Posted on by Nancy Atkinson

Great Observatories Combine for Stunning Look at Milky Way

All we can say is, “Wow!” In celebration of the International Year of Astronomy 2009, NASA’s Great Observatories — the Hubble Space Telescope, the Spitzer Space Telescope, and the Chandra X-ray Observatory — have collaborated to produce an unprecedented image of the central region of our Milky Way galaxy. This is a never-before-seen view of the turbulent heart of our home galaxy. The image is being unveiled by NASA to commemorate the anniversary of when Galileo first turned his telescope to the heavens in 1609. NASA provided this image and the individual images taken by each of the Great Observatories to more than 150 planetariums, museums, nature centers, libraries, and schools across the country.

In this spectacular image, observations using infrared light and X-ray light see through the obscuring dust and reveal the intense activity near the galactic core. Note that the center of the galaxy is located within the bright white region to the right of and just below the middle of the image. The entire image width covers about one-half a degree, about the same angular width as the full moon.

For more about the image or to download larger versions, go to this page on the HubbleSite.

Posted on by Nancy Atkinson

Multi-Planet System is Chaotic, Dusty

NASA’s Spitzer Space Telescope captured this infrared image of a giant halo of very fine dust around the young star HR 8799. Image credit: NASA/JPL-Caltech/Univ. of Ariz.

Just what is going on over at the star HR 8799? The place is a mess! But we can just blame it on the kids. Young, hyperactive planets circling the star are thought to be disturbing smaller comet-like bodies, causing them to collide and kick up a huge halo of dust. HR 8799 was in the news in November 2008, for being one of the first with imaged planets. Now, NASA’s Spitzer Space Telescope has taken a closer look at this planetary system and found it to be a very active, chaotic and dusty system. Ah, youth: our solar system was likely in a similar mess before our planets found their way to the stable orbits they circle in today.

The Spitzer team, led by Kate Su of the University of Arizona, Tucson, says the giant cloud of fine dust around the disk is very unusual. They say this dust must be coming from collisions among small bodies similar to the comets or icy bodies that make up today’s Kuiper Belt objects in our solar system. The gravity of the three large planets is throwing the smaller bodies off course, causing them to migrate around and collide with each other. Astronomers think the three planets might have yet to reach their final stable orbits, so more violence could be in store. The planets around HR 8799 are about 10 times the mass of Jupiter.

“The system is very chaotic and collisions are spraying up a huge cloud of fine dust,” said Su. “What’s exciting is that we have a direct link between a planetary disk and imaged planets. We’ve been studying disks for a long time, but this star and Fomalhaut are the only two examples of systems where we can study the relationships between the locations of planets and the disks.”

When our solar system was young, it went through similar planet migrations. Jupiter and Saturn moved around quite a bit, throwing comets around, sometimes into Earth. Some say the most extreme part of this phase, called the late heavy bombardment, explains how our planet got water. Wet, snowball-like comets are thought to have crashed into Earth, delivering life’s favorite liquid.

The Spitzer results were published in the Nov. 1 issue of Astrophysical Journal. The observations were made before Spitzer began its “warm” mission and used up its liquid coolant.

Source: JPL

Posted on by Nancy Atkinson

Spitzer Watches Planet-Forming Disk Change Quickly

This artist's conception shows a lump of material in a swirling, planet-forming disk. Image credit: NASA/JPL-Caltech

[/caption]
Something strange is going on around a young star called LRLL 31. Astronomers have witnessed a swirling disk of gas and dust which is changing rather quickly; sometimes weekly. This is likely a planet forming disk, however, planets take millions of years to form, so it’s rare to see anything change on time scales we humans can perceive. Another object appears to be pushing a clump of planet-forming material around the star, and this region is offering astronomers with the Spitzer Space Telescope a rare look into the early stages of planet formation.

Astronomer are seeing the light from this disk varying quite frequently. One possible explanation is that a close companion to the star — either a star or a developing planet — could be shoving planet-forming material together, causing its thickness to vary as it spins around the star.

