UY Scuti (BD-12°5055) is a

red supergiant Red supergiants (RSGs) are stars with a supergiant luminosity class ( Yerkes class I) and a stellar classification K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelg ...

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

, located 5,900

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s away in the constellation Scutum. It is also a pulsating variable star, with a maximum brightness of

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

8.29 and a minimum of magnitude 10.56, which makes it too dim for naked-eye visibility. It is considered to be one of the largest known stars, with a radius estimated at , thus a volume of 750 million times that of the Sun. This estimate implies if it were placed at the center of the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

, its

photosphere The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately , or equivalently, a depth from which 50% of light will esc ...

would extend past the orbit of

Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

or even the

asteroid belt The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids ...

Nomenclature and history

UY Scuti was first catalogued in 1860 by German astronomers at the Bonn Observatory, who were completing a survey of stars for the '' Bonner Durchmusterung Stellar Catalogue''.Bonner Durchmusterung (Argelander 1859–1862)
(clicking on "bd.gz" downloads the gzipped 10.1MB catalogue) It was designated BD-12°5055, the 5,055th star between 12°S and 13°S counting from 0h

right ascension Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the equinox (celestial coordinates), March equinox to the (hour circle of the) point in questio ...

. On detection in the second survey, the star was found to have changed slightly in brightness, suggesting that it was a new

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

. In accordance with the international standard for designation of variable stars, it was called UY Scuti, denoting it as the 38th variable star of the constellation Scutum. UY Scuti is located a few degrees north of the A-type star Gamma Scuti and northeast of the Eagle Nebula. Although the star is very luminous, it is, at its brightest, only 9th magnitude as viewed from Earth, due to its distance and location in the Zone of Avoidance within the Cygnus rift.

Characteristics

UY Scuti is a dust-enshrouded bright

and is classified as a

semiregular variable In astronomy, a semiregular variable star, a type of variable star, is a Red giant, giant or supergiant of intermediate and late (cooler) spectral type. It shows considerable periodicity in its light changes, accompanied or sometimes interrupted b ...

with an approximate pulsation period of 740 days. Based on an old radius of , this pulsation would be an

overtone An overtone is any resonant frequency above the fundamental frequency of a sound. (An overtone may or may not be a harmonic) In other words, overtones are all pitches higher than the lowest pitch within an individual sound; the fundamental i ...

of the fundamental pulsation period, or it may be a fundamental mode corresponding to a smaller radius. In mid 2012,

AMBER Amber is fossilized tree resin. Examples of it have been appreciated for its color and natural beauty since the Neolithic times, and worked as a gemstone since antiquity."Amber" (2004). In Maxine N. Lurie and Marc Mappen (eds.) ''Encyclopedia ...

interferometry Interferometry is a technique which uses the ''interference (wave propagation), interference'' of Superposition principle, superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important inves ...

with the

Very Large Telescope The Very Large Telescope (VLT) is an astronomical facility operated since 1998 by the European Southern Observatory, located on Cerro Paranal in the Atacama Desert of northern Chile. It consists of four individual telescopes, each equipped with ...

(VLT) in the

Atacama Desert The Atacama Desert () is a desert plateau located on the Pacific Ocean, Pacific coast of South America, in the north of Chile. Stretching over a strip of land west of the Andes Mountains, it covers an area of , which increases to if the barre ...

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

was used to measure the parameters of three red supergiants near the

Galactic Center The Galactic Center is the barycenter of the Milky Way and a corresponding point on the rotational axis of the galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a ...

region: UY Scuti, AH Scorpii, and KW Sagittarii. They determined that all three stars are over 1,000 times bigger than the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

and over 100,000 times more luminous than the Sun. The stars' sizes were calculated using the Rosseland radius, the location at which the

optical depth In physics, optical depth or optical thickness is the natural logarithm of the ratio of incident to ''transmitted'' radiant power through a material. Thus, the larger the optical depth, the smaller the amount of transmitted radiant power throu ...

is , with distances adopted from earlier publications. UY Scuti was analyzed to be the largest and the most luminous of the three stars measured, at based on an

angular diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular separation (in units of angle) describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the ''visual an ...

of and an assumed distance of (kpc) (about ) which was originally derived in 1970 based on the modelling of the spectrum of UY Scuti. The luminosity is then calculated to be at an effective temperature of , giving an initial mass of (possibly up to for a non-rotating star). A 2023 measurement based on the multimessenger monitoring of

supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...

e, puts the radius at a smaller value of , together with a smaller luminosity of and effective temperature of 3,550K. Direct measurements of the parallax of UY Scuti published in the Gaia Data Release 2 give a parallax of , implying a closer distance of approximately , and consequently much lower luminosity and radius values of around and respectively. However, the

Gaia In Greek mythology, Gaia (; , a poetic form of ('), meaning 'land' or 'earth'),, , . also spelled Gaea (), is the personification of Earth. Gaia is the ancestral mother—sometimes parthenogenic—of all life. She is the mother of Uranus (S ...

parallax might be unreliable due to a very high level of astrometric noise. The distance of UY Scuti has been re-measured by Bailer-Jones ''et al''. in 2021, based on a method that uses the stellar parallax from

Gaia EDR3 The ''Gaia'' catalogues are star catalogues created using the results obtained by ''Gaia'' space telescope. The catalogues are released in stages that will contain increasing amounts of information; the early releases also miss some stars, espec ...

, its color and apparent brightness, giving it a much closer distance of . UY Scuti has no known companion star and so its mass is uncertain. However, it is expected on theoretical grounds to be between . Mass is being lost at per year, leading to an extensive and complex circumstellar environment of gas and dust.

Supernova

Based on current models of

stellar evolution Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is consi ...

, UY Scuti has begun to fuse

helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...

and continues to fuse hydrogen in a shell around the core. The location of UY Scuti deep within the Milky Way disc suggests that it is a

metal-rich In astronomy, metallicity is the Abundance of the chemical elements, abundance of Chemical element, elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-Dark matter, dark) matt ...

star. After fusing heavy elements, its core will begin to produce iron, disrupting the balance of gravity and radiation in its core and resulting in a core collapse supernova. It is expected that a star like UY Scuti should evolve back to hotter temperatures to become a yellow hypergiant, luminous blue variable, or a

Wolf–Rayet star Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectroscopy, spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very ...

, creating a strong stellar wind that will eject its outer layers and expose the core, before exploding as a type IIb, IIn, or type Ib/Ic supernova.

References

{{DEFAULTSORT:UY Scuti Scutum (constellation) Semiregular variable stars Scuti, UY M-type supergiants Durchmusterung objects TIC objects Population I stars

Nomenclature and history

Characteristics

Supernova

See also

References