ASTRONEWS
NEIGHBORLY BEHAVIOR. Nearby star Tau Ceti may host two potentially habitable worlds slightly larger than Earth,
as well as two other planets with temperatures too extreme for life.
GIGANTIC STARS AREN’T SO RARE
HEAVENLY
HEAVYWEIGHTS.
Astronomers have
discovered an
excess of high-
mass stars in the
Tarantula Nebula.
This suggests that
massive stars are
much more common
throughout the
universe than
astronomers
previously thought,
potentially changing
our understanding
of the cosmos.
T
he universe is teeming with many more
massive stars than previously believed,
according to a study published January 5
in Science. Since massive stars play a cru-
cial role in shaping our universe —
through stellar winds, supernova explosions, and
the production of heavy elements — an excess of
heavyweights has far-reaching implications.
Researchers discovered the surplus of massive
stars in the Tarantula Nebula (30 Doradus), some
160,000 light-years away in the Large Magellanic
Cloud. This region only began producing stars
about 8 million years ago, so it serves as a perfect
laboratory to study young, massive stars.
The team used ESO’s Very Large Telescope,
part of the VLT-FLAMES Tarantula
Survey (VFTS), to gather detailed
spectroscopic observations of nearly
1,000 massive stars in the region. By
meticulously analyzing 247 of these
stars (with masses between 15 and
200 solar masses), the team deter-
mined the mass distribution of stars
born in the nebulous nursery. They
translated this catalog of stellar
birth weights into an initial mass
function (IMF), which mathematically describes
the expected distribution of masses within a
population of stars. An IMF gives astronomers
an idea of how many stars of a particular mass
will likely form in a certain population, such as
inside a star cluster or throughout a galaxy.
Astronomers once believed that massive stars
were relatively rare in the universe, with less
than 1 percent of all stars born with masses
greater than 10 times the mass of the Sun. But
this assumption was based on older IMFs cre-
ated using plenty of data from low-mass stars,
and little data from high-mass stars.
The new study fills out the high-mass portion
of the IMF, suggesting that massive stars are
much more common than prior IMFs indicated.
“We were astonished when we realized that
30 Doradus has formed many more massive
stars than expected,” Fabian Schneider, a Hintze
research fellow in the Department of Physics at
the University of Oxford and lead author of the
study, said in a press release.
Chris Evans, the principal investigator of
VFTS and co-author of the study, added: “In
fact, our results suggest that most of the stellar
mass is actually no longer in low-mass stars, but
a significant fraction is in high-mass stars.”
The researchers were not only surprised by
the number of massive stars they found, but also
that stars with masses up to 200 solar masses
were common, said co-author Hugues Sana
from the University of Leuven in
Belgium. Only recently have astron-
omers reached the consensus that
200-solar-mass stars exist at all, and
this study clearly shows such stars
200 to 300 times the mass of the Sun
can be born.
Although the study examined
only behemoth stars in one particu-
lar region, the researchers hope to
expand their study soon to deter-
mine how universal their findings are. If the
overabundance of massive stars in the Tarantula
Nebula is not a fluke, astronomers will need to
re-evaluate many of their basic assumptions
about the universe.
“Our results have far-reaching consequences
for the understanding of our cosmos. There
might be 70 percent more supernovae, a tripling
of the chemical yields, and toward four times the
ionizing radiation from massive star popula-
tions,” said Schneider. “Also, the formation rate
of black holes might be increased by 180 percent,
directly translating into a corresponding
increase of binary black hole mergers that have
recently been detected via their gravitational
wave signals.” — J.P.
Massive
stars play a
crucial role
in shaping
our universe.
20
A ST R O N O M Y • MAY 2018
NASA/ESA/STS C I/E. SABBI
GOING, GOING, GONE. In 2001,
NASA’s Mars Orbiter Camera captured
the top photo during a period of little
atmospheric activity. A month later
(bottom photo), a global dust storm
had shrouded the Red Planet’s surface.
Global dust
storms on Mars
may allow gas
to escape
Mars is occasionally enveloped
by intense storms that kick up
dust and haze, hiding large
swaths of the surface from view.
A January 22 study in Nature
Astronomy, using data collected
by NASA’s Mars Reconnaissance
Orbiter, links dust storm activity
on the Red Planet with the escape
of gas from its atmosphere.
The study found that during
mild storms, water vapor rises
along with the air being pushed
upward by the storm, leading to
subtle hydrogen loss from the
upper atmosphere. Bigger storms
likely mean more loss. This pro-
cess may have helped transform
Mars into an arid planet.
The last global dust storm in
2007 caused more than a hun-
dredfold increase in water vapor,
recent reanalysis of the data has
shown. Astronomers are now
preparing for a global dust
storm expected later this year.
Observing such a storm with
more advanced technology could
corroborate the study’s initial
findings. — A.J.