APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Comments and questions about the APOD on the main view screen.
User avatar
APOD Robot
Otto Posterman
Posts: 4077
Joined: Fri Dec 04, 2009 3:27 am

APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by APOD Robot » Wed Oct 14, 2020 4:05 am

Image The Colorful Clouds of Rho Ophiuchi

Explanation: The many spectacular colors of the Rho Ophiuchi (oh'-fee-yu-kee) clouds highlight the many processes that occur there. The blue regions shine primarily by reflected light. Blue light from the Rho Ophiuchi star system and nearby stars reflects more efficiently off this portion of the nebula than red light. The Earth's daytime sky appears blue for the same reason. The red and yellow regions shine primarily because of emission from the nebula's atomic and molecular gas. Light from nearby blue stars - more energetic than the bright star Antares - knocks electrons away from the gas, which then shines when the electrons recombine with the gas. The dark brown regions are caused by dust grains - born in young stellar atmospheres - which effectively block light emitted behind them. The Rho Ophiuchi star clouds, well in front of the globular cluster M4 visible here on the upper right, are even more colorful than humans can see - the clouds emits light in every wavelength band from the radio to the gamma-ray.

<< Previous APOD This Day in APOD Next APOD >>

User avatar
Ann
4725 Å
Posts: 10826
Joined: Sat May 29, 2010 5:33 am

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by Ann » Wed Oct 14, 2020 6:27 am

Antares Rho Ophiuchi annotated.png
Let's look at what we are seeing here.

1) This is the yellow Antares nebula. Antares itself, a red supergiant, is the bright star to the lower right inside this nebula. Antares is rounder, smaller and a bit more well-behaved than the other famous red supergiant star in the sky, Betelgeuse. The yellow color of the nebula surrounding Antares is due to several factors, such as dust reddening and some scattered red Hα light, but mostly the nebula is a reflection nebula where yellow light from Antares has been scattered.

2) This is a globular cluster, NGC 6144.

3) This is a small group of blue stars that belong to the "Antares group". The brightest of these is 22 Scorpii, a main sequence star of spectral class B3V. The star is surrounded by a blue reflection nebula, IC 4605, of its own making.

4) This is a relatively dust-reddened star of spectral class A, surrounded by nebula IC 4603.Most fascinating, however, is the fact that right next to this star, deeply embedded in dust, many new baby stars are being hatched.

5) This is the rather famous blue Rho Ophiuchi reflection nebula. It is centered on a small group of B- and A-type main seuence stars, the brightest of which is Rho Ophiuchi itself, a star of spectral class B2V. It is the blue light of these stars that is scattered in the dusty nebula to make it look blue.

6) This is Sigma Scorpii, a binary star where one of the components belongs to spectral class O9.5V and is therefore hot enough to ionize a red emission nebula. Sigma Scorpii is surrounded by both a blue reflection nebula and a red emission nebula, as can be seen in this photo by Rolf Scheffer and the Astrofarm Kiripotib Namibia.

7) This is globular cluster M4.

8) This is the large but faint red reflection nebula surrounding star Tau Scorpii, a star of spectral class B0V. It is hot enough to ionize a faint red emission nebula. The star itself can't be seen in today's APOD.

Finally, let's compare today's APOD with the much more widefield picture of the same area in a photo (and an APOD) by Mario Cogo.

You can see the large pink nebula at lower left, surrounding Tau Scorpii. That pink nebula was number 8 in my annotated version of today's APOD.

Above and to the right of the pink Tau Scorpii nebula is the yellow Antares nebula. To the right of the yellow Antares nebula is globular cluster M4. Anbove and to the right of M4 is the rather small-looking pink and blue nebula surrounding (fairly bright-looking) Sigma Scorpii. To the left of Sigma Scorpii is 22 Scorpii and its small blue nebula. The very dark dusty nebula above and to the right of 22 Scorpii is where baby stars are being born. Above it is the blue Rho Ophiuchi nebula.

Above and to the right of the Roho Ophiuchi nebula is the Blue Horse nebula. The Blue Horse appears to be staring at the star Beta Scorpii.

Below and to the right of Beta Scorpii is Delta Scorpii, surrounded by a large but faint red emission nebula.

Below Delta Scorpii is Pi Scorpii, surrounded by a red emission nebula and a very funny-looking, angular blue reflection nebula.


