Red dwarfs are the most common type of star in the galaxy. At less than half the Sun's mass, they are relatively dim. That makes them an ideal hunting ground for planets, which can easily go undetected in the glare of brighter stars.
But these little stars have big tempers. When they are forming, they shine about 10 times as bright as they later will, and can unleash powerful flares of radiation. This "adolescent" period can last a billion years, and it can be bad news for life.