APOD: The Protoplanetary Disk of HL Tauri... (2014 Nov 10)

[Guest]

Agree about Neptune and not including Plato but planets orbits diameters relative proportion, sun size, highlighted planet suggesting to be Earth but being Mars...

.. being Jupiter! Sorry

[Nitpicker]

Agree about Neptune and not including Plato but planets orbits diameters relative proportion, sun size, highlighted planet suggesting to be Earth but being Mars...

The blip I see on the fourth largest orbit would probably be Jupiter and I don't think it is suggesting Earth at all (but it isn't very high resolution).

[Chris Peterson]

Ok, away from accretion disks again ... How about the various ring systems in our solar system? How do they compare? Saturn's rings are obviously very robust while all other planets have much fainter ones. What keeps Saturn's going? They just started out like that and the other planets didn't?

Well, the formation of planetary ring systems isn't well understood. There may be more than one mechanism for providing the initial material. Saturn is the only planet that has strong evidence of a highly stable ring system, and it appears to be maintained by gravitational interaction and resonances with moons. All ring systems are characterized by being very close to their parent planets- with the inner part, at least, inside the Roche limit.

I don't find the idea that a star could have a long-lived ring system to be out of the question unless there is something about the star that blows away the rings. Hmm.

Dust particles are certainly not able to orbit a star like the Sun for very long before they lose energy to Poynting-Robertson drag and fall into it. I don't think a star with any appreciable energy output could sustain rings or any sort of dust disk unless it was very far away, in which case it would seem to bear no dynamical resemblance to planetary ring systems.

[Chris Peterson]

Isn't this image kind of unprecedented ? I've seen tiny, fuzzy photos described as possible nascent star systems before, but, at 450 light years distant, and using a ground-based observatory, this is an image of amazing detail. Does the Hubble have the instruments to capture a similar image from space ?

The Hubble Telescope lacks the resolution to capture this object with this kind of detail.

[Guest]

I did a google search for HL Tauri and came across this 2008 computer simulation of that Star System



Interesting to look at the two side-by-side, which is what I currently have as by desktop background image

[BMAONE23]

Can somebody help put a scale to this photo?
The description just states it can resolve details as small as 40 light minutes. But 40 light minutes is ~720 million KM, or just shy of where Jupiter orbits.

Does that mean the innermost dark band is approximately where Jupiter would orbit?
Here is a picture that shows the solar system in comparison.

I find the proposed solar system comparison image confussing. Shouldn't be like this one?

The caption for the image linked by Markus, suggests that the outermost orbit is Neptune's.

Yes, the 4 discernible rings in the image representing our system are the orbits of Jupiter, Saturn, Uranus, and Neptune. The two innermost clear ring gaps are at the respective distances of Jupiter and Saturn

[geckzilla]

Dust particles are certainly not able to orbit a star like the Sun for very long before they lose energy to Poynting-Robertson drag and fall into it. I don't think a star with any appreciable energy output could sustain rings or any sort of dust disk unless it was very far away, in which case it would seem to bear no dynamical resemblance to planetary ring systems.

Yes, that "silly" calculation that I came across many months ago continually reminds me that it is not so silly. Still, the idea of a ring system around a star is hard for me to let go of since it's fun. But I'll forget about it for now.

Say, HL Tau is pretty bright for being a protostar. All of this visible light is emitted by the dust colliding with itself in this dense but yet-to-fuse ball?

[Chris Peterson]

Say, HL Tau is pretty bright for being a protostar. All of this visible light is emitted by the dust colliding with itself in this dense but yet-to-fuse ball?

Just because there's no hydrogen fusion in the stellar core doesn't mean the star can't be bright. In fact, its surface is about the same temperature it will have as a main sequence star, but it has a greater diameter now. This star is bright, and will become less so when fusion starts and its collapse ends.

[Mad Ted]

I'm amazed this image is from land-based devices-one wonders how much more we'll be able to see with further advancements in land and space telescopes/cameras!

[Chris Peterson]

I'm amazed this image is from land-based devices-one wonders how much more we'll be able to see with further advancements in land and space telescopes/cameras!

Being space-based doesn't necessarily offer advantages, and in some cases it can be a disadvantage. The submillimeter band where this image was made is not resolution limited by being on Earth. The only disadvantage is that water absorbs these wavelengths, but by operating at a high elevation, atmospheric water has almost no impact. If the telescope array used here were located on the Moon or in space it would not offer any better data, but it would be much more impractical to operate.

[MarkBour]

. . .
Say, HL Tau is pretty bright for being a protostar. All of this visible light is emitted by the dust colliding with itself in this dense but yet-to-fuse ball?

Wow, really? So pretty much all of the radiation that ALMA is capturing in this image is from heat being generated from the initial gravitational collapse, with no significant fusion yet begun? But Chris said the temperature is very high, comparable to the surface of our sun already. And it appears that even the first ring is almost as hot as the central region itself ... at least it is showing almost the same yellow color in the image. Is it out of the question that some fusion has already begun, in both that central region and the first ring?

I wonder what will happen to the material in that ring. Will it also collapse, eliminating the first gap, or will it all get blown away?

[Chris Peterson]

So pretty much all of the radiation that ALMA is capturing in this image is from heat being generated from the initial gravitational collapse, with no significant fusion yet begun?

It's capturing radiation produced by the current gravitational collapse. That radiation is at about 1mm wavelength. For a blackbody, you'd expect similar emission for a 5000K body and a few hundred K. So it's not surprising that the star and the disk look similarly bright. (1mm is about the wavelength of the peak 2.7K microwave background.)

Is it out of the question that some fusion has already begun, in both that central region and the first ring?

Fusion would begin first in the center of the protostar. It's not out of the question, but I think it's unlikely. But it certainly has not, and never will begin in the disk structure, including the inner ring, which is nowhere near hot enough (by many orders of magnitude).

I wonder what will happen to the material in that ring. Will it also collapse, eliminating the first gap, or will it all get blown away?

I assume it depends on the degree to which it has accreted once the star enters the main sequence. Accreted material will survive as close planets. Dust and small particles will either be blown outwards or drag will cause it to fall into the star. Either way, the system will be cleared of most dust.

[aildoux]

I see lumps in the rings. Could be that future images of this could track these lumps and then show them orbiting the star.