Smith's Cloud
Encyclopedia
Smith's Cloud is a high-velocity cloud of hydrogen
gas located in the constellation Aquila
at Galactic coordinates l = 39°, b = −13°. The cloud was discovered in 1963 by Gail Bieger, née
Smith, who was an astronomy student at Leiden University
in the Netherlands. Smith's cloud has a mass of at least one million solar mass
es and measures 3000 parsec long by 1000 pc wide in projection. The cloud is between 11100 parsec and 13700 parsec from Earth and has an angular diameter
of 10 to 12 degrees, approximately as wide as the Orion constellation
, or about 20 times the diameter of the full moon
, although the cloud is not visible to the naked eye.
The cloud is apparently moving towards the disk of the Milky Way
at 73 ± 26 kilometers per second. Smith's Cloud is expected to merge with the Milky Way in 27 million years at a point in the Perseus arm
. Astronomers believe it will strike the Milky Way disk at a 45° angle, and its impact may produce a burst of star formation
or a supershell of neutral hydrogen.
Projecting the cloud's trajectory backwards through time, it is estimated that it had passed through the disk of the Milky Way some 70 million years ago. To have survived this previous encounter, it is thought to be embedded inside a massive dark matter halo
. The fact that it survived this previous encounter means that it is likely to be much more massive than previously thought, and may be a candidate for being a dark galaxy
.
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
gas located in the constellation Aquila
Aquila (constellation)
Aquila is a stellar constellation. Its name is Latin for 'eagle' and it is commonly represented as such. In mythology, Aquila was owned by the Roman god Jupiter and performed many tasks for him....
at Galactic coordinates l = 39°, b = −13°. The cloud was discovered in 1963 by Gail Bieger, née
NEE
NEE is a political protest group whose goal was to provide an alternative for voters who are unhappy with all political parties at hand in Belgium, where voting is compulsory.The NEE party was founded in 2005 in Antwerp...
Smith, who was an astronomy student at Leiden University
Leiden University
Leiden University , located in the city of Leiden, is the oldest university in the Netherlands. The university was founded in 1575 by William, Prince of Orange, leader of the Dutch Revolt in the Eighty Years' War. The royal Dutch House of Orange-Nassau and Leiden University still have a close...
in the Netherlands. Smith's cloud has a mass of at least one million solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
es and measures 3000 parsec long by 1000 pc wide in projection. The cloud is between 11100 parsec and 13700 parsec from Earth and has an angular diameter
Angular diameter
The angular diameter or apparent size of an object as seen from a given position is the “visual diameter” of the object measured as an angle. In the vision sciences it is called the visual angle. The visual diameter is the diameter of the perspective projection of the object on a plane through its...
of 10 to 12 degrees, approximately as wide as the Orion constellation
Orion (constellation)
Orion, often referred to as The Hunter, is a prominent constellation located on the celestial equator and visible throughout the world. It is one of the most conspicuous, and most recognizable constellations in the night sky...
, or about 20 times the diameter of the full moon
Full moon
Full moon lunar phase that occurs when the Moon is on the opposite side of the Earth from the Sun. More precisely, a full moon occurs when the geocentric apparent longitudes of the Sun and Moon differ by 180 degrees; the Moon is then in opposition with the Sun.Lunar eclipses can only occur at...
, although the cloud is not visible to the naked eye.
The cloud is apparently moving towards the disk 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...
at 73 ± 26 kilometers per second. Smith's Cloud is expected to merge with the Milky Way in 27 million years at a point in the Perseus arm
Perseus Arm
The Perseus Arm is one of two major spiral arms of the Milky Way galaxy. The second major arm is called Scutum–Centaurus Arm. Perseus Arm begins from the distal end of the long Milky Way....
. Astronomers believe it will strike the Milky Way disk at a 45° angle, and its impact may produce a burst of star formation
Star formation
Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...
or a supershell of neutral hydrogen.
Projecting the cloud's trajectory backwards through time, it is estimated that it had passed through the disk of the Milky Way some 70 million years ago. To have survived this previous encounter, it is thought to be embedded inside a massive dark matter halo
Dark matter halo
A dark matter halo is a hypothetical component of a galaxy, which extends beyond the edge of the visible galaxy and dominates the total mass. Since they consist of dark matter, halos cannot be observed directly, but their existence is inferred through their effects on the motions of stars and gas...
. The fact that it survived this previous encounter means that it is likely to be much more massive than previously thought, and may be a candidate for being a dark galaxy
Dark galaxy
A dark galaxy is a hypothetical galaxy composed of dark matter. Dark galaxies receive their name because they have no detectable stars and are theoretically invisible...
.