Category: Astronomy

Polaris with its faint companions. Image credit: Greg Bacon (STScI) Click to enlarge
We tend to think of the North Star, Polaris, as a steady, solitary point of light that guided sailors in ages past. But there is more to the North Star than meets the eye – two faint stellar companions. The North Star is actually a triple star system. And while one companion can be seen easily through small telescopes, the other hugs Polaris so tightly that it has never been seen directly – until now.

By stretching the capabilities of NASA’s Hubble Space Telescope to the limit, astronomers have photographed the close companion of Polaris for the first time. They presented their findings today in a press conference at the 207th meeting of the American Astronomical Society in Washington, DC.

“The star we observed is so close to Polaris that we needed every available bit of Hubble’s resolution to see it,” said Smithsonian astronomer Nancy Evans (Harvard-Smithsonian Center for Astrophysics).

The companion proved to be less than two-tenths of an arcsecond from Polaris – an incredibly tiny angle equivalent to the apparent diameter of a quarter located 19 miles away. At the system’s distance of 430 light-years, that translates into a physical separation of about 2 billion miles.

“The brightness difference between the two stars made it even more difficult to resolve them,” stated Howard Bond of the Space Telescope Science Institute (STScI). Polaris is a supergiant more than two thousand times brighter than the Sun, while its companion is a main-sequence star. “With Hubble, we’ve pulled the North Star’s companion out of the shadows and into the spotlight.”

By watching the motion of the companion star, Evans and her colleagues expect to learn not only the stars’ orbits but also their masses. Measuring the mass of a star is one of the most difficult tasks facing stellar astronomers.

Astronomers want to determine the mass of Polaris accurately because it is the nearest Cepheid variable star. Cepheids are used to measure the distance to galaxies and the expansion rate of the universe, so it is essential to understand their physics and evolution. Knowing their mass is the most important ingredient in this understanding.

“Studying binary stars is the best available way to measure the masses of stars,” said science team member Gail Schaefer of STScI.

“We only have the binary stars that nature provided us,” added Bond. “With the best instruments like Hubble, we can push farther into space and study more of them up close.”

The researchers plan to continue observing the Polaris system for several years. In that time, the movement of the small companion in its 30-year orbit around the primary should be detectable.

“Our ultimate goal is the get an accurate mass for Polaris,” said Evans. “To do that, the next milestone is to measure the motion of the companion in its orbit.”

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.

Original Source: CfA News Release

The Milky Way galaxy. Image credit: Serge Brunier. Click to enlarge
The most prominent of the Milky Way’s satellite galaxies – a pair of galaxies called the Magellanic Clouds – appears to be interacting with the Milky Way’s ghostly dark matter to create a mysterious warp in the galactic disk that has puzzled astronomers for half a century.

The warp, seen most clearly in the thin disk of hydrogen gas permeating the galaxy, extends across the entire 200,000-light year diameter of the Milky Way, with the sun and earth sitting somewhere near the crease. Leo Blitz, professor of astronomy at the University of California, Berkeley, and his colleagues, Evan Levine and Carl Heiles, have charted this warp and analyzed it in detail for the first time, based on a new galactic map of hydrogen gas (HI) emissions.

They found that the atomic gas layer is vibrating like a drum, and that the vibration consists almost entirely of three notes, or modes.

Astronomers previously dismissed the Magellanic Clouds – comprised of the Large and Small Magellanic Clouds – as a probable cause of the galactic warp because the galaxies’ combined masses are only 2 percent that of the disk. This mass was thought too small to influence a massive disk equivalent to about 200 billion suns during the clouds’ 1.5 billion-year orbit of the galaxy.

Nevertheless, theorist Martin D. Weinberg, a professor of astronomy at the University of Massachusetts, Amherst, teamed up with Blitz to create a computer model that takes into account the Milky Way’s dark matter, which, though invisible, is 20 times more massive than all visible matter in the galaxy combined. The motion of the clouds through the dark matter creates a wake that enhances their gravitational influence on the disk. When this dark matter is included, the Magellanic Clouds, in their orbit around the Milky Way, very closely reproduce the type of warp observed in the galaxy.

“The model not only produces this warp in the Milky Way, but during the rotation cycle of the Magellanic Clouds around the galaxy, it looks like the Milky Way is flapping in the breeze,” said Blitz, director of UC Berkeley’s Radio Astronomy Laboratory.

