What happens to the dead stars and of which, even after thousands of years, we continue to admire the light? Researchers from the University of Sydney they tried to go beyond this question in an attempt to pinpoint where they ended up in the course of 13.6 billion years the remains of celestial objects that were part of the Milky Way “Primordial”, focusing mainly on black holes And neutron stars. Both are formed when massive starswhich are eight times larger than our Sun, run out of fuel, thus triggering the process of gravitational collapse leading to the explosion supernova. At the same time, their core collapses inward. Dying stars can have two different fates: if they had a mass at least eight times that of the Sun, a neutron star is born. If, on the other hand, the star was larger than 25 solar masses, it turns into a black hole. In any case, both types of “stellar corpses” deform the space, time and matter that surrounds them. The results of the study will be published on Monthly Notices of the Royal Astronomical Societyone of the most prestigious and oldest publications on astronomy and astrophysics.
How research on stellar necropolises was born
Peter Tuthill, Professor of Astrophysics at the University of Sydney, and one of the authors of the study, explained that ‘one of the problems in finding these ancient objects is that, until now, we had no idea where to look for them: neutron stars and black holes. ancient were created when the galaxy was younger and had a different shape. Over the course of billions of years, the Milky Way has undergone complex changes. It was like trying to find the cemetery of the mythical elephant (in reference to the place where, according to the legends, the old elephants went to die in solitude, away from their group, ed). The bones of these rare massive stars must have been out there, but they seemed shrouded in mystery. ‘ In the map of the Galactic underworld, as renamed by the authors of the research, it emerged that «the extent of this galactic underworld is beyond three times greater compared to the height of the Milky Way, while a third of the galaxy’s dead stars have been ejected into intergalactic space, and will never return ».
This is because, as explained by Dr. David Sweeney, ‘Supernovae are asymmetrical, and the remains are ejected at high speeds, up to millions of kilometers per hour. And, even worse, this happens in unknown and random directions for each object. It’s a bit like in billiards: if you know which direction the ball is hit and how long it lasts, you can understand where it will go. But in space objects and speeds are much larger. Furthermore, the table is not flat, so the stellar remnants travel complex orbits that traverse the galaxy. Also there is no friction, so they never slow down: almost all remnants ever formed (of supernovae, ed) are still out there, gliding like ghosts in interstellar space ».
How the research took place
Using computer simulation systems, the team of researchers first identified and tracked the starting positions of millions of stellar bodies in the early Milky Way, that is, before the spiral arms that characterize our solar system developed. Subsequently, simulating an acceleration up to the present day, they made one map which would reveal where these dead celestial bodies over billions of years might have ended up. In essence, the researchers identified what they themselves define “a galactic underworld“, a kind of “stellar graveyard“.
The results of the study on the stellar necropolis
But what, in essence, did the researchers discover? “The compact remains of dead stars show a fundamentally different distribution and structure than the galaxy we see today,” explained Dr. Sanjib Sharma and Dr. Ryosuke Hirai of Monash University. “We expected that the galactic underworld would be slightly different, but similar in outline – continued Sharma – I did not expect such a radical change in form”. Yes, because the changes are visible in particular from two maps. The first shows how the spiral arms of the Milky Way do not exist in the “galactic underworld”. They are in fact almost invisible partly due to the age of most of the remains, and partly due to the remains that were created as a result of supernovae.
But what surprised the researchers even more was the side view of this “galactic graveyard”. In fact, the map shows that the largest concentration of stellar remains is located near the center of the galaxy, due to the kinetic energy triggered by supernovae, and which therefore distributes the bodies in a halo surrounding the Milky Way, while the other remains they are distributed on all fronts of the galaxy. But there is more. According to the researchers’ estimates, this “galactic underworld” would contain only about1 percent of the total mass of the cosmos, while the closest “stellar corpse” to Earth should be “only” 65 light-years from the sun. And the team now aims to further optimize the research, as explained by Dr Sweeney: ‘The most interesting part of this research is still ahead of us. Now that we know where to look, we are developing technologies to look for them. I bet that the “galactic underworld” will not remain shrouded in mystery for a long time ». No time, no space docet.
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