What is it like inside the Eagle nebula?
Hot or cold? Violent or calm? We take a look to see what conditions are like in this well-known nebula
The glow of the Eagle nebula is generated by the massive O- and B-type stars that populate its centre. Many times more massive than the Sun, these enormous stars burn hot and fast, ejecting ionising radiation and stellar wind into the heart of the nebula, sending shock waves through the cloud.
M16 is coming to the end of its star-forming lifetime and the remaining molecular cloud has been forced out to the edges, leaving the centre comparatively empty and bathed in ultraviolet radiation. However, There are still some pockets of star-forming activity left.
The largest stars are concentrated in the north- eastern corner of the nebula, where they have carved a semi-circular basin into the molecular cloud. The shock wave generated by these enormous stars is compressing the gas in the north bay, while sources of infrared light, that could be newly forming stars, are visible within the dust. There is also evidence of masers – water molecules in the vicinity of star- forming regions that absorb energy, emitting this out as microwaves.
To the south are the iconic Pillars of Creation, three distinctive lanes of dark dust and gas. These eerie stalagmites on the floor of the nebula have resisted erosion for far longer than the surrounding gases, forming structures several light years tall. They are bordered on either side by older, cooler stars, which would once have showered the columns with radiation, sculpting them inwards towards the heart of the nebula. As these stars aged, the columns stretched out, reaching towards the cluster of massive stars in the north bay.
Most of the material along the lengths of the pillars has been stripped away, but the caps still contain pockets of denser gas and dust. As the radiation from the ionising stars reaches the tops of the pillars, the gas is boiled away in a process known as photoevaporation, leaving visible streamers twisting out from the surface of the pillar caps.
Beneath the outer gas layers, regions of denser gas start to become visible. Known as EGGs, or evaporating gas globules, these dense pockets are larger than the Solar System and are thought to be the precursors to protostars. When buried within the pillars, the dense EGGs accumulate matter from the molecular cloud, gradually becoming massive enough to initiate nuclear fusion.
Young stars are visible within the pillars, concentrated around the locations of the EGGs, indicating recent star-formation activity, but whether new stars are still being formed in this area is unknown. It’s thought that star formation within the pillars has ceased and that as the gas and dust is blown away, the last new members of the cluster will be revealed.
On the other side of the nebula there are still areas displaying signs of active star formation. The stellar spire, often described as a fairy perched on a pedestal, projects inwards from the western edge of the nebula. It’s a 9.5-light-year stretch of molecular gas, containing dark lanes of fine carbon and silicone dust, with a band of new, hot stars near the cap. These have generated a shock wave that’s battering and compressing the molecular gas of the spire.
A dense region of gas resembling a Herbig-Haro object is visible within the cap of the spire. These objects are generated where the shock waves created by new stars collide with nearby dust and gas, lasting for just a few thousand years before dissipating to provide evidence that star formation might still be going on in the nebula.
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