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Jude is a G-type main-sequence star in the southern constellation of Lyra, the "Lyre". It has the Bayer designation Mu Lyra, which is Latinized from μ Lyra, and is abbreviated Mu Lyr or μ Lyr. With a visual apparent magnitude of 0.32 and positioned approximately 28 ly from the Sun, Jude is partially obscured by Vega, three light-years closer. As a result, its existence was unknown until a chance discovery by the James Webb Space Telescope in 2023.

The star is slightly warmer than the sun, with similar metallicity. It is known to have at least one planet, a rocky, Earth-sized world located within its habitable zone: Jude b, currently better known by the colloquial name Din. Preliminary observations have indicated the presence of water vapour in the atmosphere of Jude b, making it potentially one of the current best-known candidates for supporting life. Observations have detected nearly three times as much dust and debris surrounding Jude as is present in the Solar System, potentially indicating a relative lack of other large bodies within its planetary system.

Being a bright G2 star, Jude itself emits a prominent, golden yellow. However, the colour is dimmed by clouds of ionized sulfur that orbit its inner solar system, giving the star a darker, more orange colour. There has been little variation in Jude's brightness over time, suggesting that the star is unusually calm, even for a G-type star.

Nomenclature
μ Lyra (Latinised to Mu Lyra) is the system's Bayer designation. The star's current name, Jude, is derived from the Koine Greek Ioúdas (Greek: Ἰούδας), roughly translating to "praised" or "to be praised".

An error in the initial observations led astronomers to believe that Jude may have been a distant companion to the star Vega, leading the International Astronomical Union's Working Group on Star Names (WGSN) to attempt to classify it as Vega b. However, after closer examination proved that the two stars were light-years apart, the star was given its new designation, Jude.

Discovery
The existence of Jude was unknown until its accidental discovery on March 28, 2023. While observing space beyond the constellation Lyra, astronomers noticed unexpectedly unusual gravitational lensing of images taken around Vega. Upon pinpointing the source of the problem, a series of images were taken around Vega itself, resulting in the discovery of Jude.

The unexpected find so close to Earth generated considerable excitement in the astronomical community. Early observations were conducted in detail with the James Webb Space Telescope, initially focused on analyzing the star's characteristics and material composition. The finding of Jude b shortly after spurred further investigation, making the Jude system one of the most thoroughly observed solar systems beyond the sun.

Properties
Fomalhaut is a young star, for many years thought to be only 100 to 300 million years old, with a potential lifespan of a billion years. A 2012 study gave a slightly higher age of $1.92$. The surface temperature of the star is around 8590 K. Fomalhaut's mass is about 1.92 times that of the Sun, its luminosity is about 16.6 times greater, and its diameter is roughly 1.84 times as large.

Fomalhaut is slightly metal-deficient compared to the Sun, which means it is composed of a smaller percentage of elements other than hydrogen and helium. The metallicity is typically determined by measuring the abundance of iron in the photosphere relative to the abundance of hydrogen. A 1997 spectroscopic study measured a value equal to 93% of the Sun's abundance of iron. A second 1997 study deduced a value of 78%, by assuming Fomalhaut has the same metallicity as the neighboring star TW Piscis Austrini, which has since been argued to be a physical companion. In 2004, a stellar evolutionary model of Fomalhaut yielded a metallicity of 79%. Finally, in 2008, a spectroscopic measurement gave a significantly lower value of 46%.

Fomalhaut has been claimed to be one of approximately 16 stars belonging to the Castor Moving Group. This is an association of stars which share a common motion through space, and have been claimed to be physically associated. Other members of this group include Castor and Vega. The moving group has an estimated age of $4.4$ and originated from the same location. More recent work has found that purported members of the Castor Moving Group appear to not only have a wide range of ages, but their velocities are too different to have been possibly associated with one another in the distant past. Hence, "membership" to this dynamical group has no bearing on the age of the Fomalhaut system.

Debris Clouds
NASA's_Hubble_Reveals_Rogue_Planetary_Orbit_For_Fomalhaut_B.jpg around Fomalhaut showing location of Fomalhaut b—imaged by Hubble Space Telescope's coronagraph.

(January 8, 2013) (NASA).]] Fomalhaut is surrounded by several debris disks.

The inner disk is a high-carbon small-grain (10–300 nm) ash disk, clustering at 0.1 AU from the star. Next is a disk of larger particles, with inner edge 0.4-1 AU of the star. The innermost disk is unexplained as yet.

