APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Comments and questions about the APOD on the main view screen.
User avatar
APOD Robot
Otto Posterman
Posts: 3998
Joined: Fri Dec 04, 2009 3:27 am

APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by APOD Robot » Sun Jan 12, 2020 5:07 am

Image Stars and Dust in Corona Australis

Explanation: Cosmic dust clouds and young, energetic stars inhabit this telescopic vista, less than 500 light-years away toward the northern boundary of Corona Australis, the Southern Crown. The dust clouds effectively block light from more distant background stars in the Milky Way. But the striking complex of reflection nebulae cataloged as NGC 6726, 6727, and IC 4812 produce a characteristic blue color as light from the region's young hot stars is reflected by the cosmic dust. The dust also obscures from view stars still in the process of formation. At the left, smaller yellowish nebula NGC 6729 bends around young variable star R Coronae Australis. Just below it, glowing arcs and loops shocked by outflows from embedded newborn stars are identified as Herbig-Haro objects. On the sky this field of view spans about 1 degree. That corresponds to almost 9 light-years at the estimated distance of the nearby star forming region.

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

User avatar
Ann
4725 Å
Posts: 10569
Joined: Sat May 29, 2010 5:33 am

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by Ann » Sun Jan 12, 2020 7:30 am

Woo-hoo, or Tjo-ho!, which is woo-hoo in Swedish!

A blue, blue, blue APOD!


Note the binary blue star at lower right, which might have been taken straight out of the Pleiades! Okay, yellow smiley! :D
Color Commentator

Boomer12k
:---[===] *
Posts: 2686
Joined: Sun Apr 22, 2007 12:07 am

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by Boomer12k » Sun Jan 12, 2020 7:45 am

Awesome image... like water, flowing around little islands...just beautiful...

:---[===] *

User avatar
Ann
4725 Å
Posts: 10569
Joined: Sat May 29, 2010 5:33 am

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by Ann » Sun Jan 12, 2020 7:51 am

Stars and Dust in Corona Australis.
Credit and copyright, CHART32 Team, Processing, Johannes Schedler.
Woo-hoo, or Tjo-ho!, which is woo-hoo in Swedish! (No, I don't think Homer speaks Swedish... never mind...)

A blue, blue, blue APOD!

Note the binary blue star in the APOD at lower right, which might have been taken straight out of the Pleiades! Okay, yellow smiley! :D
And note the other double star at upper left, which are huffing and puffing to break out of their smothering dusty bluish birth cocoon!

And look at the rambunctious little siblings in the shadow of their big brothers and sisters, spitting out jets and acting up. Ahh, youth, the (sometimes) brilliant blue hues of youth!

Blue smiley!

Ann
Color Commentator

User avatar
MarkBour
Subtle Signal
Posts: 1058
Joined: Mon Aug 26, 2013 2:44 pm
Location: Illinois, USA

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by MarkBour » Sun Jan 12, 2020 10:30 am

Ann wrote:
Sun Jan 12, 2020 7:51 am
...
And look at the rambunctious little siblings in the shadow of their big brothers and sisters, spitting out jets and acting up. Ahh, youth, the (sometimes) brilliant blue hues of youth!
Ann
Yes, there are some great examples in this image. I especially like the one just a little right of center that has cleared out a goodly region.
Mark Goldfain

User avatar
JohnD
Tea Time, Guv! Cheerio!
Posts: 1238
Joined: Wed Feb 16, 2005 2:11 pm
Location: Lancaster, England

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by JohnD » Sun Jan 12, 2020 10:48 am

Between the bright (nearer?) star at 4 o'clock, and the "Harberg-Haro" object at half past eight, there's an intensely red object. What that, please?
John

User avatar
Ann
4725 Å
Posts: 10569
Joined: Sat May 29, 2010 5:33 am

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by Ann » Sun Jan 12, 2020 11:11 am

JohnD wrote:
Sun Jan 12, 2020 10:48 am
Between the bright (nearer?) star at 4 o'clock, and the "Harberg-Haro" object at half past eight, there's an intensely red object. What that, please?
John
Not sure exactly what you mean, John. But at least I have posted a part of today's APOD that we can look at when we talk about your question.

Jets in Corona Australis.png
If you take a look at the part of the APOD that I posted here, you can see one obvious pink emission nebula (at lower right) and a number of small red hydrogen alpha jets. The jets are being emitted by baby stars having tantrums as they are in the process of forming.

