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.
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.
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
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.
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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
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.”
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 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
In the microwave in your kitchen, food gets cooked (or heated) by absorbing microwave radiation, which is electromagnetic radiation between the (far) infrared and the radio, in the electromagnetic spectrum. The microwave region is rather broad, and somewhat vague, because the overlap with the radio (at around 1 meter, or 300 MHz) is not clear-cut, nor is the overlap with the sub-millimeter (or terahertz) region (at around 1 mm, or 300 GHz).
In astronomy, by far the most well-known aspect of microwave radiation is the cosmic microwave background (CMB), which has a near-perfect blackbody spectrum, of 2.73 K; this peaks at around 1.9 mm (160 GHz – the peak differs when measured by wavelength, from when measured by frequency).
The workhorse detector, in microwave astronomy (and much of radio astronomy, in general), is the radiometer, whose operation is described in considerable detail on this NRAO (National Radio Astronomy Observatory) webpage. The particular kind of radiometer which Penzias and Wilson used in their discovery of the CMB (at 7.35 cm, well away from the CMB peak) was a Dicke radiometer, designed by Robert Dicke (to search for the CMB!). And it was six differential microwave radiometers aboard the Cosmic Background Explorer (COBE) which first detected the CMB anisotropy, firmly establishing the CMB as the highly redshifted surface of last scattering (when baryonic matter and photons decoupled).
The microwave region, especially the short (millimeter) wavelength end, is a rich region for astrophysics, allowing the study of galaxy formation and evolution, stellar and planetary system birth, the composition of solar system body atmospheres, in addition to the CMB. There are already several observatories – many consortia – active in these fields; for example CARMA (Combined Array for Research in Millimeter-wave Astronomy), and ALMA (Atacama Large Millimeter/submillimeter Array) … astronomers just LOVE acronyms! (and no, that is not an acronym).
A new kind of microwave astronomical observatory has recently begun making obserations, the Allen Telescope Array, which provides instantaneous frequency coverage from 500 MHz to 11 GHz (among many other firsts). In many ways this serves as a technology demonstrator for the much more ambitious Square Kilometre Array.
When Lucas Bolyard looked at the bottom plot, he noticed the thick, black blob left of the center. He saw that this signal was positioned on the graph where it indicated a non-zero "dispersion measure," or DM. Dispersion measure is used by astronomers as an indicator of cosmic distances. The non-zero DM value of this pulse is a clue that the signal came from space, not from Earth. The other blobs on the bottom of the graph are signals at a distance of zero-- that is from here on Earth. CREDIT: NRAO/AUI/NSF
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A high-school student from West Virginia has discovered a new astronomical object, a strange type of neutron star called a rotating radio transient. Lucas Bolyard, a sophomore at South Harrison High School in Clarksburg, WV, made the discovery while participating in a project in which students are trained to search through data from the Robert C. Byrd Green Bank Telescope (GBT). Bolyard made the discovery in March, after he already had studied more than 2,000 data plots from the GBT and found nothing.
The project is the Pulsar Search Collaboratory (PSC), which allows students to do real scientific research by looking at data from the GBT, the largest radio telescope in the US. Lucas Bolyard CREDIT: NRAO/AUI/NSF
“Lucas is one of the most enthusiastic students involved in the project,” said Duncan Lorimer, astronomer from West Virginia University. “He’s one of these youngsters that never gives up, he’s very persistent and he has all the attributes that a scientist should have.”
Rotating radio transients are thought to be similar to pulsars, superdense neutron stars that are the corpses of massive stars that exploded as supernovae. Pulsars are known for their lighthouse-like beams of radio waves that sweep through space as the neutron star rotates, creating a pulse as the beam sweeps by a radio telescope. While pulsars emit these radio waves continuously, rotating radio transients emit only sporadically, one burst at a time, with as much as several hours between bursts. Because of this, they are difficult to discover and observe, with the first one only discovered in 2006.
“This neutron star is rotating very rapidly, so you have something the size of city with the mass of the sun, spinning incredibly rapidly,” said Lorimer “which also has an incredibly large magnetic field which is how we detect it with radio telescopes.”
“These objects are very interesting, both by themselves and for what they tell us about neutron stars and supernovae,” said Maura McLaughlin, also from WVU. “We don’t know what makes them different from pulsars — why they turn on and off. If we answer that question, it’s likely to tell us something new about the environments of pulsars and how their radio waves are generated.”
“They also tell us there are more neutron stars than we knew about before, and that means there are more supernova explosions. In fact, we now almost have more neutron stars than can be accounted for by the supernovae we can detect,” she added. Robert C. Byrd Green Bank Telescope CREDIT: NRAO/AUI/NSF
“I was home on a weekend and had nothing to do, so I decided to look at some more plots from the GBT,” Bolyard said. “I saw a plot with a pulse, but there was a lot of radio interference, too. The pulse almost got dismissed as interference,” he added.
Nonetheless, he reported it, and it went on a list of candidates for McLaughlin and Lorimer to re-examine, scheduling new observations of the region of sky from which the pulse came. Disappointingly, the follow-up observations showed nothing, indicating that the object was not a normal pulsar. However, the astronomers explained to Bolyard that his pulse still might have come from a rotating radio transient.
Confirmation didn’t come until July. Bolyard was at the NRAO’s Green Bank Observatory with fellow PSC students. The night before, the group had been observing with the GBT in the wee hours, and all were very tired. Then Lorimer showed Bolyard a new plot of his pulse, reprocessed from raw data, indicating that it is real, not interference, and that Bolyard is likely the discoverer of one of only about 30 rotating radio transients known.
Suddenly, Bolyard said, he wasn’t tired anymore. “That news made me full of energy,” he exclaimed. “My friends were really excited because they think I’m going to be famous!”
As of a year ago, Bolyard said he wouldn’t have thought of becoming astronomer, but this has given him second thoughts. “Making this discovery has made me very excited to get into a scientific field,” he said. “It’s a lot of hard work, but it’s worth it.”
The PSC, led by NRAO Education Officer Sue Ann Heatherly and Project Director Rachel Rosen, includes training for teachers and student leaders, and provides parcels of data from the GBT to student teams. The project involves teachers and students in helping astronomers analyze data from 1500 hours of observing with the GBT. The 120 terabytes of data were produced by 70,000 individual pointings of the giant, 17-million-pound telescope. Some 300 hours of the observing data were reserved for analysis by student teams.
The student teams use analysis software to reveal evidence of pulsars. Each portion of the data is analyzed by multiple teams. In addition to learning to use the analysis software, the student teams also must learn to recognize man-made radio interference that contaminates the data. The project will continue through 2011.
“The students get to actually look through data that has never been looked through before,” Rosen said. From the training, she added, “the students get a wonderful grasp of what they’re looking at, and they understand the science behind the plots that they’re looking at.”
