2MASS J18082002−5104378
One of the oldest stars in the universe
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2MASS J18082002−5104378 (abbreviated J1808−5104) is an ultra metal-poor (UMP) binary star system, in the constellation Ara, about 1,950 ly (600 pc)[5][6][7] from Earth, and is a single-lined spectroscopic binary (SB1). Estimated to be about 13.53 billion years old, it is one of the oldest stars known, and possibly one of the first stars in our universe — one made almost entirely of materials released from the Big Bang. A tiny unseen companion, a low-mass UMP star, is particularly unusual.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ara[2] |
| Right ascension | 18h 08m 20.02s |
| Declination | −51° 04′ 37.8″ |
| Apparent magnitude (V) | 11.9[3] |
| Characteristics | |
| Evolutionary stage | Subgiant / Red dwarf |
| Astrometry | |
| Proper motion (μ) | RA: −5.672[4] mas/yr Dec.: −12.643[4] mas/yr |
| Parallax (π) | 1.6775±0.0397 mas[4] |
| Distance | 1,950[5][6][7] ly (600 pc) |
| Details | |
| A | |
| Mass | 0.7599 ± 0.0001[1] M☉ |
| Radius | 2.44[4] R☉ |
| Luminosity | 5.311[4] L☉ |
| Surface gravity (log g) | 3.0[3] cgs |
| Temperature | 5,440 ± 100[3] K |
| Metallicity [Fe/H] | -4.1[3] dex |
| Age | 13.535±0.002[1] Gyr |
| B | |
| Mass | 0.14+0.06 −0.01[1] M☉ |
| Age | 13.535±0.002[1] Gyr |
| Other designations | |
| Gaia DR2 6702907209758894848[5] | |
| Database references | |
| SIMBAD | data |
System
J1808−5104 is an ultra metal-poor (UMP) star, one that has a logarithmic metallicity [Fe/H] less than −4, or 1/ 10,000 th of the levels in the Sun.[8] 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.[1]
J1808−5104 is the brightest UMP star, as a binary system, known,[8] and is part of the "thin disk" of the Milky Way, the part of the galaxy in which the Sun is located, but unusual for such a metal-poor and old star.[9] At 13.53 Gyr, 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.[1] Despite its age and low metallicity, 2MASS J18082002−5104378 is still too metal-rich to be considered a population III star.[10]
Primary star
The primary component of the binary star system, 2MASS J18082002−5104378 A, is a subgiant, cooler than the Sun, but larger and more luminous.[3]
Secondary star
The secondary unseen companion, 2MASS J18082002−5104378 B, thought to be a red dwarf,[5] has an orbital period P = 34.757+0.010
−0.010 days and a mass of 0.14 M☉.[1] 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.[5] It is possibly one of the first stars, a star made almost entirely of materials released from the Big Bang.[1][11][9][12][13][14][15]