“People have been trying to look at what creates this warp for a very long time,” Weinberg said. “Our simulation is still not a perfect fit, but it has a lot of the character of the actual data.”

Levine, a graduate student, will present the results of the work in Washington, D.C., on Jan. 9 during a 10 a.m. session on galactic structure at the American Astronomical Society meeting. Blitz will summarize the work later that day during a 12:30 p.m. press briefing in the Wilson C Room of the Marriott Wardman Park Hotel.

The interaction of the Magellanic Clouds with the dark matter in the galaxy to produce an enigmatic warp in the hydrogen gas layer is reminiscent of the paradox that led to the discovery of dark matter some 35 years ago. As astronomers built better and better telescopes able to measure the velocities of stars and gas in the outer regions of our galaxy, they discovered these stars moving far faster than would be expected from the observed number and mass of stars in the entire Milky Way. Only by invoking a then-heretical notion, that 80 percent of the galaxy’s mass was too dark to see, could astronomers reconcile the velocities with known theories of physics.

Though no one knows the true identity of this dark matter – the current consensus is that it is exotic matter rather than normal stars too dim to see – astronomers are now taking it into account in their simulations of cosmic dynamics, whether to explain the lensing effect galaxies and galaxy clusters have on the light from background galaxies, or to describe the evolution of galaxy clusters in the early universe.

Some physicists, however, have come up an alternative theory of gravity called Modified Newtonian Dynamics, or MOND, that seeks to explain these observations without resorting to belief in a large amount of undetected mass in the universe, like an invisible elephant in the room. Though MOND can explain some things, Weinberg thinks the theory will have a hard time explaining the Milky Way’s warp.

“Without a dark matter halo, the only thing the gas disk can feel is direct gravity from the Magellanic Clouds themselves, which was shown in the 1970s not to work,” he said. “It looks bad for MOND, in this case.”

Because many galaxies have warped disks, similar dynamics might explain them as well. Either way, the researchers say their work suggests that warps provide a way to verify the existence of the dark matter.

The starting point for this research was new spectral data released this past summer about hydrogen’s 21-centimeter emissions in the Milky Way. The survey, the Leiden-Argentina-Bonn or LAB Survey of Galactic HI, merged a northern sky survey conducted by astronomers in the Netherlands (the Leiden/Dwingeloo Survey) with a southern sky survey from the Instituto Argentino de Radioastronom?a. The data were corrected by scientists at the Institute for Radioastronomy of the University of Bonn, Germany.

Blitz, Levine and Heiles, UC Berkeley professor of astronomy, took these data and produced a new, detailed map of the neutral atomic hydrogen in the galaxy. This hydrogen, distributed in a plane with dimensions like those of a compact disk, eventually condenses into molecular clouds that become stellar nurseries.

With map in hand, they were able to mathematically describe the warp as a combination of three different types of vibration: a flapping of the disk’s edge up and down, a sinusoidal vibration like that seen on a drumhead, and a saddle-shaped oscillation. These three “notes” are about 3 million octaves below middle C.

“We found something very surprising, that we could describe the warp by three modes of vibration, or three notes, and only three,” Blitz said, noting that this rather simple mathematical description of the warp had escaped the notice of astronomers since the warp’s discovery in 1957.

“We were actually trying to analyze a more complex ‘scalloping’ structure of the disk, and this simple, elegant vibrational structure just popped out,” Levine added.

The current warp in the gas disk is a combination of these three vibrational modes, leaving one-half of the galactic disk sticking up above the plane of stars and gas, while the other half dips below the disk before rising upward again farther outward from the center of the galaxy. The results of this analysis will be published in an upcoming issue of the Astrophysical Journal.

Weinberg thought he could explain the observed warp dynamically, and used computers to calculate the effect of the Magellanic Clouds orbiting the Milky Way, plowing through the dark matter halo that extends far out into the orbit of the clouds.

What he and Blitz found is that the clouds’ wake through the dark matter excites a vibration or resonance at the center of the dark matter halo, which in turn makes the disk embedded in the halo oscillate strongly in three distinct modes. The combined motion during a 1.5-billion-year orbit of the Magellanic Clouds is reminiscent of the edges of a tablecloth flapping in the wind, since the center of the disk is pinned down.

“We often think of the warp as being static, but this simulation shows that it is very dynamic,” Blitz said.

