Light comes in many forms, including radio waves, microwaves, infrared, and others. If we only studied the cosmos in visible light—light we can detect with our eyes—we would miss the bigger picture of what’s happening in the universe. To develop a better understanding of light, astronomers use different kinds of telescopes designed to collect its different forms. X-ray astronomers observe high-energy regions of the universe where the most violent events occur, such as exploding stars known as novas and supernovas and the material near the event horizons of black holes. Because X-rays are almost entirely absorbed by Earth's atmosphere, astronomers rely on instruments that operate outside the atmosphere.

Consisting of three major parts—its X-ray telescope, its science instruments, and the spacecraft that houses these—NASA’s Chandra X-Ray Observatory was the third in the series of four Great Observatories launched by NASA. Each was developed to examine a different region of the electromagnetic spectrum. Chandra is the most sophisticated X-ray observatory built to date. It has approximately 50 times better resolution than its next-best predecessor, which makes it about 1 billion times more powerful than the first X-ray detector launched more than four decades ago.

While Chandra was not the first X-ray telescope launched into space, the Chandra team had to come up with new processes for things that had never been done before. For example, it developed a measurement system to ensure that the telescope’s cylindrical mirrors were ground correctly and polished to the right shape—thereby making them the smoothest and cleanest mirrors ever made. This compares favorably with the Hubble Space Telescope, which launched with its primary mirror ground too flat at the edges—a flaw that had to be corrected in space during a servicing mission. But the engineering design challenges extended beyond merely improving the mirrors. All of Chandra’s highly specified components had to be assembled into a spacecraft capable of surviving a launch and the extreme temperatures and microgravity of space and capable of functioning without the possibility of being repaired: Chandra’s highly elliptical orbit placed it beyond where a space shuttle crew or other personnel could repair it.

Chandra’s high-resolution images have yielded discoveries about several phenomena that continue to puzzle scientists. For example, Chandra has provided the strongest evidence yet that dark matter must exist, and has produced spectacular images of explosions produced by matter swirling toward supermassive black holes. Using Chandra’s observations, scientists have also confirmed that the expansion of the universe is accelerating, an effect attributed to the prevalence of dark energy.

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