The 1995 NASA photo called "Pillars of Creation" is one of the agency's most iconic, showing three massive columns of cold gas surrounded by the hot ultraviolet light of a cluster of young stars in the Eagle Nebula. This week, NASA released an updated version showing what's happened to the region in the last 20 years in unprecedented detail thanks to upgrades to the Hubble Space Telescope.
Nebulas are areas of recent star formation. Rich in ionized gases that glow bright, they are, as Dr. Paul Scowen, an associate research professor at Arizona State University's School of Earth and Space Exploration, says, an interstellar "Eat at Joe's" sign saying "we've just made stars!"
But the fingers in the middle of this nebula are an interesting feature, and not just because they stand out. The Eagle Nebula was first studied by French astronomer Charles Messier in the 1800s, which is where the nebula's other designation of M16 comes from. Even just using ground-based telescopes, Messier could see that there were clear, finger-looking structures in the middle of this star forming region.
Stars form in nebulae from cold, dark molecular clouds. As hydrogen atoms begin sticking together, the gas collapses under its own weight, heating in the process. Chunks of this gas become stars, which get even hotter as they get smaller.
When the stars start generating their own energy, the radiation they emit ionizes the space around them, eating away and eroding the cloud of gas they're inside. Eventually, this cavity created by ionized gas breaks out from the gas cloud. Scowen likens it to a popped zit.
That "wall" between the ionized gas and the cold gas is something that intrigues astronomers, and the fingers in the Eagle Nebula are a perfect way to study this phenomenon.
That's why Scowen and his colleagues imaged the M16's fingers with Hubble in 1995 in the first place. The goal was to gather a high resolution image that would reveal details they couldn't see from the Earth. But the original "Pillars of Creation" image wasn't as good as it could be.
The Hubble Space Telescope was launched inside the payload bay of the space shuttle Discovery on April 24, 1990. It was deployed and placed into orbit about 353 miles above the Earth. But there were problems. For one, the telescope was kept in storage for four years following the Challenger disaster, meaning that when it launched in 1990 its hardware was almost a decade old. Then there was the problem of the distorted primary mirror; Hubble couldn't see straight.
The first of five servicing missions took place in 1993 and it saw astronauts add a corrective optics system to fix Hubble's vision and also install the Wide Field and Planetary Camera 2. It was this camera that shot the "Pillars of Creation" in 1995, but its resolution was too low to take advantage of the true resolution of the telescope.
New instruments were added on four more servicing missions, and in 2009, the Wide Field and Planetary Camera 2 was replaced by the Wide Field Camera 3. This new camera has far better and more efficient charge coupled devices as well as a resolution 10 times higher than its predecessors. It was well worth revisiting the iconic pillars with the new camera to see them in more detail.
But that wasn't the only reason. Hubble can now see in different wavelengths, both optical and infrared. In the infrared, all the gas disappears. The pillars become shadowy wisps of dust consumed by a starfield, stars that are both behind and within the massive structures.
It was also worth seeing whether the pillars have changed in the last two decades, and it turns out that they are actively ablating. As the gas is ionized, it gets hot and evaporates into space. The pillars won't last; we've been lucky to catch them in their brief existence. Scowen and his colleagues also noticed a lengthening narrow jet-like feature when they compared the 1995 image with the 2014 image. The gas looks to have stretch some 60 billion miles in the last 19 years.
For Scowen, going back to the pillars was like revisiting an old friend, an old friend with some pretty interesting stories to tell. He and his colleagues are preparing a new paper based on the data in this image that will undoubtedly cement the "Pillars of Creation" as an iconic feature in the sky.