Discover 4 Milky Way Arms: Older Galaxies?

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In summary: Not sure this helps, but spiral arms are not permanent structures. They are an artifact of density waves, as stars move in and out of the arms.In summary, the new map confirms that four spiral arms wind through the Milky Way galaxy. Two arms are more prominent and jam-packed with stars, while the Sagittarius and Outer arms have as much gas as the other two arms but not as many stars. The minor arms (Sagittarius & Outer) are more tightly wound.
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TEFLing
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https://Earth'sky.org/space/new-map-confirms-four-milky-way-arms
young-stars-milky-way-e1433529533593.jpg

...four spiral arms. The arms are where most stars in the galaxy are born. They contain most of the galaxy’s gas and dust, the raw ingredients for new stars.

Two of the arms, called Perseus and Scutum-Centaurus, seem to be more prominent and jam-packed with stars, while the Sagittarius and Outer arms have as much gas as the other two arms but not as many stars.​

The "minor" arms (Sagittarius & Outer) are more tightly wound. How can one spiral galaxy have more than one type of arm winding, aren't spirals classified according to a single degree of arm winding?

Are the more tightly wound arms, which evidently lack as many bright young stellar nurseries, older structures?
 

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  • #2
Not sure this helps, but spiral arms are not permanent structures. They are an artifact of density waves, as stars move in and out of the arms.
 
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  • #3

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  • #5
Actual raw data of 21cm radiation from Molecular Clouds is much messier, like M101, obvious "swirling whorl" of dust-lanes, yet without any grandly designed arms.

Hence, our position in the "Orion Spur" arm segment is unsurprising, the whole whirling maelstrom of dust-lanes in the MWG disk is much more complex that the artist impression "cartoon" publicized widely on the web.

Obviously the artist's impression is better for outreach, yet the actual data is more complicated:

bjDoE.jpg
References:
https://astronomy.stackexchange.com...y-early-21-cm-map-of-the-milky-way-oort-et-al
https://www.researchgate.net/publication/228773700_Observations_of_Milky_Way_at_21_cm_Wavelength_at_the_Bosscha_Observatory
Milky Way nurseries with 21cm raw data twice over.png
 

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  • #6
Interesting to see the actual radio data, it could be interesting to compare it with Gaia's star map. But what causes the "shadow" in the direction of Galactic anticenter? Orion molecular cloud complex?
 
  • #7
Ratman said:
Interesting to see the actual radio data, it could be interesting to compare it with Gaia's star map. But what causes the "shadow" in the direction of Galactic anticenter? Orion molecular cloud complex?
think that's the solar system ecliptic plane, but great question
 
  • #8
The data would be more funky at 0 and 180 degrees. It is co-rotating. The distance of a pixel is determined by the blue/red shift of the gas emission. At 180 the shift is just the random motion of the gas and does not indicate distance.
 
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  • #9
From raw data:

Milky Way map with arms.jpg


Milky Way map.jpg


Offer that the Milky Way more resembles Andromeda (M31) or NGC 2841

Andromeda-Galaxy-M31-NASA.jpg


ngc2841_hstColombari_1080.jpg
 

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  • #10
Spiral structure in disk galaxies is not an exact science. See the work of Elmgreen and Elmgreen, Vassar College, on "flocculent spiral galaxies" or look at images of them on the Hubble website to see the wide variations among spirals.
 
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  • #11
lemme add one more thing :)

Hard to tell what's happening within the Solar radius of 8kpc

However, found some data on 21cm emission at large radii up to 25kpc... suggests our galaxy more resembles M101 "Pinwheel Galaxy", and that like that major spiral, our galaxy is also ~50kpc across

Milky Way map modern large.png


Milky Way map modern large annotated.png


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1. What are the 4 Milky Way arms?

The 4 Milky Way arms are named the Perseus Arm, the Sagittarius Arm, the Cygnus Arm, and the Outer Arm. They are spiral arms made up of stars, gas, and dust that extend outwards from the center of our galaxy.

2. How were these arms discovered?

These arms were discovered through observations using infrared and radio telescopes. By studying the distribution and movement of stars and gas in the Milky Way, scientists were able to identify and map out these arms.

3. Why are older galaxies important to study?

Studying older galaxies can provide valuable insights into the formation and evolution of our own Milky Way. They can also help us understand the larger scale structure and history of our universe.

4. What does the discovery of these arms tell us about the Milky Way?

The discovery of these arms confirms our understanding of the structure of the Milky Way as a spiral galaxy. It also allows us to better understand the movement and interactions of stars and gas within our galaxy.

5. How will this discovery impact future research?

This discovery will open up new avenues of research into the formation and evolution of galaxies. It will also serve as a basis for further investigations into the dynamics and composition of the Milky Way and other spiral galaxies.

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