Starship Asterisk*

Thor s Helmet

Explanation: This helmet-shaped cosmic cloud with wing-like appendages is popularly called Thor's Helmet. Heroically sized even for a Norse god, Thor's Helmet is about 30 light-years across. In fact, the helmet is actually more like an interstellar bubble, blown as a fast wind from the bright, massive star near the bubble's center sweeps through a surrounding molecular cloud. Known as a Wolf-Rayet star, the central star is an extremely hot giant thought to be in a brief, pre-supernova stage of evolution. Cataloged as NGC 2359, the nebula is located about 15,000 light-years away in the constellation Canis Major. The sharp image, made using broadband and narrowband filters, captures striking details of the nebula's filamentary structures. It shows off a blue-green color from strong emission due to oxygen atoms in the glowing gas.

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once again we have something that does not look to much like it did with lesser equipment, but doggone it, it does look terrific!!
Now its almost like there is a "Bubblely" Helmet in the middle. Or - is it more like a bubblely tortise ?

For a different perspective, see: WISE: NGC 2359: Thor's Helmet

well, its definitly not a blue tortise, but still does not resemble a helmet either. I like the blue -bubblely tortise that even has a blue head.
Maybe it would help if Thor's Hammer was near-by?

To make sense of the image, I must try to make sense of its colors, as usual.

The color balance seems slightly shifted to the red, apart from the fact that the blue color of the helmet is so obvious. But some of the stars look very orange, while none of the stars look strikingly blue. Nevertheless, some of the stars do display a faint bluish color, and many of the stars look white, so the color balance for the stars isn't that far off. The most orange one of the stars, to the upper right of the helmet, probably is very red for real.

The red "horns" of the helmet are obviously glowing red from ionized hydrogen. It is interesting that the red "arc" at lower right and the red patch at lower left are a much duller red color, particularly the "arc". Could the arc be dust-reddened, and if so, could it be more dust-reddened than the "horns"? No, it looks more like a mixture of red emission nebulosity, blue reflection nebulosity and some unlit dust, all pretty much mixed up and muted-looking.

The bubble itself is very blue from oxygen emission. It's interesting that it contains no red nebulosity at all. The reason must be that the bubble contains no hydrogen at all. The outer hydrogen shell has been blown off, and the remnants are seen as the red "horns" of the helmet.

The bubble is richly textured, and I have no idea why that is so. Could it possibly have anything at all to do with magnetism?

Fascinating!

Ann

It might be interesting to compare Thor's Helmet, a "pre-explosion" nebula, with the Crab Nebula, a "post-explosion" nebula. In the Crab, any bubble surrounding the massive star has been blown to smithereens, but it is possible that magnetism within the nebula is keeping the filaments of gas lined up the way they are.



I don't much like the color balance of this image. It looks weird to me. Nevertheless, the red tendrils have to be glowing hydrogen and the green ones have to be ionized oxygen. Or maybe the red filaments are from sulphur, the green ones from hydrogen and the blue ones (not that I can really see any blue ones) from either oxygen or helium. Whatever. Where is the "shrug" smilie?

The blue "background light" of the Crab comes from synchotron radiation, which is caused by electrons passing through a magnetic field at high speed (or something - I'd appreciate it if someone would elucidate). I once saw a spectrum of synchotron radiation, and I'm not so sure that it would look blue to the human eye.

Ann

The perspective of Thor's Helmet and the central star is amazing. It would seem that Thor's Helmet could contain not only the central star, but its planets if it had any. In other words, it seems that it is so large that it could contain our Sun and all its planets. That raises the question - might we be inside such a nebula? And, what would one of these look like from the inside?

A lot of people ask that, tom. If we were inside it we probably wouldn't be able to see it with the naked eye. in fact we are inside of something right now.

beyond wrote:well, its definitly not a blue tortise, but still does not resemble a helmet either. I like the blue -bubblely tortise that even has a blue head.
Maybe it would help if Thor's Hammer was near-by?

It kind of reminds me of a howling dog. When you click on the picture; and get the smaller view; it looks a lot better to me. The original overfills my computer screen anyway.

well that's a bit strange orin, when i click on the picture it gets bigger. And if i click again it becomes toooooo big for my screen which is 24" wide. And if i keep clicking it goes between big and almost filling the screen to toooooo big for the screen, until i click my upper left blue button that brings it back to the original size Apod displays it as.
So to me it looks even more like a blue tortise when the picture is bigger. And more Bubblelier also!

Ann wrote:The color balance seems slightly shifted to the red, apart from the fact that the blue color of the helmet is so obvious. But some of the stars look very orange, while none of the stars look strikingly blue. Nevertheless, some of the stars do display a faint bluish color, and many of the stars look white, so the color balance for the stars isn't that far off. The most orange one of the stars, to the upper right of the helmet, probably is very red for real.

