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Here is the Stingray Nebula seen by the Hubble Space Telescope in 1996 (left) and 2016 (right). The Stingray is located towards the southern constellation of Ara. What makes it go away so fast? Image via NASA / ESA / B. Balick / M. Guerrero / G. Ramos-Larios.
Twenty years is a failure on a cosmic time scale. In space most things take a very long time happen. This is why astronomers looked surprised yesterday (December 3, 2020) when they announced that two images – acquired 20 years apart – show a distinct discoloration for a distant cloud in space, known as the name Stingray Nebula, located about 18,000 light years away. The 2016 images show a nebula that has radically faded, unlike the 1996 images. In addition, the gas shells that surrounded the central star of this nebula have changed; they don’t appear as sharp as they used to be. The astronomers’ statement – posted on HubbleSite on December 3, 2020 – said:
Changes like this have never been captured with this clarity before … Luckily for us, it seems the Stingray Nebula [aka Hen 3-1357] was meant to stand out from the crowd since its inception. It was dubbed the youngest known planetary nebula in 1998 after Hubble got a rare glimpse of the later stages of the central star’s life.
Today, 20 years after its first snapshot, the Stingray Nebula is capturing the attention of astronomers for a very different reason …
Images captured by Hubble in 2016, compared to Hubble images taken in 1996, show a nebula whose luminosity has dramatically decreased and changed shape. The bright blue fluorescent tendrils and gas filaments towards the nebula’s center are all but gone, and the wavy edges that earned this nebula its aquatic-themed name are all but gone. The young nebula no longer appears against the black velvet background of the vast universe.
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Hubble images of the Stingray Nebula taken 20 years apart show the nebula’s changing shape and a dramatic loss of brightness. Find out more: https://t.co/iw0BFGeimq pic.twitter.com/UCtN8lDTLI
– Hubble (@NASAHubble) December 3, 2020
The Stingray Nebula is a planetary nebula; in this case, the name has nothing to do with the planets. These clouds in space were called planetary because they looked round, like little discs, through early telescopes. Today we know that there are dying stars at the center of planetary nebulae. The nebula is a shroud for the star, if you will. As it dies, the star swells its outer layers. Astronomers have always known that these clouds were temporary. They just didn’t know they could fade into brightness so quickly, on such a human timescale. Team member Martín A. Guerrero from the Instituto de Astrofísica de Andalucía in Granada, Spain, said in the astronomers’ statement:
It is very, very dramatic and very strange. We are witnessing the evolution of a nebula in real time. In a few years, we see variations in the nebula. We’ve never seen this before with the clarity we get from this point of view.
The researchers also discovered unprecedented changes in the light emitted by the glowing nitrogen, hydrogen and oxygen projected by the dying star at the center of the nebula, astronomers said. They said:
Oxygen emission, in particular, dropped in brightness by a factor of almost 1,000 between 1996 and 2016.
University of Washington astronomer Bruce Balick has spent his career studying planetary nebulae. He is the leader of new research. He said:
Changes in nebulae have already been observed, but what we have here are changes in the fundamental structure of the nebula. In most studies, the nebula usually enlarges. Here, it fundamentally changes shape and weakens, and on an unprecedented time scale. Also, to our surprise, it doesn’t get bigger. This is because the once shiny inner elliptical ring seems to shrink as it fades.
The researchers believe that the fading of the nebula does not match the dissipation of the nebula in space (as one would expect, but on a much longer timescale). Instead, they said the discoloration could be linked to the central star of the nebula, called SAO 244567. They said:
… The nebula’s rapid changes are a response to its central star, SAO 244567, which expands due to a drop in temperature and in turn emits less ionizing radiation.
They said they didn’t know how long it would take for the nebula to become invisible in terrestrial telescopes. At its current rate of fading, they estimate, the nebula will be barely detectable in 20 or 30 years.
Bottom line: Images taken 20 years apart show dramatic discoloration of the Stingray Nebula, formerly known as the youngest planetary nebula.
Source: The fall of the youngest planetary nebula, Hen3-1357
Via NASA
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