Image credit: Hubble
Possibly both had inside them two stars orbiting each other, which with their disappearance created that kind of “pinwheels” of gas and dust around them.
Thousands of light years from Earth, although close in spatial terms, are two young nebulae. They are NGC 7072, nicknamed the “jewel bug” and NGC 6302, known as the “Butterfly Nebula,” because of their similarities to these insects. The two have two characteristics in common: huge amounts of space dust, as well as unusual masses of gas. Therefore, scientists saw in them the perfect object of study. Why do they have those shapes? Why that level of gases and dust?
The secret may be in its stars. Or the ones that were there one day. Stars are essentially engines of nuclear fusion, allowing them to live a “placid” life for thousands and even hundreds of millions of years. However, when their end comes, they can become a kind of “crazy pinwheels”, causing a swelling of their outer layer, and expelling jets of hot gas. And that is what seems to have happened to the stars in the center of each of these nebulae, as the Hubble Space Telescope has been able to observe.
Hubble had imaged these two nebulae before, but years ago and never with the new Wide Field Camera 3 instrument over its entire wavelength range, making observations in near ultraviolet to near infrared light. “These new observations provide the most comprehensive view to date of these two spectacular nebulae,” explains Joel Kastner of the Rochester Institute of Technology, Rochester, New York, leader of the new study published in the journal “Galaxies” in a statement. “When I was downloading the images, I felt like a child in a candy store.”
The new Hubble images reveal in incredible detail how the two nebulae are moving apart on extremely short timescales, allowing astronomers to see their changes over the past two decades. In particular, the wide, multi-wavelength views of each nebula are helping researchers track the shock wave histories in them. Such collisions are typically generated when cool, fast stellar winds collide and sweep away gas and dust blown off by the star in its recent past, expanding it outward and creating well-walled, bubble-shaped cavities.
A “dance” of two stars and two theories
The researchers suspect that at the heart of each nebula there were two stars orbiting each other. Evidence for such a central “dynamic duo” comes from the strange shapes of these nebulae. Each has a pinched, dusty waist and polar lobes or outlets, as well as other more complex symmetrical patterns.
A commonly accepted theory for the generation of such structures is that the mass-losing star is one of two stars in a binary system. The two stars orbit each other close enough that they eventually interact, producing a disk of gas around one or both stars. The disc then fires jets that inflate the polarized exiting gas lobes.
Another hypothesis is that the smaller star of the pair merges with its swollen, faster-evolving stellar companion. This configuration, which tends to be short-lived in spatial terms, can also generate oscillating jets, forming the characteristic bipolar outflows commonly seen in planetary nebulae. However, the companion stars of these planetary nebulae have not been observed directly, so scientists think that they are either so small that they have not been detected yet or that they could have been swallowed by red giant stars, much larger and brighter. .
NGC 6302, commonly known as the Butterfly Nebula, exhibits a distinctive S-shaped pattern that can be seen in reddish orange in the image. Something like a giant lawn sprinkler spinning violently, spewing two S-shaped jets. However, in this case, it is not water in the air, but a star expelling gas at high speed into space. Furthermore, that “S” only appears in the images when Hubble records the near-infrared emission of individually ionized iron atoms. This iron emission is indicative of energetic collisions between slow and fast winds, which are most frequently observed in active galactic nuclei and supernova remnants.
“It is rarely seen in planetary nebulae,” says Bruce Balick of the University of Washington in Seattle and another of the study’s authors. “Importantly, the iron emission image shows that fast off-axis winds penetrate the nebula like tsunamis, destroying ancient clumps in their path and leaving only long tails of debris.”
The image of NGC 7027 indicates that it was slowly swelling, into symmetrical or spiral spheres, until very recently. “Something recently went wild in the center, producing a new cloverleaf pattern, with bullets of material fired in specific directions,” says Kastner. Without a doubt, a whole stellar spectacle of which the Hubble now reveals its result to us like never before.