• supermassive black holes at z > 7

    From jacobnavia@21:1/5 to All on Wed Mar 13 22:29:49 2019
    A team of astronomers have conducted a search for distant super massive
    black holes and they have found 83 of them. See:

    https://www.princeton.edu/news/2019/03/13/astronomers-discover-83-supermassive-black-holes-early-universe

    Here is the report about one of those: https://iopscience.iop.org/article/10.3847/2041-8213/ab0216/meta
    "Discovery of the First Low-luminosity Quasar at z > 7"
    [[Mod. note -- preprint is Matsuoka et al, arXiv:1901.10487 -- jt]]

    What is interesting is that contrary to the expectations of the big bang hypothesis, the density of those beasts is not at all higher than now.

    According to BB theory, the neutral hydrogen was reionized after the
    "dark ages". Where would the huge amount of energy necessary for
    reionization come from?

    The standard answer was that massive black holes would provide it... but apparently the density of black holes 13 Gy ago was no higher than now.

    I quote:
    "...but astronomers still don't know what provided the incredible amount
    of energy required to cause the reionization. A compelling hypothesis
    suggests that there were many more quasars in the early universe than
    detected previously, and it is their integrated radiation that reionized
    the universe.
    However, the number of quasars we observed shows that this is not the
    case," explained Robert Lupton, a 1985 Princeton Ph.D. alumnus who is a
    senior research scientist in astrophysical sciences. "The number of
    quasars seen is significantly less than needed to explain the
    reionization."

    The team supposes that they will detect super massive black holes even
    farther away... what would make the question of how a super massive
    black hole could appear in such a small amount of time: just 760 million years...

    Another quasar that is remarkable is J043947.08+163415.7 that shines
    brightly with the light of 600 trillion suns. But that object is lensed,
    so we have to divide by a factor of 50 to get the real luminosity. After
    taking the gravitational lensing into accopunt it becomes just a normal
    800 million sun masses object.

    It is just 1GY away from the supposed bang. (https://www.spacetelescope.org/news/heic1902/#1)

    We are at the limit of current scopes. I am confident that in a few
    years we will find even farther away quasars.

    [[Mod. note --
    A few comments:
    1. It's important to distinguish between quasars and supermassive black
    holes. We think that quasars are supermassive BHs which are accreting
    matter... but there may (probably are) also other supermassive BHs
    which aren't accreting much matter, and hence are "dark", not giving
    off much light or other electromagnetic radiation. There are a lot
    harder to detect.
    2. Did Matsuoka et al discuss the space density of such quasars? I don't
    see anything about that in a quick skim of their preprint.
    3. I've never seen it suggested that quasars were the *only* source of
    energetic photons for reionization. Population III stars and dwarf
    galaxies were probably also important; I don't know if we know much
    about their relative contributions (as a function of redshift).
    4. The author is surely right that in the coming years will find even
    fainter & higher-redshift/more-distant quasars. Looking at the
    planned sensitivity of the coming generation of 20-40-meter telescopes
    is enough to make an optical astronomer salivate!
    -- jt]]

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  • From Steve Willner@21:1/5 to jacobnavia on Thu Mar 28 21:56:00 2019
    In article <q6brsn$7ku$1@dont-email.me>,
    jacobnavia <jacob@jacob.remcomp.fr> writes:
    A team of astronomers have conducted a search for distant super massive
    black holes and they have found 83 of them. See:

    https://www.princeton.edu/news/2019/03/13/astronomers-discover-83-supermassive-black-holes-early-universe

    The refereed paper -- open access -- is at https://iopscience.iop.org/article/10.3847/1538-4357/aaee7a/meta

    What is interesting is that contrary to the expectations of the big bang hypothesis, the density of those beasts is not at all higher than now.

    Why do you think that's the expectation of Big Bang theory?

    Fig 13 of the paper shows the rise in QSO number density from z=6,
    the epoch the new observations address, to z=4. Other papers show
    the number density continues to rise to about z=2, then falls.

    According to BB theory, the neutral hydrogen was reionized after the
    "dark ages". Where would the huge amount of energy necessary for
    reionization come from?

    The standard expectation is hot stars in low-mass galaxies. Fig 12
    of the paper shows the z=6 luminosity function of Lyman-break
    galaxies (LBGs). JWST should do even better.

    The standard answer was that massive black holes would provide it...

    When was that ever the standard answer?

    apparently the density of black holes 13 Gy ago was no higher than now.

    What does the comparison with "now" have anything to do with
    reionization? The intergalactic medium is ionized now, so something
    had to have done that. We know in fact that it occurred at redshifts
    of something like 8 to 5 or so.

    We are at the limit of current scopes. I am confident that in a few
    years we will find even farther away quasars.

    No doubt. JWST will find some, but its field of view is tiny. LSST
    might do better, and the large ground-based telescopes will make a contribution.

    [[Mod. note --
    2. Did Matsuoka et al discuss the space density of such quasars? I don't
    see anything about that in a quick skim of their preprint.

    See Fig 10 or Table 4 of the paper I linked above.

    --
    Help keep our newsgroup healthy; please don't feed the trolls.
    Steve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA

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