Blitz, Levine and Heiles are continuing their search for anomalies in the structure of the Milky Way’s disk. Weinberg hopes to use the UC Berkeley group’s data and analysis to determine the shape of the dark matter halo of the Milky Way.

The research of the UC Berkeley group is supported by the National Science Foundation. Weinberg is partly supported by NASA and the NSF.

Original Source: UC Berkeley News Release

Superbubble complex N44 as imaged with GMOS. Image credit: University of Alaska Anchorage. Click to enlarge
Known as the N44 superbubble complex, this cloudy tempest is dominated by a vast bubble about 325 by 250 light-years across. A cluster of massive stars inside the cavern has cleared away gas to form a distinctive mouth-shaped hollow shell. While astronomers do not agree on exactly how this bubble has evolved for up to the past 10 million years, they do know that the central cluster of massive stars is responsible for the cloud’s unusual appearance. It is likely that the explosive death of one or more of the cluster’s most massive and short-lived stars played a key role in the formation of the large bubble.

“This region is like a giant laboratory providing us with a glimpse into many unique phenomena,” said Sally Oey of the University of Michigan, who has studied this object extensively. “Observations from space have even revealed x-ray-emitting gas escaping from this superbubble, and while this is expected, this is the only object of its kind where we have actually seen it happening.”

One of the mysteries surrounding this object points to the role that supernova explosions (marking the destruction of the most massive of the central cluster’s stars) could have played in sculpting the cloud. Philip Massey of Lowell Observatory, who studied this region along with Oey, adds “When we look at the speed of the gases in this cloud we find inconsistencies in the size of the bubble and the expected velocities of the winds from the central cluster of massive stars. Supernovae, the ages of the central stars, or the orientation and shape of the cloud might explain this, but the bottom line is that there’s still lots of exciting science to be done here and these new images will undoubtedly help.”

The Gemini data used to produce this image are being released to the astronomical community for further research and follow-up analysis. Note to astronomers: Data can be found at the Gemini Science Archive by querying “NGC 1929”. The image provides one of the most detailed views ever obtained of this relatively large region in the Large Magellanic Cloud, a satellite galaxy to the Milky Way, located some 150,000 light-years away and visible from the Southern Hemisphere. The images captured light of specific colors that reveal the compression of material and the presence of gases (primarily excited hydrogen gas and lesser amounts of oxygen and “shocked” sulfur) in the cloud.

Multiple smaller bubbles appear in the image as bulbous growths clinging to the central superbubble. Most of these regions were probably formed as part of the same process that shaped the central cluster. Their formation could also have been “sparked” by compression as the central stars pushed the surrounding gas outward. Our view into this cavern could really be like looking through an elongated tube, which lends the object its monstrous mouth-like appearance.

The images used to produce the color composite were obtained with the Gemini Multi-object Spectrograph (GMOS) at the Gemini South Telescope on Cerro Pachon in Chile. The color image was produced by Travis Rector of the University of Alaska Anchorage and combines three single-color images to produce the image.

Original Source: Gemini Observatory

An artist’s illustartion of the sequence of radioactive decay that gives out gamma rays. Image credit: MPE Click to enlarge
Using ESA’s Integral observatory, an international team of researchers has been able to confirm the production of radioactive aluminium (Al 26) in massive stars and supernovae throughout our galaxy and determine the rate of supernovae – one of its key parameters.

The team, led by Roland Diehl of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, determined that gamma rays from the decay of Al 26 originate from the central regions of our galaxy, implying that production of new atomic nuclei is an ongoing process and occurs in star-forming regions galaxy-wide.

Our environment is composed of chemical elements formed long ago by nuclear fusion reactions in stellar interiors and supernovae. This process of ‘nucleosynthesis’ leads to the emission of gamma rays, which easily reach us from all regions of our galaxy. ESA’s Integral observatory has been measuring such gamma rays since October 2002.

Roland Diehl and his colleagues were able to measure the Al 26 gamma-ray emissions along the plane of the inner galaxy.

However, because the disc of the galaxy rotates about its central axis, with the inner regions orbiting faster, gamma rays from decaying Al 26 observed from these regions should be moderated by the Doppler effect in a characteristic way. It is this characteristic pattern that has been found by Integral.

From this measurement, the team found that Al 26 decay gamma rays do indeed reach us from the inner regions of the galaxy, rather than from foreground regions along the same line of sight possibly caused by local and peculiar Al 26 production. These regions would not have the observed high relative velocity.

