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Messier 63
Messier 63
Messier 63
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Messier 63
Image taken by Hubble Space Telescope, on 16 November 2001 at 450 and 814 nm[1]
Observation data (J2000 epoch)
ConstellationCanes Venatici
Right ascension13h 15m 49.27385s[2]
Declination+42° 01′ 45.7261″[2]
Redshift484 km/s[3]
Distance29.3 Mly (8.99 Mpc)[4]
Group or clusterM51 Group
Apparent magnitude (V)9.3[3]
Characteristics
TypeSA(rs)bc[3]
Size110,000 ly (33.65 kpc) (estimated)[3]
Apparent size (V)12.6′ × 7.2′[3]
Other designations
M63, NGC 5055, PGC 46153, UGC 8334[3]
Center of the galaxy

Messier 63 or M63, also known as NGC 5055 or the seldom-used Sunflower Galaxy,[5] is a spiral galaxy in the northern constellation of Canes Venatici with approximately 400 billion stars.[6] M63 was first discovered by the French astronomer Pierre Méchain, then later verified by his colleague Charles Messier on 14 June 1779.[5] The galaxy became listed as 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.[7]

The shape or morphology of this galaxy has a classification of SAbc,[8] indicating a spiral form with no central bar feature (SA) and moderate to loosely wound arms (bc). There is a general lack of large-scale continuous spiral structure in visible light, so it is considered a flocculent galaxy. However, when observed in the near infrared, a symmetric, two-arm structure is seen. Each arm wraps 150° around the galaxy and extends out to 13,000 light-years (4,000 parsecs) from the nucleus.[9]

M63 is a weakly active galaxy with a LINER nucleus – short for 'low-ionization nuclear emission-line region'. This displays as an unresolved source at the galactic nucleus that is cloaked in a diffuse emission. The latter is extended along a position angle of 110° relative to the north celestial pole, and both soft X-rays and hydrogen (H-alpha) emission can be observed coming from along nearly the same direction.[10] The existence of a supermassive black hole (SMBH) at the nucleus is uncertain; if it does exist, then the mass is estimated as (8.5±1.9)×108 M☉,[11] or around 850 million times the mass of the Sun.

Radio observations at the 21-cm hydrogen line show the gaseous disk of M63 extends outward to a radius of 130,000 light-years (40 kiloparsecs), well past the bright optical disk. This gas shows a symmetrical form that is warped in a pronounced manner, starting at a radius of 33,000 light-years (10 kiloparsecs). The form suggests a dark matter halo that is offset with respect to the inner region. The reason for the warp is unclear, but the position angle points toward the smaller companion galaxy, UGC 8313.[12]

The distance to M63, based upon the luminosity-distance measurement is 29,300,000 light-years (8.99 megaparsecs).[4] The radial velocity relative to the Local Group yields an estimate of 15,200,000 light-years (4.65 megaparsecs).[8] Estimates based on the Tully–Fisher relation range over 16,000,000–34,000,000 light-years (5.0–10.3 megaparsecs). The tip of the red-giant branch technique gives a distance of 28,930,000 ± 950,000 light-years (8.87 ± 0.29 megaparsecs).[13] M63 is part of the M51 Group, a group of galaxies that also includes M51 (the 'Whirlpool Galaxy').[14]

Supernova

[edit]

One supernova has been observed in M63: SN 1971I (Type Ia, mag. 11.8) was discovered by Glenn Jolly on 24 May 1971,[15] and was discovered independently by Roger Clark on 29 May 1971.[16][17][18] It reached peak light around 26 May.[19] While the spectrum was consistent with a supernova of type I, the spectroscopic behavior appeared anomalous.[17]

[edit]
  • M63 imaged in UV light by the GALEX satellite. The UV light is produced primarily by young, massive stars, so the UV-bright areas are regions where stars are currently forming.[20] Credit NASA / WikiSky
    M63 imaged in UV light by the GALEX satellite. The UV light is produced primarily by young, massive stars, so the UV-bright areas are regions where stars are currently forming.[20] Credit NASA / WikiSky
  • Messier 63 seen in the infrared by the Spitzer Space Telescope. The infrared radiation traces the dust within the spiral arms, which does not radiate visible light. A small dust ring can be seen just outside of the galaxy's center.[21]
    Messier 63 seen in the infrared by the Spitzer Space Telescope. The infrared radiation traces the dust within the spiral arms, which does not radiate visible light. A small dust ring can be seen just outside of the galaxy's center.[21]
  • The Sunflower Galaxy M 63 taken in France by amateur astrophotographer Anthony MICHEL[22]
    The Sunflower Galaxy M 63 taken in France by amateur astrophotographer Anthony MICHEL[22]

