Really close Black Hole to Earth Discovered!

Discussion in 'Astronomy, Exobiology, & Cosmology' started by paddoboy, May 6, 2020.

  1. paddoboy Valued Senior Member

    Messages:
    27,543
    https://www.abc.net.au/news/2020-05...ver-closest-black-hole-to-earth-ever/12222154

    Astronomers discover black hole closer to Earth than any before, suggest it may not be alone:

    We've got a new galactic neighbour — a small black hole left over from the death of a fleeting young star.

    Astronomers at the European Southern Observatory have found the closest black hole to Earth yet, so near that the two stars dancing with it can be seen by the naked eye.

    Of course, close is relative on the galactic scale. This black hole is about 1,000 light-years away, which equates to roughly 9,500 trillion kilometres.

    But in terms of the cosmos and even the galaxy, it is in our neighbourhood, according to a study lead by astronomer Thomas Rivinius, who led the study.

    The previous closest black hole is probably about three times further, about 3,200 light-years, he said.

    The black hole is tiny, only 40 kilometres in diameter, and lives in the Telescopium constellation (the telescope), which neighbours the Sagittarius and Corona Australis constellations in the southern celestial hemisphere.
    more at link.....

    the paper:
    https://www.aanda.org/articles/aa/full_html/2020/05/aa38020-20/aa38020-20.html


    A naked-eye triple system with a nonaccreting black hole in the inner binary,⋆⋆

    Abstract:
    Several dozen optical echelle spectra demonstrate that HR 6819 is a hierarchical triple. A classical Be star is in a wide orbit with an unconstrained period around an inner 40 d binary consisting of a B3 III star and an unseen companion in a circular orbit. The radial-velocity semi-amplitude of 61.3 km s−1 of the inner star and its minimum (probable) mass of 5.0 M⊙ (6.3 ± 0.7 M⊙) imply a mass of the unseen object of ≥4.2 M⊙ (≥5.0 ± 0.4 M⊙), that is, a black hole (BH). The spectroscopic time series is stunningly similar to observations of LB-1. A similar triple-star architecture of LB-1 would reduce the mass of the BH in LB-1 from ∼70 M⊙ to a level more typical of Galactic stellar remnant BHs. The BH in HR 6819 probably is the closest known BH to the Sun, and together with LB-1, suggests a population of quiet BHs. Its embedment in a hierarchical triple structure may be of interest for models of merging double BHs or BH + neutron star binaries. Other triple stars with an outer Be star but without BH are identified; through stripping, such systems may become a source of single Be stars.

    . Conclusions
    HR 6819 is a hierarchical triple star with a nonaccreting BH in the inner binary. The mass estimate does not depend on difficult RV measurements of emission lines as tracers of the orbital motion of the BH (see Casares et al. 2014; El-Badry & Quataert 2020). Furthermore, the B3 III star is a fairly normal star so that the combination of the mass derived from spectral type and spectral energy distribution with the mass function leads to a solid lower mass limit on the BH of 4.2 M⊙ (for sin i = 1). The CW Cep system may be a progenitor of systems with an architecture similar as in HR 6819 and LB-1 if the 2.7 d inner binary can avoid merger through mass loss. Through stripping of the outer Be star, systems such as HR 6819, LB-1, CW Cep, and 66 Oph may become a source of single Be stars.

    The detection was facilitated by the incompatibility of the spectral sequences with a simple binary. This can be a criterion to find other nonaccreting BHs, and the case of LB-1 illustrates the scope for such searches. If about 20% of all early-type stars are triples (see Moe & Di Stefano 2017) and 0.01% of them have a system architecture similar to that of HR 6819 and LB-1, the discrepancy between expected and observed numbers of BHs in the Galaxy would shrink by several orders of magnitude but would still be very large. (In the magnitude-limited Bright Star Catalog, Hoffleit & Jaschek 1991, HR 6819 corresponds to 0.01% of all early- and late-type stars together.)

    The existence of an entire population of quiet BHs is also suggested by the relative proximity of HR 6819. The lowest distance derived to date to any Galactic BH apparently is < 400 pc, which is the distance to the accreting V616 Mon (AO 0620−00; Foellmi 2009). The Gaia parallax of 0.64 ± 0.16 mas is closer to other distance estimates of ∼1 kpc (Foellmi 2009), but would still make V616 Mon the nearest previously known BH to the Sun. At 310 ± 60 pc, the distance to HR 6819 is far smaller than 1 kpc.

    Triple systems have been invoked (Rodriguez & Antonini 2018) as the progenitors of double BHs or BH + NS systems that merged owing to Lidov-Kozai oscillations triggered by a distant third object and were detected as gravitational-wave events (Abbott et al. 2019). It would therefore be interesting to compare dynamical models to HR 6819 or LB-1. However, the two luminous components of HR 6819 have masses of only ∼6 M⊙ and are very far apart, therefore the current BH will remain the only BH in HR 6819, and neither will an NS form. It appears noteworthy that the pure binary models of Langer et al. (2020b) predict a steep decrease in the fraction of BH companions toward the masses of the inner B stars in HR 6819 and LB-1. It may be useful to extend the models to triple systems.

    HR 6819 does not share the proper motion of the young stellar associaton Sco OB2 and is probably also older than it. Any SN explosion leading to the BH formation most probably occurred outside the Local Bubble.

    A subsequent paper (Hadrava et al., in prep.) will present the results of disentangling the spectra. The results are expected to achieve a comprehensive and largely independent quantitative confirmation of the properties of HR 6819 that we presented here
     
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  3. paddoboy Valued Senior Member

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    Wow!!! Pretty exciting news methinks. And only 40 kms diameter.
    Further research and observation will be ongoing I would imagine, particularly with regards to any growth in the BH.
     
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