Saturday, May 31, 2014

The 'Serpent' Star-forming Cloud Hatches New Stars

Within the swaddling dust of the Serpens Cloud Core, astronomers are studying one of the youngest collections of stars ever seen in our galaxy. Image credit: NASA/JPL-Caltech/2MASS. Full image and caption

Stars that are just beginning to coalesce out of cool swaths of dust and gas are showcased in this image from NASA's Spitzer Space Telescope and the Two Micron All Sky Survey (2MASS). Infrared light has been assigned colors we see with our eyes, revealing young stars in orange and yellow, and a central parcel of gas in blue. This area is hidden in visible-light views, but infrared light can travel through the dust, offering a peek inside the stellar hatchery.

The dark patch to the left of center is swaddled in so much dust, even the infrared light is blocked. It is within these dark wombs that stars are just beginning to take shape.

Called the Serpens Cloud Core, this star-forming region is located about 750 light-years away in Serpens, or the "Serpent," a constellation named after its resemblance to a snake in visible light. The region is noteworthy as it only contains stars of relatively low to moderate mass, and lacks any of the massive and incredibly bright stars found in larger star-forming regions like the Orion nebula. Our sun is a star of moderate mass. Whether it formed in a low-mass stellar region like Serpens, or a high-mass stellar region like Orion, is an ongoing mystery.

The inner Serpens Cloud Core is remarkably detailed in this image. It was assembled from 82 snapshots representing a whopping 16.2 hours of Spitzer observing time. The observations were made during Spitzer's "warm mission," a phase that began in 2009 after the observatory ran out of liquid coolant, as planned.

Most of the small dots in this image are stars located behind, or in front of, the Serpens nebula.

The 2MASS mission was a joint effort between the California Institute of Technology, Pasadena; the University of Massachusetts, Amherst; and NASA's Jet Propulsion Laboratory, also in Pasadena.

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA. For more information about Spitzer, visit:

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.

whitney.clavin@jpl.nasa.gov


Friday, May 30, 2014

Violent birth announcement from an infant star

Credit: ESA/Hubble & NASA
Acknowledgements: R. Sahai (Jet Propulsion Laboratory), Serge Meunier

This new Hubble image shows IRAS 14568-6304, a young star that is cloaked in a haze of golden gas and dust. It appears to be embedded within an intriguing swoosh of dark sky, which curves through the image and obscures the sky behind.

This dark region is known as the Circinus molecular cloud. This cloud has a mass around 250 000 times that of the Sun, and it is filled with gas, dust and young stars. Within this cloud lie two prominent and enormous regions known colloquially to astronomers as Circinus-West and Circinus-East. Each of these clumps has a mass of around 5000 times that of the Sun, making them the most prominent star-forming sites in the Circinus cloud. The clumps are associated with a number of young stellar objects, and IRAS 14568-6304, featured here under a blurry fog of gas within Circinus-West, is one of them.

IRAS 14568-6304 is special because it is driving a protostellar jet, which appears here as the "tail" below the star. This jet is the leftover gas and dust that the star took from its parent cloud in order to form. While most of this material forms the star and its accretion disc — the disc of material surrounding the star, which may one day form planets — at some point in the formation process the star began to eject some of the material at supersonic speeds through space. This phenomenon is not only beautiful, but can also provide us with valuable clues about the process of star formation.

IRAS 14568-6304 is one of several outflow sources in the Circinus-West clump. Together, these sources make up one of the brightest, most massive, and most energetic outflows ever reported. Scientists have even suggested calling Circinus-West the "nest of molecular outflows" in tribute to this activity.

A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Serge Meunier.



Thursday, May 29, 2014

Failed Dwarf Galaxy Survives Galactic Collision Thanks to Full Dark-Matter Jacket

A false-color image of the Smith Cloud made with data from the Green Bank Telescope (GBT). New analysis indicates that it is wrapped in a dark matter halo. Credit: NRAO/AUI/NSF 

Like a bullet wrapped in a full metal jacket, a high-velocity hydrogen cloud hurtling toward the Milky Way appears to be encased in a shell of dark matter, according to a new analysis of data from the National Science Foundation’s Robert C. Byrd Green Bank Telescope (GBT). Astronomers believe that without this protective shell, the high-velocity cloud (HVC) known as the Smith Cloud would have disintegrated long ago when it first collided with the disk of our Galaxy.

If confirmed by further observations, a halo of dark matter could mean that the Smith Cloud is actually a failed dwarf galaxy, an object that has all the right stuff to form a true galaxy, just not enough to produce stars.

“The Smith Cloud is really one of a kind. It’s fast, quite extensive, and close enough to study in detail,” said Matthew Nichols with the Sauverny Observatory in Switzerland and principal author on a paper accepted for publication in the Monthly Notices of the Royal Astronomical Society. “It’s also a bit of a mystery; an object like this simply shouldn’t survive a trip through the Milky Way, but all the evidence points to the fact that it did.”

Previous studies of the Smith Cloud revealed that it first passed through our Galaxy many millions of years ago. By reexamining and carefully modeling the cloud, astronomers now believe that the Smith Cloud contains and is actually wrapped in a substantial “halo” of dark matter -- the gravitationally significant yet invisible stuff that makes up roughly 80 percent of all the matter in the Universe.

“Based on the currently predicted orbit, we show that a dark matter free cloud would be unlikely to survive this disk crossing,” observed Jay Lockman, an astronomer at the National Radio Astronomy Observatory in Green Bank, West Virginia, and one of the coauthors on the paper. “While a cloud with dark matter easily survives the passage and produces an object that looks like the Smith Cloud today.”

The Milky Way is swarmed by hundreds of high-velocity clouds, which are made up primarily of hydrogen gas that is too rarefied to form stars in any detectable amount. The only way to observe these objects, therefore, is with exquisitely sensitive radio telescopes like the GBT, which can detect the faint emission of neutral hydrogen. If it were visible with the naked eye, the Smith Cloud would cover almost as much sky as the constellation Orion.

Most high-velocity clouds share a common origin with the Milky Way, either as the leftover building blocks of galaxy formation or as clumps of material launched by supernovas in the disk of the galaxy. A rare few, however, are interlopers from farther off in space with their own distinct pedigree. A halo of dark matter would strengthen the case for the Smith Cloud being one of these rare exceptions.

Currently, the Smith Cloud is about 8,000 light-years away from the disk of our Galaxy. It is moving toward the Milky Way at more than 150 miles per second and is predicted to impact again in approximately 30 million years.

“If confirmed to have dark matter this would in effect be a failed galaxy,” said Nichols. “Such a discovery would begin to show the lower limit of how small a galaxy could be.” The researchers believe this could also improve our understanding of the Milky Way's earliest star formation.

***

Contact:

Charles E. Blue
Public Information Officer
(434) 296-0314
email: cblue@nrao.edu

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.