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Messier 63

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Messier 63, also known as the Sunflower Galaxy, is a located approximately 29 million light-years from Earth in the northern constellation . It exhibits a bright central bulge surrounded by two primary spiral arms interspersed with numerous short, discontinuous segments of star-forming regions, which contribute to its characteristic patchy, sunflower-like appearance in visible light. With an of 8.6, it spans about 13.2 by 8.0 arcminutes in the sky and is visible to amateur astronomers using moderate equipment under . Discovered on June 14, 1779, by French astronomer Pierre Méchain, Messier 63 was independently observed by two months later and added as the 63rd object in his famous catalog of nebulae and star clusters in 1781. Classified morphologically as SA(rs)bc—a spiral with inner ring structure and loose arms—it belongs to the M51 Group, a collection of galaxies including the prominent (M51), and shows evidence of a low-ionization nuclear emission-line region (LINER) at its core, indicating mild activity. The galaxy's arms are rich in young, blue-white giant stars and dark dust lanes, as revealed by observations from the , which highlight ongoing in its flocculent structure. Messier 63 has been the subject of extensive study in multi-wavelength astronomy, with infrared imaging uncovering more continuous spiral patterns than visible light reveals, and observations detecting hot gas and potential remnants. Its proximity and brightness make it a key target for understanding processes in non-grand-design spirals, and it hosts a faint stellar tidal stream, suggesting past interactions with a dwarf satellite galaxy.

Physical Characteristics

Coordinates and Visibility

Messier 63 occupies equatorial coordinates of 13h 15m 49.3s and +42° 01′ 45″ in the J2000.0 . In galactic coordinates, it lies at l = 106.0° and b = 74.3°. The exhibits an apparent visual magnitude of 9.3, rendering it accessible to astronomers equipped with or telescopes of 60–100 mm aperture under clear, dark skies away from . Optimal viewing conditions occur in the during late spring, particularly in May, when Messier 63 culminates high overhead in the constellation , positioned near the shared border with and approximately 1.5° north of the star 24 Comae Berenices. Observation of Messier 63 presents challenges stemming from its low , as the light from its extensive disk and spiral arms is diffused over an angular area of about 12.6′ × 7.2′, often appearing as a hazy patch with a brighter core in smaller instruments. To resolve the fainter outer arms, —shifting the gaze slightly off-center to utilize the eye's more sensitive peripheral —is commonly recommended, though revealing the full spiral structure typically requires telescopes of 150 mm aperture or larger under excellent seeing conditions.

Size, Distance, and Luminosity

Messier 63 lies at a of 28.9 ± 1.0 million light-years (8.9 ± 0.3 Mpc) from , determined through measurements of the tip of the (TRGB) using observations. The TRGB provides a reliable distance indicator by calibrating the of the tip. Earlier estimates ranged from 15 to 34 million light-years due to varying methods and limited resolution, but high-resolution HST data has standardized the value around 8.9 Mpc, resolving prior inconsistencies. The galaxy spans a physical diameter of 110,000 light-years (33.7 kpc), comparable to the Milky Way's size, with an observed of 12.6′ × 7.2′. This extent is derived by scaling the angular measurements from optical imaging with the established . In terms of luminosity, Messier 63 has an absolute V-band magnitude of -20.4, reflecting its intrinsic as a luminous , and harbors a total of approximately 60 billion solar masses (6 × 10¹⁰ M_☉), estimated from near-infrared photometry and dynamical modeling. The of z = 0.0020 implies a of 600 km/s relative to the Local Group, consistent with its membership in the M51 Group and the local Hubble flow. Its average of 22.4 mag/arcsec² underscores the diffuse nature of its disk, making it challenging to observe despite its overall .

