Understanding star formation is a key quest in astronomy. Theorists have models for the process, but as with all sciences, observations must be made to support or modify these ideas.

Image right: The Orion Nebula is the most famous stellar nursery in the northern sky. Its young stars are fully mature, while the Perseus region is still at the earliest stages of star formation. (Photo NASA/ESA)

Stars form inside relatively dense concentrations of interstellar gas and dust called molecular clouds. Within such clouds, material roils and bubbles like a boiling soup. For a time, the energy of those turbulent motions supports the cloud against gravitational collapse. Eventually, gravity begins pulling denser parts of the cloud interior together. When the material inside these clumps loses enough internal motion, they condense into cores. These cores then form into protostars.

“The dust and gas molecules have to slow down enough for gravity to begin pulling them together into a protostar,” Pineda says. “So far it has been hard to tell which cloud material is going into a protostar and which material is still too energetic.”

Since the molecular clouds do not shine in visible light, astronomers must use radio and infrared telescopes to make measurements. Using the 100-meter Byrd radio telescope in Green Bank, WV, to map temperature and motion in the cloud, Pineda and other team members have for the first time determined a sharp boundary surrounding a protostar.

“This result lets us define a zone where material inside the boundary is ‘ready to be used’ in the star formation process, while the gas outside the boundary needs to get rid of the turbulence before it can go on to form a star,” says Pineda.

Theory predicts a region around a protostar where the forming star’s gravity is slowing and capturing more and more material from the parent cloud. The actual size and shape of such a region has not been measured or accurately predicted before.

What was completely unknown was whether or not the material made a gradual or abrupt transition into what co-author Alyssa Goodman describes as “islands of calm in a more turbulent sea.”

“The identification of this sharp transition is a major breakthrough in understanding the star formation process,” says Pineda. “Our measurements now give a strong constraint on how these protostellar cores form.”

Because this is the first observation of such a marked transition, it had not previously been described in theory. “Now theorists will need to reproduce our observations in order to keep their models viable,” Pineda says.  –Dan Brocious

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The star in question is known as a white dwarf. When a sun-like star reaches the end of its life, it swells to form a red giant. Its outer layers then puff off, leaving behind a hot core of carbon and oxygen. This white dwarf is very dense, cramming half a sun’s worth of material into a sphere the size of Earth. A teaspoon of white dwarf would weigh more than a ton.

Image right: This artist’s concept shows a white dwarf star surrounded by the bits and pieces of a disintegrating asteroid. Astronomers have found a white dwarf that shredded and gulped down an object the size of Ceres. (NASA/JPL-Caltech/T. Pyle )

An international team of astronomers examined thousands of white dwarfs to look for ones with unusual chemical compositions. They followed up their strangest target with the MMT Observatory in Arizona. This target is located about 440 light-years away in the direction of the constellation Gemini. (A light-year is 6 trillion miles.)

This white dwarf showed strong signs of chemical elements like silicon, magnesium, calcium, and iron – all of which are abundant in rocky planets like Earth. Since a white dwarf’s gravity is so strong (100 thousand times Earth’s gravity), these heavy elements should have sunk out of sight below the surface. Since we can see them, they must have been deposited there relatively recently (in an astronomical sense).

The most likely source is a rocky planet that wandered too close to the white dwarf and got torn apart by tidal forces. The debris settled into a disk around the white dwarf and is raining down onto the star’s surface. Observations from the Gemini Observatory in Hawaii detected this debris disk, confirming the astronomers’ theory.

Judging from the amount of material on the white dwarf and surrounding it, the hapless planet was about the size of Ceres, the largest asteroid in our solar system.

Photo left: The Multiple Mirror Telescope. (Photo by: Howard Lester)

The team also noted that the amount of hydrogen the white dwarf has swallowed is much less than expected. (In our solar system, Ceres contains a significant amount of ice, which would split into hydrogen and oxygen if consumed by a white dwarf.) This suggests that any water or ice the dwarf planet possessed was boiled off long ago by the red giant’s heat.

“There are now more than 450 extrasolar planets known, all of them bigger than Earth, and we don’t really know much about their compositions. Here we’re seeing the remnants of an extrasolar dwarf planet, which gives us a chance to learn about the chemistry of worlds in distant planetary systems,” said Mukremin Kilic of the Smithsonian Astrophysical Observatory.

