A star‘s death is insanely wild and violent as it gets shattered with immense quakes, dropping massive amounts of stellar material out into the space surrounding it. Analyzing the gas and dust emitted during such events can help researchers better understand the way these stars die.
Now, Hubble Space Telescope has studied in great detail – more carefully than before – two of the dustiest, gassiest star deaths in the galaxy, namely two planetary nebulae called NGC 6303, or the Butterfly Nebula, and NGC 7027.
A Violent Last Breath
Hubble has used the full wavelength of its Wide Field 3 camera to analyze the violent processes that take place within them.
“When I looked in the Hubble archive and realized no one had observed these nebulae with Hubble’s Wide Field Camera 3 across its full wavelength range, I was floored,” said astronomer Joel Kastner of Rochester Institute of Technology in New York. “These new multi-wavelength Hubble observations provide the most comprehensive view to date of both of these spectacular nebulae. As I was downloading the resulting images, I felt like a kid in a candy store.”
Both nebulae are likely coming from progenitor stars about three to five times the mass of the Sun, which collapsed into white dwarfs when they died. Moreover, the two objects have high ionization and excitation, pointing out that the stars’ core is very hot.
In addition, the two nebulae have some rather interesting features: they are bipolar, have lobed shapes flowing from a tighter core that point towards some intricate engagements that once took place in the nucleus of those glowing clouds.
The new, high-resolution images have made it possible for astronomers to examine the shocks produced by periodic stellar winds crashing into the slower-moving dense clouds. These generate cavities and walls in the nebulae that can be studied to determine its activity history.
Even though the nebulae loos rather different, researchers believe that the lobed structures of both objects were created by the same activity: two stars in a binary system, locked in orbit around each other. The material discharged by the star taking its last breaths can then be absorbed by an accretion disk around its companion star and released into space in each polar direction by astrophysical jets produced by the accretion disk.
Another possibility is that the two stars combined, creating wobbling jet streams that generated patterns like those spotted in the Butterfly Nebula.
“The suspected companion stars in NGC 6302 and NGC 7027 haven’t been directly detected because they are next to, or perhaps have already been swallowed by, larger red giant stars, a type of star that is hundreds to thousands of times brighter than the Sun,” said astronomer Bruce Balick of the University of Washington.
“The hypothesis of merging stars seems the best and simplest explanation for the features seen in the most active and symmetric planetary nebulae. It’s a powerful unifying concept, so far without rival.”
Follow-up studies are currently being conducted to try to find out more about these processes and narrow it down to a somehow certain explanation. The research has been published in Galaxies.