"Color balance" doesn't mean anything in this image, because it was produced through filters that don't mimic the response of the eye. The image is a hybrid of conventional RGB (which does approximate the eye's response) along with OIII and Ha. The OIII signal was assigned to the green and blue output channels, and Ha to red. This will obviously produce something quite unlike "true" color.

The red "horns" of the helmet are obviously glowing red from ionized hydrogen. It is interesting that the red "arc" at lower right and the red patch at lower left are a much duller red color, particularly the "arc". Could the arc be dust-reddened, and if so, could it be more dust-reddened than the "horns"? No, it looks more like a mixture of red emission nebulosity, blue reflection nebulosity and some unlit dust, all pretty much mixed up and muted-looking.

Those areas look redder to me. That is, they appear to be closer to a single channel signal, while the upper areas have some signal from green and blue. The only reason the lower areas look "duller" is because they are darker. Dark pure red will look dull compared to a brighter mix of red and other colors. The only really obvious dust I see is just below the bubble itself.

The bubble itself is very blue from oxygen emission. It's interesting that it contains no red nebulosity at all. The reason must be that the bubble contains no hydrogen at all. The outer hydrogen shell has been blown off, and the remnants are seen as the red "horns" of the helmet.

It may contain hydrogen in other states of ionization, or neutral. Those would not show up as red in this image.

The bubble is richly textured, and I have no idea why that is so. Could it possibly have anything at all to do with magnetism?

It may, in part, be due to the magnetic properties of the star that threw the material off. But it is probably also a fluid dynamic effect, caused by turbulence. Filaments like this are easily created by many different forces. Magnetic fields are suggested to maintain large filamentary structures against destruction by stellar winds. That isn't happening here- the bubble is dissipating and the filaments are evaporating. In a few thousand years this object will be gone.

When I see an image of Thor's Helmet, the radio in my head always plays Elmer Fudd singing "Spear and magic helmet! And I'll give you a sammm-ple." :: trumpet call :: "North winds bro! South winds bro!" and so on.

("SMOG!")

This is a lovely shot.

beyond wrote:well that's a bit strange orin, when i click on the picture it gets bigger. And if i click again it becomes toooooo big for my screen which is 24" wide. And if i keep clicking it goes between big and almost filling the screen to toooooo big for the screen, until i click my upper left blue button that brings it back to the original size Apod displays it as.
So to me it looks even more like a blue tortise when the picture is bigger. And more Bubblelier also!

That's interesting beyond. It must be a computer thing! Actually mine stretches the picture and then jumps to the smaller version on it's own. To get the larger picture I have to click again. I wish the original version was the same size as my screen rather than being bigger than it.

orin stepanek wrote:

beyond wrote:well that's a bit strange orin, when i click on the picture it gets bigger. And if i click again it becomes toooooo big for my screen which is 24" wide. And if i keep clicking it goes between big and almost filling the screen to toooooo big for the screen, until i click my upper left blue button that brings it back to the original size Apod displays it as.
So to me it looks even more like a blue tortise when the picture is bigger. And more Bubblelier also!

That's interesting beyond. It must be a computer thing! Actually mine stretches the picture and then jumps to the smaller version on it's own. To get the larger picture I have to click again. I wish the original version was the same size as my screen rather than being bigger than it.

I think you are both saying the same thing. When you click on the APOD, it brings up the hires which on most browsers will automatically resize to fit in the window (at whatever size you have your window). Click on that and it toggles between full image size and window size. I usually have multiple windows open, so the hires is also initially smaller than the APOD for me (usually), but if I expand the window to full screen, the hires expands with it.

Orin, if you change your screen resolution size to a higher resolution, you can get the apod image to fit. I always set my screen resolution at the max.

Hi,

really nice image! I like the high resolution!

geckzilla wrote:A lot of people ask that, tom. If we were inside it we probably wouldn't be able to see it with the naked eye. in fact we are inside of something right now.

We may be about to enter something else.
http://asterisk.apod.com/vie ... 05#p122305

According to geckzilla's link, what we are in is 6000' C. So if it wasn't for the solar wind blowing against it----we would be toasted humans!!
What a predicament!! Have a sun and keep warm and get radiated --or-- not have a sun and get "welded" together because of the 6000' heat.
What a STRANGE place


also--I've got windows 7. Sometimes its just strange too!

temperature of about 6000 °C,[1] about the same temperature as the surface of the Sun. It is very tenuous, with 0.1 atoms per cubic centimeter; approximately one-fifth the density of the galactic interstellar medium (0.5 atoms/cc) and twice that of the gas in the Local Bubble (0.05 atoms/cc), the Local Bubble being an area of low-density in the interstellar medium, with the Local Cloud a small, more dense area. In comparison, Earth's atmosphere at STP has 2.7 × 1019 molecules per cubic centimeter.

