[Spitzer News] Infrared Echoes give NASA's Spitzer a Supernova Flashback

spitzer-news at lists.ipac.caltech.edu spitzer-news at lists.ipac.caltech.edu
Wed Oct 1 14:20:12 PDT 2008

Press Releases
1) Infrared Echoes give NASA's Spitzer a Supernova Flashback  (October 01, 2008)
2) Generations of Stars Pose for Family Portrait (August 22, 2008)
3) Spitzer Reveals 'No Organics' Zone Around Pinwheel Galaxy (July 21, 2008)
4) Brightest Star in the Galaxy has New Competition (July 15, 2008)

1) Spitzer Podcasts Downloaded Over 7 Million Times (September 23, 2008)
2) Water Hit with Young Star's Best Shot (September 18, 2008)
3) Spitzer Notices Star Birth Spike in Galaxies Moving to Cosmic Cities (August 6, 2008)

= Press Releases =

1) Infrared Echoes give NASA's Spitzer a Supernova Flashback  (October 01, 2008)

Hot spots near the shattered remains of an exploded star are echoing the blast's first moments, say scientists using data from NASA's Spitzer Space Telescope.

Eli Dwek of NASA's Goddard Space Flight Center in Greenbelt, Md. and Richard Arendt of the University of Maryland, Baltimore County, say these echoes are powered by radiation from Cassiopeia A 
supernova shock wave that blew the star apart some 11,000 years ago.

"We're seeing the supernova's first flash," Dwek said.

Previously, other Spitzer researchers discovered hot spots near the Cassiopeia A supernova remnant and recognized the spots' importance as light echoes of the original blast. Dwek and Arendt used 
Spitzer data to probe this hot dust and pin down the cause of the echoes more precisely.

Six knots of silicate dust near the remnant show temperatures between -173 and -123 degrees Celsius (-280 and -190 degrees Fahrenheit). Although this might seem frigid by earthly standards, such 
temperatures are downright hot compared to typical interstellar dust.

Writing in the October 1 issue of The Astrophysical Journal, the scientists show that the only event that could make the grains this hot is the powerful and short-lived pulse of ultraviolet radiation 
and X-rays that heralded the death of the star. The flash was a hundred billion times brighter than the sun, but lasted only a day or so.

"They've identified the precise event during the demolition of the star that produces the echo we see," said Michael Werner, the project scientist for Spitzer at NASA's Jet Propulsion Laboratory in 
Pasadena, Calif.

Light from the explosion reached Earth in the 17th century, but no one noticed. The Spitzer find gives astronomers a second chance to study the supernova as it unfolds.

Although the explosion originally escaped detection, its aftermath -- a hot, expanding gas cloud known as Cassiopeia A (Cas A, for short) -- is one of the best-studied supernova remnants. The blast 
zone lies 11,000 light-years away in the constellation Cassiopeia.

When a massive star runs out of nuclear fuel, its core collapses into a superdense, city-sized object called a neutron star. As the neutron star forms, it stiffens and rebounds. This triggers a 
mammoth shock wave that blows the star's outer layers to smithereens. The exiting shock creates a high-energy flash that precedes the supernova's rise in visible light.

Evidence for a flash associated with this "shock breakout" existed only in computer simulations until January 9, 2008. That's when NASA's Swift satellite detected a 5-minute-long X-ray pulse from 
galaxy NGC 2770. A few days later, a new supernova -- designated SN 2008D -- appeared in the galaxy.

The infrared echoes from Cas A arise from dust clouds about 160 light-years farther away than the remnant. The supernova's initial radiation pulse expands through space at the speed of light, then 
encounters the clouds and heats their dust grains. The dust, in turn, re-radiates the energy at infrared wavelengths.

The breakout radiation took 160 years to reach the clouds and, once heated, the dust's infrared energy had to make up the same distance. This extra travel time results in a 320-year offset between the 
supernova's initial outward-moving flash and arrival of the dust's infrared echo at Earth. The researchers plan to use the echoes to paint an intimate portrait of the explosion, the star and the 
immediate environment.

