A group of researchers from Princeton has announced, through a work presented on Nature Astronomy, to have calculated more precisely the Hubble constant, or the speed with which the universe is expanding in relation to the distance between the galaxies.
Currently, the methods used to calculate this constant are basically two: that which is based on the analysis of the cosmic background radiation and that relating to the explosions of large stars very far from us.
However, these are two methods that do not agree: the first method, the one that analyzes the cosmic background radiation, reveals that the universe is expanding faster than can be calculated with the second method. It is clear that one of them is wrong, says Kenta Hotokezaka, a researcher at Princeton and one of the authors of the study, who used a new method based on the analysis of the fusion of two neutron stars.
These are very powerful energetic events that see two neutron stars collide at very high speed before merging. This event emits very strong gravitational waves that can also be intercepted on Earth. Just the interception of one of these events, which took place on August 17, 2017, was used by Hotokezaka and colleagues to calculate the speed of expansion of the universe.
The gravitational waves that occur during these events, in fact, create a characteristic pattern that has been called “standard siren.” Researchers also used data from various radio telescopes around the world to improve the resolution of radio images related to this cosmic explosion so that the final resolution was so high that it could be compared to that of a camera that distinguishes individual hair on the head of someone from 5 km away, as specified by Adam Deller, Swinburne University of Technology, Australia, another author of the study.
Then using a supercomputer, they also analyzed the most minute changes in the position and shape of this radiation, managing to determine the orientation of neutron stars.
Comparing this data with the speed with which the galaxy containing these two neutron stars moved away from ours, they therefore performed a better measurement of the Hubble constant. The speed of the expansion of the universe is now estimated between 65.3 and 75.6 kilometers per second per megaparsec, a more precise measurement than previously calculated.
However, for researchers, the level of precision in this estimate is still not enough: they intend to insist on analyzing more collisions like the one they used for this study.