by neufer » Mon Feb 04, 2019 5:34 pm
Chris Peterson wrote: ↑Mon Feb 04, 2019 2:06 pm
NCTom wrote: ↑Mon Feb 04, 2019 12:36 pm
How would we on earth recognize our system was passing through such a superbubble/shell? None of the descriptions I read discussed the density/thickness of the shell itself, only its expanding dimensions.
It would raise the background brightness of the sky, and instrumentally, we'd observe a number of emission lines in that background, as well as evidence of structure. (Indeed, we
are currently inside a bubble which is slightly less dense than the surrounding interstellar medium, and is approximately the same size as the bubble in this APOD. Our local bubble is mapped using radio and x-ray emissions.)
https://en.wikipedia.org/wiki/Superbubble wrote:
<<A superbubble or supershell is a cavity which is hundreds of light years across and is populated with hot (10
6 K) gas atoms, less dense than the surrounding interstellar medium, blown against that medium and carved out by multiple supernovae and stellar winds. The winds, passage and gravity of newly born stars strip superbubbles of any other dust or gas. The Solar System lies near the center of an old superbubble, known as the Local Bubble, whose boundaries can be traced by a sudden rise in dust extinction of exterior stars at distances greater than a few hundred light years.
Click to play embedded YouTube video.
The superburghol HENIZE 70, a.k.a. N70 or DEM301, in the LMCloudThe most massive stars, with masses ranging from 8 to ~100 solar masses and spectral types of O and early B, are usually found in groups called OB associations. Massive O stars have strong stellar winds, and most of these stars explode as supernovae at the end of their lives. The strongest stellar winds release kinetic energy of 10
51 ergs over the lifetime of a star, which is equivalent to a supernova explosion. These winds can form stellar wind bubbles dozens of light years across. Inside OB associations, the stars are close enough that their wind bubbles merge, forming a giant bubble called a superbubble. When stars die, supernova explosions, similarly, drive blast waves that can reach even larger sizes, with expansion velocities up to several hundred km/s. Stars in OB associations are not gravitationally bound, but they drift apart at small speeds (of around 20 km/s), and they exhaust their fuel rapidly (after a few millions of years). As a result, most of their supernova explosions occur within the cavity formed by the stellar wind bubbles. These explosions never form a visible supernova remnant, but instead expend their energy in the hot interior as sound waves. Both stellar winds and stellar explosions thus power the expansion of the superbubble in the interstellar medium.
The interstellar gas swept up by superbubbles generally cools, forming a dense shell around the cavity. These shells were first observed in line emission at 21 centimeters from hydrogen, leading to the formulation of the theory of superbubble formation. They are also observed in X-ray emission from their hot interiors, in optical line emission from their ionized shells, and in infrared continuum emission from dust swept up in their shells. X-ray and visible emission are typically observed from younger superbubbles, while older, larger objects seen in 21 centimeters may even result from multiple superbubbles combining, and so are sometimes distinguished by calling them supershells.>>
https://en.wikipedia.org/wiki/Local_Bubble wrote:
<<The Local Bubble, or Local Cavity, is a relative cavity in the interstellar medium (ISM) of the Orion Arm in the Milky Way. It contains among others, the Local Interstellar Cloud, which contains the Solar System, and the G-Cloud. It is at least 300 light years across and is defined by its neutral-hydrogen density of about 0.05 atoms/cm
3, or approximately one tenth of the average for the ISM in the Milky Way, and one sixth that of the Local Interstellar Cloud. The Solar System has been traveling through the region currently occupied by the Local Bubble for the last five to ten million years.
The exceptionally sparse matter, namely gas, of the Local Bubble is the result of supernovae that exploded within the past ten to twenty million years and remains in an excited state, emitting in the X-ray band. It has been suggested that multiple supernovae in subgroup B1 of the Pleiades moving group were more likely responsible, becoming a remnant supershell.
Launched in February 2003 and active until April 2008, a small space observatory called Cosmic Hot Interstellar Plasma Spectrometer (CHIPS or CHIPSat) examined the hot gas within the Local Bubble. The Local Bubble was also the region of interest for the Extreme Ultraviolet Explorer mission (1992–2001), which examined hot EUV sources within the bubble. Sources beyond the edge of the bubble were identified, but attenuated by the denser interstellar medium.>>
[quote="Chris Peterson" post_id=289528 time=1549289180 user_id=117706]
[quote=NCTom post_id=289527 time=1549283762]
How would we on earth recognize our system was passing through such a superbubble/shell? None of the descriptions I read discussed the density/thickness of the shell itself, only its expanding dimensions.