“White dwarf science is telling us that there are many small planets similar to those in our solar system out there. Since it is not possible to detect such small objects in orbit around other stars with our current technology, studies such as this one offer a unique opportunity to learn about other planetary systems,” added lead author Patrick Dufour of the University of Montreal. –Christine Pulliam

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Image right: Asteroids that cross Earth’s orbit, like the one shown in this artist’s conception, threaten to impact our planet. The new Pan-STARRS observatory offers our first line of defense, surveying huge swaths of the sky every night looking for moving objects. (Artwork by David A. Aguilar)

Pan-STARRS is an all-purpose machine,” said Harvard astronomer Edo Berger. “Having a dedicated telescope repeatedly surveying large areas opens up a lot of new opportunities.”

PS1 has been taking science-quality data for six months, but now we are doing it dusk-to-dawn every night,” says Dr. Nick Kaiser (University of Hawaii Institute for Astronomy, or IfA), the principal investigator of the Pan-STARRS project.

Pan-STARRS will map one-sixth of the sky every month. By casting a wide net, it is expected to catch many moving objects within our solar system. Frequent follow-up observations will allow astronomers to track those objects and calculate their orbits, identifying any potential threats to Earth. PS1 also will spot many small, faint bodies in the outer solar system that hid from previous surveys.

“PS1 will discover an unprecedented variety of Centaurs [minor planets between Jupiter and Neptune], trans-Neptunian objects, and comets. The system has the capability to detect planet-size bodies on the outer fringes of our solar system,” said Smithsonian astronomer Matthew Holman.

Pan-STARRS features the world’s largest digital camera–a 1,400-megapixel (1.4 gigapixel) monster. With it, astronomers can photograph an area of the sky as large as 36 full moons in a single exposure. In comparison, a picture from the Hubble Space Telescope’s WFC3 camera spans an area only one-hundredth the size of the full moon (albeit at very high resolution).

Photograph left: Pan-STARRS PS1 Observatory just before sunrise on Haleakala, Maui. (Photo by Rob Ratkowski)

Its sensitive digital camera was rated as one of the “20 marvels of modern engineering” by Gizmo Watch in 2008. Inventor Dr. John Tonry (IfA) said, “We played as close to the bleeding edge of technology as you can without getting cut!”

Each image, if printed out as a 300-dpi photograph, would cover half a basketball court, and PS1 takes an image every 30 seconds. The amount of data PS1 produces every night would fill 1,000 DVDs.

“As soon as Pan-STARRS turned on, we felt like we were drinking from a fire hose!” said Berger. He added that they are finding several hundred transient objects a month, which would have taken a couple of years with previous facilities.

Located atop the dormant volcano Haleakala, Pan-STARRS exploits the unique combination of superb observing sites and technical and scientific expertise available in Hawaii. Funding for the development of the observing system was provided by the U.S. Air Force.

The PS1 Surveys have been made possible through contributions of the PS1 Science Consortium (PS1SC): IfA; the Pan-STARRS Project Office; the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg, Germany and the Max Planck Institute for Extraterrestrial Physics, Garching, Germany; the Johns Hopkins University; the University of Durham; the University of Edinburgh; the Queen’s University Belfast; the Harvard-Smithsonian Center for Astrophysics; the Los Cumbres Observatory Global Telescope Network, Inc.; and the National Central University of Taiwan.Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

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Image right: In this photograph of the sun taken by the Atmospheric Imaging Assembly on March 30, 2010, the color red shows emission from ionized helium at a temperature of 140,000 Fahrenheit, while green shows ionized iron at a temperature of 1,800,000 F. Credit: NASA.

Launched on Feb. 11, 2010, the observatory is the most advanced spacecraft ever designed to study the sun. During its five-year mission, it will examine the sun’s magnetic field and also provide a better understanding of the role the sun plays in Earth’s atmospheric chemistry and climate.

The observatory carries three state-of the-art instruments for conducting solar research: the Atmospheric Imaging Assembly, the Extreme Ultraviolet Variability Experiment, and the Helioseismic and Magnetic Imager. These three instruments observe the sun simultaneously, performing the entire range of measurements necessary to understand solar variations. The Smithsonian Astrophysical Observatory is a major partner in the Atmospheric Imaging Assembly, which is a group of four telescopes that photograph the sun in 10 different wavelength bands, or colors, once every 10 seconds. Its images will help astronomers link changes in the sun’s surface to interior changes. The Smithsonian Astrophysical Observatory built the four telescope assemblies and participates as a full partner in the scientific analysis activities.

This movie of the March 30, 2010 prominence eruption of the sun, starting with a zoomed in view, was taken by the new Solar Dynamics Observatory. (Video courtesy NASA)

“Everything about the AIA images is cleaner and better than anything we’ve had before. The mirrors are better, the cameras are better and the amount of data available is better. It all combines to give us a view of the corona that we’ve never had before,” said Smithsonian astrophysicist Leon Golub, a co-investigator on the Atmospheric Imaging Assembly.

