The disc containing most of the stars in the Milky Way may be much bigger than scientists previously thought.
A new survey of data from the Apogee and Lamost projects to obtain stars’ spectra, researchers have found that stars in the disc are much further out than previous estimates suggested.
Scientists now say the disk is roughly 200 thousands light-years across.
The new study from the Instituto de Astrofísica de Canarias (IAC) and the National Astronomical Observatories of Beijing (NAOC) compared the abundances of metals (heavy elements) in the stars of the galactic plane with those of the halo.
According to the researchers, there may be some stars that are situated more than four times the distance of the sun from the galactic center.
‘The disc of our galaxy is huge, around 200 thousand light-years in diameter,’ says lead author Martín López-Corredoira, a researcher at the IAC.
In the study, the researchers found that there are both disc and halo stars at great distances from the center.
Being a spiral galaxy, the Milky Way has what are known as arms and a spherical halo that surrounds it.
‘Using the metallicities of the stars in the catalogues from the high quality spectral atlases of Apogee and Lamost, and with the distances at which the objects are situated, we have shown that there is an appreciable fraction of stars with higher metallicity, characteristics of disc stars, further out than the previously assumed limit on the radius of the galaxy disc,’ says co-author Carlos Allende, a researcher at the IAC.
The Milky Way’s disc contains a major portion of its stars, the researchers explain.
Beyond this, there are comparatively few stars.
The new study provides new insight on the composition and velocity of the stars in the disc, and a more precise measurement.
‘We have not used models, which sometimes give us only the answers for which they were designed, but we have employed only the statistics of a large number of objects,’ said Francisco Garzón.
‘The results are therefore free from a priori assumptions, apart from a few basic and well established ones.’