astronomy, astronomy news, astronomy research, Infrared astronomy, spitzer space telescope

Come With Me to the Starry City

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And View it in Waves of Infrared Light

Astronomy takes you out there, thataway — and takes your breath away with cosmic visions of loveliness.  If it weren’t for the tools of astronomy that populate our spaceship of exploration, we’d still be seeing the universe in the equivalent of “black and white” TV of mid-last-century.  Those tools, like the Spitzer Space Telescope, with its infrared-sensitive detectors, open up the multi-wavelength universe and let us see things we weren’t able to see before.  Like the North American Nebula, in the constellation Cygnus, the Swan. Spitzer has just released some gorgeous imagery of this formerly mysterious region of space.

The first human to see the North American Nebula was William Herschel, back in 1786. It was merely a smudge to him, as it would be to anyone with a similar type of small telescope like he used.  I once tried to look at this nebula through a pair of fairly strong binoculars and through an 8-inch telescope, and it was faint, indeed. But, the shape of the nebula could be made out — it really does look like the outline of the North American continent.  However, this have changed since Herschel’s day. Today, we have telescopes and spacecraft that can look at wavelengths of light beyond the visible. Those have changed our perceptions of the cosmos.

Actually, what’s really changing is what we’re now able to see.  We’re detecting MORE of what’s in the nebula.  So, for example, we’re seeing infrared radiation given off by hot gas, for one thing. Inky black dust features seen in visible light are also heated, and they start to glow in the infrared view.

Different colors display different parts of the spectrum in each of these images. In the visible-light view (upper right) from the Digitized Sky Survey, colors are shown in their natural blue and red hues. The combined visible/infrared image (upper left) shows visible light as blue, and infrared light as green and red. The infrared array camera (lower left) represents light with a wavelength of 3.6 microns as blue, 4.5 microns as green, 5.8 microns as orange, and 8.0 microns as red. In the final image, incorporating the multi-band imaging photometer data, light with a wavelength of 3.6 microns has been color coded blue; 4.5-micron light is blue-green; 5.8-micron and 8.0-micron light are green; and 24-micron light is red.

This swirling landscape of stars is known as the North America nebula. In visible light, the region resembles North America, but in this new infrared view from NASA's Spitzer Space Telescope, the continent disappears. Where did the continent go? The reason you don't see it in Spitzer's view has to do, in part, with the fact that infrared light can penetrate dust whereas visible light cannot. Dusty, dark clouds in the visible image become transparent in Spitzer's view. In addition, Spitzer's infrared detectors pick up the glow of dusty cocoons enveloping baby stars. Clusters of young stars (about one million years old) can be found throughout the image. Slightly older but still very young stars (about 3 to 5 million years) are also liberally scattered across the complex, with concentrations near the "head" region of the Pelican nebula, which is located to the right of the North America nebula (upper right portion of this picture). Some areas of this nebula are still very thick with dust and appear dark even in Spitzer's view. For example, the dark "river" in the lower left-center of the image -- in the Gulf of Mexico region -- are likely to be the youngest stars in the complex (less than a million years old).

In the bottom two images, only infrared light from Spitzer is shown — data from the infrared array camera is on the left, and data from both the infrared array camera and the multi-band imaging photometer, which sees longer wavelengths, is on the right. These pictures look different in part because infrared light can penetrate dust whereas visible light cannot.

If you look back up at the “visible light” image of the nebula, you’ll see that it’s tough to make out those baby stars and the dusty cocoons where they formed. This is because they’re hidden by dark clouds, which are transparent to infrared light. This lets us peek behind the veil of gas and dust that hides star birth from us.

Baby stars are just part of the scene in the Spitzer image. We can see everything from the stellar cocoons where stars form to newborn stars sporting active jets to so-called “young adult” stars that are becoming more stable, and more capable of sustaining planetary systems.

There’s more to discover in this region of space. Not even Spitzer could reveal all the North American Nebula’s secret, hidden objects. Some of its clouds are just too dense for infrared to penetrate.  And, Spitzer now has no coolant left to chill down its detectors, so some of the longest wavelengths of infrared that it used to be able to detect are no longer available to it. But, that’s not stopping astronomers from studying these images and data. There’s still much to  learn from these observations. Stay tuned!

comet, comet dust, stardust

Stardust Gets in Our Eyes

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Close Approach to Comet Tempel 1 in 3… 2…. 1….

