In April 2019, using the Event Horizon Telescope (EHT), researchers issued the first image of a black hole in galaxy M87. Yet, that exceptional act was just the beginning of the science story to be told.
Data from 19 observatories released today promise to give a rare insight into this black hole and the system it powers, and to update analyses of Einstein’s General Theory of Relativity.
“We knew that the first uninterrupted image of a black hole would be revolutionary,” says Kazuhiro Hada of the National Astronomical Observatory of Japan, a co-author of the latest research issued in The Astrophysical Journal Letters that explains the broad set of data. “But to get the most out of this extraordinary image, we want to grasp everything we can about the black hole’s response at that time by examining over the entire electromagnetic spectrum.”
The supermassive black hole has an enormous gravitational pull that can power jets of particles that move at almost the speed of light across large distances. M87’s jets give light spanning the entire electromagnetic spectrum, from radio waves to visible rays to gamma waves. This pattern is distinctive for each black hole. Knowing this pattern provides vital insight into a black hole’s attributes—for example, its rotation and energy output—but is a challenge because the pattern varies with time.
Researchers compensated for this variability by correlating observations with many of the world’s most dominant telescopes in space and on the ground, gathering light from beyond the spectrum. These 2017 observations were the most comprehensive synchronous observing campaign ever undertaken on a supermassive black hole with jets.
Three observatories led by the Center for Astrophysics | Smithsonian and Harvard participated in the landmark campaign: the Very Energetic Radiation Imaging Telescope Array System (VERITAS) in southern Arizona; the space-based Chandra X-ray Observatory; and the Submillimeter Array (SMA) in Hilo, Hawaii.
Starting with the EHT’s now-iconic image of M87, the latest video guides viewers on a journey through the data from each telescope. Each consecutive frame presents data over multiple factors in wavelengths of light, scale, and physical size.
The sequence starts with the image of the black hole capture in April 2019. It then passes through images from other radio telescope arrays from around the globe (SMA), traveling outward in the field of view during each step. Next, the view switches to telescopes that recognize visible light, X-rays, and ultraviolet light (Chandra). The screen splits to reveal how these images, which include the same amount of the sky at the same time, are compared to one another. The sequence ends by showing what gamma-ray telescopes on the earth (VERITAS), and Fermi in space, discover from this black hole and its jet.
Each telescope gives diverse data about the impact and behavior of the 6.5-billion-solar-mass black hole at the core of M87, which is found about 55 million light-years from Earth.
“There are many teams excited to see if their models are a match for these rich observations, and we’re thrilled to see the whole community use this public data set to support us better understand the deep links between black holes and their jets,” says co-author Daryl Haggard of McGill University in Montreal, Canada.
The data were gathered by a team of 760 researchers and engineers from approximately 200 institutions, spanning 32 countries or regions, and utilizing observatories supported by institutions and agencies around the globe. The observations were collected from the end of March to the middle of April 2017.
“This unbelievable set of observations includes many of the world’s most reliable telescopes,” says co-author Juan Carlos Algaba of the University of Malaya in Kuala Lumpur, Malaysia. “This is an excellent example of scientists around the world working collectively in the pursuit of science.”
The initial results show that the intensity of the light generated by material around M87’s supermassive black hole was the lowest that had ever been recognized. This provided perfect conditions for viewing the ‘shadow’ of the black hole, as well as being able to separate the light from areas adjacent to the event horizon from those hundreds of thousands of light-years away from the black hole.
The combination of data from these telescopes, and current (and future) EHT observations, will enable researchers to conduct major lines of investigation into some of astrophysics’ most vital and challenging fields of research. For example, experts intend to utilize this data to enhance analyses of Einstein’s Theory of General Relativity. Currently, possibilities about the material revolving around the black hole and being exploded away in jets, in particular the fields that define the emitted light, represent a primary hurdle for these General Relativity analyses.
A similar question that is asked by today’s research concerns the source of energetic particles called “cosmic rays,” which constantly bombard Earth from outer space. Their energies can be a million times more powerful than what can be produced in the most strong accelerator on Earth, the Large Hadron Collider. The enormous jets launched from black holes, like the ones presented in today’s images, are considered to be the most probable source of the highest energy cosmic rays, but there are many questions about the details, including the exact locations where the particles get accelerated. Because cosmic rays generate light through their collisions, the highest-energy gamma rays can pinpoint this region, and the new research shows that these gamma rays are likely not generated near the event horizon—at least not in 2017. A sign to resolving this debate will be the comparison to the observations from 2018 and the current data being collected this week.
“Knowing the particle acceleration is primary to our knowledge of both the EHT image as well as the jets, in all their ‘colors’,” says co-author Sera Markoff from the University of Amsterdam. “These jets manage to carry energy released by the black hole out to scales greater than the host galaxy, like a huge power cord. Our results will benefit us to measure the amount of power carried, and the impact the black hole’s jets have on its environment.”
The announcement of this new treasure trove of data matches with the EHT’s 2021 observing run, which leverages a worldwide array of radio dishes, the first since 2018. Last year’s campaign was withdrawn because of the COVID-19 pandemic, and the previous year was discontinued because of unforeseen technical obstacles. This very week, for six nights, EHT astronomers are targeting diverse supermassive black holes: the one in M87 again, the one in our Galaxy called Sagittarius A*, and several more distant black holes. Compared to 2017, the array has been updated by adding three more radio telescopes: the Kitt Peak 12-meter Telescope in Arizona, the Northern Extended Millimeter Array (NOEMA) in France, and the Greenland Telescope.
“With the release of these data, consolidated with the resumption of observing and an enhanced EHT, we grasp many exciting new results are on the horizon,” says co-author Mislav Baloković of Yale University.
“I’m thrilled to notice these results come out, along with my associates working on the SMA, some of whom were directly involved in accumulating some of the data for this panoramic view into M87,” says co-author Garrett Keating, a Submillimeter Array project scientist. “And with the events of Sagittarius A* — the enormous black hole at the core of the Milky Way — coming out soon, and the resumption of observing this year, we are looking forward to evening more astonishing outcomes with the EHT for years to come.”
The EHT MWL Science Working Group et al. Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign. The Astrophysical Journal Letters, 2021; 911 (1): L11 DOI: 10.3847/2041-8213/abef71