APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

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APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by APOD Robot » Sun Jan 29, 2023 5:06 am

Image Barnard 68: Dark Molecular Cloud

Explanation: Where did all the stars go? What used to be considered a hole in the sky is now known to astronomers as a dark molecular cloud. Here, a high concentration of dust and molecular gas absorb practically all the visible light emitted from background stars. The eerily dark surroundings help make the interiors of molecular clouds some of the coldest and most isolated places in the universe. One of the most notable of these dark absorption nebulae is a cloud toward the constellation Ophiuchus known as Barnard 68, pictured here. That no stars are visible in the center indicates that Barnard 68 is relatively nearby, with measurements placing it about 500 light-years away and half a light-year across. It is not known exactly how molecular clouds like Barnard 68 form, but it is known that these clouds are themselves likely places for new stars to form. In fact, Barnard 68 itself has been found likely to collapse and form a new star system. It is possible to look right through the cloud in infrared light.

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Re: APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by Ann » Sun Jan 29, 2023 5:52 am


Don't know about you, but Barnard 68 looks like a puny little molecular cloud to me. What stars can be born from it?


Maybe a small red dwarf star and planets can be born from Barnard 68? Well... at best!
Wikipedia wrote:
Barnard 68 is a molecular cloud, dark absorption nebula or Bok globule, towards the southern constellation Ophiuchus and well within the Milky Way galaxy at a distance of about 500 light-years...

Because of its opacity, its interior is extremely cold, its temperature being about 16 K (−257 °C/-431 °F). Its mass is about twice that of the Sun and it measures about half a light-year across.

Its mass is about twice that of the Sun!!! Come on! This entire cloud weighs less than the combined Sirius A+B system!!! :shock:

Let's compare Barnard 68 with NGC 1333, which is a low- and medium-mass star forming nebula in Perseus.

Dusty NGC 1333 is seen as a reflection nebula in visible light images, sporting bluish hues characteristic of starlight reflected by dust. But at longer infrared wavelengths, the interstellar dust itself glows - shown in red in this false-color Spitzer Space Telescope image. The penetrating infrared view also shows youthful stars that would otherwise still be obscured by the dusty clouds which formed them. Notably, greenish streaks and splotches that seem to litter the region trace the glow of cosmic jets blasting away from emerging young stellar objects as the jets plow into the cold cloud material. In all, the chaotic scene likely resembles one in which our own Sun formed over 4.5 billion years ago. NGC 1333 is a mere 1,000 light-years distant in the constellation Perseus. Credit: R. A. Gutermuth (Harvard-Smithsonian CfA) et al. JPL-Caltech, NASA

Wikipedia wrote about NGC 1333:
The nebula region has a combined mass of approximately 450 M, while the cluster contains around 150 stars with a median age of a million years and a combined mass of 100 M.

So the mass of the NGC 1333 nebula is some 200 times greater than the mass of Barnard 68. And the stars that have been born from the NGC 1333 nebula weigh less than a fourth as much as the remaining nebula. So how many stars can be born from a dark cloud that weighs just twice as much as the Sun? Just saying.


My own favorite picture of a dark nebula is the infrared portrait of dark cloud FeSt 1-457 by 2MASS:



Looks good! :yes:

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Re: APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by MarkBour » Sun Jan 29, 2023 9:09 am

Nice additional examples, Ann.
Andreas Burkert and Jo ̃ao Alves in their paper do not seem to dwell on an expected solar mass, but they indicate they expect the Barnard 68 cloud could result in a star "much like our own Sun". If it begins with 2 solar masses, this is not a problem. Our Sun contains 99.86% of the mass of our solar system.
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Re: APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by orin stepanek » Sun Jan 29, 2023 1:51 pm

barnard68v2_vlt_960.jpg
Black; & Cold; Brrrr! Not very nice; but probably safer than a Black Hole1 :mrgreen:
hqdefault.jpg
Dogyys don't know either how bernard clouds form! :lol2:
Last edited by orin stepanek on Sun Jan 29, 2023 3:05 pm, edited 1 time in total.
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Re: APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by VictorBorun » Sun Jan 29, 2023 2:21 pm

Ann wrote: Sun Jan 29, 2023 5:52 am Don't know about you, but Barnard 68 looks like a puny little molecular cloud to me. What stars can be born from it?
Ann
Do I get it right: we think Barnard 68 is no farther than 500 ly away and no less than 2 solar masses because we do not happen to see any star in front of it.

