Category: Astronomy

Different concentrations of elements in a meteorite: magnesium is green, calcium is yellow, aluminium is white, iron is red and silicon is blue. Image credit: Open University. Click to enlarge.
Researchers trying to work out how the planets formed have uncovered a new clue by analysing meteorites that are older than the Earth.

The research shows that the process which depleted planets and meteorites of so-called volatile elements such as zinc, lead and sodium (in their gaseous form) must have been one of the first things to happen in our nebula. The implication is that ‘volatile depletion’ may be an inevitable part of planet formation – a feature not just of our Solar System, but of many other planetary systems too.

The researchers at Imperial College London, who are funded by the Particle Physics and Astronomy Research Council (PPARC), reached their conclusions after analysing the composition of primitive meteorites, stony objects that are older than the Earth and which have barely changed since the Solar System was made up of fine dust and gas.

Their analysis, published today in the Proceedings of the National Academy of Sciences, shows that all the components that make up these rocks are depleted of volatile elements. This means that volatile element depletion must have occurred before the earliest solids had formed.

All of the terrestrial planets in the Solar System as far out as Jupiter, including Earth, are depleted of volatile elements. Researchers have long known that this depletion must have been an early process, but it was unknown whether it occurred at the beginning of the formation of the Solar System, or a few million years later.

It might be that volatile depletion is necessary to make terrestrial planets as we know them -as without it our inner solar system would look more like the outer solar system with Mars and Earth looking more like Neptune and Uranus with much thicker atmospheres.

Dr Phil Bland, from Imperial’s Department of Earth Science and Engineering, who led the research, explains: “Studying meteorites helps us to understand the initial evolution of the early Solar System, its environment, and what the material between stars is made of. Our results answer one of a huge number of questions we have about the processes that converted a nebula of fine dust and gas into planets.”

Professor Monica Grady, a planetary scientist from the Open University and member of PPARC’s Science Committee adds, “This research shows how looking at the tiniest of fragments of material can help us answer one of the biggest questions asked: ‘How did the Solar System form?’. It is fascinating to see how processes that took place over 4.5 billion years ago can be traced in such detail in laboratories on Earth today.

For planetary scientists, the most valuable meteorites are those that are found immediately after falling to earth, and so are only minimally contaminated by the terrestrial environment. The researchers analysed around half of the approximately 45 primitive meteorite falls in existence around the world, including the Renazzo meteorite which was found in Italy in 1824.

Dr Phil Bland is a member of the Impacts and Astromaterials Research Centre (IARC), which combines planetary science researchers from Imperial College London and the Natural History Museum.

Original Source: PPARC News Release

Deep, wide field view of the Virgo Cluster showing a diffuse web of galaxies. Image credit: Chris Mihos et al. Click to enlarge.
Case Western Reserve University astronomers have captured the deepest wide-field image ever of the nearby Virgo cluster of galaxies, directly revealing for the first time a vast, complex web of “intracluster starlight” — nearly 1,000 times fainter than the dark night sky — filling the space between the galaxies within the cluster. The streamers, plumes and cocoons that make up this extremely faint starlight are made of stars ripped out of galaxies as they collide with one another inside the cluster, and act as a sort of “archaeological record” of the violent lives of cluster galaxies.

The Virgo image was captured through Case’s newly refurbished 24-inch Burrell Schmidt telescope, built in the 1930s and located at the Kitt Peak National Observatory in Arizona. Over the course of 14 dark moonless nights, the researchers took more than 70 images of the Virgo Cluster, then used advanced image processing techniques to combine the individual images into a single image capable of showing the faint intracluster light.

“When we saw all this very faint starlight in the image, my first reaction was WOW!,” project leader Chris Mihos said. “Then I began to worry about all the things we could have done wrong.” Many effects, such as stray light from nearby stars, from instruments in the observatory and even from the changing brightness of the night sky could all contaminate the image and lead to inaccurate results. “But as we corrected for each of these contaminants, not only did the faint starlight not disappear, it became even more apparent. That’s when we knew we had something big.”

