Astrophysics: Classifying Stars

Stars can be categorised on a variety of attributes including size, temperature, mass, luminosity, and lifespan.
The Hertzsprung-Russell diagram is a key tool for classifying stars. It plots a star’s absolute magnitude or luminosity against its temperature.
Most stars are found on the ‘main sequence’, which is a diagonal band stretching from the top-left (hot, bright stars) to bottom-right (cooler, dimmer stars) of the Hertzsprung-Russell diagram.
Stars fall into three main categories: dwarfs, giants, and supergiants, each with distinctive properties and locations on the Hertzsprung-Russell diagram.
A star’s temperature can be determined by its colour. Cool stars are red and have a temperature of about 2000–3000K. Hot, blue stars can have temperatures over 25,000K.
A star’s luminosity, or brightness, can be measured in Watts. A star’s absolute magnitude is a measure of the star’s luminosity from a standard distance of 10 parsecs.
Different types of stars have varied lifespans. Massive, bright stars like supergiants have short lifespans due to their rapid consumption of fuel, while smaller, cooler stars like red dwarfs have longer lifespans since they burn fuel more slowly.
Stellar spectral classes are classifications based on the absorption lines of a star’s spectrum, which is related to star’s surface temperature. The spectral classes from hottest to coolest are O, B, A, F, G, K, M.
Stars are mostly made up of hydrogen and helium, with smaller amounts of heavier elements. The proportion of different elements can also be used to classify stars.
Binary star systems consist of two stars that orbit their common centre of mass. They provide valuable information about the stars’ masses which cannot be obtained from observations of single stars.
Variable stars are stars whose brightness as seen from Earth fluctuates over time due to intrinsic changes like pulsations, eruptions, or interactions with a binary companion.
Predicting a star’s future evolution involves understanding how stars form, their main sequence lifetime, and their eventual end as a white dwarf, neutron star, or black hole.
Understanding stellar classifications, the properties of different types of stars, and the life cycle of stars is essential in Astrophysics.