When light from the Cas A supernova first reached Earth in the late 1600s, no one reported seeing a new star. On August 16, 1680, the English astronomer John Flamsteed might have seen the supernova 
without recognizing it. He recorded a faint naked-eye star near the position of Cas A, but none exists there now.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at 
the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA.


2) Generations of Stars Pose for Family Portrait (August 22, 2008)

A new image from NASA's Spitzer Space Telescope tells a tale of life and death amidst a rich family history. The striking infrared picture shows a colorful cosmic cloud, called W5, studded with 
multiple generations of blazing stars.

It also provides dramatic new evidence that massive stars - through their brute winds and radiation - can trigger the birth of stellar newborns.

"Triggered star formation continues to be very hard to prove," said Xavier Koenig of the Harvard Smithsonian Center for Astrophysics in Cambridge, Mass. "But our preliminary analysis shows that the 
phenomenon can explain the multiple generations of stars seen in the W5 region." Koenig is lead author of a paper about the findings in the December 1, 2008, issue of the Astrophysical Journal.

The image, which can be seen at http://www.nasa.gov/mission_pages/spitzer/multimedia/20080722.html, is being unveiled today at 12:30 p.m. Pacific Time at the Griffith Observatory, Los Angeles, as part 
of Spitzer's five-year anniversary celebration. Spitzer launched on August 25, 2003, from Cape Canaveral Air Force Station, Fla.

The most massive stars in the universe form out of thick clouds of gas and dust. The stars are so massive, ranging from 15 to about 60 times the mass of our sun, that some of their material slides off 
in the form of winds. The scorching-hot stars also blaze with intense radiation. Over time, both the wind and radiation blast away surrounding cloud material, carving out expanding cavities.

Astronomers have long suspected that the carving of these cavities causes gas to compress into successive generations of new stars. As the cavities grow, it is believed that more and more stars arise 
along the cavities' expanding rims. The result is a radial "family tree" of stars, with the oldest in the middle of the cavity, and younger and younger stars farther out.

Evidence for this theory can be seen easily in pictures of many star-forming regions, such as W5, Orion and Carina. For example, in the new Spitzer picture of W5, the most massive stars (some of the 
blue dots) are at the center of two hollow cavities, and younger stars (pink or white) are embedded in the elephant-trunk-like pillars as well as beyond the cavity rim. However, it is possible that 
the younger stars just happen to be near the edge of the cavities and were not triggered by the massive stars.

Koenig and his colleagues set out to test the triggered star-formation theory by studying the ages of the stars in the W5 region. They used Spitzer's infrared vision to peer through the dusty clouds 
and get a better look at the stars' various stages of evolution. They found that stars within the W5 cavities are older than stars at the rims, and even older than stars farther out past the rim. This 
ladder-like separation of ages provides some of the best evidence yet that massive stars do, in fact, give rise to younger generations.

"Our first look at this region suggests we are looking at one or two generations of stars that were triggered by the massive stars," said co-author Lori Allen of the Harvard-Smithsonian Center for 
Astrophysics. "We plan to follow up with even more detailed measurements of the stars' ages to see if there is a distinct time gap between the stars just inside and outside the rim."

Millions of years from now, the massive stars in W5 will die in tremendous explosions. When they do, they will destroy some of the young nearby stars - the same stars they might have triggered into being.

W5 spans an area of sky equivalent to four full moons and is about 6,500 light-years away in the constellation Cassiopeia. The Spitzer picture was taken over a period of 24 hours. The color red shows 
heated dust that pervades the region's cavities. Green highlights the dense clouds, and white knotty areas are where the youngest of stars are forming. The blue dots are older stars in the 
star-forming cloud, as well as unrelated stars behind and in front of the cloud.

