Cannabilizing?

[hazelm]

Let's see if I can say this straight and then ask my question.

 

Ionizing, we know, is taking away or adding electrons to/from atoms.  A book I am reading is describing the formation of new stars in molecular clouds.   These new stars light up bright, vibrant nebulae in the clouds, causing them to glow.  These dazzling patches are known as HII regions.  HII = ionized hydrogen.

 

What I am reading in "Concise Encyclopedia of the Universe" does not make it clear whether there is also regular hydrogen (H2) present in the area.  It only says (quote) "When the new stars 'turn on', they emit ultraviolet radiation, ionizing their surroundings and causing them to glow".

 

What I keep asking myself is "ionizing what?"  HII is already ionized.  Are the new stars taking electrons from nearby H2 for their own atoms?  Or, maybe the word "ionizing" has another meaning related to "ultraviolet radiation" and means nothing more than creating a glow?

 

What am I missing?  Thank you.

[exchemist]

Let's see if I can say this straight and then ask my question.

 

Ionizing, we know, is taking away or adding electrons to/from atoms.  A book I am reading is describing the formation of new stars in molecular clouds.   These new stars light up bright, vibrant nebulae in the clouds, causing them to glow.  These dazzling patches are known as HII regions.  HII = ionized hydrogen.

 

What I am reading in "Concise Encyclopedia of the Universe" does not make it clear whether there is also regular hydrogen (H2) present in the area.  It only says (quote) "When the new stars 'turn on', they emit ultraviolet radiation, ionizing their surroundings and causing them to glow".

 

What I keep asking myself is "ionizing what?"  HII is already ionized.  Are the new stars taking electrons from nearby H2 for their own atoms?  Or, maybe the word "ionizing" has another meaning related to "ultraviolet radiation" and means nothing more than creating a glow?

 

What am I missing?  Thank you.

I am not sure without some context but it rather sounds as if what is meant is that new stars ionise the clouds of gas that surround them. They do after all refer to these stars forming in molecular clouds.

 

They also refer to the ionisation being due to emission of UV light. So that would mean the ionisation process does not involve reactions that remove electrons, but ionisation via excitation of the electrons in the atoms of these clouds.

 

When electrons in atoms absorb light, they get excited to higher energy levels ("orbitals") within the atom. If the energy in the radiation is sufficient, they get excited up beyond the highest bound state and escape from the atom entirely, rather like a rocket leaving the Earth at greater than escape velocity.     

[hazelm]

All right.  Correct me if I am wrong but I think I see what you are saying.  Even though the  article first said there was an HII area growing around the new stars and then later said the stars were ionizing the atoms (perhaps H2 or HII or both), the ionization by light and excitation actually happened first - before that growth.  In fact, caused that growth?  Also, this excitation is a different method of causing the loss of electrons than the method of "removing" electrons.   Now that last sends me off to learn more about the "removal" actions.  :-)

 

Anyway,  am I reading you right? 

[exchemist]

All right.  Correct me if I am wrong but I think I see what you are saying.  Even though the  article first said there was an HII area growing around the new stars and then later said the stars were ionizing the atoms (perhaps H2 or HII or both), the ionization by light and excitation actually happened first - before that growth.  In fact, caused that growth?  Also, this excitation is a different method of causing the loss of electrons than the method of "removing" electrons.   Now that last sends me off to learn more about the "removal" actions.  :-)

 

Anyway,  am I reading you right? 

OK. I presume in these regions there is originally molecular or atomic hydrogen and, as the stars start to shine and emit UV light, some of this hydrogen gets converted to HII, i.e. ionised hydrogen.

 

The process of ionisation via excitation is different from what happens in a chemical reaction, e.g. chlorine Cl taking an electron from sodium Na to form salt NaCl (Na+Cl-). It is just the limiting case of the processes that explain the spectrum of an atom. Electrons normally occupy a "ground state" orbital in the atom but can be made to jump up to other, higher energy orbitals, further out from the nucleus, by absorbing radiation of the right frequency. There is a long "ladder" of these higher energy orbitals but the "rungs" of the ladder get closer together in energy as you go up, eventually converging to a limit, called the ionisation limit. This is the energy at which the electron has broken free from the attraction of the nucleus - and the atom is thus ionised. So radiation can ionise matter in this way.    

[hazelm]

All right.  I'll have to work on that for a while.  Tonight will do.  Thank you again. 

[hazelm]

OK. I presume in these regions there is originally molecular or atomic hydrogen and, as the stars start to shine and emit UV light, some of this hydrogen gets converted to HII, i.e. ionised hydrogen.

 

The process of ionisation via excitation is different from what happens in a chemical reaction, e.g. chlorine Cl taking an electron from sodium Na to form salt NaCl (Na+Cl-). It is just the limiting case of the processes that explain the spectrum of an atom. Electrons normally occupy a "ground state" orbital in the atom but can be made to jump up to other, higher energy orbitals, further out from the nucleus, by absorbing radiation of the right frequency. There is a long "ladder" of these higher energy orbitals but the "rungs" of the ladder get closer together in energy as you go up, eventually converging to a limit, called the ionisation limit. This is the energy at which the electron has broken free from the attraction of the nucleus - and the atom is thus ionised. So radiation can ionise matter in this way.    

