The left image shows the shape of the cluster in X-rays. The right image shows the shape of the cluster in visible light.
Adrianos: Girls, come on. I’m about to launch Adrianos’ time-ship. I’ve made some changes to the original design. Now it can function both as a time-ship and a space-ship.
98 Ianthi: What are we going to do this time, Adrianos?
Adrianos: I’ve also fitted two different panes of glass on the front windows: on the right window, I installed a special glass that lets you see only visible light. On the left window, you can see only in X-rays.
431 Nefeli: Speak slowly, Adrianos, so I can understand. If 98 Ianthi stands in front of the right window and I sit behind it, I’ll see her ‘normally’—with her skin and clothes.
98 Ianthi: But if we do the same experiment with the left window, you’ll see me like you see an X-ray. You’ll only see my bones, 431 Nefeli.
Adrianos: Very good, girls. So now you can easily understand that many things look different when you observe them in different types of light (blue, red, X-rays, radio waves, or microwaves…).
They look different because you’re seeing hidden features that you wouldn’t see otherwise—like your bones in X-rays.
I wanted us to go see a galaxy cluster using the two different windows. It must look different. In visible light, only the galaxies within the cluster can be seen. In X-rays, you can see the hot gas, which is also located in the same space along with the galaxies.
98 Ianthi: I know, I know what a galaxy cluster is.
431 Nefeli: Me too! Can I say it?
98 Ianthi: Let’s first take a look at what this beautiful picture with all the colorful balls is.
The bright blue source in the lower right corner is a star from our own galaxy, located somewhere between the Hubble Space Telescope and the Abell 370 cluster.
The image was taken by the Hubble Space Telescope.
431 Nefeli: A galaxy cluster is many galaxies grouped together in a small region of the universe.
98 Ianthi: A rich cluster can have up to 1,000 galaxies.
431 Nefeli: The galaxies within the cluster are clearly visible in visible light.
98 Ianthi: The cluster also contains hot gas that can only be seen in X-rays.
431 Νεφέλη: Intracluster medium λέγεται 98 Ιάνθη. Να είσαι πιό προσεχτική.
Adrianos: So, within the galaxy cluster, there are the galaxies and the intracluster medium.
It’s just like the next bowl with the water and the colorful stones. The colorful stones are the galaxies. The bowl is the galaxy cluster. The water inside the bowl is just like the intracluster medium. The water takes exactly the shape of the container.
Adrianos: Now that I’m looking at the picture more closely, I don’t think there’s actually any water inside. But I’m sure you can imagine it.
98 Ianthi: When are we going to Coma? I can’t wait!
431 Nefeli: Let’s go already! It’s right next door. It’s only 3,000…000 (21 zeros) kilometers away.
Adrianos: Let’s go.
431 Nefeli: I’ll sit behind the right window to see the galaxies.
98 Ianthi: I’ll sit behind the left window to see the intracluster medium.
431 Nefeli: Ahhh, come quickly and see how beautiful the Coma cluster looks, with all its galaxies!
98 Ianthi: Ahhh, you won’t believe what I’m seeing! Did you know that those two giant galaxies emit X-rays? They both appear as white dots! The intracluster medium, which fills the whole space of the cluster, looks like a purple cloud. And I love the color purple so much!
431 Nefeli: What wonderful experiences you give us, Adrianos! Thank you so much.
98 Ianthi: What did we learn today?
431 Nefeli: We learned that the appearance of everything around us depends on how we look at it. For example, if I look at you, 98 Ianthi, in visible light, I’ll see your skin and clothes. But if I look at you in X-rays, I’ll see your bones.
Adrianos: 98 Ianthi is always the same asteroid. However, under different kinds of light, other, initially unseen sides of her become visible. For example, in X-rays, you can see her bones.
Adrianos: Girls, it was a wonderful experience for me too. And there’s still so much more to learn if we stay here for a while, near the Coma galaxy cluster.
NOTES:
The Coma galaxy cluster
(Left image): in X-rays,
(Right image): in visible light.
In visible light, the galaxies belonging to the cluster are visible.
In X-rays, the hot gas within the cluster becomes visible.
Comparing the two images reveals that the shape of the cluster in X-rays is very different from what we see in visible light.
The nearly circular, concentric curves show the extent and shape of the intracluster gas, which fills the entire space within the cluster and emits X-rays.
These curves have been added to both images to make it easier to compare the distribution of the intracluster gas with the distribution of the galaxies in the cluster.
The colors in the left image indicate the intensity of the radiation:
Red marks areas of high intensity,
while blue marks areas of lower intensity.