A look back at JWST’s predecessor: NASA’s Spitzer

On January 30, 2020, NASA’s Spitzer Space Telescope was retired after 17 years.

Prior to its 2003 launch, Spitzer was completed on the ground and installed inside a Delta II rocket at Kennedy Space Center. This photo was taken on August 14, 2003.

Joining Hubble, Compton, and Chandra, Spitzer was the final of NASA’s original Great Observatories.

The fourth and final element in NASA’s family of orbiting Great Observatories, Spitzer was successfully launched from Launch Pad 17-B at Cape Canaveral on August 25, 2003.

High above Earth’s atmosphere, its infrared measurement capabilities were unprecedented.

The transmittance or opacity of the electromagnetic spectrum through the atmosphere. Note all the absorption features in gamma rays, X-rays, and the infrared, which is why the greatest of our observatories in these wavelengths are all located in space. The infrared, in particular, was spectacularly covered by NASA’s Spitzer, and is presently covered by NASA’s JWST.

Spitzer reigned as humanity’s greatest mid-infrared observatory until JWST’s operations began.

The JWST, now fully operational, has seven times the light-gathering power of Hubble, but will be able to see much farther into the infrared portion of the spectrum, revealing those galaxies existing even earlier than what Hubble could ever see, owing to its longer-wavelength capabilities and much lower operating temperatures. Galaxy populations seen prior to the epoch of reionization should abundantly be discovered, and Hubble’s old cosmic distance record has already been broken.

These 23 images highlight its greatest achievements.

This rather unspectacular-looking ‘dot’ of light is from a tiny portion of the galaxy NGC 4993, which corresponds to the location of the first neutron star-neutron star merger ever detected in gravitational waves. This is the last image of the infrared afterglow of the event ever to be imaged, as captured by Spitzer on October 16, 2017.

Among them, Spitzer excelled at measuring:

The Flame Nebula, shown here in a combination of X-ray data (from Chandra) and infrared light (from Spitzer), showcases a young, massive star cluster at the center, which carves out a spectacular shape in the surrounding gaseous material that was used for star-formation. Direct observations of the hottest, brightest, most massive stars that form inside these regions are difficult, as there are frequently large amounts of (visible) light-blocking matter intervening. After only a few million years, the star(s) primarily responsible for illuminating the Flame Nebula will all have died away.

• ultra-distant objects whose light is severely redshifted,

Distant galaxies, like the one imaged here by Hubble and Spitzer, have their light redshifted out of the ultraviolet and even visible light portions of the spectrum and into the infrared by the effects of cosmic expansion. Infrared observatories, like Spitzer, can image what even Hubble cannot.

• cool objects, which emit very little optical light,

Three separate regions illustrate various stages of a newly forming star’s life, which are totally obscured in the optical and can only be seen in the infrared. At left, a protostar emits radiation that’s shrouded in light-blocking dust. In the center, a ‘yellowball’ announces the start of nuclear fusion, but still cannot be seen in the optical due to all the surrounding matter. At right, a more evolved star has begun to blow an ionized bubble in the surrounding region. For high-mass stars, we now know that forming a singlet system, as opposed to a multi-star system, is a relative rarity.

• obscured objects located behind light-blocking dust,

Clumps of matter can be so dense that not even infrared light can penetrate them. They cast the deepest shadows of all, and Spitzer captured some of them here (in silhouette) against a backdrop of massive, newly forming stars. The white clumps are where the detector has been saturated, and are likely the locations of the newest, bluest, most massive stars of all: O-class stars, which will likely all end their lives in supernova explosions in just a few million years.

• cometary fragments,

As they orbit the Sun, comets and asteroids typically break up over time, with debris between the chunks along the path of the orbit getting stretched out to create debris streams. These streams cause meteor showers when the Earth passes through that debris stream. This image taken by Spitzer along a comet’s path shows small fragments outgassing, but also shows the main debris stream that gives rise to the meteor showers that occur in our Solar System.

• interstellar gas that’s heated by nearby stars,

Newborn stars that are just now forming light up the nebula NGC 2174, 6,400 light-years away, as imaged in the infrared by Spitzer. The warm dust that surrounds them glows in a variety of colors, while the coolest, red regions point to locations where star formation is likely still ongoing.

• remnants and ejecta from dying or recently deceased stars,

The supernova remnant 1E0102.2-7219 (inset) sits next to the nebula N76 in a bright, star-forming region of the Small Magellanic Cloud. When supernovae occur, they can unevenly enrich the interstellar medium around them with different elements in different regions. Only on long timescales will that material become well-mixed; if new stars form prior to that, they may be non-uniformly enhanced and enriched by those heavy elements.

• including supernovae and remnants,

In February of 2014, a supernova went off in the dusty, nearby galaxy of Messier 82: the Cigar galaxy. Spitzer’s infrared eyes can successfully penetrate the dust, allowing it to observe and follow the evolution of the light from this transient object.

• even ancient remnants,

This infrared view of supernova remnant RCW 86 highlights the dusty remains of all that’s left of an ancient supernova that’s thousands of years old: the earliest documented example of a supernova visible in our night sky. It happens to be a type Ia supernova, but no surviving companion has ever been found.

