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Author Topic: The Arms of NGC 4258  (Read 2829 times)
WarHorse
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« Topic Start: April 11, 2007, 08:41:31 pm »

http://antwrp.gsfc.nasa.gov/apod/ap070411.html

Can someone help me wrap my brain around this?

What is causing the blue arms/spirals?  The article mentions shock waves - from WHAT?  That is trillions of megatons!

And why don't the regular arms show this phenomena?
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« Reply #1: April 11, 2007, 08:47:57 pm »

http://antwrp.gsfc.nasa.gov/apod/ap070411.html

Can someone help me wrap my brain around this?

What is causing the blue arms/spirals?  The article mentions shock waves - from WHAT?  That is trillions of megatons!

And why don't the regular arms show this phenomena?

I'm no astrophysicist, but I notice that at the end of the paragraph the writer mentions "powerful jets originating in the galaxy's core" that he says  "likely drive the shocks into the disk". That's about all I have for ya, sorry...

Jets of gasses? Maybe?

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« Reply #2: April 11, 2007, 09:22:31 pm »

What is causing the blue arms/spirals? 

The blue is likely a "false color" (a color added in processing) as the blue and purle "arms" are said to be in visible only in radio and X-ray.

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The article mentions shock waves - from WHAT?  That is trillions of megatons!

The article styates there are powerful jets of gas coming out of the core (probably caused by a supermassive black hole absorbing a lot in incoming material -- my guess). These could easily produce the shock waves mentioned. And yes, that is a Lot of energy. But remember out little star, the Sun, puts out the equivalent of about million megatons of energy every second and a solar flare can can put out over billion megatons of energy in a minute or two.

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And why don't the regular arms show this phenomena?

The jets (and shock waves they cause) are directional.
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« Reply #3: April 12, 2007, 07:07:13 am »

The jets (and shock waves they cause) are directional.

Ah-ha!  That's what was tripping me up, I was assuming they would be omnidirectional.  Thank you!  Smiley
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« Reply #4: April 12, 2007, 08:19:10 am »

Ah-ha!  That's what was tripping me up, I was assuming they would be omnidirectional.  Thank you!  Smiley

Here's an example of just how directional these jets generally are. The galaxy in this image is an elliptical galaxy (instead of a spiral, so no arms), but the directional nature of the jet is clear.

http://apod.nasa.gov/apod/ap000706.html
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« Reply #5: April 13, 2007, 11:01:43 pm »

What is causing the blue arms/spirals? 
I think I'm going to agree with Randall on the black hole

And I suspect the curved spiral arms occur because the black hole is slowly spinning (or at least wobbling) perpendicular to it plane of rotation (notice how the outer-most arms are perturbed where the jets have crossed the galactic plane) ... Now wrap your brain around that one  Huh

I would have thought the gyro-effect of the spinning disc would have prevented that from happening, but there's the evidence. The only thing I can think of is that an instability in the accretion disc might cause the whole system to wobble

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That is trillions of megatons!
Small potatoes for a black hole in a feeding frenzy

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And why don't the regular arms show this phenomena?
The do appear to have been affected
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« Reply #6: April 14, 2007, 08:07:11 am »

And I suspect the curved spiral arms occur because the black hole is slowly spinning (or at least wobbling) perpendicular to it plane of rotation (notice how the outer-most arms are perturbed where the jets have crossed the galactic plane) ... Now wrap your brain around that one  Huh

Actually, I can!  Grin  Once I figured out (years ago) that the jets come off the poles, it all came together.

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I would have thought the gyro-effect of the spinning disc would have prevented that from happening, but there's the evidence. The only thing I can think of is that an instability in the accretion disc might cause the whole system to wobble

Maybe the thing isn't centered?  Or is close to a nebula?  Or perhaps was part of a binary system and the partner is still there?

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« Reply #7: April 14, 2007, 01:14:06 pm »

Or perhaps was part of a binary system and the partner is still there?
It would take something pretty massive to disturb a supermassive black hole, but a second black hole, orbiting it, might do it
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« Reply #8: April 16, 2007, 04:40:38 pm »

Galaxy's Ghostly Arms Finally Explained

Scientists have discovered the source of a galaxy's two extra, ghostly spiral arms that show up only in some telescope images, cracking a 45-year-old mystery.

http://www.space.com/scienceastronomy/070416_mm_ghostly_arms.html
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« Reply #9: April 16, 2007, 06:15:05 pm »

Galaxy's Ghostly Arms Finally Explained

Scientists have discovered the source of a galaxy's two extra, ghostly spiral arms that show up only in some telescope images, cracking a 45-year-old mystery.

http://www.space.com/scienceastronomy/070416_mm_ghostly_arms.html

Very cool.  Thanks!
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