Saturday, September 29, 2007

The Trifid Nebula

The Trifid Nebula. Credit & Copyright: R. Jay GaBany (

Unspeakable beauty and unimaginable bedlam can be found together in the Trifid Nebula. Also known as M20, this photogenic nebula is visible with good binoculars towards the constellation of Sagittarius.

The energetic processes of star formation create not only the colours but the chaos. The red-glowing gas results from high-energy starlight striking interstellar hydrogen gas. The dark dust filaments that lace M20 were created in the atmospheres of cool giant stars and in the debris from supernovae explosions. Which bright young stars light up the blue reflection nebula is still being investigated. The light from M20 we see today left perhaps 3000 years ago, although the exact distance remains unknown. Light takes about 50 years to cross M20.

Labels: , , ,

Friday, September 28, 2007

Planetary Nebulae

Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA) STScI-PRC07-33a

The colourful, intricate shapes in these NASA Hubble Space Telescope images reveal how the glowing gas ejected by dying Sun-like stars evolves dramatically over time.

These gaseous clouds, called planetary nebulae, are created when stars in the last stages of life cast off their outer layers of material into space. Ultraviolet light from the remnant star makes the material glow. Planetary nebulae last for only 10,000 years, a fleeting episode in the 10-billion-year lifespan of Sun-like stars.

The name planetary nebula has nothing to do with planets. They got their name because their round shapes resembled planets when seen through the small telescopes of the eighteenth century.

The Hubble images show the evolution of planetary nebulae, revealing how they expand in size and change temperature over time. A young planetary nebula, such as He 2-47, is small and dominated by relatively cool, glowing nitrogen gas. In the Hubble images, the red, green, and blue colours represent light emitted by nitrogen, hydrogen, and oxygen, respectively.

Over thousands of years, the clouds of gas expand away and the nebulae become larger. Energetic ultraviolet light from the star penetrates more deeply into the gas, causing the hydrogen and oxygen to glow more prominently, as seen near the center of NGC 5315. In the older nebulae, such as IC 4593, at bottom, left, and NGC 5307, at bottom, right, hydrogen and oxygen appear more extended in these regions, and red knots of nitrogen are still visible.
[+/-] Click here to expand

These four nebulae all lie in our Milky Way Galaxy. Their distances from Earth are all roughly the same, about 7,000 light-years. The snapshots were taken with Hubble's Wide Field Planetary Camera 2 in February 2007. Like snowflakes, planetary nebulae show a wide variety of shapes, indicative of the complex processes that occur at the end of stellar life.

He 2-47, is dubbed the "starfish" because of its shape. The six lobes of gas and dust, which resemble the legs of a starfish, suggest that He 2-47 puffed off material at least three times in three different directions. Each time, the star fired off a narrow pair of opposite jets of gas. He 2-47 is in the southern constellation Carina.

NGC 5315, the chaotic-looking nebula at top, reveals an x-shaped structure. This shape suggests that the star ejected material in two different outbursts in two distinct directions. Each outburst unleashed a pair of diametrically opposed outflows. NGC 5315 lies in the southern constellation Circinus.

IC 4593, is in the northern constellation Hercules. NGC 5307, displays a spiral pattern, which may have been caused by the dying star wobbling as it expelled jets of gas in different directions. NGC 5307 resides in the southern constellation Centaurus.

A Grand Vision for European Astronomy from ESO
A New Reduction of the Hipparcos Catalogues from ESA
Mysterious radio signal from deep space @ Cosmos Magazine
Mysterious Energy Burst Stuns Astronomers from Science Daily

Labels: , , ,

Thursday, September 27, 2007

The Ant Nebula

The Ant Nebula (Planetary Nebula Menzel 3, or Mz3) - from Hubble

The Ant Nebula (Mz3) is located about 5 000 light-years away. The central star is as bright as 10 000 Suns and has a temperature of 35 thousand degrees Celsius. It is the last phase before this solar-like star will become a white dwarf.

From ground-based telescopes, the so-called "ant nebula" resembles the head and thorax of a garden-variety ant. This dramatic 2001 NASA/ESA Hubble Space Telescope image, reveals the "ant's" body as a pair of fiery lobes protruding from a dying, Sun-like star.

The ejection of gas from the dying star at the center of Mz 3 has intriguing symmetrical patterns unlike the chaotic patterns expected from an ordinary explosion. Scientists using Hubble would like to understand how a spherical star can produce such prominent, non-spherical symmetries in the gas that it ejects.

One possibility is that the central star of Mz 3 has a closely orbiting companion that exerts strong gravitational tidal forces, which shape the outflowing gas. For this to work, the orbiting companion star would have to be close to the dying star, about the distance of the Earth from the Sun. At that distance the orbiting companion star wouldn't be far outside the hugely bloated hulk of the dying star. It's even possible that the dying star has consumed its companion, which now orbits inside of it.

A second possibility is that, as the dying star spins, its strong magnetic fields are wound up into complex shapes. Charged winds moving at speeds up to 1000 kilometers per second from the star, much like those in our Sun's solar wind but millions of times denser, are able to follow the twisted field lines on their way out into space. These dense winds can be rendered visible by ultraviolet light from the hot central star or from highly supersonic collisions with the ambient gas that excites the material into florescence.

The frugal Cosmic Ant - from ESO

These new images revealing the Ant Nebula disc, which cannot be detected with a single 8.2-m VLT Unit Telescope, were uncovered in the interferometric mode, through the MID-infrared Interferometric instrument (MIDI). Interferometry works by combining the light of two or more telescopes, so that they act as a single, giant telescope, as large as the entire group.

