Posted on by Nancy Atkinson

Hubble Confirms Cosmic Acceleration with Weak Lensing

This image shows a smoothed reconstruction of the total (mostly dark) matter distribution in the COSMOS field, created from data taken by the NASA/ESA Hubble Space Telescope and ground-based telescopes.Credit: NASA, ESA, P. Simon (University of Bonn) and T. Schrabback (Leiden Observatory)

[/caption]

Need more evidence that the expansion of the Universe is accelerating? Just look to the Hubble Space Telescope. An international team of astronomers has indeed confirmed that the expansion of the universe is accelerating. The team, led by Tim Schrabback of the Leiden Observatory, conducted an intensive study of over 446,000 galaxies within the COSMOS (Cosmological Evolution Survey) field, the result of the largest survey ever conducted with Hubble. In making the COSMOS survey, Hubble photographed 575 slightly overlapping views of the same part of the Universe using the Advanced Camera for Surveys (ACS) onboard the orbiting telescope. It took nearly 1,000 hours of observations.

In addition to the Hubble data, researchers used redshift data from ground-based telescopes to assign distances to 194,000 of the galaxies surveyed (out to a redshift of 5). “The sheer number of galaxies included in this type of analysis is unprecedented, but more important is the wealth of information we could obtain about the invisible structures in the Universe from this exceptional dataset,” said co-author Patrick Simon from Edinburgh University.

In particular, the astronomers could “weigh” the large-scale matter distribution in space over large distances. To do this, they made use of the fact that this information is encoded in the distorted shapes of distant galaxies, a phenomenon referred to as weak gravitational lensing. Using complex algorithms, the team led by Schrabback has improved the standard method and obtained galaxy shape measurements to an unprecedented precision. The results of the study will be published in an upcoming issue of Astronomy and Astrophysics.

The meticulousness and scale of this study enables an independent confirmation that the expansion of the Universe is accelerated by an additional, mysterious component named dark energy. A handful of other such independent confirmations exist. Scientists need to know how the formation of clumps of matter evolved in the history of the Universe to determine how the gravitational force, which holds matter together, and dark energy, which pulls it apart by accelerating the expansion of the Universe, have affected them. “Dark energy affects our measurements for two reasons. First, when it is present, galaxy clusters grow more slowly, and secondly, it changes the way the Universe expands, leading to more distant — and more efficiently lensed — galaxies. Our analysis is sensitive to both effects,” says co-author Benjamin Joachimi from the University of Bonn. “Our study also provides an additional confirmation for Einstein’s theory of general relativity, which predicts how the lensing signal depends on redshift,” adds co-investigator Martin Kilbinger from the Institut d’Astrophysique de Paris and the Excellence Cluster Universe.

The large number of galaxies included in this study, along with information on their redshifts is leading to a clearer map of how, exactly, part of the Universe is laid out; it helps us see its galactic inhabitants and how they are distributed. “With more accurate information about the distances to the galaxies, we can measure the distribution of the matter between them and us more accurately,” notes co-investigator Jan Hartlap from the University of Bonn. “Before, most of the studies were done in 2D, like taking a chest X-ray. Our study is more like a 3D reconstruction of the skeleton from a CT scan. On top of that, we are able to watch the skeleton of dark matter mature from the Universe’s youth to the present,” comments William High from Harvard University, another co-author.

The astronomers specifically chose the COSMOS survey because it is thought to be a representative sample of the Universe. With thorough studies such as the one led by Schrabback, astronomers will one day be able to apply their technique to wider areas of the sky, forming a clearer picture of what is truly out there.

Source: EurekAlert

Paper: Schrabback et al., ‘Evidence for the accelerated expansion of the Universe from weak lensing tomography with COSMOS’, Astronomy and Astrophysics, March 2010,

Posted on by Nancy Atkinson

Galaxies in Early Universe Experienced “Growth Spurt”

This artist’s impression of the distant galaxy SMM J2135-0102 shows large bright clouds a few hundred light-years in size, which are regions of active star formation, These “star factories” are similar in size to those in the Milky Way, but one hundred times more luminous, suggesting that star formation in the early life of these galaxies is a much more vigorous process than typically found in local galaxies. Credit: Credit: ESO/M. Kornmesser

[/caption]

Looking back in time – and through a gravitational lens – astronomers found evidence that galaxies in the early Universe went through a “growth spurt” of rapid and vigorous star formation. A distant galaxy, known as SMM J2135-0102 is making new stars 250 times faster than the Milky Way. Due to the amount of time it takes light to reach Earth the scientists observed the galaxy as it would have appeared 10 billion years ago – just three billion years after the Big Bang.

“This galaxy is like a teenager going through a growth spurt,” said Dr. Mark Swinbank from Durham University, lead author of a new paper published in Nature. “We don’t fully understand why the stars are forming so rapidly but our results suggest that stars formed much more efficiently in the early Universe than they do today. Galaxies in the early Universe appear to have gone through rapid growth and stars like our sun formed much more quickly than they do today.”

