Astrophysics & Particle Physics-APPC 2026

Cepheid variables are a group of pulsating variable stars that have periodic variations in luminosity resulting from expansions and contractions of their outer layers. They are perhaps the most fundamental objects in astronomy due to their precisely defined period-luminosity (P-L) relation, by which astronomers can determine distances within the galaxy and beyond.The period-luminosity relation, found by Henrietta Swan Leavitt in 1908, connects the pulsation period of a Cepheid with its intrinsic luminosity. By observing the duration of a Cepheid's light curve and relating its apparent brightness to its intrinsic luminosity, astronomers can precisely calculate the distance to the star and its galaxy. This makes Cepheids critical standard candles in determining the cosmic distance scale and quantifying the Hubble constant.Cepheid variables also offer information about stellar evolution. Their pulsations lie in the Hertzsprung-Russell instability strip, a stage at which stars burn helium in their cores. Detection of these pulsations improves stellar structure, mass, and internal dynamics models.Observations of Cepheids with modern technology utilize photometry at optical and infrared wavelengths, permitting accurate distance measurement even in galaxies' dusty areas.

Space telescopes such as Hubble and missions such as Gaia have greatly enhanced the calibration of Cepheid distances, pushing our reach to the nearest galaxies and improving our vision of galactic and extragalactic structure.In conclusion, Cepheid variables are pulsating stars that play a vital function in distance measurement, stellar evolution research, and charting the universe. Their periodic pulsations make them invaluable instruments for astronomers hoping to comprehend the size and constitution of the universe.