With ESO's Very Large Telescope Interferometer (VLTI), when combining two of the 8.2-m Unit Telescopes, up to 25 times finer detail can be observed than with the individual telescopes.

The observations reveal a flat, nearly edge-on disc whose major axis is perpendicular to the axis of the bipolar lobes. The disc extends from about 9 times the mean distance between the Earth and the Sun (9 Astronomical Units or 9 AU) to more than 500 AU.

At the distance of the Ant Nebula, this corresponds to having detected structures that subtend an angle of only 6 milli-arcseconds. This is similar to distinguishing a two-storey building on the Moon.

The dust mass stored in the disc appears to be only one hundred thousandth the mass of the Sun and is a hundred times smaller than the mass found in the bipolar lobes.

Team leader Olivier Chesneau, from the Observatoire de la Côte d'Azur (France) suggests "We must therefore conclude that the disc is too light to have a significant impact on the outflowing material and cannot explain the shape of the Ant Nebula. Instead, it looks more like this disc is some remnant of the material expelled by the star."

The observations also provide unquestionable evidence that the disc is primarily composed of amorphous silicate. "This," says Chesneau, "most likely indicates that the disc is young, perhaps as young as the planetary nebula itself."

The astronomers favour the possibility that the large quantity of material in the lobes was propelled by several large-scale events, triggered with the help of a cool stellar companion. The solution of the mystery thus resides in the core of the system, and requires better characterisation of the hot central star and its putative companion, currently hidden from our view by the dusty disc.
VLT Interferometer detects disc around aged star from ESO
Nasa's Galex witnesses a spiral galaxy being stripped of its star

Labels: , , ,

Wednesday, September 26, 2007

Water on Earth

Scientists believe that just after the Earth formed, it was very hot and dry. Theory also suggests that millions of water-rich comets and asteroids bombarded our planet around 3.8 billion years ago, neatly explaining why oceans later appeared.

What's more, the ratio of deuterium – or "heavy hydrogen" because it contains a neutron in addition to a proton – to hydrogen in our sea water matches the value found in water-rich asteroids, suggesting a common origin.

But Hidenori Genda and his colleague Masahiro Ikoma from the Tokyo Institute of Technology suggest another possibility. They say the Earth could have had a thick atmosphere of hydrogen, which reacted with oxides in the Earth's mantle to produce copious water.
[+/-] Click here to expand

Evidence for the thick hydrogen shroud comes from the Earth's orbit. Its orbit, like those of Venus and Mars, is very circular now, but models suggest it started out more elongated. If the planets were still submerged in a thick, hydrogen-rich solar nebula after they formed, however, the thick gas might have damped out any elongation of the orbits.

If the water on Earth did form from a thick hydrogen atmosphere, however, it should have originally had a far lower value of the deuterium-to-hydrogen ratio than we see in sea water today. But Genda and Ikoma have got round this problem. Their calculations show that the ratio would have naturally drifted upwards over time.

Several effects would have contributed to this rise, including leakage of hydrogen into space. Energy from the Sun would have made most of the hydrogen escape, but the heavier deuterium would have escaped less easily, so it would have become more concentrated.

Also, chemical reactions favour the gradual exchange of hydrogen in water molecules for deuterium. Genda and Ikoma conclude from their calculations that that the oceans might well have been chemically manufactured right here on Earth.

Kathrin Altwegg, a comet expert from Bern University in Switzerland. "We might have to rethink theories of how much water the comets could have brought." She suspects the picture might be a complex one in which water came from chemical reactions on Earth as well as asteroids and comets.

But Altwegg says much more observational evidence is needed to clarify our hazy picture of the solar system's early history. Spacecraft missions need to investigate deuterium-to-hydrogen ratios on planets, moons and comets at various locations across the solar system, she says.

One intriguing clue could come from NASA's Phoenix Mars Lander, due to arrive on the Red Planet in May 2008. It aims to measure the deuterium-to-hydrogen ratio in Martian water ice for the first time.

Life-Giving Rocks From A Depth Of 250 km from Terra Daily
Ice Age extinction by Extraterrestrial Impact? by Casey Kazam
Dawn's early light, Ceres & Vesta by Amara @ Scientific Blogging

September Full Moon

China aims for lunar base after 2020
Asian spacefarers race for the moon from Moon Daily
The Moon belongs to Asia from Second Effort Blogspot

Tuesday, September 25, 2007

Feasting Blackhole bubbles

These NASA Hubble Space Telescope images of the galaxy's central region clearly show one of the bubbles rising from a dark band of dust. The other bubble, emanating from below the dust band, is barely visible, appearing as dim red blobs in the close-up picture of the galaxy's hub (the colourful picture at right).

The background image represents a wider view of the galaxy, with the central region defined by the white box.

These extremely hot bubbles are caused by the black hole's voracious eating habits. The eating machine is engorging itself with a banquet of material swirling around it in an accretion disk (the white region below the bright bubble). Some of this material is spewed from the disk in opposite directions. Acting like high-powered garden hoses, these twin jets of matter sweep out material in their paths.

The jets eventually slam into a wall of dense, slow-moving gas, which is traveling at less than 223,000 mph (360,000 kph). The collision produces the glowing material. The bubbles will continue to expand and will eventually dissipate.

