In The Beginning
Cosmology 101 Items',
If you read Cosmology 101, you know that the Big Bang produced large
amounts of hydrogen, some helium, and a small amount of lithium. Actually, it's
likely that the Big Bang produced about as much anti-matter as matter, and it
has been a puzzle why the matter and anti-matter didn't just mutually
annihilate. Recent studies have indicated a type of quantum asymmetry that
might explain why a residual amount of matter in excess of the anti-matter was
Anyway, the result was a universe with vast clouds of hydrogen. The initial
question about that Big Bang was why there were clouds, and not just a single
uniform cloud. That is, what caused any clumping? It seemed, from the
equations, that a uniform distribution should have been created.
One answer promoted was that the primordial distribution of material (first
disconnected quarks, then particle soup, and finally the first few elements)
was not homogeneous because of quantum fluctuations in the Big Bang itself.
Earth-based radio telescope examinations of the cosmic background radiation
reveal no such fluctuations.
The COBE space probe, able to measure much smaller fluctuations in the
background radiation, detected the quantum fluctuations hard sought. The
incredible difficulties of getting the COBE built and launched are detailed in
Wrinkles in Time: Witness to the Birth of the Universe,
by George Smoot and Keay Davidson.
It is, then, the quantum fluctuations inherent in the Big Bang itself that
led to an uneven distribution of hydrogen. The image depicts such
an uneven distribution of gas. The uneven distribution allowed the
mutual gravitational attraction to operate on the unevenness, further
clumping the gas.
The Game is Afoot
This image illustrates a further clumping created by the initial
distribution, and the mutual attraction of gravity between the atoms.
Depending upon the primordial clumping, clumps of gas became more
condensed, and thin areas of distribution began to disappear. At least,
that has been the prevailing theory.
Also beginning to be apparent in this image is a slight angular motion. It
is virtually impossible for the initial clumps to have had no angular
Recall how a spinning ice skater spins faster has she pulls in her arms?
That's from the conservation of angular momentum law. Angular momentum is a
function of the distribution of mass and the angular rate. If the mass moves
closer to the center of rotation (which it will in the gas clouds from the
gravitational attraction), the angular rate will increase to conserve the
momentum. It's the same effect, by the way, that leads to neutron stars
spinning at hundreds of times a second.
The Plot Thickens (and so does the soup)
This image shows the further collapsing of the distributions of gas and the
increasing angular rate.
So why is the rotation around some invisible point in the center?
Good question. Maybe it never was like that. Then again, current ideas
on Dark Matter suggest it may have been.
Whatever the solution regarding dark matter turns out to be, it is now
recognized that most (perhaps all) galaxies have massive black holes at their
centers. Did the black holes coalesce from the hydrogen, were black holes part
of the Big Bang's creation, or does dark matter have something to do with the
early formation of black holes?
The relationship of black holes at the center of most galaxies and any
relationship between black holes and dark matter are still illusive. The image
depicts the hypothetical situation in which a black hole already exists in a
region of hydrogen. If that's the way it happened, the swirling hydrogen would
continue to collect and shrink toward the black hole, spinning more rapidly as
a result. With the current view, it's a good guess of how things frequently
The Shape Begins to Form
The further shrinking of the swirling hydrogen begins to take shape. What
shape? It could vary, but the characteristic pinwheel shape of a galaxy is
a common result.
We're talking galaxy formation here. Hydrogen is pulled toward the center
of mass, and inhomogeneities within the hydrogen cause local collapses that
lead to star formation.
Near the center, the voracious black hole begins to strip apart matter,
creating high energy x-rays and gamma rays. In this phase, the proto-galaxy
is incredibly bright, visible through Earth-based telescopes from
billions of light years away. The initial objects spotted a few decades ago
were given the name Quasars.
Now we know that the quasar is a galaxy being born, at the phase when the
black hole in the center is gorging itself on abundant material and
spewing out an enormous amount of energy.
I See It Now
Eventually, the material settles into a stable configuration. The voracious
appetite of the black hole produces so much violence around the vicinity of the
event horizon that an evacuated zone develops, pushing away other material.
This stops the feeding frenzy of the black hole. The shape of a galaxy is
recognizable now, and star formation (and planet formation) in the orbiting gas
So the history is clear, we have it before us. Or -- do we?
There are still problems with this view of galaxy formation. It first
seemed that the mutual attraction of gas in the early clumps wouldn't have
had time to form galaxies this early in the universe's development.
How long is that, by the way? About 13 billion years. Given the energy and
rapid expansion of the Big Bang, it's difficult to explain how galaxies would
exist in the abundance they display so early in the history of the universe.
That is, unless you accept the premise that dark matter is a real substance.
Models accepting the apparent abundance of dark matter do provide the
necessary impetus to cause early galaxy formation.
The fact that black holes play a part is helpful in some ways, but the
rapid clumping still isn't explained without the assumption of dark matter..
The fact of misbehaving orbital velocities of the material throughout the
galaxy is another problem. In the typical galaxy, material further from the
galactic center doesn't move as slow as a simple gravitational model would
dictate, even with the existence of the black hole taken into account. Again,
this discrepency in orbital velocity of galaxy stars can be explaned by the
acceptance of a halo of dark matter around each galaxy. No one yet knows
what dark matter is, but the nature of star motion in galaxies, and even
the rapid formation of galaxies themselves is only currently explainable if
one assumes a role for dark matter.
Ah, it was never meant to be easy. Only fascinating.
The pictures on this page were created (however crudely) with the
Gimp. The Gimp fortunately had enough tools
to give the spinning and collapsing effect I was seeking. The Gimp, by the way,
is freely available to Windows, Mac, and Linux users (I happen to favor the
Another book that gives a description of galaxy formation, the problems with
it, and how it is coupled to our knowledge of the microwave background
radiation is Steven Weinberg's The
First Three Minutes: A Modern View Of The Origin Of The Universe. If you're so inclined, I suggest first reading
this book, then Smoot's book about the COBE satellite. Weinberg's book
describes the necessity for a satellite view, which hadn't happened at the time
of his book.