Scorpius OB1
Young OB association with massive stars and active star formation.
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Scorpius OB1 is a large nebular region on the Sagittarius Arm in the constellation Scorpius, where extensive star formation has produced dozens of high-mass stars grouped into an OB association. Its core, the young open cluster NGC 6231, is visible to the naked eye as a hazy patch and is easily resolved with binoculars.
Quick Facts
- Distance
- approximately 1,600 parsecs (5,216 light-years)
- Age of massive stars
- 2.5 to 4.5 million years
- Core cluster
- NGC 6231
Facts from the source article.
Lore & Background
The Scorpius OB1 region lies near the outer edge of the Sagittarius Arm, on the side facing the Solar System in the Orion Arm. The central core is the bright cluster NGC 6231, whose stars ionize surrounding gases, notably the large ring-like cloud Gum 55, which extends up to 5°.
Along the line of sight, several minor nebular areas overlap, located 100–300 parsecs from the Sun and likely associated with the Lupus Cloud; these cause slight extinction in the region's stars. Distance estimates have varied from 600 parsecs (based on parallax measurements that yielded some negative values) to 1,900 and 2,100 parsecs, but the most commonly accepted distance is about 1,600 parsecs. The age of the central cluster is estimated at 2.5–4.5 million years for the most massive stars and 1–12 million years for lower-mass components.
Reader's Guide
Scorpius OB1 is significant as a nearby laboratory for studying massive star formation and the dynamics of OB associations. The region's star formation likely began at least ten million years ago, producing low- and intermediate-mass stars, and intensified into a starburst event 3–5 million years ago that generated the massive stars of the association. The Large Elephant Trunk, a protrusion of Gum 55 on the western edge, contains three small reflection nebulae and has been sculpted by stellar winds from NGC 6231, compressing gas and triggering a second wave of star formation.
Over half of the O-class stars in NGC 6231 are close binaries with periods under 10 days, and about a dozen are eclipsing binaries. One original component, the runaway star HD 153919, is a blue supergiant bound to the X-ray source 4U1700-37, forming a high-mass X-ray binary whose compact companion may be a neutron star or stellar black hole. A 2009 study using Chandra data identified over 1,600 X-ray sources, about 90% of which are associated with the region, revealing a substantial population of low- and intermediate-mass stars.
Frequently Asked Questions
What is Scorpius OB1?
Scorpius OB1 is a sprawling star-forming region along the Sagittarius Arm of the Milky Way, situated within the constellation Scorpius. It hosts a young OB association packed with dozens of massive stars whose intense ultraviolet radiation ionizes surrounding gas, producing the emission and dark nebulae visible in that patch of sky.
How far away is Scorpius OB1?
The association lies roughly 1,600 parsecs, or about 5,216 light-years, from Earth. That places it well beyond the nearest stellar neighborhoods but still comfortably within the galactic disk.
How old are the stars in Scorpius OB1?
The massive O-type stars in the core are only 2.5 to 4.5 million years old, while the lower- and intermediate-mass stars in the broader association span a wider range of 1 to 12 million years. This spread in ages indicates that star formation in the region has been ongoing over several million years rather than occurring in a single burst.
How can I observe Scorpius OB1 from Earth?
During summer months, scan the constellation Scorpius for a faint hazy patch centered on NGC 6231, which is visible to the unaided eye under dark skies. A pair of binoculars will readily resolve the core into its individual bright stars, while a small telescope reveals more of the surrounding nebular glow and embedded dark patches.
More in Emission, Dark and Reflection Nebulae
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Scorpius OB1 (CC BY-SA 4.0).
- Word definitions: the Codexery glossary, each quoted from its Wikipedia article.
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