The Theory of Nothing

What's so special about the sun?

What’s so special about our sun?

This also sounds like a dumb question, but it’s a very important one. The ancients had no idea there was a connection between the sun that they saw during the day and the tiny lights in the heavens at night. Eventually, astronomers realized that the stars in the night sky were in fact suns very far away. But, they were curious because, as you know, if you look up at the stars at night you see that stars have different colors. The problem is that the ancients had no idea how the sun or the stars work. They thought of the sun as a big ball of fire, but once they realized how far away the sun was and how large it was, they realized that it could not be powered by burning fuel. The true understanding of what powered the sun didn’t come until mankind knew about nuclear fusion.

Nuclear fusion is when two hydrogen nuclei stick together to form a helium nucleus. Protons, the particles that make up the hydrogen nucleus, are positively charged and, as you know, like charges repel. The only way these protons can be forced to collide and fuse is when they are heated to millions of degrees and are compressed to a very high density. This is what happens in the core of the sun. The sun is nearly a million miles in diameter and the mass (330,000 times that of the Earth) of the hydrogen gas is highly compressed by gravity, and when gas is compressed it heats up, enough in the Sun’s case to cause fusion to take place. The core of the sun is like billions of hydrogen bombs going off at the same time. If that’s the case, why doesn’t the sun explode? That doesn’t happen because of the intense gravity. There is a constant battle between fusion and gravity in the sun’s core. This balance between these two forces is what stabilizes the sun for billions of years.

We’ll look at what holds a nucleus together in another post, but for now let’s assume that there is a very powerful force that does this.

When fusion between two protons takes place to form helium, energy is released in the form of a gamma ray photon (a particle of light). This photon wants to get the hell out of the sun’s core but it can’t, as least not right away. It keeps bouncing into protons and getting absorbed and reemitted. In fact this photon takes a hundred thousand years, and sometimes a million years, to reach the surface of the sun, and by that time it has degraded to a visible light photon. When it finally escapers the surface of the sun it only takes eight minutes to get to Earth. Whew! That poor photon really got banged around before it was set free!

Astronomers, being like accountants or zoologists, like to categorize everything, and stars are no exception. They rank stars into classifications according to spectra. For the sake of simplicity, we can think of the spectra as color. The color of a star is related to its surface temperature. O-class stars have temperatures over thirty thousand degrees Kelvin and are considered blue. They have masses over sixteen times that of the sun, and luminosities over thirty thousand times that of the sun. Can you imagine our sun being thirty thousand times brighter? Wow!

G-class stars are like our sun and are yellow in color. They have surface temperatures in the five to six thousand degrees Kelvin range (the Kelvin temperature system is based on absolute zero being 0 degrees Kelvin or -273.14 degrees Centigrade). Our sun is considered a yellow dwarf star, believe it or not, because compared to some O and A-class stars, it’s tiny. Many of these O and A class behemoths are over six times the radius of our sun, which is almost a half a million miles. Imagine a star having a radius of a billion miles.

Further down the spectrum list is the K-class stars with temperatures in the 3700 to 5200 K range. They are considered orange dwarfs. M-class stars are even lower in temperature and are considered red dwarfs. The problem with them is that they’re very small and have luminosities that are fractions of what our sun has, meaning that a habitable planet orbiting them would have be in a cozy orbit in order to receive enough heat to keep surface water liquid. If this was the case, the planet could be tidal locked to the sun, only allowing one side to be turned toward the sun. This would mean that one side would be hotter than Hell and the other side frozen. Our planet Mercury is like that.

The main thing to remember here is that G-class, K-class and even M-class dwarf stars are prime candidates to have habitable planets orbiting them. The reason they’re considered to be candidates is that these dwarf stars are more common among the stars of our galaxy and they stay on the main sequence for billions of years. Stars are considered to be on the main sequence while they fuse hydrogen into helium. It’s during this time that they are stable, meaning they aren’t getting ready to die.

Yes, stars die, and when they give up the ghost they wreck havoc on the planets that orbit them.

Our star is special because it harbors a planet that has life--us. If life happened on Earth around a G-class star, then it could happen around other G-class stars. The reason K and M-class stars are included in this desirable group is because they stay on the main sequence for billions of years and that gives planets around them time to spawn life. It also gives this life that develops time to evolve into an intelligent species--like us.

Thanks for reading.