Posted on by Nicholos Wethington

An Apertif to the Next Radio Astronomy Entrée

A new detector at the Westerbork Synthesis Radio Telescope (WSRT) allows for a much wider view of the sky in the radio spectrum. In this image, the two pulsars are separated by over 3.5 degrees of arc in the sky. Image Credit: ASTRON

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To aid in the digestion of a new era in radio astronomy, a new technique for improving the is unfolding at the Westerbork Synthesis Radio Telescope (WSRT) in the Netherlands. By adding a plate of detectors to the focal plane of just one of the 14 radio antennas at the WSRT, astronomers at the Netherlands Institute for Radio Astronomy (ASTRON) have been able to image two pulsars separated by over 3.5 degrees of arc, which is about 7 times the size of the full Moon as seen from Earth.

The new project – called Apertif – uses an array of detectors in the focal plane of the radio telescope. This ‘phased array feed’ – made of 121 separate detectors – increases the field of view of the radio telescope by over 30 times. In doing so, astronomers are able to see a larger portion of the sky in the radio spectrum. Why is this important? Well, in keeping with our food course analogy, imagine trying to eat a bowl of soup with a thimble – you can only get a small portion of the soup into your mouth at a time. Then imagine trying to eat it with a ladle.

This same analogy of surveying and observing the sky for radio sources holds true. Dr. Tom Oosterloo, the Principle Investigator of the Apertif project, explains the meat of the new technique:

“The phased array feed consists of 121 small antennas, closely packed together. This matrix covers about 1 square meter. Each WSRT will have such a antenna matrix in its focus. This matrix fully samples the radiation field in the focal plane. By combining the signals of all 121 elements, a ‘compound beams'[sic] can be formed which can be steered to be pointing at any location inside a region of 3×3 degrees on the sky. By combining the signals of all 121 elements, the response of the telescope can be optimised, i.e. all optical distortions can be removed (because the radiation field is fully measured). This process is done in parallel 37 times, i.e. 37 compound beams are formed. Each compound beam basically functions as a separate telescope. If we do this in all WSRT dishes, we have 37 WSRTs in parallel. By steering all the beams to different locations within the 3×3 degree region, we can observe this region entirely.”

In other words, traditional radio telescopes use only a single detector in the focal plane of the telescope (where all of the radiation is focused by the telescope). The new detectors are somewhat like the CCD chip in your camera, or those in use in modern optical telescopes like Hubble. Each separate detector in the array receives data, and by combining the data into a composite image a high-quality image can be captured.

The new array will also widen the field of view of the radio telescope, which allowed for this most recent observation of widely separated pulsars in the sky, a milestone test for the project. As an added bonus, the new detector will increase the efficiency of the “aperture” to around 75%, up from 55% with the traditional antennas.

Dr. Oosterloo explained, “The aperture efficiency is higher because we have much more control over the radiation field in the focal plane. With the classic single antenna systems (as in the old WSRT or as in the eVLA), one measures the radiation field in a single point only. By measuring the radiation field over the entire focal plane, and by cleverly combining the signals of all elements, optical distortion effects can be minimised and a larger fraction of the incoming radiation can be used to image the sky.”

This image illustrates the larger field of view afforded by the new instrument. Image Credit: ASTRON

For now, there is only one of the 14 radio antennas equipped with Apertif. Dr. Joeri Van Leeuwen, a researcher at ASTRON, said in an email interview that in 2011, 12 of the antennas will be outfitted with the new detector array.

Sky surveys have been a boon for astronomers in recent years. By taking enormous amounts of data and making it available to the scientific community, astronomers have been able to make many more discoveries than they would have been able to by applying for time on disparate instruments.

Though there are some sky surveys in the radio spectrum that have been completed so far – the VLA FIRST Survey being the most prominent – the field has a long way to go. Apertif is the first step in the direction of surveying the whole sky in the radio spectrum with great detail, and many discoveries are expected to be made by using the new technique.

Apertif is expected to discover over 1,000 pulsars, based on current modeling of the Galactic pulsar population. It will also be a useful tool in studying neutral hydrogen in the Universe on large scales.

Dr. Oosterloo et. al. wrote in a paper published on Arxiv in July, 2010, “One of the main scientific applications of wide-field radio telescopes operating at GHz frequencies is to observe large volumes of space in order to make an inventory of the neutral hydrogen in the Universe. With such information, the properties of the neutral hydrogen in galaxies as function of mass, type and environment can be studied in great detail, and, importantly, for the first time the evolution of these properties with redshift can be addressed.”

