Fomalhaut means “mouth of the fish.” It is the brightest star in the Piscis Austrinus constellation which is also known as the “Southern Fish.” Let’s check out some more facts on the Fomalhaut Star, before we dive into the detail!
Facts About Fomalhaut Star
- Fomalhaut is a class A star with an apparent magnitude of 1.16. This makes it the 18th brightest star in our sky. Also, it is easily visible to the naked eye.
- Known as the Royal Stars, Fomalhaut, Aldebaran, Regulus, and Antares are the most important stars in Persia (modern-day Iran). They were mainly used for navigation purposes and were believed to govern the world.
- Aside from being a royal star, Fomalhaut is also nicknamed “the Loneliest Star.” It is called so because it is located in the area of night sky that appears mostly empty.
- At 1.92 solar masses, Fomalhaut is nearly twice as massive as the Sun. It is also about twice as large.
- Fomalhaut forms a three-star system with Fomalhaut B and Fomalhaut C. The distance of the stars in this system is so large that Fomalhaut C is already part of the Aquarius constellation.
- Though it is a main-sequence star like our Sun, Fomalhaut burns with about 16 times more luminosity. Because of that, it will consume its fuel faster and will have a shorter life.
- Fomalhaut is surrounded by disks that are comparable to the Kuiper belt of the solar system. The outermost part of this disk expands 133 astronomical units (AU) away from the star. One AU equals the Earth-Sun distance.
- Around 2005, the Hubble Space Telescope discovered an exoplanet orbiting Fomalhaut. It was the first time that an object from another star system was seen under visible light. It was given the designation Fomalhaut b or “Dagon.” However, the said exoplanet vanished when 2014 images from Hubble were reviewed. This remains one the biggest mystery of this star.
- At about 440 million years, Fomalhaut is still a young star. To compare, our Sun is 4.6 billion years old and is considered a middle-aged star.
The Fomalhaut Star
- Star type: A-type
- Color: White
- Apparent magnitude: 1.16
- Mass: 1.92 solar masses
- Radius: 1.8 solar radii
- Luminosity: 16.6 Suns
- Temperature: 8,590 K
- Constellation: Piscis Austrinus
- Distance: 25 light-years from Earth
Fomalhaut is a main-sequence white star. It is the brightest star in the Piscis Austrinus constellation. The name of the constellation is Latin which means the “Southern Fish.” This differentiates it from the zodiac constellation of Pisces.
The name Fomalhaut was derived from the Arabic Fum al Hut which means “mouth of the fish.” This is a description of its position in the constellation pattern as seen in the night sky. Fomalhaut, Aldebaran, Antares, and Regulus are called the Royal Stars in Persian culture.
The Fomalhaut star is 1.92 times as massive as the Sun. It is also nearly twice as big. It burns with a temperature of 8,590 K (15,002 °F or 8,316 °C). To compare, our Sun’s temperature is around 5,778 K (9,940 °F or 5,504 °C). Overall, this A-type star is one of the 20 brightest stars that we see in the night sky.
Easily Visible To The Naked Eye
Fomalhaut is located 25 light-years from us. It has an apparent magnitude of 1.16 as seen from Earth, so it is easily visible to the naked eye. It is a main-sequence star like the Sun but it burns around 16 times brighter. Because of that, it will use up its fuel faster. While the Sun will spend 10 billion years in the main sequence, Fomalhaut will only have around 1 billion years.
Fomalhaut forms a triple star system with Fomalhaut B (TW Piscis Austrini) and Fomalhaut C (LP 876-10). The star Fomalhaut C is located very far from the other two. In fact, it is already a part of the Aquarius constellation.
Excess infrared radiation has been detected on Fomalhaut which indicates that a debris disk may be surrounding it, like the star Vega. It was thought to have a planetary companion which was called Fomalhaut b. However, new findings indicate that it is more likely a dust cloud that is part of the disk and not an exoplanet.
Piscis Austrinus Constellation (The Southern Fish)
The constellation of Piscis Austrinus is located in the southern sky. It was one of the first 48 constellations that were recognized by Ptolemy in the second century. Its name means “the southern fish.” When it was cataloged in the Almagest, Ptolemy called it Ichthus Notios.
Piscis Austrinus is not an exceptionally bright constellation. In fact, only its brightest star, Fomalhaut, is brighter than the fourth magnitude. The constellation is enclosed in a four-sided polygon assigned in 1930 by Eugène Delporte.