Oh, and - you can never have enough pictures of this utterly fascinating region of the sky. Each picture shows you a new way of looking at this amazing nebular starscape. How about this beauty by Warren Keller, Jim Misti and Steve Mazlin?

Well, that's it for me today, I think!

Ann
You do not have the required permissions to view the files attached to this post.
Color Commentator

User avatar
rj rl
Ensign
Posts: 48
Joined: Tue Jul 23, 2013 3:37 am

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by rj rl » Wed Oct 14, 2020 7:37 am

Thank you for this detailed description, Ann. Seems to me that the APOD's explanation
red and yellow regions shine primarily because of emission
is not quite accurate?

User avatar
Ann
4725 Å
Posts: 10826
Joined: Sat May 29, 2010 5:33 am

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by Ann » Wed Oct 14, 2020 10:19 am

rj rl wrote:
Wed Oct 14, 2020 7:37 am
Thank you for this detailed description, Ann. Seems to me that the APOD's explanation
red and yellow regions shine primarily because of emission
is not quite accurate?
Red regions usually shine because of hydrogen emission. And hydrogen emission happens because hydrogen atoms have been ionized by energetic photons.

The illustration by Tom Whitney shows various electron shell series of the hydrogen atom, but let's stick to the very simplest discussion of the Balmer series. Basically, when an ultaviolet photon hits a hydrogen atom where the electron is in its lowest shell, the electron will (usually) be kicked "one level up" because it has absorbed energy from the photon. But the electron will soon "fall down" to its lowest shell again, and when it does so, it will emit a photon of red light at 656 nm. Normally some electrons will be kicked "two levels up", and when they fall down, they will emit a bluish cyan photon at 486 nm.

Together, the large number of red photons and the considerably smaller number of bluish cyan photons give emission nebulas their typical reddish pink color. Normally, the borders of emission nebulas are redder than the inner parts, which are more pink in color as they are closer to the ionizing source.


As for yellow nebulas, they are quite rare. I'd say that in most cases we are talking about either strong dust reddening of bluish starlight, or else scattering of yellow light, creating a yellow reflection nebula.















The Flame Nebula is one of the best known examples of a yellow nebula. Unlike the Antares Nebula, the Flame Nebula is a site of ongoing star formation. Already many stars have been born here and clearly they are emitting quite a lot of blue starlight. But because the Flame Nebula is so dusty, very much more dusty than the Antares nebula, the blue starlight is reddened to yellow light. I'd say it is also possible that dust in the nebula actually scatters the reddened starlight, so that it effectively functions as a yellow reflection nebula.

Possibly the most yellow nebula in the nearby sky in the Toby Jug Nebula. This nebula is illuminated by a red giant star, which is in its death throes so that it has begun to shed its outer, dusty atmosphere. However, the central star of the Toby Jug Nebula is still a cool red giant, even though it will moderately soon begin casting off its outer envelope altogether and transform into a blisteringly hot blue and ultraviolet white dwarf. For now, the light it emits is mostly yellow and red, and the dusty nebula of the star's own making scatters the starlight in a yellow nebula.

Ann
Color Commentator

User avatar
orin stepanek
Plutopian
Posts: 5766
Joined: Wed Jul 27, 2005 3:41 pm
Location: Nebraska

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by orin stepanek » Wed Oct 14, 2020 11:02 am

Looks great just to look at it! :clap: M4 almost gets lost in this vast display!

RhoAntares_Abolfath_1080.jpg
You do not have the required permissions to view the files attached to this post.
Orin

Smile today; tomorrow's another day!

sillyworm 2

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by sillyworm 2 » Wed Oct 14, 2020 11:38 am

Thanks Ann! Is the reason known for the central bar in M4?

User avatar
rj rl
Ensign
Posts: 48
Joined: Tue Jul 23, 2013 3:37 am

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by rj rl » Wed Oct 14, 2020 11:57 am

Very illuminating, Ann :mrgreen:

bls0326
Ensign
Posts: 91
Joined: Tue Mar 26, 2013 10:18 pm

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by bls0326 » Wed Oct 14, 2020 1:09 pm

Thanks Ann. Your annotated picture is very helpful.

User avatar
Ann
4725 Å
Posts: 10826
Joined: Sat May 29, 2010 5:33 am

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by Ann » Wed Oct 14, 2020 1:52 pm

sillyworm 2 wrote:
Wed Oct 14, 2020 11:38 am
Thanks Ann! Is the reason known for the central bar in M4?
Click to play embedded YouTube video.
No, I don't think so. But you are quite right, M4 does have a central bar. To my knowledge, no other globular cluster does.

