Astronomy and space are notorious for their size problems. The largest star, largest nebula, prettiest, most talented galaxy, largest universe, and which comet won the bikini contest. The usual blah blah.
We’re going to examine the opposite extreme of the spectrum in an effort to slightly balance the scales. We’re talking about little stars today. Before we talk about the cute small teeny little fusion factories, I’m going to finish the Gary Coleman and Emmanuel Lewis joke.
When there is enough hydrogen in one place to be many times the mass of the Sun, we can form large stars. Naturally, we’ll need less hydrogen to create smaller stars, but there’s a limit to how little hydrogen we can have before solar fusion cannot be ignited at the proper core temperature and pressure. Then it becomes a glob and a mess. In aisle Andromeda, cleanup is underway. It is they who failed to replace the lid on the H-labeled jar.
How little can stars get, then? What is the tiniest star that we are aware of? According to conventional definitions, a star is an entity with sufficient core mass and pressure to begin fusion, converting hydrogen atoms into helium.
Exothermic fusion releases energy. This energy works to repel the gravitational attraction that pulls everything inward. As a result, the star doesn’t collapse in on itself and you can determine its size.
By a strange quirk of nature, our Sun has exactly one solar mass. That’s not true at all; rather, it’s our guilt that we compare other stars to our Sun. This may be the origin of a company of this scale. We are engaged in a never-ending measurement competition to see whose star is the most massive and has the biggest circumference.
It turns found that even when a star’s mass is reduced to 7.5% of that of the sun, fusion events can still occur inside of it. This is the red dwarf that you are familiar with. We haven’t had a chance to measure many red dwarf stars, but Proxima Centauri, the closest star, is about 200,000 kilometers across and has a mass of around 12.3% that of the Sun. In other words, Jupiter would only be around 50% larger than the smallest red dwarf that could exist.
There is a significant difference; this red dwarf star would be around 80% as massive as Jupiter. It may sound absurd, but adding more hydrogen doesn’t actually enlarge the star all that much. As the star is drawn closer together by gravity, it merely becomes denser.
This is the tiniest known star at the time I’m shooting this video. It has 9% the mass of the Sun, which is just a hair larger than the smallest theoretical size.
The second-closest star to Earth after the Sun, Proxima Centauri has a mass of around 12% that of the Sun. But without a telescope, it is much too faint to be seen. In actuality, the naked eye cannot see any red dwarfs. 61 Cygni, a binary pair with one star that is just 66% the size of the Sun, is the tiniest star that you can currently view. In clear skies, you can just barely make it out because it is only 11.4 light years distant. Then comes Spock’s home planet Epsilon Eridani, which is 74% the size of the Sun, followed by Alpha Centauri B, which is 87% larger, and finally the Sun. So, now you know your new geek party trivia. The Sun ranks as the fourth-smallest star that can be seen with the naked eye. The Sun is dwarfed by every other star that can be seen. All of them are enormous, terrible monsters.
And finally, when compared to the tiniest stars in the universe, our Sun is enormously enormous. Because it belongs to us and is the source of all life on Earth, we like to conceive of our Sun as being absolutely adequate for our requirements. It is the perfect size for us. So don’t even think about the other great stars that are out there.
