Study Notes: Event Horizon Telescope (EHT)

General Science July 28, 2025 5 min read

What is the Event Horizon Telescope?

Definition: The Event Horizon Telescope (EHT) is not a single telescope, but a global network of radio telescopes working together to observe supermassive black holes.
Goal: To capture images of the “event horizon,” the boundary around a black hole beyond which nothing can escape, not even light.

Imagine trying to take a picture of an orange on the Moon from Earth. A normal camera lens isn’t big enough.
The EHT uses a technique called Very Long Baseline Interferometry (VLBI). This links telescopes all over the world to act like one giant telescope the size of Earth.
Real-World Example: Think of multiple microphones placed far apart, all recording the same concert. By combining the recordings, you get a clearer, richer sound. The EHT does this with radio waves from space.

Each telescope records radio signals from space onto hard drives.
The hard drives are flown to a central location and combined using supercomputers.
The result is a detailed image of the region around a black hole.

Black holes are regions of space where gravity is so strong that nothing can escape.
The “event horizon” is the point of no return.
Studying black holes helps scientists test Einstein’s theory of general relativity under extreme conditions.

In April 2019, the EHT released the first-ever image of a black hole, located in the galaxy Messier 87 (M87).
What was seen?: A bright ring of light (the accretion disk) surrounding a dark shadow (the black hole’s event horizon).
Why is this important?: It confirmed predictions from Einstein’s equations and showed that black holes really do cast a “shadow.”

The techniques developed for the EHT are being adapted for medical imaging (like MRI) and Earth observation satellites.

Handling petabytes of data from different locations has led to new methods in data science and cloud computing.

The EHT project involves over 200 scientists from around the world, showing the importance of international teamwork in science.

Reality: It’s a network of telescopes on different continents, working together.

Reality: It’s a computer-generated image based on radio wave data, not visible light.

Reality: Only objects that pass very close to the event horizon are captured. Planets and stars at a safe distance orbit black holes just like they orbit stars.

Reality: Only the largest and closest black holes, like those in M87 and our own Milky Way, are big enough to be imaged with current technology.

Water Analogy: The water you drink today may have been drunk by dinosaurs millions of years ago. Water cycles through the environment over time.
Black Holes: Matter that falls into a black hole is not destroyed, but its information and mass become part of the black hole. Just like water molecules are recycled, the matter and energy in the universe are constantly changing forms.

Adding more telescopes, especially in Africa and space, will make images sharper.

Scientists are working on capturing changes over time, like a movie of the material swirling around a black hole.

The EHT will target other supermassive black holes, such as the one in our own galaxy, Sagittarius A*.

Future plans include placing telescopes in orbit, avoiding weather and atmospheric interference.

2022 Study: The EHT Collaboration published a new image of the black hole at the center of our galaxy, Sagittarius A* (“First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way,” The Astrophysical Journal Letters, May 2022). This confirmed that the same techniques used for M87 could be applied to our own galaxy.
Key Finding: The size and shape of the shadow matched predictions from general relativity, further confirming Einstein’s theory.

Concept	Real-World Example/Analogy	Key Fact
EHT Network	Microphones recording a concert	Multiple telescopes act as one giant eye
Event Horizon	Point of no return in a waterfall	Boundary around a black hole
Data Handling	Shipping hard drives like parcels	Petabytes of data combined by supercomputers
Black Hole Shadow	Shadow cast by an object in light	Confirms Einstein’s predictions
Water Cycle Analogy	Drinking ancient water	Matter cycles through the universe

The EHT is a global network of telescopes using advanced technology to image black holes.
It has confirmed major predictions of general relativity.
The project is driving advances in imaging, data science, and global collaboration.
Future trends include sharper images, movies of black holes, and space-based telescopes.
Recent research continues to confirm our understanding of black holes and the laws of physics.