APOD: Coreshine from a Dark Cloud (2010 Sep 30)

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Expand view Topic review: APOD: Coreshine from a Dark Cloud (2010 Sep 30)

Re: APOD: Coreshine from a Dark Cloud (2010 Sep 30)

by dougettinger » Wed Dec 22, 2010 6:47 pm

neufer wrote:
GaryR wrote:
The article that Art posted gives me an opportunity to ask a question that I have been pondering for some times. It is well known that stars are formed inside gas and dust clouds and planets are formed within the accretion disks around the newly formed stars. However, is it also possible that planets and small bodies such as asteroids can form inside the clouds independently of the stars and never accumulate enough matter to become stars themselves? If so, wouldn't every galaxies be filled with billions or even trillions of objects too small to be detected by even the best instruments and thereby present dangers to speeding spacecrafts?
I don't think that spacecraft that have negotiated both the asteroid belt and gaps in Saturn's rings need to worry much about multi-meter sized interstellar objects. However, I do find it interesting, generally, to speculate about interstellar (ejected?) planets, asteroids and especially comets.
Thanks, Art, for referencing this asterisk topic, coreshine. The embryo formation of planets and stars is very much a problem, but coreshine helps our understanding of dust or gas particles becoming larger for accretion, but possibly not large enough.

GaryR's question is not so frivolous. If a star (even a red dwarf) with planets can form from a disk of dust, why cannot a Jupiter size planet with moons form from a smaller disk of dust ? I do agree with you that interstellar space may have ejected bodies from other star systems.

Doug Ettinger
Pittsburgh, PA

Re: APOD: Coreshine from a Dark Cloud (2010 Sep 30)

by neufer » Mon Oct 04, 2010 3:35 pm

GaryR wrote:
The article that Art posted gives me an opportunity to ask a question that I have been pondering for some times. It is well known that stars are formed inside gas and dust clouds and planets are formed within the accretion disks around the newly formed stars. However, is it also possible that planets and small bodies such as asteroids can form inside the clouds independently of the stars and never accumulate enough matter to become stars themselves? If so, wouldn't every galaxies be filled with billions or even trillions of objects too small to be detected by even the best instruments and thereby present dangers to speeding spacecrafts?
I don't think that spacecraft that have negotiated both the asteroid belt and gaps in Saturn's rings need to worry much about multi-meter sized interstellar objects. However, I do find it interesting, generally, to speculate about interstellar (ejected?) planets, asteroids and especially comets.

Re: APOD: Coreshine from a Dark Cloud (2010 Sep 30)

by GaryR » Mon Oct 04, 2010 1:56 am

The article that Art posted gives me an opportunity to ask a question that I have been pondering for some times. It is well known that stars are formed inside gas and dust clouds and planets are formed within the accretion disks around the newly formed stars. However, is it also possible that planets and small bodies such as asteroids can form inside the clouds independently of the stars and never accumulate enough matter to become stars themselves? If so, wouldn't every galaxies be filled with billions or even trillions of objects too small to be detected by even the best instruments and thereby present dangers to speeding spacecrafts?

Gary

Re: APOD: Coreshine from a Dark Cloud (2010 Sep 30)

by hstarbuck » Sun Oct 03, 2010 1:28 am

Thanks Art. What I have heard before is that we know it is possible because we see stars (and are here to see them too!).Thank goodness that even though the models don't fit perfectly, this does not stop stars from being formed.

Re: APOD: Coreshine from a Dark Cloud (2010 Sep 30)

by neufer » Sat Oct 02, 2010 9:34 pm

hstarbuck wrote:
APOD Robot wrote:
The larger dust grains indicated by coreshine could change models of the early phases of star and planet formation, a still mysterious process hidden within the interstellar clouds.
Wouldn't larger grains make collapse due to gravity more likely?
http://www.universetoday.com/74412/astronomy-without-a-telescope-a-snowballs-chance/#more-74412 wrote:
Astronomy Without A Telescope – A Snowball’s Chance
Posted in: Planetary Formation by Steve Nerlich

<<Wanna build celestial objects? I mean it sounds easy – you just start with a big cloud of dust and give it a nudge so that it starts to spin and accrete and you end up with a star with a few wisps of dust left in orbit that continue to accrete to form planets.

Trouble is, this process doesn’t seem to be physically possible – or at least nothing like it can be replicated in standard theoretical models and laboratory simulations. There’s a problem with the initial small scale accretion steps.

Dust particles seem to stick readily together when they are very small – through van der Waals and electrostatic forces – steadily building up to form millimeter and even centimeter sized aggregates. But once they get to this size those sticky forces become less influential – and the objects are still too small to generate a meaningful amount of gravitational attraction. What interaction they do have is more in the nature of bouncing collisions – which most often result in pieces being chipped off the bouncing objects, so that they start getting smaller again.

This is an astrophysics problem known as the meter barrier.

But increasingly, theorists are coming up with ways to get around the meter barrier. Firstly, it may be a mistake to assume that you start with a uniform dust cloud, in which spontaneous accretion happens everywhere throughout the cloud.

Current thinking is that it may take a nearby supernova or a closely migrating star to trigger the evolution of a dust cloud into a stellar nursery. It’s possible that turbulence in a dust cloud creates whirlpools and eddies that favor the local aggregation of small particles into larger particles. So rather than going from a uniform dust cloud to a uniform collection of very small rocks – there is just a chance formation of accreted objects here and there.

Or we can just assume a certain stochastic inevitability about anything that has the faintest chance of happening – eventually happening. Over several million years, within a huge dust cloud that might be several hundred astronomical units in diameter, a huge variety of interactions becomes possible – and even with a 99.99% likelihood that no object can ever aggregate to a size bigger than a meter, it’s still entirely likely that this is going to happen somewhere in that vast area.

