Messier 32

Coordinates: Sky map 00h 42m 41.8s, 40° 51′ 55″
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Messier 32
M32 Francione inverted.jpg
Dwarf Satellite Galaxy Messier 32
Observation data (J2000 epoch)
Right ascension00h 42m 41.8s[1]
Declination+40° 51′ 55″[1]
Redshift−200 ± 6 km/s[1]
Distance2.49 ± 0.08 million light-years (763 ± 24 kpc)[2][3][4][a]
Apparent magnitude (V)8.08[5][6]
Apparent size (V)8′.7 × 6′.5[1]
Notable featuresSatellite galaxy of the
Andromeda Galaxy
Other designations
M 32, NGC 221,[1] UGC 452,[1] PGC 2555,[1] Arp 168,[1] LEDA 2555

Messier 32 (also known as M32 and NGC 221) is a dwarf "early-type" galaxy about 2,650,000 light-years (810,000 pc) from the Solar System, appearing in the constellation Andromeda. M32 is a satellite galaxy of the Andromeda Galaxy (M31) and was discovered by Guillaume Le Gentil in 1749.

The galaxy is a prototype of the relatively rare compact elliptical (cE) class. Half the stars concentrate within an effective radius (inner core) of 330 light-years (100 pc).[7][8] Densities in the central stellar cusp increase steeply, exceeding 3×107 (that is, 30 million) M pc−3 (that is, per parsec cubed) at the smallest sub-radii resolved by HST,[9] and the half-light radius of this central star cluster is around 6 parsecs (20 ly).[10] Like more ordinary elliptical galaxies, M32 contains mostly older faint red and yellow stars with practically no dust or gas and consequently no current star formation.[11] It does, however, show hints of star formation in the relatively recent past.[12]


In this image of the Andromeda Galaxy, Messier 32 is to the left of the center.

The structure and stellar content of M32 are difficult to explain by traditional galaxy formation models. Theoretical arguments[13] and some simulations suggest a scenario in which the strong tidal field of M31 can transform a spiral galaxy or a lenticular galaxy into a compact elliptical. As a small disk galaxy falls into the central parts of M31, much of its outer layers will be stripped away. The central bulge of the small galaxy is much less affected and retains its morphology. Gravitational tidal effects may also drive gas inward and trigger a star burst in the core of the small galaxy, resulting in the high density of M32 observed today.[14] There is evidence that M32 has a faint outer disk,[15] and as such is not a typical elliptical galaxy.

Newer simulations find that an off-centre impact by M32 around 800 million years ago explains the present-day warp in M31's disk.[16] However this feature only occurs during the first orbital passage, whereas it takes many orbits for tides to transform a normal dwarf into M32. The observed colours and stellar populations of M32's outskirts do not match the stellar halo of M31,[17] indicating that tidal losses from M32 are not their source. Taken together, these circumstances may suggest that M32 already began in its compact state, and has retained most of its own stars. At least one similar cE galaxy has been discovered in isolation, without any massive companion to thresh it.[18]

Another hypothesis is that M32 is in fact the largest remnant of a former spiral galaxy, M32p, which was then the third largest member of the Local Group.[19] According to this simulation, M31 (Andromeda) and M32p merged about two billion years ago, which could explain both the unusual makeup of the current M31 stellar halo, and the structure and content of M32.[20]

Distance measurements[edit]

At least two techniques have been used to measure distances to M32. The infrared surface brightness fluctuations distance measurement technique estimates distances to spiral galaxies based on the graininess of the appearance of their bulges. The distance measured to M32 using this technique is 2.46 ± 0.09 million light-years (755 ± 28 kpc).[2] However, M32 is close enough that the tip of the red giant branch (TRGB) method may be used to estimate its distance. The estimated distance to M32 using this technique is 2.51 ± 0.13 million light-years (770 ± 40 kpc).[3][4] For several additional reasons, M32 is thought to be in the foreground of M31, rather than behind. Its stars and planetary nebulae do not appear obscured or reddened by foreground gas or dust.[21][22] Gravitational microlensing of M31 by a star in M32 was observed[when?] in one event[clarification needed].[23]

Black hole[edit]

Hubble image of Messier 32 showing resolved central region.

M32 contains a supermassive black hole. Its mass has been estimated to lie between 1.5 and 5 million solar masses.[24][25][26][27][28][29] A centrally located faint radio and X-ray source (now named M32* in analogy to Sgr A*) is attributed to gas accretion onto the black hole.[30][31]

See also[edit]


