Starship Asterisk*

Chris Peterson wrote:

Ron-Astro Pharmacist wrote: Isaac Asimov wrote a book “The Stars, Like Dust” but I’ve never understood the comma in between? It seems to me “The Stars Like Dust” might have been more appropriate.

Yes, he meant it as "the stars, like sand on a beach". But I like your interpretation, as well. Actually, I suppose stars don't "like" dust at all, as they never encounter it. As critical as dust is to the formation of stars (presumably, although not certainly), once a star turns on, that's it. No more dust, since the stellar wind blows it all away, creating a dust-free bubble around stars even in the middle of dust-rich nebulas.

http://en.wikipedia.org/wiki/John_Henry_Poynting wrote:

<<John Henry Poynting (9 September 1852 – 30 March 1914) was an English physicist. From 1872 to 1876 he was a student at Cambridge University, where he attained high honours in mathematics. In the late 1870s he worked in the Cavendish Laboratory at Cambridge under James Clerk Maxwell.

Poynting was the developer and eponym of the Poynting vector, which describes the direction and magnitude of electromagnetic energy flow and is used in the Poynting theorem, a statement about energy conservation for electric and magnetic fields. This work was first published in 1884. He performed a measurement of Newton's gravitational constant by innovative means during 1893. In 1903 he was the first to realise that the Sun's radiation can draw in small particles towards it: this was later named the Poynting-Robertson effect.

Poynting and the Nobel prizewinner J. J. Thomson co-authored a multi-volume undergraduate physics textbook, which was in print for about 50 years and was in widespread use during the first third of the 20th century. Poynting wrote most of it. Craters on Mars and the Moon are named in his honour, as is the main Physics building at the University of Birmingham and the departmental society there, the Poynting Physical Society.>>

http://en.wikipedia.org/wiki/Poynting-Robertson_effect wrote:

[b][color=#0000FF]Radiation from the Sun (S) & thermal radiation from a particle seen (a) from an observer moving with the particle and (b) from an observer at rest.[/color][/b]

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<<The Poynting–Robertson effect, also known as Poynting–Robertson drag, named after John Henry Poynting and Howard Percy Robertson, is a process by which solar radiation causes a dust grain in the Solar System to slowly spiral into the Sun. The drag is essentially a component of radiation pressure tangential to the grain's motion. Poynting gave a description of the effect in 1903 based on the "luminiferous aether" theory, which was superseded by the theories of relativity in 1905–1915. In 1937 Robertson described the effect in terms of general relativity.

Zodiacal light is a faint, roughly triangular, diffuse white glow seen in the night sky that appears to extend up from the vicinity of the Sun along the ecliptic or zodiac. Caused by sunlight scattered by space dust in the zodiacal cloud, it is so faint that either moonlight or light pollution renders it invisible. Zodiacal light covers the entire sky, being responsible for major part of the total skylight on a moonless night.

Zodiacal cloud dust forms a thick pancake-shaped cloud in the same plane as the ecliptic. The dust particles are between 10 and 300 micrometres in diameter, with most mass around 150 micrometres. The Poynting-Robertson effect forces the dust into more circular (but still elongated) orbits, while spiralling slowly into the Sun. Hence a continuous source of new particles is needed to maintain the zodiacal cloud. Cometary dust and dust generated by collisions among the asteroids are believed to be mostly responsible for the maintenance of the dust cloud producing the zodiacal light and the gegenschein.

Particles can be reduced in size by collisions or by space weathering. When ground down to sizes less than 10 micrometres, the grains are removed from the inner solar system by solar radiation pressure.

Zodiacal dust around nearby stars is called exozodiacal dust; it is a potentially important source of noise for directly imaging extrasolar planets. Nesvorny and Jenniskens have pointed out that this exozodiacal dust, or hot debris disks, can also help find planets, as planets tend to scatter the comets to the inner solar system.>>

Beyond wrote:

bystander wrote:

Kelly in Space wrote:There's a mound at the bottom of the image with 2 projections that look like Star Trek character Andorian antennae.

[url=http://hubblesite.org/newscenter/archive/releases/1999/42/image/a/][b][i]The Trifid Nebula: Stellar Sibling Rivalry[/i][/b][/url] [b][i]Credit: NASA and Jeff Hester (Arizona State University)[/i][/b]

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That is rather amazing... but we can tell it's not Andorian, as it's not blue. If it was blue... Ann would have commented on it already.

Anthony Barreiro wrote:This is a beautiful and fascinating image, thanks to everyone who contributed and to Dr. Gendler for putting it all together.

