Stars - From Beginning to End
Nothing in this universe lasts forever, and stars are no exception. Despite their amazingly long lifespan, stars will eventually go out, spreading their materials across the universe to plant the seeds of the stars that will come after them.
But let’s start somewhere that makes a little more sense.
The Beginning
Stars are born in huge clouds of gas and dust called nebulae. Before the star forms, it’s called a protostar; a collection of gas that is collapsing under the force of gravity. This phase lasts about 100,000 years before the protostar becomes a proper star.
The nuclear reactions at the core of a star provides the energy that it needs to emit light. As long as the star has fuel, it can keep on shining.
Smaller stars use up fuel slowly and last for several billion years. Very large stars, on the other hand, burn through their fuel much quicker, so they only survive a measly few hundred millennia.
Once the hydrogen that powers the nuclear reactions within a star begins to run out, the star will make its first transformation. Regardless of size, the star will expand, cool, and change colour, becoming a red giant. This is where the paths of small stars and massive stars diverge.
Image courtesy of nasa
Small Stars
Small stars, like the Sun, will gradually cool down and stop glowing.
At the end of their red giant phase, smaller stars turn into a planetary nebula. At this point, the star becomes very unstable and begins to produce strong stellar winds which tear away the outer layers of the star. All that’s left is the bright core of the star, called a white dwarf.
The white dwarf, composed of carbon and oxygen, is created during the star’s previous phases. All the material is packed into a relatively small space, making the white dwarf very dense. It’s like trying to squeeze the mass of the Sun into a space the size of the Earth!
Speaking of the Sun, if it doesn’t consume Earth in its red giant phase, our little planet’s orbit will slowly decay, and it will spiral into the dead Sun over a trillion years.
Finally, after thousands of millions of years, the star will stop glowing and become a black dwarf. It’s a rather peaceful death compared to their much larger cousins.
Massive Stars
image courtesy of nasa
Massive stars meet a much more exciting and violent end.
After its red giant phase, a massive star will collapse in on itself. The gravity of the star gets so strong that it pulls the outer layers of the star towards the centre. The outer layers bounce off the core of the star at incredible speeds, causing shock waves and triggering a supernova explosion.
Supernovas can briefly shine brighter than an entire galaxy, scattering the star’s insides across space. It sounds gory, but these materials help form the next generation of stars by gathering in nebulae.
In the aftermath of the supernova, a very dense neutron star is left in the massive star’s place. This forms when the outer layers collapse inwards. They squish the core to the point where its atoms are smashed apart and only neutrons are left behind.
With one final shock wave, the outer layers are launched into space, sending the neutron star spinning extremely fast. Some neutron stars rotate several hundred times per second!
Remember my mass comparison from before? This is even worse. Neutron stars usually have the mass of 1 or 2 Suns, but are only about 20 km across. The only thing denser than a neutron star is a black hole.
Speaking of black holes, supermassive stars can form a black hole when they explode instead of a neutron star if they’re big enough.
The End
So, after hearing all this, would you rather die a slow but peaceful death or go out with a bang?
To the rest of the universe, we humans live meager little lives, but we aren’t the only ones. Stars only last for only a fraction of a second compared to the life of the universe.
Everything is impermanent. What matters is what we leave behind, whether our legacy is a white dwarf or a black hole.
Sources
JAX YOUNG — Space enthusiast here to take you on a tour of the cosmos. Gets emotionally attached to Mars rovers. Virgo.