Caltech’s Katie Bouman explains how the Event Horizon Telescope Collaboration captured the first imager of the Sagittarius A* Supermassive black hole at the core of the Milky Way galaxy - Milky Way vs M87. Credit: Caltech
00:00Supermassive black hole at the heart of our own Milky Way galaxy, known as Sagittarius Star.
00:05But this image from the Event Horizon Telescope, or EHT, is unlike most other familiar astronomical images.
00:11It's the product of technically challenging telescope observations and innovative data processing
00:16that tackles the unique complexities in EHT data.
00:20The fundamental challenge is one of scale.
00:22The Sagittarius Star black hole is about 4 million times more massive than our Sun,
00:26extending over an area almost as large as Mercury's orbit.
00:30That may sound large, but at a distance of 27,000 light years,
00:34this is like trying to take a photograph of a single grain of salt in New York, all the way from Los Angeles.
00:40You would need a radio telescope as big as the entire Earth to take a picture of something that small.
00:45Constructing a telescope dish that big is of course impossible, so astronomers got creative.
00:50They developed algorithms that combine radio telescopes across the globe
00:54into a single virtual Earth-sized telescope.
00:57This computational telescope, the EHT, doesn't work like a regular telescope.
01:02Instead, the radio telescopes work in pairs, with each pair contributing a little bit of information to the entire image.
01:09Telescopes that are far apart can detect the smallest, sharpest features.
01:13Orientation is also important, with each angle picking up different parts of the hole.
01:17With enough samples, you can recover all the sharpest features.
01:21Telescopes that are closer together become sensitive to broader features that the wider pairs can't see.
01:27Combined, these components of the image can provide a good representation of the target being observed.
01:32Making a perfect image would require telescopes at all orientations and separations.
01:37But EHT's eight telescopes scattered around the globe only measure some of these possible pairings.
01:43Luckily, as Earth rotates, the separation and orientations between the telescopes change, providing more, but not all, of the information we need to make a perfect picture.
01:53In essence, taking a picture with the EHT is a bit like listening to a song being played on a piano that has a lot of broken keys.
02:00Since we don't know when the broken keys are being hit, there are an endless number of possible tunes that could be playing.
02:06Nonetheless, with enough functioning keys, our brains can often fill in the gaps to recognize the song.
02:12And on top of all this, in the case of Sag A Star, there was another daunting challenge.
02:17The material swirling around the black hole moved so quickly that its appearance could change from minute to minute while the data were being collected.
02:24This is a bit like changing the key of the song as it's being played on the broken piano.
02:29To tackle this and other challenges, scientists and engineers have spent years developing computational imaging algorithms that allow us to capture images of the black hole with incomplete data.
02:42These algorithms can intelligently fill in the missing information in a number of different ways.
02:47To capture the range of possible Sag A Star appearances, the EHT team produced thousands of images with different methods.
02:54Each of these images is slightly different, but they all are consistent with the EHT data.
02:59By averaging these images together, the team emphasized the common features appearing in most of the images, while suppressing features that appear infrequently.
03:08Here, a bright ring clearly pops out!
03:11But it's important to note that not all of the possible images look alike.
03:14In fact, the team found they could cluster the recovered images into four categories based on similar visual features.
03:21Three of the clusters contained a ring-like feature with different intensities around the ring.
03:25A much smaller fourth cluster contained images that did not appear ring-like.
03:30Although the non-ring images can't be fully rolled out, the vast majority of the images contain a ring of exactly the same size predicted by prior observations and theory.
03:40Through the power of computational imaging, the EHT team overcame seemingly impossible hurdles to capture the first image of Sag A Star.
03:48In the future, with more telescopes and better algorithms, we aim to get an even clearer picture and a deeper understanding of the beastly black hole lying in the heart of our galaxy.
03:57We're trying to do that since 20th century.
03:59Just a second time.
04:00We are not there and we know that it's impossible to do the same thing.
04:02We are here and we are there and we are here.
04:04That is perfect.
04:05I am happy to have the same moment on the record itself, as we must have played in the studio so our series of scores is a great idea.
04:06I am happy to have a copy of everything that we are on the left and out.
04:07This is a great idea.
04:08I am happy to have gathered and theρό to the board as not one of the others, we have developed together as I'm aware and I know.
04:09I am happy there and we have the ones for those who have anything and the people that have found their own way to the rest and they are intervening in this the world.
04:10We must often use the remainder of our galaxy.
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