Herschel Sees a Hole, Not a Cloud

This is the ghostly looking reflection nebula NGC 1999 near to the famous Orion Nebula 1,500 light years away. NGC 1999 shines from the light of a young star embedded within it, and has been known about for a while. The image is dominated by that bizzare looking extremely dark area of the nebula, a dark and dense dust cloud known as a bok globule 10 light years across, and so thick that it blocks all light from passing through…or is it?

Well no it isn’t, it’s…nothing! It’s a hole, a hole in the nebula and the ominous darkness of the cloud is actually the

blackness of space behind. Now that you look at the image from this new perspective, you’d probably say yes, of course it’s a hole. It now actually looks really like a hole knowing this new information, and not a dark black cloud.

But how do we know for certain that it actually is a cavity in the reflection nebula? Enter that nifty piece of space hardware called the Herschel Space Observatory, a incredibly valuable instument that can see the coldest things in the universe with it’s infrared detectors, the stuff of star formation. Astronomers using Herschel took a look at the “bok globule” in NGC 1999 to study it’s surroundings, and were bemused to find that the cloud didn’t show up to Herschel’s infrared instruments. It should have shown up in infrared as this is exactly the type of object that Herschel is designed to study. No matter how astronomers looked at the “cloud” it continued to show up as black.

Herschel’s view of the region, with the blue/green area showing the reflection nebula NGC 1999 surrounding the hole. Image credit Nasa

So this is actually a 10 light year cavity in the reflection nebula, but why is it there? Well something has blasted right through the cloud blowing the gas away creating this hole, and young stars are thought to be the culprits. Newly born stars are very energetic beasts and produce narrow jets of gas, and ultraviolet radiation that carve out cavities in their surrounding nebula from where they were born. Stellar winds, bipolar jets, and general turbulence have come together to blow this 10 light year wide hole, clean through the nebula.

We now see this ghostly object with fresh eyes.

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