The new image gives dramatic evidence of the violent life and death of cluster galaxies. Drawn together into giant clusters over the course of cosmic time by their mutual gravity, galaxies careen around in the cluster, smashing into other galaxies, being stripped apart by gravitational forces and even being cannibalized by the massive galaxies which sit at the cluster’s heart. The force of these encounters literally pulls many galaxies apart, leaving behind ghostly streams of stars adrift in the cluster, a faint tribute to the violence of cluster life.

“From computer simulations, we’ve long suspected this web of intracluster starlight should be there,” says Mihos, associate professor of astronomy at Case, “but it’s been extremely hard to map it out because it’s so faint.” Mihos and graduate students Craig Rudick (Case) and Cameron McBride (University of Pittsburgh, and former Case undergraduate) have developed computer simulations that track how clusters of galaxies evolve over time, to study exactly how this intracluster starlight is created.

“With the data from the telescope, we see how a cluster looks today,” Mihos explains. “But with computer simulations, we can watch how a cluster evolves over 10 billion years of time. By comparing the simulation to the real features we now see in Virgo, we can learn how the cluster formed and what happened to its many galaxies.” For example, the fact that the intracluster light in Virgo is so complex and irregular lends credence to the theory of “hierarchical assembly,” where clusters grow sporadically when groups of galaxies fall into the cluster, rather than through the smooth, slow addition of galaxies one by one.

To detect the faint intracluster light, upgrades were needed to Case’s Burrell Schmidt telescope, originally part of the original Warner and Swasey Observatory in Cleveland until its move to Kitt Peak in 1979. The improvements included the installation of a new camera system and upgrades to the telescope to make it more structurally stable and reduce unwanted scattered light.

“It’s like ‘The Little Engine that Could’,” says Case astronomer Paul Harding, who directed the refurbishment of the telescope. “It’s the smallest telescope on the mountain, but with these upgrades it’s capable of some pretty incredible science.” The telescope’s wide field of view — enough to fit three full moons across the image – proved crucial to the project, allowing the team to map out the intracluster light over a much larger part of the Virgo Cluster than would be possible using larger telescopes with their much smaller fields of view.
The Virgo Cluster of galaxies — so named because it appears in the constellation of Virgo — is the nearest galaxy cluster to the Earth, at a distance of approximately 50 million light years. The cluster contains more than 2,000 galaxies, the brightest of which can be seen with the aide of a small telescope.

The Case findings are reported in the paper “Diffuse Light in the Virgo Cluster” to be published in the September 20th issue of The Astrophysical Journal Letters. Along with Mihos team researchers included Case astronomers Heather Morrison and Paul Harding, and John Feldmeier, a National Science Foundation Fellow at the National Optical Astronomy Observatory in Tucson, Ariz. (and formerly of Case).

The wide-field image of the Virgo Cluster, along with movies of computer simulations of galaxies and galaxy clusters, can be found at http://astroweb.case.edu/hos/Virgo.

Original Source: Case Western University News Release

Artist’s concept of Jupiter-like planet orbiting a star. Image credit: NASA Click to enlarge
Using NASA’s Spitzer Space Telescope, a team of astronomers led by the University of Rochester has detected gaps ringing the dusty disks around two very young stars, which suggests that gas-giant planets have formed there. A year ago, these same researchers found evidence of the first “baby planet” around a young star, challenging most astrophysicists’s models of giant-planet formation.

The new findings in the Sept. 10 issue of Astrophysical Journal Letters not only reinforce the idea that giant planets like Jupiter form much faster than scientists have traditionally expected, but one of the gas-enshrouded stars, called GM Aurigae, is analogous to our own solar system. At a mere 1 million years of age, the star gives a unique window into how our own world may have come into being.

“GM Aurigae is essentially a much younger version of our Sun, and the gap in its disk is about the same size as the space occupied by our own giant planets,” says Dan Watson, professor of physics and astronomy at the University of Rochester and leader of the Spitzer IRS Disks research team. “Looking at it is like looking at baby pictures of our Sun and outer solar system,” he says.

“The results pose a challenge to existing theories of giant-planet formation, especially those in which planets build up gradually over millions of years,” says Nuria Calvet, professor of astronomy at the University of Michigan and lead author of the paper. “Studies like this one will ultimately help us better understand how our outer planets, as well as others in the universe, form.”

