![]() ![]() Should the subsequently released image show something unexpected and new, we will be more inclined to dive into its physical implications rather than questioning what went wrong with the observation. The first EHT image was proof of the value of new technology, and it passed the test. Only then, could it be trusted to search for unknown particles and to probe new physics. When the Large Hadron Collider in CERN started operating, it had to rediscover all the previously discovered particles. It is true that science-wise the image of M87’s black hole did not teach us anything unexpected. Therefore, we indeed “saw” a black hole although we were shown “just” a post-processed digital image. (As the product of evolution on our particular planet, our eyes are strategically designed to be sensitive to the radiation from the Sun with a complete disregard of whether it is a good frequency range for the study of the rest of the universe.) Interferometers are just the next step in the evolution of visual aids. ![]() The films and receivers also allowed us to look outside the range of visible spectra, which was extremely useful to the study of celestial objects. The films (and other receivers) afforded us much longer exposures than capable by the human eye. Then optical telescopes magnified the image and increased the light-collecting area from the pupil size to the size of the lens (and later the mirror) so smaller and fainter objects became visible in detail. The first observations were done with unaided eyes only. Over the history of astronomical observations, we have learned to employ and trust technology to help us study the sky. The involved telescopes also change their relative positions with respect to the target due to the Earth’s rotation covering larger parts of the Earth-sized mirror. EHT simultaneously collects the data from multiple telescopes spread across our planet and then correlates and analyzes the data from them jointly. This is a toy illustration of how an interferometer works. Additionally, in moving the small pieces around, one would cover more and more of the surface of the large mirror and thus get closer and closer to its full capabilities. Thus, if one finds a smart way of connecting the small mirrors and analyzes the data collected by each of them together, one may be able to reproduce the capabilities (in particular, the resolution) of the large mirror similar in size to the area across which the mirrors were scattered. Each small mirror represents a place where the fabric from the first analogy has a hole. But one can also choose to scatter them across a larger area. One can place them together tightly and construct a nice medium-sized telescope mirror. Second analogy: Imagine a handful of small mirrors. The cloth would limit the telescope’s capabilities and reduce its light-collecting area, but we still would have a mighty planet-sized telescope with high-resolution capabilities. To explain it, we will use a series of analogies.įirst analogy: Imagine a real telescope mirror equivalent to the size of planet Earth and then placing over it a black cloth with several holes. It is not practically possible to construct a mirror of such a size, but we can still achieve the required resolution, using the interferometer technique. (They observed at 1.3 mm.) However, this wavelength also implied that they needed a telescope similar in size to the diameter of our planet to resolve the black hole shadow. ETH, therefore, had to observe a wavelength of around 1 mm. A longer wavelength results in lower resolution, while a bigger telescope mirror ensures higher resolution. The angular resolution of a telescope is proportional to the observed wavelength divided by the diameter of the telescope. However, the radiation of wavelengths of about 1 millimeter (10 -3 m) and larger is not affected by the dust. This dust absorbs electromagnetic radiation of short wavelengths such as visible light (about 5.5 x 10 -7 m), infrared light (about 10 -6 m), and so on. An abundance of dust exists between our telescopes and the observed black holes. ![]() Let me start by explaining why EHT really needed an Earth-sized telescope. The data was then processed to make the image we saw in the news.īut did we really “see” a black hole when we were shown “just” a digital image? And how is it possible to create an Earth-sized telescope? They arranged for simultaneous observations of their target with multiple telescopes around the globe and correlated the data between the instruments to effectively achieve the creation of a planet-sized telescope. This remarkable technological achievement was made possible by the collective efforts of hundreds of astrophysics, engineers, and computer scientists. On April 10, 2019, we were presented with the first-ever close-up image of a black hole by the Event Horizon Telescope (EHT). ![]()
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