There are also a number of very reddened stars, which look deeply orange. The stars are so deeply reddened because of all the dust in front of them.

Does that answer your question?

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

sillyworm 2

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by sillyworm 2 » Sun Jan 12, 2020 1:39 pm

Thanks for pointing that out otherwise I would have missed those faint jets.

User avatar
JohnD
Tea Time, Guv! Cheerio!
Posts: 1238
Joined: Wed Feb 16, 2005 2:11 pm
Location: Lancaster, England

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by JohnD » Sun Jan 12, 2020 5:29 pm

Thank you, Ann! Yes that's wwhat I menat, and I hadn't noticed those smaller ones!
JOhn

User avatar
Psnarf
Science Officer
Posts: 315
Joined: Fri Feb 26, 2010 6:19 pm

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by Psnarf » Sun Jan 12, 2020 7:33 pm

I didn't know you were bluish. Just wondering, about how far apart are the glowing particles of such dust or gas fields?

User avatar
Ann
4725 Å
Posts: 10569
Joined: Sat May 29, 2010 5:33 am

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by Ann » Sun Jan 12, 2020 7:55 pm

Psnarf wrote:
Sun Jan 12, 2020 7:33 pm
I didn't know you were bluish. Just wondering, about how far apart are the glowing particles of such dust or gas fields?
The Serpens South star cluster. Photo: Spitzer Space Telescope.
Chris should answer you here. I believe that in a typical reflection nebula, like the one near the two blue stars at lower right in the APOD, the particles are so far apart that we can't even produce such a hard vacuum on Earth.

When it comes to the much more dust-choked bluish stars at upper left, the dust density is obviously much higher. I still think it is much less than the particle density in the Earth's atmosphere.

But there are dense dark nebulas in space. Stars form out of thick, cold nebulas. Take a look at the picture at right of the Serpens South star cluster. The stars can't be seen at all at visible wavelengths, but they were visible in 2007 to the (I think now defunct) Spitzer Space Telescope.

The stars of the Serpens South star cluster have definitely both used up and dispersed a lot of the gas and dust in the molecular cloud that they formed out of. But just before the formation of this cluster started, the density in the innermost parts of the nebula must have been very much higher than the atmosphere of the Earth.

Ann
Color Commentator

User avatar
Psnarf
Science Officer
Posts: 315
Joined: Fri Feb 26, 2010 6:19 pm

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by Psnarf » Sun Jan 12, 2020 8:04 pm

Thanks, Ann! I had no idea they were so close together. Could go to such gas clouds an refill the oxygen tanks. Not that such a consummation would be necessary. Probably will use a closed hydrogen-based system, burn hydrogen to get water, then separate the water into hydrogen and oxygen.
- Hank

starsurfer
Stellar Cartographer
Posts: 4061
Joined: Thu Mar 15, 2012 7:25 pm

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by starsurfer » Sun Jan 12, 2020 8:08 pm

You can find a labeled version here.

User avatar
Chris Peterson
Abominable Snowman
Posts: 15152
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by Chris Peterson » Sun Jan 12, 2020 8:36 pm

Ann wrote:
Sun Jan 12, 2020 7:55 pm
When it comes to the much more dust-choked bluish stars at upper left, the dust density is obviously much higher. I still think it is much less than the particle density in the Earth's atmosphere.

But there are dense dark nebulas in space. Stars form out of thick, cold nebulas. Take a look at the picture at right of the Serpens South star cluster. The stars can't be seen at all at visible wavelengths, but they were visible in 2007 to the (I think now defunct) Spitzer Space Telescope.
Consider looking at the Sun as it sets. We're seeing the brightness reduced by ten magnitudes or more from the light passing through no more than a few hundred kilometers of atmosphere. In most dusty nebulas, we can see for tens or hundreds of light years with much less extinction than that. If we just take it as 100 light years in a nebula producing the same extinction as 100 km in our atmosphere, we're talking about a difference in density of 16 orders of magnitude. Our atmosphere is perhaps a million billion times denser than a dusty nebula. Even the densest of globules are still many orders of magnitude less dense than our atmosphere. Still hard vacuums.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
orin stepanek
Plutopian
Posts: 5582
Joined: Wed Jul 27, 2005 3:41 pm
Location: Nebraska

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by orin stepanek » Sun Jan 12, 2020 8:46 pm

😍 Ah! So pretty; definitely a background Photo! 8-)
NGC6726_Schedler_960.jpg
You do not have the required permissions to view the files attached to this post.
Orin

Smile today; tomorrow's another day!

