Extending our View

A few years ago I worked on a book called Visions of the Cosmos with my friend and mentor John C. Brandt (now at the University of New Mexico). Our idea was to give readers a “multi-wavelength view” of the universe, and we ended up publishing a very nice work that had images AND science woven together.  It’s still out there on the market and we still get some nice notes from people about how much they enjoyed it, and more than a few folks have mentioned that it never occurred to them to think of the universe in anything other than visible-light terms. That’s understandable since humans’ primary visual response is in “visible” (often called “optical”) wavelengths of light and we don’t see much into the ultraviolet (if at all) nor much into the infrared. We definitely don’t “see” the other wavelengths, although we can feel them or hear some of them.

Nonetheless, astronomy works at all wavelengths and there are visions to behold at every stop along the electromagnetic spectrum. We often refer to these as “images” even though they’re constructed from data (essentially ones and zeros) and “visualized” with color coding and other tools to help us “see” what’s there, but just beyond our eyesight. Remember that they’re not “pictures” in the sense of a snapshot from your camera, but think of them as astrovisualizations — even the optical-light ones!

And, since I’m a sharing kinda person, I thought I’d take all of you along on a little journey of other-wavelength “visualization”, exploring the best of this past year’s multi-wavelength astronomy, rendered “visible” to our Mark II eyeballs. Here are some of my favorite visions from the multi-wavelength cosmos for 2008. Enjoy!

The Cat’s-Eye in X-rays and Optical Light

The Chandra X-ray Observatory has been peering at x-ray emissions from the cosmos for a number of years now.  In March 2008 the Chandra folks released an image made of composite data taken by the Chandra AND the Hubble Space Telescope in previous years. It’s a strikingly beautiful rendition what a distant, sun-like star looks like when it begins to die and forms a planetary nebula. If you could come back to the solar system about a billion years from now, this is what the Sun will look like as it begins to run out of fuel and shed its outer atmospheric layers. It may look tranquil and quiet, but the region surrounding the dying star is hot (millions of degrees) and windy — material is flowing out at about 6.4 million kilometers an hour.

The Hubble data is color-coded red and purple and traces out the various chemical elements that exist in the expanding cloud of gas and dust that is flowing away from the central star. The Chandra data is color-coded purple and traces out the hottest, most energetic gases surrounding the star (that is, material that is hot enough and energetic enough to emit x-rays for Chandra to “see”).

Galaxy Dance

The history of the universe is written in the interactions of galaxies with each other (and with the sea of dark matter in which they are immersed). Small galaxies become larger ones by colliding and merging with each other. Each time this happens, scads of stars are birthed in the chaos of the collision. The interactions sculpt the shapes of the galaxies, creating rings and ellipticals and spirals and interacting loops.  Watching the dance of the galaxies from a distance is fascinating for anyone who cares to see.

Hubble Space Telescope and its Wide Field Planetary Camera 2 captured a pas de deux between two galaxies that are interacting and reshaping each other. The pair, called Arp 142, lie about 400 million light-years away from us, in the direction of the constellation Cetus. The blue galaxy on the right is ablaze with star formation that was triggered by gravitational encounters with the galaxy on the left, which we see almost edge-on. What’s left of the blue galaxy’s core lies in the reddish clump of material in the lower part of the ring. Its dance partner seems relatively unscathed by the close encounter.

Speeding Gas Clouds at Radio Wavelengths

Everything in the universe is in motion. Our planet moves in an orbital dance with the Sun (and the Moon); the Sun itself moves through space and bobs its way along as one of many stars in one spiral arm of the Milky Way Galaxy, which is, itself, moving through space just as all the other galaxies in the universe do. As it turns out, there are other things out there speeding through space — like a giant cloud of hydrogen gas that is aimed right at our galaxy. Now, you can’t just look out there with an optical telescope and see it. You need  a radio telescope such as the Robert C. Byrd telescope in West Virginia.

The data you get from your observation, with color-coding, would look like a mess of streamers in space. This is Smith’s Cloud, and it contains enough hydrogen to make a million sun-like stars. When it finally hits our galaxy (in about 40 million years), it could set off a fireworks display of star formation.  It’s already interacting with gas at the outer edges of the galaxy, and astronomers think it’s either a left-over remnant from the birth of our galaxy that is falling back in or a cloud stripped away from another galaxy and being drawn in by the gravitational influence of our galaxy.

Now, if this were visible to our unaided eyes, Smith’s Cloud would cover an area of the sky roughly the size of the Orion Nebula. It’s 11,000 light-years long and 2,500 light-years wide and moving toward us at about 250 kilometers a second.

An Infrared Look at a Stellar Family Tree

When extended families get together, group portraits are almost always on the agenda. They’re usually a source of great hilarity because there’s always somebody making a funny face or not looking at the camera or blinking when the picture gets taken. But aside from their comedy value, family pictures are snapshots in time, showing how all the generations are aging and how everybody seems to have similar characteristics (because everybody shares some DNA-based traits that determine body shape, hair color, ear size, etc).

