APOD: A Night Sky over the Tatra Mountains (2024 Sep 11)

Post a reply


This question is a means of preventing automated form submissions by spambots.
Smilies
:D :) :ssmile: :( :o :shock: :? 8-) :lol2: :x :P :oops: :cry: :evil: :roll: :wink: :!: :?: :idea: :arrow: :| :mrgreen:
View more smilies
BBCode is ON
[img] is ON
[url] is ON
Smilies are ON
Topic review
   

Expand view Topic review: APOD: A Night Sky over the Tatra Mountains (2024 Sep 11)

Re: APOD: A Night Sky over the Tatra Mountains (2024 Sep 11)

by Ann » Thu Sep 12, 2024 6:30 am

AVAO wrote: ↑Thu Sep 12, 2024 5:20 am
Using the X-ray point sources from the Massive Young star-forming complex Study in Infrared and
X-rays (MYStIX) survey of OB-dominated region, the Lagoon Nebulae (1.3 kpc = app. 4200 ly) is closer then the omega nebulae ( 2.0 kpc = app. 6500 ly).
Thanks, Jac! I guess you are referring to this paper, https://iopscience.iop.org/article/10.1 ... 9/2/26/pdf. Thanks for pointing it out to me, because I would never have found it on my own.

The distance estimates you refer to are found in Table 1 in this paper. However, I'm doubtful of some of the distance estimates there. For example, the Trifid Nebula is said to be twice as distant as the Lagoon Nebula, 2.7 ± 0.5 kiloparsecs vs. 1.3+0.5 kiloparsecs. I can't believe that the Lagoon and the Trifid are so far apart.


There is no obvious connection between the Lagoon Nebula and the Trifid Nebula, the way there is between the Lagoon Nebula and the NGC 6559 complex, but in my opinion, the Lagoon and the Trifid look as if they are part of more or less the same large molecular cloud. Also, judging by the appearance of these two nebulas, the Trifid frankly looks intrinsically smaller than the Lagoon. The Trifid is circular, with just one small cluster visible right at the center, whereas the Lagoon Nebula is elongated and looks as if there have been multiple episodes of star formation in it. Also, with the exception of 9 Sagittarii, the brightest stars of the Lagoon Nebula are not (much) brighter than the central ionizing star of the Trifid, HD 164492.

The Gaia parallax of HD 164492 is 0.6843, corresponding to a distance of 1.4-1.5 kiloparsces. That makes it likely that the Trifid Nebula really is farther away than the Lagoon Nebula, but not twice as far away.

I note that the most of the distance estimates in Table 1 in the paper you referred to are from 2008. There may have been other results that have been produced after 2008 that may have revised these distance estimates.

Ann

Re: APOD: A Night Sky over the Tatra Mountains (2024 Sep 11)

by AVAO » Thu Sep 12, 2024 5:20 am

Ann wrote: ↑Wed Sep 11, 2024 9:20 am
thomasfrank wrote: ↑Wed Sep 11, 2024 4:27 am Can you tell me more about the Lagoon and Omega Nebulae, particularly their distance from Earth and their role in star formation?
Block Blast
Well, that is an interesting task you charged me with! I'll se what I can do.

First, let's take a look at the visual appearance of these two nebulas:


One thing is immediately obvious when we compare these two nebulas: We see the Lagoon Nebula face on (or more or less face on), but we see the Omega Nebula from the side.

The fact that we see the Lagoon Nebula more or less face on means that we can see stars inside it that probably, hopefully, are located more or less inside the Lagoon. If we can find out how far away some of these stars are, we can (hopefully) find out how far away the Lagoon Nebula is.

Take a look at this annotated image:


If we want to know the distances to stars, a good (but not perfect) way is to ask Gaia.
Wikipedia wrote about Gaia:

The spacecraft is designed for astrometry: measuring the positions, distances and motions of stars with unprecedented precision

Yes, Gaia is measuring the distances to stars with unprecedented precision, but not with perfect precision. Gaia measures the distances to stars by measuring their parallaxes:


A star's parallax is a measure of how much it appears to move against the background of distant stars as the Earth moves from "one end of its orbit around the Sun" to "the opposite end of its orbit around the Sun" six months later. The smaller the parallax, and the less the star appears to move, the more distant it is. Very distant stars have very small parallaxes, and a small error in the measurement can lead to huge errors.

Okay. I asked Simbad to tell me the parallaxes of 9 Sgr and Herschel 36. Simbad doesn't always provide Gaia parallaxes of stars, but in the case of 9 Sgr and Herschel 36, it does. The Gaia parallax of 9 Sgr is 0.8001±0.0728 milliarcseconds, corresponding to a distance of some 1250 parsecs, or a little more than 4,000 light-years. Note that the uncertainty of the parallax is almost 10%.

Herschel 36, at the center of the Lagoon Nebula, has a similar parallax, or a tiny bit smaller: 0.7749±0.0242, corresponding to a distance of some 4,200 light-years. We may note that the uncertainty is smaller here, for some reason. However, the two parallaxes are very similar, and it is very likely that the two stars are at very similar distances from us.

