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Posted on February 15, 2019
"The Hubble constant is one of the most important numbers in cosmology because it is essential for estimating the curvature of space and the age of the universe, as well as for exploring its destiny," said Hiranya Peiris. from University College London. Peiris, a British astrophysicist known for her work on cosmic microwave background radiation, was one of 27 scientists to receive the Breakthrough Prize in Fundamental Physics in 2018 for their "detailed maps of the first universe. ".
We live in an expanding bubble of space that exploded from a super powerful state, the Big Bang, 13.8 billion years ago. The observable universe is a bubble centered on the Earth, with a diameter of 27.4 billion light years – a bubble that grows at the rate of two light-years (one on each side) every year.
The cosmos has been expanding for 13.8 billion years and its current rate, known as the Hubble constant, indicates the time elapsed since the Big Bang. However, the two best methods used to measure the Hubble constant do not agree, suggesting that our understanding of the structure and history of the universe – called the "standard cosmological model" – may be wrong.
The study, published today in Physical Review Letters, shows how new independent data on gravitational waves emitted by binary neutron stars, called "standard sirens", will definitely break the deadlock between measurements.
"Hide in the Eye" – Neutron stars suggest unknowns known on the dark side of our universe
"We can measure the Hubble constant using two methods: one observing the stars and the Cepheid supernovae in the local universe and the other using measurements of the cosmic background radiation of the primitive universe. These methods do not give the same values, which means our standard cosmological model could be faulty. "
The team has developed a universally applicable technique that calculates how gravitational wave data will solve the problem.
Gravitational waves are emitted when binary neutron stars spiral one before the other before colliding with a light flash that can be detected by the telescopes. Indeed, UCL researchers participated in the detection of the first light of a gravitational wave event in August 2017.
Binary neutron star events are rare, but they are invaluable for providing another route to follow the evolution of the universe. Indeed, the gravitational waves they emit cause undulations in space-time that can be detected by the laser interferometer observatory (LIGO) and Virgo's experiments, giving an accurate measure of the distance from the system to Earth.
"The multiverse?" – Molten neutron stars challenge existing theories of gravity and black energy
By further detecting the light from the accompanying explosion, astronomers can determine the speed of the system and thus calculate the Hubble constant using Hubble's law.
For this study, researchers modeled the number of observations of this type needed to solve the problem of measuring the Hubble constant with precision.
"We calculated that by observing 50 binary neutron stars over the next decade, we would have enough gravitational wave data to independently determine the best measure of the Hubble constant. We should be able to detect enough mergers to answer this question in the next 5 to 10 years, "said Dr. Stephen Feeney, senior author of the Center for Computationational Astrophysics of the Flatiron Institute in New York.
"Beyond understanding!" – The creation of two supermassive black holes will prevent the discovery of the gravitational wave LIGO (the most popular of today)
"This will give us a more accurate picture of the expansion of the universe and help us improve the standard cosmological model," concluded Professor Peiris.
The study involved researchers from the Flatiron Institute (United States), UCL, Stockholm University, Radboud University (The Netherlands), and the Imperial College London and the University of Chicago. The contribution of UCL was graciously funded by the European Research Council.
Image credit: American Physical Society
The Daily Galaxy via UCL
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