Adding the radio spectrum to the visible and infrared sky surveys would help to fine-tune current theories about the Universe, as well as make new discoveries. The more eyes on the sky we have in different spectra, the better.

Though Apertif is the first such detector in use, there are plans to update other radio telescopes with the technology. Dr. Oosterloo said of other such projects, “Phased array feeds are also being built by ASKAP, the Australia SKA Pathfinder. This is an instrument of similar characteristics as Apertif. It is our main competitor, although we also collaborate on many things. I am also aware of a prototype being tested at Arecibo currently. In Canada, DRAO [Dominion Radio Astrophysical Observatory] is doing work on phased array feed development. However, only Apertif and ASKAP will construct an actual radio telescope with working phased array feeds in the short term.”

On November 22nd and 23rd, a science coordination meeting was held about the Apertif project in Dwingeloo, Drenthe, Netherlands. Dr. Oosterloo said that the meeting was attended by 40 astronomers, from Europe, the US, Australia and South Africa to discuss the future of the project, and that there has been much interest in the potential of the technique.

Sources: ASTRON press release, Arxiv, email interview with Dr. Tom Oosterloo and Dr. Joeri Van Leeuwen

Posted on by Nancy Atkinson

New Technique Could Track Down Dark Energy

Robert C. Byrd Green Bank Telescope CREDIT: NRAO/AUI/NSF

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From an NRAO press release:

Dark energy is the label scientists have given to what is causing the Universe to expand at an accelerating rate, and is believed to make up nearly three-fourths of the mass and energy of the Universe. While the acceleration was discovered in 1998, its cause remains unknown. Physicists have advanced competing theories to explain the acceleration, and believe the best way to test those theories is to precisely measure large-scale cosmic structures. A new technique developed for the Robert C. Byrd Green Bank Telescope (GBT) have given astronomers a new way to map large cosmic structures such as dark energy.

Sound waves in the matter-energy soup of the extremely early Universe are thought to have left detectable imprints on the large-scale distribution of galaxies in the Universe. The researchers developed a way to measure such imprints by observing the radio emission of hydrogen gas. Their technique, called intensity mapping, when applied to greater areas of the Universe, could reveal how such large-scale structure has changed over the last few billion years, giving insight into which theory of dark energy is the most accurate.

“Our project mapped hydrogen gas to greater cosmic distances than ever before, and shows that the techniques we developed can be used to map huge volumes of the Universe in three dimensions and to test the competing theories of dark energy,” said Tzu-Ching Chang, of the Academia Sinica in Taiwan and the University of Toronto.

To get their results, the researchers used the GBT to study a region of sky that previously had been surveyed in detail in visible light by the Keck II telescope in Hawaii. This optical survey used spectroscopy to map the locations of thousands of galaxies in three dimensions. With the GBT, instead of looking for hydrogen gas in these individual, distant galaxies — a daunting challenge beyond the technical capabilities of current instruments — the team used their intensity-mapping technique to accumulate the radio waves emitted by the hydrogen gas in large volumes of space including many galaxies.

“Since the early part of the 20th Century, astronomers have traced the expansion of the Universe by observing galaxies. Our new technique allows us to skip the galaxy-detection step and gather radio emissions from a thousand galaxies at a time, as well as all the dimly-glowing material between them,” said Jeffrey Peterson, of Carnegie Mellon University.

The astronomers also developed new techniques that removed both man-made radio interference and radio emission caused by more-nearby astronomical sources, leaving only the extremely faint radio waves coming from the very distant hydrogen gas. The result was a map of part of the “cosmic web” that correlated neatly with the structure shown by the earlier optical study. The team first proposed their intensity-mapping technique in 2008, and their GBT observations were the first test of the idea.

“These observations detected more hydrogen gas than all the previously-detected hydrogen in the Universe, and at distances ten times farther than any radio wave-emitting hydrogen seen before,” said Ue-Li Pen of the University of Toronto.

“This is a demonstration of an important technique that has great promise for future studies of the evolution of large-scale structure in the Universe,” said National Radio Astronomy Observatory Chief Scientist Chris Carilli, who was not part of the research team.