“We don’t know if planets have formed, or will form, but we are gaining a better understanding of the properties and dynamics of the fine dust that could either become, or indirectly shape, a planet,” said James Muzerolle of the Space Telescope Science Institute, Baltimore, Md. Muzerolle is first author of a paper accepted for publication in the Astrophysical Journal Letters. “This is a unique, real-time glimpse into the lengthy process of building planets.”

One theory of planet formation suggests that planets start out as dusty grains swirling around a star in a disk. They slowly bulk up in size, collecting more and more mass like sticky snow. As the planets get bigger and bigger, they carve out gaps in the dust, until a so-called transitional disk takes shape with a large doughnut-like hole at its center. Over time, this disk fades and a new type of disk emerges, made up of debris from collisions between planets, asteroids and comets. Ultimately, a more settled, mature solar system like our own forms.

Before Spitzer was launched in 2003, only a few transitional disks with gaps or holes were known. With Spitzer’s improved infrared vision, dozens have now been found. The space telescope sensed the warm glow of the disks and indirectly mapped out their structures.

Muzerolle and his team set out to study a family of young stars, many with known transitional disks. The stars are about two to three million years old and about 1,000 light-years away, in the IC 348 star-forming region of the constellation Perseus. A few of the stars showed surprising hints of variations. The astronomers followed up on one, LRLL 31, studying the star over five months with all three of Spitzer’s instruments.

The observations showed that light from the inner region of the star’s disk changes every few weeks, and, in one instance, in only one week. “Transition disks are rare enough, so to see one with this type of variability is really exciting,” said co-author Kevin Flaherty of the University of Arizona, Tucson.

Both the intensity and the wavelength of infrared light varied over time. For instance, when the amount of light seen at shorter wavelengths went up, the brightness at longer wavelengths went down, and vice versa.

Muzerolle and his team say that a companion to the star, circling in a gap in the system’s disk, could explain the data. “A companion in the gap of an almost edge-on disk would periodically change the height of the inner disk rim as it circles around the star: a higher rim would emit more light at shorter wavelengths because it is larger and hot, but at the same time, the high rim would shadow the cool material of the outer disk, causing a decrease in the longer-wavelength light. A low rim would do the opposite. This is exactly what we observe in our data,” said Elise Furlan, a co-author from NASA’s Jet Propulsion Laboratory, Pasadena, Calif.

The companion would have to be close in order to move the material around so fast — about one-tenth the distance between Earth and the sun.

The astronomers plan to follow up with ground-based telescopes to see if a companion is tugging on the star hard enough to be perceived. Spitzer will also observe the system again in its “warm” mission to see if the changes are periodic, as would be expected with an orbiting companion. Spitzer ran out of coolant in May of this year, and is now operating at a slightly warmer temperature with two infrared channels still functioning.

“For astronomers, watching anything in real-time is exciting,” said Muzerolle. “It’s like we’re biologists getting to watch cells grow in a petri dish, only our specimen is light-years away.”

Source: JPL

Posted on by Nancy Atkinson

Trigger-Happy Star Formation in Cepheus B

Cepheus B from Chandra and Spitzer: X-ray (NASA/CXC/PSU/K. Getman et al.); IR (NASA/JPL-Caltech/CfA/J. Wang et al.)

[/caption]
Combining data from the Chandra X-Ray Observatory and the Spitizer Space Telescope allowed astronomers to create this gorgeous new image of Cepheus B. Besides being incredible eye candy, the new image also provides fresh insight into how some stars are born. The research shows that radiation from massive stars may trigger the formation of many more stars than previously thought.

While astronomers have long understood that stars and planets form from the collapse of a cloud of gas, the question of the main causes of this process has remained open.

“Astronomers have generally believed that it’s somewhat rare for stars and planets to be triggered into formation by radiation from massive stars,” said Konstantin Getman of Penn State University, and lead author of the study. “Our new result shows this belief is likely to be wrong.”

