by neufer » Fri Apr 22, 2011 3:15 pm
dougettinger wrote:
EGGs are evaporation gaseous globules which are compact pockets of interstellar gas.
EGGs are evaporat
ing gaseous globules which are compact pockets of cold interstellar gas and dust strongly irradiated
from the outside.
dougettinger wrote:
Some striking examples are seen in the Eagle nebula and in star cluster NGC 602 (referenced in APOD: 2010 April 3 - NGC 602 and Beyond). They are considered to be the location for the birth of new stars. So why does the radiation pressure drive away the gases and dust from a broad region leaving behind a cone of opaque dust and gases ?
http://hubblesite.org/newscenter/archive/releases/1995/44/text/ wrote:
"It's a bit like a wind storm in the desert," said Jeff Hester. "As the wind blows away the lighter sand, heavier rocks buried in the sand are uncovered. But in M16, instead of rocks, the ultraviolet light is uncovering the denser egg-like globules of gas that surround stars that were forming inside the gigantic gas columns."
dougettinger wrote:
Supposely, a new star is forming at the tip of the cone ? How do we know this ? Why does this dark cone nebula remain opaque behind the forming star ? It does not make any sense. The forming star should create a cone that is transparent since this star birth is gathering all the dust that is passing by it.
How do astronomers know a new star instead of an old star is interrupting the outward flow of dust and gases to form these EGGs ?
It is neither an old star nor a new star but rather a gravitationally condensed globule.
http://apod.nasa.gov/apod/ap070321.html wrote:
Explanation: It may look to some like a duck, but it lays stars instead of eggs. In the center of the above image lies Barnard 163, a nebula of molecular gas and dust so thick that visible light can't shine through it. With a wing span measured in light years, Barnard 163's insides are surely colder than its exterior, allowing conditions where gas can clump and eventually form stars.
These EGGS will probably never hatch however because
the first born sibling hatch-lings will eventually evaporate them all away.
http://hubblesite.org/newscenter/archive/releases/1995/44/text/ wrote:
Ultimately, photoevaporation inhibits the further growth of the embyronic stars by dispersing the cloud of gas they were "feeding" from. "We believe that the stars in M16 were continuing to grow as more and more gas fell onto them, right up until the moment that they were cut off from that surrounding material by photoevaporation," said Hester.
This process is markedly different from the process that governs the sizes of stars forming in isolation. Some astronomers believe that, left to its own devices, a star will continue to grow until it nears the point where nuclear fusion begins in its interior. When this happens, the star begins to blow a strong "wind" that clears away the residual material. Hubble has imaged this process in detail in so-called Herbig-Haro objects.
Hester also speculated that photoevaporation might actually inhibit the formation of planets around such stars. It is not at all clear from the new data that the stars in M16 have reached the point where they have formed the disks that go on to become solar systems," said Hester, "and if these disks haven't formed yet, they never will."
http://hubblesite.org/newscenter/archive/releases/1995/44/text/ wrote:
Embryonic Stars Emerge from Interstellar "Eggs"
<<Eerie, dramatic new pictures from NASA's Hubble Space Telescope show newborn stars emerging from "eggs" — not the barnyard variety — but rather dense, compact pockets of interstellar gas called evaporating gaseous globules (EGGs). Hubble found the "EGGs," appropriately enough, in the Eagle nebula, a nearby star-forming region 6,500 light- years away in the constellation Serpens.
"For a long time astronomers have speculated about what processes control the sizes of stars — about why stars are the sizes that they are," said Jeff Hester of Arizona State University, Tempe, AZ. "Now in M16 we seem to be watching at least one such process at work right in front of our eyes."
Striking pictures taken by Hester and co-investigators with Hubble's Wide Field and Planetary Camera 2 (WFPC2) resolve the EGGs at the tip of finger-like features protruding from monstrous columns of cold gas and dust in the Eagle nebula (also called M16 — 16th object in the Messier catalog). The columns — dubbed "elephant trunks" — protrude from the wall of a vast cloud of molecular hydrogen, like stalagmites rising above the floor of a cavern. Inside the gaseous towers, which are light-years long, the interstellar gas is dense enough to collapse under its own weight, forming young stars that continue to grow as they accumulate more and more mass from their surroundings.
Hubble gives a clear look at what happens as a torrent of ultraviolet light from nearby young, hot stars heats the gas along the surface of the pillars, "boiling it away" into interstellar space — a process called "photoevaporation. "The Hubble pictures show photoevaporating gas as ghostly streamers flowing away from the columns. But not all of the gas boils off at the same rate. The EGGs, which are denser than their surroundings, are left behind after the gas around them is gone.
Some EGGs appear as nothing but tiny bumps on the surface of the columns. Others have been uncovered more completely, and now resemble "fingers" of gas protruding from the larger cloud. (The fingers are gas that has been protected from photoevaporation by the shadows of the EGGs). Some EGGs have pinched off completely from the larger column from which they emerged, and now look like teardrops in space.
By stringing together these pictures of EGGs caught at different stages of being uncovered, Hester and his colleagues from the Wide Field and Planetary Camera Investigation Definition Team are getting an unprecedented look at what stars and their surroundings look like before they are truly stars.
"This is the first time that we have actually seen the process of forming stars being uncovered by photoevaporation," Hester emphasized. "In some ways it seems more like archaeology than astronomy. The ultraviolet light from nearby stars does the digging for us, and we study what is unearthed."
"In a few cases we can see the stars in the EGGs directly in the WFPC2 images," says Hester. "As soon as the star in an EGG is exposed, the object looks something like an ice cream cone, with a newly uncovered star playing the role of the cherry on top.">>
[quote="dougettinger"]
EGGs are evaporation gaseous globules which are compact pockets of interstellar gas.[/quote]
EGGs are evaporat[b][color=#FF0000]ing[/color][/b] gaseous globules which are compact pockets of cold interstellar gas and dust strongly irradiated [b][color=#FF0000]from the outside[/color][/b].
