Man, do I love me some planetary nebulae. Here’s one for you:
That’s IC (for Index Catalog, a supplement to the original New General Catalog of astronomical objects) 4593, a nebula in Hercules, and it’s one of four nebulae images just released from Hubble. What you are seeing here is the death of a star like the Sun. I have written about them before (here and here, with some more general info here), so go read those to get the intro.
I studied planetary nebulae (or PNe) for years, and they fascinate me. The fantastic shapes are caused by the collision of winds emitted by the central stars as they turn into red giants and evolve into small, hot, white dwarfs. Normally, red giants don’t spin rapidly, so you might expect the winds to expand spherically (if the star spun quickly, the centripetal force would flatten out the wind into an oblate spheroid, like a basketball someone sat on). But actually a spherical PN is rare! Somehow, these stars are getting some kind of injection of angular momentum, and one (IMO) very good hypothesis is that the stars consume planets as they expand. As the star vaporizes the planets, the angular momentum from the planet’s orbital energy spins the star up. The winds flatten out, and you get those incredible shapes that remind me of squids and flowers.
But if you look at IC 4593, you’ll see two bright red knots of gas with long streamers; one is at the upper left and the other at the lower right. A cursory examination indicates many interesting things: they are on opposite sides of the star; the streamers point directly back to the star; the knots are mostly nitrogen (indicated by the red color in these images); they are moving rapidly compared to the rest of the gas (this can be seen by taking spectra); they are not at as high a temperature as the rest of the gas.
What are they?
They’re called FLIERs, for Fast Low-Ionization Emission Regions. Fast is obvious enough. Low ionization means that they are not hot, and not getting pelted by UV radiation from the star. Emission means they are glowing. They’re seen in lots of PNe.
I’ll cut to the chase and say they aren’t well-understood, at least as far as I can tell by looking at the literature. Most likely some are caused by some weird feature of the wind collision where gas is squeezed out under higher pressure, like a watermelon seed when you squeeze it between your fingers. But this idea doesn’t explain all the features of FLIERs seen in other PNe, and their origin is still a mystery.
An odd thing that crops up in the papers I’ve read is that the knots may not actually be moving all that quickly. The speed is inferred from the Doppler shift in the spectra, and some astronomers are wondering if perhaps that’s not showing the speed of the knot itself, but maybe is due to gas flowing around them, or from some other combination of effects.
Observations from Hubble and other ‘scopes will keep coming in, and the models will keep getting refined. Studying these objects will turn up insights into how stars like the Sun die, which in turn will tell us how they change as they age, which has a direct impact on us. Maybe not for a while yet — maybe a billion or five years — but any knowledge on this topic is a good thing.
Plus, they’re pretty. That counts too.
September 11th, 2007 at 4:43 pm
The image reminds me of a few scenes from “2001″, where Dave is seeing those weird shapes after he meets the monolith at Jupiter. If you have the time Phil, watch the film and see what you think (I assume, of coruse, that you have the movie!).
I bet the James Webb ‘scope can reveal deep mysteries in objects such as this. Could it be possible at all that those knots are planets that are being effected?
September 11th, 2007 at 5:57 pm
>>> I’ll cut to the chase and say they aren’t well-understood
Ah, well, obviously they are intelligently designed!
September 11th, 2007 at 6:08 pm
Now if we got to see pretty pictures like that in my undergraduate astronomy class, I bet more people would have paid attention rather than complaining!
That may be the prettiest nebula I’ve seen!
September 11th, 2007 at 8:15 pm
The prettiest PN I’ve personally seen is the Cat’s Eye, NGC 6543:
http://apod.nasa.gov/apod/ap070513.html
The first time I saw this Hubble image I said “That’s pretty!”
Then a few seconds later I said “It’s precessing!” because of the multiple axes of symmetry. This image is both my computers’ background.
IC4593 on the other hand is a lopsided mess! Like the Cat’s Eye it has jets, outflows from the rotational poles focused into jets by magnetic fields to be sure, but there’s so much else going on here it’s all a jumble. Where to start?
- There’s the pointy thing at 12:30 that looks angular, like a pyramid almost (don’t tell Hoagland, please!),
- Then there’s the innermost cyan-colored layer that is semi-spiraled with angular corners,
- Then there’s the “J” shape to the base of the upper jet,
- Then there’s the pinched base of the lower jet,
- Then there’s the red spot at 2:00…
It’s all a glorious mess! This’ll keep the theorists busy for years! What fun! I’ll keep the Cat’s Eye on my Macintosh, though, it’s prettier…
Rich
September 11th, 2007 at 9:16 pm
[...] easily understood manner) what happens to cause a planetary nebula, and why this one is so pretty. Link [...]
September 12th, 2007 at 4:12 am
Nebulae are very short lived (by astronomical time scales). You can see them evolve from steams of photos taken over a period of just a few years.
Phil, shouldn’t that be centrifugal?
September 12th, 2007 at 8:21 am
The terms “centrifugal” and “centripetal” are not the same thing.
You can get several hits on Google for the meanings here:
http://www.google.com/search?q=centrifugal+versus+centripetal
I’m not sure which one would be correct here.
September 12th, 2007 at 10:54 am
Looks like the well-named FLIERs are the ships that the last few of the locals are using to escape their dying star. Tricky bit of navigating, to use your entire star like an Orion booster…
September 12th, 2007 at 11:21 am
This image reminds me of scenes from the movie “The Fountain” Although that star is about to go bang. Have you seen that movie Phil? I think it would be a great one for a BA review.
September 12th, 2007 at 3:34 pm
I had a physics teacher who told me that centrifugal force doesn’t actually exist. It’s ALL centripetal force. Just sayin’ is all.
September 13th, 2007 at 12:50 am
Grade 10 Science,
If you use a rotating coordinate system, the the math works out if you use a center-fleeing (centrifugal) force, such as one that would “flatten out” stellar wind.
Since he used the phrase, “flatten out”, I thought that centrifugal (center-fleeing) would be the more appropriate term.
September 13th, 2007 at 8:24 am
[...] IC 4593 está abajo a la izquierda y se encuentra en la constelación septentrional de Hércules. Mi buen amigo Phil Plait realizó un buen escrito sobre este objeto asà que os enlazo a este sitio para ver la exclusiva. [...]
September 13th, 2007 at 12:07 pm
Great picture! I love your blog. Just found it as a matter of fact.
September 13th, 2007 at 8:49 pm
Could the mass and locations of the progenitor star’s planets be infered from the structure of the nebula? Or is what we see here actually much larger than a typical planetary system, implying that by the time the nebula has expanded enough to be larger than a point source and have any visible structure, it is vastly bigger than the orbits of any planets originally orbiting the star, and has been distorted too much to be useful? I.E., what’s the image scale? (The link says it’s about 7000 lightyears distant, which seems pretty far to see something as small as a solar system, but there’s no angular size listed that I could see.)
Anyway, if the swirls and whirls are caused by abrupt changes in angular momentum as the expanding nebula encounters and absorbs planets, then presumably the rare smooth ones are from planetless stars, and the common contorted nebulae are from stars with planets. Which means planetary nebulae have something to do with planets after all
September 15th, 2007 at 12:19 am
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September 19th, 2007 at 12:36 pm
[...] IC 4593 está abajo a la izquierda y se encuentra en la constelación septentrional de Hércules. Mi buen amigo Phil Plait realizó un buen escrito sobre este objeto asà que os enlazo a este sitio para ver la exclusiva. [...]