As far as we know Barnard 68 can be closer and smaller.

Like The Black Cloud by Fred Hoyle, 1957

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Re: APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by De58te » Sun Jan 29, 2023 4:04 pm

Something to think about. The interior which is only half a light year across is the most isolated place in the universe? Even more isolated than the intergalactic space between two galaxies that are far apart? Even though the gas must be thick in the center in order to block background light from stars. But since this dust cloud is some 500 light years away from the Earth and there are no stars seen in the foreground, wouldn't the space between it and the Earth say at 250 light years away in a straight line be more isolated than the dust in the cloud itself? By the way how can you measure it is 500 light years away since I don't think complete darkness can make a spectrogram image?

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Re: APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by Chris Peterson » Sun Jan 29, 2023 4:09 pm

De58te wrote: Sun Jan 29, 2023 4:04 pm Something to think about. The interior which is only half a light year across is the most isolated place in the universe? Even more isolated than the intergalactic space between two galaxies that are far apart? Even though the gas must be thick in the center in order to block background light from stars. But since this dust cloud is some 500 light years away from the Earth and there are no stars seen in the foreground, wouldn't the space between it and the Earth say at 250 light years away in a straight line be more isolated than the dust in the cloud itself? By the way how can you measure it is 500 light years away since I don't think complete darkness can make a spectrogram image?
I take "isolated" in this context to refer to the visible separation from the rest of the Universe. The way a person is isolated in a dark closet, even if they're only a few meters away from a bunch of people outside that closet.

You can't use spectroscopy to measure distance at all, except at cosmological distances (distant galaxies and beyond).
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Re: APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by Holger Nielsen » Sun Jan 29, 2023 4:36 pm

I am intrigued with the comparison of Barnard 68 in visible and infrared light, as presented by ESO https://www.eso.org/public/images/eso0102c/:

Image

Background stars are heavily reddened from the passage of their light through the cloud; red colour chosen to represent light from the infrared K-band. Mean wavelengths are 436 nm for B, 545 nm for V, 798 nm for I and 1215 nm for K (the first three values from https://sites.astro.caltech.edu/~george ... 43p293.pdf, the last one from Allen’s Astrophysical Quantities; I could not find a single source (book, Intenet) giving them all).

Image caption: "ESO Press Photo eso0102 shows a comparison of the central area of globule B68 in a colour composite of visible and near-infrared on the left and a false-colour composite based on a visible (here rendered as blue), a near-infrared (green) and an infrared (red) on the right."

Image credit: ESO.

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Re: APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by MoreInput » Sun Jan 29, 2023 6:15 pm

Would it be possible to make a "deep field" in visible light of this region? The idea behind is not to find more details in the barnard cloud, but try to find every object between the cloud and the earth. So we may get some brown dwarfs here, some runaway planets maybe.

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Re: APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by Cousin Ricky » Sun Jan 29, 2023 6:18 pm

APOD Robot wrote: Sun Jan 29, 2023 5:06 am What used to be considered a hole in the sky is now known to astronomers as a dark molecular cloud.
A bit of thought shows that it would be prohibitively improbable for it to be a hole in the sky, even if we didn’t have the infrared images. Such a hole would have to be a roughly conical wedge with its apex centered on our solar system, a truly impressive challenge to the Copernican principle.

