Overview: Abell 39 (also PLN 47+42.1) is a very faint planetary nebula located in the direction of the constellation Hercules, the Roman mythological hero. This nebula is the 39th object listed in George Abell’s Catalog of Planetary Nebulae finalized relatively recently in 1966 after the nebula was discovered sometime before 1955. At about 4000 light-years from earth, it resembles a near perfectly shaped sphere and has the largest known diameter for this type of object at nearly 3 light-years. Placing one edge of the sherical nebula at our sun, the other side of the sphere would reach most of the way to the nearest star, Alpha Centauri!

Details: Abell 39 has a central star clearly visible here as a bluish point of light appearing slightly off center. Initially thought to be due to interaction with the interstaller gas and dust also visible here, it has since been proposed that the central star had ejected material asymmetrically, causing it to shift in one direction away from center. The mass of the central star and the nebula itself is each about 60% of the mass of our sun. While initial glance exhibits a nebula that seems symmetrical, closer inspection reveals that one side (lower right here) is 50% brighter than the other side, possibly related to the offset of the central star.

Using spectroscopy as well as comparing early images, the estimated growth of the expanding bubble is 30-40 kilometers per second. At that speed one could circumnavigate the earth in well under 20 minutes. Running the calculations in reverse estimate an age of the bubble to originate about 11,000 years ago.

Annotations. Additionally in the above images, 100s of other non-stellar objects are visible including faint and distant galaxies.  Three of these galaxies are actually visible within or on the very edge of Abell 39. These are merely optical coincidences, as the galaxies are thousands to 100s of thousands times further away that the planetary, hence we see their light made more blue as it passes through the bluish shell of material.

Below Images: In the first image below, the same image has been processed to remove all foreground stars as these stars are all within our own Galaxy. This is what the view would appear like if no stars existed along our line of sight. Removing the stars shows more clearly the gas and dust across the image in bands and knots, as is common throughout out galaxy. Using a mouse to hover over the image, brings all of the stars back. The second image below shows an enlarged and cropped version of Abell 39 and this time hovering a mouse makes the stars disappear.