SMM J2135-0102 was found using the Atacama Pathfinder Experiment (APEX) telescope, which is operated by the European Southern Observatory (ESO). Follow-up observations were carried out by combining the natural gravitational lens of nearby galaxies with the powerful Submillimeter Array telescope based in Hawaii to magnify the galaxy even further.

The distant galaxy SMM J2135-0102, shown here in 870-micron observations by the Submillimeter Array, has been gravitationally lensed by a foreground galaxy cluster. The galaxy's light is magnified and bent by gravity to produce mirror images of each of four star-forming regions (labeled A through D). If the galaxy were seen undistorted, it would appear like the inset at upper left. Regions A and D are separated by less than 6,000 light-years. The inset at lower right shows the resolution of the SMA image. Credit: Mark Swinbank (Durham) and Steve Longmore (SAO)

“To a layperson, our images appear fuzzy, but to us, they show the exquisite detail of a Faberge egg,” said Steven Longmore of the Harvard-Smithsonian Center for Astrophysics (CfA).

“The magnification reveals the galaxy in unprecedented detail, even though it is so distant that its light has taken about 10 billion years to reach us,” said Swinbank. “In follow-up observations with the Submillimeter Array telescope we’ve been able to study the clouds where stars are forming in the galaxy with great precision.”

They found four discrete star-forming regions within the galaxy, and each region was more than 100 times brighter than star-forming regions in the Milky Way, such as the Orion Nebula, and estimate that the observed galaxy is producing stars at a rate equivalent to 250 suns per year.

“The star formation in this galaxy’s large dust clouds is unlike that in the nearby Universe,” said co-author Carlos De Breuck from ESO. “However, our observations suggest that we should be able to use underlying physics from the densest cores in nearby galaxies to understand star birth in these more distant galaxies.”

Their results provide new insight into a critical time during the Universe’s history. SMM J2135-0102 is seen at the epoch when the majority of all stars were born, and therefore when many of the properties of nearby galaxies were defined. By studying it and other distant galaxies in the young Universe, astronomers hope to learn about the history of the Milky Way and other nearby galaxies.

Sources: Durham University, Harvard-Smithsonian CfA

Posted on by Jean Tate

This is Getting Boring: General Relativity Passes Yet another Big Test!

Princeton University scientists (from left) Reinabelle Reyes, James Gunn and Rachel Mandelbaum led a team that analyzed more than 70,000 galaxies and demonstrated that the universe - at least up to a distance of 3.5 billion light years from Earth - plays by the rules set out by Einstein in his theory of general relativity. (Photo: Brian Wilson)

[/caption]
Published in 1915, Einstein’s theory of general relativity (GR) passed its first big test just a few years later, when the predicted gravitational deflection of light passing near the Sun was observed during the 1919 solar eclipse.

In 1960, GR passed its first big test in a lab, here on Earth; the Pound-Rebka experiment. And over the nine decades since its publication, GR has passed test after test after test, always with flying colors (check out this review for an excellent summary).

But the tests have always been within the solar system, or otherwise indirect.

Now a team led by Princeton University scientists has tested GR to see if it holds true at cosmic scales. And, after two years of analyzing astronomical data, the scientists have concluded that Einstein’s theory works as well in vast distances as in more local regions of space.

A partial map of the distribution of galaxies in the SDSS, going out to a distance of 7 billion light years. The amount of galaxy clustering that we observe today is a signature of how gravity acted over cosmic time, and allows as to test whether general relativity holds over these scales. (M. Blanton, SDSS)

The scientists’ analysis of more than 70,000 galaxies demonstrates that the universe – at least up to a distance of 3.5 billion light years from Earth – plays by the rules set out by Einstein in his famous theory. While GR has been accepted by the scientific community for over nine decades, until now no one had tested the theory so thoroughly and robustly at distances and scales that go way beyond the solar system.

Reinabelle Reyes, a Princeton graduate student in the Department of Astrophysical Sciences, along with co-authors Rachel Mandelbaum, an associate research scholar, and James Gunn, the Eugene Higgins Professor of Astronomy, outlined their assessment in the March 11 edition of Nature.

Other scientists collaborating on the paper include Tobias Baldauf, Lucas Lombriser and Robert Smith of the University of Zurich and Uros Seljak of the University of California-Berkeley.

The results are important, they said, because they shore up current theories explaining the shape and direction of the universe, including ideas about dark energy, and dispel some hints from other recent experiments that general relativity may be wrong.

“All of our ideas in astronomy are based on this really enormous extrapolation, so anything we can do to see whether this is right or not on these scales is just enormously important,” Gunn said. “It adds another brick to the foundation that underlies what we do.”

