Also I am currently engaged in writing out a hundred times, “symmetrical”. I knew there was something wrong with my first and second attempts at spelling it, but I forgot to look it up.

Ivan.

If it was simmetrical, it would not have attracted as much attention, but being lop-sided, we have to account for it. So if we have parts of two arms on one side, from our perspective, then we can expect more mass and/or greater extension in the view. By the way, one could see the same effect looking at a propellor or even a fan – three-bladed types of course.

Have we had enough time to get a fix on any differential movement of stars or mass of gas in those spirals?

Ivan.

Of course, the particles do interact. They collide, they have gravitational interactions, the bulk mass of the disk pulls them around, and probably fifteen other effects I haven’t thought of. Any such interaction is going to change the orbits of the objects involved. It probably won’t circularize them directly, but at the least the eccentricity and particularly the orientation of the ellipse they follow will change. If you imagine it as gradually randomizing the orientations, then after some amount of time you’ll have a lot of particles moving in ellipses, but the eliipses will be pointing every which way. If they get to the point that they’re evenly distributed, so that the typical size in every direction is the same, then you have a circular disk, even though all the orbits might be elliptical!

The orbits probably won’t stay elliptical, since elliptical orbits in an arrangement like that will be constantly crossing each other, causing lots of interactions; the system will tend to circularize (since circular orbits don’t interact so much, it’s a more stable configuration) and we’ll be back to a normal disk situation.

The interactions that happen in a circular disk situation are what allow material to migrate inward and ultimately fall into the central object. When the interactions fall off, because there just aren’t that many objects left, you’re left with a very long-lived disk or ring, like Saturn’s; it may be so sparse it’s a planetary system.

What I find really interesting about this one is that it must have gotten a kick – a particular, well-ordered kick – pretty recently, so it hasn’t had time to circularize itself. I wonder how long that process takes? I don’t even have an order-of-magnitude idea of the timescale. The shorter it is, the harder it is to believe some rare event caused this (because there’s less time for it to have happened in). So I bet the disk modelling people are having a field day with this one (and maybe a few shouted arguments with their cluster dynamics colleagues). Anyone have a number for the circularization time?

I think that question would be better answered by the BA, though, as I am a toxicologist, not an astronomer.

I wonder how the protoplanetary disk’s eccentricity effects planetary accretion? It might kick it into overdrive… Anybody you know running simulations?
Richard B. Drumm
Vice President, CAS

Oh, not that dust?

- If the near miss with HIP 12545 caused such an asymmetry for HD15115, did the close encounter leave any telltale traces on HIP12545?

- The Keck article mentions the missing mass and the lower dust level of this Blue Needle compared to its group stars nearby. If, by any chance, this points to some planets already formed around HD15115, what is the minimum time required to form planets? Somehow 12 million years sounds extremely young.

How can we rule out the possibility that such an event didn’t occur to our planetary system?

Is it possible that billions of years from now, this star HD15115, would develop into a planetary system without any evidence of its archaic encounter with HIP12545?

The prime difference, IMHO, between Scientists and *ahem* others, is that Scientists are not only not afraid of the BAM, but actually seek it out. In a sense, a real Scientist is a BAM-o-maniac…

Perhaps that’s why those of us who are fans of Science, but do not possess advanced degrees, or professions in which we can directly experience BAM come on here: We get our daily BAM fix, and that helps us get through the ‘jones’ that the world inflicts on us (As evidence, try, just try going without your daily dose of BA, or APOD, or Skepchick, or any of the other excellent Science websites for a week. Then, when you are channel surfing, FORCE yourself to flip PAST the Discovery channel, the Science channel, TLC, and even Animal Planet, but be sure to have a ready supply of your favorite calming potion handy…)

Even out? Well I think, once you disturbed that thing it will take A LOT (if not “for ever”) of time to make a nice round-shaped disk again. I’m thinking here about “entropy”, a round-shaped disk is very special I guess, so it’s unlikely that it will go back to this state.

Another point, Phil mentioned that the star has built inside a cluster of stars and they are moving out now… maybe the star is rushing to the “left” in ths picture

How much time would it take to even out? And how much time has passed since the disk was disturbed?

I’m just guessing here, admittedly, but it seems to me that the answer lies in the answer to those two questions.

Today, folks, we’re gonna make worlds!!