Spitzer captures our galaxy's bustling center
Tue Jan 10, 2006 at 21:56 UTC
A new infrared mosaic from Spitzer Space Telescope offers a stunning view of the stellar hustle and bustle that takes place at our Milky Way galaxy's center. The picture shows throngs of mostly old stars, on the order of hundreds of thousands, amid fantastically detailed clouds of glowing dust lit up by younger, massive stars.
"With Spitzer, we can peer right into the heart of our own galaxy and see breathtaking detail," said Dr. Susan Stolovy of the Spitzer Science Center at the California Institute of Technology in Pasadena. "This picture is crammed with fascinating features that we have just begun to explore."
The Milky Way's core is indeed a very busy place. Stars are packed together like subway riders as they race around the supermassive black hole that lies at the center. Our sun is located 26,000 light-years away in a more peaceful, spacious neighborhood, out in the galactic suburbs. It circles the galaxy about every 225 million years, which amounts to 20 trips over the course of its 4.5-billion-year lifetime. In contrast, stars at the galactic center complete one lap in only a few million years or less.
"One question we hope to address is how stars can form so efficiently in a place like the galactic center," said Stolovy. "Stars there are still able to form in an environment with unusually strong magnetic fields and tidal shear forces."
Viewing the center of the Milky Way from Earth can be difficult because the plane of the galaxy's spiral disk is filled with cold dust. Visible light coming from this distant region is virtually impossible to observe because dust dims it by a factor of one trillion. But infrared light can shine through this dust. The infrared light in this Spitzer view has wavelengths about 10 times longer than what the human eye can see, and is dimmed only about four times.
This infrared advantage, combined with Spitzer's superb image quality, has resulted in the deepest and sharpest view yet of an expansive stretch of the galactic center. The pictured region, located in the Sagittarius constellation, is 900 light-years across. It covers the same area on the sky that a grid of four by three full moons would occupy.
Image Credit: NASA/JPL-Caltech/S. Stolovy (SSC/Caltech)
This infrared image from Spitzer Space Telescope shows hundreds of thousands of stars crowded into the swirling core of our spiral Milky Way galaxy. In visible-light pictures, this region cannot be seen at all because dust lying between Earth and the galactic center blocks our view.
In this false-color picture, old and cool stars are blue, while dust features lit up by blazing hot, massive stars are shown in a reddish hue. Both bright and dark filamentary clouds can be seen, many of which harbor stellar nurseries. The plane of the Milky Way's flat disk is apparent as the main, horizontal band of clouds. The brightest white spot in the middle is the very center of the galaxy, which also marks the site of a supermassive black hole.
The region pictured here is immense, with a horizontal span of 890 light-years and a vertical span of 640 light-years. Earth is located 26,000 light-years away, out in one of the Milky Way's spiral arms. Though most of the objects seen in this image are located at the galactic center, the features above and below the galactic plane tend to lie closer to Earth.
Scientists are intrigued by the giant lobes of dust extending away from the plane of the galaxy. They believe the lobes may have been formed by winds from massive stars.
This image is a mosaic of thousands of short exposures taken by Spitzer's Infrared Array Camera (IRAC), showing emissions from wavelengths of 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange), and 8.0 microns (red). The entire region was imaged in less than 16 hours.
Image Credit: NASA/JPL-Caltech/S. Stolovy (SSC/Caltech)
Our Milky Way is a dusty place. So dusty, in fact, that we cannot see the center of the galaxy in visible light. But when NASA's Spitzer Space Telescope set its infrared eyes on the galactic center, it captured this spectacular view.
Taken with just one of Spitzer's cameras (at a wavelength of 8 microns), the image highlights the region's exceptionally bright and dusty clouds, lit up by young massive stars. Individual stars can also be seen as tiny dots scattered throughout the dust. The top mosaic shows a portion of the galactic center that stretches across a distance of 760 light-years.
Thanks to Spitzer's excellent resolution, the dusty features within the galactic center are seen in unprecedented detail. Four examples are shown in the magnified insets at the bottom. The farthest left box shows a pair of star-forming regions resembling owl-like cosmic eyes. To the left of the "eyes," dark lanes of dust can be seen. This object is probably located in a spiral arm between Earth and the galactic center, in contrast to the following examples, which are all located at the galactic center.
The next inset to the right includes the extremely luminous "Quintuplet" stars, a set of five massive stars believed to have buried themselves in cocoons of dust. Just below and to the right of the Quintuplet is the "Pistol" nebula, a bubble of ejected material from the central, massive Pistol star. The finger-like pillars to the left are part of a structure known as "Sickle." They are similar in size and shape to those in the famous picture of the Eagle Nebula taken by NASA's Hubble Space Telescope. Pillars like these are sculpted out of dense dust clouds by radiation and winds from hot stars. The pillars in the Sickle were likely to have been formed by a cluster of hot stars located to their right but not readily visible here.
The third inset highlights a system of long, stringy structures that are seen for the first time near the base of a region known as the "Arched Filaments." These long filaments are about 10 light-years long and less than 1 light-year wide. The bright star-forming regions to the right are some of the brightest in the infrared sky.
The final inset to the right shows the center of our galaxy, which is the brightest spot in the entire mosaic. The brightness is a result of dust being heated up by a compact cluster of hot stars. The bright spot also marks the location of a supermassive black hole, around which a rotating ring of gas and dust known as the circumnuclear disk can be seen.
This image was taken with Spitzer's Infrared Array Camera (IRAC), using its 8-micron detector. It shows emissions from heated-up molecules in dust clouds called polycyclic aromatic hydrocarbons.
Features within the new mosaic include dust clouds of a dizzying variety, such as glowing filaments, wind-blown lobes flapping outward from the plane of the galaxy, and finger-like pillars. The Spitzer image also shows newborn stars just beginning to break out of their dark and dusty cocoons, and exquisitely detailed dark clouds so dense they are opaque even in infrared wavelengths. Some of these features are located near the physical center of our galaxy, while others lie closer to Earth.
"Our Spitzer data, combined with data obtained by other telescopes, will allow us to determine which of these objects are truly at the galactic center, and which are in spiral arms along the way," said Stolovy. "This survey will help us to better understand the mass distribution and structure of our own galaxy and how it compares to other galaxies."
Stolovy and her colleagues are particularly thrilled about the high quality of the Spitzer image when they remember the challenges they overcame in obtaining it. The galactic center is very bright in infrared wavelengths, and could have potentially saturated Spitzer's sensitive detectors. The astronomers solved this problem by taking advantage of Spitzer's ability to take very short exposures. They collected the thousands of snapshots that make up their final mosaic in just under 16 hours.
The Jet Propulsion Laboratory manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech. JPL is a division of Caltech. NASA's Goddard Space Flight Center, Greenbelt, Md., built Spitzer's infrared array camera, which took the new image. The instrument's principal investigator is Dr. Giovanni Fazio of the Harvard-Smithsonian Center for Astrophysics.
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