Discovery and Observation History

Early Discovery

Messier 63 was first discovered on June 14, 1779, by the French astronomer Pierre Méchain while observing from using a 3.5-foot achromatic refractor . Méchain, a colleague and collaborator of , identified the object as a faint in the constellation , noting its position relative to nearby stars without discerning any spiral structure due to the limitations of contemporary instrumentation. Shortly after Méchain's observation, independently verified the discovery on the same date and added it to his catalog as the 63rd entry, M63. Messier described it as a "very faint " with light comparable to M59, lacking a central condensation or resolvable stars, and noted that it faded under the illumination of his micrometer wire; he also positioned it close to an 8th-magnitude star preceding it along the hour wire. This observation was conducted from the in using one of his preferred small refractors. The identification of M63 occurred amid Messier and Méchain's systematic efforts to catalog non-cometary deep-sky objects, aimed at distinguishing fixed nebulae from transient comets during their comet-hunting campaigns in the late . As Méchain's inaugural deep-sky discovery, it exemplified the collaborative astronomical work in that expanded the Messier catalog beyond comets to include such permanent sky features.

Historical Studies and Imaging

In 1845, William Parsons, the 3rd Earl of Rosse, utilized his newly completed 72-inch reflector telescope at to observe Messier 63, resolving its spiral structure for the first time and identifying it as one of the 14 "spiral nebulae" known by 1850. This observation represented a technological milestone in visual astronomy, allowing for the distinction of detailed morphological features in faint deep-sky objects beyond the , though the true extragalactic nature of such spirals remained debated for decades. During the early 20th century, advancements in photographic technology enabled deeper imaging of Messier 63 at major observatories. Plates taken at in 1910 and 1922 by George Willis Ritchey revealed the patchy, discontinuous nature of its spiral arms, later characterized as flocculent, providing the first photographic evidence of its irregular arm structure. In the mid-20th century, the advent of revolutionized studies of Messier 63 by detecting neutral (HI) emission at the 21-cm . Observations in the 1950s from early radio telescopes confirmed HI emission from the galaxy and enabled the mapping of its rotation curve, revealing a flat velocity profile indicative of extended mass distribution. These radio data extended the observable disk beyond optical limits, establishing Messier 63 as a benchmark for kinematic studies of spiral galaxies. From the late 20th to early , space-based telescopes provided unprecedented resolution of Messier 63's structure. Hubble Space Telescope images from the 1990s and 2000s captured intricate details of the spiral arm segments, showcasing the flocculent pattern with enhanced clarity in visible light. Complementing this, observations in the 2000s illuminated the symmetric inner two-arm structure, tracing dust and older stellar populations that are obscured in optical views. Post-2010 observations with advanced interferometers have further probed Messier 63's interstellar components. ALMA array data have mapped molecular gas distributions, revealing concentrations along the spiral arms and insights into triggers. Recent deep imaging studies, such as those in 2025 using ground-based telescopes like the Takahashi FSQ106EDX, have enhanced the visibility of faint stellar tidal streams around the galaxy.

Morphological Structure

Galaxy Classification

Messier 63 is classified as an Sbc according to the , featuring a prominent central bulge and moderately tightly wound spiral arms that extend outward from the nucleus. This classification highlights its intermediate position between tightly wound Sa spirals and more loosely structured Sc types, emphasizing the balance between the bulge-to-disk ratio and arm openness. In the more detailed de Vaucouleurs revised Hubble-Sandage system, Messier 63 is designated SA(rs)bc, indicating an unbarred (SA) spiral with partial inner ring structures (rs) and moderately loose outer arms (bc). This typing underscores the absence of a strong central bar while noting subtle ring-like features in the inner disk that connect to the spiral pattern. The galaxy displays a flocculent spiral morphology, characterized by numerous short, fragmented arm segments rather than long, continuous spirals, with an arm pitch angle of approximately 19°. This structure arises from localized gravitational instabilities rather than global density waves, resulting in irregular, patchy distributions of stars and gas. In contrast to grand design spirals like Messier 51, which exhibit symmetric, well-defined arms driven by strong density waves that promote organized star formation, Messier 63 shows more stochastic and fragmented patterns, with star formation occurring in isolated knots along the discontinuous segments.

