Light Signals Suggest Merging of Two Massive Black Holes

Unusual repeating light signals detected from a distant quasar - luminous galaxies with very active supermassive black holes at their centers - suggests that two such infamous objects are merging together, according to new research.

This discovery could possibly shed light on a phenomenon that has long been theorized by scientists, but has never before been observed. Called the "final parsec problem" is the long-standing failure of theoretical models to predict what the final stages of a black hole merger look like, or even how long the process might take. But astronomers now hope that these strange signals coming from the quasar known as PG 1302-102 could be the key to observing this elusive wonder.

"Until now, the only known examples of supermassive black holes on their way to a merger have been separated by tens or hundreds of thousands of light years," study co-author Daniel Stern, a scientist at NASA's Jet Propulsion Laboratory (JPL), said in a statement. "At such vast distances, it would take many millions, or even billions, of years for a collision and merger to occur. In contrast, the black holes in PG 1302-102 are, at most, a few hundredths of a light year apart and could merge in about a million years or less."

But lead author George Djorgovski of Caltech and his colleagues did not set out to find a black hole merger. Instead they studied quasar brightness, which usually emit optic signals that are chaotic. But in the case of PG 1302-102 its light signals were periodic, showing up every five years or so, surprising scientists.

"The evidence suggests that the emission originates from a very compact region around the black hole and that the speed of the emitting material in that region is at least a tenth of the speed of light," said Avi Loeb from Harvard University, who was not involved in the research. "A secondary black hole would be the simplest way to induce a periodic variation in the emission from that region, because a less dense object, such as a star cluster, would be disrupted by the strong gravity of the primary black hole."

However, the mystery remains as to whether a supermassive black hole merger is responsible for these unusual periodic light signals. But should their theory prove to be correct after further observation, it would be a major breakthrough in explaining a phenomenon that has long puzzled scientists.

The findings were published in the journal Nature.

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