Scientists Say: Red Dwarf | Science News for Students

Scientists Say: Red Dwarf

These small, relatively cool stars are the most common residents of the Milky Way
Apr 8, 2019 — 6:30 am EST
an illustration of a red dwarf behind a planet and moon crossing in front of it

Red dwarfs, such as the one pictured here glowing red in the background, are small. But that doesn’t mean that couldn’t have a planet or two, such as the planet and moon crossing in front.

D. Aguilar/Harvard-Smithsonian Center for Astrophysics/NASA/Wikimedia Commons



Red dwarf (noun, “Red DWARF”)

A red dwarf is a type of star. Red dwarfs are between 0.075 and 0.5 of a single solar mass. That means even at their biggest, they’re only half the size of our sun. Red dwarfs are also cooler than the sun. They only reach about 3,700° Celsius (6,700° Fahrenheit), compared with the 5,500 °C (9,900°F) of our sun.

Most of the stars in the Milky Way are red dwarfs. You’d never know by looking up at the sky, though. Red dwarfs are very hard to see. That’s because they are so cool. A star’s temperature determines how bright the star is and what color we perceive when we look at it. Yellow dwarf stars like our sun are hotter and give off more energy. We perceive these stars as yellow or white. The cooler temperatures of red dwarf stars means that they give off less energy, and their light is reddish. That red color is much harder to see. That means they’ll escape any stargazing that you try without a telescope. 

But just because they’re small and cold doesn’t mean these stars are lonely. Red dwarfs can have planets orbiting around them. For example, scientists know that our nearest stellar neighbor, Proxima Centauri, is a red dwarf star with at least one planet.

In a sentence

Our sun’s nearest star neighbor — Proxima Centauri — is a red dwarf star.

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Power Words

(more about Power Words)

degree     (in geometry) A unit of measurement for angles. Each degree equals one three-hundred-and-sixtieth of the circumference of a circle.

exoplanet     Short for extrasolar planet, it’s a planet that orbits a star outside our solar system.

mass     A number that shows how much an object resists speeding up and slowing down — basically a measure of how much matter that object is made from.

Milky Way     The galaxy in which Earth’s solar system resides.

red dwarf     A type of smallish star that is relatively cool (and hence emits reddish light). Red dwarfs are the most common size stars in the Milky Way.

star     The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become dense enough to sustain nuclear-fusion reactions, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.

sun     The star at the center of Earth’s solar system. It’s an average size star about 26,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.

telescope     Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.