Disk and Spiral Arms

Messier 63 features a prominent stellar disk that forms the foundation of its flocculent spiral morphology, characterized by patchy and discontinuous arm features rather than continuous grand-design spirals. In near-infrared observations, the inner disk displays a symmetric two-armed structure, interspersed with prominent lanes that trace the underlying distribution. This inner configuration contrasts with the more fragmented appearance in optical wavelengths, highlighting how obscuration affects visible-light views of the galaxy's core regions. The outer stellar disk extends further, with a surface brightness profile showing a break at approximately 15 kpc indicative of a structural transition to the low-surface-brightness halo, beyond which the stellar drops. This marks the transition to the galaxy's low-surface-brightness halo, with the disk maintaining a relatively thin vertical profile embedded within the broader spheroidal component. The spiral pattern in the disk comprises numerous short, flocculent arm segments—estimated at 10 to 15 distinct spurs—that arise from local gravitational instabilities rather than large-scale wave modes, contributing to the galaxy's irregular, woolly appearance. Overall, these disk and arm features underscore Messier 63's classification as an flocculent spiral, emphasizing localized triggers over global spiral forcing.

Central Components

Nucleus and Active Features

Messier 63 exhibits a transition nucleus with low-ionization nuclear emission-line (LINER)-like features, classified as a composite of LINER and based on optical spectra showing elevated ratios of [N II] λ6583 / Hα (≥ 0.6) and [O I] λ6300 / Hα (≥ 0.17) relative to typical H II regions. This places the nucleus among the lower-luminosity active galactic nuclei (AGN), bridging the gap between ordinary galaxies dominated by stellar processes and more vigorous Seyfert nuclei, as it lacks the high-ionization lines and broad-line components characteristic of full Seyfert activity. The emission arises from low-level nuclear activity, with mechanisms likely involving photoionization by hot, massive stars from a recent or ongoing central starburst, or weak accretion onto a ; ultraviolet spectroscopy reveals strong absorption lines from massive stars supporting a stellar origin for the continuum. The Hα emission traces this modest activity, manifesting as a compact nuclear source with an outflow-like extending along position angle 110°, though the total nuclear Hα remains low, consistent with LINER energetics. Spectral properties include optical emission lines broadened by velocities of approximately 200 km/s, reflecting turbulent gas motions or gravitational influence near the center, while the radio continuum at 1.4 GHz measures around 20 mJy from an unresolved nuclear source, indicating non-thermal emission without prominent jets. In X-rays, observations detect a compact nuclear with low (∼6 × 10^{37} erg s^{-1} in the 2–10 keV band), dominated by soft emission (fitted by a power-law with index Γ ≈ 2.3) likely from hot, diffuse gas heated by stellar processes rather than a strong relativistic jet.

Supermassive Black Hole

Dynamical modeling of the central in Messier 63 reveals evidence for a central concentration of (8.5 ± 1.9) × 10^8 M_⊙ within a radius of approximately 300 pc. This estimate derives from high-resolution Fabry-Perot of Hα emission lines, revealing a central gradient corresponding to V sin i ≈ 111 km s^{-1}, implying a point-mass-like concentration. However, the observed profiles show quasi-constant values rather than a strict decline expected for pure Keplerian motion, suggesting possible contributions from a compact stellar cluster, counter-rotating disk, or non-circular gas motions in addition to gravitational influence from a potential ; the existence of such a black hole remains uncertain. Stellar kinematics in the nuclear region, measured via integral-field , indicate a central velocity dispersion of σ_* ≈ 117 km s^{-1}, with asymmetric and dispersion profiles that align with the presence of a massive central object influencing the stellar orbits. Although direct evidence of Keplerian in nuclear stars is limited, the overall dynamical supports a significant central concentration on sub- to scales. Literature estimates using the bulge stellar velocity dispersion and the M–σ relation yield lower values consistent with nuclear measurements (σ ≈ 150 km s^{-1}). If a supermassive black hole is present, it accretes at a low rate, approximately 10^{-4} times the Eddington limit, as inferred from spectral modeling of its low-luminosity (LLAGN) in the LINER classification. This subdued activity, characterized by weak nuclear emission dominated by advection-dominated accretion flows and possible jet contributions, aligns with the galaxy's spectrum. In comparison, the in M87, with a mass of (6.5 ± 0.7) × 10^9 M_⊙, exhibits significantly higher activity, including a prominent relativistic jet and brighter emission, highlighting Messier 63's relatively quiescent state.