The new “baby planets” live within the clearings they have scoured out in the disks around the stars DM Tauri and GM Aurigae, 420 light years away in the Taurus constellation. These disks have been suspected for several years to have central holes that might be due to planet formation. The new spectra, however, leave no doubt: The gaps are so empty and sharp-edged that planetary formation is by far the most reasonable explanation for their appearance.

The new planets cannot yet be seen directly, but Spitzer’s Infrared Spectrograph (IRS) instrument clearly showed that an area of dust surrounding certain stars was missing, strongly suggesting the presence of a planet around each. The dust in a protoplanetary disk is hotter in the center near the star, and so radiates most of its light at shorter wavelengths than the cooler outer reaches of the disk. The IRS Disks team found that there was an abrupt deficit of light radiating at all short infrared wavelengths, strongly suggesting that the central part of the disk was absent. These stars are very young by stellar standards, about a million years old, still surrounded by their embryonic gas disks. The only viable explanation for the absence of gas that could occur during the short lifetime of the star is that a planet?most likely a gas giant like our Jupiter?is orbiting the star and gravitationally “sweeping out” the gas within that distance of the star.

As with last year’s young-planet findings, these observations represent a challenge to all existing theories of giant-planet formation, especially those of the “core-accretion” models in which such planets are built up by accretion of smaller bodies, which require much more time to build a giant planet than the age of these systems.

The IRS Disks team discovered something else curious about GM Aurigae. Instead of a simple central clearing of the dust disk, as in the other cases studied, GM Aurigae has a clear gap in its disk that separates a dense, dusty outer disk from a tenuous inner one. This could be either an intermediate stage as the new planet clears out the dust surrounding it and leading to a complete central clearing like the other “baby planet” disks, or it could be the result of multiple planets forming within a short time and sweeping out the dust in a more complex fashion.

GM Aurigae has 1.05 times the mass of our Sun-a near twin?so it will develop into a star very similar to the Sun. If it were overlaid onto our own Solar System, the discovered gap would extend roughly from the orbit of Jupiter (460 million miles) to the orbit of Uranus (1.7 billion miles). This is the same range in which the gas-giant planets in our own system appear. Small non-gas-giant planets, rocky worlds like Earth, would not sweep up as much material, and so would not be detectable from an absence of dust.

The Spitzer Space Telescope was launched into orbit on Aug. 25, 2003. The IRS Disks research team is led by members that built Spitzer’s Infrared Spectrograph, and includes astronomers at the University of Rochester, Cornell University, the University of Michigan, the Autonomous National University of Mexico, the University of Virginia, Ithaca College, the University of Arizona, and UCLA. NASA’s Jet Propulsion Laboratory in Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, in Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena.

University of Rochester

The Distant Gamma-Ray Burst GRB 050904. Image credit: ESO Click to enlarge
An Italian team of astronomers has observed the afterglow of a Gamma-Ray Burst that is the farthest known ever. With a measured redshift of 6.3, the light from this very remote astronomical source has taken 12,700 million years to reach us. It is thus seen when the Universe was less than 900 million years old, or less than 7 percent its present age.

“This also means that it is among the intrinsically brightest Gamma-Ray Burst ever observed”, said Guido Chincarini from INAF-Osservatorio Astronomico di Brera and University of Milano-Bicocca (Italy) and leader of a team that studied the object with ESO’s Very Large Telescope. “Its luminosity is such that within a few minutes it must have released 300 times more energy than the Sun will release during its entire life of 10,000 million years.”

Gamma-ray bursts (GRBs) are short flashes of energetic gamma-rays lasting from less than a second to several minutes. They release a tremendous quantity of energy in this short time making them the most powerful events since the Big Bang. It is now widely accepted that the majority of the gamma-ray bursts signal the explosion of very massive, highly evolved stars that collapse into black holes.

This discovery not only sets a new astronomical record, it is also fundamental to the understanding of the very young Universe. Being such powerful emitters, these Gamma Ray Bursts serve as useful beacons, enabling the study of the physical conditions that prevailed in the early Universe. Indeed, since GRBs are so luminous, they have the potential to outshine the most distant known galaxies and may thus probe the Universe at higher redshifts than currently known. And because Gamma-ray Burst are thought to be associated with the catastrophic death of very massive stars that collapse into black holes, the existence of such objects so early in the life of the Universe provide astronomers with important information to better understand its evolution.

