NGC 4631

Coordinates: Sky map 12h 42m 08s, +32° 32′ 29″
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NGC 4631
An image of NGC 4631 taken with Hubble Space Telescope
Observation data (J2000 epoch)
ConstellationCanes Venatici[1]
Right ascension12h 42m 08.0s[2]
Declination+32° 32′ 29″[2]
Redshift606 ± 3 km/s[2]
Distance30 Mly
Apparent magnitude (V)9.8[2]
Apparent size (V)15′.5 × 2′.7[2]
Notable featuresedge-on
Other designations
Whale Galaxy,[3] UGC 7865,[2] PGC 42637,[2] Arp 281,[2] Caldwell 32

NGC 4631 (also known as the Whale Galaxy or Caldwell 32) is a barred spiral galaxy in the constellation Canes Venatici about 30 million light years away from Earth. This galaxy's slightly distorted wedge shape gives it the appearance of a herring or a whale, hence its nickname.[3] Because this nearby galaxy is seen edge-on from Earth, professional astronomers observe this galaxy to better understand the gas and stars located outside the plane of the galaxy.

Starburst and superwind[edit]

NGC 4631 mosaic of two HST images; 7.2′x2′ view

NGC 4631 contains a central starburst, which is a region of intense star formation. The strong star formation is evident in the emission from ionized hydrogen[4] and interstellar dust heated by the stars formed in the starburst.[5] The most massive stars that form in star formation regions only burn hydrogen gas through fusion for a short period of time, after which they explode as supernovae. So many supernovae have exploded in the center of NGC 4631 that they are blowing gas out of the plane of the galaxy. This superwind can be seen in X-rays[6] and in spectral line emission.[4] The gas from this superwind has produced a giant, diffuse corona of hot, X-ray emitting gas around the whole galaxy.[7]

Although no supernovae have been observed in NGC 4631 yet, a luminous red nova, designated AT 2021biy, was discovered on 29 January 2021 (type LRN, mag. 18.1).[8]

Nearby galaxies and galaxy group[edit]

NGC 4631 has a nearby companion dwarf elliptical galaxy, NGC 4627. NGC 4627 and NGC 4631 together were listed in the Atlas of Peculiar Galaxies as an example of a "double galaxy" or a galaxy pair.[9]

NGC 4631 and NGC 4627 are part of the NGC 4631 Group, a group of galaxies that also includes the interacting galaxies NGC 4656 and NGC 4657.[10][11][12][13] However, exact group identification is problematic because this galaxy and others lie in a part of the sky that is relatively crowded. Estimates of the number of galaxies in this group range from 5[10] to 27,[13] and all studies identify very different member galaxies for this group.

See also[edit]

  • NGC 891, a similar edge-on spiral galaxy
  • NGC 4565, a similar edge-on spiral galaxy
  • NGC 5907, a similar edge-on spiral galaxy


  1. ^ R. W. Sinnott, ed. (1988). The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer. Sky Publishing Corporation and Cambridge University Press. ISBN 978-0-933346-51-2.
  2. ^ a b c d e f g h i "NASA/IPAC Extragalactic Database". Results for NGC 4631. Retrieved 2006-11-21.
  3. ^ a b "NGC 4631". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-08-22.
  4. ^ a b R. J. Rand; S. R. Kulkarni; J. J. Hester (1992). "Warm ionized gas in the edge-on galaxies NGC 4565 and NGC 4631". Astrophysical Journal. 396: 97–103. Bibcode:1992ApJ...396...97R. doi:10.1086/171699.
  5. ^ G. J. Bendo; D. A. Dale; B. T. Draine; C. W. Engelbracht; et al. (2006). "The Spectral Energy Distribution of Dust Emission in the Edge-on Spiral Galaxy NGC 4631 as Seen with Spitzer and the James Clerk Maxwell Telescope". Astrophysical Journal. 652 (1): 283–305. arXiv:astro-ph/0607669. Bibcode:2006ApJ...652..283B. doi:10.1086/508057. S2CID 119419587.
  6. ^ Q. D. Wang; R. A. S. Walterbos; M. F. Steakley; C. A. Norman; et al. (1994). "ROSAT detection of diffuse hot gas in the edge-on galaxy NGC 4631". Astrophysical Journal. 439: 176–184. Bibcode:1995ApJ...439..176W. doi:10.1086/175162. hdl:2060/19950011081. S2CID 121407361.
  7. ^ Q. D. Wang; S. Immler; R. Walterbos; J. T. Lauroesch; et al. (2001). "Chandra Detection of a Hot Gaseous Corona around the Edge-on Galaxy NGC 4631". Astrophysical Journal. 555 (2): L99–L102. arXiv:astro-ph/0105541. Bibcode:2001ApJ...555L..99W. doi:10.1086/323179. S2CID 15558867.
  8. ^ Transient Name Server entry for AT 2021biy. Retrieved 10 November 2023.
  9. ^ H. Arp (1966). "Atlas of Peculiar Galaxies". Astrophysical Journal Supplement. 14: 1–20. Bibcode:1966ApJS...14....1A. doi:10.1086/190147.
  10. ^ a b R. B. Tully (1988). Nearby Galaxies Catalog. Cambridge: Cambridge University Press. ISBN 978-0-521-35299-4.
  11. ^ P. Fouque; E. Gourgoulhon; P. Chamaraux; G. Paturel (1992). "Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members". Astronomy and Astrophysics Supplement. 93: 211–233. Bibcode:1992A&AS...93..211F.
  12. ^ A. M. Garcia (1993). "General study of group membership. II - Determination of nearby groups". Astronomy and Astrophysics Supplement. 100: 47–90. Bibcode:1993A&AS..100...47G.
  13. ^ a b G. Giuricin; C. Marinoni; L. Ceriani; A. Pisani (2000). "Nearby Optical Galaxies: Selection of the Sample and Identification of Groups". Astrophysical Journal. 543 (1): 178–194. arXiv:astro-ph/0001140. Bibcode:2000ApJ...543..178G. doi:10.1086/317070. S2CID 9618325.

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