In addition to Chang, Peterson, and Pen, the research team included Kevin Bandura of Carnegie Mellon University. The scientists reported their work in the July 22 issue of the scientific journal Nature.

Posted on by Nancy Atkinson

Radio Observations Provide New Explanation for Hanny’s Voorwerp

The green "blob" is Hanny's Voorwerp. Credit: Dan Herbert, Peter Smith, Matt Jarvis, Galaxy Zoo Team, Isaac Newton Telescope

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Is Hanny’s Voorwerp the result of a “light echo” of a violent event that happened long ago or perhaps is this mystifying blob of glowing gas being fueled by an ongoing, and current phenomenon? A just-released paper about the Voorwerp offers a new explanation for this perplexing, seemingly one-of-a-kind object in the constellation of Leo Minor. If you haven’t heard the remarkable story, the object was discovered in 2007 by Dutch school teacher Hanny Van Arkel while she was classifying galaxies for the Galaxy Zoo online citizen science project. Until now, the working hypothesis for the explanation of this unusual object was that we might be seeing the “light echo” of a quasar outburst event that occurred millions of years ago. But new radio observations reveal that instead, a black hole in that same nearby galaxy might be producing a radio jet, shooting a thin beam directly at this cloud of gas, causing it to light up.

Hanny’s Voorwerp (Dutch for object) consists of dust and gas – but no stars – so astronomers know it is not a galaxy, even though it is galaxy-sized. Previously, astronomers studying the object thought the gas and dust were illuminated by a quasar outburst within the nearby galaxy IC 2497. While the outburst would have faded within the last 100,000 years, the light only reached the dust and gas in time for our telescopes to see the effect. But this explanation was slightly unsatisfactory in that such an event, where an entire galaxy would flare up suddenly and briefly, is unexplained.

The naturally weighted 18 cm MERLIN radio map of IC 2497 (black contours), showing both C1 & C2, embedded within a region of smooth extended emission, overlaid over the same map with the point sources subtracted. Credit: Rampadarath, et al.

But radio observations with the European Very Long Baseline Interferometry (VLBI) Network at 18 cm, and the Multi-Element Radio Linked Interferometer Network (MERLIN) at 18 cm and 6 cm show evidence of black hole, or active galactic nuclei (AGN) activity and a nuclear starburst in the central regions of IC 2497.

This event is hard to see from our vantage point on Earth because another cloud of dust and gas sits between us on Earth and IC 2497, preventing us from directly seeing the black hole.

“The new data shows that the nucleus continues to produce a radio jet, in about the direction of Hanny’s Voorwerp,” said Bill Keel from the University of Alabama, one of the astronomers who has been studying the object intently ever since its discovery, and was part of the new observations. “The core is still too weak in the radio to be able to conclude that it puts off enough UV and X-rays to light up the gas, however. There may well be interaction between outflowing material connected with the jet and the gas outside the galaxy, helping to shape the Voorwerp, but the spectra in the discovery paper already made it clear that the gas is ionized not by shocks from such an interaction, but by radiation. ”

Keel said, though, there is still remaining uncertainty — and different astronomers have varying estimates of this likelihood – of whether the radiation from the quasar core remains strong or whether it shoots in fits and starts.

“Some active galaxies put out a lot of energy in jets and outflows compared to radiation, and we are considering the possibility that this one has switched to such a “radio mode” in the recent past,” he said. “If so, the Voorwerp would be an ionization echo, or light echo, since the re-radiation from ionized gas is not instantaneous, as scattering is.”

The Voorwerp has captured enough attention and curiosity that astronomers have trained numerous telescopes on the object in an effort to sort out the mystery. But Keel said this approach is essential in eventually figuring this out.

“Each wavelength range gives us a different, and usually complementary, piece of the story,” he said. “The earlier radio data tell us something about where all that gas came from, and we got another connection from recent data putting an apparent companion spiral galaxy at the same distance as IC 2497. Even the early X-ray data showed us that there was an interesting puzzle as to why we didn’t see the core AGN. The GALEX UV spectrum is informing our interpretation of the Hubble UV image.”

Yes, Hubble recently looked at the Voorwerp in a couple of different wavelengths, (read our article about the Hubble observations here) and while Keel couldn’t comment directly about data from the iconic telescope, (everything is still being analyzed) he did say it holds some interesting surprises.

