"Analyzing 30 years of data from the famous space telescope, the new study makes the most precise measurement yet of how fast the universe is expanding." Astronomers have known for the better part of a century that the universe is expanding, thanks to the observation that galaxies are moving away from us — and the farther away they are, the faster they're traveling. The speed at which they're moving, relative to their distance from Earth, is a figure called the Hubble constant, and measuring this value was one of the primary missions of the space telescope of the same name. To measure the Hubble constant, astronomers study distances to objects whose brightness is known well — that way, the dimmer it appears, the farther away it is. For relatively close objects within our galaxy or in nearby ones, this role is filled by Cepheids, a class of stars that pulse in a predictable pattern. For greater distances, astronomers use what are called Type Ia supernovae — cosmic explosions with a well-defined peak brightness.... For the new study, a team of scientists has now gathered and analyzed the most comprehensive catalog of these objects so far, to make the most precise measurement of the Hubble constant yet. This was done by studying 42 galaxies that contained both Cepheids and Type Ia supernovae, as imaged by the Hubble telescope over the last 30 years.
"This is what the Hubble Space Telescope was built to do, using the best techniques we know to do it," said Adam Riess, lead scientist of the team. "This is likely Hubble's magnum opus, because it would take another 30 years of Hubble's life to even double this sample size."
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