Friday, June 29, 2007

Summer Moon Illusion

Sometimes you can't believe your eyes. This weekend is one of those times. On Saturday night, June 30th, step outside at sunset and look around. You'll see a giant moon rising in the east. It looks like Earth's moon with the usual craters and seas, but something's wrong. This full moon is strangely inflated. It's huge!

You've just experienced the Moon Illusion.

Sky watchers have known for thousands of years that low-hanging moons look unnaturally big. Cameras don't see it, but human eyes do; it's a genuine illusion.

Above: A time-lapse sequence of the moon rising over Seattle. To the camera, the moon appears to be the same size no matter what its location on the sky. Credit and copyright: Shay Stephens.

Read more Summer Moon Illusion from NASA

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Thursday, June 28, 2007

NASA mission to Ceres & Vesta

Dawn Spacecraft launch from Cape Canaveral scheduled for July 7th

Dawn will conduct a detailed study of the structure and composition of two of the first bodies formed in our solar system: the "dwarf planet" Ceres and the massive asteroid Vesta. The mission's goals include determining the shape, size, composition, internal structure, the tectonic and thermal evolution of Vesta and Ceres.

Dawn, which will be the first spacecraft to orbit two planetary bodies on the same mission, is expected to reveal the conditions under which these objects formed. Comparing their different evolutionary paths will provide evidence about the role of size and water in planetary evolution.

Dawn is scheduled to fly past Mars by April 2009, and after more than four years of travel, the spacecraft will rendezvous with Vesta in 2011. The spacecraft will orbit Vesta for approximately nine months, studying its structure and composition. In 2012, Dawn will leave for a three-year cruise to Ceres. Dawn will rendezvous with Ceres and begin orbit in 2015, conducting studies and observations for at least five months.

Read more NASA's Dawn Mission from Science Daily
Artist's impression of the Dawn spacecraft. (Credit: W.K. Hartmann Courtesy / UCLA)

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Wednesday, June 27, 2007

Event Horizon & BlackHoles

Astronomers May Have Solved Information Loss Paradox To Find Black Holes Do Not Form

"Nothing there," is what Case Western Reserve University physicists concluded about black holes after spending a year working on complex formulas to calculate the formation of new black holes.

The question that the physicists set out to solve is: what happens once something collapses into a black hole. If all information about the collapsing matter is lost, it defies the laws of quantum physics. Yet, in current thinking, once the matter goes over the event horizon and forms a black hole, all information about it is lost.
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Case physicists Tanmay Vachaspati, Dejan Stojkovic and Lawrence M. Krauss report in the article, "Observation of Incipient Black Holes and the Information Loss Problem," that has been accepted for publication by Physical Review D. "It's complicated and very complex," noted the researchers, regarding both the general problem and their particular approach to try to solve it.

"If you define the black hole as some place where you can lose objects, then there is no such thing because the black hole evaporates before anything is seen to fall in," said Vachaspati.
The masses on the edge of the incipient black hole continue to appear into infinity that they are collapsing but never fall over inside what is known as the event horizon, the region from which there is no return, according to the researchers.

By starting out with something that was nonsingular and then collapsing that matter, they were determined to see if an event horizon formed, signaling the creation of a black hole.
The mass shrinks in size, but it never gets to collapse inside an event horizon due to evidence of pre-Hawking radiation, a non-thermal radiation that allows information of the nature of what is collapsing to be recovered far from the collapsing mass.

"Non-thermal radiation can carry information in it unlike thermal radiation. This means that an outside observer watching some object collapse receives non-thermal radiation back and may be able to reconstruct all the information in the initial object and so the information never gets lost," they said.

According to the researchers, if black holes exist, information formed in the initial state would disappear in the black hole through a burst of thermal radiation that carries no information about the initial state.

Using the functional Schrodinger formalism, the researchers suggest that information about the energy from radiation is long evaporated before an event horizon forms.

"An outside observer will never lose an object down a black hole," said Stojkovic. "If you are sitting outside and throwing something into the black hole, it will never pass over but will stay outside the event horizon even if one considers the effects of quantum mechanics. In fact, since in quantum mechanics the observer plays an important role in measurement, the question of formation of an event horizon is much more subtle to consider."

The physicists are quick to assure astronomers and astrophysicists that what is observed in gravity pulling masses together still holds true, but what is controversial about the new finding is that "from an external viewer's point it takes an infinite amount of time to form an event horizon and that the clock for the objects falling into the black hole appears to slow down to zero," said Krauss, director of Case's Center for Education and Research in Cosmology.

