UY Scuti

UY Scuti

An illustration of the approximate size of UY Scuti compared to the Sun.
Observation data Epoch J2000      Equinox J2000
Constellation	Scutum
Right ascension	18h 27m 36.5334s
Declination	−12° 27′ 58.866″
Apparent magnitude (V)	9.0
Characteristics
Spectral type	M4Ia
U−B color index	3.29[1]
B−V color index	2.6
Variable type	Semiregular
Astrometry
Proper motion (μ)	RA: 1.3 mas/yr Dec.: -1.6 mas/yr
Distance	2,900[2] pc
Details
Mass	32[citation needed] M☉
Radius	1,708±192[1] R☉
Luminosity	340,000[1] L☉
Surface gravity (log g)	-0.5[1] cgs
Temperature	3,365±134[1] K
Other designations
UY Sct, BD-12 5055, IRC -10422, RAFGL 2162, HV 3805
Database references
SIMBAD	data

UY Scuti is a red supergiant star in the constellation Scutum. It is one of the largest known stars by radius at around 1,708 solar radii, or approximately 7.94 astronomical units.

Physical characteristics

UY Scuti is an extremely luminous red supergiant and a semiregular variable star with a period of about 740 days.^[3] With a diameter of 2,375,828,000 kilometers it has a surface area of about 1.7733×10²² km², about 2.91 million times that of the Sun, a volume of 7.02×10³⁰ km³, approximately 5 billion times that of the Sun, and light takes approximately 9.15 hours to cross its circumference. If placed at the center of the Solar System, it would engulf all the planets all the way to Jupiter, filling more than halfway through Saturn's orbit.

The star is almost totally obscured by dust and gas, with very high mass loss due to low density and high luminosity, similar to the red hypergiant star VY Canis Majoris. Due to this its true size is still debated and may have a diameter smaller than the current estimate. The star's location within the Zone of Avoidance makes the study of this star extremely difficult. The star suffers about four magnitudes of extinction due to the intervening gases and dust.^{[citation needed]}

Its location within the Scutum-Centaurus Arm suggests that this star may be a member of the Sagittarius OB5 association, a massive grouping of stars 7,800 light-years of Earth in the direction of the Galactic Center. The stellar association is one of the largest known in our galaxy, next only to Cygnus OB2, and also includes KW Sagittarii, a red supergiant and also one of the largest stars known, and the Sh 2-15 to Sh 2-20 complex of H II regions, massive nebulae which triggers intense star formation.

Fate

UY Scuti's large distance from the Sh 2-15 to Sh 2-20 complex of H II regions, in addition to its location within the Hertzsprung-Russell diagram and its severe mass loss, shows it to be an old dying star that left the main sequence a few million years ago. Its exact future is unclear but will almost certainly involve a supernova explosion. Stars of its size, luminosity, and assumed mass do not appear to explode while red supergiants, instead evolving back to higher temperatures as they lose mass. Current models of stellar evolution do not properly predict the proportion of massive star types or the progenitors of different types of supernovae, and observations do not show sufficient mass loss to account for the observed stars. Depending on the exact rate of mass loss, it will explode as a core collapse supernova at the yellow hypergiant, luminous blue variable, or Wolf-Rayet stage. If it cannot lose sufficient mass before exploding, it will leave behind a black hole, otherwise a neutron star will remain.

See also

• NML Cygni
• VY Canis Majoris
• KW Sagittarii
• AH Scorpii

References