Expert: Philip Stahl - 2/17/2008

Question
QUESTION: How do stars form in clusters or binary when the solar winds from the stars that were formed first push all kinds of gas away to where it leaves the vicinity?  The moon does not have an atmosphere because solar winds from our sun push all gas away from its gravity.  These same solar winds would also push the atmosphere away from earth, but volcanic activity on earth protects its atmosphere from solar winds.  So the question is how could stars form in clusters or binary if solar winds from the first star formed will not allow any kind of gas to settle nearby.


ANSWER: Hello,

First of all, the Moon has no atmosphere because it lacks sufficient gravity to retain one. We know on other planets, e.g. Mars, original denser atmospheres were probably outgassed over time - because the planet's gravitational force of attraction wasn't able to keep it.

To investigate whether a gas will be retained by a particular planet or not one needs to compare the mean speed of the molecules of said gas (at a temperature appropriate to the planet's atmosphere)with the speed of escape velocity from the planet.

If the escape velocity v = (2GM/R)^1/2

where M is the planet's mass, G is the gravitational constant, and R the radius, then we must have (for a gas to be retained):

6 (3kT/m)^1/2  <  (2GM/R)^1/2

At 300 K temperature, for example, oxygen would be expected to be retained by Earth - but NOT by the Moon. Inserting the appropriate numbers (M, R) for the Earth one would find:

4092 m/s <  11,200 m/s

Thus, oxygen is retained.

For the Moon, one would find:

4092 m/s >  1690 m/s

so it is not retained.


By the same token, netiher Earth nor Moon would be expected to retain hydrogen. It is simply too low density a gas to be retained by the surface gravity of either planet.

The Moon, with 1/81 the mass of the Earth, (and with one sixth the acceleration of gravity g) would be in this situation. While solar winds are fast (200-700 km/s) bear in mind the plasma comprising it is extremely tenuous and barely 10 particles/cm^3.

My point here is that the Moon would long ago have lost any atmospheric gases - provided the condition above was met - with or without the presence of a solar wind.

Thus, there is NO way such low density plasma would ever be able to push Earth's atmosphere away. (It can deform the Earth's MAGNETOSPHERE, however) The solar wind simply isn't dense enough in particle terms to overcome the force of attraction of the Earth's gravity - to cause it to lose oxygen, nitrogen etc..

Volcanic activity doesn't "protect" our atmosphere from the solar wind at all - this is a totally new one on me. Rather such activity can alter the thermal balance and indeed - as Mt. Pinatubo's eruption in 1992 showed - cause higher proportion of particulates, dust that can mask a lot of CO2-induced global warming.

More accurately, it is the magnetosphere which takes the full brunt (if you can call it that) of the solar wind, and this means usually sending its charged particles in spiral paths oscillating between the poles. The aurorae are one sign of solar wind impact, and influence on the magnetosphere.

In reference to star cluster formation, be aware firstly, though cluster stars may be born with the same chemical composition - they will have varying masses. This is important because lower mass stars forming (and likely first) will have less stellar wind impact, velocity than more massive ones. (More massive stars one presumes will form later because it takes longer for gravity to accrete enough nebular mass to form a massive star)

These lower mass, presumably initially- formed stars,  will have solar winds that won't exceed 100-200 AU distance from the embryo star. However, the cluster stars themselves will be forming LIGHT YEARS apart in a nebula - and so be beyond the influence of most embryonic stellar winds - in terms of the latter "blowing gases away" to prevent formation. (There is, however, some chance the winds from neighboring stars in a cluster can affect or shape the nascent magnetospheres of later stars)

The very fact that we actually observes clusters such as the Pleiades shows they *must have* overcome stellar wind obstacles. Or, we wouldn't be seeing the clusters!

---------- FOLLOW-UP ----------

QUESTION: I did not see a place to rate that answer it was a 10.  I keep getting this from other astronomers that my questions are too long but this is a complicated subject and I like your comlplicated answer.  Also I watch shows about how planets are formed on PBS and there is one show there that says our poles will eventually flip, and on this show is where I heard that earths magnetic field protects our atmosphere.  I have another question. Scientists say the universe began with a big bang that sent matter hurling in all directions.  After all the matter is separated and scattered, gravity engages and starts pulling together matter that is located nearby each other.  The larger and more massive pieces will pull in the smaller less dense pieces and round solid bodies of matter will form.  When bodies of matter are formed the only possible outcome is that you will end up with a mixed bag.  You will not have one single place in the universe where gravity allowed 92.1% hydrogen, 7.8% helium and .1% other components to come together and form a body of matter.  Gravity does not have a brain where it says I am going to form a star, and then brings together exclusively hydrogen atoms to form a body.  Gravity does not allow gas to form into exclusive bodies of gas because gas is more attracted to solid dense matter than it is attracted to other gas.  Scientists claim that they know the sun is made of 92.1% hydrogen, 7.8% helium and .1% other.  If you study gravity it leaves clear evidence that confirms this is wrong.  The question is does hydrogen atoms have a brain where they can defy gravity from solid pieces of matter and travel to an empty area of space to form a body that excludes all matter?  Mysteriously the planets that ended up revolving these bodies of gas turned out to be made of matter.  Incredibly every time a star forms it tosses out the dust first.  

