Recently the first picture of a black hole has been taken; this is big news! Although this image represents significant scientific breakthroughs, it can be difficult to understand the importance of this bright and fuzzy “doughnut”. Here’s some information to help you share this information with your students.
The first thing we need to understand is that this is a radio image: the signal was picked up by radio telescopes. The colours are therefore false, although the brilliance represents the intensity of the signal (the brighter it is, the stronger the radio signal). Astronomers use radio telescopes to study many objects in the universe. It’s a common misconception that we pick up sound with radio telescopes, but radio waves are not sound waves. Radio waves are a type of light with different wavelengths, making them invisible to the eye.
What exactly are we seeing in the image? The radio waves that form the “doughnut” were diverted by the presence of the black hole in the centre. The black region, therefore, represents where the black hole is located, although the black center on the image is larger than the black hole itself.
Top 5 reasons why this image is important:
1. Black Holes are Fascinating!
Black holes are objects with extreme density: a lot of mass in a very little space. Because of this, they have such intense gravity that nothing can escape, not even light. That’s why we call them black holes, and why we can’t see them without this new method.
2. We Knew They Existed, but We Had Never Seen Them Directly
Einstein first predicted the existence of black holes more than 100 years ago. We knew they existed, but all observations so far were indirect: we couldn’t see them but we could see the effects of their presence thanks to their immense gravity. For example, we could see stars in very tight orbits around nothing. We could then conclude that this “nothing” was a black hole. April 10, 2019, is the first time humanity has seen a black hole directly!
3. This Black Hole is Super-massive, Very Big, and Far Away!
The event horizon of the black hole pictured here is huge. It lies at the centre of the galaxy Messier 87, located more than 50 million light-years away from Earth. There is no danger to us! It contains the mass of more than 6 billion suns and the black part in the centre of the image is larger than our own solar system. It’s huge! We also know of smaller black holes which have a mass equivalent to a few suns smaller than the Earth.
4. It’s a Celebration of Human Ingenuity!
Obtaining this image was quite a challenge in itself! It took 8 radio telescopes, spread over 4 continents to succeed in getting it. By combining the light (radio waves in this case) from each of the radio telescopes, scientists manage to simulate an antenna as wide as the Earth! This allows us to obtain the precision needed to photograph the black hole; because it is quite far, it would appear very small in our sky. Combining light with radio telescopes is a process that requires expertise in science, mathematics, and programming.
5. We Are Capable of Great Things When We Work Together!
More than 200 scientists collaborated on this discovery! They come from various institutions around the world. It’s by collaborating and sharing everyone’s expertise that they have achieved this feat!
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Why did we take a picture of the black hole in a galaxy so far away instead of the black hole at the centre of our own galaxy?
The Supermassive at the centre of the Milky Way galaxy is also a target for the Event Horizon Telescope and scientists are working on it. However, the radio signals we receive from it are not as stable and vary continuously, making it harder to capture an image of the event horizon.
To Go Further
The black hole itself is infinitely small, we call it a singularity. However, we often talk about the size of the black hole by what scientists call the event horizon. This is the point of no return: anything that crosses the event horizon is forever a prisoner of the black hole. In the black hole photo, the black region in the centre, called shadow, is about 2.5 times larger than the black hole’s event horizon.