From these new observations, it is possible to estimate the total amount of radioactive Al 26 in our galaxy as is equivalent to three solar masses. This is a lot, given that Al 26 is an extremely rare isotope; the fraction estimated for the early Solar System is 5/100 000 of Al 26, in proportion to its stable aluminium isotope (Al 27).

Because astrophysicists had inferred that the likely sources are mainly massive stars, which end their lives as supernovae, they could estimate the rate of such supernova events. They obtained a rate of one supernova every 50 years – consistent with what had been indirectly found from observations of other galaxies and their comparison to the Milky Way.

Integral’s study of gamma rays will continue to operate for several more years. Astrophysicists hope to increase the precision of such measurements. Project leader Roland Diehl said, “These gamma-ray observations provide insights about our home galaxy, which are difficult to obtain at other wavelengths due to interstellar absorption.”

Original Source: ESA Portal

An artist’s impression of the dusty disk orbiting IRS 46. Image credit: NASA/JPL-Caltech Click to enlarge
Astronomers at W. M. Keck Observatory have found ??bf? for the first time ??bf? some of the basic compounds necessary to build organic molecules and one of the bases found in DNA within the inner regions of a planet-forming disk. The object, known as “IRS 46,” is located in the Milky Way galaxy, about 375 light years from Earth, in the constellation Ophiuchus. The results will be published in an upcoming issue of the Astrophysical Journal Letters.

“We see prebiotic organic molecules in comets and the gas giant planets in our own solar system and wonder, where did these chemicals come from?” said Dr. Marc Kassis, support astronomer at the W. M. Keck Observatory. “The Spitzer Space Telescope is letting us study these young stellar objects in new and revealing ways, giving us exciting clues about where life may form in the universe.”

The two organic compounds found — acetylene and hydrogen cyanide — are commonly found in our own solar system, such as the atmospheres of the giant gas planets, the icy surfaces of comets, and the atmosphere of Saturn??bf?s largest moon, Titan. Another carbon-containing species detected, carbon dioxide, is widespread in the atmospheres of Venus, the Earth, and Mars.

“If you add hydrogen cyanide, acetylene and water together in a test tube, and give them an appropriate surface on which to be concentrated and react, you’ll get a slew of organic compounds including amino acids and a DNA purine base called adenine,” said Keck Astronomer Dr. Geoffrey Blake, of the California Institute of Technology in Pasadena and co-author of the paper. “Now, we can detect these same molecules in the planet zone of a star hundreds of light-years away.”

The presence of gas-rich disks around young stars is well known, but little is understood about the chemical structure inside. The discovery of acetylene and hydrogen cyanide in one of these disks will help astronomers better understand these disks, where future solar systems may someday form and possibly result in life.

“Spitzer found something very unique — a young protostar with a dusty disk that, when viewed from Earth, appears tilted on the sky, similar to how some galaxies appear,” Kassis explained. “This viewing angle let the team use Keck-NIRSPEC data to study the inner regions of the disk. The results told the team exactly how the disk was moving and suggest there may be a stellar wind coming from the inner region. Keck also helped measure the high temperatures and the particle concentration in the disk.”

The dust and gas surrounding a young star blocks visible light, but lets longer wavelengths, such as infrared light, pass through. Astronomers can find out what this gas and dust is made of by separating the light into its component wavelengths, or colors.

Since 2003, the NASA Spitzer Space Telescope has allowed astronomers to use this technique to study molecular compounds in protoplanetary disks of young stellar objects. The Spitzer “c2d legacy program” has looked at more than 100 sources in five nearby star-forming regions and only one ??bf? IRS 46 ??bf? showed clear evidence of containing the organic compounds in the warm regions close to the star where terrestrial planets are most likely to form.

“This infant system might look a lot like ours did billions of years ago, before life arose on Earth,” said Fred Lahuis of Leiden Observatory in the Netherlands and the SRON Netherlands Institute for Space Research. Lahuis is the lead author of the paper describing the results.

While the precise events leading up to self-replicating nucleic acids remains unclear, the molecules of acetylene (C2H2) and hydrogen cyanide (HCN) have been shown to produce the base compounds necessary to build RNA and DNA. The team found that the abundance of hydrogen cyanide (HCN) was nearly 10,000 times higher than that found in cold interstellar gas from which stars and planets are born.

