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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!

AAS meeting stories, astronomy, astronomy media, astronomy news, galaxies, gravitational lenses

The Astronomy Fire Hose: Distant Galaxy Edition

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Peering Into the Gravitational House of Mirrors

What is it about galaxies that SO evoke our sense of space and distance?  Is it because they’re so big and magnificent? That they stretch across immense regions of space? The idea that these cosmic cities are thronged with stars? If you look at an image of a galaxy like the Milky Way, you see stars and regions where stars are born and die, and you see (if it has one) the central core with a black hole at its heart.

But, how did galaxies get started?  How were they born?  And what is their lifestyle like?  These are questions that astronomers are still working to answer. Understanding the origin and evolution of galaxies benefits from looking at galaxies in all stages of their lives.  And, so, astronomers look through billions of years of cosmic history to study some of the earliest galaxies.

This illustrates how gravitational lensing by foreground galaxies will influence the appearance of far more distant background galaxies. This means that as many as 20 percent of the most distant galaxies currently detected will appear brighter because their light is being amplified by the effects of foreground intense gravitational fields. The plane at far left contains background high-redshift galaxies. The middle plane contains foreground galaxies; their gravity amplifies the brightness of the background galaxies. The right plane shows how the field would look from Earth with the effects of gravitational lensing added. Distant galaxies that might otherwise be invisible appear due to lensing effects.

There’s a little bit of a problem looking back that far. We have to peer through what amounts to a cosmic “house of mirrors” to see the youngest galactic objects in the universe. Everything we see in this house of mirrors is distorted by a phenomenon called gravitational lensing. This occurs when light from a distant object is distorted by a massive object that is in the foreground.

Astronomers have started to apply this concept in a new way to determine the number of very distant galaxies and to measure the amount of something called “dark matter” in the universe.

So, how does gravitational lensing work?

Albert Einstein showed that gravity will cause light to bend. The effect is normally extremely small, but when light passes close to a very massive object such as a massive galaxy, a galaxy cluster, or a supermassive black hole, the bending of the light rays becomes more easily noticeable.

When light from a very distant object passes a galaxy much closer to us, it can detour around the foreground object. Typically, the light bends around the object in one of two, or four different routes. This magnifies the light from the more distant galaxy directly behind it. What you get is a sort of “natural telescope”, called a gravitational lens. It provides a larger and brighter — though also distorted — view of the distant galaxy.

A very massive object — or collection of objects — distorts the view of faint objects beyond it so much that the distant images are smeared into multiple arc-shaped images around the foreground object. This effect is a lot like looking through a glass soft drink bottle at a light on a balcony and noticing how it is distorted as it passes through the bottle.

This is a very cool idea and I remember back in graduate school first learning about lensing, and we all thought it was almost too weird. At that time, all we could really see were the brightest, most obvious lensed objects.  Now, we can see many of these distortions. And, as we move toward fainter and more distant objects, many of the more recently observed ones pushing the limits of the Hubble Space Telescope.  Even fainter ones will need something with more observing power.  If all goes well, those next generation objects to be observed will be more effectively handled by a new space telescope on the drawing boards — the James Webb Space Telescope (JWST).

First Light and Lensing

When you look back to when the universe was young, you are seeing extremely early objects (also known as “first light” objects) that are very far away. The older and farther away the object, the more foreground universe there is to look through, which means the greater the chance that there will be something heavy in the foreground to distort the background image.  Dr. Rogier Windhorst of Arizona State University, is doing research suggests that gravitational lensing is likely to dominate the observed properties of very early galaxies, those that are at most 650-480 million years old The halos of foreground galaxies when the universe was in its heydays of star formation (when it was about 3-6 billion years old) will gravitationally distort most of these very early objects.  This leads to an effect called “gravitational lensing bias” where we are seeing many things whose light is stretched by lensing.  He reported on that work today at the AAS meeting, by way of pointing out just how useful future telescopes, especially the JWST, will be in extending our view out to the early universe and dealing with this house of mirrors effect.

JWST will have to take this bias into account. Scientists like Windhorst and his colleagues will need to design new ways of handling the data from those observations to really help them understand just what it is those early, distant gravitationally lensed galaxies are doing… and how they evolve to become the galaxies we see today.