Issues of 2007

This page lists the home pages for this web site for the year 2007. These pages constitute volume 4 of The Astrophysics Spectator.

• Issue 4.20, December 19, 2007. This issue continues the discussion of the previous issue on open star clusters; specifically, a page is added that describes various methods for deriving the distance to an open cluster without measuring the annual parallaxes of stars within the cluster.
• Issue 4.19, December 5, 2007.  Open star clusters are discussed in this issue.  Gravitationally-bound groups of stars such as the Pleiades provide convenient collections of stars for studying stellar evolution.  The properties and uses of open star clusters are discussed on a page added this issue to the “Milky Way Galaxy” topical path.
• Issue 4.18, November 21, 2007.  Theories for the dark accretion disk orbiting the central Galactic black hole are describe in a page added with this issue of the web site.
• Issue 4.17, October 31, 2007.  The outer regions of the central Galactic black hole is expected to flow directly to the black hole.  A page is added in this issue that describes this process.
• Issue 4.16, October 3, 2007.  Why the central Galactic black hole should be capturing large amounts of gas from surrounding stars is the subject of this issue of the web site.  The new page added with this issue describes the light-driven winds of massive stars.  The surprise is that despite the availability of gas, the central black hole is not a bright object.
• Issue 4.15, September 19, 2007. Many galaxies emit x-rays from their cores. Is this emission from stars and binary systems at the cores of these galaxies, or is it from massive black holes. This issue contains a page describing the difficulty of determining the origin of x-rays emitted from the center of our own Galaxy.
• Issue 4.14, September 5, 2007. The central Galactic black hole Sgr A* is primarily a radio source. The black hole emits surprisingly few x-rays, which dashes hopes that it can be used as a proxy for the distant active galactic nuclei. These points are discussed in a new page added to the site in this issue.
• Issue 4.13, August 22, 2007. The flow of the local stars within the Galactic disk is discussed in a page added to the web site with this issue. Recent work suggests that the motion of the Sun and the surrounding stars is influenced by the Galaxy's central bar and spiral arms. A commentary on manned space flight is published in this issue.
• Issue 4.12, August 8, 2007. This issue continues the discussion of previous issues on the massive stars orbiting the central Galactic black hole. In this issue, two pages are added. The first page describes how star clusters can sink to the center of the Galaxy. The second page describes how interactions between three bodies can give a star a low-eccentricity orbit close to the black hole.
• Issue 4.11, July 25, 2007. This issue of the web site adds another page about the bright stars in close orbit around the central black hole Sgr A^* to the “Milky Way Galaxy” path. The subject of the new page is the difficulty of rapidly transporting a star born far from the central Galactic black hole to a close orbit around the black hole.
• Issue 4.10, July 11, 2007. Two pages about the bright stars orbiting Sgr A^* are added with this issue. The first page describes the characteristics of these stars and their orbits, and it discusses why the characteristics of these stars present astronomers with a difficult problem in understanding where the stars were born. The second page is a table of orbital parameters for several of these stars.
• Issue 4.09, June 13, 2007. This issue adds a prequel to last issue's pages. The new page describes the Sagittarius A complex, the collection of stars, gas, and massive black hole that sit at the center of the Milky Way Galaxy.
• Issue 4.08, May 30, 2007. Two new pages are added to the Milky Way Galaxy topical path. The first page describes how the orbiting of stars around the black hole at the center of the Galaxy gives astronomers a measure of the distance to the Galactic center. The second page presents a table of the Galaxy's physical characteristics.
• Issue 4.07, May 16, 2007. This week a page is added to the Milky Way that describes the extended structure of the Galactic center.
• Issue 4.06, April 18, 2007. The first page in a series of pages on the Milky Way Galaxy is added to the site with this issue.
• Issue 4.05, March 21, 2007. Radio pulsars provide the excuse this issue for adding a page about the structure of the Milky Way galaxy. Specifically, the page discusses the distribution of radio pulsars around the Galactic disk and its implications for the lifetime of a radio pulsar.
• Issue 4.04, February 21, 2007. With this issue, a page is added to the web site that describes the radio waves and x-rays emitted by a spin-powered pulsar.
• Issue 4.03, February 7, 2007. This issue of the web site adds a page describing the association of nebulae with radio pulsars and the connection of both to supernovae.
• Issue 4.02, January 24, 2007. A page that describes the characteristics and evolution of binary pulsars and millisecond pulsars and a page that describes tests of general relativity with binary pulsars are added to the web site with this issue.
• Issue 4.01, January 10, 2007. This issue of The Astrophysics Spectator starts the year with a page on radio pulsars, also known as spin-powered pulsars.