The most probable reason why M4 has a bar is, I would guess, just coincidence. The bar is likely just a temporary stellar configuration as seen from the vantage point of the Earth.

I don't think that the bar of M4 is a "true" bar. That is, I don't think it is a gravitational feature caused by irregularities and torques in the rotating disk, because globular clusters don't have rotating disks. Gravitationally they are much like elliptical galaxies, where stars orbit around the center of the galaxy in all kinds of orbital planes.

Ann
Color Commentator

sillyworm 2

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by sillyworm 2 » Wed Oct 14, 2020 6:25 pm

Thanks Ann...That's what I thought.I just found it odd that it was described as a bar in a linked apod description.

User avatar
johnnydeep
Science Officer
Posts: 249
Joined: Sun Feb 20, 2011 8:57 pm

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by johnnydeep » Wed Oct 14, 2020 8:11 pm

Thanks Ann for your detailed explanations and image annotating! The APOD description left me fairly confused. In one reply you said:
"Basically, when an ultraviolet photon hits a hydrogen atom where the electron is in its lowest shell, the electron will (usually) be kicked "one level up" because it has absorbed energy from the photon. But the electron will soon "fall down" to its lowest shell again, and when it does so, it will emit a photon of red light at 656 nm."
I guess this is a physics question, but why doesn't the electron emit a photon of the same frequency as the one that hit it in the first place? Where does the difference in energy go?
"To Boldly Go......Beyond The Fields We Know."

User avatar
MarkBour
Subtle Signal
Posts: 1102
Joined: Mon Aug 26, 2013 2:44 pm
Location: Illinois, USA

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by MarkBour » Wed Oct 14, 2020 11:30 pm

I'll add another "Thanks, Ann !" Your annotations and descriptions were very helpful.
Mark Goldfain

User avatar
MarkBour
Subtle Signal
Posts: 1102
Joined: Mon Aug 26, 2013 2:44 pm
Location: Illinois, USA

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by MarkBour » Thu Oct 15, 2020 12:44 am

johnnydeep wrote:
Wed Oct 14, 2020 8:11 pm
Thanks Ann for your detailed explanations and image annotating! The APOD description left me fairly confused. In one reply you said:
"Basically, when an ultraviolet photon hits a hydrogen atom where the electron is in its lowest shell, the electron will (usually) be kicked "one level up" because it has absorbed energy from the photon. But the electron will soon "fall down" to its lowest shell again, and when it does so, it will emit a photon of red light at 656 nm."
I guess this is a physics question, but why doesn't the electron emit a photon of the same frequency as the one that hit it in the first place? Where does the difference in energy go?
I like this question, because I've wondered about it.

So, looking at: https://en.wikipedia.org/wiki/Emission_nebula and https://en.wikipedia.org/wiki/Balmer_series,
It seems that high-energy UV photons from an energetic star will completely ionize atomic or molecular hydrogen. The one photon results in a transition for the electron of many levels, or perhaps most often "to infinity" as viewed from the original atom that held it. Then later the electron will be captured by another ionized atom, starting out in one of the higher energy states (orbitals). After that, the electron works its way down to the lowest energy state with multiple emissions of lower-energy photons.

So it balances: one absorbed photon becomes several emitted photons. Also, some of the energy ends up as thermal energy in the gas.
Mark Goldfain

User avatar
MarkBour
Subtle Signal
Posts: 1102
Joined: Mon Aug 26, 2013 2:44 pm
Location: Illinois, USA

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by MarkBour » Thu Oct 15, 2020 12:54 am

RE:
Ann wrote:
Wed Oct 14, 2020 1:52 pm
https://www.youtube.com/watch?v=VF6J7P2cpn8

Ann
Interesting watching that simulation you posted. I saw lots of supernovae in the sequence. And it struck me that each supernova that goes off leaves behind a lot of mass in the region that we will no longer really see. If 1000 supernovas have gone off in the formation of the globular cluster, that leaves the mass of 1000 large stars in the region that you don't see much of, so you might not think to account for them in later simulations of the motions of the stars that are there. I would think that for the most part the mass remains "local, but distributed", though some portion of it may go towards building a "compact central beastie".
Mark Goldfain

