Astronomers to shed light on mystery of the black hole.
There is a very interesting piece of news for astronomy fans. During a 10-day period that concludes on April 14, the Event Horizon Telescope (EHT) or a network of eight radiofrequency observatories around the world, are pointed towards the 'supermassive' black hole, Sagittarius A (Sgr A), that hides in the Milky Way's centre. The observatories hope to gather enough data to piece together the first snapshot a black hole's event horizon - the "point of no return" threshold after which nothing can escape the black hole's gravity. These telescopes will collect radio waves emitting from Sgr A, as well as the neighbouring galaxy Messier 87, a huge elliptical galaxy in the nearby Virgo Cluster, and stitch them together into visual images. The EHT's resolution is said to be about as good as being able to count the stitches on a baseball from about 13,000km away. When astronomers "see" black holes, they are actually seeing light from a disk of material around the black hole, sitting beyond the event horizon. Anything within the event horizon itself is truly invisible, as that marks the point at which even light cannot travel fast enough to break free of the black hole's gravity and escape. But currently, astronomical instruments do not have the resolution to really see the disk closely or image its structure. This is why every "image" ever shown of a black hole in a news article or textbook is an artist's rendering, rather than an actual picture. But that is all about to change. The EHT makes use of a technique called Very Long Baseline Interferometry that requires several telescopes observing the same object from different locations to create highly detailed images of very, very small sections of the sky. The farther apart the telescopes are located, the greater the detail they can achieve. The EHT has linked the Atacama Large Millimeter/submillimeter Array in Chile, the Caltech Submillimeter Observatory in Hawaii, the Large Millimeter Telescope Alfonso Serrano in Mexico, the South Pole Telescope in Antarctica, and other facilities in France and Spain to utilise the longest baselines possible. This will allow astronomers to study not only the structure of the disk around the black hole, but also to test general relativity, get a better look at how the black hole actually feeds on material, and maybe even determine how the outflows and jets that are so common among black holes are actually created. Sgr A has a mass of about 4mn Suns. Because it is so massive and relatively close at a distance of 25,600 light-years, it is the largest black hole visible in our sky. But large is a relative term as well - current estimates place the size of the black hole at 100 Astronomical Units (AU) or less. One AU is the average distance between Earth and the Sun, 150mn km. Some estimates even indicate that the black hole could be as small as the distance between Mercury and the Sun, just 46mn km. The amount of information obtained from the EHT will be so immense that it is too large to transfer digitally - it will be stored physically and taken to the Max Planck Institute in Germany, and the Haystack Observatory in Massachusetts for processing. Some time in 2018, we may finally have our first picture of the region immediately around a 'supermassive' black hole.
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