Credits: NASA and Jeffrey Kenney (Yale University)
Journey to the Black Hole from Space dotcom
Black Holes and Naked Singularities from Science Daily
Searching for Objects Even Stranger Than Black Holes from Universe Today

Labels: , ,

Monday, September 24, 2007

Hidden Galaxies detected

Until now astronomers couldn't see foreground galaxies outshined by the dazzling quasars behind them. The difficulty in actually spotting and seeing these galaxies stems from the fact that the glare of the quasar is too strong compared to the dim light of the galaxy.

A new technique can pick apart the intense pattern of light emitted by quasars, finding irregularities in the image where "invisible" galaxies are absorbing some of the quasar light.

Quasars are small, distant and extremely bright cosmic beacons that produce more light than typically comes from an entire large galaxy. In spite of their brightness, however, some of the light is soaked up by intervening objects during its long journey to Earth's telescopes.

To locate the so-called "invisible" galaxies, Nicholas Bouche - an astronomer at the Max Planck Institute for Extraterrestrial Physics in Munich, Germany - and his team looked through huge catalogues of quasar data and picked out those with "dips" in their light signatures. Then, using the European Southern Observatory's (ESO) Very Large Telescope (VLT), located in the mountains of northern Chile, the team searched for galaxies close to the pulse of quasar light.

The astronomers capitalized on the VLT's special infrared spectrometer, called SINFONI, to pick apart 20 patches of sky around the quasars to search for galaxies from the time when the universe was about 6 billion years old. Seventy percent of the time, they found a galaxy hiding in the "headlights" of a quasar.

The astronomers who pioneered the technique have detected 14 hidden galaxies by targeting the VLT on unusual quasar light signatures. Bouche said he is surprised by not only the amount of galaxies he and his colleagues have found hiding near quasars, but also by the types of these galaxies. "These are not just ordinary galaxies," he said. "They are actively forming a lot of new stars and qualifying as starburst galaxies."

Source: Space dotcom
Quasar Jets Create Cosmic Pileups
Hidden Black Holes Found Behind Gas Veils at Quasars
Screaming to the Stars, Quasar Echos from Pamela Star Stryder

Labels: , ,

Saturday, September 22, 2007

Violent Starquakes

A neutron star is the dense core left behind when a massive star explodes as a supernova. Some have such powerful magnetic fields that they rip themselves open due to magnetic forces.

The spins of some neutron stars decrease rapidly, and extremely powerful magnetic fields that radiate electromagnetic energy may slow their rotation. This type of neutron star is called a magnetar.

New observations of a candidate magnetar have confirmed that it has a magnetic field 600 trillion times the strength of Earth's field – powerful enough to explain the 'starquake' it experienced in 2003.

Researchers used the XMM-Newton spacecraft to measure X-rays from a neutron star called XTE J1810-197, which lies about 10,000 light years from Earth in the constellation Sagittarius.

Discovered in 2003 when it had a major outburst, suddenly becoming more than 100 times brighter than normal in X-rays. The event was similar to magnetic starquakes seen on other candidate magnetars.

The idea is that the crust of the neutron star buckles and cracks due to the magnetic forces exerted by the star's own magnetic field.
[+/-] Click here to expand

There were other possible explanations of these outbursts, such as sudden changes to the magnetosphere (cloud of charged particles) that surrounds the stars.

By analysing the spectrum of X-rays coming from XTE J1810-197 since its 2003 outburst, the research team determined the existence of a hot spot about 7 kilometres wide at the neutron star's surface. The spot was heated to about 5 million degrees by the outburst, and has been cooling since then. This is consistent with the starquake theory, in which the part of the neutron star's crust that buckles releases tremendous energy and heats up its surroundings.

Jules Halpern of Columbia University in New York City, US, says further studies of such outbursts may reveal why magnetars have such short lives. The known magnetars all appear to be very young – most are less than 10,000 years old.

It may be the case that hundreds of outbursts over the lifetime of the star are responsible for dissipating most of the magnetic field. After that . . . they may turn into ordinary radio pulsars or some other type of neutron star.

Reference: The Astrophysical Journal Letters (vol 667, p 73)
Explosion Reveals Tiny Magnetic Island from Space Daily
EINSTEIN - AN EDGE SYMPOSIUM Super Strings & The Multiverse
Missing Link In The Evolution Of Magnetic Cataclysmic Stars? from Science Daily


Labels: ,

Thursday, September 20, 2007

Galaxy Plunges into Cluster

The almost 200,000 light year long comet-like tail was created as gas was stripped from ESO 137-001 while it plunges toward the center of Abell 3627, a giant cluster of galaxies.

Cool gas from the galaxy - only seen in optical images - is mixed in with hot gas from the cluster as seen in X-rays (blue).

Astronomers have found evidence that stars have been forming in the long tail of gas that extends well outside its parent galaxy. This discovery suggests that such "orphan" stars may be much more prevalent than previously thought.

This is one of the longest tails like this we have ever seen," said Ming Sun of Michigan State University, who led the study. "And, it turns out that this is a giant wake of creation, not of destruction."

"This isn't the first time that stars have been seen to form between galaxies," said team member Megan Donahue, also of MSU. "But the number of stars forming here is unprecedented."

The stars in the tail of this fast-moving galaxy, which is some 220 million light years away, would be much more isolated than the vast majority of stars in galaxies.
Orphan Stars Found in Long Galaxy Tail from Chandra

Wednesday, September 19, 2007

Primordial Black Holes

Click on Image to Enlarge. Image Credit: Sprott Physics

Were vast numbers of black holes spawned during the universe's earliest moments?