Chandra image of Cepheus B. Credit: NASA/Chandra team
Chandra image of Cepheus B. Credit: NASA/Chandra team

The new study suggests that star formation in the region of study in this image, Cepheus B, is mainly triggered by radiation from one bright, massive star outside the molecular cloud. According to theoretical models, radiation from this star would drive a compression wave into the cloud triggering star formation in the interior, while evaporating the cloud’s outer layers. The Chandra-Spitzer analysis revealed slightly older stars outside the cloud while the youngest stars with the most protoplanetary disks congregate in the cloud interior — exactly what is predicted from the triggered star formation scenario.

“We essentially see a wave of star and planet formation that is rippling through this cloud,” said co-author Eric Feigelson, also of Penn State. “Outside the cloud, the stars probably have newly born planets while inside the cloud the planets are still gestating.”

Cepheus B is a cloud of mainly cool molecular hydrogen located about 2,400 light years from the Earth. There are hundreds of very young stars inside and around the cloud — ranging from a few millions years old outside the cloud to less than a million in the interior — making it an important testing ground for star formation.

Previous observations of Cepheus B had shown a rim of ionized gas around the molecular cloud and facing the massive star. However, the wave of star formation — an additional crucial feature to identifying the source of the star formation — had not previously been seen. “We can even clock how quickly this wave is traveling and it’s going about 2,000 miles per hour,” said Getman.

The star that is the catalyst for the star formation in Cepheus B, is about 20 times as massive as the Sun, or at least five times weightier than any of the other stars in Cepheus B.

The Chandra and Spitzer data also suggest that multiple episodes of star and planet formation have occurred in Cepheus B over millions of years and that most of the material in the cloud has likely already been evaporated or transformed into stars.

“It seems like this nearby cloud has already made most of its stars and its fertility will soon wane,” said Feigelson. “It’s clear that we can learn a lot about stellar nurseries by combining data from these two Great Observatories.”

A paper describing these results was published in the July 10 issue of the Astrophysical Journal.

Source: Chandra

Posted on by Nancy Atkinson

Spitzer Finds Evidence of Violent Planetary Collision

Artists impression of the planetary smash-up. Image credit: NASA/JPL-Caltech


One of the main theories of how our Moon formed involves a violent cosmic collision between two planets. Astronomers have only been able to hypothesize what this collision was like, but now they have a better idea of what would ensue after such an event. With its infrared eyes the Spitzer Space Telescope has found the aftermath a collision between two planets, and what it shows is brutal. “This collision had to be huge and incredibly high-speed for rock to have been vaporized and melted,” said Carey M. Lisse of the Johns Hopkins University Applied Physics Laboratory, “This is a really rare and short-lived event, critical in the formation of Earth-like planets and moons. We’re lucky to have witnessed one not long after it happened.”

Watch the animation/recreation of the event in the video above.

LIsse and his team say that two rocky bodies, one as least as big as our moon and the other at least as big as Mercury, slammed into each other within the last few thousand years or so — not long ago by cosmic standards. The impact destroyed the smaller body, vaporizing huge amounts of rock and flinging massive plumes of hot lava into space.

Spitzer’s infrared detectors were able to pick up the signatures of the vaporized rock and amorphous silica — essentially melted glass — along with pieces of refrozen lava, called tektites.
[/caption]
Spitzer observed a star called HD 172555, which is about 12 million years old and located about 100 light-years away in the far southern constellation Pavo, or the Peacock (for comparison, our solar system is 4.5 billion years old).

The astronomers used an instrument on Spitzer, called a spectrograph, to break apart the star’s light and look for fingerprints of chemicals, in what is called a spectrum. What they found was very strange. “I had never seen anything like this before,” said Lisse. “The spectrum was very unusual.”

What they were seeing was the amorphous silica. Silica can be found on Earth in obsidian rocks and tektites. Obsidian is black, shiny volcanic glass. Tektites are hardened chunks of lava that are thought to form when meteorites hit Earth.