GR is one, of two, core theories underlying all of contemporary astrophysics and cosmology (the other is the Standard Model of particle physics, a quantum theory); it explains everything from black holes to the Big Bang.

In recent years, several alternatives to general relativity have been proposed. These modified theories of gravity depart from general relativity on large scales to circumvent the need for dark energy, dark matter, or both. But because these theories were designed to match the predictions of general relativity about the expansion history of the universe, a factor that is central to current cosmological work, it has become crucial to know which theory is correct, or at least represents reality as best as can be approximated.

“We knew we needed to look at the large-scale structure of the universe and the growth of smaller structures composing it over time to find out,” Reyes said. The team used data from the Sloan Digital Sky Survey (SDSS), a long-term, multi-institution telescope project mapping the sky to determine the position and brightness of several hundred million galaxies and quasars.

By calculating the clustering of these galaxies, which stretch nearly one-third of the way to the edge of the universe, and analyzing their velocities and distortion from intervening material – due to weak lensing, primarily by dark matter – the researchers have shown that Einstein’s theory explains the nearby universe better than alternative theories of gravity.

Some of the 70,000 luminous galaxies in SDSS analyzed (Image: SDSS Collaboration)

The Princeton scientists studied the effects of gravity on the SDSS galaxies and clusters of galaxies over long periods of time. They observed how this fundamental force drives galaxies to clump into larger collections of galaxies and how it shapes the expansion of the universe.

Critically, because relativity calls for the curvature of space to be equal to the curvature of time, the researchers could calculate whether light was influenced in equal amounts by both, as it should be if general relativity holds true.

“This is the first time this test was carried out at all, so it’s a proof of concept,” Mandelbaum said. “There are other astronomical surveys planned for the next few years. Now that we know this test works, we will be able to use it with better data that will be available soon to more tightly constrain the theory of gravity.”

Firming up the predictive powers of GR can help scientists better understand whether current models of the universe make sense, the scientists said.

“Any test we can do in building our confidence in applying these very beautiful theoretical things but which have not been tested on these scales is very important,” Gunn said. “It certainly helps when you are trying to do complicated things to understand fundamentals. And this is a very, very, very fundamental thing.”

“The nice thing about going to the cosmological scale is that we can test any full, alternative theory of gravity, because it should predict the things we observe,” said co-author Uros Seljak, a professor of physics and of astronomy at UC Berkeley and a faculty scientist at Lawrence Berkeley National Laboratory who is currently on leave at the Institute of Theoretical Physics at the University of Zurich. “Those alternative theories that do not require dark matter fail these tests.”

Sources: “Princeton scientists say Einstein’s theory applies beyond the solar system” (Princeton University), “Study validates general relativity on cosmic scale, existence of dark matter” (University of California Berkeley), “Confirmation of general relativity on large scales from weak lensing and galaxy velocities” (Nature, arXiv preprint)

Posted on by Nancy Atkinson

Using Gravitational Lensing to Measure Age and Size of Universe

A graviational lens image of the B1608+656 system. Image courtesy Sherry Suyu of the Argelander Institut für Astronomie in Bonn, Germany. Click on image for larger version.

[/caption]

Handy little tool, this gravitational lensing! Astronomers have used it to measure the shape of stars, look for exoplanets, and measure dark matter in distant galaxies. Now its being used to measure the size and age of the Universe. Researchers say this new use of gravitation lensing provides a very precise way to measure how rapidly the universe is expanding. The measurement determines a value for the Hubble constant, which indicates the size of the universe, and confirms the age of Universe as 13.75 billion years old, within 170 million years. The results also confirm the strength of dark energy, responsible for accelerating the expansion of the universe.

Gravitational lensing occurs when two galaxies happen to aligned with one another along our line of sight in the sky. The gravitational field of the nearer galaxy distorts the image of the more distant galaxy into multiple arc-shaped images. Sometimes this effect even creates a complete ring, known as an “Einstein Ring.”
Researchers at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) used gravitational lensing to measure the distances light traveled from a bright, active galaxy to the earth along different paths. By understanding the time it took to travel along each path and the effective speeds involved, researchers could infer not just how far away the galaxy lies but also the overall scale of the universe and some details of its expansion.

Distinguishing distances in space is difficult. A bright light far away and a dimmer source lying much closer can look like they are at the same distance. A gravitational lens circumvents this problem by providing multiple clues as to the distance light travels. That extra information allows them to determine the size of the universe, often expressed by astrophysicists in terms of a quantity called Hubble’s constant.

“We’ve known for a long time that lensing is capable of making a physical measurement of Hubble’s constant,” KIPAC’s Phil Marshall said. However, gravitational lensing had never before been used in such a precise way. This measurement provides an equally precise measurement of Hubble’s constant as long-established tools such as observation of supernovae and the cosmic microwave background. “Gravitational lensing has come of age as a competitive tool in the astrophysicist’s toolkit,” Marshall said.