Star Formation and Interstellar Medium

Star Formation Rate

Messier 63 exhibits a current rate of approximately 1 M_⊙ yr⁻¹, derived from the combination of Hα emission, which traces ionizing photons from massive young stars, and 24 μm mid-infrared flux, which accounts for dust-obscured . This value aligns with estimates from far-infrared , where LTIR ≈ 2.2 × 1010 L⊙ provides a measure of the total energy re-radiated by dust heated primarily by recent . Alternative calibrations using near-infrared Brγ recombination lines yield similar integrated rates around 1.7 M_⊙ yr⁻¹ for the galaxy disk. The specific star formation rate, normalized to the galaxy's stellar mass of ≈ 3.6 × 1010 M⊙, is roughly 3 × 10−11 yr⁻¹, placing Messier 63 among typical field spiral galaxies with moderate ongoing activity rather than starburst levels. Ultraviolet observations from GALEX reveal bright flux in the flocculent spiral arms, dominated by young O and B stars with ages under 100 Myr, highlighting that star formation is patchy and concentrated along these structures. Analyses of resolved stellar populations indicate that star formation peaked around 1 Gyr ago, particularly in the inner and outer disk regions, before transitioning to a declining phase that characterizes the current . This historical enhancement likely contributed to the buildup of the disk's stellar content, with the present lower rate reflecting a quiescent phase relative to earlier bursts. In its flocculent arms, efficiency remains low compared to grand-design spirals, adhering to the Schmidt-Kennicutt relation where the surface density of scales with gas surface density as ΣSFR ∝ Σgas1.4, indicating sublinear dependence on molecular gas content. This relation underscores the role of gas density thresholds in regulating the patchy distribution of star-forming regions.

Gas Distribution and Warp

The neutral hydrogen (HI) gas in Messier 63 forms an extended disk with a diameter of approximately 130,000 light-years, roughly twice the extent of the stellar disk, and typical column densities on the order of 102010^{20} cm−2^{-2}. This HI distribution reveals a high surface brightness core within about 10 kpc, transitioning to lower-density spiral features in the outer regions, where the gas surface density drops to around 1 M⊙M_\odot pc−2^{-2}. The molecular gas component, primarily traced by (CO) emission from the survey, is concentrated in the inner disk spanning roughly 20,000 light-years (6 kpc), with a total mass of approximately 5 × 10^9 M⊙M_\odot. This reservoir follows the spiral arm structure in the central regions, providing the primary fuel for activities observed along those features. The outer HI disk displays a pronounced warp, bending by about 20° relative to the inner and beginning at a radius of approximately 33,000 light-years (10 kpc), which may arise from a misalignment between the stellar disk and the or from ongoing gas accretion. The rotation curve of the galaxy remains flat at around 200 km s−1^{-1} beyond 10 kpc, signaling the increasing dominance of in the outer potential, which contributes over half of the total dynamical mass within 40 kpc. Magnetic fields within the disk exhibit a predominantly toroidal configuration, aligned with the spiral arms, and possess strengths of about 10 μG as derived from Faraday rotation measures. These fields show diffuse polarized emission symmetric across the minor axis, with Faraday depths peaking near -8 rad m−2^{-2}, indicating ordered large-scale structure amid the turbulent .

Environment and Interactions

Membership in the M51 Group

Messier 63 is a member of the M51 Group, a loose aggregation of galaxies in the constellation that forms a within the larger Virgo III Cloud filament extending from the . The M51 Group, also known as LGG 347 in the catalog of nearby galaxy groups, contains approximately 20 member galaxies, primarily spirals and irregulars bound by weak gravitational interactions. The group's dynamics are characterized by a low radial velocity dispersion of about 100 km/s and a total virial mass on the order of 10^{13} M_\sun, consistent with properties of small, nearby loose groups dominated by a few bright spirals. Messier 63 ranks as the second brightest member after M51 (the Whirlpool Galaxy), highlighting its prominence within the ensemble. The nearest major neighbors to Messier 63 are M51 at a projected separation of roughly 4.5 million light-years (1.4 Mpc) and its close companion NGC 5195, though Messier 63 itself exhibits relative isolation with no close physical pairs within 100 kpc.

