativity (GR). Currently, uncertainties about the material rotating around the black hole and being blasted away in jets, in particular the properties that determine the emitted light, represent a major hurdle for these GR tests.
A related question that is addressed by today's study concerns the origin of energetic particles called “cosmic rays,” which continually bombard the Earth from outer space. Their energies can be a million times higher than what can be produced in the most powerful accelerator on Earth, the Large Hadron Collider. The huge jets launched from black holes, like the ones shown in today’s images, are thought to be the most likely source of the highest energy cosmic rays, but there are many questions about the details, including the precise locations where the particles get accelerated. Because cosmic rays produce light via their collisions, the highest-energy gamma rays can pinpoint this location, and the new study indicates that these gamma-rays are likely not produced near the event horizon—at least not in 2017. A key to settling this debate will be comparison to the observations from 2018, and the new data being collected this week by EHT.
The Astrophysical Journal Letter (Vol. 911, article L11) describing these results is available here. This paper was led by thirty-three members of the EHT Multiwavelength Science Working Group, and includes as coauthors members of the following collaborations: the entire Event Horizon Telescope Collaboration; the Fermi Large Area Telescope Collaboration; the H.E.S.S collaboration; the MAGIC collaboration; the VERITAS collaboration and the EAVN collaboration. The coordinators of the EHT Multiwavelength Science Working Group are Sera Markoff, Kazuhiro Hada, and Daryl Haggard, who together with Juan Carlos Algaba and Mislav Baloković, also coordinated work on the paper.
Partner MWL facilities include: European VLBI Network (EVN); High Sensitivity Array (HSA); VLBI Exploration of Radio Astrometry (VERA); Korea VLBI Network (KVN); East Asian VLBI Network/KVN and VERA Array (EAVN/KaVA); Very Long Baseline Array (VLBA); Global Millimeter VLBI Array (GMVA); Very Large Telescope Interferometer GRAVITY Instrument (VLTI/GRAVITY); Neil Gehrels Swift Observatory (Swift); Hubble Space Telescope (HST); Chandra X-ray Observatory (Chandra); Nuclear Spectroscopic Telescope Array (NuSTAR); High Throughput X-ray Spectroscopy Mission and X-ray Multi-Mirror Mission (XMM-Newton); Fermi Gamma Ray Observatory Large Area Space Telescope (Fermi-LAT); High Energy Stereoscopic System (H.E.S.S.); Major Atmospheric Gamma Imaging Cherenkov Telescopes (MAGIC); Very Energetic Radiation Imaging Telescope Array System (VERITAS).
The 2017 campaign involved a large number of observatories and telescopes. At radio wavelengths it involved: the European Very Long Baseline Interferometry (VLBI) Network (EVN) on May 9, 2017; the High Sensitivity Array (HSA), which includes the Very Large Array (VLA), the Effelsberg 100m antenna and the 10 stations of the National Radio Astronomy Observatory (NRAO) Very Long Baseline Array (VLBA) on May 15, 16 and 20; the VLBI Exploration of Radio Astronomy (VERA) over 17 different times in 2017; the Korean VLBI Network (KVN) over seven epochs between March and December; the East Asian VLBI Network (EAVN) and the KVN and VERA Array (KaVA) , over 14 epochs between March and May 2017; the VLBA on May 5, 2017; the Global Millimeter-VLBI-Array (GMVA) on March 30, 2017; the Atacama Large Millimeter/submillimeter Array (ALMA); the Submillimeter Array (SMA) as part of an ongoing monitoring program. At ultraviolet (UV) wavelengths it involved the Neil Gehrels Swift Observatory (Swift) with multiple observations between March 22 and April 20, 2017; and at optical wavelengths: Swift; and the Hubble Space Telescope on April 7, 12, and 17, 2017. (The Hubble data were retrieved from the Hubble archive because it was part of an independent observing program.) At X-ray wavelengths it involved the Chandra X-ray Observatory on April 11 and 14, 2017; the Nuclear Spectroscopic Telescope Array (NuSTAR) on April 11 and 14, 2017; and Swift. At gamma-ray wavelengths it involved Fermi from March 22 to April 20, 2017; the High Energy Stereoscopic System (H.E.S.S); the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes, and the Very Energetic Radiation Imaging Telescope Array System (VERITAS).