Answer
Hello again,

First of all, sorry you did not see a ranking or rating option - but I chose to be "unrated" in this category from about a year ago. What I found is that too many respondents didn't know how to exercise the ratings options properly. For example, I would be receiving a '7' for timeliness, when my reply was dispatched the SAME day! (Experts have up to three days to respond). And given 6, 7 or 8 for 'clarity' when they ranked the 'knowledge' component a '10'. HOW can you know the knowledge is complete when you regard the answer as unclear???

Since there is no remuneration, and ratings are the only currency, I opted to do without rather than tolerate increasinly inept ratings. I am considering the same for the 'Astrophysics' category (which can still have my questions ranked, btw) but have taken a 'wait and see' attitude for now.

Re: "long" questions, long answers - that is always a matter of discretion. If I see a long question at least gets to some point, I will usually take it. By that I mean, at some point discrete, specific questions are asked. The answers then will be pitched to that.

I your case, I found the questions had a number of misconceptions that needed to be addressed, and I preferred to take the longer way - to try to make sure you understood where I was coming from (such as the case of atmospheres that can be lost provided certain conditions are met).

In your current cycle of questions, there are several more misconceptions that need to be cleared up. First of all, the big bang did NOT send "matter" scattering in all directions. Truth be told, there was NO MATTER for at least the first 300,000 years or more of the cosmos' existence. There was only RADIATION. Essentially a "photon gas". Formation of any particles was prohibited by the fact that the ambient cosmic temps. were simply too high.

After some hundreds of thousands of years and adequate coooling then what we call the *decoupling* of matter from radiation could occur. Even here, only the lightest gases formed first, namely hydrogen and helium.

Further organization of gas systems would occur not only via gravitational forces of attraction but also electro-magnetic forces acting. As we know, the photons are the media for the EM force. These forces probably would have played as large a role as gravity in ordering the early universe and its nascent objects.

Gas clouds later collapsing to stars in discrete galaxies would have been facilitated by gravity as well as electric and magnetic forces acting. Bear in mind here, under specific conditions of very high magnetic field embedded in a cosmic plasma,

The conductivity of a cosmic plasma can become ‘infinite’ so that even a minuscule induced voltage arising from, E = -v X B (e.g. electric field due to very small relative motion v) would produce an infinite current J.  The only way one avoids this unrealistic situation is to require the plasma motion to follow magnetic field lines rather than cut across them.

Thus, there are certain of what we call "J X B" (J cross B) forces tha can be responsible for a good deal of shaping. Obviously, we have ions in the gases that are being molded, and once J X B forces present themselves we can see a shaping ongoing. If you have ever watched an aurora you would easily see what I mean.

In Alaska, three years ago, I observed as J X B forces as well as "cross-field" currents (J _perp) actually shaped the ionized plasma into sheets then "tubes". One can imagine similar forces at work in the early cosmos in respect to shaping early galaxies, etc.

In reference to the Sun, and the elemental composition of it, don't forget the Sun is a star that formed when the universe was already 5-7 billion years old. Thus hydrogen as well as heavier elements would have formed from the solar nebula - and gravitational attraction would have been assisted by the presence of dust particles.

Indeed, molecular clouds - such as in the Orion region - are replete with not only interstellar molecules ((HCN, H2CO, CH4, HC3N etc. ) but heavier dust that would have acted as a catalyst for accretion and later stellar formation.

The composition for the Sun is deduced from not only the analysis of its spectral "fingerprints" (absorption lines in the solar spectrum) but from the use of nuclear theory - and asking - what composition can give rise to this production of solar luminosity (~ 3.9 x 10^26 Joules/sec) given this solar mass. Such questions give rise to the whole field of solar-stellar modelling. Actually using computers to "build" a model star layer by layer, attending to the pressure, temperature, weight etc. at each layer.

To get a glimpse of such solar modelling, check out Dimitri Mihalas' excellent text 'Stellar Atmospheres' and turn to the Index for 'Solar models'.

So the short answer - after the long prelude- is 'No' - hydrogen atoms have no smarts or brains. They do, however, follow physical laws and principles, in this case - those that apply to nuclear systems as well as the behavior of quanta. Ions - not necessarily "atoms" because as I noted plasma is ionized gas - travel to far reaches of (mostly) empty space via electro-magnetic processes such as the forces described earlier. Also by the solar wind which represents a mass loss (outflow) from the solar corona.

As you read and learn much more astronomy the "mystery" in these processes will cease to dominate and you will more and more come to see simply the inevitable manifestation of physical laws.

Hope this sheds further light.