Starship Asterisk*

When thermonuclear fusion begins in the core of a new star, a strong stellar wind is produced to prevent the infall of any new mass - so the theory goes.

What is the comparison in strength between this T Tauri wind and the current solar winds ? For how many AU's was this wind effective in evacuating the protostar disk's dust and gases ? Could this wind exert outward forces on bodies like the asteroids inside one AU distance and/or at the present distance of the asteroid belt ?

Is it now proposed that this wind removed most of the atmospheres from the inner terrestial planets or was the initial heat generated by gravitational collapse the culprit that made the inner planets mostly rocky ?

Doug Ettinger
Pittsburgh, PA

The claim is made that protostars with masses more than 0.08 solar masses will begin to reach temperature high enough for nuclear fusion of hydrogen. So when a sufficient core size develops, a T Tauri wind or strong stellar wind is generated to repel the infall of more material thereby limiting the size of the star.

A question arises: How can there be varying sizes or mass of stars if at a certain point the T Tauri radiation winds blow all further material away via collimating bipolar flow ?

Doug Ettinger
Pittsburgh, PA

The T Tauri wind is many, many times stronger than the Solar wind. The only thing they have in common is the word "wind"!
Most of the T Tau wind is ejected through the star's poles and can extend for a huge number of AU, possibly even up to a light-year or more. It is caused by the escape of excess material falling onto the star from the circumstellar disc. Think of the T Tau wind as being the overflow from a full bath - the excess water has to go somewhere. The excess material can't escape from the equatorial regions - that's the very region that's "causing the problem" so to speak, so it takes the easiest possible path, farthest from the equator - i.e., the poles. Many T Tau jets are visible to us, even at distances of 300 or more lightyears.
The Solar wind, on the other hand, is produced by a completely different mechanism - i.e., just the normal radiative activity of our very well-behaved Sun.
Cheers,
Mike Poxon, UK

starman wrote:The T Tauri wind is many, many times stronger than the Solar wind. The only thing they have in common is the word "wind"!
Most of the T Tau wind is ejected through the star's poles and can extend for a huge number of AU, possibly even up to a light-year or more. It is caused by the escape of excess material falling onto the star from the circumstellar disc. Think of the T Tau wind as being the overflow from a full bath - the excess water has to go somewhere. The excess material can't escape from the equatorial regions - that's the very region that's "causing the problem" so to speak, so it takes the easiest possible path, farthest from the equator - i.e., the poles. Many T Tau jets are visible to us, even at distances of 300 or more lightyears.
The Solar wind, on the other hand, is produced by a completely different mechanism - i.e., just the normal radiative activity of our very well-behaved Sun.
Cheers,
Mike Poxon, UK

I am very confused. Thanks for answering my question. My Wikipedia reference for "T Tauri winds" explains that after thermonuclear reactions start a strong stellar wind is produced, continues to grow, and evetually stops the infall of material. This same reference also states that these winds are a bipolar outflow as you have stated. I always thought these winds were Herbig-Haro (HH) objects. Perhaps the T Tauri winds create these objects.

So if the winds flow from only from the polar regions how then is the infall of material around the equatorial regions stopped ? And the question remains as to how different size stars are formed if the fusion process and T Tauri winds always begin at a certain core mass size ?

Doug Ettinger
Pittsburgh, PA

Hi Doug,
Yes, Herbig-Haro objects are the visible manifestation of a bipolar outflow. The current idea is that the infall is stopped when the star begins nuclear fusion and blows the surrounding material away through radiation pressure (possibly to then initiate further shockwave-induced star formation nearby). This again is a wind, this time of the same sort as the Solar Wind. So the sequence is:
1) Star forms by concentration and gravitational heating of the parent gas cloud
2) Positive feedback process initiated by which star acquires more mass and accretes material
3) Protostar "saturated" so that excess infalling material escapes through poles (T Tau wind)
4) Nuclear fusion stage - stellar wind dismisses circumstellar material.

(Not all stages of the star forming process are completely understood as yet!)

Mike.

starman wrote:Hi Doug,
Yes, Herbig-Haro objects are the visible manifestation of a bipolar outflow. The current idea is that the infall is stopped when the star begins nuclear fusion and blows the surrounding material away through radiation pressure (possibly to then initiate further shockwave-induced star formation nearby). This again is a wind, this time of the same sort as the Solar Wind. So the sequence is:
1) Star forms by concentration and gravitational heating of the parent gas cloud
2) Positive feedback process initiated by which star acquires more mass and accretes material
3) Protostar "saturated" so that excess infalling material escapes through poles (T Tau wind)
4) Nuclear fusion stage - stellar wind dismisses circumstellar material.

