APOD: Dark Molecular Cloud Barnard 68 (2017 Oct 08)

[APOD Robot]

Dark Molecular Cloud Barnard 68

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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[Boomer12k]

Great close up of this mysterious place...what would a person on a planet inside the thickest part of the center be able to see? How big, and dense would it have to be for them not to know there was anything beyond the darkness?

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[heehaw]

Nice to see the 2014 Dec 14 APOD again, it is a great one! And it is also wonderful that we can LOOK INSIDE that cloud, via infrared!
https://www.eso.org/public/usa/news/eso9934/

[Chris Peterson]

Great close up of this mysterious place...what would a person on a planet inside the thickest part of the center be able to see? How big, and dense would it have to be for them not to know there was anything beyond the darkness?

From much of the interior, you would see no stars at all (as there appear to be none inside the cloud). Keep in mind just how small this is- about the size of our solar system. It's also not apparent how you could ever have an inhabited planet inside such a cloud. Perhaps a planet around a fast moving star could briefly pass through such a cloud.

[neufer]

[b][color=#0000FF]The ESO Very Large Telescope (VLT) observed a classical dark globule, Barnard 68 (B68) , in front of a dense star field in the Milky Way band. CCD images were obtained in various visual wavebands with the FORS1 multi-mode instrument at the 8.2-m VLT ANTU (UT1). They were combined into a colour photo.[/color][/b]

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Unique Infrared SOFI Images of Barnard 68
Probe the Very First Stages of Star Formation
Secrets of a Dark Cloud, 2 July 1999

<<SOFI (Son OF ISAAC) is a scaled-down copy of ISAAC, the major VLT instrument that has already produced spectacular observations. SOFI is a unique instrument for the study of extended objects like B68 because of its very sensitive infrared detector and unrivalled large field-of-view.

The new SOFI images of B68 are now being studied by ESO astronomer João Alves and his collaborators, in particular Charles Lada (Harvard-Smithsonian Center for Astrophysics, Mass., USA) and Elizabeth Lada (University of Florida, USA). Several interesting conclusions can be drawn already.

Through careful measurements of the colour of the background stars that are seen through the cloud, it is now possible to determine the total amount of obscuration at the center of the cloud. It turns out to be no less than 35 magnitudes in the V-band at wavelength 0.55 µm. This number corresponds to a dimming of the starlight of a factor of no less than 10¹⁴ !

If, in a thought experiment, a sheet of dust with this high degree of obscuration were placed in front of the Sun, there would be eternal darkness on the Earth. Our central star would then shine with magnitude 9 only, i.e. it would be about 15 times too faint to be observable with the naked eye!

The small-scale structure of B68 seems to be very smooth and homogeneous. The SOFI observations rule out the presence of "clumpy" structures inside the cloud, on nearly all scales. The new data clearly show that B68 is now in the very early phase of collapse, on its way towards star formation. The duration of such a stage is relatively short, of the order of 100,000 years, and to catch a cloud in this phase is likely to be a rare occurrence. If the collapse had been going on for a little longer, it would not have been possible to see through this cloud today, since the obscuration would then have been much higher, of the order of hundreds of magnitudes. Moreover, the observed distribution of matter inside B68 provides us a first glimpse of how nature begins to form stars. These outstanding observations will now be used to test current theories of protostellar collapse.

The total mass of the dust in B68 comes to about 0.03 solar mass. If the gas-to-dust ratio in B68 is what is normally assumed, about 100, then the total mass of this cloud is about 3 solar masses. Accordingly, only a few stars will eventually form in this cloud.>>

[neufer]

Perhaps a planet around a fast moving star could briefly pass through such a cloud.

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<<Edward Emerson Barnard (December 16, 1857 – February 6, 1923) was an American astronomer best known for his discovery of the high proper motion of Barnard's Star in 1916, which is named in his honor.