As rarefied as that cloud is I don't think the 6000 degrees C would be very problematic. I would be curious to see how our early space probes would fare once they leave the confines of the sun's bubble.
Voyager! > V ger > http://www.google.com/imglanding?q=star ... yM&start=0
Will these probes eventually orbit back toward the sun; or have they broken the pull of the sun's gravity?

beyond wrote:According to geckzilla's link, what we are in is 6000' C. So if it wasn't for the solar wind blowing against it----we would be toasted humans!!

What a predicament!! Have a sun and keep warm and get radiated --or-- not have a sun and get "welded" together because of the 6000' heat.

According to recent research, it maybe about to get hotter.

The density of the particles is so low that it is less than any hard vacuum on Earth. So, although the particles radiate at a temperature of 6000' C, if you were there, you would freeze if you didn't die of explosive decompression first.

The temperature of the local interstellar cloud contributes nothing to Earth temperatures.

Chris wrote:

It may contain hydrogen in other states of ionization, or neutral. Those would not show up as red in this image.

Yes, there are other states of ionization for hydrogen than hydrogen alpha. There is hydrogen beta, for example, a higher state of ionization, which produces a blue-green light, similar to OIII radiation. So indeed, in theory the bubble may be full of hydrogen beta emission, and it would not show up as red at all.

However, Chris, hydrogen alpha is the dominant form of hydrogen ionization, or at least I have always thought so. Is it really likely that you could have significant hydrogen beta emission without having any appreciable hydrogen alpha emission at all?

Also, is it likely that you could have significant amounts of neutral hydrogen in the immediate vicinity of OIII radiation, which represents a relatively "high" state of ionization and which occurs only in very "energetic" environments?

Chris also said:

Those areas look redder to me. That is, they appear to be closer to a single channel signal, while the upper areas have some signal from green and blue. The only reason the lower areas look "duller" is because they are darker. Dark pure red will look dull compared to a brighter mix of red and other colors. The only really obvious dust I see is just below the bubble itself.

This sounds reasonable.

Finally, Chris, you said this about the filamentary structure of the bubble:

It may, in part, be due to the magnetic properties of the star that through the material off. But it is probably also a fluid dynamic effect, caused by turbulence. Filaments like this are easily created by many different forces. Magnetic fields are suggested to maintain large filamentary structures against destruction by stellar winds. That isn't happening here- the bubble is dissipating and the filaments are evaporating. In a few thousand years this object will be gone.

Thank you for your explanation!

Ann

bystander -- you mean we can do a "Tiny Tim" out in space past the solar bubble and Tip-Toe through the Hot particules while we freeze solid??

orin stepanek wrote:I would be curious to see how our early space probes would fare once they leave the confines of the sun's bubble. Voyager! > V ger > <img>. Will these probes eventually orbit back toward the sun; or have they broken the pull of the sun's gravity?

(http://www.spacetoday.org/SolSys/Voyagers20years.html)
Voyager 1 is departing the Solar System at a speed of 39,000 mph. Voyager 2 is departing the Solar System at a speed of 35,000 mph. Eventually, the Voyagers will pass other stars: Voyager 1, in 40,000 years, will float by within 1.6 light years of star AC+79 3888 in the constellation Camelopardalis. Voyager 2, in 296,000 years, will sail within 4.3 light years of Sirius.

(Wikipedia on Pioneer 10)
Pioneer 10 is heading in the direction of Aldebaran. According to the estimated trajectory, it has not yet passed the heliopause or the Oort cloud (1 December 2008). There is no longer communication with the probe; the last contact was in 2003 and in 2006 a final attempt at contact failed.

(Wikipedia on Pioneer 11)
Pioneer 11 is now estimated to be following an escape trajectory from the solar system. Pioneer 11 will pass near the star Lambda (λ) Aquilae in about 4 million years time. There is no longer communication with the spacecraft; the last contact was in November 1995.

Case wrote: Voyager 1 is departing the Solar System at a speed of 39,000 mph. Voyager 2 is departing the Solar System at a speed of 35,000 mph. Eventually, the Voyagers will pass other stars: Voyager 1, in 40,000 years, will float by within 1.6 light years of star AC+79 3888 in the constellation Camelopardalis. Voyager 2, in 296,000 years, will sail within 4.3 light years of Sirius.

Thanks Case! That was very interesting reading. Those Voyagers were built tough!

beyond wrote:According to geckzilla's link, what we are in is 6000' C. So if it wasn't for the solar wind blowing against it----we would be toasted humans!!

It's around 1500°C where the ISS orbits, and it's doing just fine. Even without a bubble around us, 6000°C interstellar gas wouldn't transfer enough energy to matter.

NASA Pioneer Mission Pages

• http://www.nasa.gov/mission_pages/pioneer/
  http://www.nasa.gov/centers/ames/missio ... oneer.html

NASA Voyager Mission Pages

• http://www.nasa.gov/mission_pages/voyager/
  http://voyager.jpl.nasa.gov/