Wednesday, May 28, 2014

Revealing the Complex Outflow Structure of Binary UY Aurigae

An international team of astronomers, led by Dr. Tae-Soo Pyo (Subaru Telescope, NAOJ), has revealed a complicated outflow structure in the binary UY Aur (Aurigae). The team observed the binary using the Gemini North's NIFS (Near-Infrared Integral Field Spectrometer) with the Altair adaptive optics system (Note 1). The team found that the primary star has a wide, open outflow, while the secondary star has a well-collimated jet.
Because many stars form together as companions in binary or multiple systems, investigating these systems is essential for understanding star and planet formation. Although jets (i.e., narrow bright streams of gas) and outflows (i.e., less collimated flows of gas) from single young stars are ubiquitous, only a few observations have shown jets or outflows from multiple, low-mass young stars. Therefore, the current team chose to examine the outflow structure of binary UY Aur, which is a close binary system composed of young stars separated by less than an arcsecond (0".89).
 
To better understand this system, the team began by trying to identify the driving source of the receding jets. To separate the binary stars and distinguish their driving sources, they used Gemini North's NIFS with its adaptive optics system to observe this close binary system in the 1-micrometer infrared wavelength region. Since ionized iron gas ([Fe II]) traces shocked gas in jets and outflows very well, the team used iron gas emissions to examine the emission gas distribution. They found that [Fe II] is associated with both the primary and the secondary stars (Figure 1).

Figure 1: Emission images of UY Aur. The large plus marks indicate the primary star, located in the upper portion of each panel and designated as "A" in the continuum image. The smaller plus marks indicate the secondary star, located below the primary star and labeled as "B" in the continuum panel. Large tick marks correspond to measures of 1 arcsecond (140 Astronomical Unit). The filled circles at the bottom right corners show the spatial resolution (=0.12"). (Credit: NAOJ)

In addition, they found that the shape of the gas distribution conformed to simulations of gas streaming between the primary and secondary stars. However, the high velocity of the gas (100 km/s or > 20,000 mile/h) indicated that it emanated from the close vicinity of stars rather than arose in the disk gas around the two stars.
Further investigation of the emission structure involved separation of the receding and approaching emissions (Figure 1). The team found that the distribution of gas was different for each of the stars. While the approaching gas was widely spread in an outflow from the primary star and slightly connected with the secondary star, the receding gas was spread widely toward the secondary star and flowing beyond it (Figure 1). 

Figure 2: Schematic drawings of the UY Aur binary.
Left: Redshifted and blueshifted outflows. The primary star (A) shows wide, open, redshifted and blueshifted outflows as well as a redshifted jet (in solid red), while the secondary star (B) shows a blueshifted jet (in solid blue). Redshifted jets from B might be within the solid red outflow area from A. (Credit NAOJ).

Right: Model of the UY Aur binary and its outflows and jets, showing the wide redshifted and blueshifted outflows of the primary star (A) and the blueshifted jet from the secondary star (B). The dotted red lines indicate where the redshifted jets from the secondary star might be. (Credit: NAOJ) 

What explains this difference? The team analyzed the system in terms of bipolar outflows, i.e., each star has a disk and ejects both blueshifted (approaching) and redshifted (receding) outflows or jets. The primary ejects wide,open bipolar outflows. Its redshifted (receding) outflow overlaps with the secondary. In contrast, the approaching gas from the secondary is distributed in a well-collimated bipolar jet, with its blueshifted flow tilted toward the wide, open wind from the primary (Figure 2). It is known from mid-infrared (wavelength of ~10 micrometer) observations that the circumstellar disk of the secondary is not aligned with the plane of the circumbinary disk. This misalignment is consistent with the jet from the secondary tilted toward the wide, open outflow from the primary star.

Two jets from a binary system can be explained if the jets emanate from each of the star-disk systems. Some binaries show only one jet or outflow. A larger sample of [Fe II] gas distribution toward binary and multiple young-star systems can clarify how typical the outflow structure of the UY Aur system is.

Figure 3: Artist's rendition of UY Aur's probable outflow system (Credit: NAOJ)

Notes:


  1. The observations were conducted as part of the Subaru/Gemini Time Exchange Program, during which astronomers from each telescope's community can mutually access some of each telescope's unique instruments.
  2. The first circumbinary disk to be resolved and imaged was around the GG Tau A system. To view this image obtained with Subaru Telescope's Coronagraphic Imager with Adaptive Optics (CIAO), go to: http://subarutelescope.org/Introduction/instrument/CIAO.html.

Reference:


Pyo, T.-S., Hayashi, M., Beck, T. L., Davis, C. J., and Takami, M. 2014 "[Fe II] Emissions Associated with the Young Interacting Binary UY Aurigae", Astrophysical Journal, Volume 786, 63.



Tuesday, May 27, 2014

NASA's WISE Findings Poke Hole in Black Hole 'Doughnut' Theory

Active, supermassive black holes at the hearts of galaxies tend to fall into two categories: those that are hidden by dust, and those that are exposed. Image credit: NASA/JPL-Caltech.   Full image and caption

This infographic explains a popular theory of active supermassive black holes, referred to as the unified model -- and how new data from NASA's Wide-field Infrared Survey Explorer, or WISE, is at conflict with the model. Image credit: NASA/JPL-Caltech/NOAO/AURA/NSF/ESO. Full image and captionenlarge image

A survey of more than 170,000 supermassive black holes, using NASA's Wide-field Infrared Survey Explorer (WISE), has astronomers reexamining a decades-old theory about the varying appearances of these interstellar objects.

The unified theory of active, supermassive black holes, first developed in the late 1970s, was created to explain why black holes, though similar in nature, can look completely different. Some appear to be shrouded in dust, while others are exposed and easy to see.

The unified model answers this question by proposing that every black hole is surrounded by a dusty, doughnut-shaped structure called a torus. Depending on how these "doughnuts" are oriented in space, the black holes will take on various appearances. For example, if the doughnut is positioned so that we see it edge-on, the black hole is hidden from view. If the doughnut is observed from above or below, face-on, the black hole is clearly visible.

However, the new WISE results do not corroborate this theory. The researchers found evidence that something other than a doughnut structure may, in some circumstances, determine whether a black hole is visible or hidden. The team has not yet determined what this may be, but the results suggest the unified, or doughnut, model does not have all the answers.

"Our finding revealed a new feature about active black holes we never knew before, yet the details remain a mystery," said Lin Yan of NASA's Infrared Processing and Analysis Center (IPAC), based at the California Institute of Technology in Pasadena. "We hope our work will inspire future studies to better understand these fascinating objects."

Yan is the second author of the research accepted for publication in the Astrophysical Journal. The lead author is a post-doctoral researcher, Emilio Donoso, who worked with Yan at IPAC and has since moved to the Instituto de Ciencias Astronómicas, de la Tierra y del Espacio in Argentina. The research also was co-authored by Daniel Stern at NASA's Jet Propulsion Laboratory in Pasadena, California, and Roberto Assef of Universidad Diego Portales in Chile and formerly of JPL.

Every galaxy has a massive black hole at its heart. The new study focuses on the "feeding" ones, called active, supermassive black holes, or active galactic nuclei. These black holes gorge on surrounding gas material that fuels their growth. 

