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The Nearby Milky Way in Cold Dust

Explanation: What shapes the remarkable dust tapestry of the nearby Milky Way Galaxy? No one knows for sure. The intricate structures, shown above, were resolved in new detail recently in a wide region of the sky imaged in far infrared light by the European Space Agency's Planck satellite. The above image is a digital fusion of three infrared colors: two taken at high resolution by Planck, while the other is an older image taken by the now defunct IRAS satellite. At these colors, the sky is dominated by the faint glow of very cold gas within only 500 light years of Earth. In the above image, red corresponds to temperatures as cold as 10 degrees Kelvin above absolute zero, while white corresponds to gas as warm at 40 Kelvins. The pink band across the lower part of the image is warm gas confined to the plane of our Galaxy. The bright regions typically hold dense molecular clouds that are slowly collapsing to form stars, whereas the dimmer regions are most usually diffuse interstellar gas and dust known as cirrus. Why these regions have intricate filamentary shapes shared on both large and small scales remains a topic of research. Future study of the origin and evolution of dust may help in the understanding the recent history of our Galaxy as well as how planetary systems such as our Solar System came to be born.

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Grammar police alert:

while white corresponds to gas as warm at 40 Kelvins.

Did you mean - as warm AS ?

HellCat wrote:Grammar police alert:

while white corresponds to gas as warm at 40 Kelvins.

Did you mean - as warm AS ?

Did you mean - as warm AS 40 Kelvin?

That's a gorgeous picture. Art, even. Wow!

10 degrees Kelvin above absolute zero

While we are picking nits, shouldn't that be either 10 Kelvin or 10 degrees above absolute zero.

It's interesting to compare this with the original IRAS image from the 1980s:

http://galaxymap.org/mwe/mwe.php?centre ... _markers=1

bystander wrote:

10 degrees Kelvin above absolute zero

While we are picking nits, shouldn't that be either 10 Kelvin or 10 degrees above absolute zero.

Yep, I subscribe to this, I wanted to make the note myself, but you was faster than me

kjardine, thank you for that link. Wow! I need to collect the whole set; they should be on canvas.

What is the wave in that picture?

it is beautiful, it makes me think of waves crashing on the beach, except there isn't a beach, just more wave-crashing below!

(( chuckling )) loved the excellent survey up top .....

Does the pink in the picture represent an average temperature along the galaxy plane that is inbetween the other 2 temps quoted?

And thanks to kjardine for pointing out that wonderful website!

bystander wrote:While we are picking nits, shouldn't that be either 10 Kelvin or 10 degrees above absolute zero.

I think it is correct (but a bit awkward) as it is. Kelvins are used without "degrees", but "degrees" by itself doesn't mean anything, so requires modification to identify the system being used- in this case, the Kelvin scale. When used as a unit by itself, however, "Kelvin" should always be written "kelvin" (uncapitalized), following SI convention.

sarahstitcher wrote:it is beautiful, it makes me think of waves crashing on the beach, except there isn't a beach, just more wave-crashing below!

http://en.wikipedia.org/wiki/The_Great_Wave_off_Kanagawa wrote:


<<The Great Wave off Kanagawa (神奈川沖浪裏, Kanagawa Oki Nami Ura?, lit. "Under a Wave off Kanagawa") is a famous woodblock print by the Japanese artist Hokusai. It was published in 1832 (Edo Period) as the first in Hokusai's series 36 Views of Mount Fuji and is his most famous work. It depicts an enormous wave threatening boats near the Japanese prefecture of Kanagawa. While sometimes assumed to be a tsunami, the wave is more likely to be a large okinami. (Japanese "ocean wave".)>>

I hope "the nearby Milky Way Galaxy" doesn't confuse anyone into thinking the Milky Way is some external galaxy like Andromeda. I trust that frequent APOD readers are clear on this (especially those who read the comments!), but at least according to one website, a majority of Americans do not know that the Earth and Sun are part of the Milky Way galaxy: http://www.sntp.net/education/education_stats.htm.

Dan Coe wrote:I hope "the nearby Milky Way Galaxy" doesn't confuse anyone into thinking the Milky Way is some external galaxy like Andromeda. I trust that frequent APOD readers are clear on this (especially those who read the comments!), but at least according to one website, a majority of Americans do not know that the Earth and Sun are part of the Milky Way galaxy: http://www.sntp.net/education/education_stats.htm.