So far, there is no hard evidence that such primordial black holes (PBHs) ever existed, but new observations just around the corner could change that.

There are a variety of ways that PBHs might have formed in the early universe. Concentrations of energy associated with exotic energy fields could collapse under their own gravity – according to Einstein's relativity, energy exerts gravity just as matter does – to make black holes. One such energy field is thought to be responsible for the rapid expansion (inflation) of the early universe.

A wide variety of masses for PBHs are possible, depending on the formation scenario. The least massive ones, with less than about the mass of a comet, or 1 trillion kilograms, would quickly evaporate through a quantum process known as Hawking radiation.

More massive PBHs, born with up to 100,000 times the mass of the Sun, could survive to put an imprint on the CMB cosmic microwave background, radiation emitted by warm matter roughly 400,000 years after the big bang.

Normally black holes would emit X-rays as they swallow matter from their surroundings, and these X-rays can escape the vicinity of the black holes to break apart, or ionise, hydrogen atoms. This would subtly affect how matter distributes itself into regions of high and low density - a distribution reflected in the CMB radiation.

This effect might explain a puzzling discrepancy between results of the Wilkinson Microwave Anisotropy Probe (WMAP), which measures the CMB, and studies of how galaxies are clustered.

The two disagree on a parameter called sigma8, which describes how matter clumped together in the early universe. But according to a recent study led by Massimo Ricotti of the University of Maryland in College Park, US, the two measurements agree if PBHs are included in the models.
[+/-] Click here to expand

But Ricotti himself says it is too soon to claim there is evidence for primordial black holes. "It is still possible that refining the measurements will bring them into agreement without invoking these exotic objects," he says.

The study also suggests that the ionising effect of PBHs would have helped spark the formation of the first stars in the universe. The presence of free electrons helps pairs of hydrogen atoms to join together to form molecular hydrogen. "You form a lot of molecular hydrogen – about 10 to 100 times more than you would form if you didn't have primordial black holes," Ricotti said.

Molecular hydrogen helps to cool gas clouds by emitting radiation, allowing the clouds to contract enough to condense into stars. Ricotti says the James Webb Space Telescope, scheduled to launch in 2013, just may be able to detect this enhancement of star formation.

Perhaps most intriguingly, if primordial black holes survive in great enough numbers today, then clouds of them could account for some or even all of the mysterious dark matter in the universe.

The main problem with this possibility is that it is not clear whether the conditions needed to form PBHs in large numbers ever occurred in our universe.

In the formation scenario involving the inflation field, for example, the number of PBHs formed depends on unknowns such as the size of fluctuations in the inflation field. In some inflationary models, you can form a lot of PBHs; in others you form very few of them.

It is possible that unusually large amounts of ionisation in the early universe - possibly due to the X-rays emitted by PBHs - could be detected by Europe's Planck satellite, scheduled to launch in mid-2008, says WMAP team member Rachel Bean of Cornell University in Ithaca, New York, US.

If convincing evidence of primordial black holes ever emerges, it would give scientists an extremely important window into the universe at very early times.

The mass of the black holes would reveal the time at which they formed, since the different scenarios for their formation occur at different times and give different masses. If they formed at the end of inflation, then their existence would reveal important information about the murky physics of this period of rapid expansion.

"You could rule out models of inflation that don't produce these black holes," says physicist James Chisholm of Southern Utah University. "Someone would probably get a Nobel prize."
Matter Surfs on Ripples of Space Time Around Black Hole
Adaptive optics leads the way to supermassive black holes
Supercomputer at RIT Takes on Black Holes and General Relativity
Herschel will have an unprecedented view of the cold universe. Herschel in Pics


Labels: , ,

Tuesday, September 18, 2007

The Magellanic Clouds

The Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) are two of the Milky Way's closest neighbouring galaxies. A stunning sight in the southern hemisphere, they were named after Ferdinand Magellan, who explored those waters in the 16th century.

For hundreds of years, these galaxies were considered satellites of the Milky Way, gravitationally bound to our home galaxy.

Although they look like glowing clouds to the unaided eye, the LMC and SMC are both irregular galaxies. The Large Magellanic Cloud is located approximately 160,000 light-years from Earth. It's about one-twentieth as large as our galaxy in diameter and holds about one-tenth as many stars. The Small Magellanic Cloud is located around 200,000 light-years from Earth. It's about ten times smaller than its companion and two hundred times smaller than the Milky Way.

Earlier this year, CfA astronomers reported measuring the 3-d velocities of the Magellanic Clouds through space with greater accuracy than ever before. The velocities were anomalously high.

Two explanations were proposed:
1) the Milky Way is more massive than previously thought, or 2) the Magellanic Clouds are not gravitationally bound to the Milky Way.

Further analysis verified the second explanation. The parabolic orbit calculated for the Clouds, based on the observed velocities, shows that both are on their first pass by the Milky Way.
[+/-] Click here to expand

This result carries several implications. For example, as a spiral galaxy the Milky Way has a large gaseous disk intermixed with billions of stars. That gaseous disk is known to be significantly warped, extending about 10,000 light-years above and below the galaxy's plane. Astronomers theorized that gravitational tides due to previous passages of the Magellanic Clouds caused this warp. However, since the Clouds arrived only 1-3 billion years ago, they are not likely to be the source of the warp.

