Variable Stars

Among the billions of stars observed by astronomers, a relatively small group draws special attention. These are variable stars – stars whose observed brightness changes over time. Variations in stellar brightness may arise from different causes: pulsations, atmospheric activity, eruptions, eclipses, or rotation. Each of these phenomena provides important insights into the stars themselves and the environments in which they are located.

Researchers from the Astronomical Observatory of the University of Warsaw, working within the OGLE project, have for years been monitoring the brightness of about two billion stars, building a database that now contains more than one trillion individual photometric measurements. This unprecedentedly vast dataset has enabled Warsaw astronomers to discover and classify over a million previously unknown variable stars of different types. In this way, the OGLE Collection of Variable Stars was created.

This collection has found numerous astrophysical applications. Pulsating stars discovered by the OGLE team have been used to precisely measure distances to nearby galaxies and to determine the structure of the Milky Way with high accuracy. These pulsating variables belong to two groups: the first are Cepheids – extremely luminous stars, sometimes shining up to ten thousand times brighter than the Sun; the second are RR Lyrae stars – also bright giants, named after a star in the constellation Lyra.

Another major outcome of variable star observations is the precise calibration of the cosmic distance scale. This was made possible through the analysis of eclipsing variable stars in the Magellanic Clouds. New classes of pulsating stars discovered by OGLE researchers have drawn the attention of astrophysicists to previously unknown evolutionary tracks of stars. It should also be mentioned that observations of stellar variability conducted by Warsaw astronomers laid the foundation for the first-ever discoveries of extrasolar planets. These were made using the transit method – in which a planet blocks part of its star’s light as it passes in front of it – and the gravitational microlensing method, which analyzes the bending of light rays caused by the gravity of a celestial body.

Other research carried out by the OGLE team with data from variable star photometry includes the search for black holes, the study of novae and supernovae explosions, and the observation of colliding stars. All these efforts would be impossible without detailed investigations of the nature of stars with variable brightness, made possible by the large-scale OGLE sky survey.