[/quote]
It would raise the background brightness of the sky, and instrumentally, we'd observe a number of emission lines in that background, as well as evidence of structure. (Indeed, we [i]are [/i]currently inside a bubble which is slightly less dense than the surrounding interstellar medium, and is approximately the same size as the bubble in this APOD. Our local bubble is mapped using radio and x-ray emissions.)[/quote][quote="https://en.wikipedia.org/wiki/Superbubble"]
<<A superbubble or supershell is a cavity which is hundreds of light years across and is populated with hot (10[sup]6[/sup] K) gas atoms, less dense than the surrounding interstellar medium, blown against that medium and carved out by multiple supernovae and stellar winds. The winds, passage and gravity of newly born stars strip superbubbles of any other dust or gas. The Solar System lies near the center of an old superbubble, known as the Local Bubble, whose boundaries can be traced by a sudden rise in dust extinction of exterior stars at distances greater than a few hundred light years.
[float=left][youtube]https://www.youtube.com/watch?v=8fIfPKpY7HQ[/youtube][b][color=#FF0000]The superburghol HENIZE 70, a.k.a. N70 or DEM301, in the LMCloud[/color][/b][/float]The most massive stars, with masses ranging from 8 to ~100 solar masses and spectral types of O and early B, are usually found in groups called OB associations. Massive O stars have strong stellar winds, and most of these stars explode as supernovae at the end of their lives. The strongest stellar winds release kinetic energy of 10[sup]51[/sup] ergs over the lifetime of a star, which is equivalent to a supernova explosion. These winds can form stellar wind bubbles dozens of light years across. Inside OB associations, the stars are close enough that their wind bubbles merge, forming a giant bubble called a superbubble. When stars die, supernova explosions, similarly, drive blast waves that can reach even larger sizes, with expansion velocities up to several hundred km/s. Stars in OB associations are not gravitationally bound, but they drift apart at small speeds (of around 20 km/s), and they exhaust their fuel rapidly (after a few millions of years). As a result, most of their supernova explosions occur within the cavity formed by the stellar wind bubbles. These explosions never form a visible supernova remnant, but instead expend their energy in the hot interior as sound waves. Both stellar winds and stellar explosions thus power the expansion of the superbubble in the interstellar medium.
The interstellar gas swept up by superbubbles generally cools, forming a dense shell around the cavity. These shells were first observed in line emission at 21 centimeters from hydrogen, leading to the formulation of the theory of superbubble formation. They are also observed in X-ray emission from their hot interiors, in optical line emission from their ionized shells, and in infrared continuum emission from dust swept up in their shells. X-ray and visible emission are typically observed from younger superbubbles, while older, larger objects seen in 21 centimeters may even result from multiple superbubbles combining, and so are sometimes distinguished by calling them supershells.>>[/quote][quote="https://en.wikipedia.org/wiki/Local_Bubble"]
[float=left][img3="The Local Bubble seems to be narrower in the galactic plane becoming shaped somewhat like an hourglass. It abuts other bubbles, including, in particular, the Loop I Bubble containing the star Antares. Several tunnels connect the cavities of the Local Bubble with the Loop I Bubble, called the 'Lupus Tunnel'."]https://upload.wikimedia.org/wikipedia/commons/3/3d/Local_bubble.jpg[/img3][/float]
<<The Local Bubble, or Local Cavity, is a relative cavity in the interstellar medium (ISM) of the Orion Arm in the Milky Way. It contains among others, the Local Interstellar Cloud, which contains the Solar System, and the G-Cloud. It is at least 300 light years across and is defined by its neutral-hydrogen density of about 0.05 atoms/cm[sup]3[/sup], or approximately one tenth of the average for the ISM in the Milky Way, and one sixth that of the Local Interstellar Cloud. The Solar System has been traveling through the region currently occupied by the Local Bubble for the last five to ten million years.
The exceptionally sparse matter, namely gas, of the Local Bubble is the result of supernovae that exploded within the past ten to twenty million years and remains in an excited state, emitting in the X-ray band. It has been suggested that multiple supernovae in subgroup B1 of the Pleiades moving group were more likely responsible, becoming a remnant supershell.
Launched in February 2003 and active until April 2008, a small space observatory called Cosmic Hot Interstellar Plasma Spectrometer (CHIPS or CHIPSat) examined the hot gas within the Local Bubble. The Local Bubble was also the region of interest for the Extreme Ultraviolet Explorer mission (1992–2001), which examined hot EUV sources within the bubble. Sources beyond the edge of the bubble were identified, but attenuated by the denser interstellar medium.>>[/quote]