Science, Engineering, and Technology Milestones From the National Radio Astronomy Observatory

1. ALMA Takes Close-up of Matter Spiraling Toward a Black Hole: Astronomers using the new Atacama Large Millimeter/submillimeter Array (ALMA) have taken the closest look ever at a stream of dense gas falling toward the supermassive black hole at the center of a nearby galaxy known as NGC 1097. This black hole is estimated to be about 120 million times more massive than our Sun. Located 45 million light-years from Earth, NGC 1097 is one of the closest examples of a Seyfert galaxy -- one with a classic spiral shape like the Milky Way, but which is actively feeding on material and emitting jets of high-energy particles. This type of galaxy is believed to be a nearby but smaller example of a quasar, a galaxy with a monstrous central black hole that is feeding voraciously on material and blasting out jets many thousands of even millions of light-years into space. By studying this galaxy with ALMA, astronomers hope to better understand the complex environment surrounding supermassive black holes and how matter behaves as it draws near these incredibly massive objects. Earlier studies with other telescopes tracked the inflow of gas in NGC 1097 to within approximately 650 light-years of its central black hole. Closer observations were thwarted by the incredibly bright emission of the increasingly hot gas and the intervening dust near the black hole. The new ALMA results traced the path of hydrogen cyanide (HCN) gas to within 130 light-years of the black hole and confirmed that the material is confined to a very thin disk, which funnels gas inward. Based on the ALMA results, the astronomers calculated that the amount of material falling in on the black hole every year is equivalent to about 20 percent the mass of our Sun. These new results help advance our understanding of the presence of active galactic nuclei across the Universe. The principal investigator of this work is Kotaro Kohno at the University of Tokyo. The work described here was led by team member and co-investigator Kambiz Fathi at Stockholm University and was published in the Astrophysical Journal Letters.

2. VLBA Makes Most Accurate Pulsar Distance Measurement: Scientists using NRAO's Very Long Baseline Array (VLBA) have set a new distance accuracy record, pegging a pulsar called PSR J2222-0137 at 871 light-years from Earth. They did this by observing the object over a two-year period to detect its parallax, the slight shift in apparent position against background objects when viewed from opposite ends of Earth's orbit around the Sun. With an uncertainty of less than 4 light-years, this distance measurement is 30 percent more accurate than that of the previous-best pulsar distance. By showing that PSR J2222-0137 is 15 percent closer than previous estimates, this impressive achievement can advance our understanding of the system. PSR J2222-0137 is orbiting an as-yet-unseen companion object, and with the distance now pinned down, proposed sensitive visible-light observations should determine the nature of the companion. If no source can be found, the companion must be a neutron star, while a white-dwarf companion will show up as a faint optical source. The VLBA observations also revealed the orientation of the system's orbit, despite the projected orbit being no larger than a dime observed at a tenth of the distance to the Moon. Finally, the researchers measured an effect called the Shapiro Delay, caused by the effect of the companion star's gravitation on the radio waves coming from the pulsar. This effect, predicted by General Relativity, has been measured in only a small number of pulsar systems. The accuracy of the new measurement promises to help in the quest to detect the elusive gravitational waves predicted by General Relativity. By monitoring an array of pulsars across the Milky Way galaxy, scientists hope to measure the distortions of space-time caused by the passage of gravitational waves. Knowing the distances to these pulsars extremely precisely can improve the sensitivity of the technique to individual sources of gravitational waves. The research, led by Adam Deller of the Netherlands Institute for Radio Astronomy, was published in the Astrophysical Journal. PSR J2222-0137 was discovered in 2007 with the Green Bank Telescope.

3. NRAO Engineer Earns Patent for New 'Reflectionless' Filter: A research engineer at the National Radio Astronomy Observatory's (NRAO) Central Development Laboratory (CDL) was awarded a U.S. patent (No. 8,392,495) for a new "reflectionless" filter. This filter is actually a novel circuit structure that prevents unwanted energy from swamping some of the sensitive electronics used in radio astronomy. Filters are essential parts of virtually all electronic systems, from cell phones and computers to radios and microwave ovens. They perform two important functions: (1) defining the frequencies at which electronics will operate; and, (2) preventing unwanted energy from spilling over into other electronic components. This is particularly important in radio astronomy because the receivers and other core components are extremely sensitive, which enables them to detect the incredibly faint signals that are emitted naturally by astronomical objects. Any stray energy or radiation in the systems would limit sensitivity and possibly obscure the signal astronomers are trying to detect. Typically, filters work by reflecting an unwanted signal back at the source. This can cause problems, however, for other components in the system by creating standing waves, which produce unwanted feedback and electronic noise. The new filter avoids this problem by simply absorbing the unwanted electronic signal. In so doing, the filter eliminates the build-up of a standing wave, which has the added benefit of lowering signal loss when compared with conventional designs.

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The VLBA, dedicated in 1993, uses ten, 25-meter-diameter dish antennas distributed from Hawaii to St. Croix in the Caribbean. It is operated from the NRAO's Domenici Science Operations Center in Socorro, NM. All ten antennas work together as a single telescope with the greatest resolving power available to astronomy. This unique capability has produced landmark contributions to numerous scientific fields, ranging from Earth tectonics, climate research, and spacecraft navigation, to cosmology."

The Robert C. Byrd Green Bank Telescopes (GBT) is the most technically advanced single-dish radio telescope in the world. Its 100-meter dish boasts more than two acres of area for collecting faint radio waves from the Universe.

ALMA, an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

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