What a Star’s Orbiting Disk Is Made Of

NY Times ^ | March 13, 2008 | DENNIS OVERBYE

[neverdem]

NASA/JPL-Caltech
An artistic rendering of a very young star encircled by a disk of gas and dust.

The winking star has sand in its eye.

Back in 2002, astronomers from Wesleyan University concluded that a star brightening and waning in an unusual 48-day rhythm was dipping in and out of stuff swirling around the star in a so-called protoplanetary disk. At the time one astronomer called the system “a Rosetta stone,” for understanding how planets form.

Now, after six more years of observation with an international group of astronomers, led by William Herbst of Wesleyan, researchers say they know what the stuff in this disk is. In a paper published on Thursday in the journal Nature, they report that it is made of sand-size grains, roughly a millimeter in diameter, which must have grown from infinitesimal dust particles over the three million years that the star, known as KH 15D, has been in existence.

“This is the first step in going from smoke particles to macroscopic things like planets and asteroids,” Dr. Herbst said in an interview, noting that these grains were about the same size as those found in many meteorites. Observing starlight reflected from these grains, he said, represented a rare opportunity to study the structure and chemical properties of material in the inner parts of another planetary system.

The discovery is part of what has become a flood of information lately as astronomers have turned increasingly powerful eyes, like the Hubble and Spitzer space telescopes and ground-based giants, on the putative planet nurseries surrounding other stars.

There are water and organic molecules in the inner regions of the disk around another young star known as AA Tauri — more good news for eventual life — according to spectroscopic measurements made with the Spitzer...

[neverdem]

Reflected light from sand grains in the terrestrial zone of a protoplanetary disk

[dyed_in_the_wool]

So they took all that time and finally figured it was only dust, eh?
Didn’t see that one coming.

[neverdem]

ping

[hosepipe]

STAR dust... reminds me of a song..

[onedoug]

KH 15D a variable.... It’ll evidently be some time until it settles into main sequence, and then, depending on its position in the galaxy, whether life may start therein, and continue God’s legacy....

[dighton]

Bump for ultra-cool images &c.

[stickman20089]

bookmark

[neverdem]

States May Warn Doctors to Follow Smoker Treatment Guidelines or be Sued for Medical Malpractice

Hong Kong closes school after pupil dies of bird flu

Oil Price Bubble? - Supply is up, demand is down, yet the price is soaring. Here's why.

FReepmail me if you want on or off my health and science ping list.

[zeestephen]

Raises an interesting question.

What is the physical mechanism that caused micron sized star dust to aggregate into millimeter sized sand grains?

Gravity between micron dust particles?

Another question, on planetary science, but way off this topic.

The “thickness” of the Milky Way is about 1000 light years.

How close to the “top” and “bottom” of the disc surface is planet Earth?

Also, do astronomers notice any change in the stars or star density near the disc surface?

neverdem - thanks - love your science and tech posts.

[notdownwidems]

What the hell’s the Spitzer space telescope doing? Looking in the window at the YWCA?

[Content Provider]

Looking in on some, uh... ‘orbiting disks’, I hear.

[Captain Beyond]

bump

[UndauntedR]

What is the physical mechanism that caused micron sized star dust to aggregate into millimeter sized sand grains?

That's a tough one. You have magnetic polarizations which could mess with diamagnets, you have ionic forces from ionizations in solar winds, you have VanderWalls forces in calm regions... Gravity would only become dominant after some seeding of particles I would think. I'm a physicist, but not an astrophysicist so I could be totally off base.

The “thickness” of the Milky Way is about 1000 light years. How close to the “top” and “bottom” of the disc surface is planet Earth?

According to these guys we're about 65 light years from the galactic plane. Most good estimates look like 60-100. Wikipedia says we oscillate "vertically" ~2.7 times per galactic orbit... which is once every ~80 million years - faster than I thought. I did a quick back of the napkin crunch and got an amplitude of about 200 light years about the galactic plane.

Also, do astronomers notice any change in the stars or star density near the disc surface?

I don't doubt it, the density profile is how the galactic disk is defined and one way to calculate your distance from it.

[SunkenCiv]

Nyah, nyah:

Astronomers find grains of sand around distant stars
PhysOrg | March 12, 2008 | Rice University
Posted on 03/13/2008 2:41:49 PM EDT by SunkenCiv
http://www.freerepublic.com/focus/f-chat/1985171/posts

In the new study, Johns-Krull and co-authors in the United States, Germany and Uzbekistan used reflected light from the sand itself to confirm the Earth-like orbit of grainy particles around a pair of stars called KH-15D...

[zeestephen]

Undaunted - Thank you - very helpful comments - I’m a very late arrival to astronomy - almost 60 years old , and, until recently, I never thought seriously about the cosmos - the most intriguing thing to me is the pure, non-emotional character of space science - it’s either true, false, or unknown - it’s a nice vacation from the shades-of-gray passions that animate politics, which has always been the great love of my life.

[SunkenCiv]

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