Spins of primordial black holes formed in the matter-dominated phase of the Universe

By T. Harada, Chul-Moon Yoo, K. Kohri, K. Nakao. 2017

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Angular momentum plays very important roles in the formation of primordial black holes in the matter-dominated phase of the Universe if it lasts sufficiently long. In fact, most collapsing masses are bounced back due to centrifugal force, since angular momentum significantly grows before collapse. For masses with q≤qc≃2.4I1/3σH1/3, where q is a nondimensional initial quadrupole moment parameter, σH is the density fluctuation at horizon entry t=tH, and I is a parameter of the order of unity, angular momentum gives a suppression factor ∼exp(-0.15I4/3σH-2/3) to the production rate. As for masses with q>qc, the suppression factor is even stronger as ∼exp(-0.0046q4/σH2). We derive the spin distribution of primordial black holes and find that most of the primordial black holes are rapidly rotating near the extreme value a*=1, where a* is the nondimensional Kerr parameter at their formation. The smaller σH is, the stronger the tendency towards the extreme rotation. Combining this result with the effect of anisotropy, we numerically and semianalytically estimate the production rate β0 of primordial black holes. Then we find that β0≃1.9×10-6fq(qc)I6σH2exp(-0.15I4/3σH-2/3) for σH≲0.005, while β0≃0.05556σH5 for 0.005≲σH≲0.2, where fq(qc) is the fraction of masses whose q is smaller than qc and we assume fq(qc) is not too small. We argue that matter domination significantly enhances the production of primordial black holes despite the suppression factor. If the end time tend of the matter-dominated phase satisfies tend≲(0.4IσH)-1tH, the effect of the finite duration significantly suppresses primordial black hole formation and weakens the tendency towards large spins.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/b7c30ee75e42ccdb2ef3418a6c9806fb9118c7b3

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Citations in the corpus

Primordial black holes from α-attractors (2018, background): “005 [84], the power spectrum peak has to be few times larger but still less than 10−4 in order to generate a significant PBH abundance.”
The evolution of primordial black holes and their final observable spins (2020, background): “PBH formation in non-standard scenarios, like during an early matter-dominated epoch [37] following inflation or from Q-balls [36], may lead to larger values of the initial spin.”
Primordial black holes confront LIGO/Virgo data: current situation (2020, background): “[2, 107] are incompatible with a primordial origin for GW190412 unless: (i) accretion is significant during the cosmic history of PBHs; (ii) PBHs can be formed with non-negligible natal spin (as in some scenarios [27, 28]), in contrast with the most likely formation scenarios [25], in which the spin”
Analytic description of primordial black hole formation from scalar field fragmentation (2019, background): “ytically the non-linear behavior of the perturbations and we thus omit here this assumption. – 21 – Additional features of a soliton collection such as asphericity, inhomogeneity and angular momentum [93,94,94] will aﬀect the collapse and the associated BH formation probability. However, a detailed ”
Steepest growth of the power spectrum and primordial black holes (2018, unknown): “1 This is motivated by the fact that there are several hints for the existence of PBHs [8], for example the progenitor BH spins of the LIGO detections being consistent with zero in most cases [9–12], which is expected for PBHs formed during radiation domination [13] (but not matter domination [14]) ”