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Star LB-1
(USNOA2 1125-3559840; WikiSky image)
Observation data
Epoch J2000      Equinox J2000
Constellation Gemini
Right ascension  06h 11m 49.0763s[1]
Declination +22° 49′ 32.686″[1]
Apparent magnitude (V) 11.51
Proper motion (μ) RA: -0.067[1] mas/yr
Dec.: -1.889[1] mas/yr
Parallax (π)0.4403 ± 0.0856[1] mas
Distanceapprox. 7,000 ly
(approx. 2,300 pc)
Period (P)78.9±0.3 d
Eccentricity (e)0.03±0.01
Semi-amplitude (K1)
B star
Luminosity7,000 L
Surface gravity (log g)3.43±0.15 cgs
Temperature19100±820 K
Database references

LB-1 is a binary star system in the constellation Gemini. It is composed of a B-type star and an unseen object that might be a black hole. If the star is an ordinary main sequence B-type star (with its luminosity in conflict with a mainstay astronomic satellite's parallax measurements), the companion which is strongly suspected to be solitary, would be a black hole having mass outside of ordinary single stellar evolution parameters.


The optically observed star, LB-1 A, or LS V+22 25, is a B-type star[3] nine times the mass of the Sun and located at least 7,000 light-years (2,100 pc) from Earth. It was found to exhibit radial velocity variations by Chinese astronomers using the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and the radial-velocity method to search for such wobbly stars.

The astronomers observed the star orbiting an unseen companion every 78.9 days,[4] in what researchers described as a "surprisingly circular" orbit.[5] Follow-up observations using the Gran Telescopio Canarias in Spain and the W. M. Keck Observatory in the United States better defined the findings.[5]

The parallax to LB-1 has been published in Gaia Data Release 2, implying a distance around 2,300 pc.[1] The observed spectral properties of the star are inconsistent with those expected for an ordinary main sequence B-type star at this distance.

A separate spectroscopic analysis of the star suggests that instead of a B-type main sequence star as had been indicated, LB-1 A is more likely a stripped helium star (whose spectrum is very similar) with only ~1 M, if at the distance determined by the Gaia satellite.[3]

Unseen companion[edit]

The unseen companion to the star was discovered by measuring the radial velocity shifts of its companion star. If it is a black hole, this would mark the first time a stellar black hole was discovered without observation of its X-ray emissions.[6][7][8][2][4][5][9][10]

If the distance from parallax is ignored, and the star is assumed to be an ordinary main sequence B-type star, the unseen companion LB-1 B or LB-1 *, could be hypothesized to be a black hole, with a mass of about 70 solar masses, more than twice the mass as the maximum predicted by most current theories of stellar evolution. It would be in the stellar-mass black hole range, below the size of intermediate-mass black holes; however, it would fall in the pair-instability gap of black hole sizes, whereby sufficiently massive black hole progenitor stars undergo pair-instability supernovae and completely disintegrate, leaving no remnant behind. LB-1 would be the first black hole discovered in the mass gap range. The companion mass would be high enough that anything other than a black hole would be expected to be easily detected.[2] According to one of the researchers, "This discovery forces us to re-examine our models of how stellar-mass black holes form [...] This remarkable result, along with the LIGO-Virgo detections of binary black hole collisions during the past four years, really points towards a renaissance in our understanding of black hole astrophysics."[4]

Alternatively, the evidence for the star to be a stripped helium star reduces the mass estimate of the compact object to as little as ~2–3 M and raises the possibility of a neutron star.[3]

See also[edit]


  1. ^ a b c d e f Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. ^ a b c d Liu, Jifeng; et al. (27 November 2019). "A wide star–black-hole binary system from radial-velocity measurements". Nature. 575 (7784): 618–621. arXiv:1911.11989. Bibcode:2019Natur.575..618L. doi:10.1038/s41586-019-1766-2. PMID 31776491.
  3. ^ a b c Irrgang, A.; Geier, S.; Kreuzer, S.; Pelisoli, I.; Heber, U. (January 2020). "A stripped helium star in the potential black hole binary LB-1". Astronomy and Astrophysics (Letter to the Editor). 633: L5. doi:10.1051/0004-6361/201937343.
  4. ^ a b c "Chinese Academy of Sciences leads discovery of unpredicted stellar black hole" (Press release). Chinese Academy of Sciences. EurekAlert!. 27 November 2019. Retrieved 29 November 2019.
  5. ^ a b c Starr, Michelle (27 November 2019). "Scientists Just Found an "Impossible" Black Hole in The Milky Way Galaxy". Retrieved 29 November 2019.
  6. ^ Roberto Soria (3 December 2019). "Did this black hole swallow a star?".
  7. ^ Jing Xuan TENG (28 November 2019). "Scientists spot black hole so huge it 'shouldn't even exist' in our galaxy". Space Daily. AFP.
  8. ^ Katie Mettler (29 November 2019). "Scientists find 'monster' black hole so big they didn't think it was possible". Washington Post.
  9. ^ Baker, Sinéad (29 November 219). "Chinese astronomers discovered a black hole so big it shouldn't exist according to current science". Business Insider. Retrieved 29 November 2019.
  10. ^ Lewis, Sophie (28 November 2019). "Astronomers discover massive black hole that "should not even exist" in the Milky Way galaxy". CBS News. Retrieved 29 November 2019.

External links[edit]

Coordinates: Sky map 06h 11m 49.076s, +22° 49′ 32.686″