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Re: APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by AVAO » Sun Jan 29, 2023 7:48 pm

orin stepanek wrote: Sun Jan 29, 2023 1:51 pm ...Black; & Cold; Brrrr! Not very nice; but probably safer than a Black Hole don't know either how bernard clouds form! :lol2:
I wouldn't be so sure about that, considering how the little black Barnard 68 puff is being sucked right into the maw of the big black Banshee dragon in the Infrared :evil:

Click to view full size image 1 or image 2
jac berne (flickr)

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Re: APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by Ann » Sun Jan 29, 2023 8:12 pm

AVAO wrote: Sun Jan 29, 2023 7:48 pm
orin stepanek wrote: Sun Jan 29, 2023 1:51 pm ...Black; & Cold; Brrrr! Not very nice; but probably safer than a Black Hole don't know either how bernard clouds form! :lol2:
I wouldn't be so sure about that, considering how the little black Barnard 68 puff is being sucked right into the maw of the big black Banshee dragon in the Infrared :evil:

Click to view full size image 1 or image 2
jac berne (flickr)
Wow, AVAO! I never asked myself where Barnard 68 is located. You just showed me that it is located right next to the Snake Nebula in Ophiuchus! And the Snake Nebula is apparently the king of a virtual zoo of cosmic dust creatures in Ophiuchus, and there is a lovely blue star there too, Theta Ophiuchi!

Barnard 68 and Snake Nebula Jac Berne.png
Barnard 68 and the Snake Nebula by Jac Berne(?)
Snake Nebula Theta Ophiuchi and the Ophiuchi Zoo StarryEarth on Flickr.png
The Snake Nebula, Barnard 68, Theta Ophiuchi (at right), Saturn (left)
and the Ophiuchi Zoo. Credit: StarryEarth on Flickr

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Re: APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by MarkBour » Mon Jan 30, 2023 1:47 am

VictorBorun wrote: Sun Jan 29, 2023 2:21 pm
Ann wrote: Sun Jan 29, 2023 5:52 am Don't know about you, but Barnard 68 looks like a puny little molecular cloud to me. What stars can be born from it?
Ann
Do I get it right: we think Barnard 68 is no farther than 500 ly away and no less than 2 solar masses because we do not happen to see any star in front of it.

As far as we know Barnard 68 can be closer and smaller.

Like The Black Cloud by Fred Hoyle, 1957
From what we can see, it has to be closer than almost all of the stars in the image. Statistically, if it were farther than any more than 1-2%, there is just no way it would be completely devoid of an intervening star or two. And it is certainly closer than the stars that can be observed through it in infrared. So, that should put an upper limit on its distance. Several articles I browsed today happily pointed out roughly this reasoning.

But whether it could be smaller and closer is a great question!

Gaia has taken data from the region, and of course all it finds for this is that there are no stars to plot there. (Evidently the Gaia mission data is using an instrument that can capture between near-UV and near-IR, so it does not look like it will measure any obscured stars that are behind the cloud.) Still, at these distances, parallax measurement will be useful for distance computation. If Barnard 68 were only 100 ly from us, for example, it would have quite a parallax motion, changing which stars it obscured at its edges.

Frustratingly, most articles I've looked at today seem to have smugly placed its distance at 500 ly, without ever giving any reference evidence that would deny a smaller distance calculation. At visible wavelengths, as is clear in the posted image for today, many stars near its edge are dimmed, presumably by the cloud material which is less at the edge of the cloud. Parallax motion should show them at least changing in brightness, if not completely disappearing/appearing as a result of our local motion. From all of the authoritative claims about its distance, one gets the impression that somebody has looked at the data and done this. But I can't find a citation for any such work.

Here's a notice in the Royal Astronomical Society of a technique that is being used on nearby Bok globules:
Distance estimation of some selected small Bok globules by A. Das, H. S. Das, A. Senorita Devi
Kudos to their creative technique, it does not need to wait for parallax data to be built up to give an estimate within about +/-20%.
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Re: APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by Ann » Mon Jan 30, 2023 10:28 am

MarkBour wrote: Mon Jan 30, 2023 1:47 am
VictorBorun wrote: Sun Jan 29, 2023 2:21 pm
Ann wrote: Sun Jan 29, 2023 5:52 am Don't know about you, but Barnard 68 looks like a puny little molecular cloud to me. What stars can be born from it?
Ann
Do I get it right: we think Barnard 68 is no farther than 500 ly away and no less than 2 solar masses because we do not happen to see any star in front of it.

As far as we know Barnard 68 can be closer and smaller.

