Posted on by Anne Minard

Researchers Propose New Model for the Most Eager Supernova Explosions

2005ke, a Type 1a supernova. Credit: NASA/Swift/S. Immler

Type 1a supernovae like 2005ke, above, are known to go off when one member of a star pair exceeds critical mass and kickstarts a runaway fusion reaction.

Researchers have long puzzled over why some of the explosions happen so fast. Now, a team of Chinese astronomers believes they’ve arrived at a probable cause for the earliest of the blasts.

A team of astronomers, led by Bo Wang from the Yunnan Observatory of the Chinese Academy of Sciences, have shown how the transfer of material from a ‘helium star’ to a compact white dwarf companion causes these cataclysmic events to take place. The new results appear in Monthly Notices of the Royal Astronomical Society.
Most type Ia supernovae are believed to occur when a white dwarf  (the superdense remnant that is the end state of stars like the Sun) draws matter from a companion star orbiting close by. Previous theories for the origins of a Type Ia include an explosion of a white dwarf in orbit around another white dwarf, or an explosion of a white dwarf in orbit around a red giant star. 
When the white dwarf mass exceeds the so-called Chandrasekhar limit of 1.4 times the mass of the Sun, it eventually collapses and within a few seconds undergoes a runaway nuclear fusion reaction, exploding and releasing a vast amount of energy as a type Ia supernova. Due to their high and remarkably consistent luminosities, astronomers use these events as ‘distance indicators’ to measure the distances to other galaxies and constrain our ideas about the Universe.

Scientists have confirmed more and more type Ia supernovae, and found that about half of them explode less than 100 million years after their host galaxy’s main star formation period. But previous models for these systems did not predict that they could be this young — so Wang and his team set out to solve the mystery.

Employing a stellar evolution computer code, they performed calculations for about 2600 binary systems consisting of a white dwarf and a helium star, a hot blue star which has a spectrum dominated by emission from helium. They found that if the gravitational field of the white dwarf pulls material from a helium star and increases its mass beyond the Chandrasekhar limit, it will explode as a type Ia supernova within 100 million years of its formation. 

 “Type Ia supernovae are a key tool to determine the scale of the Universe so we need to be sure of their properties,” said research team member Zhanwen Han, also from the Yunnan Observatory. “Our work shows that they can take place early on in the life of the galaxy they reside in.”

The team now plans to model the properties of the companion helium stars at the moment of the supernova explosions, which could be verified by future observations from the Large sky Area Multi-Object fiber Spectral Telescope (LAMOST).

LEAD IMAGE CAPTION: Supernova 2005ke shown in optical, ultraviolet and X-ray wavelengths. When it was captured, this was the first X-ray image of a Type 1a, and it provided observational evidence that Type Ia come from the explosion of a white dwarf orbiting a red giant star. Credit: NASA/Swift/S. Immler

Source: Royal Astronomical Society. The paper is available here.

Posted on by Anne Minard

Balloon Experiment Solves Mystery of Far Infrared Background

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Scientists have found a way to look past Earth’s atmosphere — and ancient cosmic dust — to glimpse galaxies that were formed in the first 5 billion years of the Universe.

A new study, released today in the journal Nature, reveals first-ever news from star-forming regions both near and far — including some from the edges of the Universe, which are racing away from us the fastest because of the Universe’s expansion.

The findings also clear up the sources of the Far Infrared Background, long shrouded in mystery.

The discoveries hail from the Balloon-borne Large Aperture Submillimetre Telescope (BLAST), which floated 120,000 feet (36,576 meters) above Antarctica in 2006.

The BLAST team chose to map a particular region of the sky called the Great Observatories Origins Deep Survey–South (GOODS-South), which was studied at other wavelengths by NASA’s three “great observatories” — the Hubble, Spitzer, and Chandra space telescopes. In one epic 11-day balloon flight, BLAST found more than 10 times the total number of submillimeter starburst galaxies detected in a decade of ground-based observations.

