Cygnus: The Swan
Observing >
In the northern summer skies, nestled in the Milky Way, is the constellation Cygnus the Swan. If you are looking for a family album of stars, this is a stellar sampler.
Finding it is easy. Facing toward the south in the late evening, find
the Milky Way brightly shining up out of the southern skies. Follow it
up and just over your head - don’t tip over! - until you discern
a star pattern in the shape of a giant cross.
This is Cygnus the Swan. But because of its striking cross configuration,
it is also called the Northern Cross. Let’s start at the "top"
of the Cross, at the bright star, Deneb.
Deneb is not anything like our own star, the sun. It is a white supergiant
star, nearly 300 times bigger than the sun.
And its energy output is prodigious. (You may want to sit down for this.)
Deneb pours out nearly 400,000 times more energy than our sun, enough
to cause major blistering. Deneb, therefore, is best viewed from far,
far, far away.
If you have a fairly decent scope you may want to scope out the North
America Nebula. It is a faint, cloudy area immediately to the "upper
left" of Deneb when viewing Cygnus as a cross.
It’s called the North America nebula because its shape resembles
a certain special continent... you guessed it!... North America. Here
in this mighty cloud of gas and dust, stars are being born in the disk
of our Galaxy.
Now let’s move our eyes farther "down" the cross. There
is a star (named Sadr) where the cross "crosses." Below that
is a fainter star, eta Cygni.
It’s in this area where there resides a very distant star - HDE 226868
- with a very strange companion possessing the sci-fi name, Cygnus X-1.
The "X" comes from the fact that this companion is spewing out
X-rays like there’s no tomorrow.
This X-ray spewer is massive, about 25 times more massive than the sun!
And it’s not very nice, either, stripping the gas right off old HDE
226868.
Most mystifying, though, is that this super-massive, X-ray emitting, star
stripper is invisible! What in the galaxy is going on? Great question!
Short answer? A black hole.
"But we can’t see black holes!" you may exclaim. That’s
correct, and that’s precisely why we need circumstantial evidence
to find one. Find a visible star with a supermassive, invisible companion
which sucks the gas off the visible star and you’ve got yourself
a black hole.
What is a black hole? It’s the core of a massive star that blew off
all its outer layers when it died in a supernova blast. The carcass of
the deceased star, way down deep, was blown inward with unimaginable force.
It is so dense now that its tremendous gravity won’t even allow light
to escape its clutches. Cygnus X-1 was the first of these critters found
in the cosmos.
A look at the Northern Cross would be incomplete without mentioning Albireo,
the "star" at the foot of the cross. Even binoculars reveal
that Albireo is really a double star. But this is no ordinary double;
through a scope it is a beautifully contrasting colored pair. Albireo
A is a red-orange giant of a star. Albireo B is its striking electric-blue
companion.
Cygnus is proof that constellations are more than just collections of
stars. For many of us, they are entire assemblages of cosmic phenomena
that make astronomy so much fun.
Until next time, clear skies!
Finding Cygnus
North America Nebula
Black Hole Binary
Albireo
Posted by Administrator at 2000.07.23 09:25 AM | Comments (0)
