![]() ![]() The direction of the electric and magnetic fields defines light's polarization. The shorter the wavelength, the more energetic the photon, but the more susceptible it is to changes in the speed of light through a medium. fields perpendicular to the direction of light's propagation. Light is nothing more than an electromagnetic wave, with in-phase oscillating electric and magnetic. However, while the Event Horizon Telescope team is still working on our black hole’s first image, the one at the center of M87 has just gotten a far more detailed image thanks to a special set of measurements that were also taken: polarization measurements. At just 0.15% of that black hole’s mass, our black hole’s features change by that same amount every single minute, making the image much more difficult to construct. At 6.5 billion solar masses, its diameter is approximately one light-day, meaning that the features in the photon ring take about ~1 day to change appreciably. The reason we have an image of the black hole at the center of M87 and not one of the black hole in our own galaxy’s center is because of its remarkable size. In other words, we need to make sure that the telescopes are properly synchronized: a tremendously difficult task. In order to make sure we’re adding the data from the same exact times together, we have to sync up the various observatories with atomic clocks, and then account for the light-travel time to each unique point on Earth’s surface. Light from a very distant source is striking our telescopes at many different locations on Earth. Event Horizon Telescope CollaborationĮven though this is usually depicted as a single image - where only the best of the four images from the four different days is shown - it’s important to recognize what’s actually happening here. This helps demonstrate the importance of syncing the different observations, rather than just time-averaging them. Note the differing appearances between the April 5/6 images and the April 10/11 images, which show that the features around the black hole are changing over time. A single-dish telescope would have to be 12,000 km in diameter to achieve this same sharpness. enabling the array to resolve the event horizon of the black hole at the center of M87. ![]() The Event Horizon Telescope's first released image achieved resolutions of 22.5 microarcseconds. In April of 2019, after two years of analysis, the first images were released: a map of the radio light that traced out the emitted photons from around the black hole in the distant galaxy M87. And the black hole at the center of the massive elliptical galaxy M87, which comes in at 6.5 billion solar masses (some 1500 times the mass of Sagittarius A*), but some 50-60 million light-years distant (about 2000 times as far).Sagittarius A*, the four million solar mass black hole at the center of our galaxy, just ~27,000 light-years away.In order to see anything, then, we had to look for black holes that were simultaneously very large, with a large angular diameter as seen from our perspective on Earth, and were also active: emitting copious amounts of radiation at radio wavelengths. This gave us the light-gathering power of all the telescopes that were part of the array, combined, but gave us the resolution of the maximum separation between the various telescopes, which was roughly the diameter of Earth. We needed to take an array of radio images (at millimeter-submillimeter wavelengths) from all around the globe at once. The way we went about imaging this was a tremendous technological achievement.
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