User avatar
Ann
4725 Å
Posts: 10569
Joined: Sat May 29, 2010 5:33 am

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by Ann » Sun Jan 12, 2020 9:06 pm

Chris Peterson wrote:
Sun Jan 12, 2020 8:36 pm
Ann wrote:
Sun Jan 12, 2020 7:55 pm
When it comes to the much more dust-choked bluish stars at upper left, the dust density is obviously much higher. I still think it is much less than the particle density in the Earth's atmosphere.

But there are dense dark nebulas in space. Stars form out of thick, cold nebulas. Take a look at the picture at right of the Serpens South star cluster. The stars can't be seen at all at visible wavelengths, but they were visible in 2007 to the (I think now defunct) Spitzer Space Telescope.
Consider looking at the Sun as it sets. We're seeing the brightness reduced by ten magnitudes or more from the light passing through no more than a few hundred kilometers of atmosphere. In most dusty nebulas, we can see for tens or hundreds of light years with much less extinction than that. If we just take it as 100 light years in a nebula producing the same extinction as 100 km in our atmosphere, we're talking about a difference in density of 16 orders of magnitude. Our atmosphere is perhaps a million billion times denser than a dusty nebula. Even the densest of globules are still many orders of magnitude less dense than our atmosphere. Still hard vacuums.
Point taken, Chris. But surely, before stars can start forming from a dust cloud, the density of the cloud must grow by many magnitudes?

Ann
Color Commentator

User avatar
Chris Peterson
Abominable Snowman
Posts: 15152
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by Chris Peterson » Sun Jan 12, 2020 9:26 pm

Ann wrote:
Sun Jan 12, 2020 9:06 pm
Chris Peterson wrote:
Sun Jan 12, 2020 8:36 pm
Ann wrote:
Sun Jan 12, 2020 7:55 pm
When it comes to the much more dust-choked bluish stars at upper left, the dust density is obviously much higher. I still think it is much less than the particle density in the Earth's atmosphere.

But there are dense dark nebulas in space. Stars form out of thick, cold nebulas. Take a look at the picture at right of the Serpens South star cluster. The stars can't be seen at all at visible wavelengths, but they were visible in 2007 to the (I think now defunct) Spitzer Space Telescope.
Consider looking at the Sun as it sets. We're seeing the brightness reduced by ten magnitudes or more from the light passing through no more than a few hundred kilometers of atmosphere. In most dusty nebulas, we can see for tens or hundreds of light years with much less extinction than that. If we just take it as 100 light years in a nebula producing the same extinction as 100 km in our atmosphere, we're talking about a difference in density of 16 orders of magnitude. Our atmosphere is perhaps a million billion times denser than a dusty nebula. Even the densest of globules are still many orders of magnitude less dense than our atmosphere. Still hard vacuums.
Point taken, Chris. But surely, before stars can start forming from a dust cloud, the density of the cloud must grow by many magnitudes?
I don't think the density of the cloud ever gets greater than what we'd consider a hard vacuum. The region where a star forms is extremely localized and small compared with the cloud as a whole. A size measured in AUs, not light years. Consider that even the density of the Sun near its surface is 10,000 times less than our own atmosphere. You start getting gravitational collapse in regions where the density is on the order of thousands of particles per cubic centimeter. Still a hard vacuum. Gravitational free fall times there are on the order of a million years.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
Ann
4725 Å
Posts: 10569
Joined: Sat May 29, 2010 5:33 am

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by Ann » Mon Jan 13, 2020 5:52 am

Chris Peterson wrote:
Sun Jan 12, 2020 9:26 pm
Ann wrote:
Sun Jan 12, 2020 9:06 pm
Chris Peterson wrote:
Sun Jan 12, 2020 8:36 pm