He continued "this is one of the factors that led us to rethink this problem, and we hope our proposal at the very least will stimulate a broader reconsideration of these issues."

Adapted from a news release by Case Western Reserve University.

If black holes exist in the universe, the astrophysicists speculate they were formed only at the beginning of time.

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Tuesday, June 26, 2007

Circinus X-1

Neutron Stars Join The Black Hole Jet Set

This artist's illustration depicts the jet of relativistic particles blasting out of Circinus X-1, a system where a neutron star is in orbit with a star several times the mass of the Sun.

The neutron star, an extremely dense remnant of an exploded star consisting of tightly packed neutrons, is seen as the sphere at the center of the disk. The powerful gravity of the neutron star pulls material from the companion star (shown as the blue star in the background) into a so-called accretion disk surrounding it.

Through a process that is not fully understood, a jet of material moving at nearly the speed of light is generated. A high percentage of the energy available from material falling toward the neutron star is converted into powering this jet.
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The image in the inset is Chandra's X-ray image of the neutron star in Circinus X-1. Low energy X-rays are shown in red, medium energy X-rays in green and high energies in blue. The jet itself is seen to the upper right corner and consists of two fingers of X-ray emission (shown in red) separated by about 30 degrees. These two fingers, located at least about 5 light years from the neutron star, may represent the outer walls of a wide jet. Alternatively, they may represent two separate, highly collimated jets produced at different times by a precessing neutron star. That is, the neutron star may wobble like a top as it spins and the jet fires at different angles at different times. The structures on the opposite side (red, to the lower left) may be evidence for counter jets. The rest of the colored areas surrounding the bright central source are instrumental artifacts and not representative of structures associated with Circinus X-1.

The jet in Circinus X-1 is helping astronomers better understand how neutron stars, and not just black holes, can generate these powerful beams. Many jets have been found originating near black holes (both the supermassive and stellar-mass variety), but the Circinus X-1 jet is the first extended X-ray jet associated with a neutron star in a binary system. This detection shows that the unusual properties of black holes -- such as presence of an event horizon and the lack of an actual surface -- may not be required to form powerful jets. The result also reveals how efficient neutron stars can be as cosmic power factories.

Circinus Constellation about 31,000 light years from Earth
Credit: X-ray: NASA/CXC/S.Heintz et al; Illustration: NASA/CXC/M.Weiss

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Swift sees double Supernova

NASA's Swift Sees Double Supernova
Credit: Stefan Immler NASA/GSFC,
Swift Science Team.

Two supernovae have flared up in an obscure galaxy in the Hercules constellation.
Never before have astronomers observed two of these powerful stellar explosions occurring in the same galaxy so close together in time.

The galaxy, known as MCG +05-43-16, is 380 million light-years from Earth. Until this year, astronomers had never sighted a supernova popping off in this stellar congregation. A supernova is an extremely energetic and life-ending explosion of a star.

Making the event even more unusual is the fact that the two supernovae belong to different types:

Supernova 2007ck is a Type II event – which is triggered when the core of a massive star runs out of nuclear fuel and collapses gravitationally, producing a shock wave that blows the star to smithereens. Supernova 2007ck was first observed on May 19.

In contrast, Supernova 2007co is a Type Ia event, which occurs when a white dwarf star accretes so much material from a binary companion star that it blows up like a giant thermonuclear bomb. It was discovered on June 4, 2007. A white dwarf is the exposed core of a star after it has ejected its atmosphere; it’s approximately the size of Earth but with the mass of our Sun.

"Most galaxies have a supernova every 25 to 100 years, so it’s remarkable to have a galaxy with two supernovae discovered just 16 days apart," says Stefan Immler. In 2006 Immler used NASA’s Swift satellite to image two supernovae in the elliptical galaxy NGC 1316, but both of those explosions were Type Ia events, and they were discovered six months apart.

The simultaneous appearance of two supernovae in one galaxy is an extremely rare occurrence, but it’s merely a coincidence and does not imply anything unusual about MCG +05-43-16.

Because the two supernovae are tens of thousands of light-years from each other, and because light travels at a finite speed, astronomers in the galaxy itself, or in a different galaxy, might record the two supernovae exploding thousands of years apart.

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Monday, June 25, 2007

A Window to the Stars

ESA’s orbiting gamma-ray observatory, Integral, has made a pioneering unequivocal discovery of radioactive iron-60 in our galaxy that provides powerful insight into the workings of massive stars that pervade and shape it.