  1. ^ a b c d e f g h i "NASA/IPAC Extragalactic Database". Results for NGC 221. Retrieved 2006-11-29.
  2. ^ a b Jensen, Joseph B.; Tonry, John L.; Barris, Brian J.; Thompson, Rodger I.; Liu, Michael C.; Rieke, Marcia J.; Ajhar, Edward A.; Blakeslee, John P. (2003). "Measuring Distances and Probing the Unresolved Stellar Populations of Galaxies Using Infrared Surface Brightness Fluctuations". Astrophysical Journal. 583 (2): 712–726. arXiv:astro-ph/0210129. Bibcode:2003ApJ...583..712J. doi:10.1086/345430. S2CID 551714.
  3. ^ a b Karachentsev, I. D.; Karachentseva, V. E.; Hutchmeier, W. K.; Makarov, D. I. (2004). "A Catalog of Neighboring Galaxies". Astronomical Journal. 127 (4): 2031–2068. Bibcode:2004AJ....127.2031K. doi:10.1086/382905.
  4. ^ a b Karachentsev, I. D.; Kashibadze, O. G. (2006). "Masses of the local group and of the M81 group estimated from distortions in the local velocity field". Astrophysics. 49 (1): 3–18. Bibcode:2006Ap.....49....3K. doi:10.1007/s10511-006-0002-6. S2CID 120973010.
  5. ^ "M32". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2009-11-29.
  6. ^ Armando, Gil de Paz; Boissier; Madore; Seibert; Boselli; et al. (2007). "The GALEX Ultraviolet Atlas of Nearby Galaxies". Astrophysical Journal Supplement. 173 (2): 185–255. arXiv:astro-ph/0606440. Bibcode:2007ApJS..173..185G. doi:10.1086/516636. S2CID 119085482.
  7. ^ Kent, S. M. (1987). "Surface photometry of six local group galaxies". Astronomical Journal. 94: 306–314. Bibcode:1987AJ.....94..306K. doi:10.1086/114472.
  8. ^ Mateo, M. L. (1998). "Dwarf Galaxies of the Local Group". Annual Review of Astronomy and Astrophysics. 36: 435–506. arXiv:astro-ph/9810070. Bibcode:1998ARA&A..36..435M. doi:10.1146/annurev.astro.36.1.435. S2CID 119333888.
  9. ^ Lauer, T. R.; Faber, S. M.; Currie, D. G.; Ewald, S. P.; Groth, E. J.; Hester, J. J.; Holtzman, J. A.; Light, R. M.; O'Neil Jr, E. J.; Shaya, E. J.; Westphal, J. A. (1992). "Planetary camera observations of the central parsec of M32" (PDF). Astronomical Journal. 104: 552–562. Bibcode:1992AJ....104..552L. doi:10.1086/116254.
  10. ^ Graham, A.W. and Spitler, L.R., Quantifying the coexistence of massive black holes and dense nuclear star clusters.
  11. ^ Kepple, George Robert; Sanner, Glen W. (1998). The Night Sky Observer's Guide. Vol. 1. Willmann-Bell. p. 17. ISBN 978-0-943396-58-3.
  12. ^ Rudenko, Pavlo; Worthey, Guy; Mateo, Mario (2009). "Intermediate age clusters in the field containing M31 and M32 stars". The Astronomical Journal. 138 (6): 1985–1989. Bibcode:2009AJ....138.1985R. doi:10.1088/0004-6256/138/6/1985.
  13. ^ Faber, S. M. (1973). "Tidal Origin of Elliptical Galaxies of High Surface Brightness". Astrophysical Journal. 179: 423–426. Bibcode:1973ApJ...179..423F. doi:10.1086/151881.
  14. ^ Bekki, Kenji; Couch, Warrick J.; Drinkwater, Michael J.; Gregg, Michael D. (2001). "A New Formation Model for M32: A Threshed Early-Type Spiral Galaxy?" (PDF). Astrophysical Journal Letters. 557 (1): L39. arXiv:astro-ph/0107117. Bibcode:2001ApJ...557L..39B. doi:10.1086/323075. S2CID 18707442.
  15. ^ Graham, A. W. (2002). "Evidence for an Outer Disk in the Prototype Compact Elliptical Galaxy M32". Astrophysical Journal Letters. 568 (1): L13–L17. arXiv:astro-ph/0202307. Bibcode:2002ApJ...568L..13G. doi:10.1086/340274. S2CID 14891401.
  16. ^ Dierickx, M.; Blecha, L.; Loeb, A. (2014). "Signatures of the M31–M32 Galactic Collision". Astrophysical Journal. 788 (2): L38. arXiv:1405.3990. Bibcode:2014ApJ...788L..38D. doi:10.1088/2041-8205/788/2/L38. S2CID 119111697.
  17. ^ Choi, P. I.; Guhathakurta, P.; Johnston, K. V. (2002). "Tidal Interaction of M32 and NGC 205 with M31: Surface Photometry and Numerical Simulations". Astronomical Journal. 124 (1): 310–331. arXiv:astro-ph/0111465. Bibcode:2002AJ....124..310C. doi:10.1086/341041. S2CID 119356072.
  18. ^ Huxor, A. P.; Phillipps, S.; Price, J. (2013). "Discovery of an isolated compact elliptical galaxy in the field". Monthly Notices of the Royal Astronomical Society. 430 (3): 1956–1960. arXiv:1302.6520. Bibcode:2013MNRAS.430.1956H. doi:10.1093/mnras/stt014. S2CID 119291374.