Another puzzle relates to the Magellanic Clouds themselves. A long trail of hydrogen gas called the Magellanic Stream extends behind the Clouds, spanning 100 degrees of the sky from the earth's viewpoint. Some astronomers suggested that the Magellanic Stream formed due to tidal interactions between the Clouds and the Milky Way. Others believed that hydrogen was stripped from the Clouds by gas pressure as they plunged through the extremely tenuous gas surrounding our galaxy. A first-passage scenario rules out both scenarios.

Finally, the star-forming history of the Clouds themselves must be revisited. Rather than forming stars continuously like the Milky Way, the Magellanic Clouds have undergone several bursts of star formation followed by long quiet periods. Astronomers thought that the starbursts coincided with previous close passes by the Milky Way. This explanation no longer holds true. Instead, interactions between the SMC and LMC may be the primary force driving star formation in both galaxies.

The Magellanic Clouds Are First-Time Visitors from CfA

New research by Gurtina Besla (Harvard-Smithsonian Center for Astrophysics) and her colleagues shows that the Magellanic Clouds are recent arrivals on their first visit to the Milky Way's neighborhood.

In the future, Besla and her colleagues intend to focus on the origin of the Magellanic Stream, conducting N-body simulations to puzzle out possible formation mechanisms. Other astronomers will make direct observations and survey the Stream. The combined power of observational and theoretical research may answer the questions generated by the current work.

The paper describing this work has been accepted for publication in the Astrophysical Journal and is available online at


Labels: , ,

Sunday, September 16, 2007

Young Suns in Cepheus

Credit & Copyright: Tony Hallas

The dusty reflection nebula NGC 7129, about 3,000 light-years away, toward the constellation of Cepheus.

The bright stars embedded in NGC 7129 are perhaps a million years young. The telltale reddish crescent shapes around NGC 7129 are associated with energetic jets streaming away from newborn stars. Surprisingly, despite the dust, far off background galaxies can be seen in the colourful cosmic vista.

Labels: ,

Friday, September 14, 2007

Coronet Cluster

The Coronet Cluster in the heart of the Corona Australis region, is one of the nearest and most active regions of ongoing star formation. At only about 420 light years away, the Coronet is over three times closer than the Orion Nebula is to Earth.

The Coronet contains a loose cluster of a few dozen young stars with a wide range of masses and at various stages of evolution, giving astronomers an opportunity to observe "protostars" simultaneously in several wavelengths.

This composite image shows the coronet in X-Rays from Chandra (purple) and infrared emission from Spitzer (orange, green, and cyan). The Spitzer image shows young stars plus diffuse emission from dust.

In the Chandra data only, many of these young stars appear as blue objects, revealing their output of high-energy X-rays and the amount of obscuring dust and gas in the region. The reason for the blue appearance is that lower energy X-rays, depicted as red and green, are absorbed by this veil of material and hence are not seen.

The Chandra data also support the idea that X-rays from very young stars are generated largely from magnetic activity in the outer atmospheres. Due to the host of young stars in different life stages in the Coronet, astronomers can use these data to pinpoint details of how the youngest stars evolve.

Coronet Cluster Images from Chandra
Building the Celestial Bestiary from Centauri Dreams
Two Cosmic Mysteries explained by the same particle?
Galaxy 'Hunting' Made Easy from European Southern Observatory

Labels: , ,

Thursday, September 13, 2007

Dark Matter - could be warm

Dark matter may be made of fast, lightweight particles, according to a new computer simulation. That could explain the peculiarly pure chemical makeup of some stars in the Milky Way, and the enormous mass of black holes that live at the hearts of large galaxies.

Because 'dark matter' reveals itself only by its gravity, astronomers have few clues to its nature. The most popular model is cold dark matter: heavy subatomic particles that tend to move very slowly.

Another possibility is warm dark matter: lighter particles that move faster. The rapid motion of these particles smoothes out the small dense knots of matter that would could or should otherwise form in the cores of galaxies, and there are hints that such dense knots are indeed missing.
[+/-] Click here to expand

Liang Gao and Tom Theuns of Durham University in the UK have built a computer simulation to compare the behaviour of cold and warm dark matter in the early universe. At first the two varieties behave alike, collapsing under gravity into a network of filaments that crisscross the universe.

But cold dark matter then coalesces into blobs or haloes, while warm dark matter does not. The random motion of its particles smoothes out these blobs, so warm dark matter filaments just keep collapsing and getting denser until there is a narrow tube of matter typically 10,000 light years long with the mass of 10 million Suns.

Ordinary gas is dragged in by the dark matter, and eventually the first stars form. They are made almost entirely of hydrogen and helium, the two main elements created in the big bang.

With cold dark matter, one large star forms in the middle of each large halo. These large stars burn fast, fusing hydrogen and helium into heavier elements. They soon exhaust their fuel and then explode to seed the universe with denser elements, which go into the next generation of stars. No pure hydrogen-helium stars survive.

But in the dense filaments formed by warm dark matter, the formation is likely to be more chaotic, with stars of different sizes forming from random-sized bits of filament.

Some would be small stars, which burn slowly, so a few pure stars formed in these filaments could still be shining today.

In the past few years, astronomers have indeed discovered small stars in the Milky Way that are very low in heavy elements. It is suggestive that maybe dark matter is warm. If astronomers see a star with absolutely no heavy elements, that will be good evidence.

These filaments may also be good at making big black holes. Although many of the isolated stars created by cold dark matter would give birth to black holes, they would only be a few times the mass of the Sun, which seems too small to seed the billion-solar-mass black holes that are known to lurk in many galaxies.

