NASA released the latest pictures from Webb. You can see a link to a dying start here:
https://webbtelescope.org/contents/news-releases/2022/news-2022-033?Collection=First%20Images
I am not sure, how it is possible that after 24 years, it seems the dying star explosion is still in a very similar size and shape. Can someone please what exactly we are observing in this picture.
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that cloud is thousands of years old and half a light year across
even moving *at* lightspeed it needs a while for that cloud to expand visibly, and its a fair bit slower
Quite simply it’s scale.
The gas cloud is expanding at a considerable rate, say 30 km/s.
But that particular cloud is about 300 light years across already.
thats about 3,000,000,000,000,000 km across
At 30 km/s for 24 years, the edge has moved… 22,720,986,720 km.
That’s about… 0.001% larger. A bit hard to notice.
Edit for clarity: Numbers above for the “carina” nebula, that big one. My mistake!
Numbers for the southern ring nebula: At 0.4 ly across (thanks cornflakes_91) we adjust the numbers to 20 km/s expansion, and get ~0.1% increase in size. Still hard to notice.
That image is huge. Like literally hundreds of millions of miles in diameter. an explosion is just a rapid expansion and while it is very rapid its also extremely big. Relative to its size its expansion is very slow.
This just goes to show how vast space really is.
That *is* an explosion, and the debris *is* going very fast, but it’s also very *big* and *far away*. So big and far away that, even after 24 years of motion, the spreading debris looks like it barely moved.
An instant on the galactic scale IS decades or centuries on the human scale, depending on the phenomena. And think of the death of a star more like sputtering out rather than a lightbulb that shuts off almost instantaneously. So chances are, that star will look similar for decades more, with that gas cloud expanding “slowly” from our perspective.
What you’re seeing is a shell of gas cast off by one of the two central stars at the end of its life. This happens to most medium-mass stars, and will probably happen to our Sun at the end of its life in about five billion years.
The cast-off layers float out into space at speeds that are very high by human standards, but the distances in space are so vast that it still takes a long time for them to dissipate. 24 years, in cosmic terms, is the blink of an eye.
Nebulas like that one last for maybe thousands of years before they dissipate. That’s a long time in human terms, but for a star (whose lifetimes are usually measured in the tens of millions to single-digit trillions of years), it’s nothing at all. If you prefer, this star is already dead, but its corpse is not yet cold. (Actually, in a broader sense, [*no* stars’ corpses are cold yet](https://en.wikipedia.org/wiki/Black_dwarf) because the Universe isn’t old enough.)
I think you are confusing the ideas of dying and death. Just like in humans, dying can be stretched out over months and years, but the final act of death is pretty much instant. Everything go through various “life stages,” and humans define when the “dying” stage begins. In the case of a star, dying means something along the lines of “not enough hydrogen left for sustained fusion.” A dying star could be in the red giant stage, where lots of mass is ejected from the surface of the star, as seen in the picture, or white dwarf stage where this mass is depleted.
The link you posted explains it:
>Since planetary nebulae exist for tens of thousands of years, observing the nebula is like watching a movie in exceptionally slow motion. […] In thousands of years, these delicate layers of gas and dust will dissipate into surrounding space.
Relative to the lifetime of a star, thousands of years *are* an instant.
>Each shell represents an episode where the fainter star lost some of its mass.
And from wikipedia:
>This hot central star of about 100,000 K has now blown off its outer layers
So it’s blowing off bit by bit, like dying breaths. Over time. 24 years is nothing to that timescale.
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