When a large nearby object, such as a galaxy, blocks a distant object, such as another galaxy, the light can detour around the blockage. But instead of taking a single path, light can bend around the object in one of two, or four different routes, thus doubling or quadrupling the amount of information scientists receive. As the brightness of the background galaxy nucleus fluctuates, physicists can measure the ebb and flow of light from the four distinct paths, such as in the B1608+656 system that was the subject of this study. Lead author on the study Sherry Suyu, from the University of Bonn, said, “In our case, there were four copies of the source, which appear as a ring of light around the gravitational lens.”

Though researchers do not know when light left its source, they can still compare arrival times. Marshall likens it to four cars taking four different routes between places on opposite sides of a large city, such as Stanford University to Lick Observatory, through or around San Jose. And like automobiles facing traffic snarls, light can encounter delays, too.

“The traffic density in a big city is like the mass density in a lens galaxy,” Marshall said. “If you take a longer route, it need not lead to a longer delay time. Sometimes the shorter distance is actually slower.”

The gravitational lens equations account for all the variables such as distance and density, and provide a better idea of when light left the background galaxy and how far it traveled.

In the past, this method of distance estimation was plagued by errors, but physicists now believe it is comparable with other measurement methods. With this technique, the researchers have come up with a more accurate lensing-based value for Hubble’s constant, and a better estimation of the uncertainty in that constant. By both reducing and understanding the size of error in calculations, they can achieve better estimations on the structure of the lens and the size of the universe.

There are several factors scientists still need to account for in determining distances with lenses. For example, dust in the lens can skew the results. The Hubble Space Telescope has infra-red filters useful for eliminating dust effects. The images also contain information about the number of galaxies lying around the line of vision; these contribute to the lensing effect at a level that needs to be taken into account.

Marshall says several groups are working on extending this research, both by finding new systems and further examining known lenses. Researchers are already aware of more than twenty other astronomical systems suitable for analysis with gravitational lensing.

These results of this study was published in the March 1 issue of The Astrophysical Journal. The researchers used data collected by the NASA/ESA Hubble Space Telescope, and showed the improved precision they provide in combination with the Wilkinson Microwave Anisotropy Probe (WMAP).

Source: SLAC

Posted on by Jean Tate

Dark Matter in Distant Galaxy Groups Mapped for the First Time

X-ray emission in the COSMOS field (XMM-Newton/ESA)

[/caption]
Galaxy density in the Cosmic Evolution Survey (COSMOS) field, with colors representing the redshift of the galaxies, ranging from redshift of 0.2 (blue) to 1 (red). Pink x-ray contours show the extended x-ray emission as observed by XMM-Newton.

Dark matter (actually cold, dark – non-baryonic – matter) can be detected only by its gravitational influence. In clusters and groups of galaxies, that influence shows up as weak gravitational lensing, which is difficult to nail down. One way to much more accurately estimate the degree of gravitational lensing – and so the distribution of dark matter – is to use the x-ray emission from the hot intra-cluster plasma to locate the center of mass.

And that’s just what a team of astronomers have recently done … and they have, for the first time, given us a handle on how dark matter has evolved over the last many billion years.

COSMOS is an astronomical survey designed to probe the formation and evolution of galaxies as a function of cosmic time (redshift) and large scale structure environment. The survey covers a 2 square degree equatorial field with imaging by most of the major space-based telescopes (including Hubble and XMM-Newton) and a number of ground-based telescopes.

Understanding the nature of dark matter is one of the key open questions in modern cosmology. In one of the approaches used to address this question astronomers use the relationship between mass and luminosity that has been found for clusters of galaxies which links their x-ray emissions, an indication of the mass of the ordinary (“baryonic”) matter alone (of course, baryonic matter includes electrons, which are leptons!), and their total masses (baryonic plus dark matter) as determined by gravitational lensing.

To date the relationship has only been established for nearby clusters. New work by an international collaboration, including the Max Planck Institute for Extraterrestrial Physics (MPE), the Laboratory of Astrophysics of Marseilles (LAM), and Lawrence Berkeley National Laboratory (Berkeley Lab), has made major progress in extending the relationship to more distant and smaller structures than was previously possible.

To establish the link between x-ray emission and underlying dark matter, the team used one of the largest samples of x-ray-selected groups and clusters of galaxies, produced by the ESA’s x-ray observatory, XMM-Newton.

Groups and clusters of galaxies can be effectively found using their extended x-ray emission on sub-arcminute scales. As a result of its large effective area, XMM-Newton is the only x-ray telescope that can detect the faint level of emission from distant groups and clusters of galaxies.

“The ability of XMM-Newton to provide large catalogues of galaxy groups in deep fields is astonishing,” said Alexis Finoguenov of the MPE and the University of Maryland, a co-author of the recent Astrophysical Journal (ApJ) paper which reported the team’s results.

