by Over the roughly 13.6 billion year history of our Milky Way Galaxy, billions of stars have formed, grown, and eventually died in spectacular supernova explosions. So, where are all their corpses hiding?
In new research published on August 25 at 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 at the beginning Galaxy (long before it developed its iconic spiral arms), then hit a cosmic fast-forward button to show where the shrunken remains of these stars might have ended up after going supernova.
The resulting map revealed a “galactic underworld” of it black holes and neutron stars (two forms of extremely dense stellar debris), lurking in every corner of our Milky Way — and far beyond it, too. According to the researchers, the galactic underworld stretches more than three times the height of the Galaxy itself, while a third of the galaxy’s dead stars have been blasted deep into space by the force of their own end-of-life explosions. , never to return.
“Supernova explosions are asymmetric and the debris is ejected at high speed — up to millions of kilometers per hour,” said lead study author David Sweeney, a PhD candidate at the University of Sydney. statement. “An astonishing 30% of the objects have been ejected from the galaxy entirely.”
The quick and the dead
In their research, the team focused on two types of stellar remnants: neutron stars – extremely dense stellar cores that pack the mass of a sun into a ball no bigger than a city – and black holes, which are massive objects so dense that not even light can escape their gravitational pull.
Both types of objects form when massive stars run out of fuel, shedding their outer layers gas in titanic supernova explosions as their cores collapse inward. If the dying star had a mass at least eight times that of Earth sun, a neutron star is born. if the star measured more than 25 solar masses, a black hole emerges.
Astronomers have detected both classes of stellar remnants in our galaxy, though not enough to attribute the billions of dead stars to our Milky Way’s past. Finding these ancient remnants is difficult for two main reasons: first, the Milky Way has changed shape significantly over the past 13 billion years, meaning that the galactic underworld does not overlap the current distribution of stars in our galaxy. and two, stars that die via supernovae can be “kicked” long distances in random directions by the force of the explosion, ending up on the fringes of the galaxy or lost in intergalactic space.
The study authors built a computer simulation to explain this randomness, as well as the changing shape of the Galaxy and many other factors. Their results showed that the largest concentration of stellar debris can be found swelling near the center of the galaxy, where a supermassive black hole exerts an extremely strong pull. The remaining dead stars are scattered wildly on all sides of the galaxy, in stark contrast to the spiral distribution of stars visible today.
“These compact remnants of dead stars show a fundamentally different distribution and structure in the visible galaxy,” Sweeney added.
The team also found that while the galactic netherworld contains only about 1% of the galaxy’s total mass, ancient stellar corpses are never far away. The nearest stellar remnant should only be about 65 light years from the sun — or closer to us than the stars of the Ursa Major constellation. Hopefully, with a better idea of where to look for them, space probes like the European Space Agency’s ongoing Gaia mission will be able to help unearth the galaxy’s ancient dead in greater numbers than ever before.
