When the Hubble Space Telescope was launched in 1990, its main goal was to measure the universe's expansion rate.

The space observatory has been helping scientists to discover and refine this accelerating rate over the past 30 year. It also helped them uncover a mystery that only brand new physics could solve.

Hubble has seen more than 40 galaxies with pulsating and exploding supernovae, allowing him to measure greater cosmic distances. These phenomena allow astronomers to measure astronomical distances, such as mile markers. They also help to determine the rate of expansion.

Astronomers discovered dark energy in 1998, as a way to see how fast our universe expands. This mysterious force acts as an accelerator and repels expansion.

There is also another twist: there is an unexplained difference in the rate at which the local universe expands compared to the distant universe just after the big bang.

Scientists are unable to explain the discrepancy but admit it is strange and may need new physics.

"You are getting the best measure of the universe's expansion rate from the gold standard telescopes and cosmic miles markers," stated Adam Riess, Nobel Laureate and distinguished professor at Johns Hopkins University in Baltimore in a statement.

This is what the Hubble space telescope was designed to do using the most advanced techniques that we know. This is Hubble's most important achievement, as it would take 30 more years for Hubble to double the sample size.

Named after Edwin Hubble (pioneering astronomer), the telescope is named in his honor. Hubble discovered that galaxies were hidden in distant clouds in 1920s astronomy. (He died in 1953.

Hubble relied upon the 1912 work of Henrietta Swan Leavitt, an astronomer who discovered the periods of brightness within pulsating stars known as Cepheid variables. Cepheids are cosmic mile markers, as they dim and brighten periodically in our galaxy and other galaxies.

Hubble's research led to the discovery that our galaxy was just one of many. This forever changed our perspective on the universe. Hubble continued his research and discovered that distant galaxies seemed to be moving quickly, suggesting that our universe is expanding.

Hubble Space Telescope celebrates thirty years of groundbreaking discoveries and inspiring images

Hubble Space Telescope celebrates thirty years of groundbreaking discoveries and inspiring images

The discovery of the universe's expanding rate led to the Nobel Prize in Physics 2011, which was awarded to Saul Perlmutter and Brian P. Schmidt "for the discovery that the universe is expanding faster through the observation of distant supernovae."

Riess is still leading SHOES, abbreviated H0 for Supernova, and Equation of State of Dark Energy. This scientific collaboration studies the expansion rate of the universe. His team published a paper in The Astrophysical Journal, which provides the most recent update on the Hubble constant as it pertains to the universe's expansion rate.