Since x-rays are the best way to find and characterize clusters, most follow-up studies have until now been limited to relatively nearby groups and clusters of galaxies.

“Given the unprecedented catalogues provided by XMM-Newton, we have been able to extend measurements of mass to much smaller structures, which existed much earlier in the history of the Universe,” says Alexie Leauthaud of Berkeley Lab’s Physics Division, the first author of the ApJ study.

COSMOS-XCL095951+014049 (Subaru/NAOJ, XMM-Newton/ESA)

Gravitational lensing occurs because mass curves the space around it, bending the path of light: the more mass (and the closer it is to the center of mass), the more space bends, and the more the image of a distant object is displaced and distorted. Thus measuring distortion, or ‘shear’, is key to measuring the mass of the lensing object.

In the case of weak gravitational lensing (as used in this study) the shear is too subtle to be seen directly, but faint additional distortions in a collection of distant galaxies can be calculated statistically, and the average shear due to the lensing of some massive object in front of them can be computed. However, in order to calculate the lens’ mass from average shear, one needs to know its center.

“The problem with high-redshift clusters is that it is difficult to determine exactly which galaxy lies at the centre of the cluster,” says Leauthaud. “That’s where x-rays help. The x-ray luminosity from a galaxy cluster can be used to find its centre very accurately.”

Knowing the centers of mass from the analysis of x-ray emission, Leauthaud and colleagues could then use weak lensing to estimate the total mass of the distant groups and clusters with greater accuracy than ever before.

The final step was to determine the x-ray luminosity of each galaxy cluster and plot it against the mass determined from the weak lensing, with the resulting mass-luminosity relation for the new collection of groups and clusters extending previous studies to lower masses and higher redshifts. Within calculable uncertainty, the relation follows the same straight slope from nearby galaxy clusters to distant ones; a simple consistent scaling factor relates the total mass (baryonic plus dark) of a group or cluster to its x-ray brightness, the latter measuring the baryonic mass alone.

“By confirming the mass-luminosity relation and extending it to high redshifts, we have taken a small step in the right direction toward using weak lensing as a powerful tool to measure the evolution of structure,” says Jean-Paul Kneib a co-author of the ApJ paper from LAM and France’s National Center for Scientific Research (CNRS).

The origin of galaxies can be traced back to slight differences in the density of the hot, early Universe; traces of these differences can still be seen as minute temperature differences in the cosmic microwave background (CMB) – hot and cold spots.

“The variations we observe in the ancient microwave sky represent the imprints that developed over time into the cosmic dark-matter scaffolding for the galaxies we see today,” says George Smoot, director of the Berkeley Center for Cosmological Physics (BCCP), a professor of physics at the University of California at Berkeley, and a member of Berkeley Lab’s Physics Division. Smoot shared the 2006 Nobel Prize in Physics for measuring anisotropies in the CMB and is one of the authors of the ApJ paper. “It is very exciting that we can actually measure with gravitational lensing how the dark matter has collapsed and evolved since the beginning.”

One goal in studying the evolution of structure is to understand dark matter itself, and how it interacts with the ordinary matter we can see. Another goal is to learn more about dark energy, the mysterious phenomenon that is pushing matter apart and causing the Universe to expand at an accelerating rate. Many questions remain unanswered: Is dark energy constant, or is it dynamic? Or is it merely an illusion caused by a limitation in Einstein’s General Theory of Relativity?

The tools provided by the extended mass-luminosity relationship will do much to answer these questions about the opposing roles of gravity and dark energy in shaping the Universe, now and in the future.

Sources: ESA, and a paper published in the 20 January, 2010 issue of the Astrophysical Journal (arXiv:0910.5219 is the preprint)

Posted on by Brian Ventrudo

A Table-Top Test of General Relativity?

[/caption]

Even Albert Einstein might have been impressed. His theory of general relativity, which describes how the gravity of a massive object, such as a star, can curve space and time, has been used to predict small shifts in the orbit of Mercury, gravitational lensing by galaxies and black holes, and the existence of gravitational waves.  Now, new research shows it may soon be possible to study the effects of general relativity in bench-top laboratory experiments.


Xiang Zhang, a faculty scientist with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and professor at the University of California Berkeley, lead a study that shows the interactions of light and matter with spacetime, as predicted by general relativity, can be studied using the new breed of artificial optical materials that feature extraordinary abilities to bend light and other forms of electromagnetic radiation.

“We propose a link between the newly emerged field of artificial optical materials to that of celestial mechanics, thus opening a new possibility to investigate astronomical phenomena in a table-top laboratory setting,” says Zhang. “We have introduced a new class of specially designed optical media that can mimic the periodic, quasi-periodic and chaotic motions observed in celestial objects that have been subjected to complex gravitational fields.”

