The current observation follows the 2019 image of a black hole (M 87*) at the centre of the galaxy Messier 87, which lies at a much greater distance from Earth. “The contribution of our Apex telescope was essential for perfectly calibrating the changing brightness of the source and providing definitive proof of the black hole shadow at the galactic centre”, says Director Karl Menten. The Max Planck Institute was also involved in the campaign with an antenna. These data were analysed by two correlators – high-performance computers located at the Max Planck Institute for Radio Astronomy and the Haystack Observatory. At a wavelength of 1.3 millimetres, they collected data for many hours at a time – similar to the long exposure time of a camera. Using interferometry, the astronomers observed the object Sagittarius A* during several nights in April 2017. In order to image it, the team created the powerful EHT, which links eight (now 11) radio observatories around the world into a single Earth-sized virtual telescope. The observations would greatly have improved the understanding of the physical processes taking place at the centres of galaxies and would provide insights into how such giant gravity traps interact with their surroundings.īecause the black hole at the centre of the Milky Way is 27,000 light years away from Earth, it appears to us in the sky about as big as a doughnut on the moon. “We were amazed at how well the size of the observed ring matched the predictions of Einstein’s general theory of relativity”, says EHT project scientist Geoffrey Bower from the Institute of Astronomy and Astrophysics at Academia Sinica in Taipei. Their light is bent by the immense gravity of the black hole. But the glowing gas around it shows a tell-tale signature – a dark central region (shadow) surrounded by a bright ring-like structure. The black hole itself is not visible in the image because it does not emit any radiation. The image is the first direct visual proof of this. “Our discovery shows that the object at the galactic centre is indeed a black hole”, says Anton Zensus, Director at the Max Planck Institute for Radio Astronomy and founding chair of the Supervisory Board of the EHT. For this work, Andrea Ghez from the University of California and Reinhard Genzel from the Max Planck Institute for Extraterrestrial Physics in Garching were awarded the Nobel Prize in 2020. For many years, researchers have been examining this area of the Milky Way and observing stars that orbit an invisible, compact, and massive object. The recently published image is the long-awaited direct view of the object at the centre of our galaxy known as Sagittarius A*. The heights of the bars indicate the relative contributions of each cluster to the averaged image at top. Thousands of images fell into each of the first three clusters, while the fourth and smallest cluster contains only hundreds of images. The bar graphs show the relative number of images belonging to each cluster. The fourth cluster contains images that also fit the data but do not appear ring-like. Three of the clusters show a ring structure but, with differently distributed brightness around the ring. An averaged, representative image for each of the four clusters is shown in the bottom row. The images can also be clustered into four groups based on similar features. The image is an average of the various images extracted by the EHT collaboration from their observations in April 2017. The image captures light bent by the strong gravity of the black hole and is four million times more massive than the sun. Although the event horizon itself is not visible because it does not emit light, glowing gas swirling around the black hole shows a tell-tale signature: a dark central region (shadow) surrounded by a bright ring-shaped structure. The EHT is named after the “event horizon”, the boundary of the black hole beyond which no light can escape. It was taken by the Event Horizon Telescope (EHT), a network that combines radio observatories around the world into a single virtual telescope the size of the Earth. Cosmic ring of fire: This is the first image of Sagittarius A*, the supermassive black hole at the centre of the Milky Way.
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