Galactic mergers responsible for supermassive black holes, relativistic jets

Strong correlations are always a relief for scientists, especially among the mysteries of deep space. Researchers conducting a survey of galaxies hosting radio-emitting jets were recently graced with just that type of correlation -- a strong link between black hole-induced relativistic jets and merging galaxies.

Almost all of the galaxies studied were currently merging or had recently merged with another galaxy, bolstering the theory that the consolidation of two supermassive black holes is responsible for radio jets. The research was made possible by data collected by the Hubble Space Telescope.

Relativistic jets are the result of extra-large supermassive black holes. Most galaxies host a supermassive black hole, but some are bigger than others. A smaller number of galaxies -- those with extremely bright centers, called active galactic nuclei (AGN) -- host black holes that eat up surrounding gas at a prodigious rate.

The large amounts of gas being swallowed by the supermassive black hole make these AGN galaxies especially luminous. The biggest of the big black holes also feature two long, bright jets of swirling plasma extending out in opposite directions, at right angles to the supermassive black hole.

"The galaxies that host these relativistic jets give out large amounts of radiation at radio wavelengths," lead study author Marco Chiaberge, a researcher at the Space Telescope Science Institute, explained in a press release. "By using Hubble's WFC3 camera we found that almost all of the galaxies with large amounts of radio emission, implying the presence of jets, were associated with mergers."

But while nearly all jets were linked with mergers, not all mergers produce jets. Most don't, in fact.

"We found that most merger events in themselves do not actually result in the creation of AGNs with powerful radio emission," said study co-author Roberto Gilli from Osservatorio Astronomico di Bologna, in Italy. "About 40 percent of the other galaxies we looked at had also experienced a merger and yet had failed to produce the spectacular radio emissions and jets of their counterparts."

Because it's not simply an influx of gaseous mass that takes supermassive black holes to the next level (the jet level), scientists believe a special type of merger -- perhaps two black holes of roughly the same size -- that is responsible for relativistic jets.