Milky Way disk spans 200,000 light years

Metal-rich stars have been discovered far beyond what was thought to be the galactic disk's boundary.
By Laurel Kornfeld | Nov 13, 2018
The Milky Way's disk, the flat, central region of the galaxy that contains mostly young stars, gas, and dust within the structure of its spiral arms, measures 200,000 light years across, making it significantly larger than initially thought, according to a new study.

Previous studies calculated the galaxy's diameter at 100,000 to 160,000 light years.

In the most recent study, scientists analyzed data collected by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) on the spectra of stars in the galactic disk.

A star's spectrum breaks down its light into different colors whose patterns reveal the specific elements present within that star.

For this study, researchers analyzed the metallicities or amounts of heavy elements, within disk stars and were surprised to find stars with high metallicities beyond the region they believed to be the boundary of the galaxy's disk.

"We have shown that there is an appreciable fraction of stars with higher metallicity, characteristic of disk stars, further out than the previously assumed limit on the radius of the galaxy disk," said Carlos Allende of the Astrophysics Institute of the Canary Islands (IAC).

Although spiral disks are usually thin, that is not the case for the Milky Way. "The disk of our galaxy is huge, around 200,000 light years in diameter," stated Martin Lopez-Corredoira, also of the Astrophysics Institute.

The newly-discovered metal-rich disk stars are located about three times further and possibly as far as four times further from the galactic center than our Sun.

One light year is equal to approximately six trillion miles (10 trillion km). A spacecraft traveling at the speed of light would take 200,000 years to cross from one end of the galaxy to the other.

A paper detailing the study's findings has been published in the journal Astronomy and Astrophysics.

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