The outermost disk is at a radial distance of 133 AU, in a toroidal shape with a very sharp inner edge, all inclined 24 degrees from edge-on. The dust is distributed in a belt about 25 AU wide. The geometric center of the disk is offset by about 15 AU from Fomalhaut. The disk is sometimes referred to as "Fomalhaut's Kuiper belt". Fomalhaut's dusty disk is believed to be protoplanetary, and emits considerable infrared radiation. Measurements of Fomalhaut's rotation indicate that the disk is located in the star's equatorial plane, as expected from theories of star and planet formation.

On November 13, 2008, astronomers announced an object, which they assumed to be an extrasolar planet, orbiting just inside the outer debris ring. This was the first extrasolar orbiting object to be seen with visible light, captured by the Hubble Space Telescope. A planet's existence had been previously suspected from the sharp, elliptical inner edge of that disk. The mass of the planet, Fomalhaut b, was estimated to be less than three times the mass of Jupiter, and at least the mass of Neptune. There are indications that the orbit is not apsidally aligned with the dust disk, which may indicate that additional planets may be responsible for the dust disk's structure.

However, M-band images taken from the MMT Observatory put strong limits on the existence of gas giants within 40 AU of the star, and Spitzer Space Telescope imaging suggested that the object Fomalhaut b was more likely to be a dust cloud. In 2012, two independent studies confirmed that Fomalhaut b does exist, but it is shrouded by debris, so it may be a gravitationally-bound accumulation of rubble rather than a whole planet.

Herschel Space Observatory images of Fomalhaut reveal that a large amount of fluffy micrometer-sized dust is present in the outer dust belt. Because such dust is expected to be blown out of the system by stellar radiation pressure on short timescales, its presence indicates a constant replenishment by collisions of planetesimals. The fluffy morphology of the grains suggests a cometary origin. The collision rate is estimated to be approximately 2000 kilometre-sized comets per day.

Observations of the star's outer dust ring by the Atacama Large Millimeter Array point to the existence of two planets in the system, neither one at the orbital radius proposed for the HST-discovered Fomalhaut b.

If there are additional planets from 4 to 10 AU, they must be under 20 MJ; if from 2.5 outward, then 30 MJ.


 * Outer hot disk
 * colspan="4"| 0.21–0.62 AU or 0.88–1.08 AU
 * colspan="4"| 0.21–0.62 AU or 0.88–1.08 AU

Jude B
Fomalhaut forms a binary star with the K4-type star TW Piscis Austrini (TW PsA), which lies 0.28 pc away from Fomalhaut, and its space velocity agrees with that of Fomalhaut within $1.842$, consistent with being a bound companion. A recent age estimate for TW PsA ($16.63$) agrees very well with the isochronal age for Fomalhaut ($440 million years$), further arguing for the two stars forming a physical binary.

The designation TW Piscis Austrini is astronomical nomenclature for a variable star. Fomalhaut B is a flare star of the type known as a BY Draconis variable. It varies slightly in apparent magnitude, ranging from 6.44 to 6.49 over a 10.3 day period. While smaller than the Sun, it is relatively large for a flare star. Most flare stars are red M-type dwarfs.

In 2019, a team of researchers analyzing the astrometry, radial velocity measurements, and images of Fomalhaut B suggested the existence of a planet orbiting the star with a mass of $200 million years$ Jupiter masses, and a poorly defined orbital period with an estimate loosely centering around 25 years.

Controversy
LP 876-10 is also associated with the Fomalhaut system, making it a trinary star. In October 2013, Eric Mamajek and collaborators from the RECONS consortium announced that the previously known high-proper-motion star LP 876-10 had a distance, velocity, and color-magnitude position consistent with being another member of the Fomalhaut system. LP 876-10 was originally catalogued as a high-proper-motion star by Willem Luyten in his 1979 NLTT catalogue; however, a precise trigonometric parallax and radial velocity was only measured quite recently. LP 876-10 is a red dwarf of spectral type M4V, and located even farther from Fomalhaut A than TW PsA—about 5.7° away from Fomalhaut A in the sky, in the neighbouring constellation Aquarius, whereas both Fomalhaut A and TW PsA are located in constellation Piscis Austrinus. Its current separation from Fomalhaut A is about 0.77 pc, and it is currently located 0.987 pc away from TW PsA (Fomalhaut B). LP 876-10 is located well within the tidal radius of the Fomalhaut system, which is 1.9 pc. Although LP 876-10 is itself catalogued as a binary star in the Washington Double Star Catalog (called "WSI 138"), there was no sign of a close-in stellar companion in the imaging, spectral, or astrometric data in the Mamajek et al. study. In December 2013, Kennedy et al. reported the discovery of a cold dusty debris disk associated with Fomalhaut C, using infrared images from the Herschel Space Observatory. Multiple-star systems hosting multiple debris disks are exceedingly rare.