Age of milky way
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The Age of the Milky Way: Insights from Recent Research
Introduction to the Milky Way's Age
Understanding the age of the Milky Way galaxy is crucial for unraveling the history and evolution of our cosmic neighborhood. Recent studies have provided detailed insights into the age distribution of various components of the Milky Way, including its 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 Milky Way's halo, along with data from the 12.5-billion-year-old globular cluster Messier 4, suggest that local field halo stars are approximately 11.4 ± 0.7 billion years old. The oldest globular clusters formed around 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, has been identified as an indicator of the age of the early in situ population of the Milky Way. Its age of 11.0 ± 0.7 billion years suggests that the Gaia-Enceladus merger, a significant event in the Milky Way's history, occurred between 11.6 and 13.2 billion years ago3.
Age of the Milky Way's Disk
Thick and Thin Disk Populations
The Milky Way's thick disk is characterized by an ancient population of stars, with an age of about 13 billion years. This population is distinct from the younger thin disk, which has a different mass-to-light ratio and contributes significantly to the baryonic dark matter in the galaxy4. The thick disk's formation challenges gradual build-up scenarios and supports a more rapid formation process.
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, with an average scale length of 1.9 kpc, contribute most of the mass at old ages6.
Age of the Milky Way's Bulge
Stellar Age Distributions
The Milky Way's bulge is predominantly composed of old stars, with ages greater than 8 billion years. The bulge experienced an initial starburst, more intense close to the plane, followed by continued star formation at supersolar metallicities until about 2 billion years ago5. The bulge's age gradient is primarily due to low-α stars, with a larger dispersion in [Fe/H] compared to the solar neighborhood9.
RR Lyrae Stars
The central kiloparsecs of the Milky Way host an old, spheroidal stellar population, including RR Lyrae stars. These stars have an extremely ancient age of 13.41 ± 0.54 billion years, suggesting they were among the first stars to form in the Milky Way. This population shows a remarkable agreement with the age profile of the stellar halo, indicating a connection between the two structures7.
Conclusion
The Milky Way galaxy, with an age of approximately 13 billion years, has a complex and varied age structure across its halo, disk, and bulge. The halo contains some of the oldest stars, formed over 13 billion years ago, while the disk and bulge have experienced different star formation histories. The thick disk is ancient, while the thin disk and bulge have younger populations. These findings provide critical insights into the formation and evolution 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.
The 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.
Highly CitedThe age of the Milky Way inner stellar spheroid from RR Lyrae population synthesis
The Milky Way's inner stellar spheroid contains some of the oldest stars in the galaxy, with RR Lyrae stars in the bulge spheroid having an extremely ancient age of 13.41 0.54 Gyr.
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.
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