Models of early solar-system chemistry have historically centered on data from our own primitive solar system, but now discoveries of protoplanetary disks have opened the field to solar systems other than our own. Theoretical models have suggested that large quantities of complex organic molecules would be present in the inner-most regions of these disks, but until now, no observational tests have been possible.

To help determine where, exactly, the organic-rich gas resides in IRS 46, the team also used submillimeter data from the James Clerk Maxwell Telescope on Mauna Kea. The faint signals observed again suggest that the material originates from the inner disk, perhaps no more 10 astronomical units from the parent star, similar in distance to where Saturn orbits the Sun in our own solar system. However, much additional work remains to be done to know this for certain.

“The gases are very warm, close to or somewhat above the boiling point of water on Earth,” said Dr. Adwin Boogert, also of Caltech. “These high temperatures helped to pinpoint the location of the gases in the disk.”

The Keck-NIRSPEC results point to the presence of a stellar wind emerging from the inner region of the disk orbiting IRS 46. The wind may eventually blow away the dusty debris in the disk, perhaps revealing the presence of rocky, Earth-like planets in several million years.

The Jet Propulsion Laboratory manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech. JPL is a division of Caltech.

The W. M. Keck Observatory is managed by the California Association for Research in Astronomy, a non-profit 501 (c) (3) corporation. The Keck I and Keck II 10-meter telescopes probe the faintest objects in the optical and infrared Universe.

Original Source: W. M. Keck Observatory

Composite Image of Geminga. Image credit: XMM-Newton Click to enlarge
A team led by Dr. Patrizia Caraveo of the Italian National Institute for Astrophysics (INAF) in Milan discovered this cometary trail with data from NASA’s Chandra X-ray Observatory Archive. The discovery follows the team’s discovery in 2003 using ESA’s XMM-Newton of Geminga’s twin X-ray tails stretching for billions of chilometers.

Together, these observations provide unique insight into the contents and density of the interstellar “ocean” Geminga is plowing through, as well as the physics of Geminga itself. Not only is Geminga close, only about 500 light years from Earth, it is cutting across our line of sight, offering a spectacular view of a pulsar in motion.

“Geminga is the only isolated pulsar we know of showing both a small comet-like trail and a larger tail structure,” said Dr. Andrea De Luca of INAF’s Istituto di Astrofisica Spaziale e Fisica Cosmica, lead author on an article about this discovery in Astronomy and Astrophysics. “This jettison from Geminga’s journey through interstellar space provides unprecedented information about the physics of pulsars.”

A pulsar is a type of rapidly spinning neutron star that emits steady pulses of radiation with each rotation, funnelled along strong magnetic field lines, much like a lighthouse beam sweeping across space. A neutron star is the core remains of an exploded star once at least eight times as massive as the sun.

These dense stars, only about 20 kilometers across, still contain roughly the mass of the sun. Neutron stars contain the densest material known. Like many neutron stars, Geminga got a “kick” from the explosion that created it and has been flying through space like a cannonball ever since.

De Luca said that Geminga’s complex phenomenology of tails and a trail must be from high-energy electrons escaping the pulsar magnetosphere following paths clearly driven by the pulsar??bf?s motion in the interstellar medium.

Most pulsars emit radio waves. Yet Geminga is “radio quiet” and was discovered 30 years ago as a unique “gamma-ray only” source (only later was Geminga seen in the X-ray and optical light wavebands). Geminga generates gamma rays by accelerating electrons and positrons, a type of antimatter, to high speeds as it spins like a dynamo four times per second.

“Astronomers have known that only a fraction of these accelerated particles produce gamma rays, and they have wondered what happens to the remaining ones,” said Caraveo, a co-author on the Astronomy & Astrophysics article. “Thanks to the combined capabilities of Chandra and XMM-Newton, we now know that such particles can escape. Once they reach the shock front, created by the supersonic motion of the star, the particles lose their energy radiating X-rays.”

Meanwhile, an equal number of particles (with a different electric charge) should move in the opposite direction, aiming back at the star. Indeed, when they hit the star’s crust they create tiny hotspots, which have been detected through their varying X-ray emission.

