3rd December 2020
Astronomers have caught a rare glimpse of a rapidly fading gas casing around an aging star. Archive data from NASA's Hubble Space Telescope shows that the Hen 3-1357 nebula, nicknamed the Stingray Nebula, has faded greatly over the past two decades. According to researchers, it is extremely rare to see such a rapid rate of change in a planetary nebula.
This image compares two dramatically different portraits of the Stingray Nebula taken 20 years apart by NASA's Hubble Space Telescope. The picture on the left, taken with the wide-field and planetary camera 2 in March 1996, shows the central star of the nebula in the last phases of life. The gas ejected by the dying star is much brighter than the image of the nebula on the right, which was taken in January 2016 with the widefield camera 3. The Stingray Nebula is towards the southern constellation Ara (the Altar). Credits: NASA, ESA, B. Balick (University of Washington), M. Guerrero (Instituto de Astrofísica de Andalucía), and G. Ramos-Larios (Universidad de Guadalajara)
This image shows the planetary nebula Hen 3-1357, nicknamed the Stingray Nebula, captured by NASA's Hubble Space Telescope in March 1996. The picture shows the last stages of life of the central star, in which a dying gas jacket is thrown off from the dying star. This image captured the Stingray Nebula in its infancy, and astronomers called it the youngest known planetary nebula. In this picture the colors shown represent the light emitted by nitrogen (red), oxygen (green) and hydrogen (blue). Credits: NASA, ESA, B. Balick (University of Washington), M. Guerrero (Instituto de Astrofísica de) Andalusia) and G. Ramos-Larios (Universidad de Guadalajara)
This image shows the planetary nebula Hen 3-1357, nicknamed the Stingray Nebula, captured by NASA's Hubble Space Telescope in January 2016. This image of the Stingray Nebula shows that brightness and shape have changed dramatically compared to his first portrait of Hubble in 1996. Comparing the imaging, the researchers discovered unprecedented changes in the light emitted by glowing nitrogen (shown in red), hydrogen ( blue) and oxygen (green) emitted, which is radiated from the dying star in the center of the nebula. NASA, ESA, B. Balick (University of Washington), M. Guerrero (Instituto de Astrofísica de Andalucía) and G. Ramos-Larios (Universidad de Guadalajara)
Images captured by Hubble in 2016 show a nebula that has been drastically reduced in brightness and shape compared to Hubble images from 1996. Bright, blue, fluorescent tendrils and filaments of gas towards the center of the nebula have all but disappeared, and the undulating edges that gave this nebula its aquatic name have all but disappeared. The young nebula no longer pops against the black velvet background of the huge universe.
"It's very, very dramatic and very strange," said team member Martín A. Guerrero of the Instituto de Astrofísica de Andalucía in Granada, Spain. "What we are observing is the development of a fog in real time. In a few years we will see variations in the fog. We have never seen it with the clarity that we get with this view."
The researchers discovered unprecedented changes in the light emitted by glowing nitrogen, hydrogen, and oxygen emitted from the dying star in the center of the nebula. Oxygen emissions in particular decreased by a factor of 1,000 between 1996 and 2016.
"Changes in the nebulae have been seen before, but we have changes in the basic structure of the nebula," said Bruce Balick of the University of Washington, Seattle, director of the new research. “In most studies, the fog usually gets bigger. Here it fundamentally changes its shape and becomes weaker, and this on an unprecedented time scale. Plus, to our surprise, it doesn't get any bigger. Indeed, the once bright inner elliptical ring appears to shrink as it fades. "
Ground observations of other planetary nebulae have shown evidence of changes in brightness over time, but these speculations have so far not been confirmed. Only Hubble can resolve the structural changes in this tiny nebula. The new paper examines every image of the Stingray Nebula from Hubble's archives.
"Given the optical stability of Hubble, we're very, very confident that the brightness of this nebula will change over time," added Guerrero. "This can only be confirmed with Hubble's visual acuity."
The researchers note that the nebula's rapid changes are a reaction to its central star SAO 244567, which expands due to a drop in temperature and in turn emits less ionizing radiation.
In a study by Nicole Reindl, now at the University of Potsdam, and a team of international researchers who also use Hubble data, it was found that the star at the center of the Stingray Nebula, SAO 244567, is something special in itself.
Observations from 1971 to 2002 showed that the star's temperature exploded from less than 40,000 to 108,000 degrees Fahrenheit, more than ten times hotter than the surface of our sun. Reindl and her research team have now shown that SAO 245567 cools down. Reindl speculates that the temperature jump was caused by a brief helium fusion flash that occurred in an envelope around the core of the central star. Recently, the star appears to be retreating into its early stages of stellar evolution.
"We are very happy to be watching it right now," said Reindl. “During a helium-shell flash like this, it evolves very quickly, and that implies short evolutionary time scales, so we usually can't see these stars evolving. We were there just in time to catch this. "
The team studying the rapid fading of the Stingray Nebula can only speculate for the moment as to what lies ahead for the future of this young nebula. At the current rate of fading, it is estimated that the mist will be barely detectable in 20 or 30 years.
The Hubble Space Telescope is an international cooperation project between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.