Incredible photos from the Hubble Space Telescope show once-invisible filaments in deep space appear as ghostly green clouds. What happened? Researchers believe they were lit up briefly by a blast of radiation from a quasar.

Quasars are believed to be galactic cores located in distant galaxies powered by a supermassive black hole. As cosmic material (dust and gas) falls towards the black hole, it heats up to incredibly high temperatures. A quasar can then form, which shoots jets high-energy radiation into space.

Researchers believe it’s these blasts of high-energy radiation that lit up the green objects seen in the image above.

“Oxygen, helium, nitrogen, sulphur and neon in the filaments absorb light from the quasar and slowly re-emit it over many thousands of years. Their unmistakable emerald hue is caused by ionised oxygen, which glows green,” the ESA said in a statement.

The green, cloudy structures above are located a long ways away from the center of their host galaxies. So far away, that it would have taken light from the quasar tens of thousands of years to reach these clouds and light them up.

These structures are also massive. They stretch for tens of thousands of light-years. But, what are they?

The structures are long tails of gas created from the collision and merger of galaxies. Now? They are just hanging out orbiting their new host galaxies.

green gas clouds orbiting galaxy

Merging galaxies are violent events. “Galactic mergers do not just alter the forms of the previously serene galaxies involved; they also trigger extreme cosmic phenomena. Such a merger could also have caused the birth of a quasar, by pouring material into the galaxies’ supermassive black holes,” according to the ESA.

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Hanny van Arkel, a Dutch schoolteacher, was the first to discover the ghostly green objects. She spotted them in the online Galaxy Zoo project, a project that turns to the public for help to classify more than a million galaxies catalogued in the Sloan Digital Sky Survey. The first object is even named after her, dubbed Hanny’s Voorwerp (that’s Dutch for Hanny’s object).

A group of volunteers poured over 16,000 images to look for objects similar to the one Hanny Van Arkel found. A team of researchers analyzed potential candidates and found 20 galaxies with gas ionized by quasars.

The researchers documented their findings in a paper published in the Astronomical Journal.

Several of the researchers who helped with the paper discussed their findings in a Google Hangout. Check it out below.

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