Found drifting in space, the radioactive isotope has been sought for long. All past reported sightings of iron-60 have been subject to controversy. Now Integral has provided unequivocal evidence.
Since late 2002, Integral has been collecting data from across the galaxy. It shows an enhancement in gamma rays at two characteristic energies, 1173 and 1333 kilo electron Volts. These are produced by radioactive decay of iron-60 into cobalt-60.
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Roland Diehl of the Max-Planck-Institut für extraterrestrische Physik, headed the work and believes it is a major step forward. “These gamma-ray lines have been detected before with some dispute. Integral, the only instrument capable of doing this, shows that iron-60 does exist in interstellar space in our Galaxy,” he says.

More than a curiosity, its presence opens a door into the very heart of the most massive stars in the cosmos. The majority of chemical elements are built inside stars from raw ingredients present during star formation from an interstellar gas cloud. In addition to hydrogen and helium produced during the Big Bang, the gas contained enrichments, known to astronomers as ‘metals’, from previous generations of stars and their nuclear reactions.

Until this detection, astronomers had only one radioactive isotope to probe into the current build-up of chemical elements in stars and their distribution with respect to future star formation. That was the radioactive isotope aluminium-26, first discovered in 1978. “The study of aluminium-26 has developed into its own branch of astronomy,” says Diehl.

Iron-60 gives astronomers valuable new insight - although produced in the same stars as aluminium-26, its production differs markedly. Iron-60 is synthesised both later in a star’s life and deeper inside.

As massive stars age, they develop a layered structure in which different chemical elements are fused together. While aluminium-26 is one rung on the ladder of nuclear reactions, iron-60 is produced from pre-existing stable iron isotopes by a process called ‘neutron capture’ in the respective layers where helium and carbon atoms are undergoing fusion.

“Iron-60 provides the entry into studying neutron capture in stars through contemporaneous radioactivity,” says Diehl. It has also prompted a number of particle accelerators to begin more detailed studies of how easily iron captures neutrons.

Unlike aluminium-26, iron-60 is only expelled into space when the star explodes at the end of its life. It then decays with a half-life of 1.5 million years, producing the gamma rays that Integral detected.

The new data pins down the ratio of iron-60 to aluminium-26, which has a half-life of 740 000 years. Previous predictions have fallen anywhere between 10 and 100 percent. Integral shows it to be 15 percent, which agrees well with current theoretical estimates. But theoreticians and nuclear physicists have been stimulated by Integral’s results to strive for more precise predictions.

Radioactive iron, a window to the stars from ESA and Max Planck Institut

Although Integral clearly sees the telltale gamma rays, they are too faint for it to map out enhancements and paucities across the Galaxy. Mapping the distribution of iron-60 is a job for the next generation of gamma-ray instruments.

Nevertheless, the team will continue observing with Integral for as long as they can, in the hope of gaining some coarse ideas about the isotope’s spread across the Galaxy.
GZK cut-off Cosmic Rays & Cosmic Showers from Bee @ Backreaction

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Sunday, June 24, 2007

New view of ETA

Composite image of the Eta Carinae from NASA's Chandra X-ray Observatory and Hubble Space Telescope shows the remnants of a massive eruption from the star during the 1840s.

Eta Carinae is a mysterious, extremely bright and unstable star located about 7,500 light years from Earth. The star is thought to be consuming its nuclear fuel at an incredible rate, while quickly drawing closer to its ultimate explosive demise.

When Eta Carinae does explode, it will be a spectacular fireworks display seen from Earth, perhaps rivaling the moon in brilliance. Its fate has been foreshadowed by the recent discovery of SN2006gy, a supernova in a nearby galaxy that was the brightest stellar explosion ever seen. The erratic behavior of the star that later exploded as SN2006gy suggests that Eta Carinae may explode at any time.

Eta Carinae, a star between 100 and 150 times more massive than the Sun, is near a point of unstable equilibrium where the star's gravity is almost balanced by the outward pressure of the intense radiation generated in the nuclear furnace. This means that slight perturbations of the star might cause enormous ejections of matter from its surface.

In the 1840s, Eta Carinae had a massive eruption by ejecting more than 10 times the mass of the sun, to briefly become the second brightest star in the sky. This explosion would have torn most other stars to pieces but somehow Eta Carinae survived.

This hot shroud extends far beyond the cooler, optical nebula and represents the outer edge of the interaction region. The X-ray observations show that the ejected outer material is enriched by complex atoms, especially nitrogen, cooked inside the star's nuclear furnace and dredged up onto the stellar surface.

