16 ASTRONOMY • DECEMBER 2019
STRANGE UNIVERSE
We’ve gotten so spoiled when it comes to
strangeness that white dwarfs no longer drop
our jaws. Since neutron stars and black holes
are much more mind-bendingly squashed, we disregard
the runners-up in the crushed-fireball sweepstakes. It’s
l i ke ig nor i ng a pterod ac t yl i n you r ga rden ju st bec au se
you r g i rl f r iend ad m it ted she’s a n a l ien si x- d i mensiona l
J-creature.
Well, white dwarfs still twist my head —
especially now, when the half-century wait-
ing period is over and we can finally see the
most famous one. I’m talking about the Pup,
companion to the Dog Star, Sirius.
That alpha star of the Big Dog constella-
tion was considered bad news for a thousand
years. In the Roman Empire, its presence was
so ill-omened that hit men were sometimes
employed to sacrifice dogs after Sirius rose.
Even Dante wrote of the star as “the scourge
of days canicular.”
The Dog Star had better press in ancient
Egypt, where they believed July’s sky-
proximity between the Sun and the brightest star
caused the summer’s heat. Even today we use the
expression “dog days” to mean sultry weather, most
people unaware that its origins echo from those van-
ished centuries.
In real life, December’s dinnertime rising of Sirius
provides not warmth but a psychedelic light show.
When that dazzling starpoint shines through cold,thick horizon air, the result is often a kaleidoscope of
rapidly changing color. I’ve received a half-dozen UFO
calls over the years that proved to be the madly mutat-
ing Dog Star. Its mongrel maelstrom of color is the
result of its spectral A-type light refracted by prismlike
air layers, transmitting alternating parts of its vivid
glow. Sirius is a great target for a spectroscope.
Of course, viewing Sirius means seeing the combined
light of two famous stars. Circling each other every
50 years in a wildly eccentric orbit, they are finally far
apart. Now and for the next few years, you can glimpse
the dim Pup a comfortable 10" from the blazing pri-
mary, especially if you nudge the scope to keep Sirius
A’s insane dazzle out of the field.
Sirius B is a sphere only about the size of Earth, yet
its mass some 350,000 times greater means it has col-
lapsed to an interesting degree. On Earth, the densest
materials are about 20 times heavier than water. But
Sirius B is about 130,000 times denser than water.
Imagine landing on its diamond-hard surface. Even
if you could shield yourself from the heat, its merciless
gravity would freeze all your motion like a frame in a
jammed projector. Your lungs could not take one breath,
nor your muscles lift a single finger to warn others. Yet
these fantastic stars are common. Of the 58 suns lying
within about 16 light-years of Earth, five are white dwarfs.
Sirius B takes honors as the nearest. But twice its dis-
tance, at 16 light-years — also optimally seen this month
— lies the easiest white dwarf to spot, and my favorite.
Simply follow the starry line that heads right from Rigel
to form Eridanus the River, and you’ll quickly reach two
matching 4th-magnitude stars. Point your trusty scope
at the bottom one. Call it 40 Eridani. Or
Omicron^2 (ο^2 ) Eridani. Or Keid. A mere 50x
shows the main star has a distant double-star
companion, discovered by William Herschel
two years after he found Uranus. This com-
pa n ion pa i r i s a n e a s y bi na r y sepa r ated by 8 ".
The brighter of these two is the white dwarf,
the first ever recognized.
And call the pound: This same patch of
December sky has yet another dog running
loose. Between Sirius and Keid we have
Procyon, sitting just 11.4 light-years away.
Can it be that the brightest star of the Little
Dog has a white dwarf companion rivaling
the Big Dog’s? And that both systems have
orbital eccentricities of about 0.4? With both orbiting
at a sepa r at ion of a rou nd 2 0 a st ronom ic a l u n it s , match-
ing the Sun-Uranus separation?
Yes, it’s true: All our Dog Stars have dense little pups.
It’s weird, but a lso k ind of cute.Our canine constellations have faithful companions
of their own.Two - d o g n i g h t
Sirius A, the Dog Star
(center), has a smaller
“pup” companion. The
white dwarf Sirius B
peeks out from the
light of its larger
companion in the
lower left-hand region
of this Hubble Space
Telescope image.
NASA, ESA, H. BOND (STSCI), AND
M. BARSTOW (UNIVERSITY OF
LEICESTER)Of the 58
suns lying
within
about 16
light-years
of Earth,
five are
white
dwarfs.
BY BOB BERMAN
Join me and Pulse
of the Planet’s
Jim Metzner
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Astounding Universe,
at http://www.astounding
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