[quote="dougettinger"]
Some striking examples are seen in the Eagle nebula and in star cluster NGC 602 (referenced in APOD: 2010 April 3 - NGC 602 and Beyond). They are considered to be the location for the birth of new stars. So why does the radiation pressure drive away the gases and dust from a broad region leaving behind a cone of opaque dust and gases ?[/quote]
[quote=" http://hubblesite.org/newscenter/archive/releases/1995/44/text/"]
[color=#0000FF]"It's a bit like a wind storm in the desert," said Jeff Hester. "As the wind blows away the lighter sand, heavier rocks buried in the sand are uncovered. But in M16, instead of rocks, the ultraviolet light is uncovering the denser egg-like globules of gas that surround stars that were forming inside the gigantic gas columns."[/color][/quote]
[quote="dougettinger"]
Supposely, a new star is forming at the tip of the cone ? How do we know this ? Why does this dark cone nebula remain opaque behind the forming star ? It does not make any sense. The forming star should create a cone that is transparent since this star birth is gathering all the dust that is passing by it.
How do astronomers know a new star instead of an old star is interrupting the outward flow of dust and gases to form these EGGs ?[/quote]
It is neither an old star nor a new star but rather a gravitationally condensed globule.
[quote=" http://apod.nasa.gov/apod/ap070321.html"]
Explanation: It may look to some like a duck, but it lays stars instead of eggs. In the center of the above image lies Barnard 163, a nebula of molecular gas and dust so thick that visible light can't shine through it. With a wing span measured in light years, Barnard 163's insides are surely colder than its exterior, allowing conditions where gas can clump and eventually form stars.[/quote]
These EGGS will probably never hatch however because [b][color=#FF0000]the first born sibling hatch-lings[/color][/b] will eventually evaporate them all away.
[quote=" http://hubblesite.org/newscenter/archive/releases/1995/44/text/"]
[color=#0000FF]Ultimately, photoevaporation inhibits the further growth of the embyronic stars by dispersing the cloud of gas they were "feeding" from. "We believe that the stars in M16 were continuing to grow as more and more gas fell onto them, right up until the moment that they were cut off from that surrounding material by photoevaporation," said Hester.
This process is markedly different from the process that governs the sizes of stars forming in isolation. Some astronomers believe that, left to its own devices, a star will continue to grow until it nears the point where nuclear fusion begins in its interior. When this happens, the star begins to blow a strong "wind" that clears away the residual material. Hubble has imaged this process in detail in so-called Herbig-Haro objects.
Hester also speculated that photoevaporation might actually inhibit the formation of planets around such stars. It is not at all clear from the new data that the stars in M16 have reached the point where they have formed the disks that go on to become solar systems," said Hester, "and if these disks haven't formed yet, they never will."[/color][/quote][quote=" http://hubblesite.org/newscenter/archive/releases/1995/44/text/"]
Embryonic Stars Emerge from Interstellar "Eggs"
<<Eerie, dramatic new pictures from NASA's Hubble Space Telescope show newborn stars emerging from "eggs" — not the barnyard variety — but rather dense, compact pockets of interstellar gas called evaporating gaseous globules (EGGs). Hubble found the "EGGs," appropriately enough, in the Eagle nebula, a nearby star-forming region 6,500 light- years away in the constellation Serpens.
"For a long time astronomers have speculated about what processes control the sizes of stars — about why stars are the sizes that they are," said Jeff Hester of Arizona State University, Tempe, AZ. "Now in M16 we seem to be watching at least one such process at work right in front of our eyes."
Striking pictures taken by Hester and co-investigators with Hubble's Wide Field and Planetary Camera 2 (WFPC2) resolve the EGGs at the tip of finger-like features protruding from monstrous columns of cold gas and dust in the Eagle nebula (also called M16 — 16th object in the Messier catalog). The columns — dubbed "elephant trunks" — protrude from the wall of a vast cloud of molecular hydrogen, like stalagmites rising above the floor of a cavern. Inside the gaseous towers, which are light-years long, the interstellar gas is dense enough to collapse under its own weight, forming young stars that continue to grow as they accumulate more and more mass from their surroundings.
Hubble gives a clear look at what happens as a torrent of ultraviolet light from nearby young, hot stars heats the gas along the surface of the pillars, "boiling it away" into interstellar space — a process called "photoevaporation. "The Hubble pictures show photoevaporating gas as ghostly streamers flowing away from the columns. But not all of the gas boils off at the same rate. The EGGs, which are denser than their surroundings, are left behind after the gas around them is gone.
Some EGGs appear as nothing but tiny bumps on the surface of the columns. Others have been uncovered more completely, and now resemble "fingers" of gas protruding from the larger cloud. (The fingers are gas that has been protected from photoevaporation by the shadows of the EGGs). Some EGGs have pinched off completely from the larger column from which they emerged, and now look like teardrops in space.
By stringing together these pictures of EGGs caught at different stages of being uncovered, Hester and his colleagues from the Wide Field and Planetary Camera Investigation Definition Team are getting an unprecedented look at what stars and their surroundings look like before they are truly stars.
"This is the first time that we have actually seen the process of forming stars being uncovered by photoevaporation," Hester emphasized. "In some ways it seems more like archaeology than astronomy. The ultraviolet light from nearby stars does the digging for us, and we study what is unearthed."
"In a few cases we can see the stars in the EGGs directly in the WFPC2 images," says Hester. "As soon as the star in an EGG is exposed, the object looks something like an ice cream cone, with a newly uncovered star playing the role of the cherry on top.">>[/quote]