See 25 Stunning Images of the Cosmos From the Chandra X-Ray Observatory as It Celebrates 25 Years in Space

Assistant Editor, Science and Innovation

Though we can’t see them, X-rays are widespread in outer space. They emanate from some of the most powerful—and mysterious—objects in the universe, including black holes, exploded stars and elusive dark energy.

On July 23, 1999, the most powerful X-ray telescope in the world launched, hitching a ride on the Space Shuttle Columbia. Called the Chandra X-Ray Observatory, it has been charting an ellipse-shaped path around the Earth ever since, orbiting at about one-third of the distance to the moon.

“For a quarter-century, Chandra has made discovery after amazing discovery,” Pat Slane, director of the Chandra X-Ray Center, located at the Smithsonian Astrophysical Observatory, says in a statement. “Astronomers have used Chandra to investigate mysteries that we didn’t even know about when we were building the telescope—including exoplanets and dark energy.”

Now, used in conjunction with other space-based observatories, Chandra has contributed to myriad scientific discoveries, including uncovering evidence of two of the most distant black holes ever seen. It has captured almost 25,000 observations in its 25 years. NASA’s Marshall Space Flight Center manages the Chandra program, while the Smithsonian Astrophysical Observatory’s Chandra X-Ray Center controls the science enabled by it.

But as NASA continues to grapple with a limited budget this year, Chandra is in danger of ending up on the agency’s chopping block and the program faces cuts in funding. Either way, as the telescope ages, it might have only ten more operative years, writes Giuseppina Fabbiano, an astrophysicist with the Center for Astrophysics, Harvard and Smithsonian, for the Conversation.

“To keep the search for answers going, astronomers will need to start designing a ‘super Chandra’ X-ray observatory that could succeed Chandra in future decades, though NASA has not yet announced any firm plans to do so,” writes Fabbiano.

In the meantime, the telescope continues to function above the level required at the start of its mission in 1999 and remains better equipped to observe X-rays than any other telescope.

“What sets it apart from the others is it has extremely high-resolution imaging capability for an X-ray telescope,” Dan Wilkins, an astronomer at Stanford University, told Scientific American’s Jonathan O’Callaghan in March. Chandra can “pinpoint sources of X-ray emissions on the sky extremely precisely” and “separate them from any other objects in the background.”

In recognition of Chandra’s quarter-century in space, astronomers have released 25 never-before-seen images captured by the telescope. The newly unveiled pictures are composites—many contain a backdrop taken by another space or ground observatory, such as the Hubble Space Telescope, the James Webb Space Telescope or the Very Large Telescope, among others, and overlaid on that is Chandra’s view of X-ray emissions, often depicted in a shade of purple.

Crab Nebula (M1)

See 25 Stunning Images of the Cosmos From the Chandra X-Ray Observatory as It Celebrates 25 Years in Space — The Crab Nebula, the first object in the Messier catalog, has long been observed by humans. X-ray: (Chandra) NASA/CXC/SAO, (IXPE) NASA/MSFC; Optical: NASA/ESA/STScI; Image Processing: NASA/CXC/SAO/K. Arcand and L. Frattare

Located in the constellation Taurus, the Crab Nebula is a cloud of gas and dust left over from a supernova explosion. Chinese astronomers documented the blast in 1054, which looked as though a star had appeared in the sky during the day, lingering for about a month. Then, in 1758, French astronomer Charles Messier briefly mistook the Crab Nebula for Halley’s Comet.

Complementing these historic sightings, Chandra also turned its eye on the nebula. The space telescope’s observations, shown in blue-violet and white, reveal a bright white, dead star that’s rapidly rotating at the heart of the “crab.” More specifically, this type of object is known as a pulsar, since it is seen to emit pulses of radio waves or other radiation as it spins. The white line emanating from the pulsar in Chandra’s image shows this beam of particles, and white rings show particles driven away from the dead star that are now reacting with gas in the nebula, producing X-rays.

Orion Nebula (M42)

The Orion Nebula represents one of the closest star-forming regions to Earth, and in our sky it can be found in the sword of Orion the Hunter. Young stars, shown here in magenta, are powerful emitters of X-rays. As such, Chandra can distinguish a cluster of newborn stars among a neighborhood of older objects.

The Eyes (NGC 4438 and 4435)

Featuring a pair of galaxies in the Virgo Cluster, this image demonstrates a slow merging of the two. With an optical telescope, each looks like a white dot. Together, they are called “the Eyes.” A purple cloud of multimillion-degree gas envelops the one at the lower left, called NGC 4438, though some of these X-ray emissions are blocked by a dense, black cloud. The galaxy NGC 4435, at the upper right, also appears shrouded in a thin, purple circle representing X-ray emissions.

