By Kathy Sawyer

The Hubble has produced astonishing images that are not only a treat to look at but have helped to revolutionize human understanding of the universe.

Among the telescope’s major achievements, it has

• determined the age of the universe—now fixed at about 13.8 billion years. This resolved a longstanding dispute among those who study such things. The telescope’s findings pinned down the rate at which the universe is expanding and suggested the ultimate fate of the cosmos—that all objects within it will expand apart into a dark infinity, rather than collapsing inward in a cosmic crunch. Of course, life on Earth will be long gone by the time any of this becomes apparent, if only because the sun—a middle-aged star—will die in about 5 billion years.

• confirmed the existence of super-massive black holes—collapsed objects with masses up to billions of times that of our sun, so compact that not even light can escape their gravity. Essentially invisible, they can be detected through the violent fireworks they generate as they consume matter. Beyond proving their existence, Hubble went on to show that black holes lurk at the heart of virtually every galaxy and may play a central role in the way galaxies evolve.

• provided visual evidence that the material to form planets—possible platforms for life—is found around most young stars. This indicated that perhaps the creation of planets is a natural outcome of star formation, thus boosting theories that life exists elsewhere in the universe.

• taken 50-hour “deep field” exposures of supposedly empty patches of sky, revealing galaxies scattered across time and space all the way back to within a billion years of the Big Bang—the genesis event in which the universe came into being and started expanding. The faint light from objects in the early universe—including objects that no longer exist—has taken billions of years to reach Earth. These surveys prompted astronomers to multiply their estimate of the number of galaxies (each with hundreds of billions of stars) and revealed that the first galaxies—fragmented and irregular—formed much earlier and faster than expected.

• provided critical measurements supporting the discovery of a “dark energy” that opposes gravity. This force, at least for now, appears to be overwhelming the attractive force of gravity at cosmic scales. It is causing the expansion of the universe to accelerate rather than slow down under the pull of gravity. The quest to solve the mysteries of this phenomenon has become one of the most competitive pursuits in cosmology.