Fomalhaut
What is Fomalhaut?
Stars· Distance 25.1 ly · size 1.8× Sun. The lone bright star of the southern autumn sky, the chief star of Piscis Austrinus. A young white star 25 light-years away, it is nicknamed the 'Eye of Sauron' for the dust ring photographed around it.
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Distance and spectral type
Fomalhaut is about 25 light-years away, a white main-sequence star (spectral type A3V), in the constellation Corvus. Its apparent magnitude is 1.2, visible to the naked eye.
Stellar figures
| Distance | 25.1 ly |
|---|---|
| Magnitude | 1.16 — eighteenth brightest |
| Type | A3 white main-sequence |
| Note | dust ring of 140 AU radius |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Behind the name
Arabic "mouth of the fish" — the Lonely Star of autumn, where Hubble imaged a planet candidate in 2008.
The three dust belts Webb found around Fomalhaut
In Hubble's pictures Fomalhaut had a single ring. But in 2023 the James Webb Space Telescope looked again in infrared light and found three belts of dust. There is an inner belt close to the star, a middle belt beyond it, and the large outer ring that Hubble had seen. The two inner belts had never been seen before. Much like the asteroid belt and Kuiper belt in our own solar system, belts of rocky and icy rubble appeared layer by layer around another star.
Between the belts are gaps with less dust. Scientists think planets that have not yet been seen may have cleared these gaps with their gravity. Meanwhile, 'Fomalhaut b', photographed inside the ring in 2008 and announced as a planet, spread out and faded in later images. A 2020 study concluded it was probably not a planet at all, but a cloud of dust from a collision between two bodies. Collisions like this are thought to be fairly common in young planetary systems.
The star in depth
Fomalhaut is the brightest star in Piscis Austrinus, the Southern Fish. At magnitude 1.16 it is the eighteenth-brightest star in the night sky, 25.1 light-years away. Its name is Arabic for 'the fish's mouth'. In old star pictures the Southern Fish drinks the water poured out by Aquarius, and Fomalhaut marks the fish's mouth.
Fomalhaut is a white star a little bigger than the Sun. It has 1.9 times the Sun's mass, 1.8 times its width and 17 times its brightness. It is about 440 million years old, roughly a tenth of the Sun's age of 4.6 billion years, so it is still young for a star. That is why plenty of dust and rubble left over from its birth still surrounds it.
What made Fomalhaut famous is that dust ring. The Hubble Space Telescope photographed a sharp ring about 140 AU in radius. One AU is the distance from Earth to the Sun, so the ring is more than four times wider than Neptune's orbit. With the star sitting in the middle of the ring, the picture reminded people of the 'Eye of Sauron' from the films, and the nickname stuck.
From September to November, look low in the southern evening sky for Fomalhaut. With almost no bright stars around it, it is sometimes called the lonely star of autumn. From New York it rises only about 20 degrees high and from London under 10, while from Sydney it passes almost overhead. In the Sky view, choose an October night and look just above the southern horizon to see it shining on its own.
Frequently asked
- How far is Fomalhaut from Earth?
- The distance of Fomalhaut is 25.1 ly.
- How bright is Fomalhaut (apparent magnitude)?
- The magnitude of Fomalhaut is 1.16 — eighteenth brightest.
- What kind of object is Fomalhaut?
- Fomalhaut is a A3 white main-sequence.
- What is notable about Fomalhaut?
- The note of Fomalhaut is dust ring of 140 AU radius.
- Which constellation is Fomalhaut in?
- Fomalhaut lies in the constellation Corvus.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.