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supermassive black holes at z 7
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/...early-universe Here is the report about one of those: https://iopscience.iop.org/article/1...13/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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supermassive black holes at z 7
In article ,
jacobnavia 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/...early-universe The refereed paper -- open access -- is at https://iopscience.iop.org/article/1...57/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 Cambridge, MA 02138 USA |
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