But each warm-dark-matter filament should eventually collapse along its length, say Gao and Theuns, forcing stars, gas clouds and small black holes close together in the perfect environment for growing much bigger black holes.

In the simulation, researchers assumed a dark matter particle with just 0.6% of the mass of an electron. That would fit the gravitino, a particle predicted by the speculative theory called - supersymmetry – although any particle as light would have a similar effect.
Did our galaxy's black hole eat its baby brother? @ SNS
Small 'Hobbit' Galaxies Made Almost Entirely of Dark Matter
Explanation of Dark Matter Might Lie in Origin of Stars @ Live Science

Labels: , ,

Wednesday, September 12, 2007

Teardrop in the Sky

A spinning star found feeding on its stellar companion, whittling it down to an object smaller than some planets. Pulsars are the cores of burnt out "neutron" stars that spin hundreds of times per second.

The object’s minimum mass is only about 7 times the mass of Jupiter. But instead of orbiting a normal star, this low-mass body orbits a rapidly spinning pulsar every 54.7 minutes, at an average distance of only about 230,000 miles (slightly less than the Earth-Moon distance).

"This object is merely the skeleton of a star," says study team member Craig Markwardt of NASA's Goddard Space Flight Center in Maryland. "The pulsar has eaten away the star's outer envelope, and all that remains is its helium-rich core."

The system was discovered in early June when NASA's Swift and Rossi X-ray Timing Explorer (RXTE) satellites picked up an outburst of X-rays and gamma rays in the direction of the Milky Way galactic center in the constellation Sagittarius, and named SWIFT J1756.9-2508.
[+/-] Click here to expand

Scientists think that several billion years ago, the system consisted of a very massive star and a smaller star about 1 to 3 times the mass of our sun. The bigger star evolved quickly and exploded as a supernova, leaving behind a spinning stellar corpse known as a neutron star. Meanwhile, the smaller star began to evolve as well, eventually puffing up into a red giant whose outer envelope encapsulated the neutron star.

This caused the two stars to draw closer together, while simultaneously ejecting the red giant's envelope into space.

After billions of years, little remains of the companion star, and it's uncertain whether it will survive. "It's been taking a beating, but that's part of nature," said study team member Hans Krimm, also of NASA Goddard.

Today, the two objects are so close to each other that the neutron star's powerful gravity siphons gas from its companion to form a spinning disk around itself. The disk occasionally dumps large quantities of gas onto the neutron star, creating an outburst like the one detected in June.

Image Credit: Aurore Simonnet/Sonoma State University

Hubble Captures Stars Going Out in Style
Planet Survives Star's Death Throes from LiveScience
The Universe through the looking glass from NASA Science

Labels: , , , ,

Monday, September 10, 2007

SNAP, Crackle, Pop

Still 'Clueless' About Mystery Force Pushing Galaxies Apart

Dark energy entered the astronomical scene in 1998, after two groups of astronomers made a survey of exploding stars, or supernovas, in a number of distant galaxies. These researchers found that the supernovas were dimmer than they should have been, and that meant they were farther away than they should have been. The only way for that to happen, the astronomers realized, was if the expansion of the universe had sped up at some time in the past.

Until then, astronomers had generally believed that the cosmic expansion was gradually slowing down, due to the gravitational tugs that individual galaxies exert on one another. But the supernova results implied that some mysterious force was acting against the pull of gravity, causing galaxies to fly away from each other at ever greater speeds.

The supernova evidence suggests that the acceleration kicked in about 5 billion years ago. At that time, galaxies were far enough apart that their gravity (which weakens with distance) was overwhelmed by the relatively gentle but constant repulsive force of dark energy. Since then, dark energy's continuing push has allegedly been causing the cosmic expansion to speed up, and it seems likely now that this expansion will continue indefinitely.

Beyond Einstein is NASA's research roadmap for five proposed mission areas to study the most compelling questions at the intersection of physics and astronomy.

Of particular interest to researchers is whether the acceleration of the expansion of the universe varies over time. So far, three specific mission plans have been studied in this area: the Supernova Acceleration Probe (SNAP), the Dark Energy Space Telescope (DESTINY), and the Advanced Dark Energy Physics Telescope (ADEPT), but the eventual Joint Dark Energy Mission (JDEM) could be any one of the three or be based on a different option altogether.

The underlying technology for a dark energy mission is, for the most part, in the prototype phase, and will require less development than most of the other missions. The potential gains for JDEM also outweigh its scientific risks, such as the possibility that the mission may not provide substantial insight beyond that provided by telescopes on the ground. The report recommends that NASA and DOE proceed immediately with a competition for mission proposals that will investigate the nature of dark energy with high precision.
Hubble Telescope: Solved and Unsolved Mysteries By Q. Choi
So what is the Shape and Topology of the Universe - from Cosmos Magazine

Saturday, September 08, 2007

Akari Galaxy Image M101

M101 is a spiral galaxy twice the size of our own Galaxy, 170 000 light-years in diameter, near the tail of the Great Bear constellation. AKARI’s new observations reveal differing populations of stars spread across its spiral arms.

Using the AKARI space infrared telescope, astronomers have been able to find the warm dust heated by the birth of stars like our Sun in M101, and cooler dust heated by stars more like the present-day Sun.

