Hypervelocity discoveries with the Gaia space telescope

Douglas Boubert

University of Oxford

Abstract:

Fast stars are the smoking guns of extreme stellar collisions and explosions, but seeing a fast star in your catalogue is more likely a sign that your methodology has fallen down. I will give a brief history of fast stars from the first detection of proper motion to the discovery of stars escaping our Milky Way. These latter stars are known as hypervelocity stars and the focus of this talk will be on the huge open questions concerning them. Why are they moving so fast? Where do they come from? What types of stars can be hypervelocity stars? The Gaia space telescope has been transformative in answering these questions and I will present both the successes and failures of the hunt for hypervelocity stars with Gaia. I will discuss the discovery of white dwarfs moving at 1000s of km/s and the proof of a massive star having been ejected from the Large Magellanic Cloud at 870 km/s. I will walk you through the mystery of the highest radial velocity star in Gaia and introduce the crucial discovery of a star in the halo moving at 1700 km/s that can be tracked back to the centre of our Galaxy.