Leo P is a small, star-forming

irregular galaxy An irregular galaxy is a galaxy that does not have a distinct regular shape, unlike a spiral or an elliptical galaxy. Irregular galaxies do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearan ...

located in the constellation

Leo Leo is the Latin word for lion. It most often refers to: * Leo (constellation), a constellation of stars in the night sky * Leo (astrology), an astrological sign of the zodiac * Leo (given name), a given name in several languages, usually mas ...

, discovered through the blind HI Arecibo Legacy Fast ALFA (

ALFALFA Alfalfa () (''Medicago sativa''), also called lucerne, is a perennial plant, perennial flowering plant in the legume family Fabaceae. It is cultivated as an important forage crop in many countries around the world. It is used for grazing, hay, ...

) survey, as an ultra-compact high-velocity cloud (UCHVC) of hydrogen gas. Its confirmation as a

dwarf galaxy A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is so ...

in 2013 suggests that other such UCHVCs are possibly undiscovered dwarf galaxies themselves. Leo P is noteworthy for harbouring one of the most metal-poor environments in the local universe. Its metallicity is just 3% that of the Sun's, meaning that its stars contain 30 times less heavy elements than the Sun. This makes Leo P similar to the pristine environments of primordial galaxies. Leo P is located on the very outskirts of the

Local Group The Local Group is the galaxy group that includes the Milky Way, where Earth is located. It has a total diameter of roughly , and a total mass of the order of . It consists of two collections of galaxies in a " dumbbell" shape; the Milky Way ...

, nearly 5.3 million light years away, and may not be part of it, instead being part of the

Antlia-Sextans Group The Antlia-Sextans Group is a small Galaxy group in the constellations Hydra (constellation), Hydra, Sextans, Antlia and Leo (constellation), Leo. It is, on average, approximately 4.3 million light-years away from the Milky Way. It is generally ...

, a small grouping of galaxies adjacent to the Local Group, sometimes considered bound to it.

Properties

Leo P imaged by the James Webb Space Telescope

Leo P is one of the smallest, least massive and faintest star-forming galaxies in the

. Its total luminosity is less than 440,000 times that of the Sun ( absolute magnitude of −9.27), and its stellar mass is only about 560,000

solar mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...

es, implying a small stellar population. Leo P is also very rich in gas, containing about 810,000 solar masses of neutral hydrogen. Leo P's

half-light radius Galaxy effective radius or half-light radius (R_e) is the radius at which half of the total light of a galaxy is emitted. This assumes the galaxy has either intrinsic circular symmetry, spherical symmetry or is at least circularly symmetric as vi ...

is about 570 pc. Leo P's stellar population consists of a strong concentration of massive, bright and blue stars in the centre of the galaxy, which may be B and A-type

main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...

stars. Some fainter and redder stars are also observed, presumably

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The stellar atmosphere, outer atmosphere is inflated and tenuous, making the radius large and the surface t ...

s from an older

stellar population In 1944, Walter Baade categorized groups of stars within the Milky Way into stellar populations. In the abstract of the article by Baade, he recognizes that Jan Oort originally conceived this type of classification in 1926. Baade observed tha ...

. 10

RR Lyrae star RR Lyrae variables are periodic variable stars, commonly found in globular clusters. They are used as standard candles to measure (extra) galactic distances, assisting with the cosmic distance ladder. This class is named after the prototype and ...

s have been detected in the galaxy, as well as one

H II region An H II region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light year ...

, which is ionised by LP26, an

O-type star An O-type star is a hot, blue star of spectral type O in the Yerkes classification system employed by astronomers. They have surface temperatures in excess of 30,000 kelvins (K). Stars of this type have strong absorption lines of ionised h ...

of 22 solar masses, the only one in Leo P.

Star formation

Leo P is one of the few

galaxies which are currently forming stars. Its star formation rate is about every year, or 1 solar mass every 20,400 years, and it is the Local Group's most metal-poor star-forming galaxy. Its star formation history shows mostly constant star formation throughout its lifetime, something which is also observed in larger irregular galaxies. Models also suggest that there was not much star formation post-reionisation, 12–8 billion years ago, and over the last 4 billion years, star formation has been happening at a constant rate.

References

Irregular galaxies NGC 3109 subgroup Leo (constellation) Astronomical objects discovered in 2013 {{Stars of Leo