Sky and Telescope - July 2018 - 11
Supergiant Runaway Star
ASTRONOMERS HAVE SPOTTED a rare
supergiant star speeding through the
Milky Way's neighboring galaxy, the
Small Magellanic Cloud, at 300 km/s
(700,000 mph). Kathryn Neugent (University of Washington) and colleagues
present the results in an upcoming issue
of Astronomical Journal.
The sighting is unique not only
because of the star's high speed but also
its advanced phase of evolution. The
star, J01020100-7122208, appears to be
a yellow supergiant, a phase that lasts
only 10,000 to 100,000 years before the
star balloons into a red supergiant.
"It's unexpected to ﬁnd a very rare
object in a very rare phase," says Warren
Brown (Harvard-Smithsonian Center
for Astrophysics), who wasn't involved
in this study. "The joint probability is
unlikely, so the implication is that runaways are quite common."
A runaway star moves signiﬁcantly
faster than other stars from its birthplace. Most known runaway stars are
in the Milky Way; this yellow supergiant is only the second known evolved
runaway in another galaxy. Neugent
and colleagues suggest the star became
a runaway when its stellar companion
exploded in a supernova, ejecting mass
from the system and enabling the star to
ﬂy away at high speed.
■ ELIZABETH HOWELL
Hubble Images Most
It's difficult to resolve stars in galaxies
outside our own, but with the help of
some cosmic lensing, the Hubble Space
Telescope has imaged a star that existed
when the universe was less than a third
of its current age, at a redshift of 1.49.
Hubble's optics were aided by two of the
universe's own lenses: The first was the
presence of a foreground galaxy cluster
known as MACS J1149-2223, whose
immense gravity bent and magnified the
light from the background star. The second was something closer to the star, with
three times the Sun's mass - perhaps
another star, a neutron star, or a stellarmass black hole - that gravitationally
tweaked the starlight in what's known as
a microlensing event. The combination of
the two gravitational lenses magnified the
star's light more than 2,000 times, making
it visible to Hubble. The star itself is a blue
supergiant much bigger, brighter, and hotter than the Sun. The results appear in the
April 2nd Nature Astronomy.
■ MONICA YOUNG
Integral Shape Filament in Orion Nebula
ESO / H. DR ASS / A LM A (ESO / N AOJ / NR AO) / A . H ACA R
Star-forming Braids in the Orion Nebula
New ALMA observations reveal ﬁber-like structures within a longer, well-studied
ﬁlament of dense gas within the Orion Nebula. These ﬁbers will eventually form
Back in 2015 Mario Tafalla (National Astronomical Observatory, Spain) and
Alvaro Hacar (now at Leiden University, The Netherlands) studied a 30-light-yearlong gaseous ﬁlament in a region forming low-mass stars. They found that the
ﬁlament was like a rope made of smaller bundles of "ﬁbers" (S&T: Oct. 2015, p. 28).
The denser ﬁbers were each typically 1½ light-years long. The seeds of future
stars - compact areas that will eventually collapse into stars but haven't yet -
can be seen as knots in these braids.
Hacar thought ﬁbers might act as the fundamental building blocks of star formation, with more massive stars requiring more ﬁbers. But it was unclear whether
the bundle-of-ﬁbers scenario would apply in denser environments, like the Orion
Nebula, where high-mass stars come together. Other teams had suggested that
the ﬁbers in such regions would be more massive rather than more numerous.
High-mass stars are rare and typically far away, making their birthplaces difﬁcult
to observe. So Hacar and colleagues used the Atacama Large Millimeter/submillimeter Array to zoom in on the 20-light-year-long Integral Shape Filament, which
crosses massive star-forming regions in the Orion Nebula. The team found a network of 55 ﬁbers that braid into the single, larger ﬁlament, a result that ﬁts into the
pattern of more ﬁbers in more massive star-forming regions. The only difference
is that Orion's ﬁbers are typically only ½ light-year long, on average three times
shorter than the ones the researchers spotted in the low-mass star-forming region.
■ MONICA YOUNG
Nearby Relic of Ancient
NGC 1277 is a stunted galaxy, largely
ungrown since the universe's early years,
observations by Michael Beasley (Canary
Islands Institute of Astrophysics, Spain)
and colleagues confirm in the March 12th
Nature. The galaxy, which lies 240 million light-years away in the center of the
Perseus Cluster, is a dense "red nugget"
- although it has twice as many stars as
the Milky Way, it's about a quarter of our
galaxy's size and filled with old stars that
formed early on. Astronomers already
suspected that NGC 1277 was frozen
in time, but Beasley's team decided to
test the idea. They hypothesized that,
if NGC 1277 were really a relic, all its
globular clusters would be rich in heavy
elements because they had formed when
the galaxy first coalesced. The team's
Hubble Space Telescope observations
confirm NGC 1277 has almost no young
globular clusters, so NGC 1277 hasn't
grown much by accreting other galaxies.
The relic offers astronomers access to a
relatively nearby example of early systems
that are much more difficult to study.
■ CAMILLE M. CARLISLE
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