The expansion of the universe is a well-known and demonstrable fact, but how fast it’s expanding has become a hotly debated topic in the last few years.
According to the standard cosmological model, the rate of expansion of the universe is constant, known as the Hubble constant. A study last year challenged this, claiming that the rate has actually changed over the ages of the universe and it’s now up to 8 percent higher than in the past.
The study last year determined the Hubble constant – the rate of acceleration – to be 73.2 kilometers per second per megaparsec (km/s/Mpc), larger than the currently accepted value of 67.8 km/s/Mpc from ESA's Planck satellite and the Sloan Digital Sky Survey.
A new series of papers published in the Monthly Notices of the Royal Astronomical Society finds the value to be 71.2 km/s/Mpc, which supports a change over time of the Hubble constant. The observation was performed by an international group of astronomers that used the Hubble Space Telescope to look at how massive galaxies bend space-time, acting as gravitational lenses.
These objects magnify and bend the light from very distant quasars but sometimes, due to their shape, the light takes longer paths and arrives at us with a delay. And it is in this delay that astronomers have looked for changes in the Hubble constant.
“Our method is the most simple and direct way to measure the Hubble constant as it only uses geometry and General Relativity, no other assumptions,” explains team co-leader Frédéric Courbin from the Federal Polytechnic School of Lausanne (EPFL), Switzerland, in a statement.
The Hubble constant is a key component in our understanding of the universe, so it is important that we get a precise value for it, and if it’s changing we need to know how and by how much. The new research reaches a precision on the value of 3.8 percent.
“The Hubble constant is crucial for modern astronomy as it can help to confirm or refute whether our picture of the Universe – composed of dark energy, dark matter, and normal matter – is actually correct, or if we are missing something fundamental,” added Sherry Suyu, the other leader of the H0LiCOW (H0 Lenses in COSMOGRAIL's Wellspring) team.
“The expansion rate of the universe is now starting to be measured in different ways with such high precision that actual discrepancies may possibly point towards new physics beyond our current knowledge of the universe” concluded Suyu.
The result is in disagreement with ESA’s Planck satellite, but the team wants to clarify that Planck looked at the very beginning of the universe while their study observed the universe today. More observations will hopefully clarify if the Hubble constant is actually not constant at all.