The "Hot" Model of the Universe

Zel’dovich, Yakov Borisovich

doi:10.1070/pu1967v009n04abeh003014

Cited by 164 publications

(142 citation statements)

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“…14 When dealing with the pre-recombination plasma we distinguish between two types of perturbations, namely between "adiabatic" and "isothermal" disturbances (Zeldovich (1967) [14]). The former include fluctuations in both the radiation and the matter component (i.e.…”

Section: Adiabatic and Isothermal Perturbationsmentioning

confidence: 99%

Magnetized cosmological perturbations

2000

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The aim of these lecture notes is to familiarize graduate students and beginning postgraduates with the basic ideas of linear cosmological perturbation theory and of structure formation scenarios. We present both the Newtonian and the general relativistic approaches, derive the key equations and then apply them to a number of characteristic cases. The gauge problem in cosmology and ways to circumvent it are also discussed. We outline the basic framework of the baryonic and the non-baryonic structure formation scenarios and point out their strengths and shortcomings. Fundamental concepts, such as the Jeans length, Silk damping and collisionless dissipation, are highlighted and the underlying mathematics are presented in a simple and straightforward manner. IntroductionLooking up into the night sky we see structure everywhere. Star clusters, galaxies, galaxy clusters, superclusters and voids are evidence that on small and moderate scales, that is up to 10 Mpc, our universe is very lumpy. As we move to larger and larger scales, however, the universe seems to smooth out. This is evidenced by the isotropy of the x-ray background, the number counts of radio sources and, of course, by the high isotropy of the Cosmic Microwave Background (CMB) radiation. The latter also provides a fossil record of our observable universe when it was roughly 10 5 years old and about 10 3 times smaller than today. So, the universe was very smooth at early times and it is very lumpy now. How did this happen? Although the details are still elusive, cosmologists believe that the reason is "gravitational instability". Small fluctuations in the density of the primeval cosmic fluid that grew gravitationally into the galaxies, the clusters and the voids we observe today. The idea of gravitational instability is not new. It was first introduced in the early 1900s by Jeans, who showed that a homogeneous and isotropic fluid is unstable to small perturbations in its density [1]. What Jeans demonstrated was that density inhomogeneities grow in time when the pressure support is weak compared to the gravitational pull. In retrospect, this is not surprising given that gravity is always attractive. As long as pressure is negligible, an overdense region will keep accreting material from its surroundings, becoming increasingly unstable until it eventually collapses into a gravitationally bound object. Jeans, however, applied his analysis to a static Newtonian fluid in an attempt to understand * e-mail address: ctsagas@maths.uct.ac.za 1 the formation of planets and stars. In modern cosmology we need to account for the expansion of the universe as well as for general relativistic effects.Despite the lack, as yet, of a detailed scenario, the rather simple idea that the observed structure in our universe has resulted from the gravitational amplification of weak primordial fluctuations seems to work remarkably well. These small perturbations grew slowly over time until they were strong enough to separate from the background expansion, turn around, and c...

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Section: Adiabatic and Isothermal Perturbationsmentioning

confidence: 99%

Magnetized cosmological perturbations

2000

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“…Primordial black holes, defined as black holes forming in the early universe without stellar progenitors, were first proposed by Zel'dovich & Novikov (1967) and Hawking (1971) as a possible consequence of the extremely high densities achieved in the big bang model. If they do indeed form in the early universe and can avoid evaporation ( Hawking 1975) up to the present day, they must still exist and they may be important.…”

Section: Introductionmentioning

confidence: 99%

Growth of Structure Seeded by Primordial Black Holes

Mack

Ostriker

Ricotti

2007

ApJ

157

187

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We discuss the possibilities for the growth of primordial black holes (PBHs) via the accretion of dark matter. In agreement with previous works, we find that accretion during the radiation-dominated era does not lead to a significant mass increase. However, during matter domination, PBHs may grow by up to 2 orders of magnitude in mass through the acquisition of large dark matter halos. We discuss the possibility of PBHs being an important component in dark matter halos of galaxies, as well as their potential to explain the ultraluminous X-ray sources (ULXs) observed in nearby galactic disks. We point out that although PBHs are ruled out as the dominant component of dark matter, there is still a great deal of parameter space that is open to their playing a role in the modern-day universe. For example, a primordial halo population of PBHs each at 10 2.5 M , making up 0.1% of the dark matter, grows to 10 4.5 M via the accumulation of dark matter halos and accounts for $10% of the dark matter mass by a redshift of z % 30. These intermediate-mass black holes may then ''light up'' when passing through molecular clouds, becoming visible as ULXs at the present day, or they may form the seeds for supermassive black holes at the centers of galaxies.

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“…If this spectrum is in fact close to this upper limit, then the situation allows for 'large' fluctuations; large enough to collapse into black holes, known as Primordial Black Holes (PBHs) (c.f. [12,13,14,15,16,17,18]). Since the uncertainties in the primordial spectrum at such small scales are dominated by instrumental noise [1], as opposed to cosmic variance which is the dominant source of uncertainties at larger angular scales, it may be that these uncertainties can be reduced in future surveys.…”

Section: Introductionmentioning

confidence: 99%

Generating primordial black holes via hilltop-type inflation models

Alabidi

Kohri

2009

Phys. Rev. D

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It has been shown that black holes would have formed in the early Universe if, on any given scale, the spectral amplitude of the Cosmic Microwave Background (CMB) exceeds P ζ ∼ 10 −4 . This value is within the bounds allowed by astrophysical phenomena for the small scale spectrum of the CMB, corresponding to scales which exit the horizon at the end of slow-roll inflation. Previous work by Kohri et. al. (2007) showed that for black holes to form from a single field model of inflation, the slope of the potential at the end of inflation must be flatter than it was at horizon exit. In this work we show that a phenomenological Hilltop model of inflation, satisfying the Kohri et. al. criteria, could lead to the production of black holes, if the power of the inflaton self-interaction is less than or equal to 3, with a reasonable number or e−folds. We extend our analysis to the running mass model, and confirm that this model results in the production of black holes, and by using the latest WMAP year 5 bounds on the running of the spectral index, and the black hole constraint we update the results of Leach et. al. (2000) excluding more of parameter space.

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The "Hot" Model of the Universe

Cited by 164 publications

References 0 publications

Magnetized cosmological perturbations

Magnetized cosmological perturbations

Growth of Structure Seeded by Primordial Black Holes

Generating primordial black holes via hilltop-type inflation models

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