Other authors include Robert Gutermuth, now at Smith College in Northampton, Mass.; Chris Brunt of the University of Exeter, England; James Muzerolle of the University of Arizona, Tucson; and Joseph 
Hora of Harvard-Smithsonian Center for Astrophysics.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at 
the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA.


3) Spitzer Reveals 'No Organics' Zone Around Pinwheel Galaxy (July 21, 2008)

The Pinwheel galaxy is gussied up in infrared light in a new picture from NASA's Spitzer Space Telescope.

The fluffy-looking galaxy, officially named Messier 101, is dominated by a mishmash of spiral arms. In Spitzer's new view, in which infrared light is color coded, the galaxy sports a swirling blue 
center and a unique, coral-red outer ring.

A new paper appearing July 20 in the Astrophysical Journal explains why this outer ring stands out. According to the authors, the red color highlights a zone where organic molecules called polycyclic 
aromatic hydrocarbons, which are present throughout most of the galaxy, suddenly disappear.

Polycyclic aromatic hydrocarbons are dusty, carbon-containing molecules found in star nurseries, and on Earth in barbeque pits, exhaust pipes and anywhere combustion reactions take place. Scientists 
believe this space dust has the potential to be converted into the stuff of life.

"If you were going look for life in Messier 101, you would not want to look at its edges," said Karl Gordon of the Space Telescope Science Institute in Baltimore, Md. "The organics can't survive in 
these regions, most likely because of high amounts of harsh radiation."

The Pinwheel galaxy is located about 27 million light-years away in the constellation Ursa Major. It has one of the highest known gradients of metals (elements heavier than helium) of all nearby 
galaxies in our universe. In other words, its concentrations of metals are highest at its center, and decline rapidly with distance from the center. This is because stars, which produce metals, are 
squeezed more tightly into the galaxy's central quarters.

Gordon and his team used Spitzer to learn about the galaxy's gradient of polycyclic aromatic hydrocarbons. The astronomers found that, like the metals, the polycyclic aromatic hydrocarbons decrease in 
concentration toward the outer portion of the galaxy. But, unlike the metals, these organic molecules quickly drop off and are no longer detected at the very outer rim.

"There's a threshold at the rim of this galaxy, where the organic material is getting destroyed," said Gordon.

The findings also provide a better understanding of the conditions under which the very first stars and galaxies arose. In the early universe, there were not a lot of metals or polycyclic aromatic 
hydrocarbons around. The outskirt of the Pinwheel galaxy therefore serves as a close-up example of what the environment might look like in a distant galaxy.

In this image, infrared light with a wavelength of 3.6 microns is colored blue; 8-micron light is green; and 24-micron light is red. All three of Spitzer instruments were used in the study: the 
infrared array camera, the multiband imaging photometer and the infrared spectrograph.

Other authors of the paper include Charles Engelbracht, George Rieke, Karl A. Misselt, J.D. Smith and Robert Kennicutt, Jr. of the University of Arizona, Tucson. Smith is also associated with the 
University of Toledo, Ohio, and Kennicutt is also associated with the University of Cambridge, England.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer 
Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA. Spitzer's infrared array camera was built by NASA's Goddard Space Flight Center, Greenbelt, 
Md. The instrument's principal investigator is Giovanni Fazio of the Harvard-Smithsonian Center for Astrophysics. Spitzer's infrared spectrograph was built by Cornell University, Ithaca, N.Y. Its 
development was led by Jim Houck of Cornell. The multiband imaging photometer for Spitzer was built by Ball Aerospace Corporation, Boulder, Colo., and the University of Arizona, Tucson. Its principal 
investigator is George Rieke of the University of Arizona.


4) Brightest Star in the Galaxy has New Competition (July 15, 2008)

A contender for the title of brightest star in our Milky Way galaxy has been unearthed in the dusty metropolis of the galaxy's center.

