Explosive Stars

Long-term photometric observations of more than two billion stars carried out by astronomers within the OGLE project make it possible to discover many fascinating stellar explosions and to study their origins and properties. These are phenomena that captivate not only scientists but also astronomy enthusiasts, as they are among the most spectacular changes in the night sky. As a result of cosmic explosions, very bright points of light appear in the sky, visible to practically everyone. However, without the systematic observations conducted within OGLE, their detailed analysis would not be possible.

The outburst of the star V1309 Scorpii (Nova Scorpii 2008) was discovered in September 2008 by a group of Japanese and Chinese amateur astronomers. Archival OGLE observations revealed that before the explosion, this was a contact binary system in which two stars orbited each other roughly every 34 hours. In contact binaries, stars are so close that they become distorted, and continuous mass transfer can occur between them. In the case of V1309 Scorpii, the orbital period – the time of mutual revolution and the distance between the stars – kept decreasing until they finally collided. This collision created a single object and provided the first direct evidence that stellar mergers can lead to the outbursts of so-called red novae.

Observations collected by OGLE have also enabled the study of dozens of classical novae, hundreds of supernovae, and the discovery of a new type of X-ray sources in the nearby Magellanic Clouds. Novae are cyclical thermonuclear explosions on stars, while supernovae is a term that encompasses several types of cosmic explosions occurring in the final stages of stellar life, often associated with stars collapsing under their own gravity. These outbursts cause the object to brighten dramatically, sometimes becoming visible to the naked eye, only to fade almost completely after weeks or months. A supernova explosion ejects most or even all of the star’s mass into space.

Thanks to OGLE’s long-term observations and analyses, astronomers have been able to identify and thoroughly describe these events, benefiting not only from the project’s wide sky coverage but also from its invaluable historical data.