2MASS J18082002−5104378 (abbreviated J1808−5104), also known as Reese's star, is an ultra metal-poor (UMP)

binary star system A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

, in the constellation

Ara ARA may refer to: Media and the arts * American-Romanian Academy of Arts and Sciences * '' Artistička Radna Akcija'', compilation album released in former Yugoslavia * Associate of the Royal Academy, denoting membership in the British Royal Aca ...

, about from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

, and is a single-lined spectroscopic binary (SB1). It is one of the oldest stars in the universe, about 13.53 billion years old, possibly one of the first stars, a star made almost entirely of materials released from the Big Bang. A tiny unseen companion, a low-mass UMP star, is particularly unusual.

System

J1808−5104 is an ultra metal-poor (UMP) star, one that has a

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 ...

e/Hless than , th of the levels in the Sun. It is a single-lined spectroscopic binary, with radial velocity variations in its spectral absorption lines interpreted as orbital motion of the visible star. The companion is invisible, but inferred from the orbit. J1808−5104 is the brightest UMP star, as a binary system, known, and is part of the "

thin disk The thin disk is a structural component of spiral and S0-type galaxies, composed of stars, gas and dust. It is the main non-centre (e.g. galactic bulge) density, of such matter. That of the Milky Way is thought to have a scale height of around ...

" of the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

, the part of the

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 System. ...

in which the Sun is located, but unusual for such a metal-poor and old star. At , the star is the oldest known thin-disk star, and several billion years older than most estimates for the age of the Milky Way's thin disk.

Primary star

The primary component of the binary star system, 2MASS J18082002−5104378 A, is a

subgiant A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution ...

, cooler than the Sun, but larger and more luminous.

Secondary star

The secondary unseen companion, 2MASS J18082002−5104378 B, thought to be a

red dwarf ''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...

, has an

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

P = days and a mass of . It is the first low-mass UMP star to be discovered, and one of the oldest stars in the universe, about 13.53 billion years old. It is possibly one of the first stars, a star made almost entirely of materials released from the

Big Bang The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the ...

References

External links

* * * (5 November 2018;

Johns Hopkins University Johns Hopkins University (Johns Hopkins, Hopkins, or JHU) is a private university, private research university in Baltimore, Maryland. Founded in 1876, Johns Hopkins is the oldest research university in the United States and in the western hem ...

) {{DEFAULTSORT:2MASS J18082002-5104378 Ara (constellation) 20181101 November 2018 events J18082002−5104378 TIC objects Spectroscopic binaries