Large quantities of orbiting silicon monoxide gas were also detected, created when much of the rock was vaporized. In addition, the astronomers found rocky rubble that was probably flung out from the planetary wreck.

The mass of the dust and gas observed suggests the combined mass of the two charging bodies was more than twice that of our moon.

Their speed must have been tremendous as well — the two bodies would have to have been traveling at a velocity relative to each other of at least 10 kilometers per second (about 22,400 miles per hour) before the collision.

“The collision that formed our moon would have been tremendous, enough to melt the surface of Earth,” said co-author Geoff Bryden of NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Debris from the collision most likely settled into a disk around Earth that eventually coalesced to make the moon. This is about the same scale of impact we’re seeing with Spitzer — we don’t know if a moon will form or not, but we know a large rocky body’s surface was red hot, warped and melted.”

We know that collisions such as this must happen frequently. Giant impacts are thought to have stripped Mercury of its outer crust, tipped Uranus on its side and spun Venus backward, to name a few examples. Such violence is a routine aspect of planet building. Rocky planets form and grow in size by colliding and sticking together, merging their cores and shedding some of their surfaces. Though things have settled down in our solar system today, impacts still occur, as was observed last month after a small space object crashed into Jupiter.

“Almost all large impacts are like stately, slow-moving Titanic-versus-the-iceberg collisions, whereas this one must have been a huge fiery blast, over in the blink of an eye and full of fury,” said Lisse.

The team’s paper will appear in the Aug. 20 issue of the Astrophysical Journal.

Source: NASA

Posted on by Anne Minard

Spitzer Changes Its Glasses, Sees Cotton Candy

Infrared picture of a cloud, known as DR22, bursting with new stars in the Cygnus region of the sky.

[/caption]

The Spitzer Space Telescope has run out of the liquid helium that kept its optics cool — but the scope has already returned compelling new images as if to say:

I don’t need no stinkin’ helium.

At five and a half years, Spitzer’s prime mission more than doubled initial expectations. It finally ran out of liquid helium in May and was retooled for a new “warm mission” that began July 27. With its two remaining infrared channels, the telescope promises to observe with roughly the same sensitivity as a 30-meter ground-based telescope.

The lead infrared image shows the dying star NGC 4361, which was once hot like our Sun before it puffed out.

This next one shows dusty gas in blue and hot clouds in orange in DR22, a cloud bursting with new stars in the Cygnus region of the sky.

Spitzer's infrared eyes can both see dust and see through dust. The blue areas are dusty clouds, and the orange is mainly hot gas.
Spitzer's infrared eyes can both see dust and see through dust. The blue areas are dusty clouds, and the orange is mainly hot gas.

The new images were snapped with the two infrared channels that still work at Spitzer’s still-quite-chilly temperature of 30 Kelvin (about minus 406 degrees F). The two infrared channels are part of Spitzer’s infrared array camera: 3.6-micron light is blue and 4.5-micron light is orange.

This last picture shows a relatively calm galaxy called NGC 4145, 68 million light-years away in the constellation Canes Venatici.

Barred Spiral Galaxy NGC 4145, 68 million light-years away in the constellation Canes Venatici.
Barred Spiral Galaxy NGC 4145, 68 million light-years away in the constellation Canes Venatici.

All of The new pictures were taken while the telescope was being re-commissioned, on July 18 (NGC 4145, NGC 4361) and July 21 (Cygnus), 2009.

Since its launch from Cape Canaveral, Florida on Aug. 25, 2003, Spitzer has made many discoveries. They include planet-forming disks around stars, the composition of the material making up comets, hidden black holes, galaxies billions of light-years away and more.

Perhaps the most revolutionary and surprising Spitzer finds involve planets around other stars, called exoplanets. In 2005, Spitzer detected the first photons of light from an exoplanet.

Warm Spitzer will address many of the same science questions as before. It also will tackle new projects, such as refining estimates of Hubble’s constant, or the rate at which our universe is stretching apart; searching for galaxies at the edge of the universe; characterizing more than 700 near-Earth objects, or asteroids and comets with orbits that pass close to our planet; and studying the atmospheres of giant gas planets expected to be discovered soon by NASA’s Kepler mission.