“We measured everything, from thousands of small clouds in our own galaxy undergoing star formation to galaxies in the Universe when it was only a quarter of its present age,” said lead author Mark Devlin, from the University of Pennsylvania.

In the 1980s and 1990s, certain galaxies called Ultraluminous InfraRed Galaxies were found to be birthing hundreds of times more stars than our own local galaxies. These “starburst” galaxies, 7-10 billion light years away, were thought to make up the Far Infrared Background discovered by the COBE satellite. Since the initial measurement of this background radiation, higher-resolution experiments have tried to detect the individual galaxies that comprise it.

The BLAST study combines telescope survey measurements at wavelengths below 1 millimeter with data at much shorter infrared wavelengths from the Spitzer Space Telescope. The results confirm that all the Far Infrared Background comes from individual distant galaxies, essentially solving a decade-old question of the radiation’s origin.

Star formation takes place in clouds composed of hydrogen gas and a small amount of dust. The dust absorbs the starlight from young, hot stars, heating the clouds to roughly 30 degrees above absolute zero (or 30 Kelvin). The light is re-emitted at much longer infrared and submillimeter wavelengths.

Thus, as much as 50 percent of the Universe’s light energy is infrared light from young, forming galaxies. In fact, there is as much energy in the Far Infrared Background as there is in the total optical light emitted by stars and galaxies in the Universe. Familiar optical images of the night sky are missing half of the picture describing the cosmic history of star formation, the authors say.

“BLAST has given us a new view of the Universe,” said Barth Netterfield of the University of Toronto, the Canadian principal investigator for BLAST, “enabling the BLAST team to make discoveries in topics ranging from the formation of stars to the evolution of distant Galaxies.”

In an accompanying News & Views piece, author Ian Smail, a computational cosmologist from Durham University in the UK, wrote that “the implication of these observations is that the active growth phase of most galaxies that are seen today is well behind them — they are declining into their equivalent of middle age.”

He also pointed out that studies of these extreme star-forming events in the early Universe will be aided by three major advances due over the next year or so: the submillimeter camera on the ESA/NASA Herschel Space Observatory; the development of large-format detectors working at submillimeter wavelengths, including one mounted on the James Clerk Maxwell Telescope; and the first phase of the Atacama Large Millimeter Array (ALMA).

“Such observations will allow astronomers to study the distribution of gas and star formation within these early galaxies,” Smail wrote, “which in turn will help to identify the physical process that triggers these ultraluminous bursts of star formation and their role in the formation of the galaxies we see in the Universe today.”

LEAD IMAGE CAPTION: The BLAST telescope just before launch in Antarctica. BLAST is in the foreground, next the 28 million cubic foot balloon, in the background is the volcano Mount Erebus. Credit: Mark Halpern

Source: Nature and a University of Pennsylvania press release (not yet online).  Images, photographs, sky maps and the complete study are available at the BLAST Web site.

Posted on by Anne Minard

Have a Cigar! New Observations of Messier 82

ESA’s space-borne X-ray observatory, XMM-Newton, has carried out an exclusive, 50-plus-hour observation of the starburst galaxy Messier 82, for the ‘100 Hours of Astronomy’ cornerstone project for the International Year of Astronomy 2009.

This first image shows bright knots in the plane of the galaxy, indicating a region of intense star formation, and emerging plumes of supergalactic winds glowing in X-rays. 

XMM-Newton has been studying the sky in X-ray, optical and ultraviolet wavelengths simultaneously, since its launch in December 1999.  

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Messier 82 has several names including: M82, the Cigar Galaxy and NGC 3034. Located in the constellation Ursa Major at a distance of about 12 million light-years, it is the nearest and one of the most active starburst galaxies, meaning it shows an exceptionally high rate of star formation.

M82 is interacting gravitationally with its neighbour, the spiral galaxy Messier 81, which is probably the cause for the violent starburst activity in the region around its center.

This second image of Messier 82, compiled from observations in the optical and infrared, shows the very bright starry disc of the galaxy with striking dust lanes. 

