Red dwarf stars are the most common stars in the universe; roughly 73% of the stars in the universe are red dwarf stars. Scientists believe that 20 of the 30 stars closest to Earth are red dwarf stars.
Unlike other stars known as ‘dying stars’, red dwarf stars do not fit into this category- in fact they live for so long that not a single one in the universe has reached an advanced stage of evolution (and therefore none have died).
It’s very possible that after trillions of years, red dwarf stars will be the last remaining light in the universe. For context, the universe is currently less than 14 billion years old.
While it’s likely to be trillions of years away, red dwarf stars will eventually burn through their fuel supply and become white dwarf stars- or, in other words, dead. Once a white dwarf has radiated all of its heat it will become a black dwarf.
The following article will break down the formation of red dwarf stars, their characteristics, how red dwarf stars are classified versus brown dwarf stars, the death of giant stars, and finally some of the red dwarf stars visible through backyard telescopes.
Formation And Characteristics Of A Red Dwarf Star
Red dwarf stars form just like other main sequence stars. In the beginning, a cloud of gas and dust comes together via gravity. The cloud begins to rotate, and the material clumps together at the center of the cloud.
The temperature rises, and when the critical temperature is met (100 million degrees), the process of fusion begins. The process of fusion involves the reaction of two hydrogen atoms combining (or fusing), which forms a helium atom. Some of the hydrogen is then converted into energy.
The category of red dwarf stars include the smallest stars, which weigh between 7.5 percent and 50 percent of the sun’s mass. This smaller size means they burn at lower temperatures- often just 6,380 degrees Fahrenheit (or 3,500 degrees Celsius).
In comparison, the sun’s temperature is 9,900 degrees Fahrenheit (or 5,500 degrees Celsius). It’s the lower temperatures of red dwarf stars that make them far dimmer than the sun.
The low temperature is also the reason that their fuel supply (hydrogen) is burned through at a slower rate, which in turn allows red dwarf stars to live as long as they do.
Massive stars, which tend to have a lifetime of a mere (ha!) 10 billion years, are only burning through the hydrogen at their core. Red dwarf stars consume the hydrogen both inside their core and outside.
Classifying A Red Dwarf
Scientists often struggle distinguishing red dwarf stars from brown dwarf stars. Brown dwarf stars likely form in the same way as red dwarf stars, and like red dwarf stars, they’re also cool and dim.
The main difference is that brown dwarf stars are so small that they never actually reach the fusion process. This means that they’re technically not even stars.
The most common way that scientists distinguish a red dwarf star from a brown dwarf star is through calculating the temperature. Brown dwarf stars are cooler than 2000 K, while red dwarf stars are warmer than 2,700. Everything between these temperatures could be either a red dwarf or a brown dwarf.
There are two other ways in which brown dwarf stars are believed to differ from red dwarf stars. Brown dwarf stars may have molecules such as ammonia or methane, as these can only survive in lower temperatures. If lithium is present in the atmosphere of a celestial object, this is also an indication that it’s a brown dwarf rather than a red dwarf star.
The Death Of Giant Stars
Giant stars, on the other hand, can be between three times the mass of our sun all the way up to 100 times the mass of our sun, at which point they would be considered hypergiants. The core of giant stars is constantly under extreme pressure purely from its own weight.
They shine intensely because so much energy is being burned up. In strong winds, particles stream out from these stars. The particles give off radio waves, which is what allows radio telescopes to pick up the presence of giant stars across the galaxy.
After about 100,000 years, the core will have fused all its available hydrogen into helium, and after this stage it takes roughly 200 years for the star to produce carbon, followed by oxygen, and then silicon.
Then iron will build up deep in the core of the star. The energy of this fusion process will stream into the atmosphere of the giant star, making it a red supergiant.
Over time the iron will require energy, making it a parasite in the core of the star. Eventually the weight of the star’s atmosphere crashes into its iron core. The electrons are smashed into protons and they form neutrons, producing a large amount of energy.
This energy propels the star’s gasses out into space, and the explosion of the dying star burns incredibly bright, which is what’s called a supernova.
Red Dwarf Stars Visible With Backyard Telescopes
Roughly 73 percent of the stars in the universe are red dwarf stars. While they litter the Milky Way, none are bright enough to be seen without a telescope. With an ordinary backyard telescope, though, there are a number of red dwarf stars visible.
These include Struve 2398, Lacaille 9352, Lalande 21185, Kapteyn’s Star, Barnard’s Star, AX Microscopii / Lacaille 8760, 40 Eridani C, and Groombridge 34.
Groombridge 34 was discovered in 1860. Its large proper motion is 2.9” arc seconds each year. Barnard’s Star is found in the second closest star system to our solar system, after Alpha Centauri.
It’s the closest single star, at six light years away. Its proper motion of 10.3” second each year is the highest of any star. Luyten’s Star is 12.36 light years away, and 1.2 light years from Procyon.
Lalande 21185 is 8.3 light years away, and at its closest it will be 4.65 light years away. In under 20,000 years it will be visible to the naked eye on Earth. Kapteyn’s Star orbits in retrograde, and at 12.76 light years away, it’s the closest halo star to Earth. It was discovered by Jacobus Kapteyn back in 1898.
Conclusion: Is A Red Dwarf A Dying Star?
A red dwarf star is not a dying star- no red dwarf stars have died in the history of the universe, as their lifespan is trillions of years. They will likely be the last light in the universe, once all other stars have burned out.
They will eventually die once they’ve burned through all of their fuel (hydrogen) at which point they’ll become white dwarf stars. Once all the heat has been radiated, they become black dwarfs. So, a red dwarf star does eventually die- just not on a timescale fathomable to humans.
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