When red giant stars run out of helium fuel and expel their outer layers to
become hot, compact white dwarf stars that are roughly the size of Earth,
planetary nebulae are created. As the carbon-enriched shed material is
gradually blasted into the interstellar medium, it produces magnificent
patterns.
The majority of planetary nebulae are circular, but others, like the
well-known "Butterfly Nebula," have an hourglass or wing-like appearance.
These structures are thought to be the consequence of the material expanding
into two lobes or "wings" due to the gravitational attraction of a second
star circling the parent star of the nebula. The wings develop over time
without altering their initial form, much like an expanding balloon.
However, recent findings indicate that something is wrong with the
Butterfly Nebula. When a group of astronomers lead by those from the
University of Washington analyzed two Hubble Space Telescope exposures of
the Butterfly Nebula made in 2009 and 2020, they discovered significant
changes in the substance within the wings. The American Astronomical
Society's 241st conference will be held in Seattle on January 12 and the
researchers will present their findings there. Strong winds are causing
intricate material changes inside the nebula's wings. They are trying to
figure out how such activity can occur from what should be a "sputtering,
mostly dead star with no fuel left."
According to team leader Bruce Balick, an emeritus professor of astronomy
at the University of Washington, "The Butterfly Nebula is extreme for the
mass, speed, and complexity of its ejections from its central star, whose
temperature is more than 200 times hotter than the sun yet is just slightly
larger than the Earth." Since I started comparing Hubble photographs, I
haven't come across anything exactly like that.
The scientists tracked the rates and trajectories of feature growth within
the nebula's wings by comparing Hubble photos taken 11 years apart at high
resolution. Lars Borchert, a doctoral student at Aarhus University in
Denmark who took part in this work as a UW undergraduate, carried out the
majority of the analyses.
About half a dozen "jets" that began approximately 2,300 years ago and
ended 900 years ago were found by Borchert to be pushing material out in a
sequence of asymmetrical outflows. The nebula's outermost regions are
expanding at a rate of around 500 miles per second, while the inner regions
are expanding at a rate of about a tenth of that pace. Jet paths intersect,
creating "messy" development patterns and structures inside the wings.
According to Balick, it is difficult to explain the nebula's multi-polar
and rapidly shifting internal structure using current ideas of how planetary
nebulae originate and develop. It's possible that the star in the nebula's
core, which is obscured by dust and debris, fused with a partner star or
sucked material from another star nearby, producing the complicated magnetic
fields and the jets.
These are all still just theories, according to Balick. This demonstrates
to us that we are still lacking a comprehensive understanding of the shaping
mechanisms involved in the formation of planetary nebulae. The James Webb
Space Telescope will be used to take pictures of the nebular core because
infrared light from the star may pass through the dust.
In the distant future, star systems and planets will develop as stars like
our sun expand into red giants and create planetary nebulae, ejecting carbon
and other comparatively heavy materials into the interstellar medium. These
recent findings, together with previous "time-lapse" investigations of
planetary nebulae, can help explain how the constituent parts of our own
galaxy were created and gathered billions of years ago, as well as how the
components of future star systems will take shape.
In our cosmos, a creation tale is repeated repeatedly, according to Balick.
"The shaping processes offer significant insight into the background and
consequences of the star activity."