Source: ESA. More images, including a downloadable poster, are here. 100 Hours of Astronomy ended on Sunday, but the website still has loads of fun information. The International Year of Astronomy 2009 celebration is, of course, ongoing!

Posted on by Anne Minard

Moon Reveals New Way to Find Oceans, Land on Other Earths

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An Australian doctoral researcher using a backyard telescope has made a potentially big discovery: Earth’s oceans and continents shine differently on the dark side of the moon.

Now, Sally Langford, a doctoral candidate in physics at the University of Melbourne, is suggesting the “earthshine” of planets around other stars could provide long-distance windows into their surface features.

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Langford's setup for moon observing. Credit: Stuart Wyithe, second author, also a physicist at the University of Melbourne.

Langford and her colleagues, from Melbourne as well as Princeton University, have shown for the first time that the difference in reflection of light from the Earth’s land masses and oceans can be seen on the dark side of the moon, a phenomenon known as earthshine. Their paper appears in this week’s edition of the international journal Astrobiology.

This is the first study in the world to use the reflection of the Earth to measure the effect of continents and oceans on the apparent brightness of a planet. Other studies have used a color spectrum and infrared sensors to identify vegetation, or for climate monitoring.

The researchers peered at the dark side of the crescent moon using a 20 cm (8 inch) telescope, on the bigger side of what most amateur astronomers use in their yards.

For three years, Langford took images of the Moon to measure the earth’s brightness as it rotated. Observations of the Moon were made from Mount Macedon in Victoria, for around three days each month when the Moon was rising or setting. The study was conducted so that in the evening, when the Moon was a waxing crescent, the reflected earthshine originated from Indian Ocean and Africa’s east coast. In the morning, when the Moon was a waning crescent, it originated only from the Pacific Ocean.

“When we observe earthshine from the Moon in the early evening we see the bright reflection from the Indian Ocean, then as the Earth rotates the continent of Africa blocks this reflection, and the Moon becomes darker,” Langford said.

Langford said the variation revealed the difference between the intense mirror-like reflections of the ocean compared to the dimmer land.

“In the future, astronomers hope to find planets like the Earth around other stars,” Langford said. “However these planets will be too small to allow an image to be made of their surface. We can use earthshine, together with our knowledge of the Earth’s surface, to help interpret the physical makeup of new planets.” 

LEAD IMAGE CAPTION: Earthshine on a crescent moon. Credit: Edward W. Szczepanski, Houston Astronomical Society (click on the photo to visit Szczepanski’s page)

Source: University of Melbourne. The paper is available here.

Posted on by Anne Minard

Hubble Scores a Ring

The NASA/ESA Hubble Space Telescope captured this image of NGC 7049 in the constellation of Indus, in the southern sky. Credit: NASA, ESA and W. Harris (McMaster University, Ontario, Canada)

Credit: NASA, ESA and W. Harris (McMaster University, Ontario, Canada)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The Hubble Space Telescope has captured a new image of NGC 7049, a mysterious looking galaxy that blurs the boundary between spiral and elliptical galaxies.

This picture, taken with a small ground-based camera, shows on its central-left portion the constellation of Indus, in the southern sky. Credit: A. Fujii
This picture, taken with a small ground-based camera, shows on its central-left portion the constellation of Indus, in the southern sky. Credit: A. Fujii

NGC 7049 is found in the constellation of Indus, and is the brightest of a cluster of galaxies, a so-called Brightest Cluster Galaxy. They represent some of the oldest and most massive galaxies, and they allow astronomers to study the elusive globular clusters lurking within.

Globular clusters are very dense and compact groupings of a few hundreds of thousands of young stars bound together by gravity. The globular clusters in NGC 7049 are seen as the sprinkling of small faint points of light in the galaxy’s halo. The halo – the ghostly region of diffuse light surrounding the galaxy – comprises myriad individual stars and provides a luminous background to the remarkable swirling ring of dust lanes surrounding NGC 7049’s core. The dust lanes appear as a lacy ring.

The image was taken by the Advanced Camera for Surveys on Hubble, which is optimized to hunt for galaxies and galaxy clusters in the remote and ancient Universe, at a time when our cosmos was very young. 

