Out of This Whirl: the Whirlpool Galaxy (M51) and Companion Galaxy

The graceful, winding arms of the majestic spiral galaxy M51 (NGC 5194) appear like a grand spiral staircase sweeping through space. They are actually long lanes of stars and gas laced with dust.

This sharpest-ever image of the Whirlpool Galaxy, taken in January 2005 with the Advanced Camera for Surveys aboard NASA's Hubble Space Telescope, illustrates a spiral galaxy's grand design, from its curving spiral arms, where young stars reside, to its yellowish central core, a home of older stars. The galaxy is nicknamed the Whirlpool because of its swirling structure.

The Whirlpool's most striking feature is its two curving arms, a hallmark of so-called grand-design spiral galaxies. Many spiral galaxies possess numerous, loosely shaped arms which make their spiral structure less pronounced. These arms serve an important purpose in spiral galaxies. They are star-formation factories, compressing hydrogen gas and creating clusters of new stars. In the Whirlpool, the assembly line begins with the dark clouds of gas on the inner edge, then moves to bright pink star-forming regions, and ends with the brilliant blue star clusters along the outer edge.

Some astronomers believe that the Whirlpool's arms are so prominent because of the effects of a close encounter with NGC 5195, the small, yellowish galaxy at the outermost tip of one of the Whirlpool's arms. At first glance, the compact galaxy appears to be tugging on the arm. Hubble's clear view, however, shows that NGC 5195 is passing behind the Whirlpool. The small galaxy has been gliding past the Whirlpool for hundreds of millions of years.

As NGC 5195 drifts by, its gravitational muscle pumps up waves within the Whirlpool's pancake-shaped disk. The waves are like ripples in a pond generated when a rock is thrown in the water. When the waves pass through orbiting gas clouds within the disk, they squeeze the gaseous material along each arm's inner edge. The dark dusty material looks like gathering storm clouds. These dense clouds collapse, creating a wake of star birth, as seen in the bright pink star-forming regions. The largest stars eventually sweep away the dusty cocoons with a torrent of radiation, hurricane-like stellar winds, and shock waves from supernova blasts. Bright blue star clusters emerge from the mayhem, illuminating the Whirlpool's arms like city streetlights.

The Whirlpool is one of astronomy's galactic darlings. Located 31 million light-years away in the constellation Canes Venatici (the Hunting Dogs), the Whirlpool's beautiful face-on view and closeness to Earth allow astronomers to study a classic spiral galaxy's structure and star-forming processes.

Image Credit: NASA, ESA, S. Beckwith (STScI), and The Hubble Heritage Team (STScI/AURA)

Explanation from: http://hubblesite.org/newscenter/archive/releases/2005/12/image/a/

Stars in NGC 602a

The Small Magellanic Cloud (SMC) is one of the Milky Way's closest galactic neighbors. Even though it is a small, or so-called dwarf galaxy, the SMC is so bright that it is visible to the unaided eye from the Southern Hemisphere and near the equator. Many navigators, including Ferdinand Magellan who lends his name to the SMC, used it to help find their way across the oceans. 

Modern astronomers are also interested in studying the SMC (and its cousin, the Large Magellanic Cloud), but for very different reasons. Because the SMC is so close and bright, it offers an opportunity to study phenomena that are difficult to examine in more distant galaxies. 

New Chandra data of the SMC have provided one such discovery: the first detection of X-ray emission from young stars with masses similar to our Sun outside our Milky Way galaxy. The new Chandra observations of these low-mass stars were made of the region known as the "Wing" of the SMC. In this composite image of the Wing the Chandra data is shown in purple, optical data from the Hubble Space Telescope is shown in red, green and blue and infrared data from the Spitzer Space Telescope is shown in red. 

Astronomers call all elements heavier than hydrogen and helium -- that is, with more than two protons in the atom's nucleus -- "metals." The Wing is a region known to have fewer metals compared to most areas within the Milky Way. There are also relatively lower amounts of gas, dust, and stars in the Wing compared to the Milky Way. 

Taken together, these properties make the Wing an excellent location to study the life cycle of stars and the gas lying in between them. Not only are these conditions typical for dwarf irregular galaxies like the SMC, they also mimic ones that would have existed in the early Universe. 

Most star formation near the tip of the Wing is occurring in a small region known as NGC 602, which contains a collection of at least three star clusters. One of them, NGC 602a, is similar in age, mass, and size to the famous Orion Nebula Cluster. Researchers have studied NGC 602a to see if young stars -- that is, those only a few million years old -- have different properties when they have low levels of metals, like the ones found in NGC 602a. 

