If the Sun were a basketball in New York City, Proxima Centauri would be a golf ball in Warsaw, almost 7,000 km away. This speaks to how empty a galaxy really is – not only because the stars are so far apart but because there’s so little in between them that we can see so many in our sky at night.
Staring us all down from 655 light years away, the Helix Nebula is the graveyard of a solar system that may have been a lot like ours. Today, what was once the solar system’s sun is now a white dwarf about the size of the Earth. Creepily, some comets still orbit around inside the nebula, like zombies wandering around a cemetery.
The Horsehead Nebula is one of the most beautiful natural spectacles in the Universe. Our only objection is that scientists obviously misnamed it — we don’t know about you, but we clearly see a duck in that main cloud rather than a horse head. The pink glow in the background is ionizing gas that is illuminated by a nearby star. East of the Duckhead Nebula there is a very active star formation region, containing very young stars with masses similar to our Sun.
In 1840, the highly British 3rd Earl of Rosse noted this object through his 0.9 meter—long telescope and sketched out what he saw. The drawing looked like a crab and so the Crab Nebula’s nome came to be. Eight years later, the 3rd Earl of Rosse had upgraded to a double—size telescope and was like, “oh wait no it doesn’t look like a crab” but no one cared, so that was that. The Crab Nebula is 6,500 light years away from us and is the fallout from a supernova that happened in 1054 AD. The effects of the supernova are still so powerful that the nebula keeps expanding at an incredible rate of about 1,500 km/s.
This cone—shaped nebula, 2,700 light years away from us and a neighbor of the festive Christmas Tree Cluster, stands an outrageous 15 light years high. If the Cone Nebula were the height of a 50—story skyscraper, our Solar System would be the size of a 10 cm drink coaster and our Sun would be the size of a silt particle, far too small to see with the naked eye.
The strong interaction is, as suggested by its name, the strongest of all interactions. It is about a hundred times stronger than electromagnetism (and about a hundred trillion trillion trillion times stronger than gravity). How is it possible that we almost never hear about this interaction if it has such an immense strength? The problem is that its range is just billionth of a millionth of a meter. It may seem that a force with such a short range would never be able to influence our universe in a significant way, but the truth is that without the strong interaction, humans would never be able to exist.
As already mentioned, the universe was flooded with elementary particles right after the Big Bang. Those then started clumping together to create composite particles – quarks started forming protons and neutrons. But what caused them to attract? Why were quarks so keen on creating more complex particles? As you may already suspect, the attraction between individual quarks was provided by the strong interaction.
It does not end here, though. The strong interaction is to blame for another crucial phenomenon of our reality – the existence of atoms. We already know from the previous chapter that the same electric charges repulse each other. However, this means that protons in the nuclei of complex atoms should repulse and escape into all conceivable directions. But the strong interaction ensures that protons remain together. If electromagnetism were just a tiny bit stronger than the strong interaction, the existence of atoms would simply be impossible.
The final force, the weak interaction, may be the least known and the least interesting of all interactions. However, this is not to say it is not important. The weak interaction has the power to turn a neutron into a proton. Why would it do that? Within some atoms, there is an unstable ratio between the number of electrons and the number of protons in the nucleus. And the weak interaction is here to make sure that this instability is eliminated. When there are too many neutrons in a nucleus, the weak force simply turns one of them into a proton. This phenomenon is called the beta decay.
As we know from the first chapter, the number of protons in the nucleus determines what atom we are dealing with. But this means that any time an atom undergoes beta decay, which adds one proton into its nucleus, the whole atom changes into a different element. The weak interaction can therefore turn carbon into nitrogen or hydrogen into helium just by turning neutrons into protons.
And that is all. We have reached the end of the story of interactions. They make sure that our universe functions the way it does and without them, we would have never existed – perhaps with the exception of the weak interaction, which is the only one that does not affect the course of the cosmos in a significant way. Now, we can focus our attention on another fascinating element of our universe – huge fusion factories which are making billions of photons each moment.
Tied with the Big Dipper for the biggest celebrity constellation, Orion is the great hunter in our night sky. If you look carefully on a clear night, you can see the great Orion Nebula right beneath Orion’s belt. The nebula contains on estimated 2,000 times the mass of our Sun and is one of the best—observed stellar nurseries — a hotbed of new stars. Observing the Orion Nebula has helped astronomers understand more about how stars and planets form.
Incredibly vast and only 1,600 light years away from us, if the North America Nebula were brighter, it would be the size of the full Moon in our sky. If we scaled the nebula down to the actual size of North America, the Earth would be the size of a grain of sand.
“Lagoon” is what you name a nebula that doesn’t look like anything. This amorphous nebula is actually pretty close to us, as far as nebulas go — only 4,100 light years away. It’s one of only two nebulae visible to the naked eye (from the northern hemisphere), but it’s pretty dim so don’t get your hopes up.
This epic space rose is 5,219 light years away from us in the Milky Way, and stretches 130 light years across. If it were the size of an actual rose, the Milky Way would be a pond 60 m across that the rose was floating in.
Keishinrei