Sky and Telescope - November 2017 - 26

Inside 30 Doradus

What's in the Tarantula Nebula
Object

Type

Description

NGC 2070

Star cluster

Massive cluster at heart of 30 Doradus;
130 light-years wide. Also known as
Caldwell 103. Possible proto-globular?

Hodge 301

Star cluster

Oldest cluster in 30 Doradus; 25 to 30
million years old. Perhaps contributed
to formation of NGC 2070.

R136

Star cluster

Portion of NGC 2070; believed to be
less than 5 million years old

R136a

Stars

Dense knot within R136; 8 stars that
range from 69 to 250 solar masses
(most massive = R136a1)

R139

Binary star

Two O-type supergiants of 78 and 66
solar masses; most massive O binary
yet discovered

VFTS 016

Star

Runaway star, ﬁrst to be detected
in 30 Doradus

VFTS 102

Star

Runaway star and fastest known
rotator. Former companion perhaps
now a pulsar?

VFTS 352

Binary star

"Overcontact binary" (its two
components orbit so closely that
their surfaces overlap)

These efforts allow astronomers to study individual stars
within 30 Doradus, many smaller than our Sun. Studying
their physical properties one at a time paints a picture of
the population as a whole. Just as the Rosetta stone was the
key to deciphering Egyptian hieroglyphs, so too is 30 Doradus seen as a unique laboratory to understand the processes
involved in giant starburst regions.

p STELLAR POWERHOUSE Left: Compact and crowded, the star cluster R136 was once thought to be a single star within NGC 2070. Less than 5
million years old, it boasts scores of extremely hot and luminous super-suns in the O and B spectral classes. These stars produce most of the energy
that makes the Tarantula Nebula visible. The area shown is about 35 light-years across. Right: A Hubble view of the same portion of R136 reveals
intense ultraviolet emission from stars within the cluster.

N O V E M B E R 2 0 17 * S K Y & T E L E S C O P E

LEF T: N ASA / ESA / P. CROW THER; RIG H T: ESA-HUBBLE / N ASA / K . A . BOSTROEM

We can only study the closest starburst regions in the
detail needed to fully understand the life cycles of stars and
what shapes galaxy evolution. Fortunately, 30 Doradus is
right in our galactic backyard. Nolan Walborn (Space Telescope Science Institute) notes that this complex nebula would
appear less than 1 arcsecond wide at the distance of the Virgo
Cluster, 65 million light-years away, leaving us unable to
resolve its individual stars.
However, it's not just the Tarantula's proximity that makes
it appealing. Seen nearly face-on to us, it offers a clear picture
of its internal layout. Similarly, because the LMC is well above
the Milky Way's central plane, there's little foreground reddening and interference. In addition, the LMC's stars contain
"metals" (all elements other than hydrogen and helium) at
abundances about half those in our solar neighborhood but
similar to the early universe's. This allows researchers to
study star formation as it must have occurred long ago, at a
rate many times what it is today.
In fact, when it comes to creating stars, 30 Doradus has
few peers. A 2011 study led by Laura Lopez (University of California, Santa Cruz) compared it with all the H II regions in 70
galaxies within 100 million light-years. Based on its amount
of hydrogen-alpha emission, a proxy for the rate of star formation, 30 Doradus ranks in the top 1% of 21,000 H II regions
in 57 spiral galaxies, and it tops the 614 H II regions found in
the study's 13 irregular galaxies by a factor of 10!
So it's hardly surprising that every major space-based telescope has targeted 30 Doradus, as have the Southern Hemisphere's big observatories. Two major programs dominate
recent research efforts. The Hubble Tarantula Treasury Project
(HTTP) dedicated 60 orbits of the orbiting observatory's time
to record 30 Doradus from the near ultraviolet to the near
infrared. In Chile, the VLT-FLAMES Tarantula Survey (VFTS)
used one of the four 8.2-meter Very Large Telescopes to
obtain spectra of some 900 massive stars.

Sky and Telescope - November 2017

Table of Contents for the Digital Edition of Sky and Telescope - November 2017