The Gamma-Ray Burst GRB050904 was first detected on September 4, 2005, by the NASA/ASI/PPARC Swift satellite, which is dedicated to the discovery of these powerful explosions.

Immediately after this detection, astronomers in observatories worldwide tried to identify the source by searching for the afterglow in the visible and/or near-infrared, and study it.

First observations by American astronomers with the Palomar Robotic 60-inch Telescope failed to find the source. This sets a very stringent limit: in the visible, the afterglow should thus be at least a million times fainter than the faintest object that can be seen with the unaided eye (magnitude 21). But observations by another team of American astronomers detected the source in the near-infrared J-band with a magnitude 17.5, i.e. at least 25 times brighter than in the visible.

This was indicative of the fact that the object must either be very far away or hidden beyond a large quantity of obscuring dust. Further observations indicated that the latter explanation did not hold and that the Gamma-Ray Burst must lie at a distance larger than 12,500 million light-years. It would thus be the farthest Gamma-Ray Burst ever detected.

Italian astronomers forming the MISTICI collaboration then used Antu, one of four 8.2-m telescopes that comprise ESO’s Very Large Telescope (VLT) to observe the object in the near-infrared with ISAAC and in the visible with FORS2. Observations were done between 24.7 and 26 hours after the burst.

Indeed, the afterglow was detected in all five bands in which they observed (the visible I- and z-bands, and the near-infrared J, H, and K-bands). By comparing the brightness of the source in the various bands, the astronomers could deduce its redshift and, hence, its distance. “The value we derived has since then been confirmed by spectroscopic observations made by another team using the Subaru telescope”, said Angelo Antonelli (Roma Observatory), another member of the team.

Original Source: ESO News Release

An artist’s impression of dust disk around the white dwarf GD 362. Image credit: Gemini Click to enlarge
Astronomers have glimpsed dusty debris around an essentially dead star where gravity and radiation should have long ago removed any sign of dust ? a discovery that may provide insights into our own solar system’s eventual demise several billion years from now.

The results are based on mid-infrared observations made with the Gemini 8-meter Frederick C. Gillett Telescope (Gemini North) on Hawaii’s Mauna Kea. The Gemini observations reveal a surprisingly high abundance of dust orbiting an ancient stellar ember named GD 362.

“This is not an easy one to explain,” said Eric Becklin, UCLA astronomer and principle investigator for the Gemini observations. “Our best guess is that something similar to an asteroid or possibly even a planet around this long-dead star is being ground up and pulverized to feed the star with dust. The parallel to our own solar system’s eventual demise is chilling.”

“We now have a window to the future of our own planetary system,” said Benjamin Zuckerman, UCLA professor of physics and astronomy, member of NASA’s Astrobiology Institute, and a co-author on the Gemini-based paper. “For perhaps the first time, we have a glimpse into how planetary systems like our own might behave billions of years from now.”

“The reason why this is so interesting is that this particular white dwarf has by far the most metals in its atmosphere of any known white dwarf,” Zuckerman added. “This white dwarf is as rich in calcium, magnesium and iron as our own sun, and you would expect none of these heavier elements. This is a complete surprise. While we have made a substantial advance, significant mysteries remain.”

The research team includes scientists from UCLA, Carnegie Institution and Gemini Observatory. The results are scheduled for publication in an upcoming issue of the Astrophysical Journal. The results will be published concurrently with complementary near-infrared observations made by a University of Texas team led by Mukremin Kilic at the NASA Infrared Telescope Facility, also on Mauna Kea.

“We have confirmed beyond any doubt that dust never does sleep!” quips Gemini Observatory’s Inseok Song, a co-author of the paper. “This dust should only exist for hundreds of years before it is swept into the star by gravity and vaporized by high temperatures in the star’s atmosphere. Something is keeping this star well stocked with dust for us to detect it this long after the star’s death.”

“There are just precious few scenarios that can explain so much dust around an ancient star like this,” said UCLA professor of physics and astronomy Michael Jura, who led the effort to model the dust environment around the star. “We estimate that GD 362 has been cooling now for as long as five billion years since the star’s death-throes began and in that time any dust should have been entirely eliminated.”

