G-type main-sequence star

A G-type main-sequence star is a kind of star that shines steadily. It turns hydrogen into helium in its core through a process called nuclear fusion. These stars have about the same amount of mass as our Sun. Their temperatures are warm, between about 5,300 and 6,000 Kelvin.

Our own Sun is a perfect example of a G-type main-sequence star. The Sun changes hydrogen into helium, releasing huge amounts of energy that keeps our planet warm and bright. Other stars like Alpha Centauri A, Tau Ceti, and 51 Pegasi are also G-type stars, similar to our Sun in many ways. These stars help us learn about how stars like our Sun shine.

Description

The term yellow dwarf can be confusing because G-type stars, like our Sun, are actually white. They may look yellow, orange, or red from Earth because of how our atmosphere changes the light, especially at sunrise or sunset.

Stars like the Sun are brighter than most stars in the Milky Way galaxy. Our Sun shines by turning hydrogen into helium for about 10 billion years. After that, it will grow bigger and cooler, becoming a red giant before shrinking down to a small, dense white dwarf.

Subdwarfs

Main article: Cool subdwarf

There are special stars called subdwarf stars. They are part of a group known as spectral class G. These stars change hydrogen into energy, just like regular stars. But because they have fewer heavy elements, they look dimmer and are not as bright as typical stars.

Spectral standard stars

The Yerkes Atlas system listed 11 stars as examples of G-type stars. Some of these stars do not perfectly fit this group anymore.

The main stars used as examples in the MK system for G-type stars are Chara (G0V), the Sun (G2V), Kappa1 Ceti (G5V), and 61 Ursae Majoris (G8V). Other important examples include HD 115043 (G1V) and 16 Cygni B (G3V). Stars like 70 Virginis (G4V) and 82 Eridani (G6V) are also often used. There are no widely accepted examples for G7V and G9V stars yet.

Habitability

Main article: Habitability of yellow dwarf systems

G-type stars, like our Sun, can support life. They shine steadily for a very long time—up to about 13 billion years. This gives life plenty of time to grow. The Sun has been shining for about 10 billion years and helps life on Earth thrive.

Planets

Besides the Sun and its planets, some of the closest stars like 61 Virginis, HD 102365, HD 147513, 47 Ursae Majoris, and Mu Arae have planets orbiting them.

Tau Ceti was once thought to have many planets, but a study in 2025 using ESPRESSO data could not prove this.