Facts about V354 Cephei

V354 Cephei is a star. Stars are given names that are combinations of a number and the name of the constellation in which they are seen. The constellation Cepheus is a group of stars which is visible in the Northern Hemisphere that was named by the Greeks. In Greek mythology, Cepheus is a king with his foot on Polaris, the Pole star.  He is the husband of Cassiopeia and the father of Andromeda.

The method modern astronomers use to name stars is to give them a number followed by the name of the constellation where they are found. The V indicates that V354 Cephei is a pulsating or variable star. V354 Cephei is a red supergiant, one of the ten largest stars in this galaxy, the Milky Way. This massive star is 38,000 times as bright as the Sun and over 1600 times the Sun’s size. This means that V354 Cephai would extend out to Saturn’s orbit if it were to replace the Sun. It would be much brighter to look at if it were not so far away. It is 9000 light years from earth, so a telescope is needed to properly appreciate it. Other smaller red giants such as Antares appear brighter because they are much closer.

Stars have a life cycle just as humans do: They are born, grow, mature and then descend into old age and death. Nebulae, giant clouds of dust and gas, are the birthplaces of stars.  They condense by gravitational forces and eventually, when the mass is great enough, burst into flame, light and life by the power of nuclear fusion reactions. Red giants and supergiants are old stars in the stages of stellar life cycles. 

Red giants began their lives as small- to medium-sized stars, while supergiants began as very large stars. All young to medium aged stars, including the Sun, convert hydrogen to helium in nuclear fusion reactions which give the stars their heat and light. When all the hydrogen is consumed, the core begins to collapse, which raises the temperature and causes the star to expand outward, becoming a red giant or a supergiant, depending on the original size of the star. 

Red supergiants are among the largest stars by size but not by their mass. There are two kinds of smaller stars, dwarfs and neutron stars, that are much heavier. The eventual fate of the Sun, because of its relatively small size, is to become a red giant. A larger star, because of its greater mass, collapses quickly, which generates more heat, so the star more rapidly enters the next phase of helium fusion. This converts the helium into the elements carbon and oxygen. The massive energy released expands the star into a supergiant.

The color of a star is an indication of its outer temperature. Very hot stars such as Sirius appear to be white or blueish white. Stars of a medium temperature, such as the Sun, appear to be yellow. Even though the core temperatures of red giants and supergiants are very high, the outer regions are much cooler (only around 4000 degrees Kelvin) and so appear to be red. When all of their fuel is spent, supergiants explode in a supernova and then form a neutron star or collapse into a black hole. This will be the eventual fate of V354 Cephei.