On Thursday, an international team of astronomers released the first image of Sagittarius A*, a supermassive black hole at the center of our own Milky Way galaxy.
Nearly all galaxies, including our own, are thought to feature these massive black holes at their centers, where light and matter cannot escape, making photographs of them extremely difficult. As light, superheated gas, and dust are pulled into the abyss, gravity bends and twists it in a chaotic manner.
The image, created by the Event Horizon Telescope (EHT) Collaboration, is the first direct visual confirmation of the existence of this unseen object, coming three years after the first sight of a black hole from a faraway galaxy.
The image depicts the blazing gas that encircles the phenomenon, which is four million times more massive than the Sun, in a dazzling ring of bending light, rather than the black hole itself, which is absolutely dark.
“These unprecedented observations have greatly improved our understanding of what happens at the very centre of our galaxy,” said EHT project scientist Geoffrey Bower, of Taiwan’s Academia Sinica.
Bower said that the discoveries have provided “new insights on how these massive black holes interact with their surroundings” in a statement released by the French National Centre for Scientific Research (CNRS).
The Astrophysical Journal Letters published the findings.
While announcing the new image, Feryal Ozel of the University of Arizona referred to the black hole as “the gentle giant in the center of our galaxy.”
Sagittarius A*, abbreviated as Sgr A* and pronounced “sadge-ay-star,” got its name from the fact that it was discovered in the direction of the constellation Sagittarius.
Its existence has been suspected since 1974 when an unusual radio emission near the galaxy’s center was discovered.
Astronomers studied the trajectories of the brightest stars near the Milky Way’s center in the 1990s, confirming the presence of a gigantic compact object there, work for which they were awarded the Nobel Prize in Physics in 2020.
Though a black hole was previously regarded to be the sole feasible explanation, the new image gives the first direct visual proof.
Because it is 27,000 light-years from Earth, it appears the same size in the sky as a doughnut on the Moon.
The EHT, a single “Earth-sized” virtual telescope, was formed by joining eight gigantic radio observatories throughout the planet to capture photographs of such a faraway object.
The Institute for Millimetre Radio Astronomy (IRAM) in Spain, which has the most sensitive single antenna in the EHT network, was one of them.
The EHT stared at Sgr A* for several hours at a time across several nights, akin to long-exposure photography.
When the group revealed the first photograph of a black hole in 2019, it followed the same procedure. It came from a galaxy 53 million light-years away, known as M87* for its location in the Messier 87 galaxy.
The black hole in the Milky Way is significantly closer, at around 27,000 light-years. 5.9 trillion miles is the length of a light-year (9.5 trillion kilometers).
Despite the fact that Sgr A* is 2,000 times smaller than M87*, the two black holes have striking similarities.
“Close to the edge of these black holes, they look amazingly similar,” said Sera Markoff, co-chair of the EHT Science Council, and a professor at the University of Amsterdam.
Both behaved as expected by Einstein’s general relativity theory, which states that gravity is caused by the curvature of space and time, and that cosmic objects alter this geometry.
Despite being significantly closer to us, imaging Sgr A* provided some distinct obstacles.
Gas around both black holes travels at the same speed, which is close to the speed of light, while it took days and weeks to orbit the bigger M87*, it only took minutes to orbit Sgr A*.
The researchers had to develop complex new tools to account for the moving targets.
The resulting image is an average of numerous photographs that revealed the invisible monster hiding at the galaxy’s center. It was created by more than 300 researchers from 80 nations over the course of five years.
Scientists are now keen to compare the two black holes in order to test hypotheses about how gasses behave around them, a phenomenon that is expected to play a role in the development of new stars and galaxies.
Investigating black holes, particularly their endlessly small and dense centers known as singularities, where Einstein’s equations fail, could aid physicists in developing a more advanced theory of gravity.
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