May 16 (UPI) -- The core of the famed Ant Nebula is home to a double star system, according to new research by an international team of astronomers. The presence of the binary star system was revealed by a rare space laser.
When stars similar to our sun die, they expel their outer layers and form an interstellar cloud of gas and dust known as a planetary nebula. The Ant Nebula is named for its two lobes, which resemble the segments of an ant's body.
Recent observations of the nebula by the European Space Agency's Herschel Space Observatory revealed an infrared laser emission. Only a few such laser beams have been previously identified.
"Such emission has only been identified in a handful of objects before," Toshiya Ueta, principal investigator of the Herschel Planetary Nebula Survey, said in a news release. "This was a remarkable discovery that we did not anticipate. There is certainly more to stellar nebulae than meets the eye!"
Donald Menzel first observed the Ant Nebula in the 1920s. The planetary nebula's official name is Menzel 3, in honor of the late astrophysicist. Menzel also surmised that a gaseous nebula, under certain conditions, could produce "light amplification by stimulated emission of radiation" -- a laser.
"When we observe Menzel 3, we see an amazingly intricate structure made up of ionized gas, but we cannot see the object in its center producing this pattern," said Isabel Aleman, an astronomer with the Leiden Observatory. "Thanks to the sensitivity and wide wavelength range of the Herschel Observatory, we detected a very rare type of emission called hydrogen recombination line laser emission, which provided a way to reveal the nebula's structure and physical conditions."
Models designed to produce a similar emission suggest the presence of extremely dense gas surrounding the stellar core at the center of the Ant Nebula -- some ten thousand times higher than the density of gas in the outer regions of the nebula's lobes.
Typically, during the explosive transition from living star to dying white dwarf, most of the gas is pushed away from the star, leaving a void.
"The only way to keep gas close to the star is if it is orbiting around it in a disc," said researcher Albert Zijlstra. "In this case, we have actually observed a dense disc in the very center that is seen approximately edge-on. This orientation helps to amplify the laser signal. The disc suggests the white dwarf has a binary companion, because it is hard to get the ejected gas to go into orbit unless a companion star deflects it in the right direction."
Scientists have not yet directly detected the companion star, but their observations and models -- detailed in the journal Monthly Notices of the Royal Astronomical Society -- suggests the presence of a pair of stars.
"This study suggests that the distinctive Ant Nebula as we see it today was created by the complex nature of a binary star system, which influences the shape, chemical properties, and evolution in these final stages of a star's life," said Göran Pilbratt, ESA's Herschel project scientist.