The Hubble Space Telescope is best known to the public for its beautiful images of space, but it is also famous for its research into the expansion of the universe. Scientists knew that the universe was expanding, but they didn't know how fast. This figure was pinned down for the first time by Hubble.
The Hubble constant is the rate of the universe's expansion and is one of the most important numbers in the field. This constant is important to understand how the universe has evolved and how old it is as the expansion can be traced back to the big bang. Scientists put the age of the universe at between 8 billion and 20 billion years old before the Hubble Space Telescope was launched. Thanks to Hubble data, this figure has been refined to a much more accurate one.
That doesn't mean the work is done. The estimate for the Hubble constant was fairly accurate in the 2000s, at 72 kilometers per second per megaparsec, but it had an error of plus or minus 8. This figure has been refined more and more, with a recent finding of 74.03.
There is a problem in this explanation. Hubble and other telescopes do not agree with the expansion rate predicted by data from the earliest stages of the universe. In order to get the most precise measurement of the Hubble constant, researchers used Hubble data to measure distances using both variable stars and Type Ia supernovae as mile markers.
This is what the Hubble Space Telescope was built to do, using the best techniques we know to do it. It would take another 30 years of Hubble's life to double this sample size, said Adam Riess, lead author of the study.
Riess's team looked at 42 supernova explosions, which act as distance markers, and were able to hone in on a figure of 73.06 for the Hubble constant, with an uncertainty of just 1.04. That is eight times more precise than Hubble was expected to be.
There is still a discrepancy between this number and that predicted by data from the earliest universe, which is measured by looking at the Cosmic Microwave Background. The Hubble constant should be around 67 according to these results.
Astronomers don't have an explanation for why the numbers differ. We have yet to learn about a new type of physics.
The number for the Hubble constant is as accurate as it is likely to get.
The Hubble constant can be used to thread a needle from the past to the present for an end-to-end test. This took a lot of work.
The research will be published in a journal.