Age of the milky way
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Age of the Milky Way: Insights from Recent Research
Introduction to the Milky Way's Age
Understanding the age of the Milky Way is crucial for unraveling the history and evolution of our galaxy. Recent studies have provided detailed insights into the age distribution of various components of the Milky Way, including the halo, bulge, and disk. This article synthesizes findings from multiple research papers to present a comprehensive overview of the Milky Way's age.
Age of the Milky Way's Halo
High-Resolution Chronographic Map
A high-resolution chronographic map of the Milky Way's halo, based on the ages of approximately 130,000 blue horizontal-branch (BHB) stars, reveals a strong central concentration of stars older than 12 billion years, extending up to 15 kpc from the Galactic Centre. The mean age of field stars decreases by 1-1.5 billion years out to 45-50 kpc, indicating a dual (inner/outer) halo system1.
White Dwarf Stars as Age Indicators
Observations of newly formed white dwarf stars in the halo, along with data from the 12.5-billion-year-old globular cluster Messier 4, suggest that local field halo stars are around 11.4 ± 0.7 billion years old. The oldest globular clusters formed approximately 13.5 billion years ago, providing a timeline for the formation of the halo2.
Gaia-Enceladus Merger
The star ν Indi, a metal-poor, alpha-element-rich star, indicates that the Gaia-Enceladus merger, a significant event in the Milky Way's history, occurred between 11.6 and 13.2 billion years ago. This merger significantly influenced the chemical and dynamical properties of the Milky Way3.
Age of the Milky Way's Disk
Thick and Thin Disk Populations
The Milky Way's thick disk is identified as a single-burst component with an age of about 13 billion years, making it a significant source of baryonic dark matter. The thin disk, in contrast, contains younger stars, with a more gradual build-up over time4.
Stellar Age Distribution
Using data from the Sloan Digital Sky Survey (SDSS)-APOGEE survey, researchers have dissected the Milky Way's disk into mono-age and mono-[Fe/H] populations. Low [α/Fe] populations show a broader profile with age, indicating disc heating and radial migration. High [α/Fe] populations are older and thicker, contributing most of the mass at old ages7.
Age of the Milky Way's Bulge
Metal-Rich Bulge Stars
The bulge region of the Milky Way predominantly consists of old stars (>8 billion years). However, a non-negligible fraction of younger stars (2-5 billion years) is also present, particularly in the plane of the bulge. This suggests an initial starburst followed by continued star formation at supersolar metallicities5.
RR Lyrae Stars in the Bulge
RR Lyrae stars in the bulge spheroid are estimated to be around 13.41 ± 0.54 billion years old, indicating that they were among the first stars to form in the Milky Way. This age profile aligns with the age of the stellar halo, suggesting a connection between the two structures8.
Conclusion
The Milky Way's age structure is complex, with different components exhibiting distinct age distributions. The halo contains some of the oldest stars, formed over 13 billion years ago, while the disk and bulge have experienced more extended periods of star formation. These findings provide critical insights into the formation and evolutionary history of our galaxy, highlighting significant events such as the Gaia-Enceladus merger and the initial starburst in the bulge.
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Most relevant research papers on this topic
The age structure of the Milky Way's halo
The new high-resolution age map of the Milky Way's halo reveals a central concentration of older stars, supporting the existence of a dual halo system and validating lambda cold dark matter cosmological theory.
The age of the Milky Way inner halo
The Milky Way's inner halo has an age of 11.4 0.7 billion years, based on observations of newly formed white dwarf stars and archival data in the globular cluster Messier 4.
Highly CitedAge dating of an early Milky Way merger via asteroseismology of the naked-eye star ν Indi
The bright naked-eye star Indi can accurately date the age of the early Milky Way population, suggesting the Gaia-Enceladus merger occurred between 11.6 and 13.2 billion years ago.
Nearby stars of the Galactic disc and halo – IV
The thick disc of the Milky Way is a single-burst component with a 20% local normalization, challenging the gradual build-up scenario for our parent spiral and challenging the hierarchical cold-dark-matter-dominated formation picture for spiral galaxies in general.
Highly CitedExploring the Stellar Age Distribution of the Milky Way Bulge Using APOGEE
The Milky Way bulge is predominantly composed of old stars (>8 Gyr), with a small fraction of younger stars at supersolar metallicities, suggesting a recent starburst and continued star formation in a thin disk until 2 Gyr ago.
Uncovering the birth of the Milky Way through accurate stellar ages with Gaia
Gaia spacecraft data reveals that red-sequence halo stars were the first to form in the Milky Way progenitor, marking the accretion of Gaia-Enceladus to the galaxy.
Highly CitedThe age–metallicity structure of the Milky Way disc using APOGEE
The Milky Way disc's structure is influenced by disc heating and radial migration, with high [Fe/H] populations contributing most mass at old ages and low [Fe/H] populations at young ages.
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