Editorial - GCNEWS, Vol. 6, November 1997


A Newsletter for Galactic Center Research
This Volume was edited by Angela Cotera & Heino Falcke
email: gcnews@aoc.nrao.edu

Volume 6, November 1997 - EDITORIAL

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EDITORIAL: Galactic Center Claims Top Spot

Sgr A* beats out NGC 4258 as best black hole candidate

Heino Falcke & Angela Cotera

The following summary of the exciting Sgr A* results presented at IAU Symposium 184 was the front page story of the "Sidereal Times" (No. 8, Tue., 26 August 1997) - the daily newspaper accompanying the XXIIIrd General Assembly in Kyoto, Japan. We wrote the article when we realized the primary players in this exciting game had already left the conference, and were therefore unable to use this unique forum to emphasize to the importance of Galactic Center research within the larger astronomical community. Of course, we also used it to further advertise GCNEWS! Since most of our readers had already left when the article appeared (or were unable to get to Kyoto) we are reprinting it here (a copy of the original article can be found on our web page):

Sgr A* beats out NGC 4258 as best black hole candidate
("Sidereal Times, No. 8., Tue., 26 Aug. 1997)

Among the highlights from Symposium 184, "The Center of the Galaxy and Galaxies", were the presentations of stellar proper motions within the central parsec of the Galaxy, probing the gravitational potential of the Galactic Center down to a few milliparsecs. Andreas Eckart and Reinhard Genzel from the MPE in Garching, presented the results of several years of high resolution NIR speckle imaging of the central star cluster, measuring stellar velocities of several hundred km/s up to ~2000 km/s, peaking near Sgr A*. Together with radial velocity dispersions derived from NIR spectroscopy, the German team has determined that there must be a dark point mass of 2.61(+/-0.2) * 106 Mo at the position of Sgr A*. These results were confirmed by the UCLA group, Andrea Ghez, Mark Morris, and Eric Becklin, using the superior resolution of the Keck telescope. With 50 milli-arcsec resolution, over the past three years using slightly different techniques, they also find that a central dark mass of 2.7(+/-0.2) * 106 Mo is necessary. From these measurements, Eyal Maoz infers that any possible alternative to a black hole, such as a cluster of stellar remnants, gives a lifetime to core collapse which is unreasonably short. Since the estimated mass of Sgr A* is smaller than the present leading black hole candidate in NGC 4258, the inferred cluster lifetime would have to be even less than for NGC 4258, making Sgr A* now the best candidate for a supermassive black hole in the known universe.

The newly determined mass estimates suggest that with future (sub)mm-VLBI techniques, we may in principle even be able to obtain a direct picture of the black hole by imaging it against the radio background of Sgr A*. The existence of such a compact component at millimeter to submm-wavelengths was inferred by the results of a recent campaign to measure the spectrum of Sgr A* simultaneously on three continents, including (here in Japan) at the Nobeyama 45m telescope (Falcke, Matsuo, Zylka, et al.).

The quality of the data obtained at the Keck in only three years, highlights the possibilities for the advancement of science with the latest generation of large ground based telescopes, and may be one of the most significant results of the Keck telescope to date. The work of Eckart and Genzel illustrates, however, that with improved techniques, smaller telescopes can still lead the way when the determination of the scientist and the cooperation of operating institution (in this case ESO) function together. (A short reference to, and an explanation of GCNEWS followed)

JD12: Electronic Publishing

Besides the IAU symposium we were also concerned with a Joint Discussion on electronic publishing, where GCNEWS was presented as a poster. Peter Boyce presented the efforts of ApJ to become fully electronic. The determination he and his colleagues have shown in pushing ApJ and the AAS in this direction are quite impressive, leaving the Europeans in the audience wondering what was going to happen with A&A (especially given the fact that the only A&A representative present had never used electronic preprint servers or anything similar). During the discussion, Peter Boyce acknowledged the contributions electronic newsletters are now making to the distribution of scientific information - reviving, in an electronic form, aspects of the pre-journal era when results were sent by personal letters from scientist to scientist. On the other hand, the A&A representative argued that those newsletters could lead to an incestuous situation, where insiders only talk to insiders. However, since all the recently developed newsletters are publically available, usually over the Internet, are carried by a number of libraries, and primarily report on papers to be published in well established journals, we considered this to be unfounded criticism. Of course, this was only a minor point of the overall discussion which led to the conclusion that electronic publishing is a tidal wave, which cannot be stopped - either you are going to adapt or you will perish. At the moment, we have no intention to perish! We are in fact quite happy to report, that for the first time an ApJ Letter (Markoff et al.) features GCNEWS in its reference list since the necessary information was nowhere else to be found!

GC Workshop 1998?!

One way to keep GC research hot and boiling are the meetings and conferences, which are needed to keep pace with the rapid developments within the field. After a number of bigger conferences, we think it is now time for reflection and discussion in a smaller workshop setting, which we (in conjunction with others) are in the process of organizing for next year (September 7-1, 1998) in Tucson. Funding is still very preliminary at the moment, so we only ask you to keep an eye open for further developments (e.g. by looking at the announcements in this and the future issues of GCNEWS).

This issue

This issue of GCNEWS obviously has a focus on the recent IAU Symposium, with this editorial and a summary of other results of this conference in the following summary article. In fact, some of those results which will be published in regular papers are presented in our big abstract section already, such as the theory results by the Arizona theory group (Coker & Melia) which are also shown on our cover image. We hope you enjoy this issue as much as you have previous issues, and we thank you for the positive feedback we have received.
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