skyandtelescope.com • SEPTEMBER 2019 59telescope. The donor star in SS 433 is
a supergiant, while consensus leans
toward a neutron star for the compact
object. The pair orbits each other every
13.1 days. The jets precess like a spin-
ning top over a period of around 163
days, producing a distinctive corkscrew
pattern — the National Radio Astron-
omy Laboratory has made a “movie”
that spans some 42 days of observation
highlighting this effect: see https://
is.gd/ss433movie. In November 2003 I
located SS 433 using my 25-inch refl ec-
tor and saw it as a stellar point with no
detail. I estimated it to be magnitude
14.5 and a little fainter than a paral-
lelogram of stars 1.5′ to its northwest.
With the help of an O III fi lter, I man-
aged to spot two of its eastern frag-
ments in my 32-inch.
So is that the end of the story? Not
quite. As often happens, once a new type
of object is identifi ed, scientists know
what to look for and so they can extend
their reach into more exotic locales. Sev-
eral years ago, preparing for the Okie-
Tex Star Party, I was researching targets
and came across P13 in NGC 7793, a
galaxy in central Sculptor a little less
than 5° south-southeast of Delta Scl. I
can see moderate detail with my 32-inch
refl ector of this 9.3-magnitude spiral(type SA) at the relatively close distance
of 12 million light-years, with a very
open structure and a size of 9.1′× 6.6′.
A 1997 extensive survey of the galaxy
identifi ed multiple supernovae remnant
candidates. Follow-up X-ray and radio
observations showed that one of these,
S26, contained both a point source and
extended features, and was later identi-
fi ed to be a microquasar. P13 is consid-
ered to be the long-sought extragalactic
analog to SS 433, but on a much bigger
scale, spanning some 1,000 × 500 light-
years. Although P13 itself is too faint to
see, I easily spotted S26 as a 19th-mag-
nitude stellaring on the northeastern
edge of NGC 7793 in a 9-mm eyepieceMicroquasars
ObjectDonor
CompanionSpectral
Type Mag(v)Orbital
Period (d) RA Dec.
Cygnus X-1 HD 226868 O9.7I 8.9 5.6 19 h 58.4m +35° 12′
LS 5039 V479 Sct ON6.5V 11.3 3.9 18 h 26.3m –14° 51′
Scorpius X-1 V818 Sco Oev E12.2 0.8 16 h 19.9m –15° 38′
V4641 Sgr — B9III 13.7 2.8 18 h 19.4m –25° 24′
SS 433 V1343 Aql A7Ib 14.2 13.1 19 h 11.8m +04° 59′
P13 — B9I 20.5 64 23 h 58.0m –32° 33′
Right ascension and declination are for equinox 2000.0.at 361× at the Okie-Tex Star Party in
late September 2016. Three of my fellow
observers confi rmed the sighting.
For those who love the complexity
and interconnectedness of the night
sky, understanding the history of
microquasars, then pursuing and suc-
cessfully observing them may evoke the
Japanese term yugen: a nearly ineffable,
deep emotional response to the mystery
and beauty of the Universe.¢DAVE TOSTESON has been an ob-
server for more than 30 years. When
he’s not working as a family physician in
Minnesota, he keeps busy by traveling to
regional star parties and solar eclipses.tSS 433 The object that kicked off microquasar re-
search, SS 433 is located some 10½′ north of HD 179285
and about 16′ southeast of 7th-magnitude HD 179104.pP13 AND S26 IN NGC 7793 The supernova remnant
S26 lies on the northeastern edge of NGC 7793, which
is where you’ll fi nd the extragalactic microquasar in our
sample, P13.PO
SS
- II^
/^ C
AL
TE
CH
/^ S
TS
CI^
/^ P
AL
OM
AR
O
BS
ER
VA
TO
RY
(^2
)
HD 179124HD 179104HD 179285HD 179493HD 179596SS 433S26