Laser emissions from Ant Nebula suggest it hides a binary star system

Gases ejected by white dwarf are likely captured by companion star.
By Laurel Kornfeld | May 23, 2018
Scientists have detected rare laser emissions coming from the Ant Nebula, also known as Menzel 3, suggesting that the stellar remnant it hosts, a white dwarf surrounded by a planetary nebula, may have a companion star.

White dwarfs are the remnants of Sun-like stars that shed their outer layers, which then come together to form a cloud of gas, known as a planetary nebula, around the dead star.

Gases at the center of the nebula fall back into the star, leaving behind an empty region surrounding the white dwarf.

However, when scientists observed the Ant Nebula, located between 3,000 and 6,000 light years from Earth, with the European Space Agency's (ESA) Herschel Space Observatory, they were puzzled to find it emitting an unusual type of laser produced only when a dense cloud of gas surrounds the stellar remnant.

"When we observe Menzel 3, we can see an amazingly intricate structure made up of ionized gas, but we cannot see the object in its center producing this pattern," noted Isabel Aleman of both the University of Sao Paulo, Brazil, and the Leiden Observatory in the Netherlands.

"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."

Because Herschel observations revealed the gas emitting the lasers is 10,000 times more dense than the typical gas within a planetary nebula, researchers suspect the white dwarf has a companion star that is capturing the dense gas it is ejecting.

While no companion has yet been directly observed, both computer models and observations support the notion that the system is a binary.

"The only way to keep gas close to the star is if it is orbiting around it in a disc. 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," explained Albert Zijlstra of the University of Manchester in the UK.

Toshiya Ueta, principal investigator of the Herschel Planetary Nebula Survey Project, said the researchers were observing the Ant Nebula to characterize its gas and dust and not for the purpose of finding laser emissions, which are relatively rare occurrences.

A paper detailing the research team's findings has been published in Monthly Notices of the Royal Astronomical Society.

 

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