For me, the experience of observing the Trifid many times through smaller and larger telescopes and teasing out as much detail as I can see makes this image much more interesting and compelling than an image of something I've never observed directly. I know where those dust lanes and bright patches are, and I can match up this gloriously detailed and colored image with my mental map of the Trifid.

Those two antennae in the bottom of the picture are reminiscent of the "Pillars of Creation" in the iconic Hubble image of the Eagle nebula. I assume that each antenna contains a young protostar (or perhaps each antenna holds a pair of protostars?) forming out of a clump of gas and dust, while the radiation from big hot stars above them in the picture is simultaneously blowing the gas and dust away, leaving a trail of gas and dust behind the young stars. Does this make sense?

Ann wrote:

Click to view full size image

The way I understand it, jets form at right angles to an accretion disk. Young stars accrete mass through accretion disks. This Hubble image of a portion of the Carina Nebula shows two "pillars of creation", which both have jets at their "tops". I'd say that a young star is forming at the very top of these two pillars. You can see that the topmost one has two distinct jets, one in either direction. The jet on the left appears to encounter a strong stellar wind, probably from one of the hot stars in the region, and there is a bow shock at the tip of this jet.

I believe there are similarities between the jets that accompany star formation and the jets that emanate from the centers of active galaxies, although these are phenomena on vastly different scales.

Ann

bystander wrote:Color CCD Imaging with Luminance Layering by Robert Gendler

DavidLeodis wrote:Thanks for that link bystander, which is appreciated. My understanding, on reading through its information, is that the information brought up through the "luminance" link in the explanation is confusing as it does not seem to be giving the same meaning of luminance that luminance does in image data.

Anthony Barreiro wrote:
So in the Trifid image, would we presume that there is a star (or a binary star? or cluster of stars?) in the "head" and that the "antennae" are jets from the star(s)?

stephen63 wrote:

DavidLeodis wrote:Thanks for that link bystander, which is appreciated. My understanding, on reading through its information, is that the information brought up through the "luminance" link in the explanation is confusing as it does not seem to be giving the same meaning of luminance that luminance does in image data.

David. The advantage of using the luminance filter/data/channel is it's relatively high signal to noise ratio(SNR). The human eye perceives detail in the luminance image. Higher SNR means we can stretch the data more without the noise becoming objectionable. Your eyes don't detect noise as easily in the color channels, so a lower SNR is acceptable. If it does get excessively noisy, just back off of the stretch, reduce the saturation, or run a noise eduction action. I'm sure there are a lot of other ways to skin a cat, but that's the gist of it. Also, when adding the luminance on top of the RGB data, it doesn't get its own channel. There are only three, as far as I know! Hope this helps!

DavidLeodis wrote:What confused me about luminance in regard to the APOD is that the information brought up through the link is that luminance (putting it simply) is the brightness of an object, yet in the explanation it stated the "image is a composite with luminance taken from an image by the 8.2-m ground-based Subaru Telescope..." which does not seem to be using luminance as the brightness but rather as a filter.

stephen63 wrote:In this case, I believe, the main component of the image are three narrow band channels(Ha/OIII/SII) from Hubble. The color data from Mr Pugh is used for the star color. I'm just guessing but its what I would do. The Luminance is indeed taken through a luminance filter. It also has a bandpass, its not just a clear piece of glass. It rejects the infra red and near infra red frequencies but passes the visible spectrum, which adds detail to the object as well as luminosity. I can't recall seeing a luminance filter ever being used by the Hubble.

Ann wrote:

Anthony Barreiro wrote:
So in the Trifid image, would we presume that there is a star (or a binary star? or cluster of stars?) in the "head" and that the "antennae" are jets from the star(s)?

Yes, I believe that that is exactly what we are seeing, although I wouldn't try to guess how many stars we actually see forming here. The most obvious "antenna" is almost certainly created by a star in the process of forming. But there are other jets here too. The other conspicuous ones may also very well be created by forming stars, but there are other, fainter and broader jets that may have other origins.

Ann

Chris Peterson wrote:No more dust, since the stellar wind blows it all away, creating a dust-free bubble around stars even in the middle of dust-rich nebulas.

ThePiper wrote:

Chris Peterson wrote:No more dust, since the stellar wind blows it all away, creating a dust-free bubble around stars even in the middle of dust-rich nebulas.

Yes, as we can see. But what's the mechanism of "blowing away" by stellar wind? Is the kinetic energy of single electrons and protons sufficient to accelerate and push entire dust molecules, particles and even clumps? The mass-relation could easy be 1: x times 1E9!