Hubble at 25!


On April 24th, the Hubble Space Telescope will celebrate 25 years since its launch. This provides an excellent opportunity to very briefly summarize what I regard as Hubble’s greatest scientific achievements. I should emphasize two things: (1) I have used my personal judgment (and biases) in creating this list; other scientists may have different opinions. (2) I do not claim that these are all exclusive Hubble discoveries. By its very nature as an all-purpose telescope, in most cases Hubble helped cement existing suggestions, rather than making singular discoveries. Nevertheless, in all the topics listed below, Hubble’s contribution has been crucial.

What do I personally regard as Hubble’s “Top 6″ scientific achievements? Here is my list:

(1) The discovery that not only is the expansion of our universe not slowing down, it is accelerating! These findings, made through monitoring distant stellar explosions (called Type Ia supernovae: Figure 1), have led (in combination with other measurements) to the realization that a mysterious form of “dark energy” constitutes about 70% of the cosmic energy budget.

Figure 1. Distant supernova explosions.

(2) The mapping of the large-scale, three-dimensional distribution of “dark matter” — matter that neither emits nor absorbs light, but which forms the scaffolding on which the cosmic structure is constructed.

(3) The determination of the history of the cosmic star-formation rate. This achievement came through a series of deep observations of the universe (Figure 2 shows the “Hubble Ultra-Deep Field 2014″).

Figure 2. The Hubble Ultra-Deep Field 2014. Credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (ASU), Z. Levay (STScI).

(4) The determination of the Hubble constant — the current rate of cosmic expansion. The uncertainty in the value of this important cosmological parameter has been reduced from a factor of two, to about 3%.

(5) The —> Read More