Article · Wikipedia archive · Last revised Aug 6, 2026

Pisces II

Pisces II is an ultra-faint dwarf-spheroidal galaxy and satellite of the Milky Way, located in the Pisces constellation 180 kpc from Earth. Discovered in 2009 by public analysis of Data Release 7 (DR7) of the Sloan Digital Sky Survey, it is classified as a dwarf spheroidal galaxy (dSph) and is one of the smallest and faintest satellite galaxies of the Milky Way.

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Pisces II
Observation data (J2000 epoch)
ConstellationPisces
Right ascension22h 58m 31s1
Declination+05° 57′ 09″1
Distance585 kly (180 kpc)1
Apparent magnitude (V)17.032
Absolute magnitude (V)−4.282
Characteristics
TypedSph
Apparent size (V)2.2+0.2
−0.2′1
Other designations
Pisces II,3 Psc II4A

Pisces II (Psc II)6A is an ultra-faint dwarf-spheroidal galaxy and satellite of the Milky Way, located in the Pisces constellation 180 kpc (587,081 light years) from Earth.1 Discovered in 2009 by public analysis of Data Release 7 (DR7) of the Sloan Digital Sky Survey,1 it is classified as a dwarf spheroidal galaxy (dSph) and is one of the smallest and faintest satellite galaxies of the Milky Way.27

Structure

Pisces is a small irregular galaxy, with a moderately-aged and older stellar population of metal-poor stars, consisting primarily of stars formed about 10 billion years ago.18 The metallicity of these old stars is low, at −2.3 < [Fe/H] < −1.7, which means that the ratio of their mass that consists of heavy metalsB is less than that of the Sun.1 Its luminosity is about 10,000 times that of the Sun (absolute magnitude of about −5), which corresponds to the luminosity of an average globular cluster.68

Potential past interactions

In 2016, follow-up work on Pisces II and Pegasus III8 highlighted that both lie relatively close to each other (within approximately 43 kiloparsecs), and share similar radial velocities in the Milky Way's rest frame.28 This suggests that these two satellite galaxies may actually be associated with one another, potentially having interacted in the past; however, further spectroscopic measurements are needed to confirm this.27

See Also

Notes

Notes

  1. Andromeda II was also given the alias Pisces II by Martin et al. (2009), who also proposed aliases for several other satellite galaxies of the Andromeda Galaxy5 However, that name was later used by a different group unaware of these names, for this object.
  2. In astronomy and physical cosmology, unlike other physical sciences, "heavy metals" refers to all elements except hydrogen and helium.
References

References

  1. Belokurov, V.; Walker, M. G.; Evans, N. W.; Gilmore, G.; Irwin, M. J.; Just, D.; Koposov, S.; Mateo, M.; Olszewski, E.; Watkins, L.; Wyrzykowski, L. (2010). "Big Fish, Little Fish: Two New Ultra-Faint Satellites of the Milky Way". The Astrophysical Journal. 712 (1): L103–L106. arXiv:1002.0504. Bibcode:2010ApJ...712L.103B. doi:10.1088/2041-8205/712/1/L103. S2CID 29195107.
  2. Richstein, Hannah; Patel, Ekta; Kallivayalil, Nitya; Simon, Joshua D.; Zivick, Paul; Tollerud, Erik; Fritz, Tobias; Warfield, Jack T.; Besla, Gurtina; Van Der Marel, Roeland P.; Wetzel, Andrew; Choi, Yumi; Deason, Alis; Geha, Marla; Guhathakurta, Puragra; Jeon, Myoungwon; Kirby, Evan N.; Libralato, Mattia; Sacchi, Elena; Sohn, Sangmo Tony (2022). "Structural Parameters and Possible Association of the Ultra-faint Dwarfs Pegasus III and Pisces II from Deep Hubble Space Telescope Photometry". The Astrophysical Journal. 933 (2): 217. arXiv:2204.01917. Bibcode:2022ApJ...933..217R. doi:10.3847/1538-4357/ac7226. S2CID 247957904.
  3. "Object No. 1 - PISCES II". NASA/IPAC Extragalactic Database.
  4. "NAME Pisces II -- Galaxy". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 24 March 2018.
  5. Martin, Nicolas F.; McConnachie, Alan W.; Irwin, Mike; Widrow, Lawrence M.; Ferguson, Annette M. N.; Ibata, Rodrigo A.; Dubinski, John; Babul, Arif; et al. (1 November 2009). "PAndAS' CUBS: Discovery of Two New Dwarf Galaxies in the Surroundings of the Andromeda and Triangulum Galaxies". The Astrophysical Journal. 705 (1): 758–765. arXiv:0909.0399. Bibcode:2009ApJ...705..758M. doi:10.1088/0004-637X/705/1/758. S2CID 15277245.
  6. "Dwarf Galaxies in Pisces - NASA Science". 2016-08-11. Retrieved 2026-04-21.
  7. Kim, Dongwon; Jerjen, Helmut; Geha, Marla; Chiti, Anirudh; Milone, Antonino P.; Mackey, Dougal; da Costa, Gary; Frebel, Anna; Conn, Blair (2016). "Portrait of a Dark Horse: A Photometric and Spectroscopic Study of the Ultra-Faint Milky Way Satellite Pegasus III". The Astrophysical Journal. 833 (1): 16. arXiv:1608.04934. Bibcode:2016ApJ...833...16K. doi:10.3847/0004-637X/833/1/16. S2CID 73677994.
  8. Garofalo, Alessia; Tantalo, Maria; Cusano, Felice; Clementini, Gisella; Calura, Francesco; Muraveva, Tatiana; Paris, Diego; Speziali, Roberto (2021-07-01). "Born in a Pair (?): Pisces II and Pegasus III*". The Astrophysical Journal. 916 (1): 10. arXiv:2105.11488. Bibcode:2021ApJ...916...10G. doi:10.3847/1538-4357/ac0253. ISSN 0004-637X.
Further reading

Further reading