“One of the first things we started checking with Hubble data was whether we have a clear view in at least the infrared to the nucleus, starting from the location of the radio source,” he said. “Also, these results give us particular reason to look at the structural details of the gas in Hanny’s Voorwerp, for signs that it may be affected by an outflow from the nucleus. I can mention that there are some interesting surprises from the HST data, which is what we always hope for!”

Keel said he also has been observing at Kitt Peak, looking at other candidate “voorwerpjes” – similar “ionized clouds on a somewhat smaller scale around AGN, where the same lifetime-versus-obscuration issues apply but we can usually see the AGN responsible,” he said.

And look for some upcoming public outreach projects on the Voorwerp based on the Hubble data, as well, including one in Bloomington, Minnesota on July 1-4 at the CONvergence, where writers and scienctists will be writing a graphic novel based on the discovery of Hanny’s Voorwerp. Check out this website for more information.

Read the team’s paper: Hanny’s Voorwerp: Evidence Of AGN Activity And A Nuclear Starburst In The Central Regions Of IC 2497.

Posted on by Nancy Atkinson

Scientist Explains New LOFAR Image of Quasar 3C196

Radio images of the quasar 3C 196 at 4 - 10 m wavelength (30 - 80 MHz frequency). Left: Data from LOFAR stations in the Netherlands only. The resolution is not sufficient to identify any substructure. Right: Blow-up produced with data from the German stations included. The resolution of this image is about ten times better and allows for the first time to distinguish fine details in this wavelength range. The colours are chosen to resemble what the human eye would see if it were sensitive to radiation at a wavelength ten million times larger than visible light. Image: Olaf Wucknitz, Bonn University (Click to enlarge image).

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We received several questions about our article on the new high-resolution LOFAR (LOw Frequency Array) image of quasar 3C196, concerning what was actually visible in this new image. We contacted LOFAR scientist Olaf Wucknitz from the Argelander-Institute for Astronomy at Bonn University in Germany, and he has provided an extensive explanation.

“3C196 is a quasar, the core of which is sitting right in the middle of the radio component,” Wucknitz said. “The core itself is not seen in radio observations but only on optical images. A possible reason for not seeing the core or the jets is that the central engine may not be very active at the moment (or rather it was not very active when the radiation left the object about 7 billion years ago). Alternatively it is possible that the inner parts of this source radiate very inefficiently so that we just do not see them in the radio images.”

In any case, he said, there must have been considerable activity earlier, because extensions of the jets that form radio lobes and hot spots are able to be seen in the image.

“The main lobes seem to be the bright SW component and the more compact NE component. When compared to observations at higher frequencies, these have the flattest spectra, i.e. they dominate at higher frequencies,” Wucknitz continued. “Then there is the other pair of components, the fuzzier E and W components. They are much weaker at higher frequencies.”

“The standard explanation for this would be that the jets from the core are changing its orientation with time (e.g. due to precession caused by a second black hole near the core, but this is very speculative). In this scenario the more extended components are older. Because of their age, the electrons causing the radiation have lost so much energy that we now see more low-frequency (i.e. low energy) radiation. The more compact components would be younger and therefore produce more high-frequency radiation.”

Interestingly, the W and E components show very different “colors” between 30-80 MHz, he said, so there must be some difference in the physical conditions in these two regions.

“Another possible explanation is that the compact components are the main lobes. There the jets interact with the surrounding medium. The matter is deflected and causes an outflow which we see as the other components.”

So basically, Wucknitz said, with the study of the data now available, they cannot draw firm conclusions, and he and his team have not had the opportunity to write a paper on the new image. “At the moment we are concentrating on getting LOFAR to run routinely and try to resist the temptation to do too much science with the first images. I hope that we can provide a real scientific analysis of this and similar images later this year.”

However, he suggested a couple of earlier papers that discuss quasar 3C196.

“Rotationally symmetric structure in two extragalactic radio sources” by Lonsdale, C. J.; Morison, I. describes the model of rotating jets for several obects including 3C196.

And this paper, Kiloparsec scale structure in the hotspots of 3C 196 by Lonsdale, C. J. discuses how previous observations by the MERLIN array revealed the presence of complex structure in each of the two bright hot spots in the quasar.

Wucknitz said he looks forward to delving into this object deeper as more of the LOFAR stations come online. “Once we can calibrate our new data better and produce slightly nicer images, we can hopefully say more and decide for one of the models,” he said.

