Ministerio de Economía y Competitividad Gobierno de Canarias Universidad de La Laguna CSIC Centro de Excelencia Severo Ochoa

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Milky Way's disk much larger than previously thought

Author/s: M. López-Corredoira, C. Allende Prieto, F. Garzón H. Wang, C. Liu, L. Deng

Reference: 2018 A&A 612 L8 | Link

The colored region is the previously known Galactic disk. The present work has extended its limits much farther away: there is a probability of 99.7% or 95.4% , respectively, that there are disk stars in the regions outside the dashed/dotted circles. The yellow dot is the position of the Sun. Background Milky Way image from “A Roadmap to the Milky Way”, artistic representation by R. Hurt, SSC-Caltech, NASA/JPL-Caltech.
The colored region is the previously known Galactic disk. The present work has extended its limits much farther away: there is a probability of 99.7% or 95.4% , respectively, that there are disk stars in the regions outside the dashed/dotted circles. The yellow dot is the position of the Sun. Background Milky Way image from “A Roadmap to the Milky Way”, artistic representation by R. Hurt, SSC-Caltech, NASA/JPL-Caltech.

Spiral galaxies, such as the Milky Way, are characterized by having a disk of small thickness where most of the stars are located. These disks have a limited size, basically no stars are to be found beyond certain distance from the Galaxy center. In fact, in our Galaxy, there was no evidence for disk stars at distances from the center larger than twice that of the Sun. Here we show for the first time that there are Galactic stars much farther away, at more than three times that distance, and even four times most likely. This conclusion is based on statistical analyses on data from the APOGEE and LAMOST surveys. The so-called Kolmogorov-Smirnov test was used to compare the abundances of metals in stars in the Galactic plane with the distributions found in another component, the Galaxy's halo, to find that there is a mixture of halo and disk stars up to the great referred distances.

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