Alpha Muscae
Encyclopedia
Alpha Muscae is a Class B2
, third-magnitude star
in the constellation
Musca.
This hot class B (B2) subgiant shines from a distance
of 306 light years at a luminosity
of 4,520 times that of the Sun
from a blue-white surface with a fairly well determined temperature
of 21,900 kelvin
s, so hot that most of the radiation
emerges in the ultraviolet
(where we cannot see it). The combination of temperature
and luminosity
indicates a radius
4.7 times that of the Sun, and these in conjunction with the theory of stellar structure and stellar evolution
tell of an eight-solar-mass star that is roughly midway through its 32-million-year hydrogen
-fusing dwarf lifetime (the "subgiant" classification is clearly inappropriate, since subgiants stars tend to give up their core
nuclear fusion
).
Like most class B stars, it rotates quickly, spinning with an equatorial velocity
of at least 114 kilometers per second
, which gives it a rotation
period of less than two day
s. Also like many stars in its class, Alpha Muscae is a Beta Cephei variable
, subtly pulsating in brightness by about one percent over a 2.2 hour period. About half a minute of arc
away is a purported 13th magnitude companion, which could also easily be a line-of-sight coincidence. Alpha Muscae is a part of the unbound "Centaurus-Crux" association of O and B type stars, all of which were born more or less at the same time from a massive interstellar cloud
.
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
, third-magnitude star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Musca.
This hot class B (B2) subgiant shines from a distance
Distance
Distance is a numerical description of how far apart objects are. In physics or everyday discussion, distance may refer to a physical length, or an estimation based on other criteria . In mathematics, a distance function or metric is a generalization of the concept of physical distance...
of 306 light years at a luminosity
Luminosity
Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...
of 4,520 times that of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
from a blue-white surface with a fairly well determined temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
of 21,900 kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
s, so hot that most of the radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
emerges in the ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
(where we cannot see it). The combination of temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
and luminosity
Luminosity
Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...
indicates a radius
Radius
In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...
4.7 times that of the Sun, and these in conjunction with the theory of stellar structure and stellar evolution
Stellar evolution
Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years to trillions of years .Stellar evolution is not studied by observing the life of a single...
tell of an eight-solar-mass star that is roughly midway through its 32-million-year hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
-fusing dwarf lifetime (the "subgiant" classification is clearly inappropriate, since subgiants stars tend to give up their core
Solar core
The core of the Sun is considered to extend from the center to about 0.2 to 0.25 solar radius. It is the hottest part of the Sun and of the Solar System. It has a density of up to 150 g/cm³ and a temperature of close to 15,000,000 kelvin...
nuclear fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
).
Like most class B stars, it rotates quickly, spinning with an equatorial velocity
Velocity
In physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...
of at least 114 kilometers per second
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
, which gives it a rotation
Rotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...
period of less than two day
Day
A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun...
s. Also like many stars in its class, Alpha Muscae is a Beta Cephei variable
Beta Cephei variable
Beta Cephei variables are variable stars which exhibit variations in their brightness due to pulsations of the stars' surfaces. The point of maximum brightness roughly corresponds to the maximum contraction of the star. Typically, Beta Cephei variables change in brightness by 0.01 to 0.3...
, subtly pulsating in brightness by about one percent over a 2.2 hour period. About half a minute of arc
Minute of arc
A minute of arc, arcminute, or minute of angle , is a unit of angular measurement equal to one sixtieth of one degree. In turn, a second of arc or arcsecond is one sixtieth of one minute of arc....
away is a purported 13th magnitude companion, which could also easily be a line-of-sight coincidence. Alpha Muscae is a part of the unbound "Centaurus-Crux" association of O and B type stars, all of which were born more or less at the same time from a massive interstellar cloud
Interstellar cloud
Interstellar cloud is the generic name given to an accumulation of gas, plasma and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium. Depending on the density, size and temperature of a given cloud, the hydrogen in it...
.