Thanks to Olaf Wucknitz for providing an explanation of this new LOFAR image. Still have questions? Post them in the comments below.

Posted on by Nancy Atkinson

First High-Res, Low Frequency Radio Image from LOFAR Array

Radio images of the quasar 3C 196 at 4 - 10 m wavelength (30 - 80 MHz frequency). Left: Data from LOFAR stations in the Netherlands only. The resolution is not sufficient to identify any substructure. Right: Blow-up produced with data from the German stations included. The resolution of this image is about ten times better and allows for the first time to distinguish fine details in this wavelength range. The colours are chosen to resemble what the human eye would see if it were sensitive to radiation at a wavelength ten million times larger than visible light. Image: Olaf Wucknitz, Bonn University (Click to enlarge image).

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Just eight of the eventual forty-four antenna stations for the LOw Frequency ARray (LOFAR) were combined to produce the first high-resolution image of a distant quasar at meter radio wavelengths. The first image shows fine details of the quasar 3C 196, a strong radio source several billion light years away, observed at wavelengths between 4 and 10 m. “We chose this object for the first tests, because we know its structure very well from observations at shorter wavelengths,” said Olaf Wucknitz from Bonn University. “The goal was not to find something new but to see the same or similar structures also at very long wavelengths to confirm that the new instrument really works. Without the German stations, we only saw a fuzzy blob, no sub-structure. Once we included the long baselines, all the details showed up.”

Five stations in the Netherlands were connected with three stations in Germany. To make detailed observations at such low frequencies, the telescopes have to be spaced far apart. When complete, the LOFAR array span across a large part of Europe.

Observations at wavelengths covered by LOFAR are not new. In fact, the pioneers of radio astronomy started their work in the same range. However, they were only able to produce very rough maps of the sky and to measure just the positions and intensities of objects.

“We are now returning to this long neglected wavelength range”, says Michael Garrett, general director of ASTRON, in The Netherlands, the institution that leads the international LOFAR project. “But this time we are able to see much fainter objects and, even more important, to image very fine details. This offers entirely new opportunities for astrophysical research.”

“The high resolution and sensitivity of LOFAR mean that we are really entering uncharted territory, and the analysis of the data was correspondingly intricate”, adds Olaf Wucknitz. “We had to develop completely new techniques. Nevertheless, producing the images went surprisingly smoothly in the end. The quality of the data is stunning.” The next step for Wucknitz is to use LOFAR to study so-called gravitational lenses, where the light from distant objects is distorted by large mass concentrations. High resolution is required to see the interesting structures of these objects. This research would be impossible without the international stations.

IS-DE1: Some of the 96 low-band dipole antennas, Effelsberg LOFAR station (foreground); high-band array (background) (Credit: James Anderson, MPIfR)

LOFAR will consist of at least 36 stations in the Netherlands and eight stations in Germany, France, the United Kingdom and Sweden. Currently 22 stations are operational and more are being set up. Each station consists of hundreds of dipole antennas that are connected electronically to form a huge radio telescope that will cover half of Europe. With the novel techniques introduced by LOFAR, it is no longer necessary to point the radio antennas at specific objects of interest. Instead it will be possible to observe several regions of the sky simultaneously.

The resolution of an array of radio telescopes depends directly on the separation between the telescopes. The larger these baselines are relative to the observed wavelength, the better the achieved resolution. Currently the German stations provide the first long baselines of the array and improve the resolution by a factor of ten over just using the Dutch stations. ASTRON officials say the imaging quality will improve significantly as more stations come online.

“We want to use LOFAR to search for signals from very early epochs of the Universe,, said Benedetta Ciardi from the Max-Planck-Institut für Astrophysik (MPA) in Garching. “Having a completely theoretical background myself, I never had thought that I would get excited over a radio image, but this result is really fascinating.”

Source: Max-Planck-Institut für Astrophysik

Posted on by Nancy Atkinson

Supernova or GRB? Radio Observations Allow Astronomers to Find Unusual Object

Core-collapse supernova explosion expelling nearly-spherical debris shell. CREDIT: Bill Saxton, NRAO/AUI/NSF

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For the first time, astronomers have found a supernova explosion with properties similar to a gamma-ray burst, but without seeing any gamma rays from it. Radio observations with the Very Large Array (VLA) showed material expelled from supernova explosion SN2009bb at speeds approaching the speed of light. The superfast speeds in these rare blasts, astronomers say, are caused by an “engine” in the center of the supernova explosion that resembles a scaled-down version of a quasar. But astronomers don’t think this blast is one-of-a-kind, and say that more radio observations will point the way toward locating many more examples of these mysterious explosions.

