This is no news that the universe is expanding since time immemorial. A look at all around us tells us about the presence of faraway galaxies. The ones shifting away from us at an incredible speed. Cosmic expansion leads to the red shifting of the light of those distant galaxies. This fact known since 1929 when relation between redshift of a galaxy and its distance calculated by an American astronomer.
In the late 1990s, two different studies associated with the distance of supernovae made a startling discovery. The studies discovered that expansion of the universe is happening at a much faster rate. Some dark energy believed to exist behind such accelerated pace of expansion of the universe.
Study of Cepheid Variables Hints at the Existence of Dark Energy
In the field of cosmology, dark energy has now become a part of the concordance model. Meanwhile, 68% of the matter-energy in the universe considered to be comprised of dark energy. Whilst there exists a trove of huge data to support the existence of dark energy, the model do come with certain problems. A new study non-existence of this.
There exists a very well defined relationship between galactic distance and galactic redshift, which is now termed as Hubble constant. It is also popularly known as Hubble parameter. With the ascertainment of Hubble parameter and through the measurement of matter density of the universe, one can determine the quantity of dark energy in the universe. It is not much of an uphill task to ascertain the redshift of a galaxy, however the measurement of distance is difficult.
Hubble determined the distance by making an observation through Cepheid variables, which come with a relationship of strong period-luminosity. Another famous American astronomer, Henrietta Swan Leavitt, who examined more than 1700 Cepheid variables, discovered this very relation. One can know about the absolute magnitude or the real brightness through measurement of the period of a Cepheid variable.