Good point. By convention, "Milky Way" usually refers to the visible structure of star lanes and dust we see in the night sky, and "Milky Way Galaxy" usually refers to the galaxy we live in. At the least, "Galaxy" could have been left off in that description. Referring to something as "nearby" when you are inside it is a bit peculiar (from the living room: I'm just going to pop into the kitchen of my nearby house...)

sarahstitcher wrote:it makes me think of waves crashing on the beach

I can see that.

I was asking about the wave (don't know what I'd call it -- too square to be sine, not square enough to be square?) that is visible in the image kjardine linked to.

owlice wrote:What is the wave in that picture?

The "wave" is part of the Sco OB2 association, the nearest OB association to our solar system. It consists of many extremely hot O and B class stars immersed in the Ophiuchus dust clouds. Many of these stars are visible without optical aid as Scorpius, the Scorpion.

You can read a bit more here on Sco OB2:

http://galaxymap.org/drupal/node/81

and see what the region looks like in false colour hydrogen-alpha (a frequency of visible light given off by ionised hydrogen gas).

owlice wrote:

sarahstitcher wrote:it makes me think of waves crashing on the beach

I can see that.

I was asking about the wave (don't know what I'd call it -- too square to be sine, not square enough to be square?) that is visible in the image kjardine linked to.

Ah, I though that you were referring to the APOD image.

If you mean the faint blue S-shaped curve in the Galaxy Map IRAS image, that is the local zodiacal dust in our solar system. The IRAS data has been re-processed to remove most of the local dust, but some of it is still visible.

Very creative poll, bystander I mean, it was you, wasn't it.

makc wrote:Very creative poll, bystander I mean, it was you, wasn't it.

not me RJN is my guess.

edit: I now believe it was Otto Posterman.

kjardine, thank you very much! I beg your indulgence; I have another question... why does the local zodiacal dust show up as a wave? Rather, how it is that it is so well organized? I thought the wave might possibly be an oscillation artifact from processing of some kind; I didn't think it'd be real data!

(I don't know whether my questions make any sense, and I apologize in advance if they don't!)

owlice wrote:kjardine, thank you very much! I beg your indulgence; I have another question... why does the local zodiacal dust show up as a wave? Rather, how it is that it is so well organized? I thought the wave might possibly be an oscillation artifact from processing of some kind; I didn't think it'd be real data!

(I don't know whether my questions make any sense, and I apologize in advance if they don't!)

It's because of the data projection. The sky is curved and the map is flat. In the usual equatorial celestial coordinates (right ascension and declination), the zodiacal dust shows up as a straight line and the Milky Way as an S-shaped arc.

See here for a recent example:

http://antwrp.gsfc.nasa.gov/apod/ap100320.html

Galactic coordinates used by Planck and the Galaxy Map images reverse this, so the galactic plane is a straight line and the local dust is bent into a curved arc.

Correction: As explained below, the zodiacal dust appears as a straight line in ecliptic coordinates, not equatorial coordinates.

owlice wrote:why does the local zodiacal dust show up as a wave? Rather, how it is that it is so well organized?

Anything that is linear on the sky- that is, lies on a plane containing the Earth, will show up as a sine-like curve on a wide field image mapped to a plane. The only exception is for objects that lie on the plane defining an inclination of zero in the data coordinates. Those objects will describe a simple line on the projection.

Imagine that you hold a hula hoop flat (inclination 0°) at eye level, and turn around inside it. Clearly it describes a line through the middle of your visual field. Now tip it (say, inclination 45°). Clearly, it will be low in your visual field when you are turned in one direction, high opposite that, and crossing diagonally through your field in between those two positions. If you were to plot the vertical position of the hoop at each angle of rotation, you'd get a sine curve.

On a very wide field astronomical image, the horizontal axis is usually the angle as the camera has rotated, and the vertical axis is the angle away from the plane of rotation.

Just to add that in celestial coordinates the zodiacal dust is a straight line because it is concentrated within the plane of our solar system.

I believe that this concentration was caused by the original debris disk out of which all eight planets (and the Sun itself) formed.

AH!! Gentlemen, thank you very much! Okay, that makes total sense to me now (and doh!!)!! Thank you!!

Just to add one correction (although I'm sure that someone else would jump in to add this if I didn't):

the zodiacal dust appears as a straight line using ecliptic coordinates, not equatorial coordinates.

With equatorial coordinates both the zodiacal dust and the galactic plane appear as sine waves as they are oriented to the Earth's equator and not to either the plane of the solar system or the Milky Way.