Second stellar population found in Milky Way's thick disk | 8/28/2019 | Staff
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A new study on the kinematics and chemical composition of a sample of stars in the vicinity of the sun, led by Dr. Daniela Carollo, researcher of the Italian National Institute for Astrophysics, has revealed that the stars that make up the thick disk of the Milky Way belong to two distinct stellar populations with different characteristics and not to a single one, as has been thought for more than two decades.

The new thick disk component, called the metal-weak thick disk (MWTD) or metal-poor thick disk, differs from the canonical one in the speed of rotation around the galactic center and its chemical composition. Indeed, stars that make up the TD have a rotational speed of about 180 km per second, while those of the MWTD rotate more slowly, at about 150 km per second. Stars belonging to the MWTD are also two times more metal-poor than those of the TD and have higher energy, a property that allows them to reach greater heights from the galactic plane.

Years - Astronomers - Puzzle - Dr - Carollo

"It was almost 30 years that astronomers tried to solve this puzzle," said Dr. Carollo, scientist at the Astrophysical Observatory of Turin the first author of the article reporting the discovery, just published in The Astrophysical Journal. "In fact, it was thought that the MWTD was nothing but an extension of the thick disk and not an independent population with different astrophysical origins."

The accurate parameters provided by the ESA Gaia mission (positions, distances and intrinsic motion of the stars), and the chemical information on a sample of 40,000 stars of the Sloan Digital Sky Survey (SDSS), allowed the team to distinguish the MWTD in a diagram showing the angular momenta combined with the chemistry.

Momenta - Quantities - Formation - Evolution - System

"The angular momenta are quantities that are conserved during the formation and subsequent evolution of a physical a system like...
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