Using Chandra, astronomers discovered extended X-ray emission, from the two most densely populated regions in NGC 602a. The extended X-ray cloud likely comes from the population of young, low-mass stars in the cluster, which have previously been picked out by infrared and optical surveys, using Spitzer and Hubble respectively. This emission is not likely to be hot gas blown away by massive stars, because the low metal content of stars in NGC 602a implies that these stars should have weak winds. The failure to detect X-ray emission from the most massive star in NGC 602a supports this conclusion, because X-ray emission is an indicator of the strength of winds from massive stars. No individual low-mass stars are detected, but the overlapping emission from several thousand stars is bright enough to be observed. 

The Chandra results imply that the young, metal-poor stars in NGC 602a produce X-rays in a manner similar to stars with much higher metal content found in the Orion cluster in our galaxy. The authors speculate that if the X-ray properties of young stars are similar in different environments, then other related properties -- including the formation and evolution of disks where planets form -- are also likely to be similar. 

X-ray emission traces the magnetic activity of young stars and is related to how efficiently their magnetic dynamo operates. Magnetic dynamos generate magnetic fields in stars through a process involving the star's speed of rotation, and convection, the rising and falling of hot gas in the star's interior. 

The combined X-ray, optical and infrared data also revealed, for the first time outside our Galaxy, objects representative of an even younger stage of evolution of a star. These so-called "young stellar objects" have ages of a few thousand years and are still embedded in the pillar of dust and gas from which stars form, as in the famous "Pillars of Creation" of the Eagle Nebula. 

Image Credit: X-ray: NASA/CXC/Univ.Potsdam/L.Oskinova et al; Optical: NASA/STScI; Infrared: NASA/JPL-Caltech

Explanation from: http://www.nasa.gov/mission_pages/chandra/multimedia/ngc602a.html

Alaskan Mountains Seen During IceBridge Transit

Alaskan mountains seen from high altitude aboard the NASA P-3B during the IceBridge transit flight from Thule to Fairbanks on March 21, 2013.

NASA's Operation IceBridge is an airborne science mission to study Earth's polar ice.

Image Credit: NASA/Goddard/Christy Hansen

Herschel Sees Through Ghostly Pillars

This Herschel image of the Eagle nebula shows the self-emission of the intensely cold nebula’s gas and dust as never seen before. Each color shows a different temperature of dust, from around 10 degrees above absolute zero (10 Kelvin or minus 442 degrees Fahrenheit) for the red, up to around 40 Kelvin, or minus 388 degrees Fahrenheit, for the blue. 

Herschel reveals the nebula's intricate tendril nature, with vast cavities forming an almost cave-like surrounding to the famous pillars, which appear almost ghostly in this view. The gas and dust provide the material for the star formation that is still under way inside this enigmatic nebula. 

Far-infrared light has been color-coded to 70 microns for blue and 160 microns for green using the Photodetector Array Camera, and 250 microns for red using the Spectral and Photometric Imaging Receiver. 

Herschel is a European Space Agency cornerstone mission, with science instruments provided by consortia of European institutes and with important participation by NASA. NASA's Herschel Project Office is based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. JPL contributed mission-enabling technology for two of Herschel's three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena, supports the United States astronomical community. Caltech manages JPL for NASA. 

Image Credit: ESA/Herschel/PACS/SPIRE/Hill, Motte, HOBYS Key Programme Consortium

Explanation from: http://www.nasa.gov/mission_pages/herschel/multimedia/pia15260.html

A Splendor Seldom Seen

NASA's Cassini spacecraft has delivered a glorious view of Saturn, taken while the spacecraft was in Saturn's shadow. The cameras were turned toward Saturn and the sun so that the planet and rings are backlit. (The sun is behind the planet, which is shielding the cameras from direct sunlight.) In addition to the visual splendor, this special, very-high-phase viewing geometry lets scientists study ring and atmosphere phenomena not easily seen at a lower phase. 

Since images like this can only be taken while the sun is behind the planet, this beautiful view is all the more precious for its rarity. The last time Cassini captured a view like this was in Sept. 2006, when it captured a mosaic processed to look like natural color, entitled "In Saturn's Shadow." In that mosaic, planet Earth put in a special appearance, making "In Saturn's Shadow" one of the most popular Cassini images to date. Earth does not appear in this mosaic as it is hidden behind the planet. 

Also captured in this image are two of Saturn's moons: Enceladus and Tethys. Both appear on the left side of the planet, below the rings. Enceladus is closer to the rings; Tethys is below and to the left. 

This view looks toward the non-illuminated side of the rings from about 19 degrees below the ring plane. 

Images taken using infrared, red and violet spectral filters were combined to create this enhanced-color view. The images were obtained with the Cassini spacecraft wide-angle camera on Oct. 17, 2012 at a distance of approximately 500,000 miles (800,000 kilometers) from Saturn. Image scale at Saturn is about 30 miles per pixel (50 kilometers per pixel). 

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo. 

Image Credit: NASA/JPL-Caltech/Space Science Institute

Explanation from: http://www.nasa.gov/mission_pages/cassini/multimedia/pia14934.html