With the aid of computers, scientists were able to pick out more than 170,000 active supermassive black holes from the WISE data. They then measured the clustering of the galaxies containing both hidden and exposed black holes -- the degree to which the objects clump together across the sky.

If the unified model were true, and the hidden black holes are simply blocked from view by doughnuts in the edge-on configuration, then researchers would expect them to cluster in the same way as the exposed ones. According to theory, since the doughnut structures would take on random orientations, the black holes should also be distributed randomly. It is like tossing a bunch of glazed doughnuts in the air -- roughly the same percentage of doughnuts always will be positioned in the edge-on and face-on positions, regardless of whether they are tightly clumped or spread far apart.

But WISE found something totally unexpected. The results showed the galaxies with hidden black holes are more clumped together than those of the exposed black holes. If these findings are confirmed, scientists will have to adjust the unified model and come up with new ways to explain why some black holes appear hidden. 

"The main purpose of unification was to put a zoo of different kinds of active nuclei under a single umbrella," said Donoso. Now, that has become increasingly complex to do as we dig deeper into the WISE data."
Another way to understand the WISE results involves dark matter. Dark matter is an invisible substance that dominates matter in the universe, outweighing the regular matter that makes up people, planets and stars. Every galaxy sits in the center of a dark matter halo. Bigger halos have more gravity and, therefore, pull other galaxies toward them.

Because WISE found that the obscured black holes are more clustered than the others, the researchers know those hidden black holes reside in galaxies with larger dark matter halos. Though the halos themselves would not be responsible for hiding the black holes, they could be a clue about what is occurring.

"The unified theory was proposed to explain the complexity of what astronomers were seeing," said Stern. "It seems that simple model may have been too simple. As Einstein said, models should be made 'as simple as possible, but not simpler.'"

Scientists still are actively combing public data from WISE, which was put into hibernation in 2011 after scanning Earth's entire sky twice. WISE was reactivated in 2013, renamed NEOWISE, and given a new mission to identify potentially hazardous near-Earth objects.

For more information about NEOWISE, visit: http://neo.jpl.nasa.gov/programs/neowise.html

For more information about WISE, visit: http://www.nasa.gov/wise

J.D. Harrington
NASA Headquarters, Washington
202-358-5241

j.d.harrington@nasa.gov

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673

whitney.clavin@jpl.nasa.gov

Monday, May 26, 2014

Confirmed: Stellar Behemoth Self-Destructs in a Type IIb Supernova

A star in a distant galaxy explodes as a supernova: while observing a galaxy known as UGC 9379 (left; image from the Sloan Digital Sky Survey; SDSS) located about 360 million light years away from Earth, the team discovered a new source of bright blue light (right, marked with an arrow; image from the 60-inch robotic telescope at Palomar Observatory). This very hot, young supernova marked the explosive death of a massive star in that distant galaxy.

A detailed study of the spectrum (the distribution of colors composing the light from the supernova) using a technique called “flash spectroscopy” revealed the signature of a wind blown by the aging star just prior to its terminal explosion, and allowed scientists to determine what elements were abundant on the surface of the dying star as it was about to explode as a supernova, providing important information about how massive stars evolve just prior to their death, and the origin of crucial elements such as carbon, nitrogen and oxygen.

The Palomar 48 inch telescope
Photo by: Iair Arcavi, Weizmann Instiute of Science

Berkeley Lab Researchers Help Catch a Wolf-Rayet Hours After it Goes Supernova

Our Sun may seem pretty impressive: 330,000 times as massive as Earth, it accounts for 99.86 percent of the Solar System’s total mass; it generates about 400 trillion trillion watts of power; and it has a surface temperature of about 10,000 degrees Celsius. Yet for a star, it’s a lightweight. 

The real cosmic behemoths are Wolf-Rayet stars, which are more than 20 times as massive as the Sun and at least five times as hot. Because these stars are relatively rare and often obscured, scientists don’t know much about how they form, live and die. But this is changing, thanks to an innovative sky survey called the intermediate Palomar Transient Factory (iPTF), which uses resources at the National Energy Research Scientific Computing Center (NERSC) and Energy Sciences Network (ESnet), both located at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), to expose fleeting cosmic events such as supernovae.

For the first time ever, scientists have direct confirmation that a Wolf-Rayet star—sitting 360 million light years away in the Bootes constellation—died in a violent explosion known as a Type IIb supernova. Using the iPTF pipeline, researchers at Israel’s Weizmann Institute of Science led by Avishay Gal-Yam caught supernova SN 2013cu within hours of its explosion. They then triggered ground- and space-based telescopes to observe the event approximately 5.7 hours and 15 hours after it self-destructed. These observations are providing valuable insights into the life and death of the progenitor Wolf-Rayet.

“Newly developed observational capabilities now enable us to study exploding stars in ways we could only dream of before. We are moving towards real-time studies of supernovae,” says Gal-Yam, an astrophysicist in the Weizmann Institute’s Department of Particle Physics and Astrophysics. He is also the lead author of a recently published Nature paper on this finding.

“This is the smoking gun. For the first time, we can directly point to an observation and say that this type of Wolf-Rayet star leads to this kind of Type IIb supernova,” says Peter Nugent, who heads Berkeley Lab’s Computational Cosmology Center (C3) and leads the Berkeley contingent of the iPTF collaboration.

“When I identified the first example of a Type IIb supernova in 1987, I dreamed that someday we would have direct evidence of what kind of star exploded. It’s refreshing that we can now say that Wolf-Rayet stars are responsible, at least in some cases,” says Alex Filippenko, Professor of Astronomy at UC Berkeley. Both Filippenko and Nugent are also co-authors on the Nature paper.

Elusive Signatures Illuminated in a Flash of Light

Some supermassive stars become Wolf-Rayets in the final stages of their lives. Scientists find these stars interesting because they enrich galaxies with the heavy chemical elements that eventually become the building blocks for planets and life.

“We are gradually determining which kinds of stars explode, and why, and what kinds of elements they produce,” says Filippenko. “These elements are crucial to the existence of life. In a very real sense, we are figuring out our own stellar origins.”

All stars—no matter what size—spend their lives fusing hydrogen atoms to create helium. The more massive a star, the more gravity it wields, which accelerates fusion in the star’s core, generating energy to counteract gravitational collapse. When hydrogen is depleted, a supermassive star continues to fuse even heavier elements like carbon, oxygen, neon, sodium, magnesium and so on, until its core turns to iron. At this point, atoms (even subatomic particles) are packed in so closely that fusion no longer releases energy into the star. It is now solely supported by electron degeneracy pressure—the quantum mechanical law that prohibits two electrons from occupying the same quantum state.

When the core is massive enough, even electron degeneracy won’t support the star and it collapses. Protons and electrons in the core merge, releasing a tremendous amount of energy and neutrinos. This, in turn, powers a shockwave that tears through the star ejecting its remains violently into space as it goes supernova.

The Wolf-Rayet phase occurs before the supernova. As nuclear fusion slows, the heavy elements forged in the star’s core rise to the surface setting off powerful winds. These winds shed a tremendous amount of material into space and obscure the star from prying telescopes on Earth.

