54 AUSTRALIAN SKY & TELESCOPE November | December 2017
NATURE UNFOLDS IN UTTER
tranquility, living out the endless
trajectories of physics and all its
derivative laws with minute precision
— though with complete disregard for
the feelings of little egos like us who
find ourselves embedded within it.
“Happiness is functioning the way a
being is organised to function,” wrote
Robert A. Heinlein, and the stars are
serene in their courses. But it’s easy
to imagine that some stars would be
pretty unhappy if they were people.
The long-period variable R Aquarii, a
red giant that’s now coming into nice
telescopic view in late evening, finds
itself having to do its slow, pulsing
heartbeat meditations next to the tiny,
eruptive fury of a severely troubled
mate who throws things. And yes, it’s
all the red giant’s fault.R Aquarii is, on first impression, a
standard Mira-type variable, pulsing
from about magnitude 6 to 11 and back
every year and three weeks. Through a
telescope it shows the orange-red colour
of a late-M giant, especially when it’s in
the faint part of its cycle. Which is where
it’s heading now; its last maximum came
in June, and minimum light is predicted
for around December 11th.
But there’s a lot more going on here.
Distantly orbiting the giant every 44
years is a hot, very faint white dwarf
contributing weak spectral features
of an O or B star to the dominant M
star’s light. Stars that show such a
combination-of-opposites spectrum are
called symbiotic stars. R Aquarii is the
closest of them at a distance of about
700 light-years. Through a telescope
the two points appear as one, but the ADAM BLOCK / MT. LEMMON SKYCENTER / UNIV. OF ARIZONAThe fuming odd couple
that is R Aquarii threw off
a ring of hydrogen about
250 years ago. The ring
shows hints of being the
neck of a larger hourglass
shape. Inside it, a pair of
hot jets stab up and down
from the goings-on at the
centre. The frame above
is about 4 arcminutes (0.9
light-year) wide.What looks like a normal pulsing red giant has a lot more going
on around it. Its next episode of weirdness may begin soon, and
variable star observers are watching.The drama-ridden story
of R Aquarii
CELESTIAL CALENDAR by Alan MacRobert