A supernova and a new technique enter the debate on the expansion of the universe

The universe is constantly expanding at a rate that is measured with the Hubble constant, but there is no agreement on its exact value, a problem that a supernova can help to solve, a pioneering technique and a theory that until now had not been possible.

The idea and technique correspond to an international team, with Spanish participation, which provides new information to determine the age of the universe with greater precision and better understand the cosmos.

The results, which are published today in two studies in Science and The Astrophysical Journal, indicate that with this new way of measuring the Hubble constant, the universe is not expanding as fast as previously thought.

In astronomy, the value of the acceleration at which the universe is expanding is called the Hubble constant and is calculated in two ways.

The first from observations of nearby supernovae, while the second uses the cosmic microwave background, which is the radiation that began to flow freely through the universe shortly after the Big Bang. However, these two measurements differ by around 10%, which has sparked a wide debate among physicists and astronomers, because if both are exact, it means that the current theory of the composition of the universe is incomplete. A team led by Patrick Kelly, from the University of Minnesota (USA), and with the participation of the Institute of Physics of Cantabria (IFCA-CSIC) and the University of the Basque Country, used a completely new approach to measure the rate of expansion of the universe. To do this, they looked at a supernova discovered in 2014 by Kelly and which is the first of which various images were taken at two times separated by a year.

These images could be captured because the supernova was discovered and observed through a gravitational lens, a phenomenon that is created by a very large concentration of matter (in this case a cluster of galaxies) that curves the space around it. Passing through that area, the light bends and acts like a lens. By having images from 2014 and 2015, the team was able to measure the Hubble constant using a theory that was developed by Norwegian astronomer Sjur Refsdal in 1964, but was previously impossible to put into practice. IFCA researcher José María Diego was in charge of modeling one of the types of lenses, said the institute in a statement.

The team concluded that the value of the Hubble constant is 66.6 kilometers per second and per megaparsec (a unit of distance equivalent to about 3.26 light-years). This measurement “favors” the value of the cosmic microwave background, although the value of the other measurement cannot be excluded, Kelly noted. Although these new calculations “do not completely settle the debate” of the Hubble constant, they do provide more information and bring physicists closer to obtaining the most accurate measure of the age of the universe.

source: https://iopscience.iop.org/journal/0004-637X