This image shows the sparkling centerpiece of Hubble’s 25th anniversary tribute this week. Westerlund 2 is a giant cluster of about 3,000 stars located 20,000 light-years away near the Gum 29 nebula in the constellation Carina. Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team
I think it’s fair to say that the Hubble Space Telescope has produced more beautiful images of the cosmos than any other telescope … ever. Part of the reason is its longevity. Another is Hubble’s unique ability to take incredibly long time exposures far above the blurring influence of Earth’s atmosphere. As an orbiting telescope, its images show pinpoint stars and spectacular detail that have only recently being replicated by ground-based telescopes using special optical techniques.
Hubble deployed by the Space Shuttle Discovery in 1990. Credit: NASA
It wasn’t always that way. Hubble was launched into low-Earth orbit in the spring of 1990, but within weeks the first images returned revealed a serious flaw — the 94-inch primary mirror had been ground precisely but to the wrong shape. This serious error meant that images returned suffered from a defect known as spherical aberration.
Basically, Hubble couldn’t focus star images sharply across its entire field of view. The defect was traced back to an instrument used to measure how precise the mirror had been ground. A lens within the device was ever so slightly out of position, resulting in the mirror being ground with the wrong figure.
The spiral galaxy M100 before and after the corrective optics package was installed. Credit: NASA
A corrective optics package was developed to reverse the aberration and installed by a team of space shuttle astronauts in December 1993. Since January 1994, Hubble’s been snapping one crisp image after another.
The telescope bears the name of Edwin Hubble, the 20th century astronomer who discovered the true enormity of the universe and the fact that it’s not static but in continual expansion. This week the Hubble Space Telescope (HST) celebrates its 25th anniversary. But in a selfless role reversal, instead of sending an anniversary card to Hubble, Hubble sent us a sumptuous image of the star cluster Westerlund 2.
These pillars are composed of dense gas and dust near Westerlund 2 are a few light-years tall and point to the central cluster. They are thought to be incubators for new stars. Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team
This amazing cluster is only 2 million years old and contains some of the brightest, most massive stars known. Powerful ultraviolet light and stellar winds streaming from the cluster’s giants tear into the clouds, sculpting them into fantastic shapes. When the stellar winds hit dense walls of gas, they create shocks, which generate a new wave of star birth along the wall of the cavity. The red dots scattered throughout the landscape are a rich population of forming stars that are still wrapped in their gas and dust cocoons.
The red dots scattered throughout the cosmic landscape captured in this Hubble image are a rich population of forming stars that are still wrapped in their gas and dust cocoons. Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team
Your eyes and mine can’t see these stars, but Hubble has the ability to peer into the thermal infrared and spot them by the heat they give off. They’re still just proto-stars, but they’ll continue to collapse and compress until one day they’re hot enough to ignite hydrogen in their cores and become true stars like the Sun.
While its legacy of photographs is what most of us associate with the Hubble, it’s also a superb research instrument that’s enlarged our understanding of the universe in so many ways. Here are five of its most ground-breaking discoveries:
Hubble Ultra-Deep field photos shows thousands of galaxies. Credit: NASA/ESA
The Hubble Deep Field and Ultra-Deep Field photos each show several thousand galaxies in two tiny specks of sky. Some of them are up to 10 billion years old and much smaller and irregularly shaped than the galaxies we see in the current era. Astronomers suspect that through mergers, these rough-hewn “building blocks” helped create the more familiar spiral and elliptical galaxies of the present.
800-light-year-wide spiral-shaped disk of dust fueling a massive black hole in the center of galaxy NGC 4261. Measuring the speed of the gas whirling around the black hole, we know it’s 1.2 billion times more massive than the Sun. Credit: NASA/ESA
Supermassive black holes are everywhere!
Hubble sharp optics and ability to see in the infrared (thermal energy beyond the red end of the spectrum) led to the discovery in 1994 of the first supermassive black hole in the center of the galaxy M87 in Virgo. Based on the motion of the material whirling about the center, the object is estimated to be about 3 billion times more massive than the Sun and concentrated into a space smaller than our solar system. By 1997 we knew that the Milky Way and 27 nearby galaxies held supermassive black holes in their cores. Now we know they’re common, showing up in nearly every large galaxy observed.
Timeline of the history of the universe from the Big Bang to the current day. Credit: Rhys Taylor, Cardiff University
Measuring the age of the cosmos
Edwin Hubble discovered the expansion of the universe in the 1920s. Since that time, astronomers have been trying to determine exactly how fast it’s expanding, a value called the Hubble Constant. In 1999, astronomers using the superior sharpness of the Hubble telescope, determined its value by measuring the distance to 18 galaxies as far away as 65 million light years. Once the expansion rate was nailed down, astronomers could “roll the tape backwards” and estimate the age of the universe. Drum roll please. It turns out this big place has been around for between 12-14 billion years. That’s now been refined to 13.7 billion years, the amount of time that’s elapsed since the birth of the universe at the Big Bang.
The universe slows down then speeds up
Through study of a the remote supernova 1997ff, astronomers discovered that gravity (from matter) slowed down the expansion of the universe after the Big Bang. Later, in 1998, two other supernova studies using data from Hubble, revealed that after slowing down for a long time, the expansion rate of the universe is now on the increase. What would cause it balloon up even faster? That’s the million dollar question. It’s called ‘dark energy’ and we’re still trying to figure out what THAT is.
Proto-planetary disk of dust and gas surrounding newborn stars in the Orion Nebula photographed by Hubble. Credit: NASA/ESA
Baby planets like pancakes
Through studies of nebulae like the famous and familiar Orion Nebula, Hubble discovered that pancake-shaped dust disks around young stars are common. And that implies planets are probably common. Scientists believe that our solar system formed from just such a disk 4.5 billion years ago with the Sun at center and the planets coalescing from the material remaining around it. In 2001, astronomers using the Hubble made the first direct detection of the atmosphere of a planet orbiting a star other than the Sun. The star, HD 209458, is located 150 light years from Earth in Pegasus.
So you see, the Hubble has a little something for everybody.