(Not all stages of the star forming process are completely understood as yet!)

Mike.

Thank you, Mike Starman. I presume this wind with no name is simply a much stronger Solar Wind of today that produced the rocky, terrestrial planets. Has its wind speed been measured or postulated? What is the known distance affect of this strong wind before its push on infalling material slows it down ? Is this wind's push strong enough to keep pushing all the way to 40 AU's, the radius of our solar system ? If the converging infalling material is blown away circumferentially how is it able to induce another star to form ? Some seed of attraction is needed.

The answer to this next question may not be known. If nuclear fusion is caused by a certain volume and density of infalling material and has a feedback control of bipolar jet outflow, how are stars of varying sizes created ?

Doug Ettinger
Pittsburgh, PA

Yes, I think that's the case. I am sure that YSO wind speeds have been calculated. Best thing to do is find a tech site and if you can search, put in "P Cygni profile" - P Cyg stars have especially energetic winds and a whole class of spectral characteristics have been named after them (even if they are not remotely like P Cyg itself!).
As regards size, all sorts of things depend on the structure of the parent gas cloud and/or immediate neighbourhood. Often the cloud will form non-single stars, such as T tau itself. Sometimes, in the early stages, when the star is forming, its fast rotation will also cause breakup. In that regard, the bipolar outflow acts as a safety valve against this.
Very little input is needed to initiate new star formation, since the process is highly sensitive. Only a small shock wave in the gas cloud will cause condensation to begin, and since the process is one of positive feedback, seemingly trivial disturbances can have far-reaching effects, and the force of the "turning-on" process appears to be more than sufficient to get the process going elsewhere. Bear in mind that often, a lot of the stars in the parent gas cloud may well be very close together. Also bear in mind that the variation in star size we observe is also related to such things as the star's age and so on.

starman wrote: As regards size, all sorts of things depend on the structure of the parent gas cloud and/or immediate neighbourhood. Often the cloud will form non-single stars, such as T tau itself. Sometimes, in the early stages, when the star is forming, its fast rotation will also cause breakup. In that regard, the bipolar outflow acts as a safety valve against this.

Very little input is needed to initiate new star formation, since the process is highly sensitive. Only a small shock wave in the gas cloud will cause condensation to begin, and since the process is one of positive feedback, seemingly trivial disturbances can have far-reaching effects, and the force of the "turning-on" process appears to be more than sufficient to get the process going elsewhere. Bear in mind that often, a lot of the stars in the parent gas cloud may well be very close together. Also bear in mind that the variation in star size we observe is also related to such things as the star's age and so on.

My question about what causes's different size star masses only refers to stars on the Main Sequence. The size range of interest is from about 1 to 100 solar masses. If YSO (young stellar objects) solar winds evacuate the protostar disk after fusion is started inside the core of the YSO after a certain density is reached, which of course happened to our Sun of one solar mass, how then are larger stars created if more infalling material is pushed away ?

Perhaps, if the protostar disk is dense enough then the gravity of the infalling materials overcomes the forces of the YSO solar winds. When a balance is achieved then the star stops growing. So then the size of the star is dependent upon the mass and density of the protostar disk. Is this thinking close to the current model ?

Doug Ettinger
Pittsburgh, PA

Hi Doug,
Certainly the higher-end mass star formation process isn't as fully understood as the solar-mass end. One possibility is that since high-mass stars are invariably confined to the galactic equator regions, where there is more ISM (and more stars) then perhaps the high-mass stars are produced by the merger of two or more stars, but recent research at the UKIRT on Mauna Kea indicates that in fact the two mass domains seem to form by similar processes.
One brief (and possibly recurrent) substage in the T Tau process is the FU Orionis (FUOR) stage. These used to be called slow novae, since it took several months, sometimes years, for the star to rise by 5 or 6 magnitudes to a maximum, and then many years for the fall. A perfect example is V1057 Cyg in the North America Nebula. After rising from magnitude 16 to 10 in 1970, this object is currently around magnitude 13. The FUOR stage appears to consist of the dumping of large quantities of the gas cloud onto the star (more or less bypassing the accretion disc) so that may be a contributory effect. Only a theory though!
Mike