• as well as planetary nebulae,

These three planetary nebulae, all imaged by Spitzer, highlight features inherent to dying Sun-like stars. From left to right, the Exposed Cranium Nebula, the Ghost of Jupiter Nebula, and the Little Dumbbell Nebula all exhibit stellar winds, ejected material consisting of different elements, and a central, luminous stellar remnant. Only objects within a specific mass range will experience this phenomenon as their ultimate fate.

• the final, luminous embers of dying Sun-like stars,

This combined image from NASA’s Spitzer Space Telescope and the ultraviolet Galaxy Evolution Explorer (GALEX). In death, the star’s dusty outer layers are unraveling into space, glowing from the intense ultraviolet radiation being pumped out by the hot stellar core. Spitzer reveals many different aspects of the stellar ejecta, now illuminated by the central white dwarf.

• as well as mapping specific elements within nearby galaxies.

This infrared portrait of the Small Magellanic Cloud, located just 199,000 light-years away, highlights a variety of features, including new stars, cool gas, and quite spectacularly (in green) the presence of polycyclic aromatic hydrocarbons: the most complex organic molecules ever found in the natural environment of interstellar space. The way that atoms link up to form molecules, including organic molecules and biological processes, is only possible because of the Pauli exclusion rule that governs electrons, and happens everywhere across the Universe where enough heavy elements are present.

Interacting galaxies are doubly spectacular.

A mix of stars (in blue and green) and warm dust (in red) are revealed in this Spitzer composite image of the interacting galaxy pair known as Arp 86. The rich red features trace out the locations of future sites of star-formation, driven by cool, dense gas. Without that gas, no new stars can form.

Gas bridges,

This infrared view of the Whirlpool Galaxy, Messier 51, reveals a plethora of active star formation and heated gas/dust lining the spiral arms. A gas bridge is being pulled from one of the extended spiral arms toward the interacting galactic companion, which itself is gas-poor and doesn’t show the same evidence of star formation.

extended star formation,

This spectacular image was created with composite Spitzer and Hubble data, and shows a tidally distorted galaxy, rich in gas and actively forming new stars, merging with an old, gas-free elliptical galaxy made up of older stars. Poetically, this is called ‘the penguin and the egg,’ where the active star-forming regions of the Penguin may create a hostile environment for life, whereas the calm environment of the Egg may be among the best places for sustained life to emerge and thrive. Matter is being ripped off of the Penguin from the outside-in, with the innermost portions being the last to be disturbed but the outermore, dark matter-rich regions being disturbed earlier and by greater amounts.

and dead, quiet galaxies all appear.

An example of a very rare ring galaxy, NGC 1291, showcases an outer galaxy that’s rich in gas and forming new stars surrounding an old, quiet center that is virtually gas-free and has scant evidence of new star formation. Both gas-rich and gas-poor galaxies are found throughout the Universe, and Spitzer’s infrared eyes are ultra-sensitive to them.

Spitzer also offered a unique perspective on otherwise familiar objects.

This infrared view of the plane of the Milky Way, taken from space by NASA’s Spitzer as part of the GLIMPSE galactic survey, is one of the most ambitious observing projects ever undertaken, taking a decade to complete. At longer wavelengths than are visible from the ground, the gas of different temperatures from our galaxy is highlighted as never before, revealing details about our home galaxy that cannot be seen in any other set of wavelengths.

Messier 83 shows a miniature Milky Way.

This infrared view of Messier 83, also known as the Southern Pinwheel Galaxy, is a miniature version of the Milky Way, about half of our size but with spiral arms, rich gas, and a central bar that extends for thousands of light-years. This infrared view helps us understand how the gas and dust in our own galaxy, which we can only see edge-on, might be distributed.

Visible jets appear around M87’s supermassive black hole.

Messier 87, best known as the supermassive galaxy whose black hole was first imaged by the Event Horizon Telescope, has its relativistic jets and the shockwaves created by their material imaged in the infrared by Spitzer, amidst the mass of shining stars (in blue). Messier 87 is the most massive (and second-brightest) galaxy within the entire Virgo cluster of galaxies, and it is the central black hole that generates these relativistic jets.

The Crab Nebula looks vaguely familiar,

This infrared view of the Crab Nebula, from Spitzer, represents a nearly 1,000 year old supernova remnant. The infrared image reveals a cloud of energetic electrons (in blue) trapped by the central neutron star’s magnetic field, along with filamentary structures (in red) that glow at mid-infrared wavelengths. This nebula, about 5 light-years across, looks extremely different from the familiar visible light image.

much like the Orion Nebula.

This infrared view of the Orion Nebula, unlike the visible light view, highlights the great cavities formed when active areas of star-formation cause ultraviolet light to evaporate large amounts of star-forming material, heating the gas inside, which then becomes rich in infrared radiation due to the increased temperatures. Spitzer took this composite image in a variety of wavelengths, with blues, greens, and whites corresponding to higher temperatures and reds to lower temperatures.

But no one had ever seen so many supermassive black holes all together.

This view of about 0.15 square degrees of space reveals many regions with large numbers of galaxies clustered together in clumps and filaments, with large gaps, or voids, separating them. Each point of light is not a galaxy, but a supermassive black hole, revealing just how ubiquitous these cosmic objects are. By estimating the black hole mass function across cosmic time, researchers have a suggestive solution to the “seeds of supermassive black holes” question, suggesting that conventional astrophysics may have given rise to the objects we observe at all cosmic times.

Farewell, Spitzer, and thanks for all the science.

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.