IK Pegasi

IK Pegasi (or HR 8210) is a binary star system located in the constellation Pegasus. This system is just bright enough to be seen with the naked eye and lies approximately 154 light years from our Solar System.

The system consists of two stars. The primary star, known as IK Pegasi A, is an A-type main-sequence star that shows small changes in its luminosity. It is classified as a Delta Scuti variable star, meaning its brightness varies in a repeating cycle about 22.9 times each day. The companion star, IK Pegasi B, is a massive white dwarf—a star that has stopped generating energy through nuclear fusion. The two stars orbit each other every 21.7 days, staying much closer together than Mercury is to the Sun.

IK Pegasi B is considered a possible predecessor for a near-Earth supernova. Although it is not the closest known supernova precursor—Wolf 1130 holds that title—scientists believe that when IK Pegasi A expands into a red giant, material from its outer layers may be pulled onto the white dwarf. If the white dwarf’s mass approaches the Chandrasekhar limit of 1.4 solar masses (M_☉), it could explode in a Type Ia supernova. This makes IK Pegasi an important object for studying stellar evolution and potential 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. By watching how the stars move, 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 dense white dwarf star. White dwarfs are stars that have reached the end of their lives and no longer produce energy through nuclear fusion. Instead, they slowly cool down over billions of years.

Most stars, including IK Pegasi B, eventually become white dwarfs. As a star uses up its fuel, it expands into a large, cool stage called a red giant. Later, it sheds its outer layers and leaves behind a small, dense core — the white dwarf. IK Pegasi B is made mostly of carbon and oxygen, with a thin layer of hydrogen on its surface. It is very dense, packing more mass than the Sun into a space about the size of Earth. This makes its surface gravity extremely strong, much stronger than Earth's. The white dwarf also shines brightly in ultraviolet light and will continue to cool slowly over time.

Future evolution

IK Pegasi is a binary star system that may one day become a Type Ia supernova or a cataclysmic variable. In the far future, the main star, IK Pegasi A, will expand into a red giant. As it grows, it may start sharing material with its companion star, IK Pegasi B, a white dwarf. This material could cause explosions called novae on the white dwarf's surface.

If enough material builds up on the white dwarf, it might eventually explode as a Type Ia supernova. This kind of explosion happens when a white dwarf reaches a certain mass limit and can no longer support itself. Though this event is possible, it is not expected to happen for about 1.9 billion years, so it poses no threat to Earth in the foreseeable future. After such an explosion, the remaining stars would move apart at high speeds.