Australian Sky & Telescope - June 2018

(Ron) #1

10 AUSTRALIAN SKY & TELESCOPE July 2018


Hubble images most
distant star
It’s dificult 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
irst was the presence of a foreground
galaxy cluster known as MACS J1149-
2223, whose immense gravity bent and
magniied 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 stellar-mass black hole — that
gravitationally tweaked the starlight in
what’s known as amicrolensing event.
The combination of the two gravitational
lenses magniied 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.
■MONICA YOUNG

Nearby galactic relic of
the ancient universe
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 conirm. The galaxy,
which lies 240 million light-years away
in the centre 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 illed 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 hypothesised that, if NGC 1277
were really a relic, all its globular star
clusters would be rich in heavy elements
because they had formed when the
galaxy irst coalesced. The team’s Hubble
Space Telescope observations conirm
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 dificult to study.
■CAMILLE M. CARLISLE ESO/H.DRASS/ALMA(ESO/NAOJ/NRAO)/A.HACAR

New ALMA observations reveal fibre-like structures within a longer, well-studied
filament of dense gas within the Orion Nebula. These fibres will eventually form
massive stars.
Back in 2015, Mario Tafalla (National Astronomical Observatory, Spain) and
Alvaro Hacar (now at Leiden University, The Netherlands) studied a 30-light-year-
long gaseous filament in a region forming low-mass stars. They found that the
filament was like a rope made of smaller bundles of ‘fibres’. The denser fibres
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 fibres might act as the fundamental building blocks of star
formation, with more massive stars requiring more fibres. But it was unclear
whether the bundle-of-fibres scenario would apply in denser environments, like the
Orion Nebula, where high-mass stars come together. Other teams had suggested
that the fibres 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 fibres that braid into the single, larger filament, a result that fits into
the pattern of more fibres in more massive star-forming regions. The only difference
is that Orion’s fibres 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

Star-forming braids in the Orion Nebula


ASTRONOMERS HAVE SPOTTED a
rare supergiant star speeding through
the Milky Way’s neighbouring galaxy,
the Small Magellanic Cloud, at 300
km/s. Kathryn Neugent (University
of Washington) and colleagues will
present the results in an upcoming issue
of the 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

Supergiant runaway star


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

Integral Shape Filament in Orion Nebula

NEWS NOTES

IN BRIEF

Free download pdf