Jura likens the disk to the familiar rings of Saturn and thinks that the dust around GD 362 could be the consequence of the relatively recent gravitational destruction of a large “parent body” that got too close to the dead star.

GD 362 is a white dwarf star. It represents the end-state of stellar evolution for stars like the sun and more massive stars like this one’s progenitor, which had an original mass about seven times the sun’s. After undergoing nuclear reactions for millions of years, GD 362’s core ran out of fuel and could no longer create enough heat to counterbalance the inward push of gravity. After a short period of instability and mass loss, the star collapsed into a white-hot corpse. The remains are cooling slowly over many billions of years as the dying ember makes its slow journey into oblivion.

Based on its cooling rate, astronomers estimate that between two billion to five billion years have passed since the death of GD 362.

“This long time frame would explain why there is no sign of a shell of glowing gas known as a planetary nebula from the expulsion of material as the star died,” said team member and Gemini astronomer Jay Farihi.

During its thermonuclear decline, GD 362 went through an extensive period of mass loss, going from a mass of about seven times that of the sun to a smaller, one-solar-mass shadow of its former self.

Although about one-quarter of all white dwarfs contain elements heaver than hydrogen in their atmospheres, only one other white dwarf is known to contain dust. The other dusty white dwarf, designated G29-38, has about 100 times less dust density than GD 362.

The Gemini observations were made with the MICHELLE mid-infrared spectrograph on the Gemini North telescope on Mauna Kea, Hawaii.

“These data are phenomenal,” said Alycia Weinberger of the Carnegie Institution. “Observing this star was a thrill! We were able to find the remnants of a planetary system around this star only because of Gemini’s tremendous sensitivity in the mid-infrared. Usually you need a spacecraft to do this well.”

The Gemini mid-infrared observations were unique in their ability to confirm the properties of the dust responsible for the “infrared excess” around GD 362. The complementary Infrared Telescope Facility near-infrared observations and paper by the University of Texas team provided key constraints on the environment around the star.

University of Texas astronomer and co-author Ted von Hippel describes how the Infrared Telescope Facility (IRTF) observations complement the Gemini results: “The IRTF spectrum rules out the possibility that this star could be a brown dwarf as the source of the ‘infrared excess,'” von Hippel said. “The combination of the two data sets provides a convincing case for a dust disk around GD 362.”

Original Source: UCLA News Release

Artist’s impression of a pulsar ‘eating’ a companion star. Image credit: ESA Click to enlarge
ESA’s Integral space observatory, together with NASA’s Rossi X-ray Timing Explorer spacecraft, has found a fast-spinning pulsar in the process of devouring its companion.

This finding supports the theory that the fastest-spinning isolated pulsars get that fast by cannibalising a nearby star. Gas ripped from the companion fuels the pulsar’s acceleration. This is the sixth pulsar known in such an arrangement, and it represents a ‘stepping stone’ in the evolution of slower-spinning binary pulsars into faster-spinning isolated pulsars.
“We’re getting to the point where we can look at any fast-spinning, isolated pulsar and say, ‘That guy used to have a companion’,” said Dr Maurizio Falanga, who led the Integral observations, at the Commissariat ? l’Energie Atomique (CEA) in Saclay, France.

‘Pulsars’ are rotating neutron stars, which are created in stellar explosions. They are the remnants of stars that were once at least eight times more massive than the Sun. These stars still contain about the mass of our Sun compactified into a sphere of only about 20 kilometres across.

This pulsar, called IGR J00291+5934, belongs to a category of ‘X-ray millisecond pulsars’, which pulse with the X-ray light several hundred times a second, one of the fastest known. It has a period of 1.67 milliseconds which is much smaller that most other pulsars that rotate once every few seconds.

Neutron stars are born rapidly spinning in collapses of massive stars. They gradually slow down after a few hundred thousand years. Neutron stars in binary star systems, however, can reverse this trend and speed up with the help from the companion star.

For the first time ever, this speeding-up has been observed in the act. “We now have direct evidence for the star spinning faster whilst cannibalising its companion, something which no one had ever seen before for such a system,” said Dr Lucien Kuiper from the Netherlands Institute for Space Research (SRON), in Utrecht.

A neutron star can remove gas from its companion star in a process called ‘accretion’. The flow of gas onto the neutron star makes the star spin faster and faster. Both the flow of gas and its crashing upon the neutron star surface releases much energy in the form of X-ray and gamma radiation.

