Great Observatories Show the Light
The Crab Nebula as seen by Hubble and Chandra

The Hubble Space Telescope and Chandra X-ray Observatory looked at the Crab Nebula at roughly the same time. The two observtories look at different light coming out of the nebula. Image credit: NASA
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A pair of galaxies interact.

Hubble frequently points its powerful intruments toward galaxies to study how they interact. The surveys can reveal much more information about the universe and how fast it is moving. Image credit: NASA
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Want to know what you’re made of? Look into space. Focus on that nebula where an opaque disk of cosmic dust points to a brilliant light. That light is a young star, and its birth has filled space with atoms that make up the fundamental elements of planets, stars, galaxies and even people on Earth.

Carbon-based life, which is what all of us are, began as atoms created in the gravity and fire of a star’s birth.

“We can look back to see where we came from,” said Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, which operates the Chandra X-ray Observatory. “It’s giving us evidence of where we came from. It explains why iron is common and gold is rare. You can trace it directly back.”

We didn’t know that with certainty until NASA launched four specialized telescopes called the Great Observatories. Three rode space shuttles from Kennedy Space Center into orbit, and one was lofted on the top of a Delta II rocket from Cape Canaveral Air Force Station.

Each was designed to look at a different kind of light, much of which is invisible to the human eye, but critical in explaining why the universe acts as it does and how it got there in the first place.

“There’s all this important stuff going on that is completely invisible,” McDowell said.

The Hubble Space Telescope was the first, launched in 1990. Hubble sees the universe much as the human eye does, looking at the same light we can see, plus portions of the ultraviolet spectrum. Its images revealed galaxies as they were created some 13 billion years ago, when the Big Bang was a relatively recent event.

The Compton Gamma Ray Observatory came next in 1991 to evaluate pulsars, quasars and neutron stars, the sources of the strongest energies found in the universe. Chandra was launched in 1999, to focus on the beams of X-rays produced throughout space. Its observations proved that black holes not only exist, but are plentiful. Many of them are so large they require two adjectives to explain them: super-massive black holes.

The Spitzer Space Telescope, which looks for infrared light, completed the suite of space-borne observatories in 2003. It found that the materials which are basic ingredients for human life are sprinkled throughout areas where planets and comets are thought to be forming.

Although each observatory has made significant findings on its own, the real strength of the program is the ability to use the facilities together to study a single part of the sky in detail and see all that is going on there.

“It’s not just that we see a different set of stars, we’re seeing fundamentally different faces of the universe,” McDowell said.

For example, the Compton could pick up signs of intense energy on its own and make groundbreaking discoveries. But adding a Hubble observation to the mix gave astronomers the chance to turn Hubble’s lens on the place the energy came from so astronomers could find out what caused the energy.

“Imagine that you could only see yellow,” said Mario Livio of the Space Telescope Science Institute, which runs the Hubble observations. “Then you get to extend (your vision) to the rest of the visible spectrum. You would see a lot more in the world.”

Dark energy was discovered in much the same manner, by focusing multiple instruments on the same part of space at about the same time. The discovery has been arguably the most dramatic find of the Great Observatories program. It has answered some questions while leading to profound new ones.

“Nobody really expected dark energy to be discovered,” Livio said. “When I studied astrophysics, nobody studied dark energy because nobody expected it to be there. Now, everybody studies dark energy.”

Before the Great Observatories, McDowell said the prevailing theory among astronomers was that nuclear fusion, which makes the sun burn, was the chief powerhouse for the universe. Now, they have found that gravity is every bit as important as fusion.

“In terms of miles per gallon, so to speak, you get much more from gravity than from fusion,” McDowell said.

All the discoveries are ones that will be studied by astronomers who have not been born yet.

“If you open any new book on astronomy, it is basically full of Hubble images,” Livio said.

The images Hubble creates are not limited to astronomy. They also are used as album covers and hung in art museums.

“Hubble has taken this beauty of the cosmos and brought it in the homes of people,” Livio said. “This has been a complete shift in the way non-scientists see the universe.” The observations by the four telescopes are being stored in large digital libraries that researchers are expected to consult for decades to come. This is due in part to the precise instruments that produce exquisite images which hold more information than even their users can explain. Future astronomers can look again and again at the images and make new discoveries.

“These studies will keep going on long after the observatories have shut down,” McDowell said.

Steven Siceloff
NASA's John F. Kennedy Space Center
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