User avatar
neufer
Vacationer at Tralfamadore
Posts: 17525
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by neufer » Thu Oct 15, 2020 1:32 am

Click to play embedded YouTube video.
sillyworm 2 wrote:
Wed Oct 14, 2020 6:25 pm

I just found it odd that it was described as a bar in a linked apod description.
https://en.wikipedia.org/wiki/Messier_4 wrote:
<<M4 is a rather loosely concentrated cluster of class IX and measures 75 light-years across. It features a characteristic "bar" structure across its core, visible to moderate sized telescopes. The structure consists of 11th-magnitude stars and is approximately 2.5' long and was first noted by William Herschel in 1783.>>
https://en.wikipedia.org/wiki/Knot_tabulation wrote: Ever since Sir William Thomson's vortex theory, mathematicians have tried to classify and tabulate all possible knots. As of May 2008, all prime knots up to 16 crossings have been tabulated (see below). The major challenge of the process is that many apparently different knots may actually be different geometrical presentations of the same topological entity, and that proving or disproving knot equivalence is much more difficult than it at first seems.

Code: Select all

n 		a(n)
..........................
1		0
2		0
3		1
4		1
5		2
6		3
7		7
8		21
9		49
10		165
11		552
12		2176
13		9988
14		46972
15		253293
16		1388705
Art Neuendorffer

User avatar
Ann
4725 Å
Posts: 10826
Joined: Sat May 29, 2010 5:33 am

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by Ann » Thu Oct 15, 2020 4:51 am

MarkBour wrote:
Thu Oct 15, 2020 12:44 am
johnnydeep wrote:
Wed Oct 14, 2020 8:11 pm
Thanks Ann for your detailed explanations and image annotating! The APOD description left me fairly confused. In one reply you said:
"Basically, when an ultraviolet photon hits a hydrogen atom where the electron is in its lowest shell, the electron will (usually) be kicked "one level up" because it has absorbed energy from the photon. But the electron will soon "fall down" to its lowest shell again, and when it does so, it will emit a photon of red light at 656 nm."
I guess this is a physics question, but why doesn't the electron emit a photon of the same frequency as the one that hit it in the first place? Where does the difference in energy go?
I like this question, because I've wondered about it.

So, looking at: https://en.wikipedia.org/wiki/Emission_nebula and https://en.wikipedia.org/wiki/Balmer_series,
It seems that high-energy UV photons from an energetic star will completely ionize atomic or molecular hydrogen. The one photon results in a transition for the electron of many levels, or perhaps most often "to infinity" as viewed from the original atom that held it. Then later the electron will be captured by another ionized atom, starting out in one of the higher energy states (orbitals). After that, the electron works its way down to the lowest energy state with multiple emissions of lower-energy photons.

So it balances: one absorbed photon becomes several emitted photons. Also, some of the energy ends up as thermal energy in the gas.
Thanks, Mark, that's very interesting!

Ann
Color Commentator

User avatar
Ann
4725 Å
Posts: 10826
Joined: Sat May 29, 2010 5:33 am

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by Ann » Thu Oct 15, 2020 5:09 am

MarkBour wrote:
Thu Oct 15, 2020 12:54 am
RE:
Ann wrote:
Wed Oct 14, 2020 1:52 pm
https://www.youtube.com/watch?v=VF6J7P2cpn8

Ann
Interesting watching that simulation you posted. I saw lots of supernovae in the sequence. And it struck me that each supernova that goes off leaves behind a lot of mass in the region that we will no longer really see. If 1000 supernovas have gone off in the formation of the globular cluster, that leaves the mass of 1000 large stars in the region that you don't see much of, so you might not think to account for them in later simulations of the motions of the stars that are there. I would think that for the most part the mass remains "local, but distributed", though some portion of it may go towards building a "compact central beastie".
I think massive stars make up a very small fraction of a globular cluster's original mass, because very massive stars are usually not that massive, and they are so rare. By contrast, low-mass stars are really not that low-mass, and they are so common.

Wikipedia's list of most massive stars lists less than 60 known stars whose mass is believed to be as high as or exceed 80 solar masses. That's not a lot. The most massive red dwarfs, by contrast, can be up to 60% of the Sun's mass, and no red dwarfs are allowed to have less than 7.5% of a solar mass in order to be able to fuse hydrogen to helium in their cores.