The Grus constellation, also known as “the crane,” was part of Piscis Austrinus before. In the late 1500s, astronomer Petrus Plancius carved it from the stars that were once part of the southern fish.
Piscis Austrinus is surrounded by the constellations Capricornus (the Sea Goat), Microscopium (the Microscope), Grus (the Crane), Sculptor (the Sculptor), and Aquarius (the Water Bearer). With Aquarius above it, the fish Piscis Austrinus is often depicted drinking the water from the Water Bearer.
After Fomalhaut, the second brightest star of Piscis Austrinus is the B-type star Epsilon Piscis Austrini. Exoplanets were also discovered in the constellation. The latest is the addition of two super-Earths in 2020. There are also deep sky objects such as the spiral galaxies NGC 7259 and NGC 7314.
Where Can You See Fomalhaut in the Night Sky?
Fomalhaut is often called the “Loneliest Star” because it lies in the area of the sky where not many bright stars can be seen. Below are the coordinates of this star:
Right ascension: 22h 57m 39.0465s
Declination: −29° 37′ 20.050″
The first thing we need to do to find Fomalhaut is to find its constellation. We can use the neighboring constellations that surround Piscis Austrinus.
The zodiac constellation of Aquarius is located in the north of the Southern Fish. In its northwest portion is another zodiac constellation, Capricornus. Microscopium is in its southwest part and to the south is Grus. Lastly, the faint constellation of Sculptor is located in the east of Piscis Austrinus.
We can easily identify the location of Fomalhaut once we find the Piscis Austrinus. This constellation forms a fish pattern and this bright star marks the mouth of the southern fish.
How and When To Find It?
The best time to see Fomalhaut depends on your location as an observer. In the Northern Hemisphere, it is seen best in autumn. That is why it got the nickname “the Autumn Star.”
Fomalhaut rises above the horizon from around September to December, making it finely visible from the continental United States. Though Fomalhaut is mostly alone in the sky, we can sometimes see it with other bright objects like Saturn and Jupiter.
From the northern latitudes, another technique we can use to find Fomalhaut is through the Great Square of Pegasus. This asterism is one of the most famous sky patterns of the northern sky in autumn.
It is part of the constellation of Pegasus (the Flying Horse) and is made up of the stars Algenib (Gamma Pegasi), Alpheratz (Alpha Andromedae), Markab (Alpha Pegasi), and Scheat (Beta Pegasi).
From this square, imagine a straight line connecting the two stars on the right-hand side (western portion) of the asterism. From the stars Scheat and Markab, extend this line about 3.5 times southward. This line will pass through the constellations of Aquarius and Pisces, which are not exceptionally bright.
You will know that you have found Fomalhaut since it is the only bright star in this region of the sky. If you have a good telescope, you can also explore the whole star system and find Fomalhaut B and Fomalhaut C. But remember, Fomalhaut C is already part of the Aquarius constellation.
The Alpha Piscis Austrini Star System
Fomalhaut forms a triple star system with the stars TW Piscis Austrini and LP 876-10. These three stars are also known as Fomalhaut A, B, and C, respectively. It is considered the widest-spanning star system because of the great distance among the three stars.
TW Piscis Austrini (Fomalhaut B)
TW Piscis Austrini or Fomalhaut B is the second star that forms the multiple star system of Fomalhaut. It is a K-type variable star with an apparent magnitude that ranges around 6.44–6.51.
Fomalhaut B is located around a light-year away from Fomalhaut A. With that distance, they are seen as visually separated stars from Earth. Fomalhaut B is smaller and less massive than the primary star, with only 0.7 times the Sun’s mass and 0.6 times its radius. It is also less luminous.
LP 876-10 (Fomalhaut C)
Fomalhaut C has a very wide visual separation from the other stars in the system. This red dwarf star lies 2.5 light-year away from Fomalhaut A and even further at 3.2 light-years from Fomalhaut B. It lies in the constellation of Aquarius.
This star was originally cataloged as LP 876-10 but in 2013 it was discovered that it shares common orbital properties with Fomalhaut A and B in constellation Piscis Austrinus. After that, it was given the designation Fomalhaut C.
Fomalhaut C is the smallest star of the three. It only has 0.2 times the Sun’s mass and an apparent magnitude of 12.6. We cannot see it with the naked eye so a telescope is needed to spot it.
Like Fomalhaut A, a disk was also found surrounding this star using the Herschel Space Telescope. This belt is thought to be home of solar system-like comets and asteroids. This star has an orbital period of about 20 million years around Fomalhaut A.
