Why Astronomers are so excited about the EHT Black Hole image

You must have seen the slightly blurry image of a black hole event horizon making the rounds on the internet in April. A bright, orange, cosmic doughnut. As an astronomer, this image was absolutely mind-blowing. In this post, I’ll share why this image is so important for science and its other benefits.

Credit: Event Horizon Telescope


We are not actually “seeing” the black hole

I just wanted to clarify this important point because it is what is so mind-blowing about this picture. We are not seeing the actual black hole. We are seeing the boundary where light can’t escape from any more because of the black hole – called the ‘Event Horizon’. The ‘dougnnut hole’ at the centre is where light has been scooped out by the black hole’s extreme gravity. Because the gravity around a black hole is so strong, the light can’t escape that region and is trapped –  causing the darkness at the centre. Black holes – as well as their event horizons – have a very small size relative to other astronomical objects, which adds to the challenge in observing them.

It shows us that the impossible isn’t always impossible

If you asked me, two years ago, whether we will ever manage to get an image of a black hole’s event horizon, my answer would have been a strong no. For most astronomers, the idea of ever getting this close to imaging a black hole would have seemed impossible. Since black holes don’t emit light and are so small – observing them was – for a long time – thought to be something we would never be able to do.  We are in an era of science where the discoveries are completely blowing away our ideas of what is and isn’t impossible – and this is largely due to the work of many people.

It will help us understand different types of galaxies

My own studies focus on galaxies, so I find this particularly interesting. Some galaxies, like M87, have what is known as an ‘active galactic nucleus’. In other words, the black hole at the centre of the galaxy being ‘fed’ gas, stars, and other material through the disk surrounding it. This results in extremely large jets, being shot out from the central region surrounding the black hole. Since not all galaxies are active, having a measurement of an active black hole and – eventually when the Event Horizon Telescopes releases the image of our own, Milky Way galaxy’s black hole – a non-active black hole will help us understand the processes that create these Active Galactic Nuclei in a lot more detail.

The galaxy M87, which contains the black hole shown in the image. M87 hosts an Active Galactic Nucleus. Credit: Hubble Space Telescope

We can use black holes to test gravity

Black holes were once only theoretical objects. They test our theories of gravity to the extreme.  Although observations within our own galaxy showed stars orbiting something that could only be a black hole, having a picture of a black hole event horizon, which matches up with simulations and theoretical predictions so well, is a good sign that these extreme objects exist. This image is a strong indicator that Einstein’s theory of general relativity – which is what we use to explain gravity – is correct.

International collaboration is the path forward for science

The idea of the ‘lone genius’ – people like Einstein, Newton and Da Vinci who were thought to have worked on their own on amazing theories, making amazing discoveries – is dying out. The type of questions that we are asking nowadays in science is far beyond the scope of a single, brilliant mind. Taking pictures of black holes, detecting faint gravitational waves, building the world’s largest radio interferometer (a type of telescope that works by linking up multiple receivers), and detecting subatomic particles require many people all working together. Our world is increasingly divided over racial, political, economic and national lines. These big projects show us that when we put our differences aside and work together – we can do impossible things.

The mysteries of the universe: What do astronomers do?

The other day I stumbled across a question on twitter. “How do astronomers know all of this”, in response to a post showing the scale of the universe and different objects within it. I replied with a simple explanation about how we use large telescopes to observe various objects and simulations to understand the physics, but I thought I would write a longer blog post on this topic. With the South African government investing heavily on some of these large telescopes, it is even more important for people to understand why this undertaking is so important.

There are two main types of astronomers or astrophysicists. On the one side the theoreticians: the ones that mainly work through complicated mathematical equations and creating mind-blowing simulations; but what I am going to talk about here is observational astrophysics, which I focus on, and where South Africa has shown great interest with the development of the Square Kilometer Array and the successful Southern African Large Telescope.

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Image of spiral galaxy M101 in four X-ray, Optical, Ultraviolet and Infrared Light taken using different telescopes

What exactly do we do?

Observational astronomers use telescopes (like MeerKAT, the Southern African Large Telescope, and several others) to study the night sky. These telescopes function as “light buckets” and collect information in the form of optical (visual) or radio light. Most land-based telescopes operate in optical or radio light because the atmosphere prevents any other light from reaching the earth, but space-based telescopes (like the famous Hubble Space Telescope) can detect X-rays, Infrared, and ultraviolet light.

This light can be used in a few different ways. We can take a picture of distant objects like galaxies to study things like their shape, structure, size and position. We can track how the light in an object like a star changes with time – which is how planets around distant stars are often discovered. Or, we can break the light up into a spectrum, which allows us to probe deeper into the chemical makeup of an object. Different types of light reveal different aspects of astronomical objects. While optical light is really good at detecting stars, the faint gas that fuels galaxies is only visible in radio wavelengths and hot, energetic events pop up as X-rays or gamma rays.

Bigger telescopes allow us to observe objects that are fainter and further away. This allows us to see further back in time, to understand the universe at earlier stages of its evolution. The further away an object is (and often the fainter an object is), the longer it takes for light to reach us here on Earth. Therefore, the light we collect with our telescopes essentially lets us look back in time to when the universe was much younger and smaller than it is today.   

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MeerKAT telescope dishes. Credit: SARAO.

Why does this matter?

Aside from being able to detect asteroids that might crash into Earth, astronomy has many benefits. Studying objects in space allows us to work on answers to some of the mysteries of physics. Gravity – something we all interact with on a daily basis (unless you are reading this from the International Space Station) – is something physicists thought we understood since Isaac Newton’s days. Until some astronomers looked at the motions of galaxies and realised that there was something invisible causing these galaxies to move in unexpected ways. This led to the discovery of dark matter – which we are still trying to figure out!

Just two years ago, the groundbreaking observation of a neutron star merger (which our very own SALT contributed to) revealed where heavy elements like gold are originally created. This event, which was detected through gravitational waves and various wavelengths of light simultaneously, was one of the most important discoveries of this decade.

Astronomy teaches us about how the universe works. Although not every discovery will have implications for our everyday life, we have a natural curiosity about the universe we live. Many people experience a sense of appreciation and wonder when they look up at the night sky, especially in the absence of city lights, and wonder what’s out there. Astronomy allows us to explore that curiosity and appreciate our universe.

(At the very least, astronomy gives us a bountiful amount of pretty pictures. You can find a new one every day on the Astronomy Picture of the Day website.)

If you are curious to learn more about how specific fields in astronomy contribute to scientific questions, I have a post on Medium that goes into much more detail! You can also learn more about astronomy through Crash Course: Astronomy and by following NASA on social media.