VictorBorun wrote: ↑Sat Jan 30, 2021 2:45 pm
By the way, when a galaxy rams into a cluster and gets shiny and blue, is the blue from blue giants and supergiants formation?
Can it be directly the galaxy gas disk hitting the cluster gas?
Thermal light is blue when it is very hot. Not 6000°K like the Sun but say 20,000°K.
At 300° thermal speed of molecules is 400 m/s (N2) or 1200 m/s (He). I guess it's 1700 m/s (H2) or 2400 m/s (H).
So at 20,000°K it's 70 times the energy or 8 times the speed, 20,000 m/s
OK, I quit. Ramming into a cluster at 3000 m/s is done, at 20,000 m/s is not.
You sort of have the right ideas.
However:
- 1) low density excited gases emit narrow individual spectral lines
... NOT continuous black body radiation.
2) colliding neutral gas atoms might well be mostly elastic and, thereby,
deposit their colliding energy into turbulence & sound waves rather than into ionization.
https://en.wikipedia.org/wiki/H_II_region wrote:
<<An H II region or HII region is a region of interstellar atomic hydrogen that is ionized.It is typically a cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light years, and density from a few to about a million particles per cubic cm.
Chemically, H II regions consist of about 90% hydrogen. The strongest hydrogen emission line, the H-alpha line at 656.3 nm, gives H II regions their characteristic red colour. (This emission line comes from excited un-ionized hydrogen.)
Typically H II regions reach temperatures of 10,000 K. They are mostly ionised gases with weak magnetic fields with strengths of several nanoteslas. Nevertheless, H II regions are almost always associated with a cold molecular gas, which originated from the same parent GMC.
H II regions are found only in spiral galaxies like the Milky Way and irregular galaxies. They are not seen in elliptical galaxies. In irregular galaxies, they may be dispersed throughout the galaxy, but in spirals they are most abundant within the spiral arms. A large spiral galaxy may contain thousands of H II regions.
The reason H II regions rarely appear in elliptical galaxies is that ellipticals are believed to form through galaxy mergers. In galaxy clusters, such mergers are frequent. When galaxies collide, individual stars almost never collide, but the GMCs and H II regions in the colliding galaxies are severely agitated. Under these conditions, enormous bursts of star formation are triggered, so rapid that most of the gas is converted into stars rather than the normal rate of 10% or less.
Galaxies undergoing such rapid star formation are known as starburst galaxies. The post-merger elliptical galaxy has a very low gas content, and so H II regions can no longer form. Twenty-first century observations have shown that a very small number of H II regions exist outside galaxies altogether. These intergalactic H II regions may be the remnants of tidal disruptions of small galaxies, and in some cases may represent a new generation of stars in a galaxy's most recently accreted gas.>>
[quote=VictorBorun post_id=310373 time=1612017932 user_id=145500]
By the way, when a galaxy rams into a cluster and gets shiny and blue, is the blue from blue giants and supergiants formation?
Can it be directly the galaxy gas disk hitting the cluster gas?
Thermal light is blue when it is very hot. Not 6000°K like the Sun but say 20,000°K.
At 300° thermal speed of molecules is 400 m/s (N2) or 1200 m/s (He). I guess it's 1700 m/s (H2) or 2400 m/s (H).
So at 20,000°K it's 70 times the energy or 8 times the speed, 20,000 m/s
OK, I quit. Ramming into a cluster at 3000 m/s is done, at 20,000 m/s is not.[/quote]
You sort of have the right ideas.
However:
[list]1) low density excited gases emit [b][u][color=#FF0000]narrow individual spectral lines[/color][/u][/b]
... NOT continuous black body radiation.
2) [b][u][color=#0000FF]colliding neutral gas atoms might well be mostly elastic[/color][/u][/b] and, thereby,
deposit their colliding energy into turbulence & sound waves rather than into ionization.[/list]
[quote=https://en.wikipedia.org/wiki/H_II_region]
<<An H II region or HII region is a region of interstellar atomic hydrogen that is ionized.It is typically a cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light years, and density from a few to about a million particles per cubic cm.
Chemically, H II regions consist of about 90% hydrogen. The strongest hydrogen emission line, the H-alpha line at 656.3 nm, gives H II regions their characteristic red colour. (This emission line comes from excited un-ionized hydrogen.)
Typically H II regions reach temperatures of 10,000 K. They are mostly ionised gases with weak magnetic fields with strengths of several nanoteslas. Nevertheless, H II regions are almost always associated with a cold molecular gas, which originated from the same parent GMC.
H II regions are found only in spiral galaxies like the Milky Way and irregular galaxies. They are not seen in elliptical galaxies. In irregular galaxies, they may be dispersed throughout the galaxy, but in spirals they are most abundant within the spiral arms. A large spiral galaxy may contain thousands of H II regions.
The reason H II regions rarely appear in elliptical galaxies is that ellipticals are believed to form through galaxy mergers. In galaxy clusters, such mergers are frequent. When galaxies collide, individual stars almost never collide, but the GMCs and H II regions in the colliding galaxies are severely agitated. Under these conditions, enormous bursts of star formation are triggered, so rapid that most of the gas is converted into stars rather than the normal rate of 10% or less.
Galaxies undergoing such rapid star formation are known as starburst galaxies. The post-merger elliptical galaxy has a very low gas content, and so H II regions can no longer form. Twenty-first century observations have shown that a very small number of H II regions exist outside galaxies altogether. These intergalactic H II regions may be the remnants of tidal disruptions of small galaxies, and in some cases may represent a new generation of stars in a galaxy's most recently accreted gas.>>[/quote]