Neutron stars have such a strong gravitational field that light passing by the star changes its direction by almost 100 degrees (in comparison light passing by the Sun is deflected by an angle which is 200 thousands times smaller). “This ‘gravitational bending’ allows us to see the back side of the star,” points out Prof. Juri Poutanen from the University of Oulu, Finland.

“This object was about ten times more energetic than what is usually observed for similar sources,” said Falanga. “Only some kind of monster emits at these energies, which corresponds to a temperature of almost a billion degrees.”

From a previous Integral result, scientists deduced that because the neutron star has a strong magnetic field, charged particles from its companion are channeled along the magnetic field lines until they slam into the neutron star surface at one of its magnetic poles, forming ‘hot spots’. The very high temperatures seen by Integral arise from this very hot plasma over the accretion spots.

IGR J00291+5934 was discovered by Integral during a routine scan of the sky on 2 December 2004, in the outer reaches of our Milky Way galaxy, when it suddenly flared. On the day after, scientists accurately clocked the neutron star with the Rossi X-ray Timing Explorer.

Rossi observations revealed that the companion is already a fraction the size of our Sun, perhaps as small as 40 Jupiter masses. The binary orbit is 2.5 hours long (as opposed to the year long Earth-Sun orbit). The full system is very tight; both stars are so close that they will fit into the radius of the Sun. These details support the theory that the two stars are close enough for accretion to take place and that the companion star is being cannibalised.

“Accretion is expected to cease after a billion of years or so,” said Dr Duncan Galloway of the Massachusetts Institute of Technology, USA, responsible for the Rossi observations. “This Integral-Rossi discovery provides more evidence of how pulsars evolve from one phase to another – from an initially slowly spinning binary neutron star emitting high energies, to a rapidly spinning isolated pulsar emitting in radio wavelengths.”

The discovery is the first of its kind for Integral (four of the first five rapidly spinning X-ray pulsars were discovered by Rossi). This bodes well in the combined search for these rare objects. Integrals’s sensitive detectors can identify relatively dim and distant sources and so, knowing where to look, Rossi can provide timing information through a dedicated observation extending over the entire two-week period of the typical outburst.

Original Source: ESA Portal

Station with active crossed dipole. Image credit: Haystack Observatory Click to enlarge
If you want to hear a little bit of the Big Bang, you’re going to have to turn down your stereo.

That’s what neighbors of MIT’s Haystack Observatory found out. They were asked to make a little accommodation for science, and now the results are in: Scientists at Haystack have made the first radio detection of deuterium, an atom that is key to understanding the beginning of the universe. The findings are being reported in an article in the Sept. 1 issue of Astrophysical Journal Letters.

The team of scientists and engineers, led by Alan E.E. Rogers, made the detection using a radio telescope array designed and built at the MIT research facility in Westford, Mass. Rogers is currently a senior research scientist and associate director of the Haystack Observatory.

After gathering data for almost one year, a solid detection was obtained on May 30.

The detection of deuterium is of interest because the amount of deuterium can be related to the amount of dark matter in the universe, but accurate measurements have been elusive. Because of the way deuterium was created in the Big Bang, an accurate measurement of deuterium would allow scientists to set constraints on models of the Big Bang.

Also, an accurate measurement of deuterium would be an indicator of the density of cosmic baryons, and that density of baryons would indicate whether ordinary matter is dark and found in regions such as black holes, gas clouds or brown dwarfs, or is luminous and can be found in stars. This information helps scientists who are trying to understand the very beginning of our universe.

Until now the deuterium atom has been extremely difficult to detect with instruments on Earth. Emission from the deuterium atom is weak since it is not very abundant in space-there is approximately one deuterium atom for every 100,000 hydrogen atoms, thus the distribution of the deuterium atom is diffuse. Also, at optical wavelengths the hydrogen line is very close to the deuterium line, which makes it subject to confusion with hydrogen; but at radio wavelengths, deuterium is well separated from hydrogen and measurements can provide more consistent results.

