Runaway stars in our Galaxy

Runaway stars are hot, young stars found faraway from the Galactic disc. They are formed in the disk as all young stars and then ejected by close encounters with other stars or after a massive companion exploded as supernova. Runaway stars are excellent tools to study the structure of our Galaxy. Knowing their velocity and proper motions they can be traced back to their point of origin in the Galactic disc. Gaia data allows an enormous improvement of accuracy compared to previous investigations. Gaia parallaxes also make it possible to carry out a systematic search for these objects for the first time. Previously runaway stars were only found as by-product of other surveys. Since most runaways are found at high galactic latitude they do not experience the heavy reddening, which makes studies, e.g., of the spiral structure of the galactic disc so difficult. Thus they can be used to trace spiral arms usually hidden due to reddening and confusion.