His father died three months before his birth in Nashville, Tennessee, so he grew up in an impoverished family and did not receive much in the way of formal education. His first interest was in the field of photography, and he became a photographer's assistant at the age of nine. In 1876 he purchased a 5-inch refractor telescope, and in 1881 he discovered his first comet, but failed to announce his discovery. He found his second comet later the same year and a third in 1882. Hulbert Harrington Warner offered $200 per discovery of a new comet. Edward discovered a total of five, and used the money to build a house for himself and his bride.

With his name being brought to the attention of amateur astronomers in Nashville, they collectively raised enough money to give Edward a fellowship to Vanderbilt University. Barnard never graduated from the school, but he did receive the only honorary degree Vanderbilt has ever awarded. He joined the staff of the Lick Observatory in 1887.

In 1889 he observed the moon Iapetus pass behind Saturn's rings. As he watched Iapetus pass through the space between Saturn's innermost rings and the planet itself, he saw a shadow pass over the moon. Although he did not realise it at the time, he had discovered proof of the "spokes" of Saturn, dark shadows running perpendicular to the circular paths of the rings. These spokes were doubted at first, but confirmed by the spacecraft Voyager 1. In 1892 he made observations of a nova and was the first to notice the gaseous emissions, thus deducing that it was a stellar explosion. The same year he also discovered Amalthea, the fifth moon of Jupiter. He was the first to discover a new moon of Jupiter since Galileo Galilei in 1609. This was the last satellite discovered by visual observation.

In 1895 he joined the University of Chicago as professor of astronomy. There he was able to use the 40-inch telescope at Yerkes Observatory. Much of his work during this period was taking photographs of the Milky Way. Together with Max Wolf, he discovered that certain dark regions of the galaxy were actually clouds of gas and dust that obscured the more distant stars in the background. He cataloged a series of dark nebulae, known as Barnard objects, giving them numerical designations akin to the Messier catalog. They begin with Barnard 1 and end with Barnard 370.>>

[John Champagne]

Without having studied the topic in any detail, I would guess that a prominent theory of the formation of these types of clouds would refer to their formation in areas far from forces that would disperse them, that would break them up. If there is stellar wind blowing and photon pressure from many directions across a span of millions of years, then material previously ejected into the interstellar void would tend to collect at a region of balance, where the push from one side roughly matches the push from another.

[Boomer12k]

Great close up of this mysterious place...what would a person on a planet inside the thickest part of the center be able to see? How big, and dense would it have to be for them not to know there was anything beyond the darkness?

From much of the interior, you would see no stars at all (as there appear to be none inside the cloud). Keep in mind just how small this is- about the size of our solar system. It's also not apparent how you could ever have an inhabited planet inside such a cloud. Perhaps a planet around a fast moving star could briefly pass through such a cloud.

Well, "planet" is Hypothetical... but it is interesting that it may be thick enough that if there WERE one with life...they would not see an outside Universe... thinking they are the "only ones".... I hope they are nice to each other.

Thanks for the viewpoint... this is actually a concept for a one of my stories... a star has wondered into such a place...people evolved and don't know about the outside...it is a MUCH LARGER molecular area, (as solar wind would blow a lot away, and does make a cavern they are in, but is so vast they are no where near exiting any time soon... but the main character points out eventually that they WILL come out of it... because HE is from the outside...
Just a story idea...
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[Jim Leff]

I've done some looking around, but can't find an answer: anyone know the density? I.e., how many particles per cubic mile in a typical dark cloud?

[neufer]

I've done some looking around, but can't find an answer: anyone know the density?
I.e., how many particles per cubic mile in a typical dark cloud?

~3 micrograms of dust per cubic mile:

• 1) 0.03 solar masses = 6 x 10³⁷ micrograms of dust
  2) "half a light-year across" ~ 2 x 10³⁷ cubic miles

<<The total mass of the dust in B68 comes to about 0.03 solar mass. If the gas-to-dust ratio in B68 is what is normally assumed, about 100, then the total mass of this cloud is about 3 solar masses. Accordingly, only a few stars will eventually form in this cloud.>>

[Jim Leff]

Scale is quite a thing!