“We think that radio observations will soon be a more powerful tool for finding this kind of supernova in the nearby Universe than gamma-ray satellites,” said Alicia Soderberg, of the Harvard-Smithsonian Center for Astrophysics.

Usually supernova explosions blasts the star’s material outward in a roughly-spherical pattern at speeds that, while fast, are only about 3 percent of the speed of light. In the supernovae that produce gamma-ray bursts, some, but not all, of the ejected material is accelerated to nearly the speed of light.

Engine-driven

When the nuclear fusion reactions at the cores of very massive stars no longer can provide the energy needed to hold the core up against the weight of the rest of the star, the core collapses catastrophically into a superdense neutron star or black hole. The rest of the star’s material is blasted into space in a supernova explosion. For the past decade or so, astronomers have identified one particular type of such a “core-collapse supernova” as the cause of one kind of gamma-ray burst.

The superfast speeds in these rare blasts, astronomers say, are caused by an “engine” in the center of the supernova explosion that resembles a scaled-down version of a quasar. Material falling toward the core enters a swirling disk surrounding the new neutron star or black hole. This accretion disk produces jets of material boosted at tremendous speeds from the poles of the disk.

“This is the only way we know that a supernova explosion could accelerate material to such speeds,” Soderberg said.

Until now, no such “engine-driven” supernova had been found any way other than by detecting gamma rays emitted by it.

“Discovering such a supernova by observing its radio emission, rather than through gamma rays, is a breakthrough. With the new capabilities of the Expanded VLA coming soon, we believe we’ll find more in the future through radio observations than with gamma-ray satellites,” Soderberg said.

Why didn’t anyone see gamma rays from this explosion? “We know that the gamma-ray emission is beamed in such blasts, and this one may have been pointed away from Earth and thus not seen,” Soderberg said. In that case, finding such blasts through radio observations will allow scientists to discover a much larger percentage of them in the future.

“Another possibility,” Soderberg adds, “is that the gamma rays were ‘smothered’ as they tried to escape the star. This is perhaps the more exciting possibility since it implies that we can find and identify engine-driven supernovae that lack detectable gamma rays and thus go unseen by gamma-ray satellites.”

One important question the scientists hope to answer is just what causes the difference between the “ordinary” and the “engine-driven” core-collapse supernovae. “There must be some rare physical property that separates the stars that produce the ‘engine-driven’ blasts from their more-normal cousins,” Soderberg said. “We’d like to find out what that property is.”

One popular idea is that such stars have an unusually low concentration of elements heavier than hydrogen. However, Soderberg points out, that does not seem to be the case for this supernova.

This research will be published in January 28 issue of the journal Nature.

Source: NRAO

Posted on by Nancy Atkinson

Giant Magnetic Loop Stretches Between Two Stars

Superposed image of a partial radio loop on Algol's inner binary. The optical-radio registration is within 0.3 mas. Credit: University of Iowa

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Using a collection of radio telescopes, astronomers have found a giant magnetic loop stretched outward from one of the stars making up the famous binary star system Algol, located in the constellation Perseus. “This is the first time we’ve seen a feature like this in the magnetic field of any star other than the Sun,” said William Peterson, of the University of Iowa.

The double star system, 93 light-years from Earth, includes a star about 3 times more massive than the Sun and a less-massive companion, orbiting it at a distance of 5.8 million miles, only about six percent of the distance between Earth and the Sun. The newly-discovered magnetic loop emerges from the poles of the less-massive star and stretches outward in the direction of the primary star. As the secondary star orbits its companion, one side — the side with the magnetic loop — constantly faces the more-massive star, just as the same side of our Moon always faces the Earth.

The scientists detected the magnetic loop by making extremely detailed images of the system using an intercontinental set of radio telescopes, including the National Science Foundation’s Very Long Baseline Array, Very Large Array, and Robert C. Byrd Green Bank Telescope, along with the Effelsberg radio telescope in Germany. These radio telescopes were used as a single observing system that offered both great detail, or resolving power, and high sensitivity to detect very faint radio waves. When working together, these telescopes are known as the High Sensitivity Array.