The next generation of high-energy gamma-ray instruments – namely, the planned Italian Space Agency’s AGILE mission and NASA’s GLAST mission – will explore the connection between the X-ray and gamma ray behaviour of pulsars to provide clues to the nature of unknown gamma-ray sources, according to Prof. Giovanni Bignami, a co-author and director of the Centre d’Etude Spatiale des Rayonnements (CESR) in Toulouse, France. Of the 271 higher-energy gamma-ray objects detected by a NASA telescope called EGRET, 170 remained unidentified in other wavebands. These unidentified objects could be “gamma-ray pulsars” like Geminga, whose optical and X-ray light might be visible only because of its nearness to Earth.

Only about a dozen other radio-quiet isolated neutron stars are known, and Geminga is the only one with tails and trails and copious gamma-ray emission. Bignami named Geminga for “Gemini gamma-ray source” in 1973. In his local Milan dialect, the name is a pun on “ghe minga,” which means “it is not there.” Indeed, Geminga was unidentified in other wavelengths until 1993, twenty years after its discovery.

The discovery team also includes Drs. Fabio Mattana and Alberto Pellizzoni of the INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica.

Original Source: INAF News Release

NGC 2467 and Surroundings. Image credit: ESO Click to enlarge
Just like Charles Dickens’ Christmas Carol takes us on a journey into past, present and future in the time of only one Christmas Eve, two of ESO’s telescopes captured various stages in the life of a star in a single image.

ESO’s first image shows the area surrounding the stellar cluster NGC 2467, located in the southern constellation of Puppis (“The Stern”). With an age of a few million years at most, it is a very active stellar nursery, where new stars are born continuously from large clouds of dust and gas.

The image, looking like a colourful cosmic ghost or a gigantic celestial Mandrill, contains the open clusters Haffner 18 (centre) and Haffner 19 (middle right: it is located inside the smaller pink region – the lower eye of the Mandrill), as well as vast areas of ionised gas.

The bright star at the centre of the largest pink region on the bottom of the image is HD 64315, a massive young star that is helping shaping the structure of the whole nebular region.

The first image was taken with the Wide-Field Imager camera at the 2.2m MPG/ESO telescope located at La Silla, in Chile.

Another image of the central part of this area is shown in ESO’s second image. It was obtained with the FORS2 instrument at ESO’s Very Large Telescope on Cerro Paranal, also in Chile.

NGC 2467 and Surroundings. Image credit: ESO Click to enlarge
However, the second image zooms in on the open stellar cluster Haffner 18, perfectly illustrating three different stages of this process of star formation: In the centre of the picture, Haffner 18, a group of mature stars that have already dispersed their birth nebulae, represents the completed product or immediate past of the star formation process. Located at the bottom left of this cluster, a very young star, just come into existence and, still surrounded by its birth cocoon of gas, provides insight into the very present of star birth. Finally, the dust clouds towards the right corner of the image are active stellar nurseries that will produce more new stars in the future.

Haffner 18 contains about 50 stars, among which several short lived, massive ones. The massive star still surrounded by a small, dense shell of hydrogen, has the rather cryptic name of FM3060a. The shell is about 2.5 light-years wide and expands at a speed of 20 km/s. It must have been created some 40,000 years ago. The cluster is between 25,000 and 30,000 light-years away from us.

Original Source: ESO News Release

NGC 2264, the Cone Nebula and Christmas Tree Cluster. Image credit: NASA/JPL-Caltech. Click to enlarge
Astronomers using NASA’s Spitzer Space Telescope have given the world a spectacular new picture of a star-forming region called the “Christmas Tree Cluster,” complete with first-ever views of a group of newborn stars still linked to their siblings.

Spitzer’s cameras are very sensitive to the infrared (heat), allowing astronomers to see through the obscuring gas and dust of the star-forming cloud that swaddles infant stars.

The Christmas Tree Cluster, also known as NGC 2264, is a well-studied region in the Monoceros (the Unicorn) constellation. The Christmas Tree Cluster was so named because it looks like a tree in visible light. The nebula is roughly 2,500 light-years away. That is, the nebula emitted the light in the new Spitzer image 2,500 years ago.

For astronomers studying the development of very young stars — stars less than a few million years old — “This region has it all,” said University of Arizona astronomer Erick T. Young.

“We see the dramatic-looking emission of cold gas — clouds that look like thunderheads. We see when the massive molecular cloud breaks up and begins to condense into clumps of stars,” Young said. “And, for the first time, because of Spitzer’s sensitivity, we can see individual stars roughly the size of our sun tightly packed within those clumps.” The cluster of stars is so tightly packed that they must be less than 100,000 years old, he added.

