Hubble Space Telescope: Ghostly Images of Quasars Past Captured by NASA/ESA Telescope

The wisps in the images were, at one point, briefly lit up by the quick blast of radiation from a quasar. (A quasar is formed when galactic material falls inwards towards the central black hole and gets increasingly hot. An extremely bright quasar emits powerful jets of energy.)

In these images, a quasar beam caused photoionization, in which oxygen, helium, nitrogen, sulphur and neon in the filaments absorb light from the quasar and slowly re-emit it over many thousands of years. The emerald hue is caused by ionized oxygen, according to the press release.

The quasars are long gone, but the green lights are a ghostly reminder until they too fade.

These celestial objects were found in a spin-off of the galaxy Zoo project, in which about 200 volunteers examined over 16,000 galaxy images in the SDSS. A team of researchers analyzed these and found a total of twenty galaxies that had gas ionized by quasars.

Reference:
"HST Imaging of Fading AGN Candidates I: Host-Galaxy Properties and Origin of the Extended Gas," William C. Keel et al., to appear in the Astronomical Journal [https://aj.aas.org, preprint: https://arxiv.org/abs/1408.5159].

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Black Hole, Ghosts, Mysterious, Nasa, National Aeronautics and Space Administration, ESA, European Space Agency, Zoo, Hubble, Hubble space telescope, NASA's Hubble Space Telescope, NASA/ESA Hubble Space Telescope, Hubble 25, Aas, American Astronomical Society