科研之友
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摘要
The early stages of massive black hole growth are poorly understood(1). High-luminosity active galactic nuclei at very high redshift(2) z further imply rapid growth soon after the Big Bang. Suggested formation mechanisms typically rely on the extreme conditions found in the early Universe (very low metallicity, very high gas or star density). It is therefore plausible that these black hole seeds were formed in dense environments, at least a Hubble time ago (z > 1.8 for a look-back time of t(H) = 10 Gyr)(3). Intermediate-mass black holes (IMBHs) of mass M. approximate to 10(2)-10(5) solar masses, Me, are the long-sought missing link(4) between stellar black holes, born of supernovae (5), and massive black holes(6), tied to galaxy evolution by empirical scaling relations(7,8). The relation between black hole mass, M., and stellar velocity dispersion, sigma(*), that is observed in the local Universe over more than about three decades in massive black hole mass, correlates M. and sigma(*) on scales that are well outside the massive black hole's radius of dynamical influence(6), r(h) approximate to GM. / sigma(2)(*). We show that low-mass black hole seeds that accrete stars from locally dense environments in galaxies following a universal M. / sigma(*) relation(9,10) grow over the age of the Universe to be above M-o approximate to 3 x 10(5)M(circle dot) (5% lower limit), independent of the unknown seed masses and formation processes. The mass M-o depends weakly on the uncertain formation redshift, and sets a universal minimal mass scale for present-day black holes. This can explain why no IMBHs have yet been found(6), and it implies that present-day galaxies with sigma(*) < S-o approximate to 40 km s(-1) lack a central black hole, or formed it only recently. A dearth of IMBHs at low redshifts has observable implications for tidal disruption(11) and gravitational wave mergers(12).
- 出版日期2017-8