The Chandra observations also show that the inner optical nebula glows faintly due to X-ray reflection. The X-rays reflected by the optical nebula come from very close to the star itself; these X-rays are generated by the high-speed collision of wind flowing from Eta Carinae's surface (moving at about 1 million miles per hour) with the wind of the companion star (which is about five times faster).

The companion is not directly visible, but variability in X-rays in the regions close to the star signals the star's presence. Astronomers don't know exactly what role the companion has played in the evolution of Eta Carinae, or what role it will play in its future.

Original Source Chandra: A new view of doomed star

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Monday, June 11, 2007

Merope Reflection

The Merope Reflection Nebula
Credit & Copyright: Jean-Charles Cuillandre (CFHT), Hawaiian Starlight, CFHT

Reflection nebulas reflect light from a nearby star. Many small carbon grains in the nebula reflect the light.

The blue colour typical of reflection nebula is caused by blue light being more efficiently scattered by the carbon dust than red light.

The brightness of the nebula is determined by the size and density of the reflecting grains, and by the colour and brightness of the neighbouring star(s).

NGC 1435, pictured above, surrounds Merope (23 Tau), one of the brightest stars in the Pleiades (M45). The Pleiades nebulosity is caused by a chance encounter between an open cluster of stars and a molecular cloud.

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Friday, June 08, 2007

Black Eyed Galaxy

A collision of two galaxies has left a merged star system with an unusual appearance as well as bizarre internal motions. Messier 64 (M64) has a spectacular dark band of absorbing dust in front of the galaxy's bright nucleus, giving rise to its nicknames of the "Black Eye" or "Evil Eye" galaxy.

Fine details of the dark band are revealed in this image of the central portion of M64 obtained with the Hubble Space Telescope. M64 is well known among amateur astronomers because of its appearance in small telescopes. It was first cataloged in the 18th century by the French astronomer Messier. Located in the northern constellation Coma Berenices, M64 resides roughly 17 million light-years from Earth.

At first glance, M64 appears to be a fairly normal pinwheel-shaped spiral galaxy. As in the majority of galaxies, all of the stars in M64 are rotating in the same direction, clockwise as seen in the Hubble image. However, detailed studies in the 1990's led to the remarkable discovery that the interstellar gas in the outer regions of M64 rotates in the opposite direction from the gas and stars in the inner regions.

Active formation of new stars is occurring in the shear region where the oppositely rotating gases collide, are compressed, and contract. Particularly noticeable in the image are hot, blue young stars that have just formed, along with pink clouds of glowing hydrogen gas that fluoresce when exposed to ultraviolet light from newly formed stars.

Astronomers believe that the oppositely rotating gas arose when M64 absorbed a satellite galaxy that collided with it, perhaps more than one billion years ago. This small galaxy has now been almost completely destroyed, but signs of the collision persist in the backward motion of gas at the outer edge of M64.

This image of M64 was taken with Hubble's Wide Field Planetary Camera 2 (WFPC2). The colour image is a composite prepared by the Hubble Heritage Team from pictures taken through four different colour filters. These filters isolate blue and near-infrared light, along with red light emitted by hydrogen atoms and green light from Strömgren y.

Credit: NASA and The Hubble Heritage Team (AURA/STScI)
Acknowledgment: S. Smartt (Institute of Astronomy) and D. Richstone (U. Michigan)

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Tuesday, June 05, 2007

Pulsating Red Giant S-Ori

Sketch of the structure of a pulsating red giant, as derived by the recent interferometric study on S Orionis. The environment around the parent star is made up by three main components: a molecular shell (inner red layer), a dust shell (outer red layer) and a maser shell (red and green speckles). Grains of aluminum oxide constitute most of the dust shell (observed in the infrared band), while the maser radio emission comes from silicon monoxide molecules. The maser spots velocities indicates that the gas is expanding, at a speed of about 10 km/s. (Credit: ESO)

A star such as the Sun will lose between a third and half of its mass during the Mira phase.
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S Orionis (S Ori) belongs to the class of Mira-type variable stars. It is a solar-mass star that, as will be the fate of our Sun in 5 billion years, is nearing its gloomy end as a white dwarf. When it will become a red giant, such as S Orionis, its average size will enshroud the orbit of Mercury, Venus, the Earth and Mars. Jupiter's orbit will be just outside the maser shell.

Mira stars are very large and lose huge amounts of matter. Every year, S Ori ejects as much as the equivalent of Earth's mass into the cosmos, and pulsates with a period of 420 days. In the course of its cycle, it changes its brightness by a factor of the order of 500, while its diameter varies by about 20%.