“When a Wolf-Rayet star goes supernova, the explosion typically overtakes the stellar wind and all information about the progenitor star is gone,” says Nugent. “We got lucky with SN 2013cu—we caught the supernova before it overtook the wind. Shortly after the star exploded, it let out an ultraviolet flash from the shock wave that heated and lit up the wind. The conditions that we observed in this moment were very similar to what was there before the supernova.”

Before the supernova debris overtook the wind, the iPTF team managed to capture its chemical light signatures (or spectra) with the ground-based Keck telescope in Hawaii and saw the telltale signs of a Wolf-Rayet star.  When the iPTF team performed follow-up observations 15 hours later with NASA’s Swift satellite, the supernova was still quite hot and strongly emitting in the ultraviolet. In the following days, iPTF collaborators rallied telescopes around the globe to watch the supernova crash into material that had been previously ejected from the star. As the days went by, the researchers were able to classify SN 2013cu as a Type IIb supernova because of the weak hydrogen signatures and strong helium features in the spectra that appeared after the supernova cooled.

“With a series of observations, including data I took with the Keck-I telescope 6.5 days after the explosion, we could see that the supernova’s expanding debris quickly overtook the flash-ionized wind that had revealed the Wolf-Rayet features. So, catching the supernova sufficiently early is hard—you’ve got to be on the ball, as our team was,” says Filippenko.

“This discovery was totally shocking, it opens up a whole new research area for us,” says Nugent. “With our largest telescopes you might have a chance of getting a spectrum of a Wolf-Rayet star in the nearest galaxies to our Milky Way, perhaps 4 million light years away. SN 2013cu is 360 million light years away—further by almost factor of 100.”

And because the researchers caught the supernova early—when the ultraviolet flash lit up the progenitor’s stellar wind—they were able to take several spectra.  “Ideally, we’d like to do this again and again and develop some interesting statistics, not just for supernovae with Wolf-Rayet progenitors but other types as well,” says Nugent.

Pipeline Upgrade Leads to Unexpected Discoveries

Since February 2014, the iPTF survey has been scanning the sky nightly with a robotic telescope mounted on the 48-inch Samuel Oschin Telescope at Palomar Observatory in Southern California. As soon as observations are taken, the data travel more than 400 miles to NERSC in Oakland via the National Science Foundation’s High Performance Wireless Research and Education Network and the Department of Energy’s ESnet. At NERSC, the Real-Time Transient Detection Pipeline sifts through the data, identifies events to follow up on and sends an alert to iPTF scientists around the globe.

The survey was built on the legacy of the Palomar Transient Factory (PTF), designed in 2008 to systematically chart the transient sky by using the same camera at Palomar Observatory. Last year Nugent and colleagues at Caltech and UC Berkeley made significant modifications to the transient detection pipeline for the iPTF project. Working with NERSC staff, Nugent upgraded the pipeline’s computing and storage hardware.  The iPTF team also made improvements to the machine learning algorithms at the heart of the detection pipeline and incorporated the Sloan Digital Star Survey III star and galaxy catalogs so the pipeline could immediately reject known variable stars.

They even added an asteroid rejection feature to the automated workflow, which calculates the orbit of every known asteroid at the beginning of the night, determines where the asteroids are in an individual image, and then rejects them.

“All of our modifications significantly sped up our real-time transient detection; we now send high quality supernova alerts to astronomers all around the globe in less than 40 minutes after taking an image at Palomar,” says Nugent. “In the case of SN 2013cu, that made all the difference.”

*** 

The automated real-time detection pipeline was created under the DOE Office of Science’s Scientific Discovery through Advanced Computing (SciDAC) program and through additional support from NASA. 

NERSC provided the storage and systems infrastructure. NERSC and ESnet are also supported by the DOE Office of Science.

Led by Shri Kulkarni of Caltech, iPTF has discovered more than 2000 supernovae during its four and a half years of observations, including many rare and exotic types of cosmic outbursts. The iPTF survey is a scientific collaboration among Caltech, Los Alamos National Laboratory, the University of Wisconsin, Milwaukee, the Oskar Klein Center, the Weizmann Institute of Science, the TANGO Program of the University System of Taiwan, and the Kavli Institute for the Physics and Mathematics of the Universe.

This research was supported by the I-CORE Program “The Quantum Universe” of the Planning and Budgeting Committee and The Israel Science Foundation; grants from the ISF, BSF, GIF, Minerva, the FP7/ERC, and a Kimmel Investigator award; support from the Hubble and Carnegie-Princeton Fellowships; support from the Arye Dissentshik career development chair and a grant from the Israeli MOST; support from the NSF; support from an NSF Postdoctoral Fellowship; support from the TABASGO Foundation, the Christopher R. Redlich Fund, and NSF grant AST-1211916. Some of the data were obtained at the W. M. Keck Observatory, which was made possible by the generous financial support of the W. M. Keck Foundation.



Saturday, May 24, 2014

Dark Stars

Dark stars, entirely speculative entities for now, are hypothesized to form in the early cosmos when dark matter condenses and associated particle annihilation reactions heat up the matter, perhaps disrupting the formation of normal stars. The image shows one result from a new simulation of the birth of the first stars: the left panel shows normal stars forming when no annihilating dark matter is present and the right panel shows one instance of what happens when dark stars form and disrupt the process.Credit: A. Stacey

The vast majority of matter is the universe, about eighty-five percent of it, is so-called "dark matter." It consists not of ordinary atoms, but of some still unknown kind of particle. Understanding this ubiquitous yet mysterious substance is a prime goal of modern astrophysics. Dark matter is detected via its gravitational influence on stars and other normal matter, and some astronomers speculate that it might have another other property besides gravity in common with ordinary matter: It might come in two forms, matter and anti-matter, that annihilate on contact emitting high energy radiation.

Several hundred million years after the big bang, the first stars began to form as gravity gradually condensed the primordial material and heated it to temperatures able to trigger nuclear burning. Scientists have speculated that something roughly similar might also have occurred to dark matter: Gravity condensed it into cores that ultimately ignite, not with nuclear burning – dark matter is not atomic and has no (normal) nuclei – but rather via annihilation radiation. These so-called "dark stars" might have shone for some time as more and more dark matter accreted onto them, powering ongoing annihilation. They may even have heated up their environment in a way that inhibited the growth of the first generation of normal stars.

CfA astronomer Avi Loeb and three of his colleagues used computer simulations of dark matter in the early universe to investigate if and how dark matter might influence the development of normal stars. The details are complex, in part because the growing clumps of matter tend to fragment into clusters within which they then scatter off one another. The scientists tested their simulations under a variety of assumptions, and found in one of the more sophisticated versions that the annihilating dark matter was considerably less effective in forming a dark star (or disrupting normal stars) than had been thought because of the disruption from scattering. They conclude that dark stars may never have existed, and hence that the formation of normal stars may not have been retarded. They caution, however, that further research is needed to refine these conclusions, not least to determine nature of the mysterious dark matter itself. Astronomers are optimistic that some of the first stars in the universe will actually be detected in this decade; some proposed space missions (like the Japanese WISH mission) set this as their primary goal. These new simulations provide a basis for interpreting those detections.