“The performance of the two short wavelength channels of Spitzer’s infrared array camera is essentially unchanged from what it was before the observatory’s liquid helium was exhausted,” said Doug Hudgins, the Spitzer program scientist at NASA Headquarters in Washington.

Credit for all images: NASA/JPL-Caltech

Source: NASA’s Spitzer site and a press release through the American Astronomical Society (AAS).

Posted on by Nancy Atkinson

Spitzer Finds a Cyclops Galaxy!

The "eye" at the center of the galaxy is actually a monstrous black hole surrounded by a ring of stars. Credit: NASA/JPL

[/caption]
Imagine peering through your telescope and having a wild creature with one Cyclops-like eye looking back at you! NASA’s Spitzer Space Telescope saw just that when it located galaxy NGC 1097, about 50 million light-years away. It has long, spindly arms of stars, and its one “eye” at the center of the galaxy is actually a monstrous black hole surrounded by a ring of stars. Plus, this creature looks to be carrying a smaller blue galaxy in its arms!

The black hole is huge, about 100 million times the mass of our sun, and is feeding off gas and dust along with the occasional unlucky star. Our Milky Way’s central black hole is tame by comparison, with a mass of a few million suns.

“The fate of this black hole and others like it is an active area of research,” said George Helou, deputy director of NASA’s Spitzer Science Center at the California Institute of Technology in Pasadena. “Some theories hold that the black hole might quiet down and eventually enter a more dormant state like our Milky Way black hole.”

The fuzzy blue dot to the left, which appears to fit snuggly between the arms, is a companion galaxy.

“The companion galaxy that looks as if it’s playing peek-a-boo through the larger galaxy could have plunged through, poking a hole,” said Helou. “But we don’t know this for sure. It could also just happen to be aligned with a gap in the arms.”

Other dots in the picture are either nearby stars in our galaxy, or distant galaxies.

The white ring around the black hole is bursting with new star formation. An inflow of material toward the central bar of the galaxy is causing the ring to light up with new stars.

“The ring itself is a fascinating object worthy of study because it is forming stars at a very high rate,” said Kartik Sheth, an astronomer at NASA’s Spitzer Science Center. Sheth and Helou are part of a team that made the observations.

In the Spitzer image, infrared light with shorter wavelengths is blue, while longer-wavelength light is red. The galaxy’s red spiral arms and the swirling spokes seen between the arms show dust heated by newborn stars. Older populations of stars scattered through the galaxy are blue.

This image was taken during Spitzer’s “cold mission,” which lasted more than five-and-a-half years. The telescope ran out of coolant needed to chill its infrared instruments on May 15, 2009. Two of its infrared channels will still work perfectly during the new “warm mission,” which is expected to begin in a week or so, once the observatory has been recalibrated and warms to its new temperature of around 30 Kelvin (about minus 406 degrees Fahrenheit).

Source: JPL

Posted on by Nancy Atkinson

The Spitzer Space Telescope Speaks Its Mind

An interview with the Spitzer Space Telescope. Credit: NASA/JPL

[/caption]
The Spitzer Space Telescope is close to running out of coolant. Around May 12, the telescope will use up the last drop of the coolant that chills the instruments to just a few degrees above absolute zero. Everyone knew this was coming, but still it is sobering news. However, even though the coolant will be depleted, Spitzer will remain cold enough to still probe the universe with its infrared detectors for at least a couple of years. But we all like to think these missions will go on forever, at least I do anyway. The Jet Propulsion Laboratory shared this news in one of the more creative press releases ever put out by any NASA center: they interviewed the telescope. That’s right, the telescope. Not the principal investigator, not the chief engineer, but the telescope itself.

