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Leo I (dwarf galaxy)
Encyclopedia
Leo I is a dwarf spheroidal galaxy
in the constellation
Leo
. At about 820,000 light-year
s distant, it is a member of the Local Group
of galaxies and is thought to be one of the most distant satellites of the Milky Way
galaxy. It was discovered in 1950 by Wilson
on photographic plate
s of the National Geographic Society - Palomar Observatory Sky Survey
, which were taken with the 48-inch Schmidt camera
at Palomar Observatory
.
of some bright red giant
s in Leo I have made possible to measure its mass. It was found to be at least (2.0 ± 1.0) × 107 MSun
. The results are not conclusive, and do not deny or confirm the existence of a large dark matter
halo around the galaxy. However, it seems to be certain that the galaxy does not rotate.
It has been suggested that Leo I is a tidal debris stream in the outer halo
of the Milky Way. This hypothesis has not been confirmed, however.
of Leo I is very low, only one percent that of the Sun
. Gallart et al. (1999) deduce from Hubble Space Telescope
observations that the galaxy experienced a major increase (accounting for 70% to 80% of its population) in its star formation rate between 6 Ga and 2 Ga (billion years ago). There is no significant evidence of any stars that are more than 10 Ga old. About 1 Ga ago, star formation in Leo I appears to have dropped suddenly to an almost negligible rate. Some low-level activity may have continued until 200-500 Ma. Therefore it may be the youngest dwarf spheroidal satellite galaxy of the Milky Way. In addition, the galaxy may be embedded in a cloud of ionized gas with a mass similar to that of the whole galaxy.
Leo I is located only 12 arc minutes
from Regulus
, the brightest star in the constellation. For that reason, the galaxy is sometimes called the Regulus Dwarf. Scattered light from the star makes studying the galaxy more difficult, and it was not until the 1990s that it was detected visually.
Dwarf spheroidal galaxy
Dwarf spheroidal galaxy is a term in astronomy applied to low luminosity galaxies that are companions to the Milky Way and to the similar systems that are companions to the Andromeda Galaxy M31...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Leo
Leo (constellation)
Leo is one of the constellations of the zodiac. Its name is Latin for lion. Its symbol is . Leo lies between dim Cancer to the west and Virgo to the east.-Stars:...
. At about 820,000 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s distant, it is a member of the Local Group
Local Group
The Local Group is the group of galaxies that includes Earth's galaxy, the Milky Way. The group comprises more than 30 galaxies , with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy...
of galaxies and is thought to be one of the most distant satellites of the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
galaxy. It was discovered in 1950 by Wilson
Albert George Wilson
Albert George Wilson is an American astronomer.He was born in Houston, Texas. He received his Ph.D. in mathematics from Caltech in 1947; his thesis title was Axially Symmetric Thermal Stresses in a Semi-Infinite Solid....
on photographic plate
Photographic plate
Photographic plates preceded photographic film as a means of photography. A light-sensitive emulsion of silver salts was applied to a glass plate. This form of photographic material largely faded from the consumer market in the early years of the 20th century, as more convenient and less fragile...
s of the National Geographic Society - Palomar Observatory Sky Survey
National Geographic Society - Palomar Observatory Sky Survey
The National Geographic Society – Palomar Observatory Sky Survey is a major photographic survey of the night sky that was completed at Palomar Observatory in 1958.-Observations:...
, which were taken with the 48-inch Schmidt camera
Schmidt camera
A Schmidt camera, also referred to as the Schmidt telescope, is a catadioptric astrophotographic telescope designed to provide wide fields of view with limited aberrations. Other similar designs are the Wright Camera and Lurie-Houghton telescope....
at Palomar Observatory
Palomar Observatory
Palomar Observatory is a privately owned observatory located in San Diego County, California, southeast of Pasadena's Mount Wilson Observatory, in the Palomar Mountain Range. At approximately elevation, it is owned and operated by the California Institute of Technology...
.
Mass
The measurement of radial velocitiesRadial velocity
Radial velocity is the velocity of an object in the direction of the line of sight . In astronomy, radial velocity most commonly refers to the spectroscopic radial velocity...
of some bright red giant
Red giant
A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
s in Leo I have made possible to measure its mass. It was found to be at least (2.0 ± 1.0) × 107 MSun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. The results are not conclusive, and do not deny or confirm the existence of a large dark matter
Dark matter
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
halo around the galaxy. However, it seems to be certain that the galaxy does not rotate.
It has been suggested that Leo I is a tidal debris stream in the outer halo
Galactic halo
The term galactic halo is used to denote an extended, roughly spherical component of a galaxy, which extends beyond the main, visible component. It can refer to any of several distinct components which share these properties:* the galactic spheroid...
of the Milky Way. This hypothesis has not been confirmed, however.
Star formation
Typical to a dwarf galaxy, the metallicityMetallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
of Leo I is very low, only one percent that of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. Gallart et al. (1999) deduce from Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
observations that the galaxy experienced a major increase (accounting for 70% to 80% of its population) in its star formation rate between 6 Ga and 2 Ga (billion years ago). There is no significant evidence of any stars that are more than 10 Ga old. About 1 Ga ago, star formation in Leo I appears to have dropped suddenly to an almost negligible rate. Some low-level activity may have continued until 200-500 Ma. Therefore it may be the youngest dwarf spheroidal satellite galaxy of the Milky Way. In addition, the galaxy may be embedded in a cloud of ionized gas with a mass similar to that of the whole galaxy.
Regulus
Minute of arc
A minute of arc, arcminute, or minute of angle , is a unit of angular measurement equal to one sixtieth of one degree. In turn, a second of arc or arcsecond is one sixtieth of one minute of arc....
from Regulus
Regulus
Regulus is the brightest star in the constellation Leo and one of the brightest stars in the night sky, lying approximately 77.5 light years from Earth. Regulus is a multiple star system composed of four stars which are organized into two pairs...
, the brightest star in the constellation. For that reason, the galaxy is sometimes called the Regulus Dwarf. Scattered light from the star makes studying the galaxy more difficult, and it was not until the 1990s that it was detected visually.