 SDO is the first mission of NASA’s Living with a Star Program, or LWS, and the crown jewel in a fleet of NASA missions that study our sun and space environment. The goal of LWS is to develop the scientific understanding necessary to address those aspects of the connected sun-Earth system that directly affect our lives and society.

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Recently, the National Institutes of Health recognized the medical potential in a grant proposal written by astrophysicist Eric Silver of the Smithsonian Astrophysical Observatory in Cambridge, Mass. Of 21,000 proposals submitted to the NIH Challenge Program, only 200 received funding. One was Silver’s.

 Photo left: Eric Silver holds a prototype X-ray mirror, which focuses incoming X-rays onto a nearby detector, creating images like the cell shown on the computer screen. (Click to enlarge)

Silver is pursuing innovative and interdisciplinary uses of his technique for chemical imaging at the cellular level. Practical benefits may someday come from the prototype instrument he and his colleagues have developed–a combination X-ray detector and electron microscope that will make chemical maps of living cells.

 “We are adapting techniques from X-ray astronomy for use in down-to-Earth applications,” Silver says.

 An X-ray is a type of very energetic light. Cosmic X-rays are produced by violent phenomena such as exploding stars, which blast out gases heated to millions of degrees. Astronomers detect X-rays with instruments like those on board the Chandra X-ray Observatory, some of which can determine the composition of the hot gas.

Photo right: This electron microscope image of a single cancer cell shows it scale in microns (millionths of a meter).

Silver recognized that the technologies used to study giant supernova remnants and other X-ray-emitting celestial objects, could also be used to examine cells chemically.

 The secret is to unite an electron microscope with a sensitive X-ray detector. Silver’s detector can simultaneously distinguish one chemical element from another more capably than any other instrument.

 In his technique, an electron microscope bombards a cell sample with negatively charged, subatomic particles. Chemical elements within the cell react by emitting X-rays, which are collected to form an image of the cell. Since different chemical elements emit X-rays of different energies, Silver can map the composition of the cell with higher precision than was possible previously.

 Silver is particularly interested in studying cancer cells in hopes that the information gained will help improve treatments. His technique should show how chemotherapy affects cancer by letting researchers see exactly where anti-cancer drugs go within cells. It may also distinguish between healthy and diseased cells.

Image right:  This photograph of Tycho’s supernova remnant combines X-ray data (yellow, green, blue) from Chandra with infrared data (red) from the Spitzer Space Telescope. They are overlaid on an optical image (white stars) of the surrounding sky.

“The goal is to better understand the cell chemistry and metabolism, which could contribute to cancer diagnostics and possibly treatment,” says Silver.

 Silver’s prototype has applications in other fields of research. For example, he has analyzed flakes of rock from the Allende meteorite. He also anticipates studying motes of comet dust from NASA’s Stardust mission, and archaeological artifacts and fine art objects in collaboration with scientists at the Smithsonian’s Museum Conservation Institute and National Museum of Natural History.

 “As you can see, this new interdisciplinary tool is finding many uses,” Silver says. –Christine Pulliam

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Our telescopes show the Milky Way galaxy only as it appears from one vantage point: our solar system. Now, using a simple but powerful technique, a group of astronomers led by Armin Rest of Harvard University has seen an exploding star or supernova from several angles.

Image right: In this Chandra X-ray Observatory image of the supernova remnant Cassiopeia A , the red, green, and blue regions in this image show where the intensity of low, medium, and high-energy X-rays, respectively, is greatest.

“The same event looks different from different places in the Milky Way,” Rest says. ”For the first time, we can see a supernova from an alien perspective.”

The supernova left behind the gaseous remnant Cassiopeia A. The supernova’s light washed over the Earth about 330 years ago. But light that took a longer path, reflecting off clouds of interstellar dust, is just now reaching us. This faint, reflected light is what the astronomers have detected.

Image left: Three light echoes from the  Cassiopeia A supernova are shown here in three rows. For each row, the left panel is a reference image while the middle panel shows the same field of view at a later time. Right panels show the difference between the two previous shots, highlighting the (changing) light echo. The position and size of the spectroscopy slit is indicated by the rectangular overlay. For all images, north is up and east is to the left.