The spacecraft, which is now in orbit around the sun more than 100-million kilometers (62-million miles) behind Earth, will heat up just a bit — its instruments will warm up from – 456 degrees Fahrenheit (-271 Celsius) to – 404 degrees Fahrenheit (-242 Celsius).

If Spitzer could talk, here’s what the telescope might say:

Interviewer: It’s cold in here.

Spitzer: Sorry. Even though I’m warming up, I still need to be quite chilly for two of my infrared channels to continue working.

Interviewer: Why do infrared telescopes need to be cold?

Spitzer: Good question. Infrared light is produced by heat. So, engineers reduce my own heat to make sure that I’m measuring just the infrared light from the objects I’m studying. This is the same reason why I circle around the sun, far behind Earth, and why I have big sun shields — to keep cool.

Interviewer: Tell me, Spitzer, about what you consider to be your greatest discovery?

Spitzer: Probably my work on exoplanets, which are planets that orbit stars other than our sun. I hate to brag, but I was the first telescope to see actual light from an exoplanet. I was also the first to split that light up into a spectrum. Oh, sorry, there I go again with the techie talk. Light is made up of lots of different wavelengths in the same way that a rainbow is made up of different colors. I was able to split an exoplanet’s light up into its various infrared wavelengths. This spectral information teaches us about planets’ atmospheres.

Interviewer: What did you learn about the planets?

Spitzer: For one thing, I learned that the hot gas exoplanets, called “hot Jupiters,” are not all alike. Some are wild, with temperatures as hot as fire and almost as cold as ice. Others are more even-keeled. I also created the first temperature map of an exoplanet, and watched a storm of colossal proportions brewing across the face of one bizarre exoplanet – it has an orbit that swings in really close to its star and then back out to about where Earth sits in our solar system.

Interviewer: You seem to really like planets.

Spitzer: Well, you know, I wasn’t even originally designed to see exoplanets! It was a complete surprise to me that I had this amazing ability. I can tell you that I do, and always will, have a thing for planetary disks. Because I have infrared eyes, I can see the warm and dusty planetary materials that swirl in disks around young stars. I can also see older disks littered with the remnants of planets. In fact, I’ve probably looked at thousands of disks so far. What’s been fun is finding them around all sorts of oddball stars, such as those that are dead, doubled up as twins and even as small as planets. Bottom line is that the process of growing planets seems to happen quite easily all over the galaxy, and perhaps the universe.

Interviewer: Does that mean aliens could be everywhere?

Spitzer: I can’t really give you a good answer for that. Yes, the studies of disks are showing us that rocky planets are common, but we don’t know if the planets could have life. Also, keep in mind that, as of now, nobody has detected any planets that are just like Earth. These would be rocky worlds around stars like our sun that have the right temperature for lakes and oceans. That job will most likely fall to NASA’s Kepler mission, which will begin hunting for them soon.

Interviewer: Did you look at other objects besides disks and planets?

Spitzer: Oh yes, certainly. I have looked at comets in our solar system, the farthest galaxies known, and everything in-between. I was really excited to find hundreds of hidden black holes billions of light-years away. Astronomers had known they were there because they shoot X-rays into space that can be detected as a diffuse glow. But the objects themselves were choked in dust. My infrared eyes, unlike your human eyes, can see through dust, so I was able to round up a lot of these missing black holes.

Interviewer: Is there any other discovery you want to mention?

Spitzer: There are too many to list, but I am particularly proud of this huge mosaic I took of a large swath of our Milky Way galaxy. It looks stunning when you print it out to poster size, and it’s the best view ever of the bustling central portion of our galaxy. You see, the middle of the Milky Way is hopping with stars and dust. It’s chaos, and visible-light cannot escape. These observations not only look cool, they also helped astronomers remap the structure of our galaxy. The new map shows just two spiral arms of stars instead of four as previously believed. How crazy is that!

Interviewer: So what lies ahead?

Spitzer: Well, I’m really looking forward to the warm mission, because now that I have just two infrared channels working, I have more time to look at larger chunks of space for longer periods of time. I can help astronomers answer some really important “big picture” questions, which we didn’t have time for before.