Either way, once you have a few seed objects, it’s hypothesised that the snowball process takes over. Once an aggregated object achieves a certain mass, its inertia will mean it becomes less engaged in turbulent flow. In other words, the object will begin to move through, rather than move with, the turbulent dust. Under these circumstances, it will behave like a snowball rolling down a snow covered hill, collecting a covering of dust as it plows through the dust cloud – increasing its diameter as it goes.

The time span required to build such snowballed planetesimals from a radius (Rsnow) of 100 meters up to 1000 kilometers is long. The modelling used suggests a time span (Tsnow) of between 1 and 10 million years is required.

It’s also possible to model planet formation around binary stars. Using orbital parameters equivalent to those of the binary system Alpha Centauri A and B, the snowball process is calculated to work more efficiently so that Tsnow is probably no more than 1 million years.

Once hundred kilometer-sized planetesimals have formed, they would still engage in collisions. But at this size, the objects generate substantial self-gravity and collisions are more likely to be constructive – eventually resulting in planets with their own orbiting debris, which then forms rings and moons.

There is evidence that some stars can form planets (at least gas giants) within 1 million years – such as GM Aurigae – while our solar system may have taken a more leisurely 100 million years from the Sun‘s birth until the current collection of rocky, gassy and icy planets fully accreted out of the dust.

So, there’s more than a snowball’s chance in hell that that this theory may contribute to a better understanding of planet formation.>>

Re: APOD: Coreshine from a Dark Cloud (2010 Sep 30)

by neufer » Fri Oct 01, 2010 1:30 am

hstarbuck wrote:
APOD Robot wrote:
The larger dust grains indicated by coreshine could change models of the early phases of star and planet formation, a still mysterious process hidden within the interstellar clouds.
Wouldn't larger grains make collapse due to gravity more likely?
Larger grains would make collapse due to Van der Waals force more likely.

I wouldn't think that grain to grain gravity would be very important until the grains became as large as fleas.

Re: APOD: Coreshine from a Dark Cloud (2010 Sep 30)

by hstarbuck » Fri Oct 01, 2010 12:33 am

APOD Robot wrote:Image Coreshine from a Dark Cloud

The larger dust grains indicated by coreshine could change models of the early phases of star and planet formation, a still mysterious process hidden within the interstellar clouds.
Wouldn't larger grains make collapse due to gravity more likely? Sure, the total mass may not change, but (offhand) I think that bigger building blocks would grow faster into "chunks" and then leading to collapse of some local area(s) forming stars, planets, etc. . In any case, our science grows (no pun intended) by the day.

Re: APOD: Coreshine from a Dark Cloud (2010 Sep 30)

by mpharo » Thu Sep 30, 2010 8:51 pm

The dark nebula Lynds is actually pretty bright in visible or infared light. The star features of this nebula vary from very faint, to bright, to very bright.

Re: APOD: Coreshine from a Dark Cloud (2010 Sep 30)

by emc » Thu Sep 30, 2010 5:09 pm

bystander wrote:
orin stepanek wrote:Wow! I got 3 oops messages while clicking on the links in the explanation.
http://www.spitzer.caltech.edu/ seems to be down!

the JPL Spitzer links are working now

Re: APOD: Coreshine from a Dark Cloud (2010 Sep 30)

by bystander » Thu Sep 30, 2010 2:04 pm

orin stepanek wrote:Wow! I got 3 oops messages while clicking on the links in the explanation.
http://www.spitzer.caltech.edu/ seems to be down!

Re: APOD: Coreshine from a Dark Cloud (2010 Sep 30)

by neufer » Thu Sep 30, 2010 1:01 pm

Image
http://en.wikipedia.org/wiki/Florsheim_Shoes wrote:
<<Florsheim Shoes is a shoe brand in the United States. It was founded in 1892 by Milton S. Florsheim and his father Sigmund. Until the mid-1990s, almost every mall in the United States had a Florsheim store. However, with the rise of such shoe stores as Journeys and Finish Line, and the de-emphasis of shoe stores in American malls, most Florsheim stores closed down by the early 2000s. This followed the fate of other companies such as Kinney Shoes and Thom McAn.>>

Re: APOD: Coreshine from a Dark Cloud (2010 Sep 30)

by orin stepanek » Thu Sep 30, 2010 12:42 pm

Wow! I got 3 oops messages while clicking on the links in the explanation. :? I thought infrared wavelengths made it easier to look inside of interstellar clouds. :?:

Re: APOD: Coreshine from a Dark Cloud (2010 Sep 30)

by bystander » Thu Sep 30, 2010 7:15 am

APOD: Coreshine from a Dark Cloud (2010 Sep 30)

by APOD Robot » Thu Sep 30, 2010 4:00 am

Image Coreshine from a Dark Cloud

Explanation: Stars and their planets are born in cold, dark, interstellar clouds of gas and dust. While exploring the clouds at infrared wavelengths, astronomers have made a surprising discovery -- dozens of cases where dense cloud cores shine by reflecting infrared starlight. Based on archival Spitzer Space Telescope data, these panels illustrate the newly described phenomenon, known as coreshine. At longer infrared wavelengths (right) the core of cloud Lynds 183 is dark, but at shorter infrared wavelengths (left) the core clearly shines, scattering light from nearby stars. As seen in these panels, the elongated core covers a mere 1.5 light-years. The scattering requires dust grains that are about 10 times larger than previously thought to exist in the clouds, about 1 micron in size instead of 0.1 micron. For comparison, a human hair is about 100 microns thick. The larger dust grains indicated by coreshine could change models of the early phases of star and planet formation, a still mysterious process hidden within the interstellar clouds. Dark nebula Lynds 183 lies around 325 light-years away in the constellation Serpens.

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