Fomalhaut Debris Disk
Looking at the images from the Hubble Space Telescope, the disks that surround the star Fomalhaut makes it look like the Eye of Sauron. The debris that surround the star spans around 25 AU across.
Fomalhaut does not only have one but several disks. The disk closest to the star is made up fine particles and the debris seems to grow larger going outward. The innermost disk lies close at around 0.1 AU from the star. After it is a larger disk around 0.4-1 AU from the hot blue star. The outermost disk has a torus shape and is 133 AU from the star.
Dagon (Fomalhaut b) : The Disappearing Exoplanet
In 2008, the Hubble Space Telescope spotted an exoplanet surrounding the blue white star Fomalhaut. It was a remarkable event because that was the first time that an exoplanet was discovered through direct imaging. Its existence was confirmed in 2012.
The exoplanet was designated Fomalhaut b. In 2015, it was given the official name Dagon, which has a Semitic origin. Dagon was thought to be a gas planet, about 2 to 3 times the mass of Jupiter, or comparable to Neptune’s mass.
Years later, astronomer András Gáspár was going through Hubble images from 2014 when he noticed that Dagon was nowhere to be seen. Gáspár and George Rieke, another astronomer from the University of Arizona, reviewed the data and found out that it has indeed vanished. The images revealed that the exoplanet had faded away over time.
The most probable explanation for this is that Dagon was not really a planet. According to astronomers, it must be a debris cloud from two objects that may have collided. These objects are estimated to be around 200 kilometers or 125 miles wide, with a composition similar to that of comets.
Another thing to consider is that Dagon did not emit infrared radiation. Infrared radiation is expected among young planets but none was detected from it. In contrast, the orbit-crossing characteristic of this object is consistent with being a planet.
Still, the nature of Fomalhaut b remains a big mystery. However, it is most likely that there was never a planetary system in the first place.
Fomalhaut Star in History & Mythology
Fomalhaut was considered a Royal Star in Persian culture. Together with it are Aldebaran (Taurus), Antares (Scorpius), and Regulus (Leo). These are the most important stars for the Persian Empire as they are thought to be the guardians that govern the sky.
Except Fomalhaut, the three stars are from the zodiac constellations. They lie near the ecliptic or the apparent path of the Sun. Fomalhaut was choosen as the fourth Royal Star because of the bright star Fomalhaut. The Capricornus constellation has no bright star so the Persians chose one from constellation Piscis Austrinus. This dark area in the sky is called the “ceslestial sea.”
It was believed that the sky was divided into four and that the Royal Stars were the guardians of each district. Each of them are the brightest in their constellations. They were highly regarded by the people that used them for guidance. Persians believed that major world events were largely connected to them.
They were used for navigation and understanding sky phenomena, among others. Also, as they were thought to posses good and evil, people used to look upon these stars for predictions. It was believed that good things will happen if these stars are positively aligned. When it is the other way around, this meant disasters and bad events.
Piscis Austrinus Mythology
The constellation of Piscis Austrinus where Fomalhaut belongs has several mythological stories across cultures. In Egypt, it was said that the major goddess Isis placed it in the sky as a reward for saving her life.
In Greek mythology, this constellation is known as Great Fish and that the two fish of Pisces came from it. According to another story, this fish earned its place in the night sky after saving Aphrodite’s daughter.
Fomalhaut Star – Sources:
Fomalhaut Star – Image Sources:
Fomalhaut Star: https://upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Heic0821f.jpg/800px-Heic0821f.jpg
Piscis Austrinus Constellation (The Southern Fish): https://upload.wikimedia.org/wikipedia/commons/thumb/8/8d/Piscis_Austrinus_constellation_map.svg/1024px-Piscis_Austrinus_constellation_map.svg.png
Great Square of Pegasus: https://www.star-facts.com/wp-content/uploads/2019/09/Fomalhaut-and-the-Great-Square-of-Pegasus.jpg
Fomalhaut Debris Disk: https://upload.wikimedia.org/wikipedia/commons/thumb/f/fe/Fomalhaut_B_entire-Hubble_Telescope.jpg/1024px-Fomalhaut_B_entire-Hubble_Telescope.jpg
Dagon (Fomalhaut b) : The Disappearing Exoplanet: https://upload.wikimedia.org/wikipedia/commons/thumb/a/a3/Fomalhaut_with_Disk_Ring_and_extrasolar_planet_b.jpg/1280px-Fomalhaut_with_Disk_Ring_and_extrasolar_planet_b.jpg