Pisces II (Psc II) is a dwarf spheroidal galaxy situated in the Pisces

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

and discovered in 2010 in the data obtained by the

Sloan Digital Sky Survey The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project began in 2000 a ...

. The galaxy is located at the distance of about 180 kpc (kilo parsecs) from the Sun. It is classified as a dwarf spheroidal galaxy (dSph) meaning that it has an elongated shape with the half-light radius of about 60 pc and ratio of the axis of about 5:3. Pisces II is one of the smallest and faintest satellites of the Milky Way—its integrated

luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...

is about 10,000 times that of the Sun ( absolute magnitude of about −5), which corresponds to the luminosity of an average globular cluster. The stellar population of Pisces II consists mainly of moderately old stars formed 10–12 billion years ago. The

metallicity In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as a ...

of these old stars is low at , which means that the percentage of their mass that consists of "heavy metals" is no more than of the corresponding percentage in the Sun. In 2016, follow-up work on

Pegasus III Pegasus ( grc-gre, Πήγασος, Pḗgasos; la, Pegasus, Pegasos) is one of the best known creatures in Greek mythology. He is a winged divine stallion usually depicted as pure white in color. He was sired by Poseidon, in his role as hor ...

highlighted that both it and Pisces II lie relatively close to each other (within approximately 43 kpc) and share similar radial velocities in the Galactic standard of rest frame (note: this is not the same as the LSR). This suggests that these two satellite galaxies may actually be associated with one another, and there is also a possibility that there was an even closer passage about 1 billion years ago. However, further spectroscopic measurements are required to confirm their association.

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