From  zeus.clr.com!mercury.hq.nasa.gov!NASANews
From: zeus.clr.com!luna.osf.hq.nasa.gov!NASANews (NASA HQ Public Affairs Office)
To:   mercury.hq.nasa.gov!press-release-org
Date: Thu, 2 Nov 1995 15:51:45 -0500

Don Savage
Headquarters, Washington, DC          November 2, 1995
(Phone:  202/358-1547)                               

Fred Brown
Goddard Space Flight Center, Greenbelt, MD
(Phone:  301/286-5566)

Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone:  410/338-4514)

RELEASE:  95-190

            EMBRYONIC STARS EMERGE FROM INTERSTELLAR "EGGS"

     Dramatic new pictures from NASA's Hubble Space Telescope show 
newborn stars emerging from 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 7,000 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," says Jeff Hester of Arizona State University, Tempe.  "Now we 
seem to be watching at least one such process at work right in front 
of our eyes." 

     Pictures taken by Hester and co-investigators with Hubble's Wide 
Field Planetary Camera-2 (WFPC2) resolve the EGGs at the tip of 
finger-like features protruding from monstrous columns of cold gas in 
the Eagle nebula (also called M16 -- 16th object in the Messier 
column).  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. 

     "It's a bit like a wind storm in the desert," said 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." 

     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 how stars and their surroundings appear 
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." 

     Ultimately, photoevaporation inhibits the further growth of the 
embryonic 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." 

     Hester plans to use Hubble's high resolution to probe other 
nearby star-forming regions to look for similar structures.  
"Discoveries about the nature of the M16 EGGs might lead astronomers 
to rethink some of their ideas about the environments of stars forming 
in other regions, such as the Orion Nebula," he predicted. 

     The Space Telescope Science Institute is operated by the 
Association of Universities for Research in Astronomy, Inc., for NASA, 
under contract with the Goddard Space Flight Center, Greenbelt, MD.  
The Hubble Space Telescope is a project of international cooperation 
between NASA and the European Space Agency. 


EDITOR'S NOTE:  Three images depicting the dramatic pillars in the 
Eagle Nebula and "EGGs" are available to news media representatives by 
calling the Headquarters Imaging Branch at 202/358-1900.   NASA Photo 
Numbers are: 

                            Color                B&W
    M16 3 Pillars          95-HC-631          95-H-643
    M16 1 Pillar           95-HC-632          95-H-644
    M16 B&W Detail                            95-H-645

Image files in GIF and JPEG format and captions may be accessed on the 
Internet via anonymous ftp from ftp.stsci.edu in /pubinfo: 

    M16 3 Pillars      gif/M16Full.gif         jpeg/M16Full.jpg
    M16 1 Pillar       gif/M16WF2.gif          jpeg/M16WF2.jpg
    M16 B&W Detail     gif/M16HaBW.gif         jpeg/M16HaBW.jpg

Higher resolution versions (300 dpi JPEG) of the release photographs 
will be available temporarily in /pubinfo/hrtemp: 95-44a.jpg,  95-
44b.jpg and 95-44c.jpg.  

GIF and JPEG images, captions and press release text are available via 
World Wide Web at URL 
http://www.stsci.edu/pubinfo/PR95/44.html, or via links in:
http://www.stsci.edu/Latest.html and
http://www.stsci.edu/pubinfo/Pictures.html.

                    -end-

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