Caoimhín's Content

For today, we will be looking at stars. I know that we look the stars in every piece, one way or the other. Even if we are talking more about the planets or something like that, the stars are always behind them, the stars are in the sky. We’re still looking at them while we are looking for the planets or some other thing. Today however, we’re going to talk about the stars themselves, the life of the star. At least, we’ll look at where and how they begin.

We aren’t going to be able to look at any place where stars begin from the city, at least during this time of the year. One of the most famous place that stars come from, Orion’s Sword, is still behind the Sun at this time of the year. As I always mention when I’ve attached an Irish language video, Orion is also known as An Bodach in Irish. If we look at the morning sky with the atmosphere removed, we can certainly see the planets. Venus and Jupiter are visible at this time of the year, though Jupiter is still pretty close to sunrise. If we push ahead here, we’ll see Betelgeuse rising more or less with the Sun. Then Orion’s Belt and Orion’s Sword will rise, with the Sun very much above the horizon. They aren’t directly behind the Sun, they are a little under the Sun, but they are still on the wrong side of the sky for us to look at. We’re able to see Orion’s Sword with the atmosphere off at least, and it’s one of the places in which stars begin. If we zoom in we’ll be able to see a nebula. That’s the Orion Nebula or Orion’s Sword Nebula and it is a HII region, a place in which stars begin. A HII region is a H-2 or Haitch-two region, “H” for hydrogen and two for the fact that the hydrogen is ionized. There are loads of this kind of nebula.

Hydrogen is the most common element in the whole Universe, hydrogen is the most common atom, stuff, material out there. For that reason, the majority of everything we can see is made of hydrogen, the stars are made of hydrogen and the majority of nebulae are made of hydrogen as well. From the city, we’re not able to see any of these nebulae, and even with the stars helping us, Orion’s Sword is hard enough to see from the city as well. If we head out to the countryside, Orion’s Sword would be a lot easier to see, but at this time of the year we can look into the middle of the Milky Way, a place that is full of nebulae. If the majority of nebulae are HII regions then the majority of the nebulae towards the core of the galaxy should be as well, and they are. These nebulae are places where stars begin, as these nebulae are areas with a lot of hydrogen close together, and the stars are made of hydrogen. Particularly in the darker areas, the places that are so full of hydrogen that you aren’t able to see the light of the stars behind them. Those parts of the nebula have too much hydrogen too densely associated for us to see the light behind them.

The Eagle Nebula is a very good example of this. It is broadly bright, a reddish emission nebula, but with distinct lobes or pillars of dark cloud. The central ones in particular are called The Pillars of Life or the Pillars of Creation, and the hydrogen in here is gathering together due to gravity. If you are out in space, even if you are down here on Earth, everything has gravity, everything has a pull. If there is a cloud of hydrogen, when a couple of hydrogen atoms draw close together, there’ll be more gravity coming from the place with a couple of more atoms, Once a few atmos cluster together, then more and more atoms are pulled. After a while you have a whole a collection of atoms, a swirling ball of gas, and that’s the collection of hydrogen that you have to get to create nuclear power, to perform nuclear fusion. In order to create energy from nuclear fusion, atoms need to collide. For this, you need to collect a lot of atoms together, so that the pressure on the atoms is so high that the atoms have to collide. The atoms are happy to sort of, collect up in a ball, swirling around without collisions. You need to get a lot of mass, to generate a lot of gravity, to put a lot of pressure on the atoms in order to push them so close together that they collide in the right way to do nuclear fusion.

Once the stars start creating that energy, they start to clear the nebula around them. The light and heat from the stars open up spaces in the nebula. We can see these in almost any HII nebula we look at. When we look at such a nebula, normally they aren’t completely dark, as there are a couple of stars already after starting. The light from the new stars illuminates the nebula. Taking a look at the Lagoon Nebula, there are a lot of stars, very close together, in the center. That is a cluster of stars that began within the nebula. The light and heat from those stars is pushing on the nebula. Around the sides are more of those pillars starting again. Each pillar has a cluster hydrogen near its tip, a sort of proto-star, the star isn’t burning or fusing anything yet. The light and the heat from the stars that are after starting, their solar wind is gathering the hydrogen together. There was a cluster of hydrogen in the center, now the hydrogen is collecting out along the edges, and new stars will be made their.

That’s one of types of star cluster. There’s another star cluster that we have discussed before on this website, a spherical or globular cluster of stars. That’s a sort of different type of star cluster, composed of old stars that have collected up at the edge of our galaxy the Milky Way. The clusters of young stars are open clusters, composed of new stars that are after starting in their nebula, but are on their way sort of out of that nebula. Their solar wind is pushing the nebula out of the way. The Seven Sisters or the Pleiades are the example I normally use for an open cluster of stars. Taking a close look, there’s a little nebulosity that we can see, but there isn’t much trace of their first nebula, the place from whence they came. The stars are still close together, but they are still older than the cluster of stars we can see still embedded in the Lagoon Nebula. The Pleiades are still an open cluster of stars, they are a little bit older, but still they are very close together.

That’s the way in which the stars begin, and after a while they spread out more and more. The Pleiades are certainly visible in the morning, with the Hyades, just next to Venus, coming up closer to sunrise. They form a sort of triangle or V shape, with the bright star Aldebaran on one limb. The majority of those stars are still moving the same way at almost the same speed, because they came from the same nebula. They are still considered an open cluster. Even if we look at the Plough or the Big Dipper, the tail and the back of the Big Bear Ursa Major, the majority of those stars are also still moving in the same way at the same speed, as they came from the same place. They form a moving group, all moving in the same direction and the same speed, but not close enough to be called an open cluster any more. Not every single star of the Plough is part of the same team, but the majority of them are. Just the two ends, Dubhe on one side and Alkaid on the other, move in a different way. Stars spread out like that over the course of their very long lives, but I will have to save that bit about how long their lives are and how they change over their lives for another time.

I hope that you enjoyed this piece talking about the start of a stars life, how they begin, from where do they come, and maybe in another piece we’ll have the chance to look at where they are going. If you did enjoy this piece make sure you press the button that says that you liked it, and also if you enjoy this sort of topic generally, then you can subscribe to this website and my YouTube channel. Thank you very much for reading and I’ll see you next time.