The constellation of Indus, or the Indian, is one of the least conspicuous in the southern sky. It was named in the 16th century by Dutch astronomer Petrus Plancius from observations made by Dutch navigator Pieter Dirkszoon Keyser and Dutch explorer Frederick de Houtman.

Source: NASA/ESA Hubble site

Posted on by Anne Minard

New Image Reveals M33 is Bigger Than Thought (and it’s Headed Our Way)

The Triangulum Galaxy. Image credit: NASA/JPL-Caltech/University of Arizona

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NASA’s Spitzer Space Telescope has captured this new image of M33, also known as the Triangulum Galaxy, and released it as part of the “Around the World in 80 Telescopes” event for the International Year of Astronomy.

Besides the pretty colors, the new image reveals something else about M33: it’s more than meets the eye.

M33 is located about 2.9 million light-years away in the constellation Triangulum. It is a member of what’s known as our Local Group of galaxies. Along with our own Milky Way and Andromeda, the group of about 50 galaxies travels together in the universe, bound to one another by gravity. In fact, M33 is one of the few galaxies that is moving toward the Milky Way despite the fact that space is expanding, causing most galaxies in the universe to grow farther and farther apart. 

The new image reveals M33 to be surprising large – bigger than its visible-light appearance would suggest. With its ability to detect cold, dark dust, Spitzer can see emission from cooler material well beyond the visible range of M33’s disk. Exactly how this cold material moved outward from the galaxy is still a mystery, but winds from giant stars or supernovas may be responsible. 

The image is a three-color composite showing infrared observations from two of Spitzer instruments. Stars appear as glistening blue gems (several of which are actually foreground stars in our own galaxy), while dust rich in organic molecules glows green. The diffuse orange-red glowing areas indicate star-forming regions, while small red flecks outside the spiral disk of M33 are probably distant background galaxies. 

As for the technical details, the blue parts of the image represents combined 3.6- and 4.5-micron light, and green shows light of 8 microns, both captured by Spitzer’s infrared array camera. Red is 24-micron light detected by Spitzer’s multiband imaging photometer.

Source: NASA’s Spitzer site

Posted on by Anne Minard

Humble Little Pulsar Puts on a Big Show

This is a quiz.

This X-ray nebula pictured above measures 150 light-years across. At its center is a very young and powerful pulsar known as PSR B1509-58, or B1509 for short.

How big is the pulsar?

B1509 is only 12 miles (19 km) across! 

The small, dense pulsar is a rapidly spinning neutron star which is spewing energy out into the space around it to create complex and intriguing structures, including one that resembles a large cosmic hand. In this image, the lowest energy X-rays that Chandra detects are red, the medium range is green, and the most energetic ones are colored blue. Astronomers think B1509 is about 1,700 years old, and located about 17,000 light years away.

Neutron stars are created when massive stars run out of fuel and collapse. B1509 is spinning completely around almost seven times a second and is releasing energy into its environment at a prodigious rate — presumably because it has an intense magnetic field at its surface, estimated to be 15 trillion times stronger than the Earth’s magnetic field.

The combination of rapid rotation and ultra-strong magnetic field makes B1509 one of the most powerful electromagnetic generators in the Galaxy, pushing an energetic wind of electrons and ions away from the neutron star. As the electrons move through the magnetized nebula, they radiate away their energy and create the elaborate nebula seen by Chandra.

In the innermost regions, a faint circle surrounds the pulsar, and marks the spot where the wind is rapidly decelerated by the slowly expanding nebula. In this way, B1509 shares some striking similarities to the famous Crab Nebula. However B1509’s nebula is 15 times wider than the Crab’s diameter of 10 light years.

Finger-like structures extend to the north, apparently energizing knots of material in a neighboring gas cloud known as RCW 89. The transfer of energy from the wind to these knots makes them glow brightly in X-rays (orange and red features to the upper right). The temperature in this region appears to vary in a circular pattern around this ring of emission, suggesting that the pulsar may be precessing like a spinning top and sweeping an energizing beam around the gas in RCW 89.

