A ‘galactic underworld’ of ancient, blown-up stars lurks just beneath the Milky Way’s surface

During the Milky Way’s roughly 13.6-billion-year history, billions of stars have formed, grown and ultimately died in spectacular supernova explosions. So, where are all of their corpses hiding?

In new research published Aug. 25 in the Monthly Notices of the Royal Astronomical Society , astronomers set out to dig up those long lost stellar bodies (so to speak). Using a computer simulation, the team modeled the initial positions of millions of stars in the early Milky Way (long before its iconic spiral arms developed), then hit a cosmic fast-forward button to show where the shriveled remains of those stars may have ended up after going supernova.

The resulting map revealed a “galactic underworld” of black holes and neutron stars (two forms of extremely dense stellar remnants), which lurks in every corner of the Milky Way — and far beyond it as well. According to the researchers, the galactic underworld stretches more than three times the height of the Milky Way itself, while as many as one third of the galaxy’s dead stars have been jettisoned deep into space by the force of their own end-of-life explosions, never to return.

“Supernova explosions are asymmetric, and the remnants are ejected at high speed — up to millions of kilometers per hour,” lead study author David Sweeney, a doctoral candidate at the University of Sydney, said in a statement . “An amazing 30% of objects have been completely ejected from the galaxy.”

In their research, the team focused on two types of s