Starship Asterisk*

by **west of west** » Wed Nov 18, 2009 6:03 am

mark wrote:Triggering Ia events is not that simple but much more interesting. Observations and modeling of these Ia events show that unregulated carbon/oxygen burning takes place just prior to the Chandrasekhar limit. This conclusion was established many years (a decade?) ago.
mgo

Actually, according to Wheeler, the idea that Type Ia supernovae events were triggered when the Chandrasekhar limit was attained went out the window in the 1960's among astronomers in the field. However, the scientifically literate public (as well as perhaps astronomers in other fields) have not gotten the message yet.

Here's a link to the book:

http://www.cambridge.org/catalogue/cata ... 0521857147

and to the author's web site:

http://www.as.utexas.edu/~wheel/

by **neufer** » Wed Nov 18, 2009 4:15 am

http://en.wikipedia.org/wiki/R_Aquarii wrote:
<<R Aquarii (R Aqr) is a variable star in the constellation Aquarius.

R Aquarii is a symbiotic star believed to contain a white dwarf and a Mira-type variable in a binary star system. The main Mira-type star is a red giant, and varies in brightness by a factor of several hundred and with a period of slightly more than a year; this variability was discovered by Karl Ludwig Harding in 1810.

By its gravitational pull, the white dwarf draws in material from the red giant and occasionally ejects some of the surplus in weird loops to form the nebula seen in the linked image.

The whole system appears reddened because it is situated in a very dusty region of space, and its blue light is absorbed before reaching us.

The nebula around R Aquarii is also known as Cederblad 211. According to Tom Polakis, as of 1998 no one had succeeded to observe this challenging object visually. It is possible that the nebula is the remnant of a nova-like outburst, which may have been observed by Japanese astronomers, in the year 930 AD.>>

by **Eamon Shute** » Wed Nov 18, 2009 12:25 am

According to the Wiki link, L5 is only stable if the ratio of M1/M2 is greater than 24.96. Not many binary stars have such a large mass ratio!

by **Chris Peterson** » Wed Nov 18, 2009 12:23 am

neufer wrote:Why not an L5 Lagrangian point?

Since the two stars are close enough to exchange material, we know that the planet must be very close to them as well. Way too close for there to be liquid on the surface; maybe too close even for there to be solid rock.

by **neufer** » Tue Nov 17, 2009 11:07 pm

Chris Peterson wrote:
NoelC wrote:A long while back I read that planetary orbits around multiple star systems are not likely to be stable. Is that true (and thus an image like this, with the observer's planet and satellites? so close to the suns would not be possible) or have I been mislead
There are relatively stable solutions for planetary systems around binary stars, but they are the exception, and normally depend on the planets orbiting one star while the other star is far away. This is a system with two closely paired stars; I don't think there's any way you could have any planets in stable orbits around this pair.

Why not an L5 Lagrangian point?

by **Chris Peterson** » Tue Nov 17, 2009 7:29 pm

NoelC wrote:A long while back I read that planetary orbits around multiple star systems are not likely to be stable. Is that true (and thus an image like this, with the observer's planet and satellites? so close to the suns would not be possible) or have I been mislead

There are relatively stable solutions for planetary systems around binary stars, but they are the exception, and normally depend on the planets orbiting one star while the other star is far away. This is a system with two closely paired stars; I don't think there's any way you could have any planets in stable orbits around this pair. Add to that the bizarre moons: they are orbiting on a radically different plane than the ecliptic plane of the system. So presumably, the planet's axis is highly inclined, and I doubt that the moon system would be stable, either.

There is so much wrong with this image (what force is pulling the transferred material into a narrow beam? We should be seeing intersecting Roche lobes.) I think it is a disappointing APOD. I like fantasy space art just fine, but I like it on the cover of sci-fi books. There is good space art that does a much better job of presenting a realistic view of things we can't image, but this isn't in that category.

by **nz1m** » Tue Nov 17, 2009 6:52 pm

Indigo_Sunrise wrote:
Eamon Shute wrote:The lighting in this painting is all wrong!

The crescent moons indicate the direction of the main light source, which should be where these two lines intersect. There is nothing there!

You could send an email to the artist and tell him so..... (his contact info is directly underneath the image.)