The image was released today as part of the ongoing “100 Hours of Astronomy” celebration, which is just one of many global activities as part of the International Year of Astronomy 2009. 

Video, additional images and other information on this result can be found at the Chandra sites run by Harvard and NASA.

Posted on by Anne Minard

And the Winner Is …

Earlier this week, the Hubble Space Telescope photographed the winning target in the Space Telescope Science Institute’s “You Decide” competition in celebration of the International Year of Astronomy.

The winning object, above, received 67,021 votes out of the nearly 140,000 votes cast for the six candidate targets.


Arp 274, also known as NGC 5679, is a system of three galaxies that appear to be partially overlapping in the image, although they may be at somewhat different distances. The spiral shapes of two of these galaxies appear mostly intact. The third galaxy (to the far left) is more compact, but shows evidence of star formation.

Two of the three galaxies are forming new stars at a high rate. This is evident in the bright blue knots of star formation that are strung along the arms of the galaxy on the right and along the small galaxy on the left.

The largest component is located in the middle of the three. It appears as a spiral galaxy, which may be barred. The entire system resides at about 400 million light-years away from Earth in the constellation Virgo.

Hubble’s Wide Field Planetary Camera 2 was used to image Arp 274. Blue, visible, and infrared filters were combined with a filter that isolates hydrogen emission. The colors in this image reflect the intrinsic color of the different stellar populations that make up the galaxies. Yellowish older stars can be seen in the central bulge of each galaxy. A bright central cluster of stars pinpoint each nucleus. Younger blue stars trace the spiral arms, along with pinkish nebulae that are illuminated by new star formation. Interstellar dust is silhouetted against the starry population. A pair of foreground stars inside our own Milky Way are at far right.

The International Year of Astronomy is the celebration of the 400th anniversary of Galileo’s first observations with a telescope. The ongoing “100 Hours of Astronomy,” April 2 to 5, is part of the fun, geared toward encouraging as many people as possible to experience the night sky.

Image credit: NASA, ESA, and M. Livio and the Hubble Heritage Team (STScI/AURA)

For images, videos, and more information about Arp 274, visit the Hubble site,  the Hubble Heritage Project , NASA’s Hubble site or 100 Hours of Astronomy. 


Posted on by Anne Minard

Titan (Weirdness) is More Than Meets The Eye

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Think Titan looks pretty round?

Not quite, according to new data released today by the Cassini radar team — and slight irregularities in the shape of the bizarre moon may account for the concentration of lakes at the highest latitudes, among other perplexing features. 

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NASA/JPL

The radar image above, obtained by Cassini’s radar instrument during a near-polar flyby in 2007, shows a big island smack in the middle of one of the larger lakes imaged on Saturn’s moon Titan. The island is about 90 kilometers (62 miles) by 150 kilometers (93 miles) across, about the size of Kodiak Island in Alaska or the Big Island of Hawaii.  The image is centered at about 79 north degrees north (north is left) and 310 degrees west, adding weight to the theory that most of Titan’s lakes occur near the poles. 

Titan is an intriguing object partly because its climate cycles are reminiscent of Earth’s, but tend to rely on hydrocarbons like methane and ethane instead of water — which couldn’t exist in a liquid state at temperatures hundreds of degrees below zero. Methane and ethane fill the air with a smoggy haze that rains down as ash. Sometimes it’s washed away by hydrocarbons that flow like gasoline and collect in black lakes with surfaces as smooth as glass.

Cassini has been orbiting Saturn for four years, observing Titan periodically with multiple radar instruments. A research team led by Howard Zebker, a geophysicist at Stanford University, has been using the radar data to estimate the surface elevation. Combined, two instruments — a nadir-pointing radar altimeter and a multiple-beam synthetic aperture radar (SAR) imaging system  — measure the time delay of the altimeter echoes and the precise radar beam angles to points on the surface.

“These techniques show that the poles of Titan lie at lower elevations than the equator, and that the topography also varies longitudinally,” the authors report in today’s Science Express..