Reference(s): 

"The Mutual Interaction Between Population III Stars and Self-Annihilating Dark Matter," Athena Stacy, Andreas H. Pawlik, Volker Bromm and Abraham Loeb, MNRAS 441, 822, 2014.


Friday, May 23, 2014

Pitch Black: Cosmic Clumps Cast the Darkest Shadows

Astronomers have found cosmic clumps so dark, dense and dusty that they throw the deepest shadows ever recorded. Image credit: NASA/JPL-Caltech/University of Zurich.  Full image and caption

Astronomers have found cosmic clumps so dark, dense and dusty that they throw the deepest shadows ever recorded. Infrared observations from NASA's Spitzer Space Telescope of these blackest-of-black regions paradoxically light the way to understanding how the brightest stars form.

The clumps represent the darkest portions of a huge, cosmic cloud of gas and dust located about 16,000 light-years away. A new study takes advantage of the shadows cast by these clumps to measure the cloud's structure and mass.

The dusty cloud, results suggest, will likely evolve into one of the most massive young clusters of stars in our galaxy. The densest clumps will blossom into the cluster's biggest, most powerful stars, called O-type stars, the formation of which has long puzzled scientists. These hulking stars have major impacts on their local stellar environments while also helping to create the heavy elements needed for life.

"The map of the structure of the cloud and its dense cores we have made in this study reveals a lot of fine details about the massive star and star cluster formation process," said Michael Butler, a postdoctoral researcher at the University of Zurich in Switzerland and lead author of the study, published in The Astrophysical Journal Letters.

The state-of-the-art map has helped pin down the cloud's mass to the equivalent of 7,000 suns packed into an area spanning about 50 light-years in diameter. The map comes courtesy of Spitzer observing in infrared light, which can more easily penetrate gas and dust than short-wavelength visible light. The effect is similar to that behind the deep red color of sunsets on smoggy days -- longer-wavelength red light more readily reaches our eyes through the haze, which scatters and absorbs shorter-wavelength blue light. In this case, however, the densest pockets of star-forming material within the cloud are so thick with dust that they scatter and block not only visible light, but also almost all background infrared light.

Observing in infrared lets scientists peer into otherwise inscrutable cosmic clouds and catch the early phases of star and star cluster formation. Typically, Spitzer detects infrared light emitted by young stars still shrouded in their dusty cocoons. For the new study, astronomers instead gauged the amount of background infrared light obscured by the cloud, using these shadows to infer where material had lumped together within the cloud. These blobs of gas and dust will eventually collapse gravitationally to make hundreds of thousands of new stars.

Most stars in the universe, perhaps our sun included, are thought to have formed en masse in these sorts of environments. Clusters of low-mass stars are quite common and well-studied. But clusters giving birth to higher-mass stars, like the cluster described here, are scarce and distant, which makes them harder to examine.

"In this rare kind of cloud, Spitzer has provided us with an important picture of massive star cluster formation caught in its earliest, embryonic stages," said Jonathan Tan, an associate professor of astronomy at the University of Florida, Gainesville, and co-author of the study.

The new findings will also help reveal how O-type stars form. O-type stars shine a brilliant white-blue, possess at least 16 times the sun's mass and have surface temperatures above 54,000 degrees Fahrenheit (30,000 degrees Celsius). These giant stars have a tremendous influence on their local stellar neighborhoods. Their winds and intense radiation blow away material that might draw together to create other stars and planetary systems. O-type stars are short-lived and quickly explode as supernovas, releasing enormous amounts of energy and forging the heavy elements needed to form planets and living organisms.

Researchers are not sure how, in O-type stars, it is possible for material to accumulate on scales of tens to 100 times the mass of our sun without dissipating or breaking down into multiple, smaller stars. 

"We still do not have a settled theory or explanation of how these massive stars form," said Tan. "Therefore, detailed measurements of the birth clouds of future massive stars, as we have recorded in this study, are important for guiding new theoretical understanding."

NASA's Jet Propulsion Laboratory, Pasadena, California, manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

For more information about Spitzer, visit: http://spitzer.caltech.edu and  http://www.nasa.gov/spitzer

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, California

whitney.clavin@jpl.nasa.gov



Thursday, May 22, 2014

Very Distant Galaxy Cluster Confirmed

Hubble Space Telescope image of the center of the newly-confirmed JKCS 041 galaxy cluster, located at a distance of 9.9 billion light years. The galaxies located in the cluster are circled. Blue circles show the few galaxies that continue to form new stars, while yellow circles show those that have already entered quiescence. A larger version is available here.

Pasadena, CA - The structures and star populations of massive galaxies appear to change as they age, but much about how these galaxies formed and evolved remains mysterious. Many of the oldest and most massive galaxies reside in clusters, enormous structures where numerous galaxies are found concentrated together. Galaxy clusters in the early universe are thought to be key to understanding the lifecycles of old galaxies, but to date astronomers have located only a handful of these rare, distant structures.

New research from a team led by Carnegie’s Andrew Newman has confirmed the presence of an unusually distant galaxy cluster, JKCS 041. It is published by The Astrophysical Journal.

“Our observations make this galaxy cluster one of the best-studied structures from the early universe,” Newman said.

Although the team began studying JKCS 041 in 2006, it has taken years of observing with many of the world’s most powerful telescopes to finally confirm its distance. The team used the Hubble Space Telescope to capture sharp images of the distant cluster and split the starlight from the galaxies into its constituent colors, a technique known as spectroscopy. They found 19 galaxies at precisely the same great distance of 9.9 billion light years, the tell-tale sign of an early galaxy cluster.

A previous study using the Chandra X-ray Observatory discovered X-ray emissions in the location of JKCS 041.

“These X-rays likely originate from hot gas in JKCS 041, which has been heated to a temperature of about 80 million degrees by the gravity of the massive cluster,” said team member Stefano Andreon of the Osservatorio Astronomico di Brera, who led a companion paper published by Astronomy & Astrophysics.

Today the largest and oldest galaxies are found in clusters, but there is a mystery about when and why these giant galaxies stopped forming new stars and became dormant, or quiescent. Peering back to a time when the galaxies in JKCS 041 were only 1 billion years old---or 10 percent of their present age---the team found that most had already entered their quiescent phase.

“Because JKCS 041 is the most-distant known cluster of its size, it gives us a unique opportunity to study these old galaxies in detail and better understand their origins,” Newman said.

Once massive galaxies enter their quiescent phase, they continue expanding in overall size. This is thought to occur as galaxies collide with one another and evolve into a new, larger galaxy. Early clusters are suspected to be prime locations for these collisions, but to the team’s surprise they found that the galaxies in JKCS 041 were growing at nearly the same rate as non-cluster galaxies.

The international team included Newman, Andreon, Ginevra Trinchieri of the Osservatorio Astronomico di Brera, Richard Ellis of Caltech, Tommaso Treu of the University of California at Santa Barbara, and Anand Raichoor of the Observatorie di Paris.