Consider looking at the Sun as it sets. We're seeing the brightness reduced by ten magnitudes or more from the light passing through no more than a few hundred kilometers of atmosphere. In most dusty nebulas, we can see for tens or hundreds of light years with much less extinction than that. If we just take it as 100 light years in a nebula producing the same extinction as 100 km in our atmosphere, we're talking about a difference in density of 16 orders of magnitude. Our atmosphere is perhaps a million billion times denser than a dusty nebula. Even the densest of globules are still many orders of magnitude less dense than our atmosphere. Still hard vacuums.
Point taken, Chris. But surely, before stars can start forming from a dust cloud, the density of the cloud must grow by many magnitudes?
I don't think the density of the cloud ever gets greater than what we'd consider a hard vacuum. The region where a star forms is extremely localized and small compared with the cloud as a whole. A size measured in AUs, not light years. Consider that even the density of the Sun near its surface is 10,000 times less than our own atmosphere. You start getting gravitational collapse in regions where the density is on the order of thousands of particles per cubic centimeter. Still a hard vacuum. Gravitational free fall times there are on the order of a million years.
All right, Chris. You and I actually mean the same thing, although we express ourselves differently. I stand corrected about how diffuse a nebula like the one enveloping the two stars breaking out of their birth cloud in the APOD really is, but you actually agree with me that the part of a nebula where a star actually begins forming must be really dense, and (I guess) much denser than the atmosphere of the Earth.

Let's put it like this. The mass of the Sun, last time I put a scale under it - I mean, last time I googled it - is about 330,000 times that of the Earth. I don't know the mass of the Earth's atmosphere, but clearly, when the Sun was forming, a nebular mass of, perhaps, a tenth of the Sun's current mass? 33,000 Earth masses? had to get pretty concentrated and start collapsing.

Ann
Color Commentator

User avatar
Chris Peterson
Abominable Snowman
Posts: 15152
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by Chris Peterson » Mon Jan 13, 2020 2:09 pm

Ann wrote:
Mon Jan 13, 2020 5:52 am
Chris Peterson wrote:
Sun Jan 12, 2020 9:26 pm
Ann wrote:
Sun Jan 12, 2020 9:06 pm

Point taken, Chris. But surely, before stars can start forming from a dust cloud, the density of the cloud must grow by many magnitudes?
I don't think the density of the cloud ever gets greater than what we'd consider a hard vacuum. The region where a star forms is extremely localized and small compared with the cloud as a whole. A size measured in AUs, not light years. Consider that even the density of the Sun near its surface is 10,000 times less than our own atmosphere. You start getting gravitational collapse in regions where the density is on the order of thousands of particles per cubic centimeter. Still a hard vacuum. Gravitational free fall times there are on the order of a million years.
All right, Chris. You and I actually mean the same thing, although we express ourselves differently. I stand corrected about how diffuse a nebula like the one enveloping the two stars breaking out of their birth cloud in the APOD really is, but you actually agree with me that the part of a nebula where a star actually begins forming must be really dense, and (I guess) much denser than the atmosphere of the Earth.

Let's put it like this. The mass of the Sun, last time I put a scale under it - I mean, last time I googled it - is about 330,000 times that of the Earth. I don't know the mass of the Earth's atmosphere, but clearly, when the Sun was forming, a nebular mass of, perhaps, a tenth of the Sun's current mass? 33,000 Earth masses? had to get pretty concentrated and start collapsing.
It's an interesting question. But I don't think that the nebula from which a star forms every becomes as dense as our atmosphere. Eventually, the central part of the star does, and blobs of dirt and rock and ice that become planets, asteroid, and comets do. But even in the protoplanetary disk, the dust and gas density must still be very low. I do know that the stars start collapsing out at a very low density, though (high compared to the surrounding nebula, but still just measured in thousands of particles per cubic centimeter, which means close to a vacuum). We're still looking at approximately a solar mass distributed over a huge volume of space, a sphere the size of a solar system.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
neufer
Vacationer at Tralfamadore
Posts: 17276
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Stars and Dust in Corona Australis (2020 Jan 12)

Post by neufer » Mon Jan 13, 2020 4:08 pm

https://en.wikipedia.org/wiki/Star_formation wrote:
<<Star formation is the process by which dense regions within molecular clouds in interstellar space, sometimes referred to as "stellar nurseries" or "star-forming regions", collapse and form stars. Star formation theory, as well as accounting for the formation of a single star, must also account for the statistics of binary stars and the initial mass function. Most stars do not form in isolation but as part of a group of stars referred as star clusters or stellar associations.