Zhang, a principal investigator with Berkeley Lab’s Materials Sciences Division and director of UC Berkeley’s Nano-scale Science and Engineering Center, has been one of the pioneers in the creation of artificial optical materials. Last year, he and his research group made headlines when they fashioned unique metamaterials – composites of metals and dielectrics – that were able to bend light backwards, a property known as a negative refraction that is unprecedented in nature. More recently, he and his group fashioned a “carpet cloak” from nanostructured silicon that concealed the presence of objects placed under it from optical detection. These efforts not only suggested that true invisibility materials are within reach, Zhang said, but also represented a major step towards transformation optics that would “open the door to manipulating light at will.”

Now he and his research group have demonstrated that a new class of metamaterials called “continuous-index photon traps” or CIPTs can serve as broadband and radiation-free “perfect” optical cavities. CIPTs can control, slow and trap light in a manner similar to such celestial phenomena as black holes and gravitational lenses. This equivalence between the motion of the stars in curved spacetime and propagation of the light in optical metamaterials engineered in a laboratory is referred to as the “optical-mechanical analogy.”

Zhang says that such specially designed metamaterials can be valuable tools for studying the motion of massive celestial bodies in gravitational potentials under a controlled laboratory environment. Observations of such celestial phenomena by astronomers are often impractical because of the long time scales of the interactions on a astronomical scale.

“If we twist our optical metamaterial space into new coordinates, the light that travels in straight lines in real space will be curved in the twisted space of our transformational optics,” says Zhang. “This is very similar to what happens to starlight when it moves through a gravitational potential and experiences curved spacetime. This analogue between classic electromagnetism and general relativity, may enable us to use optical metamaterials to study relativity phenomena such as gravitational lens.”

In their demonstration studies, the team used a composite structure of air and the semiconductor Gallium Indium Arsenide Phosphide (GaInAsP). This material provided operation at the infrared spectral range and featured a high refractive index with low absorption.

In their paper, Zhang and his coauthors cite as a particularly intriguing prospect for applying artificial optical materials to the optical-mechanical analogy the study of the phenomenon known as chaos. The onset of chaos in dynamic systems is one of the most fascinating problems in science and is observed in areas as diverse as molecular motion, population dynamics and optics. In particular, a planet around a star can undergo chaotic motion if a perturbation, such as another large planet, is present. However, because of the large spatial distances between the celestial bodies, and the long periods involved in the study of their dynamics, the direct observation of chaotic planetary motion has been a challenge. The use of the optical-mechanical analogy may enable such studies to be accomplished on demand in a bench-top laboratory setting.

“Unlike astronomers, we will not have to wait 100 years to get experimental results,” Zhang says.

The paper titled “Mimicking Celestial Mechanics in Metamaterials” is now available on-line in the journal Nature Physics.

Source: Lawrence Berkeley National Lab

Posted on by Nancy Atkinson

First Extra-Galactic Planet May Have Been Detected

Panel on the right shows The upper panel shows the simulated light curve (black dots) of a planetary event in M31. Credit: Ingrosso, et al.

[/caption]

Using a technique called Pixel-lensing, a group of astronomers in Italy may have detected a planet orbiting another star. But this planet is unique among the 300-plus exoplanets discovered so far, as it and its parent star are in another galaxy. The Andromeda Galaxy, to be exact. Technically, the star in M31 was found to have a companion about 6 times the mass of Jupiter, so it could be either a brown dwarf or a planet. But either way, this is a remarkable feat, to find an object of that size in another galaxy.

Pixel-lensing, or gravitational microlensing was developed to look for MAssive Compact Halo Objects MACHOs in the galactic halo of the Milky Way. Because light rays are bent when they pass close to a massive object, the gravity of a nearby star focuses the light from a distant star towards Earth. This method is sensitive to finding planets in our own galaxy, ranging is sizes from Jupiter-like planets to Earth-sized ones. And recently, astronomers used gravitational microlensing to be able to see about a dozen or so stars in M31, an extraordinary accomplishment in itself.

The advantage of microlensing is that it works best for more distant objects, therefore in theory it would seem to be ideal for planet hunting in other galaxies. So, the researchers from the National Institute of Nuclear Physics in Italy, led by Gabriele Ingrosso decided to see if this method would work to detect planets orbiting the stars seen in Andromeda. They used a Monte Carlo approach, where they selected the physical parameters of the binary lens system –a star hosting a planet– and calculated the pixel-lensing light curve, taking into account the finite source effects. The team thought they should be able to detect a planet with about 2 Jupiter masses.

The light from one of the stars they studied in Andromeda showed a distinct variability, most likely from a companion, which could be an orbiting planet based on the object’s mass.

One disadvantage to microlensing is that exposures are available for a few days at most, so the team is hoping for another chance to follow up on their discovery.

The team notes in their paper that perhaps an extrasolar planet in M31 might have already been detected since an anomaly in a pixel-lensing light curve was previously reported by another research team in 2004, who claimed that a possible binary system in M31 was responsible for an observed anomaly in an observed light curve.

