Sunday Science: Red Dwarfs and Main Sequence

TRAPPIST-1 Red Dwarf and its planets. Photo: NASA / JPL-Caltech

No you smeghead, I'm not talking about the smash Brit comedy Red Dwarf.

Accounting for 80% of the stellar population, Red Dwarfs are the most common type of star in the universe.

​They are smaller than our Sun with between 7.5% and 40% of its mass. Their reduced mass means they have a cooler surface temperature of approximately 3,500K, compared to 5,750K for our Sun. ​A Red Dwarf generates energy in the same way as our Sun, fusing hydrogen into helium.

​Because they are small and cool stars, there's less nuclear fusion and so Red Dwarfs emit only around 10% of the Sun's light - some of the smallest examples have just one ten-thousandth of the Sun's luminosity.

​One of the major differences between Red Dwarfs and other stars is that they're "convective". What this means is that when hydrogen fuses to form helium, the helium does not accumulate in the core. Instead, the helium is continually being mixed throughout the star.

​This means that the nuclear reactions in the star are slowed down and Red Dwarfs have a very long lifetime. It's estimated that a Red Dwarf with a tenth of the Sun's mass will live for at least 10 trillion years. And the lighter a red dwarf is, the longer it lives. ​Because they have such a long life, Red Dwarfs are used to calculate the age of star clusters. 

​Computer modelling suggests Earth-type planets are more likely to form around Red Dwarf stars. One Red Dwarf hit the headlines in February when NASA announced it had seven Earth-sized planets, with two planets orbiting the star in its habitable zone. The TRAPPIST-1 Red Dwarf is 39 light years away from Earth.

A quick note on star classifications

Image from http://www.atlasoftheuniverse.com

Main sequence stars are classified by their temperature. The hottest are blue stars and the coolest are our Red Dwarfs.

76% of main sequence stars are Red Dwarfs (Deadpool, Flash and Ironman - classification M), 23% are Yellow Dwarfs (Aquaman - F, G and K) and 1% are Blue Stars (Aquaman's hand O, B and A)

Extra reading

Did you know that about 40% of Red Dwarfs host "super earth" planets? Click here to read 10 interesting facts about our universe's most popular stars. Here's a great little video explaining Red Dwarf stars:

And I couldn't live with myself if I didn't include one video from the Red Dwarf show, here are the top 10 highlights from the sci-fi comedy:

What is Sunday Science?

Hello. I’m the freelance writer who gets tech. I have two degrees in Physics and, during my studies, I became increasingly frustrated with the complicated language used to describe some outstanding scientific principles. Language should aid our understanding — in science, it often feels like a barrier.
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So, I want to simplify these science sayings and this blog series “Sunday Science” gives a quick, no-nonsense definition of the complex-sounding scientific terms you often hear, but may not completely understand. 

If there’s a scientific term or topic you’d like me to tackle in my next post, fire an email to [email protected] or leave a comment below. If you want to sign up to our weekly newsletter, click here