Back when I was in graduate school, I studied comets for a living. The hunka hunka sublimating solar system ice I spent the most time on was Comet Halley.  My advisor, Jack Brandt, was part of the the Large-Scale Phenomenon Network of the International Halley Watch, and so my job was to go through all the images we had of Halley and select the best ones to do science with.

And do science we did! We tracked changes in the comet’s tail as it rounded the Sun during its orbit, and then afterwards came to some solid conclusions about how the plasma tail (the one made of ionized (charged) gas molecules) was affected by the action of the solar wind. It turns out that the plasma tail of a comet can magnetically disconnect — that is, break off — when it passes into a region of the solar wind that has a different electrical polarity than the one it formed in. If you know where the comet is in the solar wind, and you know the rotation rate of the streams in the solar wind, you can calculate about when the plasma tail will disconnect at different points in its orbit. And, if you take a series of images of the comet, you can capture that break-off and track the old tail as it floats away. Very cool stuff.  As an added bonus, you learn something about the solar wind, which is ever more important in these days when we have so many technologies that can be knocked out by a big solar outburst.

I didn’t know a lot about comets when I started on the project, but by the end, I could look at an image of Comet Halley and tell you when it was taken and if the plasma tail had disconnected. It was up to my colleague Yu Yi (who was working on his Ph.D thesis using Comet Halley data) to tell us what the conditions in the solar wind WERE for various times in the orbit.

We didn’t pay as much attention to the dust tails of our comets, nor to the coma clouds that formed around the nucleus, since they don’t respond the same way to the solar wind. Not that we ignored them, but they weren’t our primary focus. But they have their own tale to tell, and there’s an upcoming mission to explore another comet’s nucleus and coma. It’s called Stardust and it already has some solid, successful observations.

The first image of comet Tempel 1 taken by NASA's Stardust spacecraft is a composite made from observations on Jan. 18 and 19, 2011. The panel on the right highlights the location of comet Tempel 1 in the frame. On Valentine's Day (Feb. 14 in U.S. time zones), Stardust will fly within about 200 kilometers (124 miles) of the comet's nucleus. Image credit: NASA/JPL-Caltech

I was thinking about the good ol’ comet study days when I was reading about the upcoming close approach of Comet Tempel 1 by the Stardust spacecraft. That little visit will take place on Valentine’s Day, Feburary 14, 2011.  Unlike our team, which focused on those glowing blue plasma tails, the Stardust team will be focused on images of the comet’s nucleus, and measure the size, composition, and flux (flow) of dust that makes up the coma — the cloudy “crown” that surrounds the icy nucleus of the comet.

The nuclear centers of most (if not all) comets contain materials that date back to the formation of the solar system some 4.6 billion years ago. So, studying the gases that flow from a comet (which come from the cometary ices as they sublimate (dissolve away) as well as the dust that is embedded in those ices and which streams away from the comet, will tell scientists more about the frozen materials that existed in the nebula that formed the Sun and planets.  Chemically, they should be able to tell something about the conditions the comet has experienced (that is, how much those ices have been heated, what proportions of different ices there are in the comet, which could be a clue as to where they formed in the original solar nebula), as well.

In addition to the ices, comets have dust — and those dust grains also harken back to the early days of the solar system. They existed in the solar nebula, but their origins far predate the solar nebula — as grains of interstellar dust whose origins stem from elements ejected as older stars died and spread THEIR substance to the interstellar medium.

So, the Stardust folks aren’t just looking at a comet. They’re looking at a cosmic history ark — one that encapsulates our own solar system history, and maybe some clues to older, long-gone stars.  The scientists will be ecstatic as close approach day gives them that long-awaited closeup of the comet. I, for one, think it’s great that we’re lifting the veil on these orbiting ice chunks.  There’s so much they can tell us about our solar system’s early history.  And, for people who have never seen a comet up-close and personal, it will be a great exploration. Check it out and stay tuned!

Exploring Science and the Cosmos

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