Pisces VII
Dwarf satellite galaxy of Triangulum
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Pisces VII (Psc VII), or Triangulum III, is an ultra-faint dwarf galaxy and a possible satellite of the Triangulum Galaxy (Messier 33).[2] It is likely a small elliptical or irregular galaxy, and is one of the faintest objects within the Local Group, with an apparent magnitude of only 13.6.[2] It was first reported in 2020 by amateur astronomer Giuseppe Donatiello during a review of an astronomical survey, and was later confirmed by the Italian Galileo National Telescope, therefore making it first galaxy within the Local Group to have been discovered by an amateur astronomer.[3][1]
| Pisces VII/Triangulum III | |
|---|---|
Pisces VII/Triangulum III, taken by the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Survey (LSI); due to its high magnitude, it is barely visible | |
| Observation data (J2000 epoch) | |
| Constellation | Pisces |
| Right ascension | 20h 50m 08s[1] |
| Declination | +26° 23′ 27.6″[1] |
| Distance | 1,050 kpc (3.4 Mly)[1] |
| Apparent magnitude (V) | 13.6 ± 2[1] |
| Absolute magnitude (V) | -6.1 ± 2[1] |
| Surface brightness | 2.2+0.5 −0.7×104 L☉[1] |
| Characteristics | |
| Mass | (2.0±0.1)×104[2] M☉ |
| Half-light radius (physical) | 119 ± 48 megaparsecs |
Discovery
Donatiello discovered the galaxy while analyzing the Dark Energy Camera Legacy Survey (DECaLS), a public astronomy survey conducted by the Cerro Tololo Inter-American Observatory using the Blanco 4M telescope.[4][5] He reported it after identifying an unresolved over-density of stellar mass within the Pisces constellation; it was later confirmed by the Galileo National Telescope, making it the first Local Group object to have been discovered by an amateur astronomer.[2][6]
Characteristics
Pisces VII is primarily composed of smaller, old red-dwarf stars, contributing to its unusually high apparent magnitude (13.6) in spite of its close proximity to Earth; a small population of younger blue giants have also been observed within the galaxy.[2][1] It orbits 97 ± 6 kiloparsecs (316,372 ± 341.56 light years) away from Triangulum's galactic center, lying primarily within the galaxy's dark-matter halo.[1]
Due to the slightly warped structure of Triangulum, it is theorized that it made a close flyby with the Andromeda Galaxy within the past few billion years,[7] and thus it is likely that much of the matter of Pisces VII was tidally stripped and pulled into Andromeda, leaving a much dimmer, fainter structure.[4]
Observation
Pisces VII is visible in the namesake constellation of Pisces at a right ascension of 20h 25m 8.4s and a declination of 26° 23′ 27.6″, in the J2000 epoch.[4] Due to its high magnitude, it cannot be seen with the naked human eye, and is extremely difficult to resolve and observe with amateur telescopes.
See Also
- Giuseppe Donatiello
- Magellanic Clouds, dwarf satellite galaxies of the Milky Way
- Messier 32, dwarf satellite of Messier 31
- Pisces II, dwarf satellite galaxy of the Milky Way