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

https://astrobackyard.com/types-of-stars/

https://www.schoolsobservatory.org/learn/astro/stars/cycle 

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JAX YOUNG — Space enthusiast here to take you on a tour of the cosmos. Gets emotionally attached to Mars rovers. Virgo.

Black Holes - Brilliant but Deadly

Black holes! You know ‘em, you love ‘em. What’s not to like about giant vacuums that turn you into a spaghetti noodle if you get too close?

In more scientific terms, black holes are a huge amount of matter packed into a very small space. The result is a gravitational pull that’s so strong that nothing can escape, not even light.

But how do they happen?

If a star is big enough (around 3 times the size of the sun), nothing can keep it from collapsing under the influence of gravity, causing a supernova explosion. At one point, the surface of the star will reach the “event horizon.” When it reaches this point, time on the star slows and literally stops.

Then, because time is standing still, the star can’t collapse any further. It remains frozen in the middle of caving in on itself and becomes a black hole.

Types of black holes

There are 2 major kinds of black holes: stellar mass and supermassive.

Stellar mass black holes are the average Joes of black holes. They are the remnants of massive stars and are all over the universe. In fact, scientists predict that there are ten million to a billion stellar mass black holes in the Milky Way alone.

Image courtesy of nasa

On the other end of the spectrum of giant space vacuums, supermassive black holes are millions, if not billions of times as massive as the Sun. Astronomers believe that supermassive black holes are at the centre of almost all large galaxies, including our own.

The formation of supermassive black holes is theorized to be a chain reaction of collisions of stars that results in extremely huge stars, which promptly collapse to form medium-sized black holes. All these black holes gravitate towards the centre of the galaxy and merge together to create a supermassive black hole.

So, there’s only two sizes of black holes with no in between? Well, that’s what scientists thought until recently.

The newly discovered mid-mass black hole has the mass of about 500 to 1000 Suns, and kind of wrecked a bunch of theories about the formation of black holes.

What’s inside?

The center of a black hole is called the singularity. It doesn’t really exist.

I want to call it the point of no return to be dramatic, but honestly if you’re anywhere near a black hole, you’ve already reached that point.

The singularity is the place where matter sucked into the black hole is compressed down to an infinitely tiny point… theoretically.

Or it could be where matter gets squished into the smallest possible volume, a Planck length. Everything that has ever entered the black hole gets compressed into a microscopic ball… theoretically.

Black holes could be filled with dark energy—the stuff that causes the universe to expand. As things get sucked in, they can’t actually get past the event horizon because of all that dark energy and instead remains on the surface… theoretically.

All this to say, we don’t know for sure what’s inside of black holes. I mean, it’s not like we can send someone inside to go check.

Rotating Black Holes

All of the fun stuff I’ve mentioned already are about boring, stationary black holes, but rotating black holes are where things get beyond cool (if the theories are correct, that is).

Image courtesy of pixabay

The spin of a rotating black hole turns the singularity into a ring. Once you pass through the ring, you enter a real-life wormhole that spits you out into an entirely different part of the universe.

Of course, if you were to encounter the inside of a rotating black hole, you would be faced with a wall of infinitely energetic radiation.

The black hole is pulling radiation in, but the rotation speed of the singularity ring pushes the radiation back. The turning point is called the inner horizon.

That’s the entire past history of the universe blasted into your face in less than a second!

Too bad you’ll be too busy being a noodle to notice.

Sources

https://science.nasa.gov/astrophysics/focus-areas/black-holes

https://chandra.harvard.edu/xray_sources/blackholes.html

https://www.space.com/what-happens-black-hole-center

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JAX YOUNG — Space enthusiast here to take you on a tour of the cosmos. Gets emotionally attached to Mars rovers. Virgo.

The mystery of dark matter

Wondering what space is made of? Well, so is everyone else.

It all started with Swiss astronomer Fritz Zwicky in 1933. He was measuring the speed at which the Coma galaxy cluster spun and noticed that the cluster was moving at a speed that implied much more mass than what was visible. Zwicky theorized there was some sort of “missing mass” keeping the galaxies from escaping the cluster’s gravitational pull.

In the 1970s, American astronomer Vera Rubin and her colleagues confirmed Zwicky’s theory. They observed that the mass of the stars within an average galaxy is only about 10 percent of what is required to keep those stars orbiting the galaxy’s centre.

Thus, the mystery of dark matter was born.

Composition

But what is all this “missing mass”? Space fog? Alien interference? Billions of tonnes of invisible primordial soup, the first ever forbidden snack? Maybe.

Image courtesy of unsplash

The truth is, we know more about what dark matter is not than what it is.

The first thing we know is that it isn’t visible to the eye. Dark matter is, well… dark. Its presence is detected by its gravitational pull rather than its luminosity or its ability to reflect light. This means that scientists need to get creative when it comes to measuring dark matter (but I’ll get to that later).

It also isn’t antimatter. Dark matter doesn’t produce the unique gamma rays antimatter does when it collides with regular matter.

Finally, it is not the same as the dark clouds of matter in and between galaxies. These gases are made up of baryons (protons, neutrons and the like), familiar and recognizable to any scientist with a degree in astrophysics. But a common belief is that dark matter isn’t baryonic at all. Instead, it’s assumed to be made up of particles that exist in theory but have yet to be observed.

That’s a longer way of saying we have no idea what this stuff is made of.

Measurement

It’s later, and now is the time to talk about measuring dark matter!

Scientists can indirectly measure dark matter through a method called gravitational lensing. Like with optical lenses, light passing through a gravitational lens gets bent, not unlike myself when I advise my brother to put anything but hot sauce on his vegetables.

When light from distant stars passes through a galaxy, the gravity of the matter in that galaxy causes the light to bend. As a result, the light looks like it’s coming from somewhere other than its actual origin. Many NASA scientists use the Hubble Space Telescope to observe the amount of bending to learn about the dark matter present in a certain galaxy or cluster.

image courtesy of unsplash

Theories

There are no small number of theories surrounding dark matter, but I’ll only cover some of the major ones.

Dark matter could be brown dwarfs—stars that never ignited because they lacked the necessary mass. Or maybe the remnants of the cores of dead small or medium sized stars, called white dwarfs. Dark matter might even be neutron stars, or giant galaxy-sized black holes, or literally magic.

Okay, probably not that last one.

The issue with those theories is that there just aren’t enough failed or dead stars to account for the amount of dark matter in the universe.

Dark matter makes up roughly 30 percent of the universe’s matter-energy composition (literally everything in the universe). I mean, that’s a substantial percentage, but it’s not that much, right? It may seem that way until you learn that everything on Earth and everything NASA has ever observed with all their fancy telescopes adds up to less than 5 percent of the universe. What a way to make you feel small.

The rest of the composition is dark energy, but that’s a whole other can of worms.

Conclusion

To this day, the nature of dark matter remains one of the greatest astronomical mysteries. Despite being aware of it for nearly a century, we know very few things about dark matter that aren’t (at least in part) theoretical. All we know for sure is that it’s there, and it’s keeping all those really pretty galaxies together. Everyone say thank you, dark matter!

Sources

https://www.britannica.com/science/dark-matter

https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy

https://www.nasa.gov/audience/forstudents/9-12/features/what-is-dark-matter.html

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JAX YOUNG — Space enthusiast here to take you on a tour of the cosmos. Gets emotionally attached to Mars rovers. Virgo.