In a new study published by Australian astronomers who have combined ever observation of supernovae that has ever been made have determined that the strength of gravity has stayed constant for the last nine billion years.
This is all to do with Newton’s gravitation constant, which is known as G. G describes the attractive force that runs between two objects, as well as the separation between the objects and their masses. Previous theories and research had suggested that since the Universe began 13.8 billion years ago with the Big Bang, G could have been changing.
If previous studies had been accurate, and G had been decreasing over time, then the Earth’s distance from the Sun could have been greater in the past. That would have meant that the Earth’s seasons would have been longer.
But the Australian team from Swinburne University of Technology have cast doubt on that, after analysing 580 separate supernova explosions, from both nearby and further away in the Universe. These studies have shown that the strength of gravity has remained constant.
Professor Jeremy Mould, one of the scientists involved said that while looking back in cosmic time to discover potential changes to the laws of physics was not a new concept, but supernova cosmology has now allowed them do it with gravity.
They looked at many Type la supernovas. These are the violent deaths of white dwarf stars, which are as huge as the sun, but packed into a ball no larger than the earth.
Telescopes are capable of detecting the light from these explosions, and then using the brightness as a ‘standard candle’ which can be used to measure distance in the University. This was used by Professor Brian Schmidt, who won the 2011 Nobel Prize for discovering Dark Energy.
Professor Mould and student Syed Uddin at Swinburne, assumed these supernovas happened when a critical mass was reached within the white dwarf, or if it collided with another star.
Professor Mould said that the critical mass was dependant on G, as it allowed them to monitor it over billions of years, as opposed to the decades that were possible previously.
Despite the huge differences in time spans, the results concurred with the findings that were gained from the Lunar Laser Ranging Experiment. This had been used to measure the distance between the Earth and the Moon, after it was left on the moon during the Apollo missions. This had allowed scientists to measure variations in G at a high precision.
Mr Uddin said that this cosmological analysis complemented efforts to describe the laws of physics over constant time and in a new way.
In this recent publication, researchers from Swinburne have set a new upper limit on the change of G (Newton’s gravitational constant). They have set this at 0.00000001% per year (over the last 9 billion years).
This research was done at the ARC Centre of Excellence for All-Sky Astrophysics (CAASTRO). It is a collaboration between The University of Sydney, The Australian National University, Swinburne University of Technology, The University of Melbourne, The University of Western Australia, The University of Queensland, and Curtin University. Curtin University, and The University of Western Australia participate as one institution, known as the International Centre for Radio Astronomy Research. The Australian Research Council Centre of Excellent funds CAASTRO. Other funding comes from the NSW State Government’s Science Leveraging Fund, and the seven universities involved.
This research is published in the Publications of the Astronomical Society of Australia.
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