Astronomers are calling this compact collection of bright protostars within the Christmas Tree Cluster the “Snowflake Cluster” because of how they are spaced. The newborn stars are patterned like a single feathery crystal of snow, or geometrically spaced like spokes in a wheel.

The Spitzer observations show that just as theory predicts, the density and temperature of the initial star-forming cloud dictates the spacing between the protostars.

Young is deputy principal investigator for Spitzer’s Multiband Imaging Photometer (MIPS), a UA-built camera that took the longest wavelengths of infrared light used in Christmas Tree Cluster mosaic. Astronomers combined light from MIPS and Spitzer’s Infrared Array Camera (IRAC), developed by the Smithsonian Astrophysical Observatory, in constructing in the picture.

The infant stars appear as pink and red specks in the snowflake cluster that adorns the larger Christmas Tree Cluster in the IRAC and MIPS image. The larger, yellowish spheres are massive stars within the NGC 2264 region. The organic molecules mixed in with dust that surrounds the cluster are illuminated as wisps of green. The blue dots smeared across the image are older Milky Way stars at various distances along the telescope’s line of sight.

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

Original Source: UA News Release

An accurate illustration of young galaxies twe<lve billion light years awayClick to enlarge/a>
Astronomers have found clear indications that clumps of dark matter are the nursing grounds for new born galaxies about twelve billion light years away. A single nest of dark matter can nurture several young galaxies. These results from researchers at the Space Telescope Science Institute, the National Astronomical Observatory of Japan, and the University of Tokyo confirm predictions of the currently dominant theory of cosmology known as the Cold Dark Matter model.

Recent studies suggest that dark matter out weighs ordinary matter by a factor of seven. Although dark matter cannot be seen directly through a telescope, it reveals itself to astronomers by its strong gravitational pull on nearby stars and gas, and even galaxies.

Galaxies are often clustered together and how they cluster is determined mostly by gravity.

By studying how galaxies cluster, it is possible to determine how dark matter is distributed and how it affects the birth and growth of galaxies. In the past, it was extremely difficult to study the clustering of young galaxies. Young galaxies appear faint due to their great distances, and finding enough of them to study how they cluster was an observational challenge.

Masami Ouchi from the Space Telescope Science Institute and colleagues used the Subaru telescope and its Suprime-Cam camera to study a piece of the sky in the constellation Cetus (the Whale) called the Subaru/XMM-Newton Deep Survey Field (SXDS). This piece of sky covers an area five times the size of the full moon. By taking deep and sensitive images of the field in three colors of visible light, the SXDS team was able to find about seventeen thousand (17,000) young galaxies twelve billion light years away. This number is ten times larger than previous studies of such young galaxies.
Based on these data, the team found that:

1) There are many pairs of galaxies with separations less than eight hundred thousand (800,000) light years.
2) Even at large distances, galaxies are strongly clustered.

Both of these results are expected if the galaxies are nestled within clumps of dark matter. The SXDS team compared the observational results in detail to theoretical predictions based on a Cold Dark Matter model by team member Takashi Hamana and found that the average clump of dark matter nests weighs as much as six hundred billion (600,000,000,000) Suns, and that a single clump of dark matter harbors multiple young galaxies.

Independently, Nobunari Kashikawa from the National Astronomical Observatory of Japan and colleagues also used Subaru’s Suprime-Cam camera to study an area of sky in the constellation Coma Berenices (Berenice’s Hair) called the Subaru Deep Field (SDF). This field is only the size of one full moon but the data available are twice as sensitive as the SXDS field data. The SDF team found about five thousand (5,000) young galaxies at a distance of twelve billion light years, and eight hundred (800) even younger galaxies at a distance of twelve billion five hundred million light years. The SDF team was also able to double check the identities of the young galaxies by taking spectral data of the galaxies with the Subaru and Keck telescopes. The SDF team independently obtained the results 1)+2) described above, and concluded that some single clumps of dark matter harbours multiple young galaxies. In the SDF images, it is possible to see several new born galaxies huddled together in a small area. By comparing the SDF data in detail to high precision computer simulations of the growth of clumps in Cold Dark Matter by team member Masahiro Nagashima of Kyoto University, the SDF team concludes that heavier clumps of dark matter have more bright galaxies, and that this preference produces the correlations found in real observation.

