The Biggest Thing Ever in Space?
S A N D I E G O, Jan. 9, 2001 -- A supercluster of quasars and galaxies massedtogether across 600 million light years of space is the largeststructure in the observable universe, astronomers say.
In a study presented Monday at the national meeting of theAmerican Astronomical Society, researchers reported that thestructure, which includes billions upon billions of stars, isbelieved to be 6.5 billion light years away.
“We have found nothing bigger in the [astronomy] literature andnobody has brought to our attention anything bigger,” said GerardWilliger, a researcher at the National Optical AstronomyObservatories now working at NASA’s Goddard Space Flight Center inGreenbelt, Md.
Just Below Leo
When viewed from Earth, the structure is just below the centerof the constellation Leo the Lion. It stretches across an expanseof the sky of two degrees by five degrees, or an area about fortytimes that of the full moon as seen from Earth.
Williger said it is not known if the gathering of quasars andgalaxies is bound together gravitationally or if it is a chancecluster formed by a ripple in the smooth expansion of the universethat followed the Big Bang, which is thought to have set off theformation of the universe.
“This may be an artifact of the Big Bang,” he said,speculating that conditions at that point in space may have beenuniquely ripe for the quick formation of stars, galaxies andquasars.
That such a large structure could form so quickly after the BigBang calls into question some of the traditional theories of howthe universe evolved, Williger said, since it is difficult toexplain how gravity could pull together such an immense cluster ina relatively short time. Further study, which would includecalculations of the mass in the structure, may yield newunderstanding.
“A successful theory has to explain the extremes,” saidWilliger.
It's Not Just Big — It's Also Very Old
Light from the galaxies began its long journey about 6.5 billionyears ago when the universe was just a third of its present age andthe solar system, including the Earth, had not yet been formed, hesaid.
The structure includes at least 11 galaxies and 18 quasars in anarea where the expected density of objects would be expected toinclude only two or three quasars and perhaps four galaxies, hesaid.
Quasars are galaxies with very active and bright center objects,thought to be powered by black holes. Quasars can shine with thebrilliance of a trillion suns and astronomers can use this light tosilhouette objects nearer Earth. Average galaxies, such as thesun’s home, the Milky Way, can contain 100 billion stars. A lightyear is the distance light travels in a year in space, about 6trillion miles.
Williger and his colleagues, using the four-meter telescope atthe Cerro Tololo Inter-American Observatory in Chile, detected thesupercluster’s non-quasar galaxies indirectly, by analyzing thelight received from quasars that are even farther away. This lightis absorbed by the halos of gas surrounding the galaxies, producingshadows that reveal the presence of the galaxies.
There are other clusters of quasars in distant space, but noneare as densely grouped as the supercluster in Leo, said Williger.
Williger said the Leo supercluster is more than twice the sizeof The Great Wall, a gathering of galaxies much closer to theEarth. The Great Wall is about 250 million light years across.