Like The Black Cloud by Fred Hoyle, 1957
From what we can see, it has to be closer than almost all of the stars in the image. Statistically, if it were farther than any more than 1-2%, there is just no way it would be completely devoid of an intervening star or two. And it is certainly closer than the stars that can be observed through it in infrared. So, that should put an upper limit on its distance. Several articles I browsed today happily pointed out roughly this reasoning.

But whether it could be smaller and closer is a great question!

Gaia has taken data from the region, and of course all it finds for this is that there are no stars to plot there. (Evidently the Gaia mission data is using an instrument that can capture between near-UV and near-IR, so it does not look like it will measure any obscured stars that are behind the cloud.) Still, at these distances, parallax measurement will be useful for distance computation. If Barnard 68 were only 100 ly from us, for example, it would have quite a parallax motion, changing which stars it obscured at its edges.

Frustratingly, most articles I've looked at today seem to have smugly placed its distance at 500 ly, without ever giving any reference evidence that would deny a smaller distance calculation. At visible wavelengths, as is clear in the posted image for today, many stars near its edge are dimmed, presumably by the cloud material which is less at the edge of the cloud. Parallax motion should show them at least changing in brightness, if not completely disappearing/appearing as a result of our local motion. From all of the authoritative claims about its distance, one gets the impression that somebody has looked at the data and done this. But I can't find a citation for any such work.

Here's a notice in the Royal Astronomical Society of a technique that is being used on nearby Bok globules:
Distance estimation of some selected small Bok globules by A. Das, H. S. Das, A. Senorita Devi
Kudos to their creative technique, it does not need to wait for parallax data to be built up to give an estimate within about +/-20%.
Mark, let me present an argument that Barnard 68 is probably at a distance of ~500 light-years, using pictures of nebulas and Hipparcos and Gaia parallaxes of stars to make my case.

Let me begin with a picture:


So Barnard 68 is located very close to the Snake Nebula. Yes, but Barnard 68 (and the Snake Nebula) are located in an area in Ophiuchus that is chock full of dust structures, including the large Pipe Nebula and a long dust lane leading straight up to the Antares/Rho Ophiuchi cloud complex:

Barnard 68 Pipe Nebula Theta Oph Rho Ophiuchi Naoyuki Kurita.png
Barnard 68 among many dust structures in Ophiuchus.
Credit: Naoyuki Kurita

As you can see, there is a huge number of large and small dust clouds in the vicinity of Barnard 68. One of them is the very large Pipe Nebula, and another is a very long structure leading up to the Antares/Rho Ophiuchi cloud complex. I argue that there can be no doubt that the dust lane leading up to the Antares/Rho Ophiuchi complex must be a remnant of the same nebula that gave birth to Antares, Rho Ophiuchi and many other stars in this colorful cloud complex.

Very many of the stars in the Antares/Rho Ophiuchi cloud complex are too bright for Gaia to measure their parallaxes, but a quick search turned up two whose parallaxes had been measured by Gaia: HD 147196, with a Gaia parallax of 7.2448 milliarcseconds (with an uncertainty of 0.0265 mas), and HD 146706, with a Gaia parallax of 7.0808 ± 0.0504 mas. Disregarding the uncertainties, these parallaxes put the two stars at 450 and 460 light-years.

I want to draw your attention to another star, Theta Ophiuchi, a hot blue star of spectral class B2IV. Even though this is not a blisteringly hot star of spectral class O, I argue that it is still hot enough, and it blows a sufficiently strong stellar wind, to strongly affect the dust structures around it. For example, I argue that the rounded shape of the Pipe Nebula could very well be a result of Theta Oph blowing the dust and gas of the Pipe Nebula away from it.

I also argue that the Pipe Nebula and the long dust structure leading up to the Antares/Rho Ophiuchi complex are connected. I can't prove it, but it seems very likely to me. This in turn leads me to conclude that most (if not all) of the dust structures inside the large arc formed by the Pipe Nebula and the dust lane feeding the Antares/Rho Ophiuchi complex are part of the same huge (if fractured) dust complex. And if so, they should be at more or less the same distance from us.