Algol is visible to the naked eye and well-known to amateur astronomers. As seen from Earth, the two stars regularly pass in front of each other, causing a notable change in brightness. The pair completes a cycle of such eclipses in less than three days, making it a popular object for amateur observers. The variability in brightness was discovered by an Italian astronomer in 1667, and the eclipsing-binary explanation was confirmed in 1889.

The newly-discovered magnetic loop helps explain phenomena seen in earlier observations of the Algol system at X-ray and radio wavelengths, the scientists said. In addition, they now believe there may be similar magnetic features in other double-star systems.

Source: EurekAlert

Posted on by Nancy Atkinson

Time-Lapse Movie Shows Massive Stars Form Similarly to Smaller Stars

It has been difficult for astronomers to see how massive stars form, since these stars are rare, form quickly and tend to be enshrouded in dense, dusty material which obscures them from view. But astronomers using the Very Long Baseline Array (VLBA) radio telescope were able to take images of the wavelengths of light emitted by a massive young star located 1,350 light years away in the Orion constellation. The created a ‘movie’ from the data, which they say shows the first evidence that young massive stars form from an accretion disk, just as smaller stars form.

“It is the first really ironclad confirmation that massive young stars are surrounded by orbiting accretion disks, and the first strong suggestion that these disks launch magnetically driven winds,” said Mark Krumholz, from the University of California at Santa Cruz.

The astronomers, led by Lynn D. Matthews from the Haystack Observatory at MIT, were able to see a disk of gas swirling close to the young massive star, known as Source I (said like “Source Eye”) in the high-resolution time-lapse movie they created.

By assembling 19 individual images of Source I taken by the VLBA at monthly intervals between March 2001 and December 2002, the high-resolution movie reveals thousands of masers, radio emitting gas clouds that can be thought of as naturally occurring lasers, located close to the massive star. According to Matthews, only three massive stars in the entire galaxy are known to have silicon monoxide masers. Because the silicon monoxide masers emit beams of intense radiation that can pierce the dusty material surrounding Source I, the scientists could probe the material close to the star and measure the motions of individual gas clumps.

Click here to see the time-lapse movie.

For almost 20 years, astronomers have known that low-mass stars form as a result of disk-mediated accretion, or from material formed from a structure rotating around a central body and driven by magnetic winds. But it had been impossible to confirm whether this was true for massive stars, which are eight to 100 times larger than low-mass stars. Without any hard data, theorists proposed many models for how massive stars might form, such as via collisions of smaller stars.

“This work should rule out many of them,” Krumholz said.

Because massive stars are believed to be responsible for creating most of the chemical elements in the universe that are critical for the formation of Earth-like planets and life, understanding how they form may help unravel mysteries about the origins of life.

The VLBA consists of a network of 10 radio telescope dishes located across North America, and can be thought of as a virtual telescope 5,000 miles in diameter. Used as a zoom lens to penetrate the dusty cloud surrounding the massive star, the VLBA captured images up to 1,000 times sharper than those previously obtained by other telescopes, including NASA’s Hubble Space Telescope.

The team’s paper was published in the Jan. 1 issue of the Astrophysical Journal.

Lead image caption: Artist’s conception of the rotating disk of hot, ionized gas surrounding Orion Source I, blocking the star from our view. A cool wind of gas is driven from the upper and lower surfaces of the disk and is sculpted into an hourglass shape by tangled magnetic field lines. Image: Bill Saxton, National Radio Astronomy Observatory/Associated Universities, Incorporated/National Science Foundation

Source: MIT

Posted on by Nicholos Wethington

ALMA Telescope Links Third Antenna

Well, they’re 1/22 of the way there: the Atacama Large Millimeter/submillimeter Array (ALMA), planned to be one of the largest ground-based observatories in the world, successfully linked 3 of its 66 antennas together. This is the next step in working out all of the bugs associated with linking together the whole array, which should happen sometime in 2012.

ALMA is a “microwave” telescope array that will be the largest such ground-based observatory in the world once it is completely online. Telescopes like ALMA are called interferometers because they use the principle of very-long baseline interferometry – by linking separate telescopes together, a larger telescope of the effective resolution of the distance between the separate elements is achieved.

