Milky Way Star Cemetery Revealed

These stellar remnants show a distribution and structure different from the visible galaxyexplains in a statement David Sweeney, a PhD student at the Institute of Astronomy affiliated with the University of Sydney and lead author of the work published in Monthly Notices of the Royal Astronomical Society  (New window)(English).

If the subterranean galactic world does not assume the spiral shape of our galaxy, it nevertheless roughly follows its shape. More diffuse, this galaxy ghost spanning an area three times larger than the galactic disk.

Mälkevej 101

  • At the center of the galaxy is a bright core, called a bulge, from which spiral arms radiate outwards, forming a huge flattened disk.
  • At the center of the bulge is Sagittarius A*, a supermassive black hole.
  • The bulb and disc are surrounded by a spherically shaped area called the halo.
  • The galaxy includes over 100 billion stars, interstellar dust and gas.
  • Our Sun is located on one of the spiral arms, about 27,000 light years (1 AL = 9460 billion kilometers) from the center of the Milky Way.

The Milky Way observed by the Gaia telescope.

Photo: ESA

heavenly necropolis

The map, created by Australian astrophysicists, shows the location of neutron stars and stellar black holes, which form when massive stars – more than eight times the size of our Sun – run out of fuel and collapse in on themselves.

This runaway reaction causes the outer layers of massive stars to explode in supernovae, while their cores continue to compress themselves until, depending on their initial mass, they become a neutron star or a hole. blackexplains the press release.

Color representation of the visible Milky Way and the galactic underworld.

Color representation of the visible Milky Way (right) and the galactic underworld (left).

Photo: University of Sydney

It is largely its mass that determines whether a star becomes a neutron star or a black hole.

In the first case, the nucleus is so dense that electrons and protons are forced to combine at the subatomic level to form neutrons, thus compressing its total mass into a sphere smaller than a city.

In the second case, when the mass of the original star is more than 25 times that of our Sun, its collapse continues until the core is so dense that it becomes a black hole.

These two types of star-like corpses, which would represent just under 1% of the Milky Way’s stellar mass, distort the space, time and matter around them.

Since the birth of the Milky Way, billions of stars have been born and died. The simulation indicates that almost a third of these stars have been ejected from the galaxy and are now in the intergalactic medium.

% de toutes les étoiles à neutrons produites, mais seulement 2% des trous noirs stellaires durant toute l’évolution de la galaxie. […] Au total, environ 0,4% de la masse stellaire de notre Voie lactée l’aurait quittée depuis sa naissance”,”text”:”Ces expulsions représenteraient environ 40% de toutes les étoiles à neutrons produites, mais seulement 2% des trous noirs stellaires durant toute l’évolution de la galaxie. […] Au total, environ 0,4% de la masse stellaire de notre Voie lactée l’aurait quittée depuis sa naissance”}}”>These ejections would represent about 40% of all neutron stars produced, but only 2% of stellar black holes throughout the galaxy’s evolution. […] In total, about 0.4% of our Milky Way’s stellar mass would have left it since its birth.the researchers note.

Cosmic coroners

By carefully recreating the complete life cycle of extinct stars, astrophysicists have produced the first detailed map showing where their remains lie.

At first, this work was not easy, as the researchers did not know where to look. The oldest neutron stars and black holes were created when the galaxy was younger and had a different shape. They then underwent complex changes spanning billions of years.says Professor Peter Tuthill, who also signs the study.

The oldest neutron stars and black holes are like ghosts that still haunt a house that was torn down long ago. They are therefore harder to find. »

A quote from Peter Tuthill, University of Sydney

PhD student David Sweeney adds that there is another difficulty that complicates our ability to determine the distribution of dead stars: Supernova explosions are asymmetric, so the debris is ejected at high speed, up to millions of kilometers per hour, in random directions to each object.

It’s a bit like billiards. If you know which direction the ball hits and with what force, then you can determine where it will land. But in space, objects and speeds are much greater. Also, the table is not flat, and the remnants of stars follow complex trajectories through the galaxy. »

A quote from David Sweeney

Also, there is no friction in space, so objects never slow down.

Almost all of the debris that formed there is still there, drifting like ghosts through interstellar space. »

A quote from David Sweeney

To locate them, the team first used data collected from recently discovered neutron stars and black holes in the current galactic shape.

She then coded the birth and death sites of older stars to assess their dispersion during the galaxy’s evolution.

The end result is a distribution map of the Milky Way’s stellar necropolis that surprises its creators as it doesn’t quite match the appearance of the visible Milky Way.

In modeled maps, the characteristic spiral arms of the Milky Way have disappeared into the galactic underworld.

Enlarge image (New window)

The Milky Way (top image) and the galactic underworld (bottom image).

Photo: University of Sydney/SIfA

In modeled maps (see images above), the Milky Way’s characteristic spiral arms (top image) have disappeared into the galactic underworld (bottom image). These have disappeared entirely due to the age of most of the remnants and the blurring effects associated with the supernova explosions that created them.

David Sweeney now wants to use this new knowledge to develop even more accurate models of the galactic underworld.

The most exciting part of this research is still ahead of us. I bet the galactic underworld won’t stay shrouded in mystery for longpleases the doctoral student.

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