Cat’s Paw Nebula (NGC 6334)

It may resemble the footprint of a feline—toe pads and all. The Cat’s Paw Nebula, located in the constellation Scorpius, is full of newborn stars. At about 5,500 light-years away from Earth, it’s one of the most prolific star-forming regions in our galaxy. The swirls of gas appear red due to the presence of ionized hydrogen. In the center and upper left of the image are tiny-looking but extremely hot young stars that Chandra observed, shown in purple.

Galactic Center

Our own Milky Way is a dazzling spectacle to behold from a dark-sky site on Earth. But to some astronomers hoping to view objects in the heart of the galaxy, all its gas and dust gets in the way.

Observing with X-rays, which can penetrate cosmic dust, offers a way around this problem. Chandra can see outbursts from our nearest black hole and threads of superheated gas at the Milky Way’s core. The telescope’s observations appear here as orange, green, blue and purple. At the lower right, a pale green-white burst represents Sagittarius C, a star-forming region.

Eagle Nebula (M16)

The Eagle Nebula (M16) lies in the constellation Serpens. The section pictured here, perhaps the nebula’s best-known due to a famous image from the Hubble Space Telescope, is called the Pillars of Creation—so named because stars are actively forming. Chandra’s data in red and blue highlight young stars, including one embedded in a majestic pillar.

Bat Shadow (Serpens Cloud)

Like the signal displayed over the city of Gotham, the shadows formed by a young star in the Serpens Cloud appear to form the wings of a bat. The star, HBC 672, is surrounded by a disk of debris that may one day coalesce into orbiting planets. It’s this disk that casts the bat-like shadow on nearby clouds of blue and gray. Chandra’s purple detections of stars dot the image.

NGC 7469

NGC 7469 is a spiral galaxy some 230 million light-years from Earth in the constellation Pegasus. It harbors a growing supermassive black hole at its center, shown as a bright white spot ringed in purple. The galaxy’s face-on orientation toward our planet allows for a spectacular view of its arcing arms—and produces the red, star-like diffraction spikes, which come from Webb’s contribution to the composite image.

Virgo Cluster

In the Virgo Cluster, some 2,000 galaxies lie in an area of sky small enough to be covered by your fist, held at arm’s length. While this conglomeration of worlds could be obscured by a soup of multimillion-degree gas, Chandra can “see” through this haze and discern what lies behind it.

The large, pink-and-white blob just right of center is the elliptical galaxy M86, which is traveling at about three million miles per hour. It’s enveloped in a purple smear, which denotes hot gas being pulled from the galaxy, detected by Chandra.

WR 124

In a short-lived and rarely seen phenomenon, a Wolf-Rayet star is depicted in a dramatic, late phase of its life. Not every star becomes a Wolf-Rayet, but particularly massive, hot and bright stars have a good chance at it.

The star, now burning through some of the heavier elements in its core, emits powerful outward winds. These gusts strip away part of the star’s atmosphere, enveloping it in a bubble-like orb of gas and dust. Chandra observed WR 124 on four occasions between July 10 and 14, 2017, picking up emissions from several stars. To capture an image of such an ephemeral phase of a star’s life is unusual, but it preserves the moment forever.

Supernova Remnant G21.5-0.9

Without Chandra’s data, the nebula around this exploded star, or supernova remnant, appears as a small gold dot at the center. But add in the telescope’s observations, and the sphere around the star grows much larger, revealing a diffuse cloud of X-rays in purple. This radiation is also debris that was expelled in the past explosion.

Centaurus A

A supermassive black hole blasting jets into space lies at the center of the galaxy Centaurus A. Located in the southern constellation Centaurus, one of the largest constellations, the galaxy is neighbors in our sky with Alpha Centauri, the nearest known star system to Earth.

The black hole’s jets are detected by Chandra, as well as a faint blue bubble, seen especially at the lower right of the galaxy, that was created by the rapid jets of particles and radiation.

Cassiopeia A

When a star explodes as a supernova, it hurls its contents out into the cosmos in a bright outburst. Light from the supernova remnant Cassiopeia A first reached Earth around 340 years ago, making it one of the youngest known supernova remnants in the Milky Way.

Chandra has observed Cassiopeia A for more than two million seconds since the start of its mission, and its data adds a web of blue veins to this image, depicting hot debris from the explosion and its associated blast wave. Taken together with Webb’s data, this view gives Cassiopeia A the looks of a “giant, crackling, electric blue donut.”

Wishing Well Cluster (NGC 3532)

To a creative thinker, this smattering of stars resembles the spots of light glinting off a handful of coins at the bottom of a well—and for that reason, it’s often called the Wishing Well Cluster. Some of its stars are visible with the naked eye from the Southern Hemisphere and lie in the constellation Carina (home to the dazzling Carina Nebula famously imaged in the James Webb Space Telescope’s first dispatch to Earth).

This star cluster, called NGC 3532, spans nearly twice the size of the full moon in our sky. These distant stars are middle-aged on the grand scale of stellar time—about 300 million years old. Chandra’s contributions to the image appear in purple and white, representing X-ray emissions from stars.

