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--- courses:ast403:virgo-cluster [2026/03/09 10:16] – shuvo
+++ courses:ast403:virgo-cluster [2026/03/09 10:18] (current) – shuvo
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 The Virgo Cluster is the closest massive concentration of galaxies to the Milky Way, located at a distance of approximately 16 to 18 megaparsecs (Mpc). It represents a significant peak in the large-scale structure of the local Universe and serves as a fundamental laboratory for studying cluster dynamics and galaxy evolution.
-**Classification and Morphology:**
+===== Classification and Morphology =====
 The Virgo Cluster is classified as an irregular cluster due to its lumpy, non-spherical distribution of galaxies. It extends over a region of approximately 10° × 10° on the sky. Unlike "relaxed" regular clusters that are compact and symmetric, Virgo exhibits strong substructure, suggesting it is a young system still in the process of formation through the merger of smaller entities. Observations indicate the cluster consists of at least two primary sub-clumps centered around the massive elliptical galaxies M87 and M49, separated by about 1 Mpc.
-**Membership and Galactic Population:**
+===== Membership and Galactic Population =====
-The cluster contains approximately 250 large galaxies** and more than 2,000 smaller ones. Its population follows a distinct //morphology–density relation//:
+The cluster contains approximately 250 large galaxies and more than 2,000 smaller ones. Its population follows a distinct //morphology–density relation//:
 **Central Region:** Dominated by early-type galaxies (ellipticals and S0s), which have little ongoing star formation and consist primarily of old stars.
@@ Line 35: / Line 35: @@
 Virgo contains several unique intergalactic components:
-**HI Clouds:** Large clouds of neutral hydrogen have been detected that are not associated with any optically luminous galaxy; one such cloud appears dominated by dark matter.
+//HI Clouds//: Large clouds of neutral hydrogen have been detected that are not associated with any optically luminous galaxy; one such cloud appears dominated by dark matter.
-**Vagabond Stars:** Approximately 10% to 20% of the cluster's stars and planetary nebulae exist in the intergalactic space between galaxies, likely stripped from their parent systems during past tidal interactions or mergers.
+//Vagabond Stars//: Approximately 10% to 20% of the cluster's stars and planetary nebulae exist in the intergalactic space between galaxies, likely stripped from their parent systems during past tidal interactions or mergers.
-**Cosmological Context and Infall**
+===== Cosmological Context and Infall =====
 The Virgo Cluster exerts a massive gravitational pull on its surroundings. The Local Group (including the Milky Way) is currently moving toward the cluster at a speed of approximately 270 km s⁻¹, a phenomenon known as Virgocentric infall. Because of its proximity, the cluster was a primary target for the Hubble Space Telescope's Key Project to identify Cepheid variables, a crucial step in calibrating the Hubble constant ($H_0$) and determining the expansion rate of the Universe.