Read the team’s paper here.

Source: arXiv, Technology Review Blog

Posted on by Nancy Atkinson

Oldest and Most Distant Water in the Universe Detected

The image is made from HST data and shows the four lensed images of the dusty red quasar, connected by a gravitational arc of the quasar host galaxy. The lensing galaxy is seen in the centre, between the four lensed images. Credit: John McKean/HST Archive data

[/caption]
Astronomers have found the most distant signs of water in the Universe to date. The water vapor is thought to be contained in a maser, a jet ejected from a supermassive black hole at the center of a galaxy, named MG J0414+0534. The radiation from the water maser was emitted when the Universe was only about 2.5 billion years old, a fifth of its current age. “The radiation that we detected has taken 11.1 billion years to reach the Earth, said Dr. John McKean of the Netherlands Institute for Radio Astronomy (ASTRON). “However, because the Universe has expanded like an inflating balloon in that time, stretching out the distances between points, the galaxy in which the water was detected is about 19.8 billion light years away.”

The water emission is seen as a maser, where molecules in the gas amplify and emit beams of microwave radiation in much the same way as a laser emits beams of light. The faint signal is only detectable by using a technique called gravitational lensing, where the gravity of a massive galaxy in the foreground acts as a cosmic telescope, bending and magnifying light from the distant galaxy to make a clover-leaf pattern of four images of MG J0414+0534. The water maser was only detectable in the brightest two of these images.

“We have been observing the water maser every month since the detection and seen a steady signal with no apparent change in the velocity of the water vapor in the data we’ve obtained so far, McKean said. “This backs up our prediction that the water is found in the jet from the supermassive black hole, rather than the rotating disc of gas that surrounds it.”

Detection of the earliest and most distant water. CREDIT: Milde Science Communication, STScI, CFHT, J.-C. Cuillandre, Coelum.
Detection of the earliest and most distant water. CREDIT: Milde Science Communication, STScI, CFHT, J.-C. Cuillandre, Coelum.

Although since the initial discovery the team has looked at five more systems that have not had water masers, they believe that it is likely that there are many more similar systems in the early Universe. Surveys of nearby galaxies have found that only about 5% have powerful water masers associated with active galactic nuclei. In addition, studies show that very powerful water masers are extremely rare compared to their less luminous counterparts. The water maser in MG J0414+0534 is about 10,000 times the luminosity of the Sun, which means that if water masers were equally rare in the early Universe, the chances of making this discovery would be improbably slight.

“We found a signal from a really powerful water maser in the first system that we looked at using the gravitational lensing technique. From what we know about the abundance of water masers locally, we could calculate the probability of finding a water maser as powerful as the one in MG J0414+0534 to be one in a million from a single observation. This means that the abundance of powerful water masers must be much higher in the distant Universe than found locally because I’m sure we are just not that lucky!” said Dr McKean.

The discovery of the water maser was made by a team led by Dr. Violette Impellizzeri using the 100-metre Effelsberg radio telescope in Germany during July to September 2007. The discovery was confirmed by observations with the Expanded Very Large Array in the USA in September and October 2007. The team included Alan Roy, Christian Henkel and Andreas Brunthaler, from the Max Planck Institute for Radio Astronomy, Paola Castangia from Cagliari Observatory and Olaf Wucknitz from the Argelander Institute for Astronomy at Bonn University. The findings were published in Nature in December 2008.

The team is now analyzing high-resolution data to find out how close the water maser lies to the supermassive black hole, which will give them new insights into the structure at the center of active galaxies in the early Universe.

“This detection of water in the early Universe may mean that there is a higher abundance of dust and gas around the super-massive black hole at these epochs, or it may be because the black holes are more active, leading to the emission of more powerful jets that can stimulate the emission of water masers. We certainly know that the water vapour must be very hot and dense for us to observe a maser, so right now we are trying to establish what mechanism caused the gas to be so dense,” said Dr McKean.

McKean presented the team’s findings at the European Week of Astronomy and Space Science in the UK this week.

Source: RAS

Posted on by Nancy Atkinson

Water ‘Way Out There

Detection of the earliest and most distant water. CREDIT: Milde Science Communication, STScI, CFHT, J.-C. Cuillandre, Coelum.

[/caption]
A long time ago in a galaxy far, far away there was water. Astronomers have found tell-tale signatures of water molecules in a galaxy more than 11 billion light years from Earth. Using the giant, 100-meter-diameter radio telescope in Effelsberg, Germany, along with the Very Large Array (VLA) in New Mexico, scientists detected the most distant water yet seen in the Universe. Previously, the most distant water had been seen in a galaxy less than 7 billion light-years from Earth. Since it is so far away, we’re actually seeing it as it was long ago; as when the Universe was one-sixth the age it is now. The astronomers were able to take advantage of two types of natural “amplification” to detect the water in this galaxy. The galaxy, dubbed MG J0414+0534 has a quasar — a supermassive black hole powering bright emission — at its core. In the region near the core, the water molecules are acting as masers, the radio equivalent of lasers, to amplify radio waves at a specific frequency. Additionally, another galaxy was used as a gravitational lens to magnify the radio signals used to detect the water molecules.