In addition, our modern lifestyle, filled with gadgets that use radio waves, presented quite a challenge to the team trying to detect the weak deuterium radio signal. Radio frequency interference bombarded the site from cell phones, power lines, pagers, fluorescent lights, TV, and in one case from a telephone equipment cabinet where the doors had been left off. To locate the interference, a circle of yagi antennas was used to indicate the direction of spurious signals, and a systematic search for the RFI sources began.

At times, Rogers asked for help from Haystack’s neighbors, and in several instances replaced a certain brand of answering machine that was sending out a radio signal with one that did not interfere with the experiment. The interference caused by one person’s stereo system was solved by having a part on the sound card replaced by the factory.

The other members of the team working with Rogers are Kevin Dudevoir, Joe Carter, Brian Fanous and Eric Kratzenberg (all of Haystack Observatory) and Tom Bania of Boston University.

The Deuterium Array at Haystack is a soccer-field size installation conceived and built at the Haystack facility with support from the National Science Foundation, MIT and TruePosition Inc.

Original Source: MIT News Release

XMM-Newton image of galaxy cluster. Image credit: ESA Click to enlarge
ESA?s X-ray observatory, XMM-Newton, has for the first time allowed scientists to study in detail the formation history of galaxy clusters, not only with single arbitrarily selected objects, but with a complete representative sample of clusters.

Knowing how these massive objects formed is a key to understanding the past and future of the Universe.
Scientists currently base their well-founded picture of cosmic evolution on a model of structure formation where small structures form first and these then make up larger astronomical objects.

Galaxy clusters are the largest and most recently formed objects in the known Universe, and they have many properties that make them great astrophysical ?laboratories?. For example, they are important witnesses of the structure formation process and important ?probes? to test cosmological models.

To successfully test such cosmological models, we must have a good observational understanding of the dynamical structure of the individual galaxy clusters from representative cluster samples.

For example, we need to know how many clusters are well evolved. We also need to know which clusters have experienced a recent substantial gravitational accretion of mass, and which clusters are in a stage of collision and merging. In addition, a precise cluster mass measurement, performed with the same XMM-Newton data, is also a necessary prerequisite for quantitative cosmological studies.

The most easily visible part of galaxy clusters, i.e. the stars in all the galaxies, make up only a small fraction of the total of what makes up the cluster. Most of the observable matter of the cluster is composed of a hot gas (10-100 million degrees) trapped by the gravitational potential force of the cluster. This gas is completely invisible to human eyes, but because of its temperature, it is visible by its X-ray emission.

This is where XMM-Newton comes in. With its unprecedented photon-collecting power and capability of spatially resolved spectroscopy, XMM-Newton has enabled scientists to perform these studies so effectively that not only single objects, but also whole representative samples can be studied routinely.

XMM-Newton produces a combination of X-ray images (in different X-ray energy bands, which can be thought of as different X-ray ?colours?), and makes spectroscopic measurements of different regions in the cluster.

While the image brightness gives information on the gas density in the cluster, the colours and spectra provide an indication of the cluster?s internal gas temperature. From the temperature and density distribution, the physically very important parameters of pressure and ?entropy? can be also derived. Entropy is a measure of the heating and cooling history of a physical system.

The accompanying three images illustrate the use of entropy distribution in the ?X-ray luminous? gas as a way of identifying various physical processes. Entropy has the unique property of decreasing with radiative cooling, increasing due to heating processes, but staying constant with compression or expansion under energy conservation.

The latter ensures that a ?fossil record? of any heating or cooling is kept even if the gas subsequently changes its pressure adiabatically (under energy conservation).

These examples are drawn from the REFLEX-DXL sample, a statistically complete sample of some of the most X-ray luminous clusters found in the ROSAT All-Sky Survey. ROSAT was an X-ray observatory developed in the 1990s in co-operation between Germany, USA and UK.

The images provide views of the entropy distribution coded in colour where the values increase from blue, green, yellow to red and white.

Original Source: ESA Portal

Pulsar path over about 2.5 million years. Image credit: Bill Saxton, NRAO/AUI/NSF Click to enlarge
A speeding, superdense neutron star somehow got a powerful “kick” that is propelling it completely out of our Milky Way Galaxy into the cold vastness of intergalactic space. Its discovery is puzzling astronomers who used the National Science Foundation’s Very Long Baseline Array (VLBA) radio telescope to directly measure the fastest speed yet found in a neutron star.

