by Ann » Sat Apr 08, 2023 5:12 am
johnnydeep wrote: ↑Fri Apr 07, 2023 8:54 pm
So, Ann, if Rigel is not responsible for the red in the part of Bernard's Loop that it is near, what is?
Britannica wrote:
H II region, also called diffuse nebula or emission nebula, interstellar matter consisting of ionized hydrogen atoms. The energy that is responsible for ionizing and heating the hydrogen in an emission nebula comes from a central star that has a surface temperature
in excess of 20,000 K. The density of these clouds normally ranges from 10 to 100,000 particles per cubic cm; their temperature is about 8,000 K.
Wikipedia wrote:
Usually, a young star will ionize part of the same cloud from which it was born, although only massive, hot stars can release sufficient energy to ionize a significant part of a cloud. In many emission nebulae, an entire cluster of young stars is contributing energy.
Stars that are
hotter than 25,000 K generally emit enough ionizing ultraviolet radiation (wavelength shorter than 91.2 nm) to cause the emission nebulae around them to be brighter than the reflection nebulae. The radiation emitted by cooler stars is generally not energetic enough to ionize hydrogen, which results in the reflection nebulae around these stars giving off more light than the emission nebulae.
Since the surface temperature of Rigel is ~ 12,000 K, Rigel's ability to create a (blue) reflection nebula around itself is much greater than its ability to ionize a (red) emission nebula. But the strong wind of Rigel can scatter and spread out the glowing red clouds of hydrogen that are a part of Barnard's Loop, and which have been ionized by other means.
Nebulosity around Rigel. Credit: Stanislav Volskiy.
So what caused Barnard's Loop, then?
Wikipedia wrote about Barnard's Loop:
The loop extends over about 600 arcminutes as seen from Earth, covering much of Orion. It is well seen in long-exposure photographs, although observers under very dark skies may be able to see it with the naked eye.
Recent estimates place it at a distance of either 159 pc (518 light years)[1] or 440 pc (1434 ly) giving it dimensions of either about 100 or 300 ly across respectively. It is thought to have originated in a supernova explosion about 2 million years ago, which may have also created several known runaway stars, including
AE Aurigae,
Mu Columbae and
53 Arietis, which are believed to have been part of a multiple star system in which one component exploded as a supernova.
The Wikipedia info on AE Aurigae, Mu Columbae and 53 Arietis doesn't quite corroborate the suggestion that there was a supernova in Orion some 2 million years ago... but, you know. Estimating exactly when something happened out there in space is a tricky business!
We may also ask why Barnard's Loop, if it is a supernova remnant, is so "one-sided". Shouldn't it look like a "full circle"?
Not necessarily. Other supernova remnants are also asymmetrical, like, for example, RCW 86.
Ann
[quote=johnnydeep post_id=330269 time=1680900870 user_id=132061]
So, Ann, if Rigel is not responsible for the red in the part of Bernard's Loop that it is near, what is?
[/quote]
[quote][url=https://www.britannica.com/science/H-II-region]Britannica[/url] wrote:
H II region, also called diffuse nebula or emission nebula, interstellar matter consisting of ionized hydrogen atoms. The energy that is responsible for ionizing and heating the hydrogen in an emission nebula comes from a central star that has a surface temperature [b][size=120][color=#00e6ff]in excess of 20,000 K[/color][/size][/b]. The density of these clouds normally ranges from 10 to 100,000 particles per cubic cm; their temperature is about 8,000 K.[/quote]
[quote][url=https://en.wikipedia.org/wiki/Emission_nebula#General_information]Wikipedia[/url] wrote:
Usually, a young star will ionize part of the same cloud from which it was born, although only massive, hot stars can release sufficient energy to ionize a significant part of a cloud. In many emission nebulae, an entire cluster of young stars is contributing energy.
Stars that are [b][size=120][color=#00a0ff]hotter than 25,000 K[/color][/size][/b] generally emit enough ionizing ultraviolet radiation (wavelength shorter than 91.2 nm) to cause the emission nebulae around them to be brighter than the reflection nebulae. The radiation emitted by cooler stars is generally not energetic enough to ionize hydrogen, which results in the reflection nebulae around these stars giving off more light than the emission nebulae.[/quote]
Since the surface temperature of Rigel is ~ 12,000 K, Rigel's ability to create a (blue) reflection nebula around itself is much greater than its ability to ionize a (red) emission nebula. But the strong wind of Rigel can scatter and spread out the glowing red clouds of hydrogen that are a part of Barnard's Loop, and which have been ionized by other means.
[float=left][attachment=0]Rigel detail Volskiy.png[/attachment][c][size=85][color=#0040FF]Nebulosity around Rigel. Credit: Stanislav Volskiy.[/color][/size][/c][/float]
[clear][/clear]
So what caused Barnard's Loop, then?
[quote][url=https://en.wikipedia.org/wiki/Barnard%27s_Loop]Wikipedia[/url] wrote about Barnard's Loop:
The loop extends over about 600 arcminutes as seen from Earth, covering much of Orion. It is well seen in long-exposure photographs, although observers under very dark skies may be able to see it with the naked eye.
Recent estimates place it at a distance of either 159 pc (518 light years)[1] or 440 pc (1434 ly) giving it dimensions of either about 100 or 300 ly across respectively. It is thought to have originated in a supernova explosion about 2 million years ago, which may have also created several known runaway stars, including [url=https://en.wikipedia.org/wiki/AE_Aurigae]AE Aurigae[/url], [url=https://en.wikipedia.org/wiki/Mu_Columbae]Mu Columbae[/url] and [url=https://en.wikipedia.org/wiki/53_Arietis]53 Arietis[/url], which are believed to have been part of a multiple star system in which one component exploded as a supernova.[/quote]
The Wikipedia info on AE Aurigae, Mu Columbae and 53 Arietis doesn't quite corroborate the suggestion that there was a supernova in Orion some 2 million years ago... but, you know. Estimating exactly when something happened out there in space is a tricky business!
We may also ask why Barnard's Loop, if it is a supernova remnant, is so "one-sided". Shouldn't it look like a "full circle"?
Not necessarily. Other supernova remnants are also asymmetrical, like, for example, RCW 86.
[img3="Asymmetrical supernova RCW 86. Image Credit & Copyright: Martin Pugh"]https://science.nasa.gov/files/styles/image_gallery_scale_960w/public/atoms/RCW86_MP1024.jpg?itok=vXP60agT[/img3]
Ann