These measurements reduce the chances the large disparity is an accident from one in 3,000 to only one in 100,000, suggesting that new physics may be needed to better understand the cosmos.
"This mismatch has been growing and has now reached a point that is really impossible to dismiss as a fluke", Riess said in a statement. Because these stars brighten and dim at predictable rates, and the periods of these variations give us their luminosity and hence distance, astronomers use them as cosmic mileposts.
"When Hubble uses precise pointing by locking onto guide stars, it can only observe one Cepheid per each 90-minute Hubble orbit around Earth". Using their new method called DASH (Drift And Shift), the researchers using Hubble as a "point-and-shoot" camera to look at groups of Cepheids, thereby allowing the team to observe a dozen Cepheids in the same amount of time it would normally take to observe just one.
But when astronomers have tried to directly measure how fast the universe is expanding today - a more hard task, because everything is farther apart now - things seem to be moving faster than those calculations would predict.
The history of the measurement of Hubble's Constant has been always fraught with challenges and unexpected revelations. Riess says it's not just two experiments disagreeing noting that the two projects are measuring something fundamentally different.
Riess is leading a project called the SH0ES team that worked on this research.
The previous Hubble constant estimates have ranged from between around 67 to 73 kilometres per second per megasec.
Various scenarios have been proposed to explain the discrepancy, but there is yet to be a conclusive answer. The other is a prediction based on the physics of the early universe and on measurements of how fast it ought to be expanding.
What they found directly contradicts predictions made based on observations from the European Space Agency's Planck satellite, which measured the speed of the universe 380,000 years after the Big Bang.
For now, astronomers don't have an explanation for the changing expansion rate, although many have mused about dark energy, dark matter, a new subatomic particle, and other possibilities. Dark energy may also be the reason for the universe's accelerated expansion today.
Astrophysicists were surprised to discover that the universe is expanding much faster than expected, potentially needing new physics to find an answer. Many recent studies have indicated that the values of the Hubble constant derived from monitoring cosmic microwave background (the faint afterglow of the early Universe) don't match well with the estimates derived from far younger stars - even when taking into account, for example, dark energy, which is thought to accelerate the expansion of the Universe.
"If these values don't agree, there becomes a very strong likelihood that we're missing something in the cosmological model that connects the two eras", he said. An invisible form of matter called dark matter may interact more strongly with normal matter than astronomers previously thought.
Before Hubble was launched in 1990, estimates of the Hubble constant varied by a factor of two.
Many theories have been made, yet the true explanation remains an enigma.
The uncertainty attached to this number is just 1.9%, the researchers said.