The astronomers say their discovery indicates that such giant water masers were more common in the early Universe than they are today. At the galaxy’s great distance, even the strengthening of the radio waves done by the masers would not by itself have made them strong enough to detect with the radio telescopes.

With the help of gravitational lensing from another galaxy, nearly 8 billion light-years away, located directly in the line of sight from MG J0414+0534 to Earth, the foreground galaxy’s gravity served as a lens to further brighten the more-distant galaxy and make the emission from the water molecules visible to the radio telescopes.

Effelsberg Telescope.
Effelsberg Telescope.

The astronomers first detected the water signal with the Effelsberg telescope. They then turned to the VLA’s sharper imaging capability to confirm that it was indeed coming from the distant galaxy. The gravitational lens produces not one, but four images of MG J0414+0534 as seen from Earth. Using the VLA, the scientists found the specific frequency attributable to the water masers in the two brightest of the four lensed images.

The radio frequency emitted by the water molecules was Doppler shifted by the expansion of the Universe from 22.2 GHz to 6.1 GHz.

“We were only able to discover this distant water with the help of the gravitational lens,” said Violette Impellizzeri, an astronomer with the Max-Planck Institute for Radioastronomy (MPIfR) in Bonn, Germany. “This cosmic telescope reduced the amount of time needed to detect the water by a factor of about 1,000,” she added.

Water masers have been found in numerous galaxies at closer distances. Typically, they are thought to arise in disks of molecules closely orbiting a supermassive black hole at the galaxy’s core. The amplified radio emission is more often observed when the orbiting disk is seen nearly edge-on. However, the astronomers said MG J0414+0534 is oriented with the disk almost face-on as seen from Earth.

“This may mean that the water molecules in the masers we’re seeing are not in the disk, but in the superfast jets of material being ejected by the gravitational power of the black hole,” explained John McKean, also of MPIfR.

The team’s paper will be published in the Dec. 18 edition of Nature.

Source: NRAO

Posted on by Nancy Atkinson

‘Cosmic Eye’ Helps Focus on Distant Galaxy’s Formation

Cosmic Eye. Credit: Hubble Space Telescope

[/caption]
Using gravitational lensing, astronomers have been able to see a young star-forming galaxy in the distant universe as it appeared only two billion years after the Big Bang. Appropriately enough, the galaxy used as a zoom lens was the “Cosmic Eye” galaxy, named so because through the effect of gravitational lensing, it looks like a giant eye in space. The researchers, led by Dr. Dan Stark, of Caltech, say this distant galaxy may provide insights into how our own galaxy may have evolved to its present state.

The astronomers used the ten meter Keck telescope in Hawaii, which is equipped with a laser-assisted guide star adaptive optics (AO) to correct for blurring in the Earth’s atmosphere. By combining the powerful telescope with the magnifying effect of the gravitational field of the foreground galaxy – called gravitational lensing – they were able to study the distant star system, which lies 11 billion light years from Earth. The Cosmic Eye, the foreground galaxy, is 2.2 billion light years from Earth.

The distortion of light rays enlarged the distant galaxy eight times.

This allowed the scientists to determine the galaxy’s internal velocity structure and compare it to later star systems such as the Milky Way.

In the image, the red source in the middle is the foreground lensing galaxy, while the blue ring is the near-complete ring image of the background star-forming galaxy.

Watch a movie of the gravitational lensing view.

Research co-author Dr. Mark Swinbank, in The Institute for Computational Cosmology, at Durham University, said, “This is the most detailed study there has been of an early galaxy. Effectively we are looking back in time to when the Universe was in its very early stages.

Stark said, “Gravity has effectively provided us with an additional zoom lens, enabling us to study this distant galaxy on scales approaching only a few hundred light years.

“This is ten times finer sampling than previously. As a result for the first time we can see that a typical-sized young galaxy is spinning and slowly evolving into a spiral galaxy much like our own Milky Way.”

Data from the Keck Observatory was combined with millimeter observations from the Plateau de Bure Interferometer, in the French Alps, which is sensitive to the distribution of cold gas destined to collapse to form stars.

Dr. Swinbank added, “Remarkably the cold gas traced by our millimetre observations shares the rotation shown by the young stars in the Keck observations.

“The distribution of gas seen with our amazing resolution indicates we are witnessing the gradual build up of a spiral disk with a central nuclear component.”

These observations has astronomers looking forward to the capabilities of the European Extremely Large Telescope (E -ELT) and the American Thirty Metre Telescope (TMT), which are being built and will be available in about 10 years.

Source: Durham University