NGC 7027

In Cygnus

From Jim Kaler's STARS; Return to Planetary Nebulae

NGC 7027 NGC 7027
"Exceedingly bright" (Curtis). NGC 7027 lies in the thick of the Milky Way in Cygnus, 5.5 degrees southeast of Deneb. With no popular name or following, it's not only among the most examined of planetary nebulae, but is without much doubt historically among the most enigmatic, mostly the result of a huge amount of local circum-nebular dust that grossly distorts the optical view and hides the central star, giving the appearance that this planetary has none at all (which could not possibly be the case). On the left is Curtis's century old composite drawing that gives a good sense of 7027's appearance through a modestly large telescope. On the right is the spectacular Hubble view, a composite of optical and infrared images, that (1) shows that the nebula has a common bi-polar structure (already known from radio images), (2) reveals the central star, and (3) dramatically shows the dark dust lanes that hide much of the nebula in the visible part of the spectrum.

Compare the two. In the old image on the left, north is directly to the top, while in the Hubble image, north is tilted from the top to the left by about 15 degrees. The visual structure on the left is then quite obviously the result of the nebula's light shining through the regions that are clear of the dark dust, which cuts across the center, hiding the star. The dust, both circum-nebular and interstellar, reduces the brightness of even the optical view by more than three magnitudes. In spite of the odd structure and dust, NGC 7027 is the standard object against which the measured brightnesses of other nebulae are compared.

The distance of 2900 light years (known with an accuracy of about 15 percent) is found by comparing the expansion of the radio image with an expansion velocity of around 18 kilometers per second (though one source suggests 2200 ly). With a maximum angular extent of 16 seconds of arc, the nebula has a physical span of just under a quarter of a light year. The temperature of the 16th magnitude (16.3) exciting star, 185,000 Kelvin, is one of the highest known. Still in a heating and shrinking phase at near constant luminosity, the star pumps out the energy of 5000 Suns, the vast majority of it in the energetic ultraviolet. Highly enriched in carbon from nuclear reactions in the precursor advanced giant star, as the nebula grows and dissipates, it will add another load of this and other newly- created elements into the interstellar medium for use by the new stars yet to come.

Left: Image and quote by H. D. Curtis from Publications of the Lick Observatory, Volume 13, Part III, 1918. Right: William B. Latter (SIRTF Science Center/Caltech) and NASA.