The glorious guts of a dying star are the means by which astronomers are hoping to discover the very earliest origins of how our planet was born.
In the midst of the Butterfly Nebula NGC 6302, located some 3,400 light-years from Earth in the southern constellation of Scorpius, astronomers have found compelling evidence of dust crystallizing as it cools from hot gas.
“For years, scientists have debated how cosmic dust forms in space. But now, with the help of the powerful James Webb Space Telescope, we may finally have a clearer picture,” says astrophysicist Mikako Matsuura of Cardiff University in the UK.
“We were able to see both cool gemstones formed in calm, long-lasting zones and fiery grime created in violent, fast-moving parts of space, all within a single object. This discovery is a big step forward in understanding how the basic materials of planets come together.”
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Cosmic dust is what it sounds like: dust that drifts around the space between the stars. It’s thought to form primarily in the outer layers of dying stars, seeding the nebular material that is taken up into newly forming stars and the worlds that orbit them.
The Butterfly Nebula is the gorgeous swansong of just such a dying star. It’s what we call a planetary nebula (because the first known examples of its kind were round, like planets). This is the expanding cloud of material that forms around a star as it shucks its outer layers into space as it dies.
At the center of this nebula is a white dwarf – the remnant of a giant star that has already completed its death throes. You’ll also notice that the nebula is not nice and neat and round, but a pair of violently expelled outflows, like the wings of a butterfly.
Wrapped around the central white dwarf – which burns exceedingly hot with the residual heat of its death and reformation – is a thick torus of dust. Matsuura and her colleagues used the infrared power of JWST to peer into this dust to literally see what it is made of.
Most wavelengths of light are blocked and scattered by the dust, but long, infrared wavelengths can pierce through, making JWST the perfect tool to probe this enigmatic environment.
The researchers combined JWST infrared observations with radio observations from the Atacama Large Millimeter/submillimeter Array (ALMA). These observations revealed new details about the processes taking place in the heart of the Butterfly Nebula.
The dusty donut, the researchers found, has infrared signatures of both amorphous dust grains, like soot, and lovely neat crystalline structures. The glinting light suggests also that these grains are quite large for dust, on the scale of microns – suggesting that it has been hanging out there and growing for some time.
The composition of the dust is also fascinating, containing crystals of the silicate minerals forsterite, enstatite, and quartz.
Around the outside of the torus, there’s a clear gradation in the atoms and molecules. Those ions that require the most energy to form are closer to the center of the nebula, while the ions that don’t require much energy to form concentrate farther from the center.
Other features identified in the JWST data include large jets of iron and nickel streaming away from the star in opposite directions; and quite a significant concentration of polycyclic aromatic hydrocarbons, or PAHs. This is particularly interesting.
PAHs are sooty molecules based on rings of carbon atoms that drift through space in high abundance. They feature heavily, therefore, in theories about the origin of carbon-based life. Finding them in the heart of the oxygen-rich Butterfly Nebula gives us new clues about how the building blocks of life might be formed: when powerful winds from the star slam into the material around it.
We can’t rewind the Solar System to find out how it all came together from a cloud in space. Instruments like JWST, and objects like the Butterfly Nebula, give scientists the crucial insight to figure out how we all got here, from dust from a dying star.
The research has been published in The Monthly Notices of Royal Astronomical Society.
