Background
Nebulae, the plural form of nebula and pronounced “Neb-you-lee”, are amongst the most spectacular sightings in our universe and are, although not without help, are responsible for the formation of stars.
Perhaps you've heard of some of them before, such as the Orion Nebula or the Horse Head Nebula, maybe not! But you can even spot them with the naked eye on a clear night in some dark sky areas.
If you're interested in knowing the location of a dark sky area near you, then feel free to check out this website (It's very handy).
Now, the first thing to understand is that nebulae can vary a lot in size, with the smallest known nebula being the Cat’s Eye Nebula, which is around 0.4 light years across, and the largest being the Tarantula Nebula, coming in at a whopping 1,860 light years, which is even bigger than some dwarf galaxies!
But what actually are they, and do they come from?
A close-up image of the Horse Head Nebula. Image Credit: NASA
Interestingly, nebulae essentially come from themselves.
Overtime, gravity and dark matter pulls the nebulae together to form a single or perhaps multiple clusters of highly dense, hot gas that we call protostars.
These protostars then evolve into main sequence stars, like our Sun, and one way or another end up ejecting their own matter into space again, creating another nebula.
The reason why I say "one way or another" is that the process differs from star to star depending on how massive they are, and I go into more detail about processes in this article here.
Although I'll briefly describe the cycle below for sake of ease.
The collision of atoms at the very core of a star is what’s responsible for the outward force that’s stopping the star from collapsing under its own gravitational force, but there’s only so many atoms that can collide.
After what’s mostly billions of years for the average star, the atoms available for nuclear fusion, which is the process of two atomic nuclei colliding together, is insufficient enough for the outward force produce by said atoms to equal the force of gravity that’s trying to collapse the star.
At this point, the star begins to collapse in on itself and depending on its mass, several different outcomes can happen.
If it’s a massive star then either a black hole or neutron star will be formed, and if it’s a less massive star, then a white dwarf will form.
In the case of the Sun, it’s predicted that a white dwarf will form due to the Sun having a relatively small mass.
Taking a step back...
Imagine pouring water through a pipe - there’s only so much pressure that the pipe can take and if it’s too much, it will burst open - similar situation with a star, only this "burst" is one of the most powerful events that we can recognise in our universe.
This explosion is called a supernova, or in the case of really massive stars, a hypernova, which is thought to be 10-100 times more powerful than a supernova.
That's the outcome for stars with enough mass, but for those who aren't quite massive enough like the Sun, they simply expand outwards until the gases are so far away from the centre of mass that they lose their binding attraction and achieve velocities higher than the escape velocity at that distance.
Therefore, they simply run off into the cosmos forming a planetary nebula.
Think of it as a star shedding its skin.
The energy released during a supernova is unimaginable, but if you’re feeling optimistic, try thinking about this:
If the sun were to go supernova in approximately 4 billion years, it’s expected that the amount of energy that will be released during this explosion will be equivalent or even surpass the amount of energy that the sun will have released over it’s entire 10 billion year lifespan….
10 billion years worth of energy released in seconds!
All this mass (well some is left behind in either of the 3 forms that we talked about earlier) is ejected into space at speeds of over 15,000 miles per second.
If you’ve read my article about the life cycle of a star, then you’ll know that the mass that’s ejected comprises of all the elements that we know of today in the form of what we call star dust.
Star dust is essentially a refinement of the word nebula - they're both somewhat interchangeable with each other, in that a nebula consists of star dust.
Have you ever wondered where all the elements on Earth come from?
The oxygen, the gold, the carbon, the iron... etc
Everything that you can think of came from star dust.
As a star thrived, it produced every element up to Iron (which again is explained in the other article) but as it began to collapse, heavier atomic nuclei began to fuse together to form the nuclei of gold, platinum etc...
I would say just take a look at the periodic table, but we’re discovering more elements as technology advances so it’s hard to give an “up to this element” statement.
And here's the Crab Nebula - there's also a pulsar at the centre of this which formed from the supernova (along with the nebula of course). Credit - NASA
This star dust that’s now spread across space as a cloud-like formation is what we call a nebula.
They come in many different designs, lots of which oddly resemble things on Earth quite well I think (although some are definitely questionable...)
The next generation
What’s remarkable though is that over time, parts of the nebula start to clump together once again due to the combined attractive forces of dark matter and gravity.
As they become bigger and more massive, their gravitational field strength increases and they start to pull in even more matter, which consequently increases the pressure of the atoms at the centre of this clump.
I have several articles about the dark universe in draft form, so definitely consider signing up so that you can be notified when they go live!
As this happens over millions of years, it starts to get the point where, if there’s enough matter present, these clumps will become so big that the pressure at the cores will start to become great enough to force hydrogen nuclei together, forming helium and releasing an immense amount of energy.
The release of energy is in accordance with Einstein's theory of special relativity, which outlines the mass-energy equivalence in the famous equation e =mc².
Einstein proposed that mass and energy are manifestations of the same thing, and can be directly converted from one to the other, where even a small mass is proportional to an inconceivably large quanta of energy.
The c in e =mc² stands for the speed of light which is 300 million m/s.
As you can imagine, 300 million squared multiplied by virtually any mass value would be an incredible amount of energy.
Now what you have is the beginning of the next generation of stars in our universe, and in many cases planets too.
If you’re wondering why some clumps of gas become stars and other planets, then check at my posts about the Saturn here
So a nebula essentially becomes a nursery for potentially tens of stars.
Over the course of millions of years, many possibilities can happen - some stars might collide with others to form even bigger stars, some stars will start to orbit other ones close by so you end up with binary star systems like in Star Wars, and some stars might completely dissociate with the group.
Here's the Tarantula Nebula, which is the largest known nebula, coming in at over 1,800 light years across! Image Credit: NASA
In fact the nearest star system to us, Alpha-Centauri, is a triplet star system where you have 2 stars orbiting quite closely to each other, and another one third partying on the outskirts.
If you’re an avid star-gazer, then you’ll probably know that one of the coolest things you can see in the night sky is the Pleiades, otherwise knows as the Seven Sisters, which is a collection of 7 very bright, young stars that are currently thriving under the same nebula nursery.
They’re estimated to only be a couple of hundred million years old (which might come as a surprise is very young by the standards of the universe), so if you haven’t seen them yet, then don't worry, because you’ve got at least another 250 million years to see them in this state!
I think we’ll conclude this article by saying that nebulae are essentially the beginning of new ends, and are some of the most spectacular things that you can see with a pretty basic 6-8 inch reflecting telescope.
If you're interested in investing in a good quality telescope, then I'd recommend checking out my product reviews here.
To round it off, meet the Cat's Eye Nebula, which is the smallest known nebula, at around 0.4 light years across. Image Credit: NASA
Thanks for reading!