Although such stars are enormous - they are typically larger than the current Sun by a factor of a few hundred, i.e. they encompass the orbit of the Earth around the Sun - they are also distant and to peer into their deep envelopes requires very high resolution. This can only be achieved with interferometric techniques.

The maser emission comes from silicon monoxide (SiO) molecules and can be used to image and track the motion of gas clouds in the stellar envelope roughly 10 times the size of the Sun.

The astronomers observed S Ori with two of the largest interferometric facilities available: the ESO Very Large Telescope Interferometer (VLTI) at Paranal, observing in the near- and mid-infrared, and the NRAO-operated Very Long Baseline Array (VLBA), that takes measurements in the radio wave domain.

Because the star's luminosity changes periodically, the astronomers observed it simultaneously with both instruments, at different epochs. The first epoch occurred close to the stellar minimum luminosity and the last just after the maximum on the next cycle.

The star's diameter varies between 7.9 milliarcseconds and 9.7 milliarcseconds. At the distance of S Ori, this corresponds to a change of the radius from about 1.9 to 2.3 times the distance between the Earth and the Sun, or between 400 and 500 solar radii!

As if such sizes were not enough, the inner dust shell is found to be about twice as big. The maser spots, which also form at about twice the radius of the star, show the typical structure of partial to full rings with a clumpy distribution. Their velocities indicate that the gas is expanding radially, moving away at a speed of about 10 km/s.

The multi-wavelength analysis indicates that near the minimum there is more dust production and mass ejection: in these phases indeed the amount of dust is significantly higher than in the others. After this intense matter production and ejection the star continues its pulsation and when it reaches the maximum luminosity, it displays a much more expanded dust shell. This supports a strong connection between the Mira pulsation and the dust production and expulsion.

Astronomers further found that grains of aluminum oxide - also called corundum - constitute most of S Ori's dust shell: the grain size is estimated to be of the order of 10 millionths of a centimetre, that is one thousand times smaller than the diameter of a human hair.

"Because we are all stardust, studying the phases in the life of a star when processed matter is sent back to the interstellar medium to be used for the next generation of stars, planets... and humans, is very important" - Markus Wittkowski.

Original source ESO Press Release
Note: A maser is the microwave equivalent to a laser, which emits visible light. A maser emits powerful microwave radiation instead and its study requires radio telescopes. An astrophysical maser is a naturally occurring source of stimulated emission that may arise in molecular clouds, comets, planetary atmospheres, stellar atmospheres, or from various conditions in interstellar space.

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Sunday, June 03, 2007

XMM Newton. The Next Decade

Science Worshops

Thanks to the recent generation of high energy observatories, astrophysics is witnessing a golden age of discovery in the X-ray domain.

Current technical evaluation demonstrates that the XMM-Newton spacecraft and its scientific instruments can continue to provide first class X-ray observations far into the next decade.

Other missions to be launched soon, like Herschel, Planck, GLAST, as well as new ground-based developments, will open up new challenging opportunities for multi-wavelength and follow-up observations to which XMM-Newton is ideally placed to make a major contribution.

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Friday, June 01, 2007

Star Formation

A new Star is Born

Star formation results in a complicated system in which the young star is surrounded by a disc of gas and dust. This matter then follows one of three different routes. It finds its way onto the star through magnetic funnels, or stays in the disc to form planets, or is thrown clear of the system in a wind or jet created by the overall magnetic field.

XMM-Newton was used to target stars in the nearby Taurus Molecular Cloud. This vast cloud in space is one of the star-forming regions nearest to Earth and contains over 400 young stars.

The results defy astronomers’ expectations, as the streams of falling matter interact with the hot corona, cooling it, while the ejected streams of gas heat up in shocks as they are ejected from the star.

Most of these stars are still accumulating matter, a process known as accretion. As falling matter strikes the surface of the star, it typically doubles the temperature of the surface from 5000 Kelvin to 10 000 Kelvin. This produces an excessive amount of ultraviolet radiation emitted by the star and detected by XMM-Newton’s Optical Monitor. Astronomers had thought that the same shock waves that caused the emission of the ultraviolet excess should also produce an excess of X-rays.

Taurus Molecular Cloud Credits:(FCRAO), Gopal Narayanan / Mark Heyer
X-ray young stars in Taurus region Credits: ESA/XMM-Newton/Paul Scherrer Institut
XMM-Newton reveals X-rays from gas streams around young stars from ESA
XMM-Newton deciphers the magnetic physics around forming stars
Special feature from Astronomy & Astrophysics

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