Editorial - GCNEWS, Vol. 18, July 2004


A Newsletter for Galactic Center Research
This Volume was edited by Sera Markoff, Loránt Sjouwerman, Joseph Lazio, Cornelia Lang, Rainer Schödel & Robin Herrnstein
email: gcnews@aoc.nrao.edu

Volume 18, July 2004 - In the News

[Home] [New Abstracts] [Newsletter] [Newsflash] [Articles] [Conferences] [Subscribers] [Subscription] [Submission]

[Next page] [Previous page] [Cover page]

In the News - Joseph Lazio & Cornelia Lang

Welcome to the second GCNEWS of 2004. Since the last GCNEWS, we've seen a number of new results on the size and nature of Sgr A* itself and ongoing studies of the interstellar medium in this unique region. Many GC folks have also taken a pause to commemorate the (almost accidental!) discovery of Sgr A* which occurred only a little over 30 years ago.

In other news, we welcome Robin Hernnstein to our editorial staff. As always, please feel free to contact any of us with GC newsworthy items or future article ideas. We also remind our readers to please submit their abstracts to GCNEWS. As you know, GCNEWS promises rapid delivery of your results to fellow GC researchers. While astro-ph is a valuable resource, GCNEWS directly targets those readers with an acknowledged interest in GC science.

In this Volume

In this volume, we report on a conference devoted to Sgr A* and its environment, and also provide an update of GC research presented at the summer AAS meeting in Denver.

We are especially excited to have a comprehensive, invited review article by Sheperd Doeleman and Geoff Bower. In their article, they demonstrate how far we have come in understanding the structure of Sgr A* since its discovery. Their article describes the methods used to model and constrain the size of the radio source from radio interferometric data and also highlights future observational prospects - they point out that we are poised on the edge of being able to use such techniques to image the shadow of Sgr A*.

A number of GC abstracts have come in this spring and summer (and as mentioned before, we could always use more!) and are listed at the end of the issue.

Happy 30th Sgr A*! - Cornelia Lang

A small workshop commemorating the 30th anniversary of the discovery of Sgr A*, the radio source associated with the supermassive black hole at the center of our Galaxy, was held in Green Bank, West Virginia, on March 25 and 26. There were 60 participants from a variety of international and national institutes and many of the NRAO scientific staff. The program consisted of a day and a half of scientific talks, a banquet, and a ceremony and dedication of a plaque on the 45-foot telescope that commemorates the original discovery. A reception for all participants and Green Bank staff followed at the Green Bank Science Center.

The discoverers of Sgr A*, Bruce Balick (right) and Bob Brown (left) receive a commemorative poster from NRAO director Fred Lo (far left). In the background the commemorative plaque attached to the 45-foot telescope. (Photo by Bill Saxton)

The discovery of the compact radio source at the center of the Milky Way was made by Bruce Balick and Bob Brown in 1974 February. They had originally been searching for compact regions of star formation in the vicinity of the Galactic Center. The placement of the 45-foot telescope near Huntersville, West Virginia, as the 35 km outstation for the NRAO Green Bank radio link interferometer (consisting of three, 85-foot antennas at Green Bank), was crucial for resolving out the extended confusion from Sgr A West and providing spatial resolutions of 0.3'' (at 3.7 cm) and 0.7'' (at 11 cm) and detecting the very compact radio source, Sgr A*.

An opening review talk on massive objects at the centers of galaxies was given by Roger Blandford, followed by a series of historical talks given by the original observers, Bruce Balick and Bob Brown, and the Green Bank site director at that time, Dave Hogg. A number of fascinating letters from Balick to Brown were shown which provided additional insight into the details of the discovery (also summarized recently by Goss, Brown, & Lo 2003, Astron. Nachr., S1, 1). Roy Booth, K. Y. Lo, and Ron Ekers also presented accounts of early work on the size and structure of Sgr A* based on some of the first aperture synthesis studies at Jodrell Bank, Owens Valley Radio Observatory, and the VLA.

Following the historical talks on the discovery of Sgr A*, a series of talks on recent results were presented. Don Backer gave an overview of interstellar scattering properties toward Sgr A*, and Geoff Bower and Zhi-Qiang Shen reported on VLBA closure phase techniques used to constrain the size of this compact source. Results on the linear and circular polarization of Sgr A* were given by Geoff Bower. Andrea Ghez, Rainer Schödel, Jun Hui-Zhao and Fred Baganoff confirmed that variability of Sgr A* on a number of timescales has now been detected across the spectrum from radio to near-IR to X-rays. Progress reports by Ramesh Narayan, Sera Markoff, Eliot Quataert, and Fulvio Melia followed, describing the various models to explain the spectrum, polarization, and variability of Sgr A*. Perspectives on the current state and characteristics of the modeling were given by Heino Falcke. The stellar and interstellar environment surrounding Sgr A* was discussed in a series of talks on Friday morning. The scientific talks concluded at noon with a thoughtful review by Mark Morris.

Following the scientific program, a dedication ceremony was held at the 45-foot antenna, where NRAO director Fred Lo presented Bruce Balick and Bob Brown with commemorative framed posters (see picture). A plaque on the 45-foot antenna and an informational adjacent sign for visitors were unveiled. An informal scientific session was held on Friday evening to discuss prospects for future millimeter and sub-millimeter VLBI observations of Sgr A*. The next generation of telescopes will provide an excellent opportunity for imaging on the scale of the event horizon, allowing for detailed tests of accretion models and general relativity.

The scientific program, PDF and PPT versions of the talks, and photographs are available at http://www.aoc.nrao.edu/~gcnews/GCconfs/SgrAstar30/.

GC appearances at Denver AAS in June 2004 - Cornelia Lang

A number of GC results were presented at the summer American Astronomical Society meeting in Denver, Colorado (May 30-June 3). We describe briefly those papers with a GC component at the AAS meeting, with apologies to anybody whose work we might have missed. The AAS paper number is in parentheses at the end of each summary.

The enigmatic, magnetic ``non-thermal filaments'' (NTFs) in the GC made an appearance in a number of presentations and posters this summer:

The combination of Green Bank single dish data with Very Large Array interferometric data was a highlight of the poster by C. Law et al. (and also the previously mentioned 59.03 poster):

There were two press releases by NRAO on the combination of GBT and VLA datasets (59.02, 59.03). See http://www.nrao.edu/pr/2004/filaments/ and http://www.nrao.edu/pr/2004/GBTlobe/ for more details.

Several posters were focused on the interstellar medium in the GC region, on large and small scales:

Other GC highlights:

[Next page]

[Home] [New Abstracts] [Newsletter] [Newsflash] [Articles] [Conferences] [Subscribers] [Subscription] [Submission]


  • The GCNEWS Logo at the top of this page shows a 20cm radio map of the GC (Sgr A) made by Yusef-Zadeh & Morris.
  • The GCNEWS newsletters, newsflashes and web pages are based on scripts originally developed by Heino Falcke.
  • Internet access for GCNEWS is currently sponsored by the National Radio Astronomy Observatory in Socorro NM/USA.
    Page currently maintained by L. O. Sjouwerman. File last modified on Tuesday 27 July 2004 [09:13 MDT].

    [Home] [New Abstracts] [Newsletter] [Newsflash] [Articles] [Conferences] [Subscribers] [Subscription] [Submission]