There is a relatively loose grouping of stars on the eastern (left) side of the Lagoon Nebula, NGC 6530:


One of the stars of NGC 6530 is HD 164906. Its parallax is 0.7443±0.0371, corresponding to a distance of some 4,400 light-years.

My conclusion from the parallaxes of three stars that appear to be located in the Lagoon Nebula is that the distance of the Lagoon Nebula is a bit more than 4000 light-years, but probably less than 4,500 light-years.

As for star formation in the Lagoon Nebula, Herschel 36 is very young. According to this site, Herschel 36 is about one million years old. Also, according to Wikipedia, four Herbig-Haro objects from embedded very young stars have been found near Herschel 36. But the loose clustering of stars called NGC 6530 is some 4-6 million years old, according to Wikipedia.


The Omega Nebula is a harder nut for me to crack than the Lagoon Nebula, because we see it from the side, so that no stars are visible inside it in optical light. Stars inside it are indeed visible at infrared wavelengths, but I don't think that Gaia can detect stars in infrared. Also I don't know the designations of any stars inside the Omega Nebula, and I don't know how to search for them.

But let's see what Wikipedia has to say about the Omega Nebula:
Wikipedia wrote:

The Omega Nebula is between 5,000 and 6,000 light-years from Earth and it spans some 15 light-years in diameter. The cloud of interstellar matter of which this nebula is a part is roughly 40 light-years in diameter and has a mass of 30,000 solar masses. The total mass of the Omega Nebula is an estimated 800 solar masses.

It is considered one of the brightest and most massive star-forming regions of our galaxy. Its local geometry is similar to the Orion Nebula except that it is viewed edge-on rather than face-on.

The open cluster NGC 6618 lies embedded in the nebulosity and causes the gases of the nebula to shine due to radiation from these hot, young stars; however, the actual number of stars in the nebula is much higher – up to 800, 100 of spectral type earlier than B9, and 9 of spectral type O,[citation needed] plus over a thousand stars in formation on its outer regions. It is also one of the youngest clusters known, with an age of just 1 million years.
I remember reading that the star formation inside the Omega Nebula has led to a "champagne flow" of gas out of the nebula, which is a phenomenon that is not seen in many star forming regions. We don't see it in the Orion Nebula, for example. Here is a good picture of the "champagne flow":


According to Wikipedia, there are nine stars of spectral class O in the Omega Nebula. That's a lot. There is only one O-type star in the Orion Nebula, Theta 1C Orionis, and then four more in constellation Orion (such as Meissa, Lambda Orionis, which is located quite far from the Orion Nebula). But the Omega Nebula is still a little bit similar to the Orion Nebula, according to Wikipedia:

Its local geometry is similar to the Orion Nebula except that it is viewed edge-on rather than face-on.

A recent APOD featured the Omega Nebula. In the discussion thread, AVAO (Jac) posted a fascinating picture of the Omega Nebula in infrared, revealing stars inside:


I pointed out that there is a little group of stars there that resembles the Trapezium in the Orion Nebula:

Trapezium like cluster in M17 NASA ESA SST jac berne.png
Trapezium in M17, the Omega Nebula?

Now let's try to compare the Lagoon Nebula and the Omega Nebula. The latter may be a bit more distant, although I'm not sure of it, but I do think that it definitely contains more O-type stars and almost certainly more ongoing star formation than the Lagoon.

Ann

Using the X-ray point sources from the Massive Young star-forming complex Study in Infrared and
X-rays (MYStIX) survey of OB-dominated region, the Lagoon Nebulae (1.3 kpc = app. 4200 ly) is closer then the omega nebulae ( 2.0 kpc = app. 6500 ly).

Re: APOD: A Night Sky over the Tatra Mountains (2024 Sep 11)

by Ann » Wed Sep 11, 2024 9:20 am

thomasfrank wrote: Can you tell me more about the Lagoon and Omega Nebulae, particularly their distance from Earth and their role in star formation?
Well, that is an interesting task you charged me with! I'll se what I can do.

First, let's take a look at the visual appearance of these two nebulas:


One thing is immediately obvious when we compare these two nebulas: We see the Lagoon Nebula face on (or more or less face on), but we see the Omega Nebula from the side.

The fact that we see the Lagoon Nebula more or less face on means that we can see stars inside it that probably, hopefully, are located more or less inside the Lagoon. If we can find out how far away some of these stars are, we can (hopefully) find out how far away the Lagoon Nebula is.

Take a look at this annotated image:


If we want to know the distances to stars, a good (but not perfect) way is to ask Gaia.
Wikipedia wrote about Gaia:

The spacecraft is designed for astrometry: measuring the positions, distances and motions of stars with unprecedented precision

Yes, Gaia is measuring the distances to stars with unprecedented precision, but not with perfect precision. Gaia measures the distances to stars by measuring their parallaxes:


A star's parallax is a measure of how much it appears to move against the background of distant stars as the Earth moves from "one end of its orbit around the Sun" to "the opposite end of its orbit around the Sun" six months later. The smaller the parallax, and the less the star appears to move, the more distant it is. Very distant stars have very small parallaxes, and a small error in the measurement can lead to huge errors.

