A gigantic burst of gamma radiation in an apparently empty region of space has befuddled astronomers for much of 2007.

A research team that includes a Penn State University astrophysicist thinks a yet unseen galactic tail might have produced this year's biggest heavenly burst.

But for now, the intergalactic thriller dubbed "the shot in the dark" still lacks a star.

"It was like a whodunit," said Derek Fox, assistant professor of astrophysics at Penn State.

They are hoping the Hubble Space Telescope can confirm their best theory.

On Jan. 25, satellites recorded a burst of gamma radiation in the constellation Gemini. Within hours, Dr. Fox and California Institute of Technology astronomers began investigating.

Gamma ray bursts, or GRBs, occur in a flash but cannot be seen with the naked eye. Instead, satellite-borne radiation detectors are used to spot them. But a GRB energizes surrounding dust and gas to produce an afterglow that can be seen and studied for days, even weeks. Afterglows are Dr. Fox's specialty.

"We move as quickly as we can when a GRB is announced," he said. "We got this pretty quickly on a telescope and saw the afterglow."

Observations by NASA's Swift satellite controlled from its Mission Operation Center at Penn State pinpointed the explosion named GRB 070125, which reflects the date it occurred. Astronomers then observed the afterglow in detail through two of the world's largest telescopes in Hawaii.

The team soon determined that the burst occurred at least 9.4 billion light-years away. Theory holds that it likely involved a massive star whose collapse produced the huge burst of gamma radiation.

But astronomers found no galaxy in that region. No galaxy typically means no stars -- and no GRBs.

"Many Swift discoveries have left astronomers scratching their heads in befuddlement," said Swift lead scientist Neil Gehrels of NASA Goddard Space Flight Center in Greenbelt, Md. "But this discovery of a long GRB with no host galaxy is one of the most perplexing of all."

Dr. Fox said 1 percent of all stars are formed in tidal tails -- tails of gas and dust created by the gravitational pull of passing galaxies. With no tail evident, the team turned to other theories to explain how the burst could occur in the middle of nowhere.

"If we found a GRB that didn't seem to come from a massive star, that would be a very big deal and upset all our theories," Dr. Fox said.

Another rejected consideration was that a rogue star existing outside a galaxy collapsed to produce the burst.

The team did determine that the burst occurred at least 88,000 light-years away from the nearest bright galaxy. That spawned theories that a galaxy in that general region has a tidal tail too faint to detect easily from 9.4 billion light-years away.

"It took a while to figure out, but that was our best guess," said Dr. Fox, co-author of the research to be published in Astrophysical Journal.

The team hopes the Hubble can detect a tidal tail with a long-exposure image.

GRBs can produce and already may have produced dire consequences on Earth. One theory suggests that GRBs in Earth's neighborhood of the Milky Way Galaxy caused one or more mass extinctions by disrupting the planet's atmosphere and producing environmental consequences.

Dr. Fox said GRBs also pique interest because they release enormous amounts of energy in short periods of time and help explain the formation and destruction of stars.