If the "two" moons are lit by the same source (the local sun) wouldn't both have the same angle of light? And both near "new" moon would mean that they are "close to each other" in orbit just "closer and farther" so that should mean they both would have the same angle of light, too? Just curious // nice art, however.

by **apodman** » Tue Nov 17, 2009 5:21 pm

All I see is a cross-eyed face with a side order of plasma on the brain.

---

NoelC wrote:A long while back I read that planetary orbits around multiple star systems are not likely to be stable. Is that true (and thus an image like this, with the observer's planet and satellites? so close to the suns would not be possible) or have I been mislead?

http://en.wikipedia.org/wiki/Binary_star wrote:
Planets around binary stars

Planets that orbit just one star in a binary pair are said to have "S-type" orbits, whereas those that orbit around both stars have "P-type" or "circumbinary" orbits. It is estimated that 50–60% of binary stars are capable of supporting habitable terrestrial planets within stable orbital ranges. ...

A study of fourteen previously known planetary systems found three of these systems to be binary systems. All planets were found to be in S-type orbits around the primary star. In these three cases the secondary star was much dimmer than the primary and so was not previously detected.

by **NoelC** » Tue Nov 17, 2009 5:20 pm

Lighting problems in the image notwithstanding...

A long while back I read that planetary orbits around multiple star systems are not likely to be stable. Is that true (and thus an image like this, with the observer's planet and satellites? so close to the suns would not be possible) or have I been mislead?

-Noel

by **geckzilla** » Tue Nov 17, 2009 4:48 pm

And to think I was just posting about how these illustrations always bug me in the other forum section and specifically mentioned an example like this one. Ah well, can't say this one bothers me any less than the others. I hadn't seen it though and it has far more worth in the idea than the execution of the art itself. I don't think I could have thought of such a scene.

by **Star*Hopper** » Tue Nov 17, 2009 1:45 pm

Eamon Shute wrote:The lighting in this painting is all wrong!
The crescent moons indicate the direction of the main light source, which should be where these two lines intersect. There is nothing there!
http://apod.nasa.gov/apod/ap091117.html

I think I see your point, but I don't neccessarily agree. If one were to 'split hairs', there's not "nothing there" -- there's a slight thickening of the line indicating the plasma flow which could indicate a flattened & elongated 'chunk' of far-away plasma. If you think in terms of perspective, perhaps that contains enough 'brilliance' to light up the center part of the moons' illumination, while the clumps above & below (the lower one 'fanned' somewhat as it's being pulled away) are lighting the upper & lower parts of the crescents.

In either regard, the author can always claim 'artistic license' - a force at times more powerful than even science fiction!
Just think Picasso.

~S*H

by **mark** » Tue Nov 17, 2009 1:01 pm

This statement

...mass will accumulate onto the white dwarf star until it passes its Chandrasekhar limit ...[then it] will explode in a tremendous supernova.

is wrong. Triggering Ia events is not that simple but much more interesting. Observations and modeling of these Ia events show that unregulated carbon/oxygen burning takes place just prior to the Chandrasekhar limit. This conclusion was established many years (a decade?) ago.

Its a subtle distinction but it has important implications and shows up as slight differences in light curves as the dwarf star undergoes deflagration and delayed detonation.

APOD authors should introduce the public to the latest understanding of these Ia events and not repeat this old, erroneous concept of how these kinds of supernovas occur.

J. Craig Wheeler harps on this outdated scenario for about a page in his wonderful book, Cosmic Catastrophes.

mgo

by **Indigo_Sunrise** » Tue Nov 17, 2009 12:07 pm

Eamon Shute wrote:The lighting in this painting is all wrong!

The crescent moons indicate the direction of the main light source, which should be where these two lines intersect. There is nothing there!

You could send an email to the artist and tell him so..... (his contact info is directly underneath the image.)

by **Eamon Shute** » Tue Nov 17, 2009 7:51 am

The lighting in this painting is all wrong!

The crescent moons indicate the direction of the main light source, which should be where these two lines intersect. There is nothing there!

http://apod.nasa.gov/apod/ap091117.html

Starship Asterisk*

Dawn Before Nova (APOD 17 November 2009)

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