SIP/ASTRO 3D: Star-Quake Vibrations Estimate Milky Way Age

[bystander]

Star-Quake Vibrations Lead to New Estimate for Milky Way Age
ARC Centre of Excellence for All Sky Astrophysics in Three Dimensions (ASTRO-3D) |
via Science in Public | 2019 Dec 04

Data gathered by NASA’s now defunct Kepler telescope provides a solution to an astronomical mystery.

An artist impression of the Milky Way, showing the thick and thin discs. Credit: NASA/JPL Caltech/R.Hurt/SSC

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Star-quakes recorded by NASA’s Kepler space telescope have helped answer a long-standing question about the age of the “thick disc” of the Milky Way.

In a paper ... a team of 38 scientists ... use data from the now-defunct probe to calculate that the disc is about 10 billion years old. ...

The Milky Way – like many other spiral galaxies – consists of two disc-like structures, known as thick and thin. The thick disc contains only about 20 per cent of the Galaxy’s total stars, and, based on its vertical puffiness and composition, is thought to be the older of the pair.

To find out just how much older, Dr Sharma and colleagues used a method known as asteroseismology – a way of identifying the internal structures of stars by measuring their oscillations from star quakes. ...

This age-dating allows researchers to essentially look back in time and discern the period in the Universe’s history when the Milky Way formed; a practice known as Galactic-archaeology. ...

The K2-HERMES Survey: Age and Metallicity of the Thick Disc ~ Sanjib Sharma et al

• Monthly Notices of the RAS 490(4):5335 (Dec 2019) DOI: 10.1093/mnras/stz2861
• arXiv.org > astro-ph > arXiv:1904.12444 > 29 Apr 2019

[Ann]

It would have been interesting if they had tried to estimate the age of the thin disk too, using the same method.

Ann

[bystander]

Second Stellar Population Found in Milky Way's Thick Disk
Italian National Institute for Astrophysics | via phys.org | 2019 Dec 11

The Milky Way from the Andes in Chile. Credit: G. Hüdepohl/ESO

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A new study led by Dr. Daniela Carollo -- researcher of the Italian National Institute for Astrophysics -- on the kinematics and chemical composition of a sample of stars in the vicinity of the Sun, revealed that the stars that make up the thick disk of our galaxy, 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 metal weak thick disk (MWTD) or metal poor thick disk, differs from the canonical one, the thick disk (TD), in particular for the speed of rotation around the galactic center and for the 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 larger energy, a property that allows them to reach higher distances from the galactic plane. ...

The very 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. ...

Evidence for the Third Stellar Population in the Milky Way's Disk ~ Daniela Carollo et al

• Astrophysical Journal 887(1):22 (2019 Dec 10) DOI: 10.3847/1538-4357/ab517c
• arXiv.org > astro-ph > arXiv:1904.04881 > 09 Apr 2019 (v1), 29 Oct 2019 (v3)