It is hard to be sure about something you cannot see. But there is one certainty about the monsters of the universe, those voracious and enigmatic objects whose gravitational grip can stop light cold: A black hole will never turn down a meal.

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That's how they get to be so massive.

But the most massive black holes seem to be relatively nearby in cosmic terms, which implies that they are old, having evolved for billions of years. Thing is, most don't seem to be eating much these days.

Growing to supermassive proportions in tiny spaces, early black holes were incorrigibly active, even if not yet fully grown. They signaled their gluttony in a chomping heard, or rather seen, 'round the cosmos.

"When supermassive black holes dine, their manners are abominable," said Paul Green, a researcher at the Harvard-Smithsonian Center for Astrophysics (CFA). "They spew."

From their sloppy jowls ooze blizzards of X-rays, created when matter spirals fast and close to the point of no return and is superheated just before being devoured. For the past year and a half, Chandra has been noting these emissions, billions of years later, as they arrive at its perch above Earth's atmosphere, which otherwise blocks X-rays from our study.

Amy Barger of the University of Hawaii uses Chandra to examine these objects, following up with optical observations from the Keck Observatory atop Mauna Kea.

"The most violent episodes of black hole growth certainly occurred at early times," Barger said.

The difference was stark. Barger's calculations show that supermassive black holes each downed the equivalent of 10 Suns, on average, every year when the universe was young. Nowadays, the average rate of consumption is down to just one-hundredth of a Sun per black hole per year.

Now a ground-based telescope at the European Southern Observatory in Chile has weighed in, providing a strikingly detailed look at how the beasts were fed way back when. Merging galaxies were responsible for the menu proffered to black holes, the ESO image suggests.

The new infrared image shows a quasar, or quasi-stellar radio source, at the center of a galaxy whose light has taken 10 billion years to reach us. Some 15,000 distant quasars have been found since they were first misidentified as strange, nearby stars in the 1960s. Researchers are now nearly certain that quasars simply primitive galaxies, very far away and powered by highly active, supermassive black holes.

"In the brightest cases this radiation [from the central object] outshines the total radiation of the galaxy by 10 to 100 times or even higher," explained Klaus Jäger of the Universitäts-Sternwarte Göttingen in Germany, who helped produce the new image. "Then we call it quasar."

The ESO image, which was refined by the scientists to highlight details, reveals several bright spots embedded in two long, octopus-like arms of the main galaxy. The longer arm, reaching downward, extends across more than 150,000 light-years of space -- one-and-a-half times the diameter of our entire Milky Way galaxy.

Jäger told SPACE.com that two or three of the brightest knots are thought to be galaxies, each some 10,000 light-years wide. Several fainter knots may be galaxies, but need to be analyzed further.

Barger said the contorted shape strongly suggests "dramatic gravitational interactions taking place between the quasar host galaxy and its close companion galaxies."