Space Telescope photo
Courtesy of NASA

After astronauts fixed the lens on the Hubble space telescope, the satellite began sending back pictures of the cosmos that left all onlookers in awe. The beauty of those images often overshadowed the legitimate scientific progress the Hubble enabled.

So, in honor of the Hubble’s final servicing mission, and Mario Livio, a senior astrophysicist at the Space Telescope Science Institute and author of Is God A Mathematician?, look past the pretty pictures and count down the ten most important scientific discoveries that the Hubble made possible.

The Source of Long Gamma Ray Bursts

10. The Source of Long Gamma Ray Bursts

In the 1960s, US satellites designed to detect gamma radiation from Russian nuclear testing began picking up huge radiation bursts from deep in space. For decades, no one knew where the bursts were coming from. When the Hubble went on line, scientists were able to track the gamma ray bursts back to galaxies with rapid star production, like the Large Magellanic Cloud galaxy (pictured). According to Livio, the gamma ray bursts occur when one of the galaxy’s massive stars collapses in on itself.
Accurate Measurement of the Hubble Constant

9. Accurate Measurement of the Hubble Constant

For years, scientists argued over the value of the Hubble Constant, a key component in the equation that measures the speed at which the universe expands. “Before the Hubble telescope, the estimates for the Hubble Constant were different by at least a factor of two,” said Livio. After analyzing Hubble pictures of far-off super novae (the remnants of one are pictured here), astronomers narrowed the value of the Hubble Constant down to within an error of five percent.
Stellar Populations

8. Stellar Populations

While some of the Hubble’s most notable pictures involved looking deep into space and time, it also made some important observations closer to home… if you consider 2.5 million light years close to home. Scientists knew very little about the histories of even our closest galactic neighbors (like the Andromeda galaxy shown here). But the Hubble, which can focus on individual stars in these galaxies, has allowed scientists to better understand the history of our corner of the universe.
Collision Images

7. Collision Images

Speaking of close to home, Hubble took one of its most important pictures of a planet right here in our own solar system. In 1994, fragments of the comet Shoemaker-Levy 9 hit Jupiter (pictured here), and Hubble provided the first ever recorded images of a collision between two bodies in space. Aside from simply looking cool, photos of the scars left by the collision provided new insights into the makeup of Jupiter’s atmosphere.
Counting Planets

6. Counting Planets

Naturally, being the egocentric species that we are, contemplating the mysteries of the cosmos inevitably leads to the question of whether life exists on other planets. To answer that question, we need to know just how many other planets there are. Pictures from the Hubble went a long way towards answering that question. By capturing images of the solar debris disks that eventually coalesce into planets (like the disk shown here around a star in the Orion nebula), the Hubble showed that planets are far more common than scientists previously thought.
Extrasolar Planets

5. Extrasolar Planets

And while we’re on the subject of extrasolar planets, the Hubble also snapped the first shot of a planet outside of our solar system. Before this picture of a planet around the star Fomalhaut was taken, scientists had to calculate whether a star had a planet by evaluating the star’s wobble. With the Hubble, the astronomers could just take a picture of the planet itself.
Black Holes

4. Black Holes

Astronomers had been theorizing that super massive black holes laid at the center of galaxies for years, but it wasn’t until the Hubble actually took a shot of one of those black holes that the debate was put to rest. “Not only did Hubble discover that there are black holes in the center of the galaxies, but it discovered that there was correlation between the size of the black hole and the size of the bulge,” said Mario Livio, a senior astrophysicist at the Space Telescope Science Institute and author of Is God A Mathematician?. “Before that, we did not know that there was a black hole in the center, and definitely did not know that relationship.”
Deep Field Shot

3. Deep Field Shot

This is one of the cases where the aesthetic beauty of one of Hubble’s pictures matched up with its scientific value. The Hubble Deep Field Shot, the most magnified picture of a spot of the sky ever taken with optical light, provided this gorgeous image, and gave scientists the information they needed to accurately calculate the age of the universe.
Dark Matter

2. Dark Matter

Long theorized and to this date never directly observed, dark matter may make up as much as 22 percent of the material in the universe. Because dark matter doesn’t reflect or emit light (hence the name), it cannot be viewed with a telescope. However, dark matter still exerts a gravitational pull on the light that passes by it, bending the light like a lens. The Hubble was able to take a picture of light bent by the gravitational lens of nearby dark matter, thus detecting the previously undetectable. This is a picture of light from the galaxy cluster Abell being warped by a gravitation lens from dark matter.
Dark Energy

1. Dark Energy

According to the theory of General Relativity, the gravitational pull of every object in the universe would eventually slow, and then reverse, the expansion of the universe. For years, that’s what astronomers assumed was happening. Then came Hubble. “Arguably the most important Hubble discovery is that of dark energy, which is this form of energy that propels the expansion of the universe,” said Livio. “We knew since the late 1920s that the universe was expanding, but thought that this expansion would be slowing down. Instead, we discovered in 1998 that this expansion was speeding up.” This momentous discovery came from measuring light emitted by super novae, like the explosion of the star Sanduleak -69° 202a, pictured here.