The technique is based on the familiar concept of an echo, but applied to light instead of sound. If you yell, “Echo!” in a cave, sound waves bounce off the walls and reflect back to your ears, creating echoes. Similarly, light from the supernova reflects off interstellar dust to the Earth. The dust cloud acts like a mirror, creating light echoes that come from different directions depending on where the clouds are located.

“Just like mirrors in a changing room show you a clothing outfit from all sides, interstellar dust clouds act like mirrors to show us different sides of the supernova,” Rest explains.

Moreover, an audible echo is delayed since it takes time for the sound waves to bounce around the cave and back. Light echoes also are delayed by the time it takes for light to travel to the dust and reflect back. As a result, light echoing from the supernova can reach us hundreds of years after the supernova itself has faded away.

Not only do light echoes give astronomers a chance to directly study historical supernovae, they also provide a 3-D perspective since each echo comes from a spot with a different view of the explosion.

Most people think a supernova is like a powerful fireworks blast, expanding outward in a round shell that looks the same from every angle. But by studying the light echoes, the team discovered that one direction in particular looked significantly different than the others.

They found signs of gas from the stellar explosion streaming toward one point at a speed almost 9 million miles per hour (2,500 miles per second) faster than any other observed direction.

“This supernova was two-faced!” said Smithsonian co-author and Clay Fellow Ryan Foley. “In one direction the exploding star was blasted to a much higher speed.”

By combining the new light-echo measurements and the movement of the neutron star with X-ray data on the supernova remnant, astronomers have assembled a 3-D perspective, giving them new insight into the Cas A supernova.

“Now we can connect the dots from the explosion itself, to the supernova’s light, to the supernova remnant,” said Foley.

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Image right: A moasic photo of part of the Moon’s southern Mare Serenitatis showing wrinkle ridges.

This new book is a primer on the many different surface features that exist on the planets  in our solar system, the internal and external forces that created these features and what they reveal about the conditions on the planets where they are found. From the wrinkle ridges of the moon, to the surface grooves of an asteroid or the fracture belts of Venus, Planetary Tectonics is a studious look at the complex interplay of powerful forces that act upon planetary crusts and the mechanical properties of the crusts themselves.

The number and diversity of tectonic landforms in our solar system “is truly remarkable,” Watters and Schultz write in the preface of their book. Photographs of these structures have stimulated a range of scholarly investigations, “from the characterization and modeling of individual classes of tectonic landforms to the assessment of regional and global tectonic systems,” the scientists write. Planetary Tectonics is an overview of the major themes of this research as they relate to each planet and small body. The book contains methods for mapping and analyzing planetary tectonic features and is illustrated with many diagrams and spectacular images. Planetary Tectonics, which is extensively referenced, provides a springboard to other sources of information, and is an essential reference for researchers and students alike. Published by Cambridge University Press, additional information about this new volume can be accessed at the Web address: www.cambridge.org/catalogue/catalogue.asp?isbn=9780521765732

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A team of astronomers led by Gijs Roefols of the Harvard-Smithsonian Center for Astrophysics recently examined this pair of stars known to astronomers as RX J0806.3+1527 or, HM Cancri. The two stars are both white dwarfs—the hot cores of dead, sun-like stars. They squeeze as much mass as half our Sun into a globe the size of the Earth. A teaspoon of white dwarf material would weigh about five tons.

This artist’s video depicts a pair of white dwarf stars known as HM Cancri, swirling closer together, traveling in excess of a million miles per hour. As their orbit gets smaller and smaller, leading up to a merger, the system should release more and more energy in gravitational waves. This pair of stars might have the smallest orbit of any known binary system. They complete an orbit in 321.5 seconds–just over five minutes.
(Credit: GSFC/D.Berry)

Scientists knew HM Cancri’s brightness varied on a five-minute timescale, but debated whether that variation was due to a tight orbit or other causes. In-depth studies were difficult because HM Cancri is very faint: about a million times fainter than what can be seen with the unaided eye. The team used the giant 30-foot Keck I telescope in Hawaii to gather enough light to confirm that the varying brightness was due to the speedy orbit of these two stars.

The stars move quickly because they are very close to each other, separated by only about one-fourth the distance from the Earth to the Moon. As a result, they share strong gravitational forces. They were once farther apart but have spiraled closer together over time. Billions of years from now, they will crash together and merge.

The stars drag together because they are gradually losing energy. Einstein’s General Theory of Relativity predicts that they are emitting gravitational waves, or ripples in the fabric of space-time. Those ripples carry energy away from the system, as shown in the artist’s conception accompanying this articles.

Future observatories like the proposed Laser Interferometer Space Antenna should somedy be able to detect gravitational waves coming from HM Cancri.