“If we posit that the lakes are surface expressions of a more or less continuous liquid organic ‘water table,’ then the lower elevations of the poles could lead to the observed preponderance of lakes at high latitudes,” they add. In other words, the lower elevations of poles may make them the only places where any continuous, liquid “water table” would be close enough to the moon’s surface to appear as lakes. 

Titan’s overall shape, they suggest, might be that a sphere slightly flattened at the top and bottom. The exact mechanisms behind the oblate shape are unclear. Titan is also elongated toward Saturn, due to the tides raised by Saturn’s gravity. 

Source: The paper appears online at the Science Express website. More Titan images are available at the Cassini website.

Posted on by Anne Minard

New View of Young, High-Mass Binary Star at Heart of Orion

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A new glimpse inside the heart of Orion has confirmed the separation between the binary star system that orbit each other so closely, astronomers once believed they could be a single star.

The research team, led by Stefan Kraus and Gerd Weigelt from the Max-Planck-Institute for Radio Astronomy (MPIfR) in Bonn, Germany, used ESO’s Very Large telescope Interferometer (VLTI) to obtain the sharpest ever image of the young double star Theta 1 Ori C in the Orion Trapezium Cluster.

The binary stars represent the most massive star in the nearest high-mass star-forming region to Earth. 

Theta 1 Ori C is the dominant and most luminous star in the Orion star nursery. Located at a distance of only about 1,300 light years, it provides a unique laboratory to study the formation process of high-mass stars in detail. The intense radiation of Theta 1 Ori C is ionizing the whole Orion nebula. With its strong wind, the star pair also shapes the famous Orion proplyds, young stars still surrounded by their protoplanetary dust disks.

Although Theta 1 Ori C appeared to be a single star, both with conventional telescopes and the Hubble Space Telescope, the team discovered the existence of a close companion.

VLTI.
VLTI.

“VLTI interferometry with the AMBER instrument allowed us, for the first time, to obtain an image of this system with the spectacular angular resolution of only 2 milliarcseconds”, says Stefan Kraus. “This corresponds to the resolving power of a space telescope with a mirror diameter of 130 meters.”

The new image clearly separates the two young, massive stars of this system. The observations have a spatial resolution of about 2 milliarcseconds, corresponding to the apparent size of a car on the surface of the Moon. 

The VLTI image reveals that in March 2008 the angular distance between the two stars was only about 20 milliarcseconds. Additional position measurements of the binary system have been obtained over the last 12 years using the technique of bispectrum speckle interferometry with 3.6- to 6-meter-class telescopes, allowing high-angular resolution observations even at visual wavelengths down to 440 nm.

The collection of measurements shows that the two massive stars are on a very eccentric orbit with a period of 11 years. Using Kepler’s third law, the masses of the two stars were derived to be 38 and 9 solar masses. Furthermore, the measurements allow a trigonometric determination of the distance to Theta 1 Ori C and, thus, to the very center of the Orion star-forming region.

The resulting distance of 1,350 light-years is in excellent agreement with the work of another research group led by Karl Menten, also from MPIfR, who measured trigonometric parallaxes of the nonthermal radio emission of Orion Nebula stars using the Very Long Baseline Array. These results are important for studies of the Orion region as well as the improvement of theoretical models of high-mass star formation.

The researchers say the results highlight new possibilities of high-resolution stellar imaging achievable with infrared interferometry. The technique allows astronomers to combine the light from several telescopes, forming a huge virtual telescope with a resolving power corresponding to that of a single telescope with 200 meters diameter. 

“Our observations demonstrate the fascinating new imaging capabilities of the VLTI,” said Gerd Weigelt. “This infrared interferometry technique will certainly lead to many fundamental new discoveries.”

LEAD IMAGE CAPTION: VLTI/AMBER image of Theta 1 Ori C in the Orion Trapezium Cluster, plus position measurements of the binary system obtained over the last 12 years. Credit: Max Planck Institute/VLTI/AMBER

Sources: Max Planck Institute press release (emailed through Eurekalert), and the original paper.