![]() Such diverse perspectives are essential to a more comprehensive understanding of the underlying nature of black holes. In contrast, gravitational wave detectors monitor stellar mass black holes that range from five to several dozen solar masses. The supermassive black hole at the center of M87 studied by the EHT collaboration is 6.5 billion times more massive than the sun. In addition to providing a brand-new test for all alternative formulations of gravity, it also connects the constraints from black hole images to those from other gravitational experiments. The new EHT paper focuses on a previously unexplored parameter space for black hole research. Gravitational waves propagate through the fabric of spacetime like ripples on a pond given the dynamic nature of spacetime as predicted by general relativity. Examples include the detection of gravitational waves at the Laser Interferometer Gravitational-Wave Observatory (LIGO). More recently, tests have been conducted to probe gravity outside the solar system and on a cosmological scale. During the 1919 solar eclipse, the first evidence of general relativity was seen based on the displacement of starlight, traveling along the curvature of spacetime caused by the sun’s gravity. Gravitational tests have been conducted in a variety of cosmic settings. The result is a murky no man’s land just beyond the point of no return, which appears to observers as a shadow. While light cannot escape from the interior of a black hole, it is possible-though unlikely-for light to escape from the region surrounding the event horizon, depending on its trajectory. ![]() Whereas a physical object casts a shadow by preventing light from passing through it, a black hole can create the effect of a shadow by siphoning light towards itself. The black hole shadow is unlike the shadows encountered in everyday life. “This test will be even more powerful once we image the black hole in the center of our own galaxy and in future EHT observations with additional telescopes that are being added to the array.” We have now shown that it is possible to use an image of a black hole to test the theory of gravity,” explained Medeiros. A test of gravity at the edge of a supermassive black hole represents a first for physics and offers further proof that Einstein’s theory remains intact even under the most extreme conditions. By measuring this visual distortion, the research team found that the size of the black hole shadow corroborates the predictions of general relativity. The intense gravity of a black hole curves spacetime, acting as a magnifying glass and causing the black hole shadow to appear larger. ![]() This research, published in Physical Review Letters, was led by Dimitrios Psaltis (IAS Member, 2001–03) of the University of Arizona, Lia Medeiros of the Institute for Advanced Study (IAS), and Feryal Özel (IAS Member, 2002–05) and Pierre Christian, both of the University of Arizona, and was co-authored by the EHT collaboration. Based on an analysis of the black hole’s shadow, the team conducted a unique test of general relativity, deepening understanding about the unusual properties of black holes and ruling out many alternatives. If a picture is worth a thousand words, what might the first horizon-scale image of a black hole tell us? A new paper by researchers from the Event Horizon Telescope (EHT) collaboration, which famously imaged M87’s central black hole, has provided a number of enlightening answers.
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