Massive black holes and light-element nucleosynthesis in a baryonic universe

Abstract

We reexamine the model proposed by Gnedin and Ostriker (1992) in which Jeans' mass black holes (M BH 10 6 M) form shortly after decoupling. There is no nonbaryonic dark matter in this model, but we examine the possibility that b is considerably larger than given by normal nucleosynthesis. Here we allow for the fact that much of the high baryon-to-photon ratio material will collapse, leaving the universe of remaining material with light element abundances more in accord with the residual baryonic density (10 ?2) than with 0 and the initial baryonic density (10 ?1). We nd that no reasonable model can be made with random phase density uctuations, if the power on scales smaller than 10 6 M is as large as expected. However, phase correlated models of the type that might occur in connection with topological singularities can be made with b h 2 = 0:013 0:001, 0:15 < 0 < 0:4 which are either at (= 1 ? 0) or open (= 0) and which satisfy all the observational constraints which we apply, including the large baryon to total mass ratio found in the X-ray clusters. The remnant baryon density is thus close to that obtained in the standard picture (b h 2 = 0:0125 0:0025, Walker et al 1991). The spectral index implied for uctuations in the baryonic isocurvature scenario, ?1 < m < 0, is in the range expected by other arguments based on large scale structure and microwave uctuation constraints. The dark matter in this picture is in the form of massive black holes. Accretion onto them at early epochs releases high energy photons which signi cantly heat and reionize the universe. But photodissociation does not materially change light element abundances. A typical model gives y 1 10 ?5 , n e =n H (z = 30) 0:1 and a di use-ray background at 100 KeV near the COBE limit of the order of 10% of that observed which originates from high redshift quasars. Reionization in { 3 { this model occurs at redshift 600 and reaches (H II=H tot) 0:1 ? 0:2. { 4 {

[ITAL]COBE[/ITAL] Constraints on Baryon Isocurvature Models

“…It satisfies dynamical observations which suggest a low-density universe ⍀ 0 3 0.2-0.3, forms structure without the aid of hypothetical dark matter, and can alter light-element nucleosynthesis sufficiently to make an ⍀ 0 ϭ ⍀ b baryonic universe acceptable (Gnedin & Ostriker 1992;Gnedin, Ostriker, & Rees 1995). Moreover, recent measurements of a large Hubble constant H 0 ϭ 100 h km s Ϫ1 Mpc Ϫ1 , h ϭ 0.80 H 0.17 (Freedman et al 1994) would be easier to accommodate in such a low-density universe.…”

“…Peebles (1994) suggests the addition of cold dark matter or defects and Gnedin et al (1995) propose non-Gaussian fluctuations. Small admixtures of adiabatic fluctuations may also be added.…”

Implications of the gravitational wave event GW150914

“…[151] argue that if ∼ 10 − 100 M ⊙ black holes (whose number density is not strongly limited by microlensing; see [151]) comprise most to all dark matter then the plausible capture rate is in the remarkably broad range of 1.1 × 10 −4 to 1400 Gpc −3 yr −1 depending on very uncertain details regarding clustering. However, accretion onto these black holes would produce extra z > ∼ 10 ionization that would leave an imprint on the cosmic microwave background [153,154,155,156,157]; [158,159] argue that this limits the fractional contribution to dark matter from such black holes to < ∼ 10 −5 , which suggests that this is an improbable mechanism. Consistent with this, [152] find that the merger rate estimate from GW150914 implies that at most a small fraction of dark matter can be in ∼ 30 M ⊙ black holes.…”

Is Deuterium in High‐Redshift Lyman Limit Systems Primordial?

“…These distances indicate that significant deuterium production, as well as destruction, by 4 He/ 2 H photo-disintegration should be regarded as an improbable process. Nevertheless, such scenarios of BBN can only agree with observationally inferred primordial abundance constraints if a variety of criteria are met, such as the efficient collapse of high-density regions, the presence of a cutoff for isocurvature fluctuations on mass scales Jedamzik & Fuller 1995;Gnedin, Ostriker, & Rees 1995;Kurki-Suonio, Jedamzik, & Mathews 1996), and the moderate to significant 7 Li-depletion in low-metallicity PopII stars. Note that contrary to recent claims (Copi, Olive, & Schramm 1996) In conclusion, it is difficult to envision a compelling model for differential D/H destruction/production in LLSs that could explain the apparent observationally-inferred discordance.…”