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| M51 (Whirlpool Galaxy) | |
|---|---|
| Name | Whirlpool Galaxy |
| Other names | Messier 51, M51a, NGC 5194 |
| Type | SA(s)bc pec |
| Constell | Canes Venatici |
| Distance | ~23 million light-years |
| Apparent magnitude | 8.4 |
| Size | 11.2′ × 6.9′ |
| Redshift | 463 km/s |
| Notable | Interaction with NGC 5195 |
M51 (Whirlpool Galaxy) is a grand-design spiral galaxy notable for its prominent spiral arms and a close companion, NGC 5195. Located in the constellation Canes Venatici, it has been a key object for studies by observers such as Charles Messier, William Herschel, and missions like the Hubble Space Telescope and Spitzer Space Telescope. M51 serves as a benchmark for research in galaxy interaction, star formation, active galactic nucleus physics, and interstellar medium structure.
M51, catalogued by Charles Messier in the 18th century and included in the Messier catalogue, is often referred to in observational work by names used in the New General Catalogue and by modern surveys such as the Sloan Digital Sky Survey and Two Micron All-Sky Survey. Its proximity to the Local Group and location in Canes Venatici make it accessible to instruments from historical observatories like Royal Observatory, Greenwich to contemporary facilities like the Very Large Array and the Atacama Large Millimeter/submillimeter Array.
M51 was first noted by Charles Messier in 1773 and later sketched by Lord Rosse who resolved spiral structure with the Leviathan of Parsonstown. Systematic photometry and spectroscopy were advanced by observers at Mount Wilson Observatory and Palomar Observatory. The galaxy featured in work by Edwin Hubble on spiral classification and later in rotation curve studies by Vera Rubin and Kent Ford. Space-based imaging by Hubble Space Telescope and multiwavelength campaigns including Chandra X-ray Observatory and Spitzer Space Telescope refined understanding of its star-forming regions and supernova detections such as SN 1994I.
M51 is classified as an SA(s)bc pec spiral in the Hubble sequence with an estimated mass in stars on the order of 10^10–10^11 solar masses, comparable to Milky Way estimates. Its distance estimates range from measurements anchored to the Cepheid variable scale calibrated by the Hubble Space Telescope Key Project and methods using the tip of the red giant branch and the planetary nebula luminosity function. The systemic radial velocity and redshift measurements were made with instruments used by teams at Max Planck Institute for Astronomy and Harvard–Smithsonian Center for Astrophysics. M51's dust content and molecular gas reservoirs have been mapped with facilities such as IRAM and SMA.
M51 exhibits a grand-design two-armed spiral morphology in optical imaging from Hubble Space Telescope, with well-defined spiral density wave features that are prominent in near-infrared images from Spitzer Space Telescope and ground-based observatories like Keck Observatory. Rotation curve and kinematic maps derived from observations at Very Large Array and ALMA show differential rotation and non-circular motions influenced by tidal perturbations. Studies invoking theories from Toomre and simulations performed by research groups at Princeton University and California Institute of Technology model its spiral arm stability, pattern speed, and resonance locations.
The gravitational encounter with the dwarf companion NGC 5195 has been central to M51's morphology; interaction scenarios were modeled in seminal papers from teams at Columbia University and University of California, Berkeley. Tidal features, bridges, and induced spiral density waves are evident in HI maps from Westerbork Synthesis Radio Telescope and CO maps from IRAM. Numerical simulations using N-body and hydrodynamic codes developed at University of Oxford and University of Toronto reproduce features such as the pronounced tidal tail and the offset between stellar and gaseous arms, supporting a history of one or more close passages within the last few hundred million years.
M51 hosts vigorous star formation along its spiral arms, with giant H II regions catalogued by observers at Mount Wilson Observatory and in surveys like the SINGS program. Young stellar clusters and associations have been studied with Hubble Space Telescope photometry and spectroscopy by groups at Space Telescope Science Institute and European Southern Observatory. Molecular cloud complexes traced by CO emission in observations from ALMA and IRAM correlate with far-infrared emission mapped by Herschel Space Observatory, indicating active conversion of gas into stars. The population of massive stars, supernova remnants, and compact clusters informs comparisons with star formation laws derived by researchers at Max Planck Institute for Astrophysics and University of Cambridge.
The nucleus of M51 exhibits low-luminosity active galactic nucleus characteristics identified in radio surveys by Very Large Array teams and X-ray studies by Chandra X-ray Observatory and XMM-Newton. Emission-line diagnostics in optical spectra obtained at Keck Observatory and Palomar Observatory suggest a Seyfert-like nucleus, while high-resolution radio imaging reveals compact jets and knots analyzed by groups at National Radio Astronomy Observatory. X-ray point sources, ultraluminous X-ray sources, and diffuse emission have been catalogued by teams at Harvard–Smithsonian Center for Astrophysics and linked to both accreting compact objects and hot interstellar gas heated by star formation and interaction-driven shocks.
Category:Spiral galaxies