Science & Technology (Commonwealth Union) – The expanding universe has been on the radar of astronomers for many years.
Scientists looking into the explosive aftermath of a massive cosmic collision have produced a new estimate of how quickly the Universe is expanding.
The international research team, led by scientists from Swinburne University of Technology and CSIRO, combined observations from telescopes with gravitational wave measurements to investigate the true value of the Universe’s expansion rate, known as the Hubble Constant.
Getting a precise finding of the expansion speed of the Universe is crucial as it permits researchers to determine the distances and sizes of cosmic objects, to better know the influence of dark matter for cosmic evolution. It also helps in receiving insights into the start and its eventual future of the Universe.
For more than a decade, two different methods of measuring the Hubble Constant have produced conflicting results, creating a major debate among cosmologists.
Lead researcher at CSIRO, Dr Kelly Gourdji, explained that the two separate approaches for measuring the Universe’s expansion rate are at the centre of what scientists call the “Hubble tension”.
Dr Gourdji indicated that one approach relies on observations from the early Universe, specifically the cosmic microwave background radiation, to calculate the expansion rate. The other method uses observations of much closer objects, such as supernovae, providing a measurement based on the more recent Universe.
The fact that these highly accurate measurements produce different results presents a major challenge for scientists. It suggests that either one of the measurements contains an unknown error, or that current theories about the fundamental physics shaping the Universe may be incomplete. As a result, the true value of the Hubble Constant remains uncertain.
Dr Gourdji pointed out that their gravitational wave-based measurement is considered a late-Universe approach, yet their findings are closer to the value predicted by early-Universe measurements.
The spectacular merger of two neutron stars, observed by telescopes and accompanied by the detection of gravitational waves on Earth, gave researchers a rare chance to make this new calculation.
Neutron stars are the second most compact objects known in the Universe after black holes, containing an enormous amount of mass packed into an extremely small volume. Their extraordinary density produces a powerful gravitational force, estimated to be more than 100 billion times stronger than Earth’s gravity.
The neutron star merger released an immense amount of energy, creating distortions in the fabric of space-time known as gravitational waves, while also launching high-speed jets of energetic material into the cosmos.
Professor Adam Deller from the Swinburne University of Technology, who led the radio observations that supported the study, said these jets produced by the collision played a crucial role in enabling the researchers to carry out the measurement.
“These jets are launched for only a couple of seconds, but as they slam into the surrounding gas, they glow for months afterwards. We analysed almost a year of observations from the Hubble Space Telescope and two different arrays of radio telescopes spread across the USA and Europe,” explained Professor Deller.
By integrating all the available data, the researchers calculated a new estimate for the Hubble Constant. Although this result is not as precise as the leading measurements involved in the Hubble tension debate, it represents a more accurate determination than earlier estimates based on gravitational wave observations. The finding provides the strongest evidence so far that gravitational waves may eventually help resolve the disagreement.
Professor Deller highlighted the importance of the result.
Professor Deller indicated that certain scientists have suggested that both conflicting measurements could be accurate if there are changes needed to our current understanding of cosmology. However, their findings provide strong evidence against that possibility.
Dr Gourdji added that further observations and additional data will be required to validate the result.
