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."

Comments

Re:Spiral form

[Doctor Fishboy]

I thought that standard opinion on spiral forms (e.g. galaxies) was that they were created by interaction with massive companions.

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

Re:Jupiter and/or Saturn

[CheshireCatCO]

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.