The image shows the visible light (green), the far-ultraviolet light (cyan) from young stars, the warm dust (red) and the cooler dust (blue). This warm dust is mainly along the spiral arms, with hot spots along the galaxy's outer edge. These hot spots are giant star-forming regions, and it is unusual to find these on the edges of a galaxy.

Commenting on this image Dr Stephen Serjeant from The Open University said, "The evidence points to M101 having experienced a close encounter or near collision with a neighbour or companion galaxy, and it could be that it yanked material out of its neighbour which is now raining down on one side of galaxy and triggering this star formation."

Galaxies near and far from Akari - In Depth Article - from ESA

Labels: , ,

Friday, September 07, 2007

Ultra Deep Space

The Cosmic Bacground Radiation CMB was first discovered in the mid-1960s by the Bell Labs researchers Arno Penzias and Robert Wilson. While completing a radio wave survey, their horn shaped antenna picked up a strange hiss. After they reported the result to the physicist Robert Dicke of Princeton, he calculated its temperature and found that it matched the predictions of the Big Bang theory.

This discovery confirmed the existence of an ultra-hot beginning to the universe. It was not precise enough, however, to reveal the fine details of the primordial distribution of matter and energy.

In the early 1990s, thanks to the Nobel prize–winning work of John Mather and George Smoot, using NASA's Cosmic Background Explorer (COBE) satellite, the precise frequency distribution of the microwave background radiation was mapped and established, beyond a shadow of a doubt, that it matched precisely what would be expected for a once-fiery universe cooled down over billions of years.

Smoot and his group discovered a mosaic of minute temperature fluctuations (called anisotropies) throughout the sky, pointing to subtle early differences in the densities of various regions of the cosmos. These fluctuations showed how in the nascent universe slightly denser "seeds" existed that would attract more and more mass and eventually grow into the hierarchical structures (stars, galaxies, clusters of galaxies, and so forth), that we observe today.

The quest to map out the ripples in the CMB with greater and greater precision has continued throughout the past two decades. Uniquely, these provide a wealth of accessible information about the state of the cosmos many billions of years ago. It's like a rare cuneiform tablet that, with improving translations, provides richer and richer insights into ancient history each time it's read.
Galaxy Building Blocks in the Hubble Ultra Deep Field Hubblesite
Hubble & Spitzer find building-block galaxies in early Universe from ESA

Tuesday, September 04, 2007


Problems such as how to cool a 27 km-circumference, 37,000 tonne ring of superconducting magnets to a temperature of 1.9 K using truck-loads of liquid helium are not the kind of things that theoretical physicists normally get excited about.

Strings 07 kicked off their main conference this year with an update on the latest progress being made at the Large Hadron Collider (LHC) at CERN, which is due to switch on next May.

The possibility, that evidence for string theory might turn up in the LHC's 14 TeV proton–proton collisions was prominent among discussions at the five-day conference, held in Madrid in late June.

Talks were peppered with the language of real-world data, particles and fields - particularly in relation to cosmology. Admittedly these more tangible concepts were buried within the esoteric grammar of higher-dimensional mathematics, where things like "GUT-branes", "tadpoles" and "warped throats" lurk. However, Strings07 was clearly a physics event, and not one devoted to mathematics, philosophy or perhaps even theology.

Continue Reading: Stringscape Page One Superstring Revolution Page Two
Dimensions & Across the Landscape
Page Three String Cosmology Page Four
The early universe may allow us to 'see' additional dimensions by Physics World
CERN in 3 minutes


Labels: , ,

Saturday, September 01, 2007

Lisa Randall CERN 2007

Black Holes and Quantum Gravity at the LHC
The talk focused on models with higher dimensions of quantum gravity in the context of a low quantum gravity scale. How low ? Well, as low as one can hope for - about 1 TeV or so. Naturally, at the LHC one would expect quite dramatic signatures.

Should LHC be looking at black hole production or elsewhere ?
The questions experimentalists have to ask themselves at the start of a project like the LHC, which will explore unknown new energy scale and domains: - “Are we optimizing existing searches for the signatures we might have access to ?” and “Are we sure we are not missing possible searches ?”
[+/-] Click here to expand

One interesting question, connected to the scope of Lisa’s talk, is: “If there is new physics, but it lies at a higher energy scale than the one directly accessible by the machine, how do we maximize our chances to see it ?”

Historically, the reason that black holes appear so promising as compared with other possible signatures is the predicted huge cross section for their production if there is a low quantum gravity scale. Lisa ventured to compute that if quantum gravity turns on at a scale of a TeV, one gets 100 pb which for 100 fb-1 luminosity would yield ten million events.

The basic reason why this cross section is so large compared to the production of a particle with TeV mass in a typical beyond the SM theory is the lack of any small couplings, such as gauge couplings in the cross section and absence of phase space suppression factors. However, this estimate ignores several major considerations and uncertainties in the black hole production and decay cross sections.

There is no suppression from gauge couplings, so it is indeed a large signal. Also, the signature is spectacular, since these objects are predicted to decay into large multiplicity final state, with highly spherical distributions. Very distinctive, unmistakable new physics.

But the problem is that the idyllic picture is not very realistic. The onset of a non-perturbative regime where black holes are produced and decay with those signatures is much above the QG scale, and this appears to be above the reach of even the LHC.

The Large Hadron Collider (LHC) at CERN has not emitted the first burp yet, and it is already criticized for being a midget. In any case, at threshold one would not see the striking signatures, but maybe something can be saved.

