Scutum Supershell
Superbubble in the Scutum-Centaurus arm
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Scutum Supershell (also known as Scutum Superbubble) is a giant expanding bubble of hot gas and hydrogen in space. It is located ~11,000 ly away from the earth inside the Scutum-Centaurus Arm of the Milky Way. The superbubble is formed by exploding stars and strong cosmic winds. It was discovered by astronomer Matthew B. Callaway and his colleagues in 1999.[2]
| Nebula | |
|---|---|
| Superbubble | |
Location of the Scutum Supershell on a map | |
| Observation data: J2000 epoch | |
| Right ascension | 18h 42m 00s[1] |
| Declination | −18° 00′ 00″[1] |
| Distance | ~11,000 ly |
| Constellation | Scutum and Sagittarius |
| Physical characteristics | |
| Radius | ~472 ly |
| Designations | GS 018–04+44[1] |
Physical Structure
Scutum supershell is large and has a diameter of approximately 290 pc and extends about 400 pc from the galactic plane, which was derived from a kinematic distance of 3.3 kpc calculated from using D.P. Clemen's formula.[3] Because the superbubble is not cleary distinguishable, a radius of ~29 pc is estimated. Studies indicate that the infrared emission shows the presence of molecular hydrogen in the high column density regions.[4] The infrared emissions 100 μm and 60 μm are the main emission lines in infrared with surface brightness 6.23 MJy sr⁻¹ and 1.64 MJy sr⁻¹ respectively.[2]
Scutum supershell is mostly visible through H I, with the top of the shell appearing to be blown away, leaving a column of neutral hydrogen (H I) and superheated gas pouring directly into the galactic plane at l = 18° and lying between b = -9° and b = -12°, which created a high-latitude cloud that has a distance of ~630 pc from the galactic plane. The high-latitude cloud has an estimated X-ray luminosity of ~1³⁶ ergs s⁻¹. The high-latitude cloud was formed through supernova remnants, H II regions, and OB associations.[5] Two O-type Blue giant stars HD 175754 (O8II(n)((f))p)[6] and HD 175876 (O6.5III(n)(f))[6] most likely formed in this very cloud and were ejected from it, or formed recently at their current distance.[7][2] The Far Ultraviolet Spectroscopic Explorer (FUSE) detected highly ionized absorption lines like O IV, Si IV, and C IV near the blowout spot.[5]
H II regions Sh 2-45 and Sh 2-55 are H II regions that dominate the Hα emissions with the brightest Hα feature located in Sh 2-45 which lies at +20 km s⁻¹. The close proximity of Sh 2-45 causes some confusion regarding membership in the superbubble. Sh 2-55 is most likely in the superbubble, as it has an H I column density of 1.21 x 10²² cm⁻¹ using conversion ratio from Diplas & Savage.[8][9][2]
The galactic worms GW 14.9-1.6 and GW 16.9-3.8 are elongated vertical filamentary structures of neutral hydrogen (H I) that form the walls of the superbubble. GW 16.9-3.8 influences the rightmost edge of the bow-shock Hα emission and overlaps with [S II] line emission and both 60μm and 100μm infrared emission.[10] Simulations show that the outflow and bow-shock are likely formed by many supernovae events.[10] X-ray binary LS 5039 is also speculated as the contributing event from the supernova or hypernova and formation of a magnetar or black hole in the system.[10]