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
Credit: Caltech
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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 love it.
04:00Thank you, Mr. Sheree.
04:02Aselessically.
04:03Anwalt-UCAS-VALL-T