Interviewer: Can you list some specific projects you’ll be working on?

Spitzer: I plan to continue studying exoplanets, including new “hot Jupiters” that Kepler is expected to find. I will also refine estimates of the rate at which our local universe, or space, is expanding. And I will stare at the very distant universe, trying to see some of the farthest objects possible. Oh, and I am also going to survey thousands of asteroids in our neck of the solar system, and get the first real estimate of their size distribution. This will tell us approximately how often big asteroids might come close to Earth.

Interviewer: That sounds scary.

Spitzer: Actually, this information will help us prepare for them. And NASA tracks near-Earth objects diligently. More information can only help.

Interviewer: Will you still take the pretty pictures?

Spitzer: You think my pictures are pretty? Thank you! Yes, I will still snap a lot of pictures. For instance, I will continue to probe cloudy star-forming regions in our galaxy, which often make dramatic pictures.

Interviewer: Anything else you’d like to add?

Spitzer: My cool years have been more than I could ask for, and I look forward to more adventures to come. I’d also like to thank all of the scientists and engineers who have worked so hard to make my mission an ongoing success. And, if any of my fans out there want more info, they can go to www.spitzer.caltech.edu/spitzer.

Posted on by Nancy Atkinson

Why Are Galaxies Smooth? Star Streams

NGC 2841, a smooth galaxy. Credit: NASA

[/caption]
Look at the disk of any large spiral galaxy, and outwardly it appears smooth, with stars evenly distributed throughout. But when young stars are forming, they are clustered together in dense clouds of dust and gas. So what happens as the galaxy matures to allow for the smooth distribution seen in galaxies like the Milky Way? Using NASA’s Spitzer Space Telescope, an international team of astronomers has discovered streams of young stars flowing from their natal cocoons in distant galaxies. These distant rivers of stars provide an answer to one of astronomy’s most fundamental puzzles.

Astronomers know that the clusters where stars form begin to disappear when their ages reach several hundred million years. A few mechanisms are thought to explain this: some clusters evaporate when random internal motions kick out stars one by one, and other clusters disperse as a result of collisions among the clouds where they were born. Zooming out to mechanisms operating on larger scales still, shearing motions caused by the galaxy’s rotation around its center disperses the clusters of clusters of young stars.

“Our analysis now answers the grand puzzle. By finding a myriad of streams of young stars all over the disks of galaxies we studied, we see that the mechanism for pulling the clusters of young stars apart is shearing motions of the parent galaxy. These streams are the ‘missing link’ we needed to understand how the disks of galaxies evolve to look the way they do,” said team leader David Block of the University of the Witwatersrand in South Africa.

Crucial to this discovery was finding a way to image previously hidden young stellar streams in galaxies millions of light-years away. To do this the team used high-resolution infrared observations from the Spitzer.
Using infrared rather than visible light to look at the galaxies allowed the group to pick out stars at just the right age when the stars are just starting to spread out from their clusters.
Credit: NASA/ Spitzer team
“Spitzer observes in the infrared where 100-million-year-old populations of stars dominate the light,” noted co-author Bruce Elmegreen, from IBM’s Research Division in New York. “Younger regions shine more in the visible and ultraviolet parts of the spectrum, and older regions get too faint to see. So we can filter out all the stars we don’t want by taking pictures with an infrared camera.”

Infrared is also important because light in this part of the spectrum can penetrate the dense dust clouds surrounding the clusters where stars form.

“Dust blocks optical starlight very effectively,” said Robert Gehrz of the University of Minnesota, “but infrared light with its longer wavelength goes right around the dust particles blocking our view. This allows the infrared light from young stars to be seen more clearly.”

But even when the images are taken in the infrared, they are still dominated by the light from the smooth older disks of galaxies, not the faint tracks of young dispersing clusters. Special mathematical manipulations were needed to pick out the clusters, whose faint tracks can still be seen precisely because they are not smooth.

