H Atom 21 cm Line

Is the Milky Way a Spiral Galaxy like this one?

Because of the scattering by gas and dust in the disk

S   1-4

Because of the scattering by gas and dust in the disk S   1-4 We can only see (in the visible) about 1/6 (ca 6000ly) of the way to the Galactic Centre

View towards the Galactic Centre

Nuclear and electron spins paired

Nuclear and electron spins parallel

F = I+S = 0 F = I+S = 1 Nuclear and electron spins paired Nuclear and electron spins parallel

F = I+S = 0 F = I+S = 1 Fermi and Hargreaves Contact Term Nuclear and electron spins paired Nuclear and electron spins parallel

Classical picture of the nucleus as a spinning charge shell which gives rise to two magnetic field regions B = B int + B ext

Classical picture of the nucleus as a spinning charge shell which gives rise to two magnetic field regions B = B int + B ext

Classical picture of the nucleus as a spinning charge shell which gives rise to two magnetic field regions B = B int + B ext B int internal uniform magnetic field

Classical picture of the nucleus as a spinning charge shell which gives rise to two magnetic field regions B = B int + B ext B int internal uniform magnetic field B ext external magnetic field dipolar

s electron Electron density r

s electron p electron Electron density r

s electron p electron Electron density r H = B nucleus.  electron

r H =  B nucleus (r).  e (r) d 

s electron density r H =  B nucleus (r).  e (r) d 

s electron density r External dipolar term H =  B nucleus (r).  e (r) d 

s electron density r dipolar term H =  B nucleus (r).  e (r) d  B nucleus = (B int + B ext )

s electron density r dipolar term H =  B nucleus (r).  e (r) d  B nucleus = (B int + B ext ) H =  B int (r).  e (r) d  + B ext (r).  e (r)d 

s electron density r dipolar term H =  B nucleus (r).  e (r) d  B nucleus = (B int + B ext ) H =  B int (r).  e (r) d  + B ext (r).  e (r)d 

s electron density r dipolar term H =  B nucleus (r).  e (r) d  B nucleus = (B int + B ext ) H =  B int (r).  e (r) d 

s electron density r dipolar term B nucleus  I H =  B nucleus (r).  e (r) d  B nucleus = (B int + B ext ) H =  B int (r).  e (r) d 

s electron density r dipolar term B nucleus  I  e  S H =  B nucleus (r).  e (r) d  B nucleus = (B int + B ext ) H =  B int (r).  e (r) d 

s electron density r dipolar term B nucleus  I  e  S H = a I. S H =  B nucleus (r).  e (r) d  B nucleus = (B int + B ext ) H =  B int (r).  e (r) d 

s electron density r dipolar term B nucleus  I  e  S H = a I. S Fermi contact term H =  B nucleus (r).  e (r) d  B nucleus = (B int + B ext ) H =  B int (r).  e (r) d 

a = (8  /3h) g e  B g H  N  (0)  2

g e electron g factor

a = (8  /3h) g e  B g H  N  (0)  2 g e electron g factor  B Bohr magneton

a = (8  /3h) g e  B g H  N  (0)  2 g e electron g factor  B Bohr magneton g H proton g factor

a = (8  /3h) g e  B g H  N  (0)  2 g e electron g factor  B Bohr magneton g H proton g factor  N nuclear magneton

a = (8  /3h) g e  B g H  N  (0)  2 g e electron g factor  B Bohr magneton g H proton g factor  N nuclear magneton  (0)  2 absolute value of the electron density at the nucleus squared

 1s = (  a o 3 ) -1/2 exp (-r/a 0 )

 1s (0)  2 = 1/  a o 3

 1s = (  a o 3 ) -1/2 exp (-r/a 0 )  1s (0)  2 = 1/  a o 3 a = MHz

 1s = (  a o 3 ) -1/2 exp (-r/a 0 )  1s (0)  2 = 1/  a o 3 a = MHz ca 21 cm

Historical Summary Fermi and Hargreaves calculated a in 1930

Historical Summary Fermi and Hargreaves calculated a in 1930 Rabi measured in lab 1949

Historical Summary Fermi and Hargreaves calculated a in 1930 Rabi measured in lab 1949 Van der Hulst suggested that this line might be detectable from space about 1945

Historical Summary Fermi and Hargreaves calculated a in 1930 Rabi measured in lab 1949 Van der Hulst suggested that this line might be detectable from space about 1945 Ewan and Purcell detected radio spectrum in 1951 Harry Kroto 2004

Doppler Shift  /  =  / = v/c  -v Blue shifted +v Red shifted  Harry Kroto 2004

 Sun Harry Kroto 2004

 Sun  1.6 H atoms per cc Harry Kroto 2004

E

E

a E

a b E

a b c E

a b c E

a b c E a’ Harry Kroto 2004

a b c E b’ a’ Harry Kroto 2004

a b c E b’ c’ a’ Harry Kroto 2004

a b c E b’ c’ a’ Harry Kroto 2004

a b c E b’ c’ a’ Harry Kroto 2004

a and b Blue Shifted c Red shifted - v 0 +v Intensity a b c Harry Kroto 2004

The data that indicate that the Milky Way is a Spiral Galaxy Harry Kroto 2004

The Doppler shifts not great enough to spatially resolve the clouds in this segment Harry Kroto 2004