A dimming quasar identified by astronomers is being described by some investigators as a "black hole on a diet."

Quasars are highly-energetic objects which radiate vast quantities of radiation to the Universe, powered by massive black holes. As they evolve, these celestial objects were known to move between bright and dim ages.

Yale University researchers noticed, for the first time ever, a quasar with a "changing look," behaving like a light bulb attached to a dimmer switch. Comparison of images from a segment of sky called Stripe 82 taken a few years apart revealed a quasar that dimmed to just one-sixth or one-seventh of its original level during that time.

"We've looked at hundreds of thousands of quasars at this point, and now we've found one that has switched off. This may tell us something about their lifetimes," C. Megan Urry, a professor of astronomy and astrophysics at Yale University, said.

Broad emission lines, revealing the presence of gas just outside the reach of the black hole, also dimmed significantly in the time between the images. This told astronomers that the massive body reduced the amount of matter it was consuming, essentially going on a celestial diet.

"This is like a dimmer switch. The power source just went dim. Because the life cycle of a quasar is one of the big unknowns, catching one as it changes, within a human lifetime, is amazing," Stephanie LaMassa of Yale University stated in a press release.

A variety of techniques were employed and observations utilized in the analysis of the data, to make certain the observed dimming was not caused by an independent event, such as the passage of a dust cloud between the Earth and quasar.

Quasars are currently believed to be super-energetic galaxies, driven by tremendous black holes, before the mysterious objects become dormant. Massive black holes are now believed to reside at the cores of nearly all galaxies, including our own Milky Way, but not all are quasars. Investigation of this strange dimming quasar could provide new insights into how our own galaxy came to be the way it is today.

Astronomers could learn more about the life-cycle of black holes from this new finding, including new data on how the objects come to the end of their life cycles.

The first quasars were noted in the 1950's by a pair of American astronomers, Allan Sandage and Thomas Matthews. The objects were originally recorded as radio signals with no known visible sources.

Analysis of the dimming quasar will be published in a future issue of The Astrophysical Journal.