More Stellar Nursery “Eggs” Discovered in Carina Nebula

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MORE STELLAR NURSERY “EGGS” DISCOVERED IN CARINA NEBULA

New evidence of cosmic EGGs-small
cocoons of gas and dust surrounding newly forming stars, and known
more formally as evaporating gaseous globules-has been discovered in
the Great Carina Nebula, a Rice University astronomer announced
today.

Analysis of photos taken by the Hubble Space Telescope with the
Wide-Field & Planetary Camera-2 (WFPC2) reveal the third and oldest,
largest and most distant grouping of EGGs known, Reginald Dufour,
Professor of Space Physics and Astronomy at Rice University,
reported today at the American Astronomical Society meeting in San
Antonio, Texas.

The unexpected finding indicates that star formation is taking
place in a star cluster region older than other areas where
astronomers have found EGGs. The discovery promises to shed new
light on the evolution of star-forming clusters and how long these
clusters remain active birthing sites.

Dufour’s team retrieved the new images with the Hubble Space
Telescope (HST) while observing a larger field in the Great Carina
Nebula as a secondary effort to its study of the spectrum of the
famous eruptive star, Eta Carinae. The “surprise” result
demonstrates the power of HST to make new discoveries by taking”snapshots” while performing other scientific studies, Dufour said.

Other team members include Douglas J. Van Orsow of the Space
Telescope Science Institute in Baltimore, Md.; J. Jeff Hester of
Arizona State University in Tempe, Ariz.; Douglas G. Currie of
the University of Maryland in College Park, Md.; and Donald K.
Walter of South Carolina State University in Orangeburg, S.C.

Cosmic EGGs are believed to be small, dark globules of gas and
dust enshrouding newly forming stars in starbirthing regions in the
Milky Way and almost certainly other galaxies. Hester (Ph.D. ’85,
Rice) and Paul Scowen (Ph.D. ’92, Rice) also of Arizona State
University, coined the term EGGs in a November 1995 study of HST
images of the H II region the Eagle Nebula (M16).

An H II region is an area where luminous volumes of gaseous
plasma surrounds very hot stars. Hester, C. Robert O’Dell of Rice
University and their collaborators previously discovered similar
dark protostellar objects in the Orion Nebula (M42), the nearest
known H II region to Earth.

“Our chance discovery indicates that some of these globules hang
around for a long time in the outer parts of a star-forming
region, several tens of millions of years at least, and this makes
for a spread in what can be called the ‘age’ of a star cluster,”
Dufour said. He suggested that ultimately, the cocoon of gas and
dust around these young stars will evaporate and they will emerge as
what astronomers call “T-Tauri Stars” and “Herbig-Haro” objects,
which are seen in many H II regions.

The Great Carina Nebula is among the largest H II regions known
in our galaxy, and only visible to observers in the Southern
Hemisphere, where it appears as a prominent blur in the
constellation Carina. It is a giant (some 500 light years in
diameter) complex of young stars and hot excited gas, located about
8,000 light years away from the Earth. Included in this star-forming
region are several of the hottest and most massive stars known in
the Galaxy. Dark lanes of dusty cool gas protrude into the regions
of the hot emitting gas excited by several young clusters of hot
stars, giving another name for the nebula as the “Keyhole Nebula.”

Just north of the Keyhole lies the region observed by HST, near
the center of the relatively inconspicuous star cluster called
Collinder 232 (Cr 232), some 8 arc minutes north of Eta Carinae
itself. Compared to several of the other star clusters in the Carina
Nebula, relatively little is known about Cr 232 because it appears
only as a loose aggregation of stars. This fact attracted Dufour and
his colleagues to take advantage of this ppportunity to image the
cluster and surrounding gas with HST while studying Eta Carinae.

“Originally, our aim was to measure the properties of faint
stars in Cr 232 because it was relatively little studied and we
hoped to be able to