NGC 7000 & IC 5070 — two O stars, a continent of dust, and the wrong map in the sky

It takes little imagination to see a map in this nebula: North America on the left with its Gulf coast and Central America, a pelican with beak and neck on the right. The finest twist is that almost none of these coastlines is a real edge. Dark dust lies in front of glowing gas and draws the continents as a silhouette. Space supplies the red background; LDN 935 plays the cartographer.

William Herschel discovered the extended nebulosity in 1786, but through the telescope he saw no continent yet. Only Max Wolf's long-exposure photographic plate of 1890 made the shape clear enough for him to call it the “America Nebula”. Photography did not invent the nebula, but it did invent the view of it we still use. A fitting bit of trivia: the modern name Bajamar Star means, roughly, low tide. On the sky map the star sits, of all places, off the supposed coast of Florida — near the “Bahamas”.

A nebula with several labels. NGC 7000 denotes the bright North America portion, IC 5070 the Pelican. Physically both belong to the extended H II region Sh2-117 / W80. The dark division is not an empty gap but the foreground complex LDN 935 of cold dust and molecular gas. At a modern Gaia-based distance of roughly 700 to 800 pc, the astrometrically solved field of 3.164 × 2.109° spans about 130 × 86 light-years. The panorama is therefore not a collection of small separate nebulae but a cross-section through a star-forming landscape.

For 115 years the wrong lamp was suspected. Deneb was the first prominent candidate but, as an A supergiant, is not hot enough. In 1952 HD 199579 moved to center stage: a bright O6.5 V star in the northern part of the field, energetic enough to ionize its surroundings. Only the directions of the bright rims did not fit it, and the spectrum of the nebula as a whole demanded an even earlier O class. George Herbig therefore concluded in 1958 that the true engine had to be hidden behind LDN 935.

In 2005 Comerón and Pasquali found 2MASS J20555125+4352246 there, today the Bajamar Star: an extremely hot, heavily reddened O system. More recent spectroscopy describes it as a binary with a very early O3.5 component. Dust dims its visible light by about nine magnitudes — several thousandfold. An inconspicuous point in the image nonetheless supplies the largest share of the ionizing photons for a complex more than a hundred light-years across. Gaia also shows that Bajamar and HD 199579 both belong to the young system and are moving relative to their birth groups. The correct short version is therefore: two real O stars in the field, but Bajamar as the main engine of W80.

The nebula's edges are a physics diagram. At the Cygnus Wall, ultraviolet radiation meets dense molecular gas. The thin boundary layer glows brightly in Hα, while denser clumps erode more slowly and remain standing as pillars, fingers and cometary globules. Ionization shadows form behind them. Their axes point away from the dominant light source, like cast shadows. It was precisely this geometry that gave a decisive hint that HD 199579 alone cannot explain the whole scene.

The dark cloud is by no means only a backdrop. Hundreds of young stars, jets and Herbig-Haro objects sit in its “Gulf of Mexico”. Molecular gas observations show cloud groups on the near and far sides of the W80 bubble; some are being pushed away by the expansion, others are moving toward it. The flat photograph shows only the projection of that, but the frayed edges and bright fronts are the visible skin of this three-dimensional interaction.

What the colors mean. Red is Hα, the cool blue O III — the two windows of the dual-band filter. Positions, shapes and relative brightnesses are reliable; an exact line ratio must not be read off the color balance.