Piecing together cosmic history
A new, sweeping analysis fills in 11 billion years of the history of our universe in unprecedented detail.
The big picture: Previous studies have illuminated the very earliest days of the universe and others have detailed the cosmos' more recent history, but until now, there's been an 11 billion year gap in knowledge of our roughly 13.8 billion year old universe.
Details: A collaboration — called the extended Baryon Oscillation Spectroscopic Survey (eBOSS) — collected data about 2 million galaxies and quasars.
- That information, which traces the 11 billion year gap, was combined into a map with other data that pieces together the expansion history of the universe from just 300,000 years after the Big Bang to now.
- It took about 10 years for the astronomers working on eBOSS to gather enough data to come out with these results.
- "What makes this so difficult is simply that the volume is so large, the signals we are seeking are so weak, and the galaxies are so faint," Kyle Dawson, eBOSS principal investigator, told me via email. "Even with an advanced instrument such as the BOSS spectrograph, it took us a decade to observe enough faint galaxies and quasars to make the measurements that we are reporting today."
The intrigue: The new analysis further complicates measurements of the rate of the expansion of the universe — a value known as the Hubble constant.
- The eBOSS map suggests that the expansion rate — thought to be spurred on by dark energy — is actually about 10% lower than the rate found when measuring the distances to other galaxies using different means.
- That number closely hews to others that are in line with the standard model of cosmology, but other means of measuring the Hubble constant have diverged in recent years, complicating that picture.