Evidence of Past Interactions

Observational evidence indicates that Messier 63 has experienced gravitational interactions with companion galaxies, manifesting as subtle distortions in its gaseous and stellar components. Faint extensions in the neutral hydrogen (HI) distribution, extending beyond the optical disk, suggest material stripped during an ancient merger event approximately 1 Gyr ago. These HI features, combined with a prominent warp in the HI disk tilting by about 20°, are interpreted as remnants of tidal disruption from a low-mass encounter. The spiral arms of Messier 63 exhibit notable asymmetries, potentially linked to past interactions within the M51 Group. Deep imaging reveals additional plumes extending from the arms, potentially linking tidal debris to these structural imbalances. Halo distortions are evident in the form of stellar streams detected through deep photometric surveys. These faint, arc-like features, spanning up to 29 kpc, show colors consistent with metal-poor stars from the disrupted companion, integrated into Messier 63's outer halo. Recent deep imaging (as of 2025) calibrated to data confirms these streams from accretion of a dwarf with a mass around 3.5 \times 10^8 solar masses. N-body simulations of minor mergers reproduce these streams and the observed disk warp as a remnant of misaligned gas infall during the satellite's disruption. Despite its membership in the M51 Group, Messier 63 occupies a stable orbit with no signs of an ongoing merger, as its velocity and position relative to group members indicate dynamical equilibrium. The last major interaction occurred over 500 Myr ago, allowing the galaxy to retain a relatively undisturbed core while preserving these subtle historical signatures.

Notable Events

Supernova 1971I

SN 1971I, the only confirmed recorded in Messier 63, is a Type Ia event discovered on May 24, 1971, by astronomer Glenn Jolly at an apparent photographic magnitude of 12.5; it was independently discovered and confirmed on May 29, 1971, by Roger N. Clark at the same magnitude. The was absent on plates taken two weeks earlier, with a of 17. Its position is at 13h 15m 43s and +42° 01' 02" (equinox B1950.0), corresponding to an offset of approximately 4 arcminutes from the galactic nucleus, situated within one of the outer spiral arms. The of SN 1971I peaked at a visual magnitude of 11.8 in the V-band around May 26, 1971 (Julian Date 2441080), with an initial post-peak decline rate of 0.02 mag day⁻¹ that steepened to 0.05 mag day⁻¹, consistent with normal Type Ia supernovae. Detailed modeling of the yields a decline parameter Δm₁₅ = 1.1 mag. Spectroscopic observations obtained shortly after discovery revealed broad absorption features characteristic of a Type I supernova, including prominent lines from Si II, , and Ca II. Notably, the Ca II H and K absorption lines exhibited unusually high velocities extending to ~25,000 km s⁻¹, anomalous for typical Type Ia spectra and suggestive of interaction with circumstellar material ejected by a system. The B-V at peak was 0.1 mag, reddening to 0.8 mag about 30 days later, further supporting its classification as a normal-branch Type Ia event.

Other Transients and Phenomena

Messier 63 has exhibited no additional supernovae beyond the Type Ia event SN 1971I, with comprehensive catalogs confirming only this historical outburst in the galaxy. Despite the galaxy's flocculent spiral arms hosting regions of active that could produce core-collapse supernovae, none have been detected as of 2025, consistent with expected rates for galaxies at this distance and . Variable stars, including classical Cepheids, are present in Messier 63 and have been utilized in broader calibrations of the for distance measurements to nearby spirals like this one, though primary distance estimates for M63 rely on the tip of the method. No classical novae outbursts or confirmed candidates have been associated with the galaxy, as archival Fermi Large Area Telescope data reveals no positional overlaps with high-energy events. Optical transient surveys such as the have not reported intrinsic flares or microlensing events definitively linked to M63 in recent years.

References

  1. https://academic.oup.com/mnras/article/501/3/3621/6006291
  2. https://science.[nasa](/page/NASA).gov/mission/hubble/science/explore-the-night-sky/hubble-messier-catalog/messier-63/
  3. https://.u-strasbg.fr/simbad/sim-id?Ident=M63
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  5. https://ui.adsabs.harvard.edu/abs/2011AJ....142..166C/abstract
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