Condor Galaxy (NGC 6872)

At the center, the large spiral galaxy NGC 6872 stretches its elongated arms toward the corners of the image. But it isn’t alone—to the upper left of the spiral lies another, smaller galaxy, which seems to be pulling gas from NGC 6872 to feed its supermassive black hole. The fuzzy purple cloud detected by Chandra shows how hot gas is being transferred to the smaller galaxy.

Located in the southern constellation Pavo, the spiral, also called the Condor Galaxy, was found to be the largest known spiral galaxy in 2013. It stretches 522,000 light-years from end to end, making it more than five times as long as the Milky Way.

Hb 5

This “bulbous bow tie” is planetary nebula Hb 5, a shroud of gas and dust cast off by a dying sun-like star. Despite their name, planetary nebulas are not related to planets. This particular nebula was discovered by the American astronomer Edwin Hubble, the namesake of the Hubble Space Telescope.

Overlaid atop a Hubble image of Hb 5, Chandra’s observations appear in blue and white, highlighting X-rays.

Abell 2125

In this far-off galaxy cluster, located roughly three billion light-years from Earth, gold and neon purple dots represent entire galaxies. Purple clouds of superheated gas, viewed by Chandra, are merging across the cluster, called Abell 2125. The bright spot of gold at the center is a galaxy, with diffraction spikes captured by the Kitt Peak National Observatory in Arizona.

NGC 3324

The luminous Carina Nebula was a crowd favorite when imaged by the James Webb Space Telescope. Here, at its northwest corner, is the open star cluster NGC 3324, where new stars are formed. The region is given another dimension with Chandra’s purple detections of young stars in two clusters. A blue mist, captured by Webb, surrounds each of these groupings.

NGC 1365

Some 56 million light-years from Earth, in the southern constellation Fornax, the barred spiral galaxy NGC 1365 harbors a supermassive black hole at its center. The purple X-ray glow detected by Chandra hints at this, suggesting the supermassive black hole—as well as smaller black holes or neutron stars—is pulling material from companion stars. In the core of the galaxy, new stars rapidly form.

MSH 15-52

This ghostly, glowing shape bears an uncanny resemblance to a “skeletal hand.” The cloud of blue gas is known as a pulsar wind nebula, formed when the rapid rotations of a pulsing dead star clear gas away. The pulsar itself appears as a bright spot at the “wrist” of the hand, while the blue fingers are X-ray gas in the nebula. In gold, Chandra has observed a low-energy X-ray cloud, which appears to be in the grasp of the eerie fingers.

Arp 220

What happens when two Milky Way-sized galaxies collide? You get Arp 220—a dramatic, galactic merger that began about 700 million years ago. The galaxy mash-up spans only about 5 percent of the Milky Way’s diameter, but both contain roughly the same amount of gas. Here, the galaxy’s optical and infrared light is overlaid with a rose-pink cloud of X-ray gas, captured by Chandra.

Arp 220, which earned the 220th place in American astronomer Halton Arp’s Atlas of Peculiar Galaxies, is located 250 million light-years from Earth.

Jupiter

Some of Chandra’s subjects aren’t so far from home. On December 18, 2000, the space telescope turned toward our nearest gas giant, Jupiter. For 9 hours and 57 minutes, it observed the planet, making note of its poles, which are known to produce X-ray auroras, seen faintly in purple in this image. Jupiter’s auroras are much more powerful than those on Earth and driven by fluctuations in the gas giant’s magnetic field. To the sides of the planet, Chandra observed X-ray clouds.

NGC 1850

The double star cluster NGC 1850 is the second-brightest star cluster in the Large Magellanic Cloud, a dwarf galaxy that orbits the Milky Way. It contains a black hole with as much mass as about 11 suns.

A blue-tinted cloud of gas, likely emitted by explosions of massive stars, snakes up the left side of the grouping. Chandra’s detections appear as just the point sources of X-rays from hot stars; without any large emission of X-rays around the black hole, the Chandra data suggests it isn’t eating much material from its companion star.

MACS J0035

Galaxy clusters are the universe’s largest structures that are held together by gravity. And this one, called MACS J0035, is a whopping 10.5 billion years away from Earth.

Each yellow dot in this image is its own galaxy, and with a close look, some even appear to have a spiral structure. All these galaxies sit in a cloud of gas as hot as millions of degrees Fahrenheit, shown by Chandra as a purple haze.

SN 1987A

In February 1987, astronomers spotted a bright supernova—the closest to Earth in almost 400 years. The outburst was a stellar explosion in the Large Magellanic Cloud some 160,000 light-years away. Earlier this year, the James Webb Space Telescope determined a neutron star lies at the center of the carnage. Chandra’s observations form a pink-purple ring around the collapsed core, representing material ejected tens of thousands of years before the star went supernova. As the blast wave from the explosion hits and energizes the ring, the material glows with X-rays.