Triangulum II


Coordinates: Sky map 02h 13m 17.4s, +36° 10′ 42.4″

Triangulum II (Tri II or Laevens 2) is a dwarf galaxy close to the Milky Way Galaxy. Like other dwarf spheroidal galaxies, its stellar population is very old: the galaxy was quenched before 11.5 billion years ago.[2] It contains only 1000 stars, yet is quite massive, having a solar mass to light ratio of 3600.[3] This is an unusually high mass for such a small galaxy.[4]

Triangulum II
Observation data (J2000 epoch)
Right ascension02h 13m 17.4s[1]
Declination+36° 10′ 42.4″[1]
Distance97.8 ± 6.5 kly (30 ± 2 kpc)[1]
Mass/Light ratio3600 (V)[1] M/L
Apparent size (V)3.9′[1]
Other designations
Triangulum II, Tri II, Laevens 2, Lae 2

The distance from the centre of the Milky Way is 26 kpc (85 kly). The luminosity is 450 times that of the Sun.[3] This makes it one of the dimmest known galaxies.[3] The 2D half light radius is 34 pc (110 ly). The galaxy was discovered in images taken by Pan-STARRS by Benjamin P. M. Laevens in 2015.[1][3]

Triangulum II is a candidate for detecting WIMPs as a source of dark matter.[4]


  1. ^ a b c d e f Laevens, Benjamin P. M.; Martin, Nicolas F.; Ibata, Rodrigo A.; Rix, Hans-Walter; Bernard, Edouard J.; Bell, Eric F.; Sesar, Branimir; Ferguson, Annette M. N.; Schlafly, Edward F.; Slater, Colin T.; et al. (31 March 2015). "A New Faint Milky Way Satellite Discovered in the PAN-STARRS1 3π Survey" (PDF). The Astrophysical Journal. 802 (2): L18. arXiv:1503.05554. Bibcode:2015ApJ...802L..18L. doi:10.1088/2041-8205/802/2/L18.
  2. ^ Sacchi, Elena; Richstein, Hannah; Kallivayalil, Nitya; Van Der Marel, Roeland; Libralato, Mattia; Zivick, Paul; Besla, Gurtina; Brown, Thomas M.; Choi, Yumi; Deason, Alis; Fritz, Tobias; Geha, Marla; Guhathakurta, Puragra; Jeon, Myoungwon; Kirby, Evan; Majewski, Steven R.; Patel, Ekta; Simon, Joshua D.; Tony Sohn, Sangmo; Tollerud, Erik; Wetzel, Andrew (2021). "Star Formation Histories of Ultra-faint Dwarf Galaxies: Environmental Differences between Magellanic and Non-Magellanic Satellites?". The Astrophysical Journal Letters. 920 (1): L19. arXiv:2108.04271. Bibcode:2021ApJ...920L..19S. doi:10.3847/2041-8213/ac2aa3. S2CID 236965965.
  3. ^ a b c d Kirby, Evan N.; Cohen, Judith G.; Simon, Joshua D.; Guhathakurta, Puragra (16 November 2015). "Triangulum II: Possibly a Very Dense Ultra-Faint Dwarf Galaxy". The Astrophysical Journal. 814 (1): L7. arXiv:1510.03856. Bibcode:2015ApJ...814L...7K. doi:10.1088/2041-8205/814/1/L7.
  4. ^ a b Dajose, Lori (18 November 2015). "Dark matter dominates in nearby dwarf galaxy". Retrieved 19 November 2015.; Lori Dajose (November 18, 2015). "Dark Matter Dominates in Nearby Dwarf Galaxy". Caltech. Retrieved December 16, 2015.