The two teams together have found the first concrete evidence that young galaxies in the early universe are nestled within clumps of dark matter, and that a single clump of dark matter nurses several young galaxies. Both teams took advantage of the Subaru telescope’s unique ability to take deep sensitive images over a large area of sky.

Original Source: NAOJ News Release

An artist’s concept of a hypothetical supernova in our galaxy. Image credit: David A. Aguilar (CfA). Click to enlarge
A team of astronomers has found faint visible echoes of three ancient supernovae by detecting their centuries-old light as it is reflected by clouds of interstellar gas hundreds of light-years removed from the original explosions.

Located in a nearby galaxy in the southern skies of Earth, the three exploding stars flashed into short-lived brilliance at least two centuries ago, and probably longer. The oldest one is likely to have occurred more than six hundred years ago.

The light echoes were discovered by comparing images of the Large Magellanic Cloud (LMC) taken years apart. By precisely subtracting the common elements in each image of the galaxy and looking by eye to see what variable objects remain, the team looked for evidence of invisible dark matter that might distort the light of stars in a transitory way, as part of a sky survey called SuperMACHO.

This careful image analysis also revealed a small number of concentric, circular-shaped arcs that are best explained as light moving outward over time, and being scattered as it encounters dense pockets of cool interstellar dust. Team members then fit perpendicular vectors to the curves of each arc system, which were found to point backwards toward the sites of three supernovae remnants, which were previously known and thought to be relatively young.

“Without the geometry of the light echo, we had no precise way of knowing just how old these supernovae were,” said astronomer Armin Rest of the National Optical Astronomy Observatory (NOAO), lead author of a paper on the discovery in the December 22, 2005, issue of Nature. “Some relatively simple mathematics can help us answer one of the most vexing questions that astronomers can ask-exactly how old is this object that we are looking at?”

Just as a sound echo can occur when sound waves bounce off a distant surface and reflect back toward the listener, a light echo can be seen when light waves traveling through space are reflected back toward the viewer-in this case, the Mosaic digital camera on the National Science Foundation’s Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory (CTIO) in Chile.

This technique can be extended to famous supernovae in history. “Imagine seeing light from the same explosion first seen by Johannes Kepler some 400 years ago, or the one recorded by Chinese observers in 1006,” said Christopher Stubbs of the Harvard-Smithsonian Center for Astrophysics (CfA), co-author of the paper and principal investigator for the SuperMACHO program. “These light echoes give us that possibility.”

In principle, astronomers can split the light echo into a spectrum to investigate what type of supernova occurred. “We have the potential with these echoes to determine the star’s cause of death, just like the archaeologists who took a CT scan of King Tut’s mummy to find out how he died,” said co-author Arti Garg of CfA.

Astronomers can also use supernova light echoes to measure the structure and nature of the interstellar medium. Dust and gas between the stars are invisible unless illuminated by some light source, just as fog at night is not noticeable until lit by a car’s headlights. A supernova blast can provide that illumination, lighting up surrounding clouds of matter with its strobe-like flash.

“We see the reflection as an arc because we are inside an imaginary ellipse, with the Earth at one focus of the ellipse and the ancient supernovae at the other,” explained Nicholas Suntzeff of NOAO. “As we look out toward the supernovae, we see the reflection of the light echo only when it intersects the outer surface of the ellipse. The shape of the reflection from our vantage point appears to be a portion of a circle.”

An unusual aspect of the arcs is that they generally appear to move much faster than the speed of light. This does not violate the cosmic speed limit, which states that any object cannot move faster than the speed of light. “What our telescopes see is the reflection moving, and not any physical object,” Suntzeff added. “It is also very exciting that our observations confirm the visionary prediction of Fritz Zwicky in 1940 that light from ancient supernovae could be seen in echoes of the explosion.”

Two additional high-resolution color graphics to illustrate this result are available at http://www.noao.edu/outreach/press/pr05/pr0512.html.

Other co-authors of the Nature paper are Knut Olsen and Chris Smith (CTIO); Jose Luis Prieto (Ohio State University); Douglas Welch (McMaster University, Ontario); Andrew Becker and Gajus Miknaitis (University of Washington); Marcel Bergmann (Gemini Observatory); Alejandro Clocchiatti and Dante Minniti (Pontifica Universidad Catolica de Chile); and, Kem Cook, Mark Huber and Sergei Nikolaev (Lawrence Livermore).

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.

Original Source: CfA News Release