When looking at glorious images of cosmic phenomena, like black holes and supernovae, with striking colors set against the stark, dark backdrop of the universe, it’s important to remember that before that picture could be made, it started as a researcher’s hypothesis. Ideas of these brilliant, stunning celestial forces start as data points on a page before scientists can even develop a sense of what they might look like.

Many objects in the universe don’t even emit visible light, and can’t be detected without the help of powerful telescopes that can “see” different kinds of light waves like X-rays.

About 6,500 light-years from Earth, the Crab Nebula is the remains of a star whose explosion was visible in 1054 CE. The combination of rapid rotation and a strong magnetic field in the Crab Nebula generates an intense electromagnetic field that creates jets moving away from the north and south poles of the pulsar, and an intense wind flowing out in the equatorial direction. This image shows the Chandra X-rays alongside optical and infrared light. X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA-JPL-Caltech
The Cat’s Eye Nebula (NGC 6543), about 3,000 light-years from Earth, represents a phase that our Sun will experience several billion years from now. At this stage, the Sun will expand to become a red giant and then shed most of its outer layers, leaving behind a hot core that contracts to form a dense white dwarf star. The X-ray emission that Chandra detected in the Cat’s Eye (shown with Hubble optical data) is caused by shock waves as wind from the dying star collides with the ejected atmosphere. X-ray: NASA/CXC/SAO; Optical: NASA/STScI
PSR B1509-58 contains a 1,700-year-old pulsar only 12 miles in diameter that is in the center of this Chandra image. The pulsar, located about 17,000 light-years from Earth, is spewing energy out into the space around it, forming a complex and intriguing structure that spans 150 light-years. The pulsar is spinning around nearly seven times a second and has a magnetic field at its surface that is estimated to be 15 trillion times stronger than the Earth’s magnetic field. NASA/CXC/SAO/P.Slane, et al.
Chandra’s view of the Rosette Nebula (shown over an optical image of the wider nebula about 5,000 light-years away from Earth) reveals hundreds of young stars in the central cluster and fainter clusters on either side. The central cluster appears to have formed first, producing a burst of radiation and stellar winds that caused the surrounding nebula to expand, triggering formation of two neighboring clusters. X-ray (NASA/CXC/SAO/J. Wang et al), Optical (DSS & NOAO/AURA/NSF/KPNO 0.9-m/T. Rector et al)
Sagittarius A* is the supermassive black hole at the center of the Milky Way about 26,000 light-years from Earth. Chandra has monitored Sagittarius A* periodically over the course of its mission and has caught it flaring numerous times. How quickly the flares rise and fall indicates that they are occurring near the event horizon, or point of no return, around the black hole. Chandra has also discovered more than 2,000 other X-ray sources, which this image shows, and huge lobes of 20-million degree gas. The lobes indicate that enormous explosions occurred near the black hole several times over the last 10,000 years. NASA/CXC/Univ. of Wisconsin/Y.Bai. et al.
The W49B supernova remnant about 26,000 light-years from Earth may contain the most recent black hole formed in the Milky Way galaxy. Most supernova explosions that destroy massive stars are generally symmetrical. In the W49B supernova, however, it appears that the material near its poles (left and right sides) was ejected at much higher speeds than that at its equator. This image combines Chandra data with infrared and radio data. X-ray: NASA/CXC/MIT/L.Lopez et al.; Infrared: Palomar; Radio: NSF/NRAO/VLA

Even for scientists, imagining theoretical concepts in astronomy is challenging. For example, if someone had asked astrophysicist Harvey Tananbaum if he thought that black holes existed in the late 1960s when he was still a physics student at MIT, he says he would have answered, “probably not.” Black holes had only then been theorized and there was no experimental evidence of their existence. And even if they were out there, finding them seemed like an impossible feat.

Massive star cluster
Cygnus OB2, about 4,700 light-years away, is the closest massive star cluster to Earth. It contains 1,500 young stars shimmering brightly with X-ray light. These infant suns range in age from one million to seven million years old. Long observations with Chandra reveal how the outer atmospheres of these young stars behave. The image also shows optical and infrared light. Astronomers study objects like Cygnus OB2 to better understand how star factories like it form and evolve. X-ray: NASA/CXC/SAO/J.Drake et al, Optical: Univ. of Hertfordshire/INT/IPHAS, Infrared: NASA/JPL-Caltech
planetary nebula
The Ant Nebula, or Menziel 3, is a planetary nebula about 3,000 lightyears from Earth. Astronomers in previous centuries dubbed these objects planetary nebulas because some of them resemble a planet when viewed through a small telescope. In fact, they have nothing to do with planets, but rather represent the late stages of a Sun-like star’s life, when its outer layers puff out. In this X-ray, infrared, and optical image of the Ant Nebula, dynamic elongated clouds envelop bubbles of multimillion degree gas produced by high-velocity winds from dying stars. X-ray: NASA/CXC/RIT/J.Kastner et al.; Optical/IR: BD +30 & Hen 3: NASA/STScI/Univ. MD/J.P.Harrington; NGC 7027: NASA/STScI/Caltech/J.Westphal & W.Latter; Mz 3: NASA/STScI/Univ. Washington/B.Balick

But Tananbaum, who served as director of NASA’s Chandra X-ray Center from 1991 to 2014, would go on to help conceive of and construct a telescope that would bring what was once theoretical physics into reality, completely changing science’s understanding of black holes—and of the cosmos at large. The Chandra X-Ray Observatory, the most powerful X-ray telescope ever built, was piggybacked to the space shuttle Columbia and launched into space in 1999.

