A cosmic chicken-and-egg question may have been solved by astronomers who now say black holes came before galaxies.
The findings were presented at a major astronomy meeting in California.
Most if not all galaxies, including our own Milky Way, are believed to have massive black holes at their cores.
It was unclear whether black holes came first, helping create galaxies by pulling matter towards them, or whether they arose in already formed galaxies.
"It looks like the black holes came first," said Dr Chris Carilli, from the US National Radio Astronomy Observatory in Socorro, New Mexico, who took part in the study. "The evidence is piling up."
The evidence was unveiled at the 213th American Astronomical Society meeting in Long Beach, California.
Earlier studies of nearby galaxies had revealed an intriguing link between the masses of black holes and the central "bulges" of stars and gas in galaxies.
Generally, the mass of a black hole was observed to be about 1,000th that of the mass of the surrounding galactic bulge.
This constant ratio indicated an "interactive relationship" between the black hole and the bulge, say the researchers. But it was not clear whether one grew before the other, or whether they grew together.
In the latest study, researchers used radio telescopes to peer back to near the beginning of the Universe, thought to be some 13.7 billion years ago, when the first galaxies were forming.
"We finally have been able to measure black-hole and bulge masses in several galaxies seen as they were in the first billion years after the Big Bang," said co-author Fabian Walter of the Max-Planck Institute for Astronomy in Heidelberg, Germany.
"The evidence suggests that the constant ratio seen [in nearby galaxies] may not hold in the early Universe."
He added: "The implication is that the black holes started growing first."
The astronomers say the next challenge is to figure out how the black hole and the bulge affect each others' growth.
Dr Carilli said powerful new radio telescopes now under construction would help to unravel the mystery.
These include the Expanded Very Large Array (EVLA) in New Mexico and the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.