New Delhi: Astronomers have discovered a stream of particles escaping from Westerlund 1, a star cluster at a distance of 13,000 lightyears from the Earth.
The cluster is four million years old, and contains hundreds of massive stars, packed within a region measuring six lightyears across. For comparison, the Sun is 4.5 billion years old. This is the first time that a particle wind escaping from a star cluster in the form of a particle stream has been detected. The stream can leave the galactic disk and feed the halo, contributing to the chemical evolution of a galaxy.
For three years now, scientists knew that Westerlund 1 acts as a natural particle accelerator, accelerating cosmic rays composed mainly of protons, electrons and a small amount of heavier nuclei. In 2022, gamma radiation was discovered encompassing Westerlund-1, with electrons accelerated to dizzying speeds at the fringes of the cluster by the collective magnetic winds of 100,000 stars. The radiation appeared as a ring around the cluster, as well as a tail that pointed away from the plane of the galaxy. Scientists were able to determine that gamma radiation is escaping from the cluster in form of particles propagating through interstellar space, over more than 500 lightyears.
Modelling used to probe processes
Researchers modelled the phenomena to understand the long tail of radiation. According to the model, electrons accelerated at the edge of the cluster are propelled out of it, perpendicular to the plane of the galaxy and towards the halo. The most energetic electrons lose their energy rapidly, and are only visible in the vicinity of the cluster, where the produce the gamma radiation. At greater distances from the cluster, only electrons that have lost some energy are detected, giving rise to a more diffused gamma emission. The research helps better understand how galaxies regulate themselves and evolve over time. A paper describing the research has been published in Nature Communications.
