Messier 63
A flocculent spiral galaxy in Canes Venatici.
Messier 63 (M63), also cataloged as NGC 5055 and commonly called the Sunflower Galaxy, is a spiral galaxy found in the northern constellation Canes Venatici. French astronomer Pierre Méchain first spotted it, and Charles Messier confirmed the sighting on June 14, 1779, later listing it as object 63 in his catalog. In the mid-1800s, Anglo-Irish astronomer Lord Rosse detected spiral patterns within it, making M63 one of the earliest galaxies known to have such features.
Its morphological classification is SAbc, meaning it is a spiral without a central bar (SA) and has arms that are moderately to loosely wound (bc). In visible light, the galaxy lacks a large, continuous spiral structure, earning it the description of a flocculent galaxy. However, near-infrared observations reveal a symmetrical two-arm structure, with each arm wrapping 150 degrees around the galaxy and extending about 13,000 light-years (4,000 parsecs) from the nucleus.
M63 is a weakly active galaxy with a LINER-type nucleus—short for low-ionization nuclear emission-line region. This appears as an unresolved bright spot at the core, surrounded by diffuse emission that stretches along a position angle of 110 degrees relative to the north celestial pole. Soft X-rays and hydrogen-alpha emission are observed along roughly the same direction. Whether a supermassive black hole exists at the center is uncertain; if one does, its mass is estimated at 850 million times the Sun’s mass, give or take 190 million.
Radio observations at the 21-centimeter hydrogen line show that M63’s gaseous disk extends to a radius of 130,000 light-years (40 kiloparsecs), far beyond its bright optical disk. This gas is symmetrical but becomes noticeably warped starting at a radius of 33,000 light-years (10 kiloparsecs). The warp suggests that the galaxy’s dark matter halo is offset from its inner region. The cause of the warp is unknown, but its position angle points toward the smaller companion galaxy UGC 8313.
Distance estimates for M63 vary. A luminosity-distance measurement gives 29.3 million light-years (8.99 megaparsecs). Radial velocity relative to the Local Group suggests 15.2 million light-years (4.65 megaparsecs). The Tully–Fisher relation yields a range from 16 million to 34 million light-years (5.0 to 10.3 megaparsecs).
- Discoverer
- Pierre Méchain, later verified by Charles Messier
- Messier catalogue date
- 14 June 1779
- Morphological classification
- SAbc
- Distance luminosity distance
- 29,300,000 light-years (8.99 megaparsecs)
- Distance tip of red giant branch
- 28,930,000 ± 950,000 light-years (8.87 ± 0.29 megaparsecs)
- Supermassive black hole mass estimate
- (8.5±1.9)×10^8 M☉ (if present)
- Supernova observed
- SN 1971I (Type Ia, mag. 11.8, discovered 24 May 1971)
Lore & Background
Messier 63 was first discovered by French astronomer Pierre Méchain, then later verified by his colleague Charles Messier on 14 June 1779, becoming object 63 in the Messier Catalogue. In the mid-19th century, Anglo-Irish astronomer Lord Rosse identified spiral structures within the galaxy, making this one of the first galaxies in which such structure was identified. The galaxy's morphology is classified as SAbc, indicating a spiral form with no central bar feature and moderate to loosely wound arms. It is considered a flocculent galaxy due to a general lack of large-scale continuous spiral structure in visible light, though near-infrared observations reveal a symmetric two-arm structure, each arm wrapping 150° and extending 13,000 light-years from the nucleus.
M63 is a weakly active galaxy with a LINER nucleus, displaying an unresolved source cloaked in diffuse emission extended along a position angle of 110°. Soft X-rays and hydrogen (H-alpha) emission are observed along nearly the same direction. The existence of a supermassive black hole at the nucleus is uncertain; if present, its mass is estimated at (8.5±1.9)×10^8 M☉. Radio observations at the 21-cm hydrogen line show the gaseous disk extends to a radius of 130,000 light-years, well past the bright optical disk, and is warped starting at 33,000 light-years. The warp's position angle points toward the smaller companion galaxy UGC 8313.
The distance to M63 varies by measurement method: luminosity-distance gives 29.3 million light-years, radial velocity relative to the Local Group gives 15.2 million light-years, Tully–Fisher estimates range from 16 to 34 million light-years, and the tip of the red-giant branch technique gives 28.93 ± 0.95 million light-years. M63 is part of the M51 Group, which also includes M51 (the Whirlpool Galaxy). One supernova has been observed: SN 1971I, a Type Ia supernova discovered on 24 May 1971, reaching peak light around 26 May, with an anomalous spectroscopic behavior.
Reader's Guide
Messier 63 holds significance as one of the earliest galaxies recognized to have spiral structure, identified by Lord Rosse in the mid-19th century. Its flocculent appearance in visible light, lacking continuous spiral arms, contrasts with the symmetric two-arm structure revealed in near-infrared, illustrating how different wavelengths can unveil hidden morphology. The galaxy's LINER nucleus and uncertain supermassive black hole highlight ongoing questions about its active galactic nucleus. The warped gaseous disk, extending far beyond the optical disk and pointing toward companion UGC 8313, suggests interactions with dark matter or tidal forces. Multiple distance estimates—ranging from 15.2 to 34 million light-years—underscore the challenges in measuring extragalactic distances. As a member of the M51 Group, M63 provides context for studying galaxy interactions and group dynamics. The single observed supernova, SN 1971I, with its anomalous Type Ia spectrum, adds to the galaxy's legacy as a subject of astrophysical interest.
Did You Know?
- M63 was one of the first galaxies in which spiral structure was identified, by Lord Rosse in the mid-19th century.
- The distance to M63 is uncertain, with estimates ranging from 15.2 to 34 million light-years depending on the method.
- Only one supernova has been observed in M63: SN 1971I, a Type Ia with anomalous spectroscopic behavior.
More in Messier Objects, Part 2 1-24
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