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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. It contains only 1000 stars, yet is quite massive, having a solar mass to light ratio of 3600. This is an unusually high mass for such a small galaxy.

The distance from the centre of the Milky Way is 26 kpc (85 kly). The luminosity is 450 times that of the Sun. This makes it one of the dimmest known galaxies. 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.

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

References

1. ^ 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. S2CID 54179272.
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. ^ 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. S2CID 13600560.
4. ^ Dajose, Lori (18 November 2015). "Dark matter dominates in nearby dwarf galaxy". Phys.org. Retrieved 19 November 2015.; Lori Dajose (November 18, 2015). "Dark Matter Dominates in Nearby Dwarf Galaxy". Caltech. Retrieved December 16, 2015.

v t e Constellation of Triangulum
List of stars in Triangulum Triangulum in Chinese astronomy
Stars	Bayer α (Mothallah) β γ δ ε ι Flamsteed 1 5 7 10 11 12 13 14 15 Variable R V X RW XX HR 490 523 564 HD 9446 13189 Other B324 HAT-P-38 (Horna) LSPM J0207+3331 M33-013406.63 M33 X-7 Romano's Star Ross 19 Var 83
Exoplanets HAT-P-38b (Hiisi) HD 9446 b c HD 13189 b
Nebulae 588 595 604
Galaxies	NGC Triangulum Galaxy 608 634 669 670 672 684 688 735 736 739 740 750 751 769 777 784 804 805 819 855 860 861 890 925 931 940 941 953 959 970 973 1060 Numbered I II Other Arp 166 RD1
Category

v t e Milky Way
Location	Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow (→) may be read as "within" or "part of".
Structure	Galactic Center Sagittarius A Sagittarius A* Fermi bubbles Supermassive black hole Galactic Center filaments Disk Carina–Sagittarius Norma–Cygnus Orion–Cygnus Perseus Scutum–Centaurus Near 3 kpc Arm Far 3 kpc Arm Halo Aquarius Stream Fimbulthul stream Gaia Sausage Helmi stream Magellanic Stream Monoceros Ring Palomar 5 stream Pisces-Eridanus stream Sagittarius Stream Virgo Stream
Satellite galaxies	Magellanic Clouds Large Magellanic Cloud Small Magellanic Cloud Magellanic Bridge Dwarfs Antlia II Boötes I Boötes II Boötes III Canes Venatici I Canes Venatici II Canis Major Carina Coma Berenices Crater 2 Draco Eridanus II Fornax Hercules Leo I Leo II Leo IV Leo V Leo T Phoenix Pisces Overdensity Pisces II Reticulum II Sagittarius Spheroidal Segue 1 Segue 2 Sculptor Sextans Triangulum II Ursa Major I Ursa Major II Ursa Major III Ursa Minor Virgo I Willman 1
Related	Alternate names Andromeda–Milky Way collision Baade's Window In mythology Zone of Avoidance
Astronomy portal Category

• Dwarf galaxies
• Triangulum
• Milky Way Subgroup
• Astronomical objects discovered in 2015