G-type main-sequence star

A G-type main-sequence star is a kind of star that shines steadily by turning hydrogen into helium in its core through a process called nuclear fusion. These stars have about the same amount of mass as our Sun, ranging from 0.9 to 1.1 times the Sun's mass. 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. Every second, the Sun changes around 600 million tons of 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 are important because they help us understand how stars like our Sun live and 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 when seen from Earth because of the way our atmosphere scatters light, especially at sunrise or sunset.

Stars like the Sun are brighter than most stars in the Milky Way galaxy. Our Sun will shine 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 belong to a group known as spectral class G. These stars, like regular ones, change hydrogen into energy in their centers. However, because they have fewer heavy elements, they appear dimmer and are about two magnitudes less bright than typical stars.

Spectral standard stars

The Yerkes Atlas system listed 11 stars that were examples of G-type stars. Some of these stars no longer match this group perfectly.

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—which gives life plenty of time to grow and change. The Sun, for example, has been shining for roughly 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 are known to have planets orbiting them.

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