This work was based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program number GO-12927, which was supported under NASA contract NAS 5-26555. The work was also supported by the agreement ASI-INAF I/009/10/0 and the Osservatorio Astronomico di Brera.

The Astrophysical Journal paper is available here.

The Astronomy & Astrophysics sister paper is available here.


Wednesday, May 21, 2014

A Star Cluster in the Wake of Carina

The colourful star cluster NGC 3590

The star cluster NGC 3590 in the constellation of Carina

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Videos

Zooming in on the colourful star cluster NGC 3590
Zooming in on the colourful star cluster NGC 3590

The colourful star cluster NGC 3590
The colourful star cluster NGC 3590


This colourful new image from the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory in Chile shows the star cluster NGC 3590. These stars shine brightly in front of a dramatic landscape of dark patches of dust and richly hued clouds of glowing gas. This small stellar gathering gives astronomers clues about how these stars form and evolve — as well as giving hints about the structure of our galaxy's pinwheeling arms.

NGC 3590 is a small open cluster of stars around 7500 light-years from Earth, in the constellation of Carina (The Keel). It is a gathering of dozens of stars loosely bound together by gravity and is roughly 35 million years old.

This cluster is not just pretty; it is very useful to astronomers. By studying this particular cluster — and others nearby — astronomers can explore the properties of the spiral disc of our galaxy, the Milky Way. NGC 3590 is located in the largest single segment of a spiral arm that can be seen from our position in the galaxy: the Carina spiral feature.

The Milky Way has multiple spiral arms, long curved streams of gas and stars stretching out from the galactic centre. These arms — two major star-filled arms, and two less populated minor arms — are each named after the constellations in which they are most prominent [1]. The Carina spiral feature is seen from Earth as a patch of sky heavily populated with stars, in the Carina-Sagittarius minor arm.

The name of this arm — Carina, or The Keel — is quite appropriate. These spiral arms are actually waves of piled up gas and stars sweeping through the galactic disc, triggering sparkling bursts of star formation and leaving clusters like NGC 3590 in their wake. By finding and observing young stars like those in NGC 3590, it is possible to determine the distances to the different parts of this spiral arm, telling us more about its structure.

Typical open clusters can contain anything from a few tens to a few thousands of stars, and provide astronomers with clues about stellar evolution. The stars in a cluster like NGC 3590 are born at around the same time from the same cloud of gas, making these clusters perfect test sites for theories on how stars form and evolve.

This image from the Wide Field Imager (WFI) on the MPG/ESO 2.2-metre telescope at La Silla, shows the cluster and the gas clouds surrounding it, which glow in orange and red hues due to the radiation coming from nearby hot stars. WFI's large field of view also captures a colossal number of background stars.
To obtain this image, multiple observations were made using different filters to capture the different colours of the scene. This image was created by combining images taken in the visible and infrared parts of the spectrum, and a special filter that collected only light coming from glowing hydrogen.

Notes

[1] These four arms are named the Carina-Sagittarius, Norma, Scutum-Centaurus, and Perseus arms.

More information

ESO is the foremost intergovernmental astronomy organisation in Europe and the world's most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world's largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world's biggest eye on the sky”.

Links

Contacts

Richard Hook
ESO, Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email:
rhook@eso.org

Source: ESO

Monday, May 19, 2014

ESA's new X-ray optics for observing the hot Universe

Artist's impression of a galaxy that is releasing material via two strong jets (shown in red/orange) as well as via wide-angle outflows (shown in gray/blue). Both jets and outflows are being driven by the black hole located at the galaxy's centre.

Black holes, which lurk unseen at the centres of almost all galaxies, are regarded as one of the keys to understanding galaxy formation and evolution. Copyright: ESA/AOES Mediala.  Hi-Res (JPG)

Stacked telescope mirrors of ESA's current XMM-Newton
Curved mirrors stacked within one of three optical modules of ESA's XMM-Newton telescope. Each one contains 58 mirrors with a total telescope optical surface of more than 120 m2 – bigger than a tennis court. Copyright: ESA


Silicon pore optics mirror stack
A silicon pore optics mirror stack consisting of 35 mirror plates. The plates are made of silicon wafers. Hundreds of pores allow the X-rays to propagate through the mirror stack and be reflected on the coated stripes. Copyright: cosine Research. Hi-Res (JPG)

A silicon pore optics mirror module is mounted in a test adapter for vibration tests. Acceleration sensors are connected to the module to measure the vibration levels. Copyright: ESA

A new idea to use super-polished silicon wafers as the heart of a telescope is set to reveal more of the hot, high-energy Universe, peering back into its turbulent history. 

Invisible X-rays tell us about the very hot matter in the Universe – black holes, supernovas and superheated gas clouds. Today’s X-ray observatories, ESA’s XMM-Newton and NASA’s Chandra, were launched in the last century, and are still delivering world-class science.  But they are starting to age. 

To replace them, ESA is planning a much more capable X-ray observatory for launch in 2028, which would probe 10 to 100 times deeper into the Universe than the current generation of X-ray telescopes. 

“This demands a whole new type of X-ray mirror,” explains Marcos Bavdaz, leading the technology push for ESA’s future science missions. “To reach the kind of size needed, this new mission’s mirrors will have to be 10 times lighter than XMM’s, while delivering even sharper images.” 

The problem is that energetic X-rays do not behave like typical light waves – try to reflect them with a standard mirror and they are absorbed inside. Instead, X-rays can only be reflected at shallow angles, like stones skimming along water. 

That means multiple mirrors must be stacked together to build a large-enough telescope. XMM has 174 gold-plated nickel mirrors, nested inside one another like Russian dolls. 

But to reach the performance required for ESA’s next X-ray mission, tens of thousands of densely packed mirror plates will be needed. How can this be done? 

A new approach is required. ‘Silicon pore optics’, developed by ESA, draws on high-tech equipment and materials from the semiconductor industry.  

“We make use of industrial silicon wafers, normally used to manufacture microprocessors,” adds Eric Wille, optical system engineer for the X-ray optics development. 

“We take advantage of their stiffness and super-polished surface, stacking a few dozen at a time together to form a single ‘mirror module’.” 

Many hundreds of these modules will be fitted together to form the optics of the X-ray mission. 

Grooves are cut into the wafers, leaving stiffening ribs and paper-thin mirrors, which are then covered with reflective metal. For maximum accuracy, semiconductor manufacturing techniques are applied for the stacking process. 

“Stacking is done by a specially designed robot, aiming for micron-scale precision,” Eric describes. “We’ve seen big jumps in quality as the robotics improve.” 

“All the stacking takes place in a cleanroom, since tiny dust particles risk large deformations in the mirror stack. 

“The semiconductor industry is improving the quality of silicon wafers, which will further improve the mirror quality in future.

 Source: ESA

Sunday, May 18, 2014

Hubble sees a flickering light display on Saturn

Credit: NASA, ESA
Acknowledgement: J. Nichols (University of Leicester)

Astronomers using the NASA/ESA Hubble Space Telescope have captured new images of the dancing auroral lights at Saturn’s north pole. Taken from Hubble’s perspective in orbit around the Earth, these images provide a detailed look at Saturn’s stormy aurorae — revealing previously unseen dynamics in the choreography of the auroral glow.

