Universe Today Astronomy Picture of the Week – NGC 6188: An Interstellar Portrait

Just one glimpse at this photo by Don Goldman tells a thousand words. Residing in the southern constellation of Ara, this incredible dust cloud is at home in Ara OB1 association, which covers a full degree of sky. Some 4000 light years away in the disk of our Galaxy, NGC 6188 sprawls across the edge of an expanding bubble of gas that could be as much as 300 light years wide.

Emission nebula NGC 6188’s fueling/illuminating source is open star cluster NGC 6193 buried deep inside its obscuring dust. Two nearby O-type giants, HD 150135 and HD 150136, cast their light upon dark space and reveal both the emission and the dust in fascinating detail. Roughly three million years old, NGC 6193 began forming and evolving unusually close binary stars. HD 150136 is one such star – an incredible binary whose O3 and O6V stars are so close they nearly touch each other. As their stellar winds combine, huge amounts of x-rays are created. The gentle red glow you see is hydrogen gas, heated by the bright stars and framed by molecular cloud which may have originated in the atmospheres of cooler stars and supernova ejecta.

The red glow visible throughout the photograph arises from hydrogen gas heated by the bright stars in Ara OB1. The dark dust that blocks much of NGC 6188’s light was likely formed in the outer atmospheres of cooler stars and in supernovae ejecta. All the while, ultra-violet radiation is quietly eroding the edges of the giant cloud. Just as the original bubble of neutral hydrogen gas spawned the creation of the Ara OB1 association, this erosion could be setting into motion new star formation.

For those who live in the southern hemisphere, you’ll find this glorious cloud named NGC 6188 located at RA 16:40.5 Dec -48: 47, but don’t expect to see a vision at the eyepiece. Even with large aperture telescopes, this nebula is whisper soft. NGC 6188 was discovered by John Herschel in 1836 who wrote: “consists of about a dozen stars 10..11 magnitude, and perhaps as many less, with stragglers, which fill field. In its preceding part is a fine double star … and yet more preceding is a very large, faint nebula, in which the preceding part of the cluster is involved.” Far more visible is open cluster NGC 6193. In dark southern skies, NGC 6193 is about a fingerwidth east/southeast of Epsilon Normae. At around magnitude 5, it’s an easy catch, but also a small one. For Caldwell fans, congratulations on capturing object 82!

But no photo such as this can go without words from its creator: Don Goldman: “My image was taken at our remote site at Macedon Ranges Observatory about 2 hours north of Melbourne, Australia. ~11 hours of Ha/SII/OIII (5nm, 5nm, 3nm respectively) and RGB taken with an Apogee Alta U16M at -20C, Apogee 7- position square CFW, Astrodon filters, and 12.5″ RC truss at a plate scale of 0.65″/pix. This area reminds me of “The Wall” in NGC 7000 Pelican region up here in the north. Hope you like the close-up. .”

Oh, we do, Don… We do!