We reported on the first image taken by two of the antennas back in November. Information from a pair of the antennas was gathered to test the electronic functioning of the system, but errors from the system itself and those that creep in because of the atmosphere were weeded out by this latest test that included a third antenna. This test is called a “closure phase”, essentially the self-calibration of the antennas in terms of reconciling the information they are taking in with the signals present from noise.

Fred Lo, director of the National Radio Astronomy Observatory (NRAO) – which is the contributing organization of North America to the ALMA array – said of the test in a press release,”This successful test shows that we are well on the way to providing the clear, sharp ALMA images that will open a whole new window for observing the Universe. We look forward to imaging stars and planets as well as galaxies in their formation processes.”

ALMA can gather information in the electromagnetic spectrum at a wavelength that is less than 1 millimeter. Because the planned array is so large, it will eventually be able to resolve unprecedented images of some of the first galaxies to form after the Big Bang, and will also be able to capture the formation of planets around stars, as well as information on the late stages in the life of stars.

ALMA is located in the Atacama desert in Chile at about 5,000 meters (16,500 feet) above sea level. This high and dry location allows the telescope to receive more of the light in the submillimeter; water vapor in the atmosphere of the Earth absorbs light in this part of the spectrum.

Source: NRAO press release

Posted on by Nancy Atkinson

Exploring to the Beat of Pulsars

PULSE@Parkes project. Credit: Andrew Crosling

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An innovative project that provides high school students in Australia the opportunity to work with the famous Parkes radio telescope will soon make the data available to schools around the world. The PULSE@Parkes project allows for hands-on remote observing of pulsars producing real-time data, which then becomes part of a growing database used by professional astronomers. “Students can help monitor pulsars and identify unusual ones or detect sudden glitches in their rotation,” said Rob Hollow from the Australia Telescope National Facility, and coordinator for the PULSE@Parkes project. “They can also help determine the distance to existing pulsars.”

Initially, the project was only available to schools in Australia, but PULSE@Parkes hopes to expand globally, allowing students to collaborate on monitoring pulsar data. The first international session will be held on Dec. 7, 2009 at Cardiff University in the UK.

“We had the challenge to develop and implement simulation radio astronomy activities for high school students, providing the opportunity for them to actually use a radio telescope facility and engage with professional scientists,” said Hollow, speaking at the .Astronomy (dot Astronomy) conference this week in Leiden, The Netherlands. “We also wanted to have students doing science that is appropriate for them and useful for professional astronomers.”

Students in Sydney controlling the Parkes radio telescope. Credit: R. Hollow, CSIRO
Students in Sydney controlling the Parkes radio telescope. Credit: R. Hollow, CSIRO

Hollow said that even though radio astronomy data consists of squiggly lines, students are still engaged by the results, even without the pretty pictures produced by other astronomical instruments. “It works surprisingly well, and the visuals haven’t been as big an issue and we thought,” Hollow said. “But in looking at pulsars, the students do get the pulse profiles and they get immediate feedback.”

Plus, when the dish actually moves in response to the students’ inputs, they really become engaged. “There’s a real ‘wow’ factor in being able to control the telescope,” Hollow said. “The students pick it up quickly, and they really like that they are contributing to science.”

Recently, the first science paper was published using results obtained by students.

The program is done remotely, and students view webcams of the telescope and control room. They control the telescope directly via the internet, monitor the data in real time, and use Skype to communicate with astronomers at Parkes.

So far, Hollow said, they have done 25 sessions, with 28 schools, working with about 450 students. “This project is not just for gift and talented students,” he said, “and any school can apply.”

The Parkes Radio Telescope. Credit: R. Hollow, CSIRO
The Parkes Radio Antenna. Credit: R. Hollow, CSIRO

Parkes is a 64 m diameter radio antenna that was built in 1961. Hollow said the dish has received regular updates and is still on the cutting edge of science. Most famously, Parkes was to receive video from the Apollo mission to the Moon.

Hollow said he sees PULSE@Parkes as just the beginning of working with students. The Australian Square Kilometre Array Pathfinder (ASKAP) will be coming online in just a couple of years, with thirty-six 12-meter dishes. “This will provide for very fast surveys that will increase the area of coverage and increase the capability for sensitivity,” Hollow said. “From ASKAP, we’ll be getting massive data sets, which will provide more opportunity for student and public involvement.

For more information, including an audio of what a pulsar “sounds” like, as well as info for schools and teachers, requirements, and how to apply visit the PULSE@Parkes website