The disc of the Milky Way is bigger than we thought

The disc of the Milky Way is bigger than we thought
Credit: Instituto de Astrofisica de Canarias (IAC)

A team of researchers at the Instituto de Astrofísica de
Canarias (IAC) and at the National Astronomical Observatories
of Beijing (NAOC) have published a paper which suggests that
if we could travel at the speed of light it would take us
200,000 years to cross the disc of our galaxy.


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 , and it is probable that some stars are
at more than four times the distance of the Sun from the
.

“The disc of our galaxy is huge, around 200 thousand
light-years in diameter,” says Martín López-Corredoira, a
researcher at the IAC and the first author of the article
recently published in the journal Astronomy &
Astrophysics
, and whose authors come from both the IAC and
the NAOC.

In broad terms, we can think of 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. “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, characteristic of disc , further out than the previously assumed
limit on the radius of the galaxy disc” explains Carlos
Allende, a researcher at the IAC and a co-author of this
publication.

Francisco Garzón, an IAC researcher who is another of the
authors of the article explains, “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. The results are therefore free from a priori
assumptions, apart from a few basic and well established ones.”

Explore further:
Is the Milky
Way getting bigger?

More information: M. López-Corredoira et al. Disk stars
in the Milky Way detected beyond 25 kpc from its center,
Astronomy & Astrophysics (2018). DOI: 10.1051/0004-6361/201832880

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