Exchemist, I am following fine until the very end.  Maybe I am oversimplifying in what I think is happening.  I have been going from one online link to another and am finding nothing in answer to my question.  Electrons are "knocked out of" an atom.  Then what happens?  Where do they go or what do they become?  The picture I have in my mind is freed electrons floating around in space.  That can't be it.  There is more to it. 

[exchemist]

Exchemist, I am following fine until the very end.  Maybe I am oversimplifying in what I think is happening.  I have been going from one online link to another and am finding nothing in answer to my question.  Electrons are "knocked out of" an atom.  Then what happens?  Where do they go or what do they become?  The picture I have in my mind is freed electrons floating around in space.  That can't be it.  There is more to it. 

Not really, you are right.

 

The electrons must float around in space. And then, from time to time, they get captured by a positively charged ion, resulting in an emission of light as they drop down from a high energy free state to one of the lower energy bound orbitals. Doesn't the passage you quote say that these clouds "glow"? It's a kind of fluorescence, isn't it? 

[hazelm]

Not really, you are right.

 

The electrons must float around in space. And then, from time to time, they get captured by a positively charged ion, resulting in an emission of light as they drop down from a high energy free state to one of the lower energy bound orbitals. Doesn't the passage you quote say that these clouds "glow"? It's a kind of fluorescence, isn't it? 

Ah, of course.  And you know what.  All that is vaguely ringing bells with me.  I got too fixated on "gone where?" and forgot the capture and the energy which is never destroyed.  it just "becomes". 

 

Thank you very much. 

[JMJones0424]

The electrons must float around in space. And then, from time to time, they get captured by a positively charged ion, resulting in an emission of light as they drop down from a high energy free state to one of the lower energy bound orbitals. Doesn't the passage you quote say that these clouds "glow"? It's a kind of fluorescence, isn't it? 

 

Please forgive my ignorance, but this thread has led me to a question that I hadn't had before.  It is easy for me to understand a star as a gravitationally bound ball of ions, but I don't think I had considered the fate of the ions created in the stellar nebula caused by photons liberating electrons from atomic nuclei.  It seems reasonable that the vast majority of these electrons get captured, but must all of them?  Is it not possible that some small percentage escape due to something like solar wind.  For that matter, is not solar wind an ejection of charged particles from a star?  Since electrons have significantly less mass than protons, wouldn't it be safe to assume that a charge imbalance must occur over time in stellar systems?

 

I don't think that we measure this to be the case.  What am I missing?

[hazelm]

Good question, JM.  I shall await answers with you.  Fascinating what is going on up there over our heads.  And hank goodness we have a few people who are able to provide answers. 

[exchemist]

Please forgive my ignorance, but this thread has led me to a question that I hadn't had before.  It is easy for me to understand a star as a gravitationally bound ball of ions, but I don't think I had considered the fate of the ions created in the stellar nebula caused by photons liberating electrons from atomic nuclei.  It seems reasonable that the vast majority of these electrons get captured, but must all of them?  Is it not possible that some small percentage escape due to something like solar wind.  For that matter, is not solar wind an ejection of charged particles from a star?  Since electrons have significantly less mass than protons, wouldn't it be safe to assume that a charge imbalance must occur over time in stellar systems?

 

I don't think that we measure this to be the case.  What am I missing?

Good question, which I have just seen after getting back from my holiday. I don't know how this works myself but, looking it up, I found this partial explanation on wiki:

 

" The Sun's corona, or extended outer layer, is a region of plasma that is heated to over a million kelvin. As a result of thermal collisions, the particles within the inner corona have a range and distribution of speeds described by a Maxwellian distribution. The mean velocity of these particles is about 145 km/s, which is well below the solar escape velocity of 618 km/s. However, a few of the particles achieve energies sufficient to reach the terminal velocity of 400 km/s, which allows them to feed the solar wind. At the same temperature, electrons, due to their much smaller mass, reach escape velocity and build up an electric field that further accelerates ions away from the Sun.^[25]"

 

This suggests that electrons do indeed tend to stream off more readily due to their small mass but this creates an electric field that accelerates +ve ions (the electron deficit will create a buildup of +ve charge that will repel +ve ions, while increasing the barrier to the escape of electrons). I imagine this is implying there is a net +ve charge on the sun sufficient to bring the rate of emissions into electrical balance. But I would like to see this confirmed somewhere, I must admit.  

[hazelm]

Exchemist, excuse my ignorance but what is +ve?  Thank you.  Hazel

[exchemist]

Exchemist, excuse my ignorance but what is +ve?  Thank you.  Hazel

Oh sorry, it's just an abbreviation, quite widely used in physical sciences, for "positive" .

 

And likewise "-ve" for "negative".

[hazelm]

Oh, all right.  Thanks.