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how does astronomers come up with such specific pictures of a galaxy or planet?

Like how are you guys able to make such specific predictions and when actually taking a picture, figuring out it was similar or almost exactly same?
Like the black hole picture for example, recently it was discovered and almost exactly as it was predicted to be.

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Anuj’s Answer

It feels like magic when a real space photograph perfectly matches a drawing or a computer simulation made years before. But it isn't magic—it is the ultimate proof that the laws of physics work.When scientists make a visual prediction of a black hole or a distant planet, they aren’t just guessing or making "space art." They are taking strict mathematical equations and feeding them into supercomputers.Here is exactly how astronomers make such incredibly accurate predictions, and how those match reality when the actual photos are taken.1. The Recipe: Math, Gravity, and Light BendingTo predict what a black hole looks like, scientists rely entirely on Einstein's Theory of General Relativity. Einstein’s math tells us exactly how much a massive object’s gravity will warp the space and time around it. We know that gas and dust get pulled toward a black hole, swirling around it at nearly the speed of light and heating up until it glows intensely. Astronomers use a technique called GRMHD (General Relativistic Magnetohydrodynamics). This is a massive computer program that simulates the physics of superheated gas, magnetic fields, and intense gravity. By running these physics equations, the computer generates a highly detailed, hypothetical image of a black hole long before a telescope ever looks at it. 2. The "Blur" Trick: Matching the Telescope's VisionWhen supercomputers render a black hole, they create a crisp, high-definition image. However, astronomers know that our real telescopes on Earth have limitations.To see if their prediction is accurate, scientists take their perfect computer simulation and deliberately blur it to match the exact maximum resolution that their network of telescopes can see. When the Event Horizon Telescope team blurred their theoretical models to match the radio telescope array's resolution, the simulation looked identical to a glowing donut with a dark shadow in the center. When they finally processed the real data from the telescopes, the real image lined up almost perfectly with that blurred prediction. 3. How Real Space Pictures Are ConstructedTaking a picture of something millions of light-years away is vastly different from snapping a photo on your phone. Planets and black holes require two entirely different photographic pipelines:For Black Holes: Turning the Earth into a Giant MirrorThe black hole in the M87 galaxy is 55 million light-years away. To photograph it, a single telescope would need to be the size of the entire planet Earth. The Solution: Astronomers used a technique called VLBI (Very-Long-Baseline Interferometry). They linked eight different radio telescopes across the globe (from Antarctica to Europe) to work together simultaneously. The Process: As the Earth rotated, these telescopes captured fragments of radio waves emitted by the black hole. Supercomputers then ran advanced mathematical algorithms to stitch those pieces together, filling in the gaps to reveal the final image.
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Tillson’s Answer

Hi Purna!

You touched the answer in your question: predictable physics allows for us to do observe these stellar objects.

While humans are confined to the visible light range, telescopes can take advantage of the full spectrum of light (radio, microwave, infrared, visible, x-ray, gamma) to observe stellar objects. Additionally, astronomers can figure out the chemical composition of a stellar object using spectroscopy (if you pass the light from an object through a prism, you can see its components). This helps 'fingerprint' stellar objects from a distance and without needing a precise visual picture.

In the recent black hole picture, we already knew that the galaxy M87 is an 'active galaxy', meaning it has large black hole at its core. Galaxies also move very slowly as it appears to us, so we could predict the location of this black hole.

Some further reading if you're interested:

  • NASA, "How Scientists Captured the First Image of a Black Hole"
  • SpaceTelescope.org, "Black Holes, Quasars, and Active Galaxies"
  • Wikipedia, "Astronomical spectroscopy" (more dense reading)
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