Randall was very clear in stating that the LHC is unlikely to make classical BH states decaying with Hawking radiation. She appeared to be interested in assessing the damage: and the answer is that, if you have a low quantum gravity scale and you cross it, you will have a change in the two-particle final states. Things are not calculable, but there appear to still be distincitve experimental signatures that are capable of distinguishing among different models.

You have to go well above M, the energy scale of quantum gravity, to be sure to hit the striking signatures publicized in the past. The parton distribution functions of the proton drop rapidly with the fraction of parton momentum, and since we are by necessity near threshold, the value of the latter is very important in determining what the rate of the new process is going to be. To make matters worse, M is convention-dependent. Factors of - fly around easily, and although one knows these are only conventions and what one cares for is just the actual threshold, there is a big difference between 1 TeV and 2 TeV for the LHC. So the picture is fuzzy.

Bubble Chamber: Leonard Susskind & Lisa Randall

Lisa discussed some of the models and the resulting conventions and equations for the schwarzschild radius, the energy scale, and the other main characteristics.

One point which looked important is that in the models considered, the black hole lifetime is bigger than the inverse of the energy scale of quantum gravity. This drives some of the phenomenology of the black hole decay. Another point is that every degree of freedom should carry an insignificant amount of energy with respect to the total; and since we are never going to get far above threshold at the LHC, we will have to be careful to call what we produce a real classical black hole. These things have low entropy close to threshold, and the multiplicity of the decay will be affected.

A critical factor in the computation of the number of particles emitted in the black hole decay is the assumption of the dimensionality of the space: particles emitted in the bulk have more directions in which to oscillate. Furthermore, since the threshold for producing black holes is not M, but a higher energy, even if we did see a black hole, we would not be able to extract M from the total cross section, because of inelasticity effects: not all the energy of the colliding partons goes in the creation of the black hole, due to initial state radiation.

The difficult question to answer is in fact, what fraction of the energy gets trapped inside the horizon? It is of course important since the PDF fall rapidly with energy. What is clear is that the inelasticity effectively increases the threshold. The reduction in cross section due to this effect is enormous, and it is the lack of considering it, which has brought some overoptimistic predictions in the past.

So, the upshot is that BH production threshold is higher than originally thought. It means a lower production cross section, a lower reach in black hole mass, and it translates into lower entropy reach as well. The conclusion of Lisa Randall is that we will not produce classical thermal black holes at the LHC. What will we still be able to produce, then ? And what kind of multiplicities should we expect ?

Lisa discussed the calculation of the multiplicity of final state particles. She said that the calculation is totally unreliable. But one thing stays clear: low multiplicity final states will dominate even if we call it black holes. So we have to face the facts, and study 2-body final states: jets and leptons. Can they be distinguished from backgrounds by rate, kinematics, bra size? Yes. For jets, transversality is the key. QCD is dominated by t-channel exchange, i.e., forward scattering. Black hole events are isotropic. So this is really becoming like any other compositeness search: massive states produced at low rapidity.

While describing a scenario where the LHC will have to walk the walk of unclear kinematical analyses rather than being hit in the face by those firework-like signatures that experimentalists have started to dream more and more frequently as of late, Randall was careful to insist that the LHC is indeed a powerful machine, although she fell short of declaring it will make everything clear about quantum gravity.

After discussing the signature of black holes, Randall delved into the possible signatures of the same kind from alternative models of quantum gravity, such as a weakly coupled string theory. There one apparently expects a resonance behaviour, followed by a dramatic drop in transverse cross section, which can be used to distinguish the stringy behavior from the simple production of a new Z’ boson, ...

In addition to the resonance, you would also see a drop in the quantity. This could also allow to distinguish models: you could decide you are finding a stringy state, and you could even distinguish different stringy models, because the correlation between and the cross section is different for different models. In summary, black holes are not as spectacular as advertised in the past. However, they may still provide lots of information about quantum gravity, through careful studies of processes.

Lisa also said she would love to see these studies done by Atlas and CMS: energy-dependent angle studies in dijet production.

Tommaso Dorigo asked the question: "I know from previous blogging on the issue that when one reaches a quantum gravity regime, the QCD cross section of dijet production has to go down, but Lisa had not discussed this feature." She explained that before one reaches the regime when QCD 2-particle cross section gets reduced, the cross section has to go up, in any case. So the dijet cross section reduction that Sabine has first studied happens at a regime that LHC will fail to cover.

Source: Lisa Randall: black holes out of reach of LHC
by Tommaso Dorigo @ A Quantum Diaries Survivor.
Lisa Randall: Unification in warped extra dimensions and bulk holography
Lisa Randall: Smashing open the Universe @ Prospect Magazine.
Event probability for Production of Single Top Quarks using Matrix Elements


Labels: , ,

Blowing Cosmic Super Bubbles

Image Credit: early universe by Adolf Schuller

Some 200,000 light years away in the Small Magellanic Cloud (SMC), Astronomers used Chandra to peer into one particular area of clouds of gas and plasma where stars are forming.

This area, known as N19, is filled with ionized hydrogen gas and it is where many massive stars are expelling dust and gas through stellar winds. When the X-ray data (blue and purple) are combined with the other wavelengths, researchers find evidence for the formation of a so-called superbubble.

Superbubbles are formed when smaller structures from individual stars and supernovas combine into one giant cavity.
Blowing Cosmic Super Bubbles from Chandra Harvard
The Universe Through the Looking Glass
HERO - Where no Telescope Has Gone Before
Could the Universe be like a Swiss Cheese & light as a Malteeser?

Labels: , ,