Milky Way disc much bigger than thought: study

  • It would take us 200,000 years to cross the disc of our galaxy if we could travel at the speed of light, say scientists who found that the disc of the Milky Way is bigger than thought.
  • Spiral galaxies, such as the Milky Way, have discs which are really thin, in which the major fraction of their stars are found. These discs are limited in size, so that beyond certain radius there are very few stars left.
  • In our Galaxy, we were not aware that there are stars in the disc at distances from the centre more than twice that of the Sun. This means that our own star was apparently orbiting at about half the galactic radius.
  • However, now we know that there are stars quite a bit further out, at more than three times this distance, and it is probable that some stars are at more than four times the distance of the Sun from the Galactic centre.
  • The disc of our Galaxy is huge, around 200 thousand light years in diameter.
  • In broad terms we can think of galaxies like the Milky Way as being composed of a rotating disc, which includes spiral arms, and a halo, spherical in shape, which surrounds it.
  • This piece of research has compared the abundances of metals (heavy elements) in the stars of the Galactic plane with those of the halo, to find that there is a mixture of disc and halo stars out to the large distances indicated.
  • The researchers came to these conclusions after make a statistical analysis of survey date from APOGEE and LAMOST, two projects which obtain spectra of stars to extract information about their velocities and their chemical compositions.


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