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Image right: The newly discovered red giant star S1020549 dominates this artist’s conception. The primitive star contains 6,000 times less heavy elements than our Sun, indicating that it formed very early in the history of the Universe. (Image credit: David Aguilar/CfA)

“This star likely is almost as old as the Universe itself,” says Smithsonian astronomer Anna Frebel.

Scientists think that our Milky Way galaxy grew to its current size by swallowing many such mini-galaxies over billions of years. (In general, most galaxies are believed to form this way.) The newfound star supports this theory because its chemical make-up is very similar to the Milky Way’s oldest stars.

Finding this stellar relic wasn’t easy. It is 60,000 times dimmer than the faintest star visible to the unaided eye. The team also had to distinguish it from many surrounding stars that aren’t so old. Just like an archaeological dig, the hunt succeeded through a combination of patience and clever use of technology.

“This was harder than finding a needle in a haystack. We needed to find a needle in a stack of needles,” says astronomer Evan Kirby of the California Institute of Technology, developer of the search technique. “We sorted through hundreds of candidates to find our target.”

Video: In this computer simulation, dwarf galaxies swarm like bees around a beehive, crashing together to form a large spiral galaxy similar to our Milky Way.
(Video credit: Fabio Governato/University of Washington)

Once located, the star was studied in detail. Astronomers determined that it contained 6,000 times less “metals” than our Sun. (To astronomers, “metals” are chemical elements heavier than hydrogen or helium.) Because metals are produced by stars and grow in abundance over time, they were rare in the early Universe, so old stars tend to be metal-poor.The oldest and most metal-poor stars in the Milky Way reside in a spherical halo that surrounds the galactic center, extending for thousands of light-years in all directions. (A light-year is 6 trillion miles.) Finding a similar star in a nearby miniature, or dwarf, galaxy supports the idea that large galaxies attain their size by absorbing their smaller neighbors.

“If you watched a time-lapse movie of our galaxy, you would see a swarm of dwarf galaxies buzzing around it like bees around a beehive,” Frebel explains. “Over time, those galaxies smashed together and mingled their stars to make one large galaxy–the Milky Way.”

The researchers expect that further searches will discover additional metal-poor stars in dwarf galaxies, although the distance and faintness of the stars pose a challenge for current telescopes. The next generation of extremely large optical telescopes, such as the proposed 24.5-meter Giant Magellan Telescope, will open up a new window for studying the growth of galaxies through the chemistries of their stars. –Christine Pulliam

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These supernovae, called Type Ia, serve as cosmic mile markers to measure expansion of the universe because they can be seen at large distances, and they follow a reliable pattern of brightness. However, until now, scientists have been unsure what actually causes the explosions.

This NASA/Chandra X-ray Observatory animation shows two white dwarf stars merging into a supernova.

“These are such critical objects in understanding the universe,” said Marat Gilfanov of the Max Planck Institute for Astrophysics in Germany and lead author of the study that appears in the Feb. 18 edition of the journal Nature. “It was a major embarrassment that we did not know how they worked. Now we are beginning to understand what lights the fuse of these explosions.”

Most scientists agree a Type Ia supernova occurs when a white dwarf star—a collapsed remnant of an elderly star—exceeds its weight limit, becomes unstable and explodes. Scientists have identified two main possibilities for pushing the white dwarf over the edge: two white dwarfs merging or accretion, a process in which the white dwarf pulls material from a sun-like companion star until it exceeds its weight limit.

Image left: X-ray, optical and infrared composite image of galaxy M32, one of six galaxies used in a study to examine properties of Type Ia supernovas

Because these two scenarios would generate different amounts of X-ray emission, Gilfanov and Bogdan used Chandra to observe five nearby elliptical galaxies and the central region of the Andromeda galaxy. A Type 1a supernova caused by accreting material produces significant X-ray emission prior to the explosion. A supernova from a merger of two white dwarfs, on the other hand, would create significantly less X-ray emission than the accretion scenario.

The scientists found the observed X-ray emission was a factor of 30 to 50 times smaller than expected from the accretion scenario, effectively ruling it out. This implies that white dwarf mergers dominate in these galaxies.

“Our results suggest the supernovae in the galaxies we studied almost all come from two white dwarfs merging,” said co-author Akos Bogdan, also of Max Planck. “This is probably not what many astronomers would expect.”

“To many astrophysicists, the merger scenario seemed to be less likely because too few double-white-dwarf systems appeared to exist,” said Gilfanov. “Now this path to supernovae will have to be investigated in more detail.”

NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra’s science and flight operations from Cambridge, Mass.

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