Starship Asterisk*

[quote=Ann post_id=332177 time=1688967235 user_id=129702]
[img]https://asterisk.apod.com/download/file.php?id=47854&t=1[/img]Likely mechanism for creating the red ridge of NGC 6559
[/quote]

This ridge— judging by visible brightness of the likely stellar wind sources — should drift in 2 o'clock direction.

I wonder if we know some H-alpha triple peaks somewhere

[img]https://images.squarespace-cdn.com/content/v1/5486978ce4b0997b9acf758a/1452642589397-XYBLXL3XTLBXT30FRC19/image-asset.png[/img]

[attachment=1]NGC6559_Block_960.jpg[/attachment]
The dark nebula looks somewhat like a snake :roll:
[attachment=0]Toilet-Paper-660x371.jpg[/attachment]
Naughty doggy! :lol2:

Thanks. That makes a lot of sense.

[quote="Chris Peterson" post_id=332193 time=1689005440 user_id=117706]


Most of the volume of space is free of any particles (other than virtual ones). A true vacuum. But the density of particles is high enough that in most of the Universe the volume of particle free areas is small- cubic millimeters or less.
[/quote]

[quote=zendae post_id=332192 time=1689004643 user_id=143056]
"...the dust boils away, the gas gets swept away..."

There are a lot of tiny motes out there getting swept and blown hither and thither. I wonder if there is a 'particle to 3D area' ratio that determines when there is and when there is not a vacuum. Or is a vacuum such an absolute that it doesn't actually exist. Between visible and dark matter, is space a vacuum anywhere? Is it only a quantum size state. Is any space that has no particle in it a tiny vacuum.
[/quote]

Most of the volume of space is free of any particles (other than virtual ones). A true vacuum. But the density of particles is high enough that in most of the Universe the volume of particle free areas is small- cubic millimeters or less.

"...the dust boils away, the gas gets swept away..."

There are a lot of tiny motes out there getting swept and blown hither and thither. I wonder if there is a 'particle to 3D area' ratio that determines when there is and when there is not a vacuum. Or is a vacuum such an absolute that it doesn't actually exist. Between visible and dark matter, is space a vacuum anywhere? Is it only a quantum size state. Is any space that has no particle in it a tiny vacuum.

Just wanted to give a hearty shoutout to the OpenStax Astronomy textbook that anyone can either read for free online or download the full 1133 page PDF and read offline with an e-reader. One big benefit of all the textbooks available at OpenStax is that they are constantly being updated to reflect new information, such as the JWST images from the [url=https://openstax.org/books/astronomy-2e/pages/21-1-star-formation]link[/url] about star formation provided in the APOD text.

Good stuff! - see https://openstax.org/details/books/astronomy-2e

[float=left][attachment=1]APOD 10 July 2023 annotated.png[/attachment][c][size=85][color=#0040FF]Stars, Dust and Nebula in NGC 6559
Image Credit & Copyright: Adam Block, Telescope Live[/color][/size][/c][/float][float=right][attachment=0]Likely mechanism for creating red ridge in APOD 10 July 2023.png[/attachment][c][size=85][color=#0040FF]Likely mechanism for creating the red ridge of NGC 6559[/color][/size][/c][/float]
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NGC 6559 is a young region of star formation. It is full of gas and dust. A long winding dust lane seems to connect the hot O-type star 11 Sagittarii (HD 165921) with the blue reflection nebula illuminated by newborn B-type stars. The reason why the the reflection nebula is blue is because the B-type stars are not hot enough to ionize a red emission nebula. The likely reason why the red ridge is so very red is that it is being "pushed from two directions" and ionized by clashing stellar winds. Of course the ultraviolet light from 11 Sgr also contributes strongly to the ionization of ridge.

There are some similarities between the NGC 6559 region (the subject of today's APOD) and the star forming region of Perseus and Taurus:


[float=left][img3="The California nebula (left), IC 348 (center) and the Pleiades (right). Credit: Rogelio Bernal Andreo."]https://external-preview.redd.it/DF2Pr6jQh-_KnwO5krIElFgE21Hrnz9HpicLM0J8Vm8.jpg?width=1080&crop=smart&auto=webp&v=enabled&s=ef75ae48dd9b21590d7fb13271a43ab4bbd2b228[/img3][/float][float=right][img3="The California Nebula and ionizing star Xi Per (right). Credit: Yannick Akar."]https://apod.nasa.gov/apod/image/2103/NGC1499_Akar_960.jpg[/img3][/float]
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The California Nebula is being both "pushed" and ionized by O-type star Xi Per.

Perhaps the mechanism for creating the red ridge of NGC 6559 is slightly similar.

Ann

[url=https://apod.nasa.gov/apod/ap230710.html] [img]https://apod.nasa.gov/apod/calendar/S_230710.jpg[/img] [size=150]Stars, Dust and Nebula in NGC 6559[/size][/url]

[b] Explanation: [/b] When stars form, pandemonium reigns. A [url=https://openstax.org/books/astronomy-2e/pages/21-1-star-formation]textbook[/url] case is the star forming region [url=https://en.wikipedia.org/wiki/NGC_6559]NGC 6559[/url]. Visible in the [url=https://www.adamblockphotos.com/ngc-6559.html]featured image[/url] are red glowing [url=https://en.wikipedia.org/wiki/Emission_nebula]emission nebula[/url]s of [url=https://www.nasa.gov/topics/technology/hydrogen/index.html]hydrogen[/url], blue [url=https://en.wikipedia.org/wiki/Reflection_nebula]reflection nebulas[/url] of [url=https://apod.nasa.gov/apod/ap030706.html]dust[/url], dark [url=https://astronomy.swin.edu.au/cosmos/D/Dark+Nebula]absorption nebulas[/url] of dust, and the stars that formed from them. The [url=https://apod.nasa.gov/apod/ap030610.html]first massive stars[/url] formed from the dense gas will emit [url=https://science.nasa.gov/ems/10_ultravioletwaves]energetic light[/url] and [url=https://esahubble.org/wordbank/stellar-wind/]winds[/url] that erode, fragment, and [url=https://apod.nasa.gov/apod/ap070606.html]sculpt[/url] their birthplace. And then they [url=http://heasarc.gsfc.nasa.gov/docs/snr.html]explode[/url]. The resulting [url=https://sounddogconnection.com/wp-content/uploads/2018/07/Toilet-Paper-660x371.jpg]morass[/url] can be as beautiful as it is [url=https://apod.nasa.gov/apod/ap200706.html]complex[/url]. After tens of millions of years, the dust [url=https://youtu.be/1uUFI0w5Tj0]boils[/url] away, the gas gets swept away, and all that is left is a bare [url=https://en.wikipedia.org/wiki/Open_cluster]open cluster[/url] of stars.


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