Does a star form rapidly so to be observed?

[nycpaull]

Perhaps one of the most read phrases in my decades long, daily viewing of APOD is the term "star-forming region" which would lead one to think that looking at that region long enough would allow one to observe a star forming. Somehow, my mind can not imagine a star forming (or can I say igniting) slowly. My mind's eye imagines some gaseous material collecting into a dark hot ball and at some time a thermo nuclear reaction in the interior turns it into a bright, burning globe. Have I missed one of your beautiful animations showing the time-line for star formation? Is it relatively fast enough to be observed or do those nasty dust clouds keep us from seeing the "birthday" of a star?

[Chris Peterson]

Perhaps one of the most read phrases in my decades long, daily viewing of APOD is the term "star-forming region" which would lead one to think that looking at that region long enough would allow one to observe a star forming. Somehow, my mind can not imagine a star forming (or can I say igniting) slowly. My mind's eye imagines some gaseous material collecting into a dark hot ball and at some time a thermo nuclear reaction in the interior turns it into a bright, burning globe.

Star formation is not instantaneous. Material heats up over tens of thousands of years or more due to gravitational collapse, and ultimately creates a protostar. We see many of these (although they are dust shrouded for much of their existence). As the gravitational collapse continues, the protostar gets hotter, and eventually is hot enough for fusion to begin. This is the transition from protostar to star, and while it is probably fast, it isn't visually apparent. The star doesn't suddenly get brighter or change in character. All that changes is that the primary energy source changes from gravitational collapse to nuclear fusion. The temperature doesn't change when fusion starts (although it begins to get hotter over thousands of years).

[geckzilla]

There have been cases where we thought at first maybe we were seeing light from a new star but they turned out to be variable nebulas instead. I think in order to watch new stars light up you'd need to combine many observations over the years. Young stellar objects are dynamic enough that we can watch the jets emitted from them and see them move significantly over just a few years. I know the HST has done this and probably some others as well but the problem is we've only been able to do this for a couple of decades and that's not very long.

It would be a very cool long-term project to get acquire pictures of the same active star-forming area at regular intervals and see what kind of animation came out of it after say, 100 years. Not sure that would be enough to note much change, but it might inspire astronomers to keep the project going indefinitely. Simulations are nice and all but wouldn't it be great to have some real observations? The rough part would be getting them done in infrared. It's really great at cutting through at least part of the dust. The chances of having a stable infrared space telescope (or more likely, multiple telescopes) over a hundred year period seems low.

[nycpaull]

Oh geck! You're my kinda thinker. An animated photo GIF of infrared heat growing hotter and hotter until optical light pops on. It is strange however that such a common event has no greater description than dust collecting together. Thought Experiment: you are floating in a dusty nebula and suddenly to your right some dust clumps together. Why that clump? What else is flying by? How varied are dust densities in the volume around you? Do pressure waves from different sides have to push dust together to start the process like making a snow ball? How many unfinished clumps of stuff never got born as stars? Interesting thought picture swimming through a dusty nebula and you suddenly come across a star fetus or dust ball or star dust. APOD is so, so cool.

[Chris Peterson]

Oh geck! You're my kinda thinker. An animated photo GIF of infrared heat growing hotter and hotter until optical light pops on. It is strange however that such a common event has no greater description than dust collecting together.

It doesn't work that way. We're talking about blackbodies. As the material grows hotter, its peak spectral output shifts to shorter wavelengths. The process is a continuum. Long before it becomes a star, it is glowing brightly in the visible spectrum (having gotten brighter and bluer over thousands of years). The boundary between a protostar and a star is the point where fusion becomes dominant, but that doesn't change the visual appearance. So there's no "popping on" of light at any point in the process.

Thought Experiment: you are floating in a dusty nebula and suddenly to your right some dust clumps together. Why that clump? What else is flying by? How varied are dust densities in the volume around you? Do pressure waves from different sides have to push dust together to start the process like making a snow ball?

There is only a small amount of dust, and a very large amount of hydrogen. The gravitational mass of the hydrogen cloud is what keeps the dust localized. Electromagnetic processes dominate in causing the dust to clump initially. Only once these massive objects become quite large- centimeters at least- does gravity become the dominant force in bringing them together.

How many unfinished clumps of stuff never got born as stars?

Most, probably. Once a star is well into its development, it dissipates the dust and gas around it.

[nycpaull]

Thanks so much Chris. I really appreciate your input and time. I just found the "Sixty Minutes" story on ALMA which filled in some visuals to your comments.
http://www.cbsnews.com/news/alma-telesc ... rses-past/ I'm sure APOD will be passing on what those guys find.

Holy cow. Look was the ALMA web page is showing. http://www.almaobservatory.org/en/press ... d-by-alma-

God I love this internet for what you can learn with a few keystrokes.

[geckzilla]

If you find something you think is interesting and should be on APOD, you can always post it here:
http://asterisk.apod.com/viewtopic.php?f=29&t=33714