• LIGO/VIRGO stats and numbers of black holes?

    From stargene@21:1/5 to All on Sat Jul 3 14:01:44 2021
    at https://www.sciencenews.org/article/gravitational-waves-ligo-first-black-hole-neutron-star-merger
    and https://www.sciencemag.org/news/2021/06/ripples-spacetime-reveal-black-holes-slurping-neutron-stars
    two separate black hole-neutron star mergers are confirmed for the
    first time. Have LIGO and VIRGO yet enabled any statistical estimates
    on the general population numbers of black holes per galaxy, say, in
    the universe, and maybe their mass distributions?

    [[Mod. note -- Yes.

    Another excellent article on this past week's announcement
    (of the detection of two BH-NS mergers by Ligo/Virgo) is
    This includes a link to the full research paper (which is open-access).
    It also has a cute subtitle. :)

    To return to the author's question, there has been a lot of work done
    on trying to estimate the population distribution of black holes. It's
    tricky both because of the small number of observed coalescences, and
    because of the strong selection biases in the observations (lower-mass
    black holes produce weaker gravitational waves, and so are less likely
    to be observed).

    For example, GW 190814 was the coalescence of a 23 Msun black hole and
    a 2.6 Msun "compact object" (maybe a small black hole, or maybe a neutron
    star near the upper limit of possible NS masses). In Astrophysical Journal 896, L44 (https://doi.org/10.3847/2041-8213/ab960f), the authors estimated
    the density of "GW190814-like" systems as 7 +16/-6 (i.e., between 1 and 23) mergers/year per cubic gigaparsec. For systems with more comparable masses, arXiv:1811.12940 estimated a density of 53 +56/-27 (i.e., between 26 and 109) mergers/year per cubic gigaparsec. (There might be a more up-to-date
    estimate published that I haven't seen.)

    We don't yet have any direct gravitational-wave observations of
    supermassive black holes (e.g., in galaxy or quasar centers), although
    there are strong astronomical reasons to suspect that most galaxies
    contain supermassive black holes). The European Space Agency's planned
    LISA mission (currently scheduled for 2034) should directly observe gravitational waves from these systems (among others), which will give
    us direct information about their properties and how common they are.
    -- JT]]

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)