The cause of the changing patterns in Saturn's aurorae is an ongoing mystery in planetary science. These ultraviolet images, taken by Hubble’s super-sensitive Advanced Camera for Surveys, add new insight by capturing moments when Saturn’s magnetic field is affected by bursts of particles streaming out from the Sun.
Saturn has a long, comet-like magnetic tail known as a magnetotail — as do Mercury, Jupiter, Uranus, Neptune and Earth [1]. This magnetotail is present around planets that have a magnetic field, caused by a rotating core of magnetic elements. It appears that when bursts of particles from the Sun hit Saturn, the planet’s magnetotail collapses and later reconfigures itself, an event that is reflected in the dynamics of its aurorae.

Some of the bursts of light seen shooting around Saturn’s polar regions travelled at over three times faster than the speed of the gas giant’s rotation!

The new images also formed part of a joint observing campaign between Hubble and NASA's Cassini spacecraft, which is currently in orbit around Saturn itself. Between them, the two spacecraft managed to capture a 360-degree view of the planet’s aurorae at both the north and south poles. Cassini also used optical imaging to delve into the rainbow of colours seen in Saturn’s light shows. On Earth, we see green curtains of light with flaming scarlet tops. Cassini’s imaging cameras reveal similar auroral veils on Saturn, that are red at the bottom and violet at the top.

Notes

[1] A magnetosphere is the area of space around an astronomical object in which charged particles are controlled by that object’s magnetic field. The magnetosphere is compressed on the side of the sun, and on the other side it extends far beyond the object. It is this extended region of the magnetosphere that is known as the magnetotail.  

Saturday, May 17, 2014

Views of Venus day and night side

Views of Venus day and night side
Copyright: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA

This sequence of images was taken by the Ultraviolet/Visible/Near-Infrared spectrometer (VIRTIS) on board ESA’s Venus Express spacecraft between 12 and 19 April 2006, during the first orbit (capture orbit) around the planet.

The images were obtained at six different time slots and different distances from the planet (top left: 12 April, from 210 000 kilometres; top centre: 13 April, from 280 000 kilometres; top right: 14 April, from 315 000 kilometres; bottom left:16 April, from 315 000 kilometres; bottom centre: 17 April, from 270 000 kilometres; bottom right: 19 April, from 190 000 kilometres), while the spacecraft moved along a long ellipse around Venus. The separate images can be downloaded here [ VOI_1_12_04_2006_b,  VOI_2_13_04_2006_b,  VOI_3_14_04_2006_b,  VOI_4_16_04_2006_b,  VOI_5_17_04_2006_b,  VOI_6_19_04_2006].

Each image is the composite of the day side of Venus (left, in blue, taken in visible light at 380 nanometres) and the night side (right, in a red colour scheme, taken in infrared light at 1.7 microns).

The visible part shows solar radiation reflected by the atmosphere. The infrared part shows complex cloud structures, revealed by the thermal radiation coming up from different atmospheric depths. Venus Express can resolve these structures by use (for the first time from orbit) of the so so-called ‘infrared windows’ present in the atmosphere of Venus. In fact, if observed at certain wavelengths, it is possible to detect thermal radiation leaking from the deepest atmospheric layers, revealing what lies beneath the dense cloud curtain situated at about 60 kilometres altitude.

In the colour scheme of the presented infrared images, the brighter the colour, the more radiation comes up from the lower layers.

Source: ESA

Friday, May 16, 2014

Starbursts in the wake of a fleeting romance

Credit: ESA/Hubble & NASA
Acknowledgement: Kathy van Pelt

This image shows galaxy NGC 4485 in the constellation of Canes Venatici (The Hunting Dogs). The galaxy is irregular in shape, but it hasn’t always been so. Part of NGC 4485 has been dragged towards a second galaxy, named NGC 4490 — which lies out of frame to the bottom right of this image.

Between them, these two galaxies make up a galaxy pair called Arp 269. Their interactions have warped them both, turning them from spiral galaxies into irregular ones. NGC 4485 is the smaller galaxy in this pair, which provides a fantastic real-world example for astronomers to compare to their computer models of galactic collisions. The most intense interaction between these two galaxies is all but over; they have made their closest approach and are now separating. The trail of bright stars and knotty orange clumps that we see here extending out from NGC 4485 is all that connects them — a trail that spans some 24 000 light-years.

Many of the stars in this connecting trail could never have existed without the galaxies’ fleeting romance. 

When galaxies interact hydrogen gas is shared between them, triggering intense bursts of star formation. The orange knots of light in this image are examples of such regions, clouded with gas and dust.

A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Kathy van Pelt, and won sixth prize in the “basic image searching” category.



Thursday, May 15, 2014

Hubble Shows that Jupiter's Great Red Spot Is Smaller than Ever Seen Before

Photo Credit: NASA, ESA, and A. Simon (Goddard Space Flight Center).  Acknowledgment: C. Go, H. Hammel (Space Science Institute and AURA), and R. Beebe (New Mexico State University).  Science Credit: A. Simon (Goddard Space Flight Center), G. Orton (Jet Propulsion Laboratory), J. Rogers (University of Cambridge, UK), and M. Wong and I. de Pater (University of California, Berkeley)

Jupiter's monster storm, the Great Red Spot, was once so large that three Earths would fit inside it. But new measurements by NASA's Hubble Space Telescope reveal that the largest storm in our solar system has downsized significantly.
Jupiter's trademark Great Red Spot — a swirling anticyclonic storm feature larger than Earth — has shrunken to the smallest size ever measured. Astronomers have followed this downsizing since the 1930s.

"Recent Hubble Space Telescope observations confirm that the Great Red Spot (GRS) is now approximately 10,250 miles across, the smallest diameter we've ever measured," said Amy Simon of NASA's Goddard Space Flight Center in Greenbelt, Md. Historic observations as far back as the late 1800s gauged the GRS to be as big as 25,500 miles on its long axis. The NASA Voyager 1 and Voyager 2 flybys of Jupiter in 1979 measured the GRS to be 14,500 miles across.

Starting in 2012, amateur observations revealed a noticeable increase in the spot's shrinkage rate. The GRS's "waistline" is getting smaller by 580 miles per year. The shape of the GRS has changed from an oval to a circle. The cause behind the shrinking has yet to be explained.

"In our new observations it is apparent that very small eddies are feeding into the storm," said Simon. "We hypothesized that these may be responsible for the accelerated change by altering the internal dynamics and energy of the Great Red Spot."

Simon's team plans to study the motions of the small eddies and also the internal dynamics of the GRS to determine if these eddies can feed or sap momentum entering the upwelling vortex.

In the comparison images one Hubble photo was taken in 1995 when the long axis of the GRS was estimated to be 13,020 miles across. In a 2009 photo, the GRS was measured at 11,130 miles across.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, DC.

