A bit about Galaxies
|Estimates, or, intelligent guesses, but ultimately, unknowns.|
Who knows how many stars there are?
How many galaxies that contain them all?
We do not know. Maybe we never will.
The galaxías kýklos is certainly one of a very great many.
It is second largest of the Local Group,
Which are part of the Virgo Supercluster,
Which is in its turn a subset of the Laniakea Supercluster
An immense heaven at the beck and call of the Great Attractor,
Or perhaps the Shapley Supercluster,
Gravity nested within like some Russian doll.
Via lactea, a milky circle in the sky. Spurt from Hera's pap.
Surrounding, encompassing, a solar system, a world.
On the inner rim of Orion's arm. A bit of local fluff.
Our solar system, our world. Significant only to those who live upon it.
Just one amongst a multitude.
We know so little.
Even this, the barred spiral in which we live, is a matter of much conjecture.
We do not know how many stars it comprises, maybe we never will.
Nor do we know, how far across it is spread, and estimates vary greatly.
Though we work hard to observe more, and improve in accuracy.
And the bar might be a stellar nursery, though this is a hypothesis,
As is much else besides. A best guess, based on what we know so far.
There is power in its flexibility, and its ability to be changed.
To encompass new data, and enriched lines of thought.
Heavy sound, stirs around, but not tightly wound.
A quasistatic density wave at the center formed the bar,
Channelling in gas from the spiral arms through orbital resonance,
The gravitational pull of stars at different radii
Rotating through the stars and the gas and the dust,
Compressing then releasing, and maintaining the spiral,
Preventing winding, although spellbinding.
Heavy sound. Stirring the cream that swirls on the coffee in the cup.
Lindblad Resonance, driving the spiral density wave. The spoon invisible.
The epicycle frequency of stars, recurringly reaching their furthest
From the centre of mass, is some simple multiple of the forcing frequency
Of the spiral arms themselves. Clink of metal on fine bone china.
At the center, coined Sagittarius A* could well be, by far,
The largest black hole in the whole milky bar.
Supermassively inferred, though not observed, and radio actively exciting.
Galactic Center, surrounded by its cohort of ancient stars, the bulge.
Holy indeed, a stellar spheroidal halo, and beyond this another halo of hot gas
Reaching out almost to le Grand Nuage et le Petit Nuage,
Irregular dwarf Magellanic spiral galaxies, and in orbit about the Milky Way
North and South of the core, and hard to ignore, are bubbles that store,
X-rays and Gamma rays galore.
Currently thought to be magnetized outflow from the further formation of stars.
Beyond the bar, for oh so far, the arms extend and curl around,
From their composition, and because they contain an excess of red giants,
Two of the arms are considered to be major.
They are named Perseus, and Carina–Sagittarius
But here is a dilemma, for nothing is clear cut, and confusion does abound.
As reckoned by young stars and gas, there are four major arms.
So add Scutum–Centaurus and the Orion–Cygnus Arm, so far, so good.
Oh, but there is more, lets expand the 3 kpc Arms both Far and Near.
3 kilo parallax of one arcsecond, by a very small angle a huge number is reckoned.
Nor may we forget Norma, your attention is also drawn to the Outer arm.
It is impossible to see the without from within, so far from knowing,
It is inferring from data that we begin. Unmaking our unknowns,
Endlessly enumerating. So far we have come, so much further to go.