Light from the Void: Twenty Years of Discovery with NASA's Chandra X-ray Observatory

Light From the Void showcases rarely-seen celestial phenomena such as black holes, planetary nebulae, galaxy clusters, gravitational waves, stellar birth and death, and more.

Equipped with four pairs of highly sophisticated mirrors, Chandra records the data from X-ray light waves emanating off celestial objects. The mirrors each reflect a specific range of X-ray wavelengths. The X-rays bounce off the mirrors and move along a 26-foot tube towards the scientific instruments.

The largest region of star formation
NGC 604, about 2.7 million light-years from Earth, is the largest region of star formation in the nearby Triangulum galaxy, also called Messier 33. This image of Chandra X-ray and Hubble optical data shows an area where some hundreds of hot, young, massive stars reside. Giant bubbles in the cooler gas and dust in the field have been generated by powerful stellar winds, which are then filled with hot, X-ray-emitting gas. X-ray: NASA/CXC/CfA/R. Tuellmann et al.; Optical: NASA/AURA/STScI
 a star-forming region more commonly known as the Pillars of Creation
The Eagle Nebula is a star-forming region more commonly known as the Pillars of Creation about 5,700 light-years from Earth. Chandra’s unique ability to resolve and locate X-ray sources made it possible to discover and identify hundreds of very young stars and those still in the process of forming, known as protostars. The Chandra data were added to Hubble’s data to create this spectacular image of stellar birth. X-ray: NASA/CXC/SAO; Optical: NASA/STScI

When NASA scientists get that data, every X-ray is then given a corresponding color based on where it hit the mirrors and how intense it was, essentially making what is “invisible to the human eye into something that our brain can process,” says Megan Watzke, a Chandra X-ray Observatory spokesperson.

That’s how Chandra generates beautiful images of objects in space that couldn’t be otherwise seen—all of which started out as wild scientific ideas. A collection of Chandra’s images is the subject of Light From the Void, a new release from Smithsonian Books and the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts. The book features reflections by Chandra team members Kimberly Arcand, Grant Tremblay, Megan Watzke, `Belinda J. Wilkes and Martin C. Weisskopf and an essay by Col. Eileen Collins, commander of Space Shuttle Columbia, STS-93, as well as dozens of stunning depictions of nebulas, supernovae, galaxy clusters, exploded and colliding stars, and supermassive black holes.

Image of two exploded stars
DEM L316: This cat-shaped image is produced by the remnants of two exploded stars in the Large Magellanic Cloud 160,000 light-years from Earth. Chandra data show that the shell of hot gas on the upper left contains considerably more iron than the one on the lower right. This implies that stars with very different ages exploded to produce these objects. The two shells, shown in optical light in this image, are quite distant from one another, and appear close together only given their superposition along the same line of sight. X-ray: NASA/CXC/U.Illinois/R.Williams & Y.-H.Chu; Optical: NOAO/CTIO/U.Illinois/R.Williams & MCELS coll
Tarantual Nebula
30 Doradus, the Tarantula Nebula, is located in the Large Magellanic Cloud, a galaxy near our Milky Way, 160,000 light-years from Earth. Chandra reveals gas that has been heated to millions of degrees by winds from stars and supernova explosions. This high-energy stellar activity creates shock fronts, similar to sonic booms. Optical data reveal light from massive stars at various stages of their birth, while infrared emission maps show cooler gas and dust. X-ray: NASA/CXC/PSU/L.Townsley et al.; Optical: NASA/STScI; Infrared: NASA/JPL /PSU/L.Townsley et al.

The images Chandra produces contribute to a deeper and more expansive understanding of the universe. “Chandra's discoveries have impacted virtually every aspect of astrophysics. The Observatory was recently involved in the direct proof of dark matter's existence,” according to a NASA and Chandra X-ray Center press release. “It has witnessed powerful eruptions from supermassive black holes. Astronomers have also used Chandra to map how the elements essential to life are spread from supernova explosions.”

A cluster of young stars
Westerlund 2 is a cluster of young stars about 20,000 light-years from Earth, each of which is about one to two million years old. Data in visible light from Hubble reveal thick clouds where the stars are forming. High-energy radiation in the form of X-rays, however, can penetrate this cosmic haze, enabling Chandra to detect it. Westerlund 2 contains some of the hottest, brightest, and massive stars in the Milky Way galaxy. X-ray: NASA/CXC/SAO/Sejong Univ./Hur et al; ; Optical: NASA/STScI
a star between 100 and 150 times more massive than our Sun
Eta Carinae is a star between 100 and 150 times more massive than our Sun about 7,500 light-years from Earth. Astronomers think this unusual system underwent a giant eruption during the 1840s. X-ray data from Chandra show where material from that explosion has collided with nearby gas and dust. Optical data reveal material ejected from the star has formed a bipolar structure. The star is thought to be consuming its nuclear fuel at an incredible rate and will explode as a supernova. X-ray: NASA/CXC/GSFC/M.Corcoran et al.; Optical: NASA/STScI

When it launched in 1999, Chandra’s primary mission was planned for just five years. Twenty years later, the engineers believe it might last another decade or more. Belinda Wilkes, who succeeded Tananbaum as Chandra’s director, writes in Light From the Void, that “Chandra remains without peer in its capabilities.”

The powerful legacy of this astronomical tool, two decades after it captured its first X-rays, is making the invisible visible and in doing so, inspiring future generations of astronomers to advance our understanding of the cosmos. “It’s really easy to get caught up in the daily grind of things,” Watzke says. “But if you can get people to take a moment and look up, think about and realize the really cool and amazing universe that we live in and we’re still learning more about, then maybe they can think about things a bit differently. If we can contribute to that with Chandra, then that’s a good day.”

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