Universe Today
When low- to middleweight stars like our Sun approach the end of their life cycles they eventually cast off their outer layers, leaving behind a dense, white dwarf star. These outer layers became a massive cloud of dust and gas, which is characterized by bright colors and intricate patterns, known as a planetary nebula. Someday, our Sun will
turn into such a nebula
, one which could be viewed from light-years away.
This process, where a dying star gives rise to a massive cloud of dust, was already known to be incredibly beautiful and inspiring thanks to many images taken by
Hubble.
However, after viewing the famous Ant Nebula with the
European Space Agency's (ESA) *Herschel Space Observatory*
, a team of astronomers discovered
an unusual laser emission
that suggests that there is a double star system at the center of the nebula.
The study, titled "
Herschel Planetary Nebula Survey (HerPlaNS): hydrogen recombination laser lines in Mz 3
", recently appeared in the
Monthly Notices of the Royal Astronomical Society
. The study was led by Isabel Aleman of the
University of São Paulo and the Leiden Observatory, and included members from the Herschel Science Center, the Smithsonian Astrophysical Observatory,
the
Institute of Astronomy and Astrophysics
, the
Royal Observatory of Belgium
and multiple universities.
[caption id="attachment_123958" align="aligncenter" width="580"]
The life cycle of a Sun-like star, from its birth on the left side of the frame to its evolution into a red giant on the right after billions of years. Credit: ESO/M. Kornmesser
[/caption]
The Ant Nebula (aka. Mz 3) is a young bipolar planetary nebula located in the
constellation Norma
, and takes its name from the twin lobes of gas and dust that resemble the head and body of an ant. In the past, this nebula's beautiful and intricate nature was imaged by the
NASA/ESA *Hubble Space Telescope*
. The new data obtained by Herschel also indicates that the Ant Nebula beams intense laser emissions from its core.
In space, infrared laser emissions are detected at very different wavelengths and only under certain conditions, and only a few of these space lasers are known. Interestingly enough, it was astronomer Donald Menzel - who first observed and classified the Ant Nebula in 1920 (hence why it is officially known as Menzel 3 after him) - who was one of the first to suggest that lasers could occur in nebula.
According to Menzel, under certain conditions natural "light amplification by the stimulated emissions of radiation" (aka. where we get the term laser from) would occur in space. This was long before the discovery of lasers in laboratories, an occasion that is celebrated annually on May 16th, known as
UNESCO's International Day of Light
. As such, it was highly appropriate that this paper was also published on May 16th, celebrating the development of the laser and its discoverer, Theodore Maiman.
As Isabel Aleman, the lead author of a paper, described the results:
[caption id="attachment_109310" align="aligncenter" width="580"]
Artist's impression of the Herschel Space Telescope. Credit: ESA/AOES Medialab/NASA/ESA/STScI
[/caption]
"Such emission has only been identified in a handful of objects before and it is a happy coincidence that we detected the kind of emission that Menzel suggested, in one of the planetary nebulae that he discovered," she added.
The kind of laser emission they observed needs very dense gas close to the star. By comparing observations from the Herschel observatory to models of planetary nebula, the team found that the density of the gas emitting the lasers was about ten thousand times denser than the gas seen in typical planetary nebulae, and in the lobes of the Ant Nebula itself.
Normally, the region close to the dead star – in this case, roughly the distance between Saturn and the Sun – is quite empty because its material was ejected outwards after the star went supernova. Any lingering gas would soon fall back onto it. But as Professor Albert Zijlstra, from the Jodrell Bank Center for Astrophysics and a co-author on the study, put it:
[caption id="attachment_139212" align="aligncenter" width="580"]
The planetary nebula Abell 39. According to a new study, our Sun will similarly become a luminous planetary nebula by the end of its life cycle. Credit: WIYN/NOAO/NSF
[/caption]
While astronomers have not yet seen the expected second star, they are hopeful that future surveys will be able to locate it, thus revealing the origin of the Ant Nebula's mysterious lasers. In so doing, they will be able to connect two discoveries (i.e. planetary nebula and laser) made by the same astronomer over a century ago. As Göran Pilbratt, ESA's Herschel project scientist, added:
Next-generation space telescopes that could tell us more about planetary nebula and the life-cycles of stars include the
*James Webb Space Telescope*
(JWST). Once this telescope takes to space in 2020, it will use its advanced infrared capabilities to see objects that are otherwise obscured by gas and dust. These studies could reveal much about the interior structures of nebulae, and perhaps shed light on why they periodically shoot out "space lasers".
Further Reading: University of Manchester, ESA, MNRAS