Nicknamed the "Peony nebula star," the bright stellar bulb was revealed by NASA's Spitzer Space Telescope and other ground-based telescopes. It blazes with the light of an estimated 3.2 million suns.

The reigning "brightest star" champion is Eta Carina, with a whopping solar wattage of 4.7 million suns. But according to astronomers, it's hard to pin down an exact brightness, or luminosity, for 
these scorching stars, so they could potentially shine with a similar amount of light.

"The Peony nebula star is a fascinating creature. It appears to be the second-brightest star that we now know of in the galaxy, and it's located deep into the galaxy's center," said Lidia Oskinova of 
Potsdam University in Germany. "There are probably other stars just as bright if not brighter in our galaxy that remain hidden from view." Oskinova is principal investigator for the research and 
second author of a paper appearing in a future issue of the journal Astronomy and Astrophysics.

Scientists already knew about the Peony nebula star, but because of its sheltered location in the dusty central hub of our galaxy, its extreme luminosity was not revealed until now. Spitzer's 
dust-piercing infrared eyes can see straight into the heart of our galaxy, into regions impenetrable by visible light. Likewise, infrared data from the European Southern Observatory's New Technology 
Telescope in Chile were integral in calculating the Peony nebula star's luminosity.

"Infrared astronomy opens extraordinary views into the environment of the central region of our galaxy," said Oskinova.

The brightest stars in the universe are also the biggest. Astronomers estimate the Peony nebula star kicked off its life with a hefty mass of roughly 150 to 200 times that of our sun. Stars this 
massive are rare and puzzle astronomers because they push the limits required for stars to form. Theory predicts that if a star starts out too massive, it can't hold itself together and must break 
into a double or multiple stars instead.

Not only is the Peony nebula star hefty, it also has a wide girth. It is a type of giant blue star called a Wolf-Rayet star, with a diameter roughly 100 times that of our sun. That means this star, if 
placed where our sun is, would extend out to about the orbit of Mercury.

With so much mass, the star barely keeps itself together. It sheds an enormous amount of stellar matter in the form of strong winds over its relatively short lifetime of a few million years. This 
matter is pushed so hard by strong radiation from the star that the winds speed up to about 1.6 million kilometers per hour (one million miles per hour) in only a few hours.

Ultimately, the Peony nebula star will blow up in a fantastic explosion of cosmic proportions called a supernova. In fact, Oskinova and her colleagues say that the star is ripe for exploding soon, 
which in astronomical terms mean anytime from now to millions of years from now.

"When this star blows up, it will evaporate any planets orbiting stars in the vicinity," said Oskinova. "Farther out from the star, the explosion could actually trigger the birth of new stars."

In addition to the star itself, the astronomers noted a cloud of dust and gas, called a nebula, surrounding the star. The team nicknamed this cloud the Peony nebula because it resembles the ornate flower.

"The nebula was probably created from the spray of dust leaking off the massive Peony nebula star," said Andreas Barniske of Potsdam University, lead author of the study.

Wolf-Rainer Hamann, also of Potsdam University, is another co-author of the paper and the principal investigator of a Spitzer program enabling this research.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer 
Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA. Spitzer's infrared spectrograph, which was used to determine the luminosity of the Peony 
nebula star, was built by Cornell University, Ithaca, N.Y. Its development was led by Jim Houck of Cornell.

==== Features ====

1) Spitzer Podcasts Downloaded Over 7 Million Times (September 23, 2008)

Podcasting -- producing audio & video content for computers and mobile devices -- has grown in popularity over the past several years. NASA's Spitzer Space Telescope hit a new milestone in August: 7 
million downloads of its various podcasts.

Today, NASA missions and centers produce over 50 podcasts, but Spitzer was one of the first to embrace the new technology. The original "Spitzer Audio Podcast" launched on August 3, 2005. This podcast 
covers news and science from Spitzer, delivering information as short-form audio presentations.