Team member Ivanio Puerari of the Instituto Nacional de Astrofisica, Optica y Electronica in Puebla, Mexico used a technique invented by mathematician Jean Baptiste Fourier in the early 1800’s. The technique is effectively a spatial filter that picks out structure on the physical scale where star formation occurs. “The structures cannot be seen on the original Spitzer images with the human eye,” noted Puerari.

“The combination of the Fourier filtering and infrared images highlighted regions of just the right size and the right age. To then unveil so many star streams in the disks of galaxies was unimaginable a year ago. This discovery continues to highlight the enormous potential of the Spitzer Space Telescope to make contributions none of us could have dreamed possible,” commented Giovanni Fazio from the Harvard-Smithsonian Center for Astrophysics, project leader for the Spitzer Infrared Array Camera team used to take the pictures, and co-author of the discovery.

“Galileo, as both astronomer and mathematician, would have been proud. It is a wonderful interplay between the use of astronomical observations and mathematics and computers, exactly 400 years since Galileo used his telescope to examine our Milky Way galaxy in 1609,” Fazio said

Source: Spitzer

Posted on by Nancy Atkinson

Ancient Solar Systems Found Around Dead Stars

Asteroids Around Dead Stars. Credit: NASA/JPL

[/caption]
Were there once habitable planets long ago around stars that are now dead? A team of astronomers have found evidence that between 1-3 percent of white dwarf stars are orbited by rocky planets and asteroids, suggesting these objects once hosted solar systems similar to our own. White dwarf stars are the compact, hot remnants left behind when stars like our Sun reach the end of their lives. Using data from the Spitzer Space Telescope, an international team of astronomers have determined that asteroids are found in orbit around a large number of white dwarfs, perhaps as many as 5 million in our own Milky Way Galaxy.

The atmospheres of these white dwarf stars should consist entirely of hydrogen and helium but are sometimes found to be contaminated with heavier elements like calcium and magnesium. The new observations suggest that these Earth-sized stars are often polluted by a gradual rain of closely orbiting dust that emits infrared radiation picked up by Spitzer.

Presenting his team’s findings at the European Week of Astronomy and Space Science conference at the University of Hertfordshire, Dr. Jay Farihi of the University of Leicester said that the data from Spitzer suggest that at least 1 in 100 of white dwarf stars are contaminated in this way and that the dust originates from rocky bodies like asteroids (also known as minor planets). In our Solar System, minor planets are the left over building blocks of the rocky terrestrial planets like the Earth.

“In the quest for Earth-like planets, we have now identified numerous systems which are excellent candidates to harbour them,” said Farihi. “Where they persist at white dwarfs, any terrestrial planets will likely not be habitable, but may have been sites where life developed during a previous epoch. “

The new findings indicate the dust is completely contained within the Roche limit of the star — close enough that any object larger than a few kilometers would be ripped apart by gravitational tides (the same phenomenon which led to the creation of Saturn’s rings). This backs up the team’s hypothesis that the dust disks around white dwarfs are produced by tidally disrupted minor planets. In order to pass this close to the white dwarf, an asteroid must be perturbed from its regular orbit further out – and this can occur during a close encounter with as yet unseen planets.

Because white dwarfs descend from main sequence stars like the Sun, the team’s work implies that at least 1% to 3% of main sequence stars have terrestrial planets around them.

Emissions from the White Dwarf System GD 16. Credit: NASA, JPL -Caltech, University of Leicester
Emissions from the White Dwarf System GD 16. Credit: NASA, JPL -Caltech, University of Leicester

Perhaps the most exciting and important aspect of this research is that the composition of these crushed asteroids can be measured using the heavy elements seen in the white dwarf.

Farihi sees this as a crucial step forward. “With high quality optical and ultraviolet observations (e.g. the Hubble Space Telescope), we should be able to measure up to two dozen different elements in debris-polluted white dwarfs. We can then address the question, “Are the rocky extrasolar planets we find similar to the terrestrial planets of our Solar System?”

Source: RAS