James Di Francesco is an astrophysicist at the Herzberg Astronomy and Astrophysics Research Centre in Victoria, BC, Canada. He was my research advisor for the three years that I was a postdoctoral researcher. He writes a daily newsletter about an object or topic in astronomy. I will be re-posting some of his newsletter content here.
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As we get closer to Hallowe'en, ever spookier astronomy images are being released. For example, a recent Astronomy Picture of the Day is a haunting image of the "Ghost of Cassiopeia" and its surrounding nebulosity. The “Ghost of Cassiopeia” is also known more simply as the Ghost Nebula and sometimes just as IC 63. It’s the rightmost bright white/blue object surrounded by red in the middle-left of the image. To the left is another “ghost,” a similar nebula known as IC 59. The two ghosts to the left are located about 550 lightyears form the Sun. They both point back to a bright blue star known as gamma Cassiopeiae, or “Navi,” which is the middle star of the “W” in the constellation Cassiopeia that can be easily seen across the North Star from the Big Dipper.
The Ghost Nebula (IC 63) and its surrounding nebulosity. Credit: Louis Leroux-Géré, Thibault Rouillée, Vincent Martin, Cédric de Decker (Starfront Observatories)
(Fun sidebar: Navi’s official name is actually “Tiansi,” a Chinese name for “Heavenly Quadriga,” and was considered to represent one of the four horses pulling the chariot of legendary warrior Wangliang. The star got its unofficial name Navi, however, during NASA’s Apollo 9 mission because it was used as a handy navigational reference point. Also, Navi is “Ivan” backwards, making it an honour to Apollo 1 astronaut Virgil Ivan “Gus” Grissom, who tragically died during a pre-launch test earlier in the program. (Happily, the star is not named for the irritating fairy from The Ocarina of Time video game, or the blue humanoids from the Avatar movies.)
The dramatic colours shown in the image have two sources. First, the extended red colour comes from hydrogen gas near the bright stars in the region that has been illuminated (and ionized) by these stars’ ultraviolet light. Second, the extended blue colour comes from nearby dust reflecting the light from the stars. (The thicker blue smudges on each side of Navi may be due to dust built up as this star barrels through this extended gas cloud.) The thin blue tendrils seen throughout the image but prominently in the upper right are light coming from oxygen atoms mixed in with gas. Indeed, they may be shells of gas previously cast off by the central star they curl around, whose ultraviolet light is also illuminating (and ionizing) them. These particular tendrils were only discovered in this very deep image, which took about 100 hours to make by the astrophotographer team. APOD considers these tendrils to be “new ghosts” in this increasingly eerie location of space.
One last nugget of info about this image is that it was taken from Starfront Observatory, located near Rockwood, Texas. I hadn’t heard of this place before but I have to say it is quite impressive, consisting of over 900 (!) telescopes across 14 large buildings with retractable roofs. The site seems to serve as a berth for hosting astrophotographers’ private equipment, giving their users remote access to a dark sky location (for a fee). What an interesting idea!