IK Pegasi

IK Pegasi (or HR 8210) is a binary star system in the constellation Pegasus. You can see it with your eyes alone. It is about 154 light years from our Solar System.

The system has two stars. The bigger star, IK Pegasi A, is an A-type main-sequence star. Its brightness changes a little. It is called a Delta Scuti variable star because its light shines and dims 22.9 times each day. The other star, IK Pegasi B, is a white dwarf. This star has stopped making energy through nuclear fusion. The two stars go around each other every 21.7 days. They stay much closer together than Mercury is to the Sun.

IK Pegasi B might one day become a near-Earth supernova. Scientists think that when IK Pegasi A grows into a red giant, material from its outer layers could move onto the white dwarf. If the white dwarf gets close to the Chandrasekhar limit of 1.4 solar masses (M_☉), it could explode in a Type Ia supernova. This makes IK Pegasi important for learning about how stars change and possible supernovae.

Observation

This star system was first listed in old star guides and later named IK Pegasi. Astronomers found that it is a binary star system, meaning it has two stars orbiting each other. They learned that the stars take about 21.7 days to orbit each other.

Scientists measured how far away IK Pegasi is by watching its slight shift in position as Earth moves around the Sun. This showed that IK Pegasi is about 150 light years from us. They also studied how the star moves across the sky and toward or away from Earth to learn more about its speed and direction.

IK Pegasi A

IK Pegasi A is a bright star that is part of a binary star system. It is what astronomers call a "main sequence" star, meaning it is steadily burning hydrogen in its core. This star has tiny, regular changes in its brightness caused by pulsations, or slight expansions and contractions, in its outer layers.

These pulsations happen because parts of the star’s atmosphere absorb and release energy in a cycle, causing it to expand and then shrink back again. IK Pegasi A is classified as a Delta Scuti variable, a type of star known for these short, regular brightness changes. The star’s composition is slightly richer in metals—elements heavier than helium—than our Sun.

IK Pegasi B

The companion star in the IK Pegasi system is a white dwarf star. White dwarfs are stars that have ended their lives and no longer make energy through nuclear fusion. Instead, they slowly cool down over many years.

Most stars, including IK Pegasi B, become white dwarfs at the end of their lives. A star grows big and cool, called a red giant. Then it loses its outer layers and leaves a small, dense core — the white dwarf. IK Pegasi B is made mostly of carbon and oxygen, with a thin layer of hydrogen on top. It is very dense, holding more mass than the Sun in a space about the size of Earth. This makes its surface gravity very strong, much stronger than Earth's. The white dwarf shines brightly in ultraviolet light and will keep cooling slowly over time.

Future evolution

IK Pegasi is a pair of stars that orbit each other. One day, it might become something very bright in the sky, called a Type Ia supernova.

Right now, one of the stars, called IK Pegasi A, will grow bigger in the future. As it grows, it might share material with the other star, IK Pegasi B, which is a small, dense star called a white dwarf. This sharing could cause small explosions on the white dwarf.

If the white dwarf gets enough extra material, it might explode as a Type Ia supernova. This happens when the white dwarf gets too heavy and can’t hold itself up anymore. This won’t happen for about 1.9 billion years, so it isn’t something to worry about now. After the explosion, the stars would move away from each other quickly.