March 28, 2001
Photo No: H2001-11
Massive Infant Stars Rock Their Cradle
Extremely intense radiation from newly born, ultra-bright stars has
blown a glowing spherical bubble in the nebula N83B, also known
as NGC 1748. A new NASA Hubble Space Telescope image has
helped to decipher the complex interplay of gas and radiation of a
star-forming region in a nearby galaxy. The image graphically
illustrates just how these massive stars sculpt their environment by
generating powerful winds that alter the shape of the parent gaseous
nebula. These processes are also seen in our Milky Way in regions
like the Orion Nebula.
The Hubble telescope is famous for its contribution to our knowledge
about star formation in very distant galaxies. Although most of the
stars in the Universe were born several billions of years ago, when the
Universe was young, star formation still continues today. This new
Hubble image shows a very compact star-forming region in a small
part of one of our neighboring galaxies - the Large Magellanic Cloud.
This galaxy lies only 165,000 light-years from our Milky Way and
can easily be seen with the naked eye from the Southern Hemisphere.
Young, massive, ultra-bright stars are seen here just as they are born
and emerge from the shelter of their pre-natal molecular cloud.
Catching these hefty stars at their birthplace is not as easy as it may
seem. Their high mass means that the young stars evolve very rapidly
and are hard to find at this critical stage. Furthermore, they spend a
good fraction of their youth hidden from view, shrouded by large
quantities of dust in a molecular cloud. The only chance is to observe
them just as they start to emerge from their cocoon - and then only
with very high-resolution telescopes.
Astronomers from France, the U.S., and Germany have used Hubble
to study the fascinating interplay between gas, dust, and radiation from
the newly born stars in this nebula. Its peculiar and turbulent
structure has been revealed for the first time. This high-resolution
study has also uncovered several individual stars that are responsible
for lighting up this cloud of gas.
The apparently innocuous-looking star at the very center of the
nebula, just below the brightest region, is actually about 30 times
more massive and almost 200,000 times brighter than our Sun. The
intense light and powerful stellar "winds" from this ultra-bright star
have cleared away the surrounding gas to form a large cavity. The
bubble is approximately 25 light-years in diameter - about the
same size as the famous star-forming Orion Nebula. The Orion
Nebula is sculpted by intense radiation from newly born stars in
the same way as N83B. Astronomers estimate that the spherical
void in N83B must have been carved out of the nebula very
recently - in astronomical terms - maybe as little as 30,000 years ago.
The hottest star in N83B is 45 times more massive than the Sun and is
embedded in the brightest region in the nebula. This bright region,
situated just above the center, is only about 2 light-years across. The
region's small size and its intense glow are telltale signs of a very
young, massive star. This star is the youngest newcomer to this part of
the Large Magellanic Cloud. The Hubble image shows a bright arc
structure just below the luminous star. This impressive ridge may have
been created in the glowing gas by the hot star's powerful wind.
Measurements of the age of this star and neighboring stars in the
nebula show that they are younger than the nebula's central star.
Their formation may have been "triggered" by the violent wind from
the central star. This "chain-reaction" of stellar births seems to be
common in the Universe. About 20 young and luminous stars have
been identified in the region, but it may well be that many more
massive stars remain undetected in other areas of the Large
Magellanic Cloud, hidden by dust in small clusters like N83B.
To the right of the glowing N83B is a much larger diffuse nebula,
known as DEM22d, which is partly obscured by an extended lane
of dust and gas.
This image is composed of three narrow-band-filter images obtained with
Hubble's Wide Field Planetary Camera 2 in May 2000. The colors are red
(ionized hydrogen, H-alpha), green (ionized oxygen), and blue (ionized
hydrogen, H-beta). The blue corresponds to the warmest regions, the red
to the coldest. The full image is 66 x 133 arc-seconds, which
corresponds to 55 x 108 light-years at the distance of the Large
Credit: NASA, ESA, Mohammad Heydari-Malayeri (Observatoire de Paris,