It’s not terribly different for family snaps of stars and starbirth regions. They give you a wonderful way to compare the different stars born at different times from the same cloud of gas and dust. Spitzer Space Telescope — an infrared-sensitive observatory — took a look at the star-forming region called W5. It found multiple generations of stars, ranging from older stars (the blue dots) to bright younger stars just emerged from their cocoons and lined up along the rims of dusty caverns like glittering lights. White knotty areas are places where stars are still forming, still somewhat veiled by the clouds of gas and dust that form their creches. The spiky “fingers” are thicker clouds of gas and dust that may have stars forming within. The dark red areas are big clouds of dust that are being heated by the nearby stars.

See the Sky With Gamma-ray Eyes

Gamma rays are the extremophiles of the electromagnetic spectrum. They emanate from extremely, extremely energetic (read: hot, highly magnetized, active) events and objects in the cosmos. You can’t see them, not even at their brightest. But, the Fermi Gamma-ray Telescope can because that’s its mission: to boldly seek out gamma-ray sources.

If you had “gamma-ray” eyes, this is what you’d see. The all-sky image shows gas and dust in the plane of the Milky Way glowing in gamma rays due to collisions with accelerated nuclei called cosmic rays. The famous Crab Nebula and Vela pulsars also shine brightly at these wavelengths. These are fast-spinning neutron stars, which form when massive stars die. They were originally discovered by their radio emissions. The image’s third pulsar, named Geminga and located in Gemini, is not a radio source. It was discovered by an earlier gamma-ray satellite.

A fourth bright spot in the LAT image lies some 7.1 billion light-years away, far beyond our galaxy. This is 3C 454.3 in Pegasus, a type of active galaxy called a blazar. It’s now undergoing a flaring episode that makes it especially bright.

Astronomers expect to use the Fermi Gamma-ray Space Telescope to search out more radio-quiet pulsars and other objects that are gamma-ray “bright.”

Ultraviolet Clues to Cosmic Activity

Ultraviolet wavelengths of light are tracers of much activity in the cosmos.  Hot young stars are bright in ultraviolet, and when they are born in batches and clumps in starburst regions, they can really light up a galaxy!  The Galaxy Evolution Explorer (GALEX) has as its main mission to study galaxies by sifting out their ultraviolet light from among all the wavelengths they emit.

GALEX took a look at the galaxy M106, which lies about 22 million light-years away from us in the direction of the constellation Canes Venatici.  As you can see in its view, the spiral arms are ablaze with starbirth (traced out in blue). The gold-tinted regions don’t contain as many hot, young stars; instead they’re settled with older, cooler stars and clouds of dust.

You can also make out other galaxies in the image.  NGC 4248 is just to the  right of M106. It’s an irregular galaxy that looks more like a yellow smudge and has a bluish-white bar in the center. The galaxy’s outer golden glow indicates a population of older stars, while the blue central region shows a collection of much younger stars.

The dwarf galaxy UGC 7365 also is emerging into the view at the bottom center of the frame as a faint yellow smudge directly below M106. This galaxy is not forming any new stars, and looks much smaller than M106 even though it’s closer to Earth, at 14 million light-years away.

Visualizing a Sea  of Stars

When we step outside on a clear, dark night, we see the optical light from thousands of stars. If we take an image of the sky, we capture the view of our galaxy from our vantage point on the inside. If we’re in a truly dark-sky place, the view can be spectacular.

My friends at Gemini Observatory have this kind of skyview every night from high atop Mauna Kea in Hawai’i.  I saw it with my own eyes for a number of nights in 1996 when I was at the old University of Hawaii 2.3-meter telescope doing an observing run. Each night I’d step outside and look up and each night it felt as if I was about to fall up into that sky. It was THAT spectacular. (Gemini was under construction, and the Kecks were down the hill from me.)

Now, this image shows what the sky would look  like if I could go capture a time-exposure photograph of Gemini Observatory as it deploys its laser guide star system. If you were to stand outside and look at this scene, it wouldn’t look  like this to your naked eye. The laser shows up in time-lapse photographs because the camera collects that continuous output of light, but otherwise the laser not as bright to the unaided eye as it appears in this image. The same is true of the starlight the camera collects and gathers together in the image we see.

But, if you want to know what a visible-light view of our galaxy looks like (with or without a laser stream), this is it.

This ends our multi-wavelength journey for 2008 (and yes, I know that the last image was taken in 2006… ).  There are thousands and thousands of visualizations of the cosmos out there for astronomers to study — and they come from an amazing array of  ground-based and space-based observatories. These places truly are our eyes and ears on the universe.  Happy gazing!