Okay. I asked Simbad to tell me the parallaxes of 9 Sgr and Herschel 36. Simbad doesn't always provide Gaia parallaxes of stars, but in the case of 9 Sgr and Herschel 36, it does. The Gaia parallax of 9 Sgr is 0.8001±0.0728 milliarcseconds, corresponding to a distance of some 1250 parsecs, or a little more than 4,000 light-years. Note that the uncertainty of the parallax is almost 10%.

Herschel 36, at the center of the Lagoon Nebula, has a similar parallax, or a tiny bit smaller: 0.7749±0.0242, corresponding to a distance of some 4,200 light-years. We may note that the uncertainty is smaller here, for some reason. However, the two parallaxes are very similar, and it is very likely that the two stars are at very similar distances from us.

There is a relatively loose grouping of stars on the eastern (left) side of the Lagoon Nebula, NGC 6530:


One of the stars of NGC 6530 is HD 164906. Its parallax is 0.7443±0.0371, corresponding to a distance of some 4,400 light-years.

My conclusion from the parallaxes of three stars that appear to be located in the Lagoon Nebula is that the distance of the Lagoon Nebula is a bit more than 4000 light-years, but probably less than 4,500 light-years.

As for star formation in the Lagoon Nebula, Herschel 36 is very young. According to this site, Herschel 36 is about one million years old. Also, according to Wikipedia, four Herbig-Haro objects from embedded very young stars have been found near Herschel 36. But the loose clustering of stars called NGC 6530 is some 4-6 million years old, according to Wikipedia.


The Omega Nebula is a harder nut for me to crack than the Lagoon Nebula, because we see it from the side, so that no stars are visible inside it in optical light. Stars inside it are indeed visible at infrared wavelengths, but I don't think that Gaia can detect stars in infrared. Also I don't know the designations of any stars inside the Omega Nebula, and I don't know how to search for them.

But let's see what Wikipedia has to say about the Omega Nebula:
Wikipedia wrote:

The Omega Nebula is between 5,000 and 6,000 light-years from Earth and it spans some 15 light-years in diameter. The cloud of interstellar matter of which this nebula is a part is roughly 40 light-years in diameter and has a mass of 30,000 solar masses. The total mass of the Omega Nebula is an estimated 800 solar masses.

It is considered one of the brightest and most massive star-forming regions of our galaxy. Its local geometry is similar to the Orion Nebula except that it is viewed edge-on rather than face-on.

The open cluster NGC 6618 lies embedded in the nebulosity and causes the gases of the nebula to shine due to radiation from these hot, young stars; however, the actual number of stars in the nebula is much higher – up to 800, 100 of spectral type earlier than B9, and 9 of spectral type O,[citation needed] plus over a thousand stars in formation on its outer regions. It is also one of the youngest clusters known, with an age of just 1 million years.
I remember reading that the star formation inside the Omega Nebula has led to a "champagne flow" of gas out of the nebula, which is a phenomenon that is not seen in many star forming regions. We don't see it in the Orion Nebula, for example. Here is a good picture of the "champagne flow":


According to Wikipedia, there are nine stars of spectral class O in the Omega Nebula. That's a lot. There is only one O-type star in the Orion Nebula, Theta 1C Orionis, and then four more in constellation Orion (such as Meissa, Lambda Orionis, which is located quite far from the Orion Nebula). But the Omega Nebula is still a little bit similar to the Orion Nebula, according to Wikipedia:

Its local geometry is similar to the Orion Nebula except that it is viewed edge-on rather than face-on.

A recent APOD featured the Omega Nebula. In the discussion thread, AVAO (Jac) posted a fascinating picture of the Omega Nebula in infrared, revealing stars inside:


I pointed out that there is a little group of stars there that resembles the Trapezium in the Orion Nebula:

Trapezium like cluster in M17 NASA ESA SST jac berne.png
Trapezium in M17, the Omega Nebula?

Now let's try to compare the Lagoon Nebula and the Omega Nebula. The latter may be a bit more distant, although I'm not sure of it, but I do think that it definitely contains more O-type stars and almost certainly more ongoing star formation than the Lagoon.

Ann

APOD: A Night Sky over the Tatra Mountains (2024 Sep 11)

by APOD Robot » Wed Sep 11, 2024 4:06 am

Image A Night Sky over the Tatra Mountains

Explanation: A natural border between Slovakia and Poland is the Tatra Mountains. A prominent destination for astrophotographers, the Tatras are the highest mountain range in the Carpathians. In the featured image taken in May, one can see the center of our Milky Way galaxy with two of its famous stellar nurseries, the Lagoon and Omega Nebula, just over the top of the Tatras. Stellar nurseries are full of ionized hydrogen, a fundamental component for the formation of Earth-abundant water. As a fundamental ingredient in all known forms of life, water is a crucial element in the Universe. Such water can be seen in the foreground in the form of the Bialka River.

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

Top