1.One light year is the distance travelled by light in one year: ≈ 9.5 × 1012 km.
2.By modern standards, there were several issues with Zwicky’s original estimate, including the wrong value of the Hubble constant, which is the current expansion rate of the Universe, crude estimates for the luminosity, the cluster radius and poor statistics; nonetheless, his main result survived, and the current value for the mass-to-light ratio (the ratio of total mass to luminosity) of galaxy clusters incidentally asymptotically approaches 400.
Rubin, V.C., Burstein, D., Ford, W.K. Jr and Thonnard, N. (1985) Rotation velocities of 16 Sa galaxies and a comparison of Sa, Sb, and Sc rotation properties. Astrophysical Journal, 289, p. 81. doi: 10.1086/162866.
Bosma, A. (1981) 21-cm line studies of spiral galaxies. II. The distribution and kinematics of neutral hydrogen in spiral galaxies of various morphological types. Astronomical Journal, 86, p. 1825. doi: 10.1086/113063.
6.Einstein first discussed the gravitational lensing by stars in 1936, while Zwicky proposed gravitational lensing by galaxies in 1937, a subject that once again was ignored until much later, until the 1970s, with the first galactic lens being discovered in 1979.
7.This radiation was emitted about 380,000 years after the Big Bang, when the Universe was filled with a hot, ionised gas. Once electrons combined with protons to form neutral hydrogen atoms, photons could start to travel freely through space.
et al. (Planck Collaboration) (2016) Planck 2015 results. XIII. Cosmological parameters. Astronomy and Astrophysics, 594, p. A13. doi: 10.1051/0004-6361/201525830.
Frieman, J.A., Turner, M.S. and Huterer, D. (2008) Dark energy and the accelerating universe. Annual Review of Astronomy and Astrophysics, 46, p. 385. doi: 10.1146/annurev.astro.46.060407.145243.
Frenk, C.S. and White, S.D.M. (2012) Dark matter and cosmic structure. Annalen der Physik, 524, p. 507. doi: 10.1002/andp.201200212.
11.Primordial nucleosynthesis describes the formation of the light elements 2H, 3He, 4He and 7Li from about 10 s to 20 min after the Big Bang. The resulting abundances once nucleosynthesis ends, which are compared with those measured in astronomical objects where little stellar nucleosynthesis occurred, depend on the baryon-to-photon number ratio, and are thus a measure of the amount of baryons, or ordinary matter, in the early Universe.
Moniez, M. (2010) Microlensing as a probe of the Galactic structure: 20 years of microlensing optical depth studies. General Relativity and Gravitation, 42, p. 2047. doi: 10.1007/s10714-009-0925-4.
Strigari, L.E. (2013) Galactic searches for dark matter. Physics Reports, 531, p. 1. doi: 10.1016/j.physrep.2013.05.004.
14.The electronvolt (eV) is the characteristic energy scale of atomic physics processes, e.g. the ionisation energy of the hydrogen atom is 13.6 eV. The kiloelectronvolt (keV) is the energy scale of X-rays, while the megaelectronvolt (MeV) is typical for nuclear-physics processes. The gigaelectronvolt (GeV) scale is characteristic for the rest mass energy of a proton, the hydrogen atom’s nucleus, while at the LHC, the proton–proton collider near Geneva, protons are accelerated up to kinetic energies of 7000 GeV.
15.The abundance of dark matter is given in terms of the critical density ρ
= 3 H
2 / (8π) = 1.88 × 10−29 g cm−3 with the Hubble constant H
0 ≈ 70 km (s Mpc) −1 and the Planck mass M
Pl = 1019 GeV, namely ΩDM = ρ
. The critical density ρ
corresponds to about 6 hydrogen atoms per cubic metre of space.
16.Supersymmetry is a spacetime symmetry that proposes a relationship between particles with half-integer spin (fermions) and particles with integer spin (bosons). Examples for fermions are electrons and protons; examples for bosons are photons and gluons.
17.C stands for charge conjugation, P for parity transformation; the CP operation is not conserved in the weak interaction.
Peccei, R.D. and Quinn, H.R. (1977) CP conservation in the presence of pseudoparticles. Physical Review Letters, 38, p. 1440. doi: 10.1103/PhysRevLett.38.1440.
Preskill, J., Wise, M.B. and Wilczek, F. (1983) Cosmology of the invisible axion. Physics Letters B, 120, p. 127. doi: 10.1016/0370-2693(83)90637-8.
et al. (Particle Data Group) (2014) Review of particle physics. Chinese Physics C, 38, p. 090001. doi: 10.1088/1674-1137/38/9/090001.
Baudis, L. (2016) Dark matter searches. Annalen der Physik, 528, p. 74. doi:10.1002/andp.201500114.
Goodman, M.W. and Witten, E. (1985) Detectability of certain dark-matter candidates. Physical Review D, 31, p. 3059. doi: 10.1103/PhysRevD.31.3059.
Drukier, A., Freese, K. and Spergel, D. (1986) Detecting cold dark-matter candidates. Physical Review D, 33, p. 3495. doi: 10.1103/PhysRevD.33.3495.
Read, J.I. (2014) The local dark matter density. Journal of Physics G, 41, p. 063101. doi: 10.1088/0954-3899/41/6/063101.
Baudis, L. (2012) Direct dark matter detection: The next decade. Physics of the Dark Universe, 1, p. 94. doi: 10.1016/j.dark.2012.10.006.
(ADMX Collaboration) (1983) Experimental tests of the ‘invisible’ axion. Physical Review Letters, 51, p. 1415. doi: 10.1103/PhysRevLett.51.1415.