I argue that Theta Ophiuchi is a key player in this dust structure. I believe that this star was born from this dust, so that it should be at more or less the same distance as the dust clouds. Moreover, I argue that Theta Ophiuchi is very similar to the bright blue stars of the Antares/Rho Ophiuchi complex, so that it was born at more or less the same time and with a similar mass as the bright blue stars of upper Scorpius. So how far is Theta Ophiuchi? Unfortunately, Theta Oph is too bright for Gaia to measure its parallax, but Hipparcos puts it at 7.48 ± 0.17 mas, which corresponds to 436 light-years.

To summarize: I argue that the numerous scattered dust structures in Ophiuchus, including Barnard 68, are remnants of a major starforming event that took place some - oh, 15 million years ago? - and which are all located some 400-500 light-years away from us.

It is of course possible that Barnard 68 is a foreground or a background object that has nothing to do with all the other dust clouds around it. But Occam's Razor says that we should assume that Barnard 68 is located at more or less the same distance as all the other dust structures around it, unless we have good reasons to believe otherwise.

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Re: APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by VictorBorun » Tue Jan 31, 2023 7:00 pm

Ann wrote: Mon Jan 30, 2023 10:28 am I argue that the numerous scattered dust structures in Ophiuchus, including Barnard 68, are remnants of a major starforming event that took place some - oh, 15 million years ago? - and which are all located some 400-500 light-years away from us.

It is of course possible that Barnard 68 is a foreground or a background object that has nothing to do with all the other dust clouds around it. But Occam's Razor says that we should assume that Barnard 68 is located at more or less the same distance as all the other dust structures around it, unless we have good reasons to believe otherwise.
so this is not a small curious black cloud coming our way after all…

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Re: APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by VictorBorun » Tue Jan 31, 2023 7:04 pm

MarkBour wrote: Mon Jan 30, 2023 1:47 am Parallax motion should show them at least changing in brightness, if not completely disappearing/appearing as a result of our local motion.
a whole new field of the astrometry, watch the brightness of the stars at the edge of a Dark Cloud as Earth orbits Sun

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Re: APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by MarkBour » Fri Feb 03, 2023 12:24 am

VictorBorun wrote: Tue Jan 31, 2023 7:00 pm
Ann wrote: Mon Jan 30, 2023 10:28 am I argue that the numerous scattered dust structures in Ophiuchus, including Barnard 68, are remnants of a major starforming event that took place some - oh, 15 million years ago? - and which are all located some 400-500 light-years away from us.

It is of course possible that Barnard 68 is a foreground or a background object that has nothing to do with all the other dust clouds around it. But Occam's Razor says that we should assume that Barnard 68 is located at more or less the same distance as all the other dust structures around it, unless we have good reasons to believe otherwise.
so this is not a small curious black cloud coming our way after all…
Ann, that makes sense. I'm convinced !
Too bad; I liked the sci-fi reference, Victor, I had never heard of "The Black Cloud" it sounds like a great plot.
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Re: APOD: Barnard 68: Dark Molecular Cloud (2023 Jan 29)

Post by johnnydeep » Fri Feb 03, 2023 3:09 pm

MarkBour wrote: Fri Feb 03, 2023 12:24 am
VictorBorun wrote: Tue Jan 31, 2023 7:00 pm
Ann wrote: Mon Jan 30, 2023 10:28 am I argue that the numerous scattered dust structures in Ophiuchus, including Barnard 68, are remnants of a major starforming event that took place some - oh, 15 million years ago? - and which are all located some 400-500 light-years away from us.

It is of course possible that Barnard 68 is a foreground or a background object that has nothing to do with all the other dust clouds around it. But Occam's Razor says that we should assume that Barnard 68 is located at more or less the same distance as all the other dust structures around it, unless we have good reasons to believe otherwise.
so this is not a small curious black cloud coming our way after all…
Ann, that makes sense. I'm convinced !
Too bad; I liked the sci-fi reference, Victor, I had never heard of "The Black Cloud" it sounds like a great plot.
You can read a lot more about that book at the link below - at a site appropriate named "Black Gate", no less! - though if you haven't already read the book the article/review risks spoiling the plot:

https://www.blackgate.com/2020/05/07/a- ... ack-cloud/
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