NRAO Media Tip Sheet: May 2016

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have made the first high-resolution image of the cometary belt (a region analogous to our own Kuiper belt) around HR 8799, the only star where multiple planets have been imaged directly. The shape of this dusty disk, particularly its inner edge, is surprisingly inconsistent with the orbits of the planets, suggesting that either they changed position over time or there is at least one more planet in the system yet to be discovered. “These data really allow us to see the inner edge of this disk for the first time,” explains Mark Booth from Pontificia Universidad Católica de Chile and lead author of the study. “By studying the interactions between the planets and the disk, this new observation shows that either the planets that we see have had different orbits in the past or there is at least one more planet in the system that is too small to have been detected.” The disk, which fills a region 150 to 420 times the Sun-Earth distance, is produced by the ongoing collisions of cometary bodies in the outer reaches of this star system. ALMA was able to image the emission from millimeter-size debris in the disk; according to the researchers, the small size of these dust grains suggests that the planets in the system are larger than Jupiter. Previous observations with other telescopes at shorter wavelengths did not detect this discrepancy in the disk. It is not clear if this difference is due to the low resolution of the previous observations or because different wavelengths are sensitive to different grain sizes, which would be distributed slightly differently. HR 8799 is a young star approximately 1.5 times the mass of the Sun located 129 light-years from Earth in the direction of the constellation Pegasus. “This is the very first time that a multi-planet system with orbiting dust is imaged, allowing for direct comparison with the formation and dynamics of our own Solar System,” explains Antonio Hales, co-author of the study from the National Radio Astronomy Observatory in Charlottesville, Va. The astronomers are reporting their results in the Monthly Notices of the Royal Astronomical Society.

Astronomers using the National Science Foundation’s Very Long Baseline Array (VLBA) have found 15 new examples of a rare type of object that may yield valuable clues about how radio-emitting galaxies and their environments evolve in their early stages of development. The objects, called compact symmetric objects (CSOs), are small, young versions of the supermassive black hole-powered “engines” that propel fast-moving jets of material outward from radio galaxies. Following up on a large-scale VLBA survey done in 2006, the scientists made more-detailed observations of objects they identified as possible CSOs. Of 103 such candidates, they confirmed 24, 15 of which are newly identified as CSOs. Using McDonald Observatory’s Hobby-Eberly Telescope, they determined distances to some of the objects, which allowed them to measure the objects’ sizes. “This doubles the number of these objects known,” said Steven Tremblay, of Curtin University in Australia. Enlarging the sample of known CSOs, the astronomers said, can be a big help to understanding radio galaxies in general. With sizes as small as 5 light-years across, and ages from only 20 to 2,000 years, CSOs represent an important early stage in the development of the much larger and older radio-emitting galaxies. Even at this early stage, the scientists said the CSOs in their sample show a distinction between higher-powered and lower-powered objects that also typifies older radio galaxies. “Understanding these young objects is vital to understanding their larger cousins,” said Greg Taylor, of the University of New Mexico. The astronomers are reporting their results in the Monthly Notices of the Royal Astronomical Society.

Reference: “Compact Symmetric Objects and Supermassive Binary Black Holes in the VLBA Imaging and Polarimetry Survey,” Tremblay et al.; Monthly Notices of the Royal Astronomical Society, May 2016. Preprint: http://arxiv.org/abs/1603.03094

Galen Watts, an engineer at the National Radio Astronomy Observatory’s Green Bank Microwave Electronics Group, received a patent (U.S. Patent Number: 9,343,815) for a surface treatment application for radiometers that aids in their self-calibration. Radiometers are devices that measure the actual energy of microwaves and other forms of electromagnetic radiation. Radio astronomers and other researchers use microwave radiometry to discover the molecular and atomic composition as well as the temperature of many objects on Earth and even the most distant celestial objects. They do this by examining the content of these objects’ naturally emitted microwave signals. To make accurate readings, however, a radiometer has to be properly calibrated. The new surface treatment application, developed by Watts, aids in radiometer self-calibration by reflecting an image of the feed horn back onto itself in a manner that doesn’t set up standing waves. Similar applications could also be useful for reducing antenna side-lobes (extraneous readings in radio astronomy), reducing radar cross-sections of objects, and eliminating resonances from stray reflections in quasi-optical component assemblies.

NRAO engineers Mathew A. Morgan and Tod A. Boyd have been awarded jointly the 2015 IEEE Antenna and Propagation Society Harold A. Wheeler Applications Prize Paper Award, which is presented to the authors of the best applications paper published in the IEEE Transactions on Antennas and Propagation during the previous year. Their paper, “A 10-100 GHz Double-Ridged Horn Antenna and Coax Launcher,” was published in August 2015 and reports on the development of a novel radio antenna. It is described as an ultra-wideband, double-ridged horn antenna with a bandwidth that covers a ten-fold range in frequencies. This is believed to be the first such decade-bandwidth horn in the millimeter-wave frequency range, covering — in this case — 10-100 GHz. Such horns can be used for test and measurement applications, including material characterization. It was originally designed as a scale model for an even higher-frequency horn covering 100 GHz – 1 THz. For this award, they will each receive a certificate and share in the $1,000 honorarium. The award will be presented at the IEEE APS/URSI Symposium Awards Ceremony, June 29, 2016, in Fajardo, Puerto Rico.

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

ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of South Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ.

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Contacts:

Charles Blue, Public Information Officer
(434) 296-0314; cblue@nrao.edu

Dave Finley, Public Information Officer
(575) 835-7302; dfinley@nrao.edu