Also red dwarfs are believed to be by far the most common type of star in the Milky Way. Because of that, and because of their not inconsiderable mass, they may make up perhaps as much as 30-40% of the stellar mass of the Milky Way. The contribution of O-type stars to the total stellar mass of the Milky Way, by contrast, is indeed negligible.

So I don't think that the explosion of a number of supernovas in a globular cluster will affect its mass that much, except by driving off gas from the cluster and blowing away some of the jettisoned mass of the progenitor star out of the globular cluster.

Ann
Color Commentator

User avatar
MarkBour
Subtle Signal
Posts: 1102
Joined: Mon Aug 26, 2013 2:44 pm
Location: Illinois, USA

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by MarkBour » Thu Oct 15, 2020 3:35 pm

Ann wrote:
Thu Oct 15, 2020 5:09 am
MarkBour wrote:
Thu Oct 15, 2020 12:54 am
RE:
Ann wrote:
Wed Oct 14, 2020 1:52 pm
https://www.youtube.com/watch?v=VF6J7P2cpn8

Ann
Interesting watching that simulation you posted. I saw lots of supernovae in the sequence. And it struck me that each supernova that goes off leaves behind a lot of mass in the region that we will no longer really see. If 1000 supernovas have gone off in the formation of the globular cluster, that leaves the mass of 1000 large stars in the region that you don't see much of, so you might not think to account for them in later simulations of the motions of the stars that are there. I would think that for the most part the mass remains "local, but distributed", though some portion of it may go towards building a "compact central beastie".
I think massive stars make up a very small fraction of a globular cluster's original mass, because very massive stars are usually not that massive, and they are so rare. By contrast, low-mass stars are really not that low-mass, and they are so common.

Wikipedia's list of most massive stars lists less than 60 known stars whose mass is believed to be as high as or exceed 80 solar masses. That's not a lot. The most massive red dwarfs, by contrast, can be up to 60% of the Sun's mass, and no red dwarfs are allowed to have less than 7.5% of a solar mass in order to be able to fuse hydrogen to helium in their cores.

Also red dwarfs are believed to be by far the most common type of star in the Milky Way. Because of that, and because of their not inconsiderable mass, they may make up perhaps as much as 30-40% of the stellar mass of the Milky Way. The contribution of O-type stars to the total stellar mass of the Milky Way, by contrast, is indeed negligible.

So I don't think that the explosion of a number of supernovas in a globular cluster will affect its mass that much, except by driving off gas from the cluster and blowing away some of the jettisoned mass of the progenitor star out of the globular cluster.

Ann
Thanks, that's helpful. I hadn't thought about the fact that they're probably only a very small portion of the stars that get created.
Mark Goldfain

String Theory

Re: APOD: The Colorful Clouds of Rho Ophiuchi (2020 Oct 14)

Post by String Theory » Thu Oct 29, 2020 6:00 pm

neufer wrote:
Thu Oct 15, 2020 1:32 am
Click to play embedded YouTube video.
sillyworm 2 wrote:
Wed Oct 14, 2020 6:25 pm

I just found it odd that it was described as a bar in a linked apod description.
https://en.wikipedia.org/wiki/Messier_4 wrote:
<<M4 is a rather loosely concentrated cluster of class IX and measures 75 light-years across. It features a characteristic "bar" structure across its core, visible to moderate sized telescopes. The structure consists of 11th-magnitude stars and is approximately 2.5' long and was first noted by William Herschel in 1783.>>
https://en.wikipedia.org/wiki/Knot_tabulation wrote: Ever since Sir William Thomson's vortex theory, mathematicians have tried to classify and tabulate all possible knots. As of May 2008, all prime knots up to 16 crossings have been tabulated (see below). The major challenge of the process is that many apparently different knots may actually be different geometrical presentations of the same topological entity, and that proving or disproving knot equivalence is much more difficult than it at first seems.

Code: Select all

n 		a(n)
..........................
1		0
2		0
3		1
4		1
5		2
6		3
7		7
8		21
9		49
10		165
11		552
12		2176
13		9988
14		46972
15		253293
16		1388705

A string walks into a bar. Bartender says,"Hey, aren't you a string? We don't serve your kind here" and escorts the string out to the street. Outside, the string thinks a moment, ties himself into a bowand then throws himself to the ground and scuffs himself all up. He then walks back into the bar where the bartender says,"Hey, aren't you a string?" String shakes his head, sits down at the bar and says,"Frayed knot!"