Astronomy:2MASS J18082002−5104378

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Short description: One of the oldest stars in the universe
2MASS J18082002−5104378[1]
Observation data
Equinox J2000.0]] (ICRS)
Constellation Ara[2]
Right ascension  18h 08m 20.02s
Declination −51° 04′ 37.8″
Apparent magnitude (V) 11.9[3]
Evolutionary stage Subgiant / Red dwarf
Proper motion (μ) RA: −5.672[4] mas/yr
Dec.: −12.643[4] mas/yr
Parallax (π)1.6775 ± 0.0397[4] mas
Distance1,950[5][6][7] ly
(600 pc)
Mass0.7599 ± 0.0001[1] M
Radius2.44[4] R
Luminosity5.311[4] L
Surface gravity (log g)3.0[3] cgs
Temperature5,440 ± 100[3] K
Metallicity [Fe/H]-4.1[3] dex
Age13.535±0.002[1] Gyr
[1] M
Age13.535±0.002[1] Gyr
Other designations
Gaia DR2 6702907209758894848[5]
Database references

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). 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.


J1808−5104 is an ultra metal-poor (UMP) star, one that has a metallicity [Fe/H] less than −4, ​110,000th 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]

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
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][10][11][9][12][13][14][15]


  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Schlaufman, Kevin C.; Thompson, Ian B.; Casey, Andrew R. (5 November 2018). "An ultra metal-poor star near the hydrogen-burning limit". The Astrophysical Journal 867 (2): 98. doi:10.3847/1538-4357/aadd97. Bibcode2018ApJ...867...98S. 
  2. "Finding the constellation which contains given sky coordinates". 2018. 
  3. 3.0 3.1 3.2 3.3 3.4 Meléndez, Jorge; Placco, Vinicius M.; Tucci-Maia, Marcelo; Ramírez, Iván; Li, Ting S.; Perez, Gabriel (2016). "2MASS J18082002-5104378: The brightest (V = 11.9) ultra metal-poor star". Astronomy and Astrophysics 585: L5. doi:10.1051/0004-6361/201527456. Bibcode2016A&A...585L...5M. 
  4. 4.0 4.1 4.2 4.3 4.4 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode2018A&A...616A...1G.  Gaia DR2 record for this source at VizieR.
  5. 5.0 5.1 5.2 5.3 5.4 "One of Milky Way's oldest stars discovered". 6 November 2018. 
  6. 6.0 6.1 Crockett, Christopher (12 November 2018). "Puny star might be [a specimen from [the] early universe"]. 
  7. 7.0 7.1 Williams, Matt (9 November 2018). "Ancient star found that's only slightly younger than the universe itself". 
  8. 8.0 8.1 Ezzeddine, Rana; Frevbel, Anna (27 September 2018). "Revisiting the iron abundance in the hyper iron-poor star HE 1327−2326 with UV COS/HST data". The Astrophysical Journal 863 (2): 168. doi:10.3847/1538-4357/aad3cb. Bibcode2018ApJ...863..168E. 
  9. 9.0 9.1 Rosen, Jill (5 November 2018). "Johns Hopkins scientist finds elusive star with origins close to Big Bang - The newly discovered star's composition indicates that, in a cosmic family tree, it could be as little as one generation removed from the Big Bang" (Press release). Johns Hopkins University. Retrieved 5 November 2018.
  10. Wehner, Mike (5 November 2018). "Astronomers spot one of the oldest stars ever". 
  11. "A tiny old star has a huge impact". Gemini Observatory. 5 November 2018. 
  12. "Johns Hopkins scientist finds elusive star with origins close to Big Bang" (Press release). Johns Hopkins University. 5 November 2018. Retrieved 5 November 2018 – via EurekAlert!.
  13. Starr, Michelle (5 November 2018). "Astronomers have detected one of the oldest stars in the entire universe". 
  14. Irving, Michael (5 November 2018). "13.5 billion year old star was born just after the Big Bang - and it's in our neighborhood". 
  15. Malewar, Amit (5 November 2018). "Johns Hopkins scientists may have found one of the universe's oldest stars - One of the universe's oldest stars". 

External links

Coordinates: Sky map 18h 08m 20.02s, −51° 04′ 37.8″