The neutron star is the remnant of a massive star born in the constellation Cygnus that exploded about two and a half million years ago in a titanic explosion known as a supernova. Ultra-precise VLBA measurements of its distance and motion show that it is on course to inevitably leave our Galaxy.

“We know that supernova explosions can give a kick to the resulting neutron star, but the tremendous speed of this object pushes the limits of our current understanding,” said Shami Chatterjee, of the National Radio Astronomy Observatory (NRAO) and the Harvard-Smithsonian Center for Astrophysics. “This discovery is very difficult for the latest models of supernova core collapse to explain,” he added.

Chatterjee and his colleagues used the VLBA to study the pulsar B1508+55, about 7700 light-years from Earth. With the ultrasharp radio “vision” of the continent-wide VLBA, they were able to precisely measure both the distance and the speed of the pulsar, a spinning neutron star emitting powerful beams of radio waves. Plotting its motion backward pointed to a birthplace among groups of giant stars in the constellation Cygnus — stars so massive that they inevitably explode as supernovae.

“This is the first direct measurement of a neutron star’s speed that exceeds 1,000 kilometers per second,” said Walter Brisken, an NRAO astronomer. “Most earlier estimates of neutron-star speeds depended on educated guesses about their distances. With this one, we have a precise, direct measurement of the distance, so we can measure the speed directly,” Brisken said. The VLBA measurements show the pulsar moving at nearly 1100 kilometers (more than 670 miles) per second — about 150 times faster than an orbiting Space Shuttle. At this speed, it could travel from London to New York in five seconds.

In order to measure the pulsar’s distance, the astronomers had to detect a “wobble” in its position caused by the Earth’s motion around the Sun. That “wobble” was roughly the length of a baseball bat as seen from the Moon. Then, with the distance determined, the scientists could calculate the pulsar’s speed by measuring its motion across the sky.

“The motion we measured with the VLBA was about equal to watching a home run ball in Boston’s Fenway Park from a seat on the Moon,” Chatterjee explained. “However, the pulsar took nearly 22 months to show that much apparent motion. The VLBA is the best possible telescope for tracking such tiny apparent motions.”

The star’s presumed birthplace among giant stars in the constellation Cygnus lies within the plane of the Milky Way, a spiral galaxy. The new VLBA observations indicate that the neutron star now is headed away from the Milky Way’s plane with enough speed to take it completely out of the Galaxy. Since the supernova explosion nearly 2 and a half million years ago, the pulsar has moved across about a third of the night sky as seen from Earth.

“We’ve thought for some time that supernova explosions can give a kick to the resulting neutron star, but the latest computer models of this process have not produced speeds anywhere near what we see in this object,” Chatterjee said. “This means that the models need to be checked, and possibly corrected, to account for our observations,” he said.

“There also are some other processes that may be able to add to the speed produced by the supernova kick, but we’ll have to investigate more thoroughly to draw any firm conclusions,” said Wouter Vlemmings of the Jodrell Bank Observatory in the UK and Cornell University in the U.S.

The observations of B1508+55 were part of a larger project to use the VLBA to measure the distances and motions of numerous pulsars. “This is the first result of this long-term project, and it’s pretty exciting to have something so spectacular come this early,” Brisken said. The VLBA observations were made at radio frequencies between 1.4 and 1.7 GigaHertz.

Chatterjee, Vlemmings and Brisken worked with Joseph Lazio of the Naval Research Laboratory, James Cordes of Cornell University, Miller Goss of NRAO, Stephen Thorsett of the University of California, Santa Cruz, Edward Fomalont of NRAO, Andrew Lyne and Michael Kramer, both of Jodrell Bank Observatory. The scientists presented their findings in the September 1 issue of the Astrophysical Journal Letters.

The VLBA is a system of ten radio-telescope antennas, each with a dish 25 meters (82 feet) in diameter and weighing 240 tons. From Mauna Kea on the Big Island of Hawaii to St. Croix in the U.S. Virgin Islands, the VLBA spans more than 5,000 miles, providing astronomers with the sharpest vision of any telescope on Earth or in space.

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

Headquartered in Cambridge, Massachusetts, the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists organized into seven research divisions study the origin, evolution, and ultimate fate of the universe.

Original Source: CfA News Release