Protostars reach temperatures of 2,000 to 3,000 degrees Kelvin. They glow a dull red and contain most of their energy in the infrared. Protostars are surrounded by dust that blocks their light and makes them hard to see in the visible spectrum
A protostar is not a star, because its core is not yet hot enough for fusion to occur. When protostars rotate, they create a strong magnetic field. The magnetic field creates an outward flow of particles into space. Protostars also send high streams of gas into space. Protostars become stars when their core temperatures exceed 10 million degrees Kelvin, which is the temperature required for fusion to occur. The mass of the star determines how long it takes to transform. Larger protostars are transformed into main sequence stars more quickly than smaller ones.