Something Is Throwing Stars Out of the Milky Way... Sagittarius A*

There is a star leaving the Milky Way, and it is never coming back. It is a brilliant blue-white sun moving at nearly four million miles an hour — fast enough to escape the gravity of our galaxy. Trace its path backward and it points to one place: the dead centre of the Milky Way. Sagittarius A*. At the centre of our galaxy sits a supermassive black hole, four million times the mass of the Sun. It is an ancient anchor. But it is also something stranger: a gravitational engine that can tear a pair of stars apart, keep one, and throw the other out of the galaxy. This film follows the mechanism Jack Hills predicted in 1988, the first hypervelocity stars found in the Milky Way halo, the discovery of S5-HVS1, the paradox of youth around Sagittarius A*, the invisible swarm of dead stellar remnants near the Galactic Centre, and the fate of a star exiled into the space between galaxies. One twin is captured. One twin is thrown. Neither of them was lucky. CHAPTERS: 00:00 — A Star Leaving the Milky Way 01:53 — The Prediction 05:56 — The Separation 09:10 — The Cage 12:21 — The Drain 14:29 — The Exile 18:30 — The Shallows KEY IDEAS: • Hypervelocity stars • S5-HVS1 and its traceback to Sagittarius A* • Jack Hills’ 1988 prediction • The Hills mechanism: one star captured, one star ejected • Sagittarius A* and the S-stars • The paradox of youth • Dynamical friction and mass segregation • Invisible stellar-mass black holes near the Galactic Centre • Hypervelocity stars with possible planets • The exile of a star into intergalactic space • Why Earth is safe only because we live far out in the galactic shallows Note: Close-up visuals of Sagittarius A*, binary disruption, S-star orbits, compact remnants, and intergalactic exile are artistic scientific interpretations based on published models and observations. — Atta, The Quiet Observatory Sources and further reading: Jack Hills — Hyper-velocity and tidal stars from binaries disrupted by a massive Galactic black hole https://doi.org/10.1038/331687a0 Brown et al. — Discovery of an Unbound Hyper-Velocity Star in the Milky Way Halo https://arxiv.org/abs/astro-ph/0501177 Koposov et al. — Discovery of a nearby 1700 km/s star ejected from the Milky Way by Sgr A* https://arxiv.org/abs/1907.11725 S5 Collaboration — Hypervelocity star S5-HVS1 press materials https://s5collab.github.io/hyper_velo... Warren Brown — Hypervelocity Stars review https://doi.org/10.1146/annurev-astro... UCLA Galactic Center Group — Stellar orbits around Sagittarius A* https://galacticcenter.astro.ucla.edu... UCLA Galactic Center Group — Black hole science https://www.astro.ucla.edu/~ghezgroup... ESO — S2 star orbiting Sagittarius A* https://www.eso.org/public/news/eso2006/ ESO — Why the Galactic Centre is hidden by dust https://www.eso.org/public/blog/our-q... NASA / Chandra — Black hole bounty near the Milky Way centre https://www.nasa.gov/image-article/bl... Hailey et al. — A density cusp of quiescent X-ray binaries in the central parsec of the Galaxy https://doi.org/10.1038/nature25029 Ginsburg, Loeb & Wegner — Hypervelocity planets and transits around hypervelocity stars https://arxiv.org/abs/1201.1446 NASA — Solar System facts / Galactic orbit of the Sun https://science.nasa.gov/solar-system... Harvard-Smithsonian CfA — Intergalactic Medium https://www.cfa.harvard.edu/research/... ------------------------------------------------- The observatory also lives on Substack: the episodes as pure audio, quiet versions for sleep, and just the voice on its own. quietobservatory.substack.com