Slashdot Mirror
Hubble Captures a Protoplanetary Disk
Astroturtle writes "The Hubble Space Telescope's new Advanced Camera for Surveys (ACS) has
captured a detailed image of spiral rings in a distant protoplanetary
disk -- the pancake-shaped cloud of gas and dust around a young star in
which planets are expected to condense. But contrary to earlier
suggestions, the intricate structure of this particular disk is probably
caused by a nearby companion star rather than by embedded planets starting
to form."
I'm having a little trouble understanding your question, but I think what you're asking is "Would a massive companion body, be it a star or planet, aid in the formation of inner planets?" The answer to that is: kind of. They don't necessarily aid in the formation, but a large body would have the tendency to deflect smaller bodies, thus clearing the areas close to the star of debris. In our case this obviously helped with the formation of life. If the geometry or timeline changed a bit, however, it can be easy to see how a massive companion could inhibit the formation of smaller bodies. Assuming Jupiter was a bit closer to the sun, and was around before any largish planetesimals formed, it's gravity would tend to disperse the planet-forming materials, and lead to a system without close-in rocky planets. So it could really go either way, depending on the timeline you choose.
----
Striving to put right what once went wrong, and hoping each time that his next leap, will be the leap ho
Spirals in galaxies and these spirals in protoplanetary disks have different origins, and in the galactic spirals case, you don't need a binary companion to cause spiral structure.
Who has ever proposed that internal bodies can cause a spiral form?
OK, this is probably a gross simplification, so if there are any disk formation astronomers out there (you know who you are!), they'll give a much better description than this one!
It partially depends on the viscosity of the material in the disk, and where most of the mass resides. If the mass of the disk is much smaller than the mass of the central star, the disk structure is dominated by the gravitational field of the central star and this tends to smooth out any spiral structure in the disk, and then you need a binary companion to stir up spiral modes in the disk.
If the disk itself is massive enough, and the viscocity of the material is low enough, the disk's gravitational field can amplify up any spiral patterns that occasionally appear. So no, you don't need a binary compantion if the disk is massive enough. In this specific case, though, the disk mass is small, and so there's probably a binary companion acting as a swizzle stick.
For galaxies, nearly all the mass resides in the disk of the galaxy and not in the centre (the mass of the black hole in the centre of the galaxy is tiny compared to the rest of the mass in our galaxy, and there's a honking huge halo of dark matter, I know, I know...) and so spiral modes tend to be self-reinforcing as they sweep around the galaxy.
Blurgh, too early on Saturday morning...
Dr Fish
Sorry, but not right. The proto-solar nebula was probably pretty well-mixed in elemental abundances. The reason you get rocky/metallic planets in close and icey giant planets further out is purely a matter of temperature. The inner disk is much hotter than the other disk, so that hydrogen compounds like methane, water and ammonia cannot condense into solid forms. Since there are 10 times as much of these compounds as metals and silicates, planets forming father out (past the "frost line" where water first can freeze out) have much more material to build with. Thus this build faster and into more massive bodies. At around 10 Earth-masses, the cores can start to hang on to nebular gasses like hydrogen and helium. And you get a giant planet. Inside the frost line, you're struck building with rocks and metals, and you get a smaller planet.
No pushing or pulling of specific elements/compounds is involved.
Translation: :-) in the constellation Libra (which is largely irrelevent, really.). It's brightness seen from Earth (presumably) is about a factor of two fainter than the faintest star you can see on a clear, dark night.
"The star is a young fairly massive and hot star 320 light-years away (I'll let you look that one up if you don't already know it
Here's the URL
Debunking the "59 Deceits"
As for your second question, it's to do with the way the stars orbit in a galaxy. If you could draw all the orbits of the stars in a spiral galaxy, you would see a badly stacked set of hula-hoops, - most orbits are nearly circular, and they all go around the galaxy in the same direction. With an elliptical galaxy, the orbits would resemble a tangled hairnet. There's no perferred axis of rotation, and there are many very eccentric orbits.
You tend to see giant elliptical galaxies sitting in the middle of groups of smaller spiral galaxies, and it is thought that collisions between spiral galaxies lead to formation of giant elliptical galaxies. The interaction of the two spiral galaxies' gravitational potentials then scrambled the orbits of the stars together.
Spiral structure NEEDS ordered co-rotating material in which to form, so that's why ellipticals don't form them -the orbits of the stars are too randomised to form them.
I hope this makes some sense!
Dr Fish
Just adding to that excellent explanation, the arcane code HD 141569A merely gives the star's listing in the Henry Draper Catalogue, a gigantic star catalogue (over 250,000 entries) first compiled about a century ago. The spectral class A does denote that HD 141569A is a young, fairly massive, and hot star- its surface temperature should be between 7,500 - 10,000K, and it should be white to blue-white in color. Another example of an A type star would be Sirius.
I also wanted to point out that the story submitter gets it a bit wrong- which is more the fault of the story, which fails to make this clear- HD 141569A is not in a binary system with a single companion star, it is in a three star system with two other stars. These other two stars, HD 141569B and HD 141569C, are in a binary relationship with each other, and together perturb the disk around HD 141569A, which is over 100 billion miles from the pair. This paper (.pdf file) from 1999 on the Arxiv gives more details on the star system and protoplanetary disk.
"FDA staff reviewers expressed concern about the number of patients who were left out of the study because they died."