The First Photo of a Black Hole: How Was It Taken?

In April 2019, scientists unveiled the first-ever image of a black hole, a groundbreaking achievement that confirmed key predictions of Einstein’s general relativity and opened a new window into the cosmos. But how was such a photo even possible, considering that black holes, by definition, do not emit light? This article explores the scientific feat behind capturing the silhouette of a black hole and explains the global collaboration that made it happen.

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1. What Was Photographed?

The image captured the supermassive black hole at the center of Messier 87 (M87), a giant elliptical galaxy located about 55 million light-years from Earth. The black hole is roughly 6.5 billion times the mass of the Sun.

What we see in the image is not the black hole itself—since light cannot escape from it—but the “shadow” it casts on a glowing disk of superheated matter spiraling around it. This surrounding material emits powerful radio waves that can be detected.

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2. The Event Horizon Telescope (EHT)

The image was taken by the Event Horizon Telescope (EHT), not a single telescope but a global array of radio observatories working in unison.

Key Details:

• 8 radio telescopes across the globe, from Antarctica to Spain
• Combined to form an Earth-sized virtual telescope using Very Long Baseline Interferometry (VLBI)
• Operated at a wavelength of 1.3 mm (230 GHz) to penetrate the dense material around the black hole

This technique gave the EHT a resolving power capable of seeing an object the size of an orange on the surface of the Moon.

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3. Why Use Radio Waves?

Radio waves are essential for peering through the dense gas and dust that surround black holes. Unlike visible light, radio waves at millimeter wavelengths can pass through interstellar material relatively unimpeded.

Also, the material falling into the black hole in M87 emits synchrotron radiation, a type of radio emission produced by electrons spiraling in magnetic fields. This makes the black hole's surroundings particularly bright at radio frequencies.

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4. How Was the Image Constructed?

Step 1: Synchronized Observation

Over the course of several nights in April 2017, all participating telescopes pointed at M87’s core simultaneously. Each observatory recorded massive amounts of raw data—up to 5 petabytes (that’s 5 million gigabytes).

Step 2: Data Correlation

Because internet speeds were too slow to transfer such huge datasets, the data was flown on hard drives to central processing centers at MIT and the Max Planck Institute in Germany.

The data was then synchronized using atomic clocks, accurate to a billionth of a second.

Step 3: Image Reconstruction

Teams of scientists used algorithms to combine the data and reconstruct an image. The most important algorithm was CHIRP (Continuous High-resolution Image Reconstruction using Patch priors).

To ensure unbiased results, four separate teams worked independently before comparing their outputs.

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5. What Did the Image Show?

The final image revealed a bright ring of emission surrounding a dark central region—the shadow of the black hole.

Scientific Confirmation:

• Matched predictions from general relativity simulations
• Proved that black holes have event horizons
• Provided measurements of M87’s black hole mass and spin characteristics

This was the first direct visual evidence of a black hole's existence.

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6. Why Was This Important?

The image confirmed that the laws of physics still apply under extreme conditions. It also opened up new pathways for studying black hole environments, accretion disks, and jet formation mechanisms.

Moreover, the EHT project marked a new era of global scientific collaboration, involving over 200 researchers from multiple continents.

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7. What Came After?

Since 2019, the EHT has continued to improve its resolution and has imaged the black hole at the center of our own galaxy, Sagittarius A* in 2022.

Future Goals:

• Create time-lapse images ("black hole movies")
• Observe black hole jets in real time
• Incorporate more telescopes to enhance clarity

The Event Horizon Telescope is not just about images—it's about understanding the fundamental laws of the universe.

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Conclusion

The first photo of a black hole wasn’t just a triumph of technology—it was a profound moment in human curiosity and cooperation. By capturing the shadow of the invisible, scientists turned one of the universe’s most mysterious objects into something we could finally "see." It stands as a reminder of what we can achieve when the world works together in pursuit of knowledge.

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References

• EHT Collaboration (2019). First M87 Black Hole Image. Astrophysical Journal Letters.
• Doeleman, S. et al. (2012). Imaging an Event Horizon. Science.
• NASA Black Hole Resources: https://www.nasa.gov