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CosmosUp | August 14, 2022

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Hubble Spots Green Remnants Of Colliding Galaxies Near Dead Quasars

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Hubble Spots Green Remnants Of Colliding Galaxies Near Dead Quasars

Quasars are known to be super-energetic and compact regions surrounding a supermassive black hole at the center of a galaxy. Quasars usually get their luminosity and electromagnetic energy from the nearby black holes that spew back tons of energy in various forms while they feed on the mass from their surroundings.

But quasars have continuously puzzled astronomers due to their extreme brightness that reach us despite being located so far from our planet. On April 2, astronomers using the Hubble Space Telescope have photographed eight unusual looped structures – ephemeral ‘ghosts’ of quasars that flickered to life and then faded.

The first of these mysterious structures was discovered by Dutch schoolteacher Hanny van Arkel in 2007. He found it while participating in Galaxy Zoo, an amateur research project where ordinary people classify galaxies online.

Intrigued, Bill Keel, an astronomer at the University of Alabama, Tuscaloosa, decided to investigate further. He enlisted 200 volunteers to look at 15,000 galaxies that were home to quasars. They found eight with the mysterious green objects. Each one was a different shape, with some looped and others braided or spiraled.

The green wisps are illuminated by blasts of ultraviolet radiation coming from quasars at the core each galaxy. Keel believes the strange objects are the remnants of colliding galaxies.

‘However, the quasars are not bright enough now to account for what we’re seeing; this is a record of something that happened in the past,’ said Keel.

The quasar beam caused the once invisible filaments in deep space to glow through a process called photoionization. Oxygen atoms in the filaments absorb light from the quasar and slowly re-emit it over many thousands of years. Other elements detected in the filaments are hydrogen, helium, nitrogen, sulfur, and neon.

“The heavy elements occur in modest amounts, adding to the case that the gas originated in the outskirts of the galaxies rather than being blasted out from the nucleus,” Keel said.


The green filaments are believed to be long tails of gas pulled apart like taffy under gravitational forces resulting from a merger of two galaxies.

Rather than being blasted out of the quasar’s black hole, these immense structures, tens of thousands of light-years long, are slowly orbiting their host galaxy long after the merger was completed.

“We see these twisting dust lanes connecting to the gas, and there’s a mathematical model for how that material wraps around in the galaxy,” Keel said.

“Potentially, you can say we’re seeing it 1.5 billion years after a smaller gas-rich galaxy fell into a bigger galaxy.”

Bottom line: The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington. Read more at:



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