For additional information, contact:

Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514

dweaver@stsci.edu / villard@stsci.edu

Amy Simon
Goddard Space Flight Center, Greenbelt, Maryland
301-286-6738

amy.simon@nasa.gov

Source: Hubble Site


Wednesday, May 14, 2014

Magnetar Formation Mystery Solved?

Artist’s impression of the magnetar in the star cluster Westerlund 1

PR Image eso1415b
The star cluster Westerlund 1 and the positions of the magnetar and its probable former companion star

The star cluster Westerlund 1

Wide-field view of the sky around the star cluster Westerlund 1

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Videos

Flying through the young star cluster Westerlund 1 (artist's impression)
Flying through the young star cluster Westerlund 1 (artist's impression)


Magnetars are the bizarre super-dense remnants of supernova explosions. They are the strongest magnets known in the Universe — millions of times more powerful than the strongest magnets on Earth. A team of European astronomers using ESO’s Very Large Telescope (VLT) now believe they’ve found the partner star of a magnetar for the first time. This discovery helps to explain how magnetars form — a conundrum dating back 35 years — and why this particular star didn’t collapse into a black hole as astronomers would expect.

When a massive star collapses under its own gravity during a supernova explosion it forms either a neutron star or black hole. Magnetars are an unusual and very exotic form of neutron star. Like all of these strange objects they are tiny and extraordinarily dense — a teaspoon of neutron star material would have a mass of about a billion tonnes — but they also have extremely powerful magnetic fields. Magnetar surfaces release vast quantities of gamma rays when they undergo a sudden adjustment known as a starquake as a result of the huge stresses in their crusts.

The Westerlund 1 star cluster [1], located 16 000 light-years away in the southern constellation of Ara (the Altar), hosts one of the two dozen magnetars known in the Milky Way. It is called CXOU J164710.2-455216 and it has greatly puzzled astronomers.

“In our earlier work (eso1034) we showed that the magnetar in the cluster Westerlund 1 (eso0510) must have been born in the explosive death of a star about 40 times as massive as the Sun. But this presents its own problem, since stars this massive are expected to collapse to form black holes after their deaths, not neutron stars. We did not understand how it could have become a magnetar,” says Simon Clark, lead author of the paper reporting these results.

Astronomers proposed a solution to this mystery. They suggested that the magnetar formed through the interactions of two very massive stars orbiting one another in a binary system so compact that it would fit within the orbit of the Earth around the Sun. But, up to now, no companion star was detected at the location of the magnetar in Westerlund 1, so astronomers used the VLT to search for it in other parts of the cluster. They hunted for runaway stars — objects escaping the cluster at high velocities — that might have been kicked out of orbit by the supernova explosion that formed the magnetar. One star, known as Westerlund 1-5 [2], was found to be doing just that.

“Not only does this star have the high velocity expected if it is recoiling from a supernova explosion, but the combination of its low mass, high luminosity and carbon-rich composition appear impossible to replicate in a single star — a smoking gun that shows it must have originally formed with a binary companion,” adds Ben Ritchie (Open University), a co-author on the new paper.

This discovery allowed the astronomers to reconstruct the stellar life story that permitted the magnetar to form, in place of the expected black hole [3]. In the first stage of this process, the more massive star of the pair begins to run out of fuel, transferring its outer layers to its less massive companion — which is destined to become the magnetar — causing it to rotate more and more quickly. This rapid rotation appears to be the essential ingredient in the formation of the magnetar’s ultra-strong magnetic field.

In the second stage, as a result of this mass transfer, the companion itself becomes so massive that it in turn sheds a large amount of its recently gained mass. Much of this mass is lost but some is passed back to the original star that we still see shining today as Westerlund 1-5.

“It is this process of swapping material that has imparted the unique chemical signature to Westerlund 1-5 and allowed the mass of its companion to shrink to low enough levels that a magnetar was born instead of a black hole — a game of stellar pass-the-parcel with cosmic consequences!” concludes team member Francisco Najarro (Centro de Astrobiología, Spain).

It seems that being a component of a double star may therefore be an essential ingredient in the recipe for forming a magnetar. The rapid rotation created by mass transfer between the two stars appears necessary to generate the ultra-strong magnetic field and then a second mass transfer phase allows the magnetar-to-be to slim down sufficiently so that it does not collapse into a black hole at the moment of its death.

Notes

[1] The open cluster Westerlund 1 was discovered in 1961 from Australia by Swedish astronomer Bengt Westerlund, who later moved from there to become ESO Director in Chile (1970–74). This cluster is behind a huge interstellar cloud of gas and dust, which blocks most of its visible light. The dimming factor is more than 100 000, and this is why it has taken so long to uncover the true nature of this particular cluster.

Westerlund 1 is a unique natural laboratory for the study of extreme stellar physics, helping astronomers to find out how the most massive stars in the Milky Way live and die. From their observations, the astronomers conclude that this extreme cluster most probably contains no less than 100 000 times the mass of the Sun, and all of its stars are located within a region less than 6 light-years across. Westerlund 1 thus appears to be the most massive compact young cluster yet identified in the Milky Way galaxy.

All the stars so far analysed in Westerlund 1 have masses at least 30–40 times that of the Sun. Because such stars have a rather short life — astronomically speaking — Westerlund 1 must be very young. The astronomers determine an age somewhere between 3.5 and 5 million years. So, Westerlund 1 is clearly a newborn cluster in our galaxy.

[2] The full designation for this star is Cl* Westerlund 1 W 5.

[3] As stars age, their nuclear reactions change their chemical make-up — elements that fuel the reactions are depleted and the products of the reactions accumulate. This stellar chemical fingerprint is first rich in hydrogen and nitrogen but poor in carbon and it is only very late in the lives of stars that carbon increases, by which point hydrogen and nitrogen will be severely reduced — it is thought to be impossible for single stars to be simultaneously rich in hydrogen, nitrogen and carbon, as Westerlund 1-5 is.

More information

The research presented in this ESO Press Release will soon appear in the research journal Astronomy and Astrophysics (“A VLT/FLAMES survey for massive binaries in Westerlund 1: IV.Wd1-5 binary product and a pre-supernova companion for the magnetar CXOU J1647-45” by J. S. Clark et al.). The same team published a first study of this object in 2006 (“A Neutron Star with a Massive Progenitor in Westerlund 1” by M. P. Muno et al., Astrophysical Journal, 636, L41).


The team is composed of Simon Clark and Ben Ritchie (The Open University, UK), Francisco Najarro (Centro de Astrobiología, Spain), Norbert Langer (Universität Bonn, Germany, and Universiteit Utrecht, the Netherlands) and Ignacio Negueruela (Universidad de Alicante, Spain).


The astronomers used the FLAMES instrument on ESO’s Very Large Telescope at Paranal, Chile to study the stars in the Westerlund 1 cluster.


ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links

Contacts

Simon Clark
The Open University
Milton Keynes, United Kingdom
Tel: +44 207 679 4372
Email:
jsc@star.ucl.ac.uk

Richard Hook
ESO, La Silla, Paranal and E-ELT Press Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Email:
rhook@eso.org

Source: ESO