In October of 2005, the Spitzer education and public outreach team quickly responded to the addition of video podcast subscriptions to iPods and iTunes. Its repurposed web video series, "Ask an 
Astronomer," became one of the very first available video podcasts. This series features real NASA astronomers answering everyday astronomy questions using rich graphics to help communicate complex 
ideas. Though geared primarily at school children, the video podcast is popular with adults as well, with over 3.5 million downloads to date.

Inspired by the success of "Ask an Astronomer," the Spitzer team developed a new video podcast to share Spitzer's spectacular imagery and science results. "The Hidden Universe" launched on May 2, 
2006, and within a year became one of the first podcasts to offer a high-definition (HD) format. The HD version has proven remarkably successful -- on iTunes it consistently ranks as the #1 NASA 
podcast and in the "Science & Medicine" top 10 (it achieved the #1 spot for all US podcasts in Fall 2007). A Spanish version of select episodes premiered in September 2007.

On January 15, 2008, "IRrelevant Astronomy" (that's "infrared-relevant"!) was launched. This new video podcast breaks from the typical model for science podcasts, using comedy and CG animation to tell 
stories that incorporate real astronomy news & concepts. The podcast offers several different shows including "Spaceship Spitzer," a sci-fi spoof starring Spitzer astronomer Dr. Michelle Thaller, and 
"Robot Astronomy Talk Show," featuring robots scheming to take over the Universe through astronomy.

Collectively, Spitzer podcasts have received numerous awards, including several Telly Awards, Aegis Awards, and the CINE Golden Eagle. And with the popularity of the podcasts growing every day, the 7 
million mark seems to be only the beginning.

You can browse all of Spitzer's podcast products by visiting http://www.spitzer.caltech.edu/podcasts


2) Water Hit with Young Star's Best Shot (September 18, 2008)

Water is being blasted to pieces by a young star's laser-like jets, according to new observations from NASA's Spitzer Space Telescope.

The discovery provides a better understanding of how water -- an essential ingredient for life as we know it -- is processed in emerging solar systems.

"This is a truly unique observation that will provide important information about the chemistry occurring in planet-forming regions, and may give us insights into the chemical reactions that made 
water and even life possible in our own solar system," said Achim Tappe, of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.

A young star forms out of a thick, rotating cloud of gas and dust. Like the two ends of a spinning top, powerful jets of gas emerge from the top and bottom of the dusty cloud. As the cloud shrinks 
more and more under its own gravity, its star eventually ignites and the remaining dust and gas flatten into a pancake-like disk, from which planets will later form. By the time the star ignites and 
stops accumulating material from its cloud, the jets will have died out.

Tappe and his colleagues used Spitzer's infrared eyes to cut through the dust surrounding a nascent star, called HH 211-mm, and get a better look at its jets. These particular jets are exceptionally 
young at 1,000 years old, and they are some of the most collimated, or focused, known. An instrument on Spitzer called a spectrometer analyzed light from one of the jets, revealing information about 
its molecules.

To the astronomers' surprise, Spitzer picked up the signature of rapidly spinning fragments of water molecules, called hydroxyl, or OH. In fact, the hydroxyl molecules have absorbed so much energy 
(through a process called excitation) that they are rotating around with energies equivalent to 28,000 Kelvin (27,700 degrees Celsius). This far exceeds normal expectations for gas streaming out of a 
stellar jet. Water, which is abbreviated H2O, is made up of one oxygen atom and two hydrogen; hydroxyl, or OH, contains one oxygen and one hydrogen atom.

The results reveal that the jet is ramming its head into a wall of material, vaporizing ice right off the dust grains it normally coats. The jet is hitting the material so fast and hard that a shock 
wave is also being produced.

"The shock from colliding atoms and molecules generates ultraviolet radiation, which will break up water molecules, leaving extremely hot hydroxyl molecules," said Tappe.

Tappe said this same process of ice being vaporized off dust occurs in our own solar system, when the sun vaporizes ice in approaching comets. In addition, the water that now coats our world is 
thought to have come from icy comets that vaporized as they rained down on a young Earth.

