The expansion of the Universe
Among his accomplishments, Dr. Edwin Hubble discovered that the Universe is expanding. With additional work, he and later cosmologists observed that this expansion is actually accelerating. This meant that galactic objects that were further away from the observer were receding faster than object that were closer. The rate of that acceleration has been dubbed the Hubble Constant.
New observations with more precise instruments have shown variances in the Hubble Constant that are as yet unexplained. Some physicists think these variances might hint at new sub-atomic particles or even new physics. This article is from today's New York Times and it's well-written for the layman like me:
https://www.nytimes.com/2017/02/20/science/hubble-constant-universe-expanding-speed.html?hp&action=click&pgtype=Homepage&clickSource=story-heading&module=second-column-region®ion=top-news&WT.nav=top-news&_r=0
Additionally, there are some spectacular space photographs and images that accompany the article.