If a cloud is massive enough that the gas pressure is insufficient to support it, the cloud will undergo gravitational collapse. The mass above which a cloud will undergo such collapse is called the Jeans mass. The Jeans mass depends on the temperature and density of the cloud, but is typically thousands to tens of thousands of solar masses. During cloud collapse dozens to ten thousands of stars form more or less simultaneously which is observable in so-called embedded clusters. Turbulence is instrumental in causing fragmentation of the cloud, and on the smallest scales it promotes collapse. The end product of a core collapse is an open cluster of stars.

In triggered star formation, one of several events might occur to compress a molecular cloud and initiate its gravitational collapse. Molecular clouds may collide with each other, or a nearby supernova explosion can be a trigger, sending shocked matter into the cloud at very high speeds. (The resulting new stars may themselves soon produce supernovae, producing self-propagating star formation.) Alternatively, galactic collisions can trigger massive starbursts of star formation as the gas clouds in each galaxy are compressed and agitated by tidal forces. The latter mechanism may be responsible for the formation of globular clusters.

As it collapses, a molecular cloud breaks into smaller and smaller pieces in a hierarchical manner, until the fragments reach stellar mass. In each of these fragments, the collapsing gas radiates away the energy gained by the release of gravitational potential energy. As the density increases, the fragments become opaque and are thus less efficient at radiating away their energy.

During the collapse, the density of the cloud increases towards the center and thus the middle region becomes optically opaque first. This occurs when the density is about 10−13g/cm3 [~1 M within a ~100 AU "solar system" radius]. A core region, called the First Hydrostatic Core, forms where the collapse is essentially halted. It continues to increase in temperature. The gas falling toward this opaque region collides with it and creates shock waves that further heat the core. The dust within the cloud becomes heated to temperatures of 60–100 K, and these particles radiate at wavelengths in the far infrared where the cloud is transparent. Thus the dust mediates the further collapse of the cloud.

When the core temperature reaches about 2000 K, the thermal energy dissociates the H2 molecules. This is followed by the ionization of the hydrogen and helium atoms. These processes absorb the energy of the contraction, allowing it to continue on timescales comparable to the period of collapse at free fall velocities. After the density of infalling material has reached about 10−8g/cm3, that material is sufficiently transparent to allow energy radiated by the protostar to escape. The combination of convection within the protostar and radiation from its exterior allow the star to contract further. This continues until the gas is hot enough for the internal pressure to support the protostar against further gravitational collapse—a state called hydrostatic equilibrium. When this accretion phase is nearly complete, the resulting object is known as a protostar.

Accretion of material onto the protostar continues partially from the newly formed circumstellar disc. When the density and temperature are high enough, deuterium fusion begins, and the outward pressure of the resultant radiation slows (but does not stop) the collapse. Material comprising the cloud continues to "rain" onto the protostar. In this stage bipolar jets are produced called Herbig–Haro objects. This is probably the means by which excess angular momentum of the infalling material is expelled, allowing the star to continue to form.

When the surrounding gas and dust envelope disperses and accretion process stops, the star is considered a pre-main-sequence star (PMS star). The energy source of these objects is gravitational contraction, as opposed to hydrogen burning in main sequence stars. The PMS star follows a Hayashi track on the Hertzsprung–Russell (H–R) diagram. The contraction will proceed until the Hayashi limit is reached, and thereafter contraction will continue on a Kelvin–Helmholtz timescale with the temperature remaining stable. Stars with less than 0.5 M thereafter join the main sequence. For more massive PMS stars, at the end of the Hayashi track they will slowly collapse in near hydrostatic equilibrium, following the Henyey track.

Finally, hydrogen begins to fuse in the core of the star, and the rest of the enveloping material is cleared away. This ends the protostellar phase and begins the star's main sequence phase on the H–R diagram.

The stages of the process are well defined in stars with masses around 1 M or less. In high mass stars, the length of the star formation process is comparable to the other timescales of their evolution, much shorter, and the process is not so well defined. The later evolution of stars are studied in stellar evolution. Complicating this picture of a collapsing cloud are the effects of turbulence, macroscopic flows, rotation, magnetic fields and the cloud geometry. Both rotation and magnetic fields can hinder the collapse of a cloud.>>
Art Neuendorffer