A tidal tail is a thin, elongated region of

star A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...

s and

interstellar gas In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstella ...

that extends into space from a

galaxy A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar Sys ...

. Tidal tails occur as a result of

galactic tide A galactic tide is a tidal force experienced by objects subject to the gravitational field of a galaxy such as the Milky Way. Particular areas of interest concerning galactic tides include galactic collisions, the disruption of dwarf or satel ...

forces between interacting galaxies. Examples of galaxies with tidal tails include the Tadpole Galaxy and the

Mice Galaxies NGC 4676, or the Mice Galaxies, are two spiral galaxies in the constellation Coma Berenices. About 290 million light-years distant, they have begun the process of colliding and merging. Their name refers to the long tails produced by tidal action� ...

. Tidal forces can eject a significant amount of a galaxy's gas into the tail; within the Antennae Galaxies, for example, nearly half of the observed gaseous matter is found within the tail structures. Within those galaxies which have tidal tails, approximately 10% of the galaxy's stellar formation takes place in the tail. Overall, roughly 1% of all stellar formation in the known universe occurs within tidal tails. Some interacting galaxy pairs have two distinct tails, as is the case for the Antennae Galaxies, while other systems have only one tail. Most tidal tails are slightly curved due to the rotation of the host galaxies. Those that are straight may actually be curved but still appear to be straight if they are being viewed edge-on.

History

The phenomena now referred to as tidal tails were first studied extensively by Fritz Zwicky in 1953. Several astrophysicists expressed their doubts that these extensions could occur solely as the result of tidal forces, including Zwicky himself, who described his own views as "unorthodox". Boris Vorontsov-Velyaminov argued that the tails were too thin and too long (sometimes as large as 100,000

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, a ...

s) to have been produced by gravity alone, as gravity should instead produce broad distortions. However, in 1972, renowned astronomer Alar Toomre proved that it was indeed tidal forces that were responsible for the tails.

Gallery

Galaxy with an ejected supermassive black hole.jpg, Arc-shaped tidal tails in galaxy 3C186.

Notes

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