Tappe is the lead author of a paper on this topic, which was published in a recent issue of the Astrophysical Journal. Co-authors on the paper include Charlie Lada, and August Muench, also of the 
Harvard-Smithsonian Center for Astrophysics; and J. H. Black, of the Chalmers University of Technology, in Onsala, Sweden.


3) Spitzer Notices Star Birth Spike in Galaxies Moving to Cosmic Cities (August 6, 2008)

New evidence from NASA's Spitzer Space Telescope reveals that most galaxies undergo a huge stellar baby boom when they first enter a "cosmic city", or galaxy cluster. And the more distant the galaxy 
cluster, the greater the star formation rate.

"The infrared Spitzer observations let us peek at otherwise hidden, powerful star formation harbored in some of these cluster galaxies," says Dr. Amelie Saintonge, of the Institute for Theoretical 
Physics, University of Zurich, in Switzerland. "By looking at both nearby and distant galaxy clusters, we can look back in time and observe an increase in the fraction of galaxies undergoing these 
intense star-forming events."

Sanitonge and Dr. Kim-Vy Tran, also of the University of Zurich, studied a total of 1,300 galaxies in eight clusters spread across 7 billion light-years. The galaxies were observed by Spitzer's 
Multiband Imaging Photometer (MIPS), and archived for the astronomical community to use.
Moving to the City

Across the Universe, galaxies reside in communities big and small. Like big cities on Earth, there are densely populated galactic communities called galaxy clusters. Thousands of galaxies live within 
the limits of a cluster, which are connected by a web of dusty "highways" called filaments. Sprinkled along each filament are smaller galactic communities, or the celestial suburbs. Over time, 
astronomers suspect that all galactic suburbanites will be gravitationally pulled into the cluster, traveling there by way of the filaments.

Scientists believe that when a galactic suburbanite first falls into a cluster, the galaxy slams into the cluster's hot gas, producing shockwaves that trigger dusty gas clouds in the galaxy to 
collapse. Like raindrops, stars will form in these condensing cosmic clouds.

In their baby years, these stars are optically invisible - shrouded by the dust cloud that condensed to form them. Eventually, the stars will develop powerful winds, strong enough to blow away 
surrounding dust. Until then, only Spitzer's dust-piercing infrared eyes can glimpse the infant stars.

According to Saintonge, Spitzer is the first telescope able to produce sensitive images of galaxies located 7 billion light-years away in the mid-infrared, at 24 microns. At this wavelength, 
astronomers can see most of the dust-obscured star formation in a distant galaxy.

Previously the Infrared Space Observatory mission hinted that as much as 90 percent of star formation in cluster galaxies is hidden at optical wavelengths. However, Spitzer is the only telescope that 
allows astronomers to observe very distant clusters and confirm that the effect is increasing with distance - meaning, the farther away the cluster is, the more galaxies it has that are forming stars 
in very dusty environments.

Although scientists are currently unsure about the physical mechanisms that induce the exuberant star formation in these galaxies, they believe that the more distant galaxies form more stars because 
of the epoch they are located in. Light needs time to travel, so humans never see cosmic objects as they currently are, only as they were in the distant past. For example, the light from an object 
that is located 7 billion light-years away needs to travel for 7 billion years to reach our eyes.

Approximately 7 billion years ago, when the universe was only half the age it is now, galaxy clusters across the Universe were actively accreting galaxies. The gas clouds in these infalling galaxies 
were shocked and began condensing to form stars.

"There has been growing observational evidence that the increase in star formation with look back time is driven by cluster assembly and galaxy infall, the Spitzer observations not only confirm this 
scenario, but also show that the effect is even stronger than previously thought," says Saintonge. "By unveiling star formation events hidden at optical wavelengths, Spitzer finally lets us see more 
than the tip of this dusty iceberg."

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