Special stars http://washedoutastronomy.com/taxonomy/term/39/all en Hunting the Great White Dwarf http://washedoutastronomy.com/content/hunting-great-white-dwarf <!-- google_ad_section_start --><p>In the early 1900s astronomers were stunned to discover that some stars had masses comparable to the Sun's but packaged into earth-sized volumes. The first such stars discovered were spectral type A (white) and thus became known as <em>White Dwarfs.</em> The most famous white dwarf is Sirius B, the companion to Sirius. Most white dwarfs don&rsquo;t make good targets for washed-out astronomers because they are faint, inconspicuous stars or are hard to see companions to bright stars such as Sirius. But there is one white dwarf that is easy: 40 Eridani B.</p> <p><img width="166" hspace="4" height="94" align="left" title="40 Eridani A, B, and C by David Darling" alt="40 Eridani A, B, &amp; C by David Darling" src="/sites/washedoutastronomy.com/files/u3/40_Eridani_ABC.jpg" />40 Eridani (also known as &omicron;<sup>2</sup> Eridani or Keid) is a relatively bright 4<sup>th</sup> magnitude star. Even in urban areas, it is easy to find by star-hopping from Rigel going via &beta; Eri, &mu; Eri, and &nu; Eri. I recently did it from my light polluted front yard using a 50mm finder. Even looking directly over my neighbor&rsquo;s very bright holiday lights it was an easy hop. 40 Eridani is a triple star system. The primary has magnitude 4.4. Component B&mdash;the white dwarf&mdash;has magnitude 9.5 and is widely separated from A (83&rdquo;, PA 105&deg;) making it easy to see in even small telescopes.<em> (</em><a href="http://www.daviddarling.info/encyclopedia/A/40_Eridani.html"><em>Image courtesy of David Darling</em></a><em>)</em></p> <p>As a special prize, the third component C is a red dwarf flare star of magnitude 11.2. The B-C separation is much tighter at about 8&rdquo; but it isn&rsquo;t hard to split except for the faintness of the C component. You&rsquo;ll probably need at least a 4 inch (100mm) aperature to see C in washed-out skies, but it&rsquo;s rather easy with 6 inches (150mm) or more. In my 10 inch (250mm) Dob, it looks pretty much like the photo above.</p> <p>So don&rsquo;t miss the chance to &ldquo;bag&rdquo; a white dwarf. If you want to learn more about white dwarfs, read the excellent <a title="White Dwarfs at Wikipedia" href="http://en.wikipedia.org/wiki/White_dwarf">Wikipedia article</a>. Now 40 Eridani is interesting for several other reasons, including a connection to <em>Star Trek</em>....</p> <!-- google_ad_section_end --><p><a href="http://washedoutastronomy.com/content/hunting-great-white-dwarf" target="_blank">read more</a></p> http://washedoutastronomy.com/content/hunting-great-white-dwarf#comments Double stars Special stars Wed, 30 Dec 2009 17:03:54 +0000 Washed-out Astronomer 24 at http://washedoutastronomy.com Black Hole Hunting http://washedoutastronomy.com/content/black-hole-hunting <!-- google_ad_section_start --><p>Cygnus X-1 is almost certainly a black hole. It was discovered in 1964 as a strong X-ray source, and has ever since been the object of intense study. Cygnus X-1 turns out to be too compact to be any known kind of object besides a black hole. It has a mass of about 8.7 solar masses (which exceeds the theoretical maximum mass of a neutron star of about 3 solar masses), but based on how quickly its x-ray intensity fluctuates, Cygnus X-1 has to be less than about 60 km wide.&nbsp; Assuming Cygnus X-1 is a black hole, its event horizon is currently estimated to have a radius of about 26 km.</p> <p><img width="250" vspace="2" hspace="6" height="156" align="right" alt="" src="/sites/washedoutastronomy.com/files/u3/Cygnus_X-1_0.png" />Most interestingly, Cygnus X-1 orbits the blue supergiant star HDE&nbsp;226868 at a separation of about 0.2 AU.&nbsp;Cygnus X-1 has distorted HDE&nbsp;226868 into a tear-drop shape and is eating it away (although whether X-1 is actively stripping away 226868&rsquo;s outer layers or simply sucking up 226868&rsquo;s solar wind is unclear; the edge of material gravitationally bound to 226868 is close to the star&rsquo;s surface).&nbsp;For washed-out astronomers, the most interesting aspect is that HDE 226868 is a 9<sup>th</sup> magnitude star, making it an easy target for even small telescopes in urban environments.&nbsp;And while you can&rsquo;t actually see Cygnus X-1 itself, it&rsquo;s still pretty cool to be looking at a star that&rsquo;s being eaten alive by a black hole. <em>(ESA/Hubble illustration)</em></p> <p>&nbsp;Here&rsquo;s how to find HDE 226868 (and Cygnus X-1)&hellip;</p> <p>&nbsp;</p> <!-- google_ad_section_end --><p><a href="http://washedoutastronomy.com/content/black-hole-hunting" target="_blank">read more</a></p> http://washedoutastronomy.com/content/black-hole-hunting#comments Special stars Black holes Wed, 23 Sep 2009 02:04:41 +0000 Washed-out Astronomer 20 at http://washedoutastronomy.com