Working Together As A “virtual Telescope,” Observatories Around The World Produce First Direct Images Of A Black Hole (Event Horizon Telescope 4/10/19)

Wednesday, April 10, 2019
by Jennifer Chu

Jennifer Chu | MIT News Office
April 10, 2019

Images reveal supermassive black hole at the heart of the Messier 87 galaxy.

An international team of over 200 astronomers, including scientists from MIT’s Haystack Observatory, has captured the first direct images of a black hole. They accomplished this remarkable feat by coordinating the power of eight major radio observatories on four continents, to work together as a virtual, Earth-sized telescope.

In a series of papers published today in a special issue of Astrophysical Journal Letters, the team has revealed four images of the supermassive black hole at the heart of Messier 87, or M87, a galaxy within the Virgo galaxy cluster, 55 million light years from Earth.

All four images show a central dark region surrounded by a ring of light that appears lopsided — brighter on one side than the other.

Albert Einstein, in his theory of general relativity, predicted the existence of black holes, in the form of infinitely dense, compact regions in space, where gravity is so extreme that nothing, not even light, can escape from within. By definition, black holes are invisible. But if a black hole is surrounded by light-emitting material such as plasma, Einstein’s equations predict that some of this material should create a “shadow,” or an outline of the black hole and its boundary, also known as its event horizon.

Based on the new images of M87, the scientists believe they are seeing a black hole’s shadow for the first time, in the form of the dark region at the center of each image.

Relativity predicts that the immense gravitational field will cause light to bend around the black hole, forming a bright ring around its silhouette, and will also cause the surrounding material to orbit around the object at close to light speed. The bright, lopsided ring in the new images offers visual confirmation of these effects: The material headed toward our vantage point as it rotates around appears brighter than the other side.

From these images, theorists and modelers on the team have determined that the black hole is about 6.5 billion times as massive as our sun. Slight differences between each of the four images suggest that material is zipping around the black hole at lightning speed.

“This black hole is much bigger than the orbit of Neptune, and Neptune takes 200 years to go around the sun,” says Geoffrey Crew, a research scientist at Haystack Observatory. “With the M87 black hole being so massive, an orbiting planet would go around it within a week and be traveling at close to the speed of light.”

“People tend to view the sky as something static, that things don’t change in the heavens, or if they do, it’s on timescales that are longer than a human lifetime,” says Vincent Fish, a research scientist at Haystack Observatory. “But what we find for M87 is, at the very fine detail we have, objects change on the timescale of days. In the future, we can perhaps produce movies of these sources. Today we’re seeing the starting frames.”

“These remarkable new images of the M87 black hole prove that Einstein was right yet again,” says Maria Zuber, MIT’s vice president for research and the E.A. Griswold Professor of Geophysics in the Department of Earth, Atmospheric and Planetary Sciences. “The discovery was enabled by advances in digital systems at which Haystack engineers have long excelled.”

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Image: The Event Horizon Telescope (EHT) — a planet-scale array of eight ground-based radio telescopes forged through international collaboration — was designed to capture images of a black hole. In coordinated press conferences across the globe, EHT researchers revealed that they succeeded, unveiling the first direct visual evidence of the supermassive black hole in the center of Messier 87 and its shadow.