The calculations will be published in the June 27 issue of the journal Nature. If true, they will help solve one vexing puzzle while also creating a separate headache for theorists.
The puzzle
Quasars are powered by supermassive black holes, compact invisible objects loaded with the mass of billions of stars. They shine brightly because as matter spirals inward, it is accelerated to nearly the speed of light and becomes superheated, emitting radiation in all manner of wavelengths, from radio to visible light to X-rays.
Here's the strange thing: The farthest quasars, seen when the universe was less than one-tenth its present age, have been observed to be as bright as those that are much closer -- objects that have had much longer to develop.
To account for the measured brightness of these quasars, 100 Suns worth of gas would have to fall into each of their central black holes every year.
"An interesting question then arises," Loeb told SPACE.com. "How did these very massive black holes form so early in the evolution of the universe?"
Perhaps they didn't, at least not as often as observations suggest.
Cosmic magnifying glass
"A gravitational lens focuses the light from a background quasar, just like a telescope lens does," Loeb explained. However, less than 1 percent of quasars are known to be magnified by in this way at intermediate distances.
Loeb and his colleague say that the increased distance to the farthest quasars makes it more likely for a galaxy to cross the line-of-sight. Further, they find a very large enhancement in the lensing probability, due to a so-called "magnification bias." There are many more faint quasars than bright ones, Loeb explains, and so even if a small fraction of the faint quasars are lensed, the increase in the number of bright quasars due to lensing is very substantial.
The new calculations are based, quite simply, on the number of galaxies in the universe that could serve as a lens.
If the work is correct, then young bright quasars are not always so bright as observed and the whole problem "is eased significantly," says Edwin Turner of the Princeton University Observatory.
"The problem would not be entirely resolved though, as a quasar powered by a black hole ten times less massive and absorbing matter ten times more slowly still poses an interesting theoretical challenge," Turner writes in an analysis of the new study, also to be published in Nature.
A new headache
In partially solving one problem, the study would also create another.
Turner says that if Wyithe and Loeb are correct, then some of what is assumed about the early universe may need to be rethought. Calculations of radiation from the quasars and its effects on the temperature of gas that filled the space between galaxies -- thought to have comprised most of the ordinary mass in the early universe -- would have to be revised, for example.
Such revisions, however, would then contain more layers of uncertainty, Turner said.
The bright and distant quasars were discovered using data collected by the Sloan Digital Sky Survey (SDSS), a project that seeks to map the universe in three dimensions using ground-based telescopes. The objects' distances are measured in redshift, a gauge of how much light has been stretched over time on its journey to Earth.
The most faraway quasar is at a redshift of 6.28.
Only four quasars have been found by the SDSS at a redshift of about 6, which is the category covered by the new Harvard study. But Loeb said about 20 such objects are expected to be found in the full data set upon further examination.
Proof of the new study's merits won't be too hard to come by.
Observations with the Hubble Space Telescope are planned to see if any of the high-redshift quasars are in fact gravitationally lensed. Hubble's resolution -- much finer than the ground-based telescopes -- should be able to detect the multiple images generated by a cosmic lens.
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