by investigating astronomer
Dr. You-Hua Chu
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The Tarantula Nebula with SN 1987A
30 Doradus (also known as the Tarantula Nebula
and as NGC 2070) in the Large Magellanic Cloud is
the closest and most active starburst region in
the nearby universe. At the center of 30 Doradus
is the spectacular R136 cluster, whose massive stars
shine brightly in the far ultraviolet, ionizing
the surrounding gas to produce the visible 30 Doradus
nebula. 30 Doradus is luminous in X-rays as well,
indicating the existence of gas shock-heated to
millions degrees Kelvin by supernova remnants. The
R136 cluster, at a tender young age of 2-3 Myr,
still has all of its massive stars intact. Who are
responsible for the generation of X-rays in 30 Doradus?
To find the responsible party, we need not look
too far from R136. Projected at 140 light years
from R136 is the cluster Hodge 301.
Hodge 301 and R136 show sharp contrast between
each other both in stellar content and interstellar
environment. Hodge 301 is a sparsely populated cluster
of which the most luminous stars are early B supergiants,
while R136 is a highly concentrated dense cluster
which contains a large number of the earliest O
stars. Hodge 301 is bathed in an X-ray halo and
surrounded by delicate filaments in visible light,
as opposed to the rustic ionized clouds and wild
elephant trunks around R136.
To study the cluster Hodge 301 and to show the
contrast between Hodge 301 and R136, You-Hua Chu
(University of Illinois), Eva Grebel (University
of Washington) and collaborators have obtained HST
WFPC2 images of Hodge 301 with exactly the same
filters and camera
orientation as those of R136. They find that the
contrast between Hodge 301 and R136 can be explained
entirely by the age difference between the two clusters.
Hodge 301 is about 20 Myr old. Its most massive
stars have ended their lives in supernova explosions.
The supernova ejecta have shocked the ambient gas
and compressed it into thin sheets and filaments.
Hidden amidst these filaments are numerous supernova
remnants, including one expanding at 300 km/s, the
fastest in 30 Doradus!
30 Doradus reveals that a starburst is a complex,
multi-generation process. The Generation-X cluster
R136 contain the most luminous stars, but does not
generate the bulk X-ray emission from 30 Doradus.
The older, baby-boomer cluster Hodge 301 has a thinning
population, but it still holds the shocking power!
Rancho Del Sol Observatory Image of the Tarantula Nebula
Image courtesy of K. Crawford (Camino, CA)