  19. ^ "The Milky Way's long-lost sibling finally found". University of Michigan News. 2018-07-23. Retrieved 2018-07-23.
  20. ^ D’Souza, Richard; Bell, Eric F. (2018-07-23). "The Andromeda galaxy's most important merger about 2 billion years ago as M32's likely progenitor". Nature Astronomy. 2 (9): 737–743. arXiv:1807.08819. Bibcode:2018NatAs...2..737D. doi:10.1038/s41550-018-0533-x. ISSN 2397-3366. S2CID 119502746.
  21. ^ Ford, H. C.; Jacoby, G. H.; Jenner, D. C. (1978). "Planetary nebulae in local group galaxies. VI – an observational determination that M32 is in front of M31". Astrophysical Journal. 223: 94–97. Bibcode:1978ApJ...223...94F. doi:10.1086/156239.
  22. ^ van Dokkum, P. G.; Franx, M. (1995). "Dust in the Cores of Early-Type Galaxies". Astronomical Journal. 110: 2027. arXiv:astro-ph/9507101. Bibcode:1995AJ....110.2027V. doi:10.1086/117667. S2CID 118939047.
  23. ^ Paulin-Henriksson, S.; Baillon, P.; Bouquet, A.; Carr, B. J.; Creze, M.; Evans, N. W.; Giraud-Heraud, Y.; Gould, A.; Hewett, P.; Kaplan, J.; Kerins, E.; Lastennet, E.; Le Du, Y.; Melchior, A.-L.; Smartt, S. J.; Valls-Gabaud, D.; Point-Agape Collaboration (2002). "A Candidate M31/M32 Intergalactic Microlensing Event". Astrophysical Journal Letters. 576 (2): L121–L124. arXiv:astro-ph/0206387. Bibcode:2002ApJ...576L.121P. doi:10.1086/343887. S2CID 2554622.
  24. ^ Tonry, J. L. (1984). "Evidence for a central mass concentration in M32". Astrophysical Journal Letters. 283: L27. Bibcode:1984ApJ...283L..27T. doi:10.1086/184326.
  25. ^ Bender, R.; Kormendy, J.; Dehnen, W. (1996). "Improved Evidence for a 3×106 M Black Hole in M32: Canada–France–Hawaii Telescope Spectroscopy with FWHM = 0.47" Resolution". Astrophysical Journal Letters. 464 (2): L123–L126. Bibcode:1996ApJ...464L.123B. doi:10.1086/310098.
  26. ^ Joseph, C. L.; Merritt, D.; Olling, R.; Valluri, M.; Bender, R.; Bower, G.; Danks, A.; Gull, T.; Hutchings, J.; Kaiser, M. E.; Maran, S.; Weistrop, D.; Woodgate, B.; Malumuth, E.; Nelson, C.; Plait, P.; Lindler, D. (2001). "The Nuclear Dynamics of M32. I. Data and Stellar Kinematics". Astrophysical Journal. 550 (2): 668–690. arXiv:astro-ph/0005530. Bibcode:2001ApJ...550..668J. doi:10.1086/319781. S2CID 999283.
  27. ^ Verolme, E. K.; Cappellari, M.; Copin, Y.; van der Marel, R. P.; Bacon, R.; Bureau, M.; Davies, R. L.; Miller, B. M.; de Zeeuw, P. T. (2002). "A SAURON study of M32: measuring the intrinsic flattening and the central black hole mass". Monthly Notices of the Royal Astronomical Society. 335 (3): 517–525. arXiv:astro-ph/0201086. Bibcode:2002MNRAS.335..517V. doi:10.1111/j.1365-2966.2009.15832.x. S2CID 119238097.
  28. ^ Valluri, M.; Merritt, D.; Emsellem, E. (2004). "Difficulties with Recovering the Masses of Supermassive Black Holes from Stellar Kinematical Data". Astrophysical Journal. 602 (1): 66–92. arXiv:astro-ph/0210379. Bibcode:2004ApJ...602...66V. doi:10.1086/380896. S2CID 16899097.
  29. ^ van den Bosch, R. C. E.; de Zeeuw, P. T. (2010). "Estimating black hole masses in triaxial galaxies". Monthly Notices of the Royal Astronomical Society. 401 (3): 1770–1780. arXiv:0910.0844. Bibcode:2010MNRAS.401.1770V. doi:10.1111/j.1365-2966.2009.15832.x. S2CID 119238097.
  30. ^ Ho, Luis C.; Terashima, Yuichi; Ulvestad, James S. (2003). "Detection of the "Active" Nucleus of M32". Astrophysical Journal. 589 (2): 783–789. arXiv:astro-ph/0303060. Bibcode:2003ApJ...589..783H. doi:10.1086/374738. S2CID 10268471.
  31. ^ Yang, Yang; Li, Zhiyuan; Sjouwerman, Loránt O.; Wang, Q. Daniel; Gu, Qiusheng; Kraft, Ralph P.; Yuan, Feng (2015). "Detection of a Compact Nuclear Radio Source in the Local Group Elliptical Galaxy M32". Astrophysical Journal Letters. 807 (1): L19. arXiv:1502.03231. Bibcode:2015ApJ...807L..19Y. doi:10.1088/2041-8205/807/1/L19. S2CID 119292353.

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