Calculating the Hubble’s constant with ever more accuracy has been one of the challenges that cosmologists are eager to pin down, however it continues to elude them, and as a consequence there may be fundamental flaws in our understanding of the universe.
Hubble’s constant dictates the precise rate at which our universe expands and hence it has bearing on the age and even the size of the universe.
The value of the constant was first calculated by Edwin Hubble to be 500 km/sec/Mpc and since then we have been trying to measure it with ever more precision and we have had a range of values it. The trouble is that as we measure the constant using different techniques, the answers that they yield differ slightly, none of them agree with each other, calling into question not only our ideas of the age of the universe, but also our ability to understand the fundamental physics of the universe.
Wendy Freedman, astronomer at the University of Chicago, said in a NASA press release that this uncertainty in pinning down the value of the Hubble’s constant may be due to some aspect that we don’t yet understand or it may be because our cosmological model is incomplete, or maybe even both.
Freedman was tasked with calculating the latest value of the Hubble’s constant and she undertook the onerous task using a different method, measuring the brightness of red giant stars in different galaxies.
They are useful as a standard candle in measuring distances as they reach uniform size and brightness. She calculated the constant to be 69.8 km/sec/Mpc. Though the study has not yet been published by the Astrophysical journal, it has been accepted.
There were already two different values for the Hubble’s constant floating around and her work was supposed to put an end to this ambiguity and nail down the exact value, however this method has given astronomers a third value to grapple with.
This value was a tad lower than what was calculated by a different method that relied on a different kind of star and higher than what was calculated using yet another different approach, using the light from the Cosmic Microwave Background Radiation.
Freedman remarked in the press release that the scope for the Hubble’s constant is huge as it sets the absolute scale, size and the age of the universe. As the uncertainty still remains with the exact value of the constant, it could mean that our understanding of the processes that drive the expansion may be incomplete.
According to a New Scientist article published last week, there is only one in a 3.5 million chance that the previous results came out of a random chance, thereby giving credence to the previous studies.
NASA has its hopes in the Wide Field Infrared Survey Telescope, launching in the middle of the next decade, to resolve the conundrum and to be able to precisely measure the value of the Hubble’s constant.
Duke University astronomer Daniel Scolnic told New Scientist that this gap in our understanding of the rate of expansion of our universe may provide new insights into other unsolved problems in cosmology, like dark energy and dark matter.