2018/03/09 by Manvendra Pratap Rajvanshi, Rajvanshi, Manvendra Pratap, Tuneer Chakraborty +3
Physics and Astronomy · #Advanced Thermodynamics and Statistical Mechanics #Black Holes and Theoretical Physics #Cosmology and Gravitation Theories #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #General Relativity and Quantum Cosmology (gr-qc) #Popular Physics (physics.pop-ph) #astro-ph.CO #gr-qc #physics.pop-ph
paper · pdf · doi:10.48550/arxiv.1803.04267
17 pages, 7 figures. Accepted for publication in Resonance, journal of science education
openalex publication_date 2018/03/09 · arxiv created 2019/01/13 · arxiv updated 2019/01/17 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Observations show that the expansion of the Universe is accelerating. This requires that the dominant constituent of matter in the Universe has some unusual properties like negative pressure. This exotic component has been given the name dark energy. We work with the simplest model of dark energy, the cosmological constant introduced by Einstein. We study the evolution of spherical over-densities in such a model and show that there is a minimum over-density required for collapse: perturbations with a smaller amplitude do not collapse. This threshold is interesting as even perturbations with a positive over-density and negative energy do not collapse in finite time. Further, we show that perturbations with an amplitude larger than, but comparable to the threshold value, take a very long time to collapse. We compare the solutions with the case when dark energy is absent.