Thursday, November 30, 2006


It may end with a whimper, but most cosmologists agree that our universe surely began with a bang; bursting forth from an infinite singularity and period of universal inflation en route to the cosmos that we continue to marvel over some 13.7 billion years later.


New images from NASA's Spitzer Space telescope are giving cosmologists their share of early times. The above figure shows how far Spitzer has gone in its survey of the Hubble Ultra Deep Field (HUDF), back approaching an epoch of some of the universe's earliest galaxies.


Theorists still scuffle over details involving the formation of the very first galaxies. Historically, galaxy formation sagas involved either a top down or bottom up scenario. The top down version has it that the first galactic structure in the universe formed from patterns imprinted on the fabric of the early cosmos itself.

The bottom up theory allows for galaxies to have formed piecemeal from an ongoing accretion of smaller structure such as dwarf galaxies into mature galaxies, like our own "grand design" spiral galaxy, that we see throughout the present day universe.

Observations, however, are finally catching up with theory. Some cosmologists are continually surprised at how early in the history of the universe, the earliest galaxies formed.
This image shows one of two early galaxies studied with the combined efforts of NASA's Hubble and Spitzer space telescopes as it appeared an estimated 700 million years after the big bang.

Image: Ivo Labbé and Rychard Bouwens

As reported in a recent issue of Astrophysical Journal Letters, researchers believe these baby galaxies could have formed only half a billion years after the big bang. They were certainly quick about it. But it’s unclear whether such new observations will quell debate over the ultimate mechanisms that affected how these galaxies first started their formation process.


As David Koo, an observational cosmologist at the University of California at Santa Cruz told, the debate is no longer top down or bottom up.

"There’s not too much question about the basic tenets of the bottom up theory,” said Koo. “That means that usually you start off with smaller objects and over time things aggregate together to form larger and larger systems.”
Koo isn’t even surprised to find galaxies at such early times. In fact, he believes that galaxies were probably forming even earlier than half a billion years after the big bang. The problem now is not that these galaxies are out there, but there’s still no good census of them.

The more interesting question, says Koo, is not that there were such galaxies so early in the universe, but rather did supermassive black holes precede them? And, if so, how did such primordial black holes form? Were they merely the product of random density fluctuations in the early universe?

(Above) A NASA black hole computer simulation.

“Finding large numbers of supermassive black holes at very high redshift,” said Koo, “would be interesting. That could indicate there may have been seeds of black holes back in the very beginning of the universe, which were fed gas and grew; in turn, becoming seeds of the earliest galaxies.”


R2K said...

Odd: how can the big bang be larger than the current universe in that image?

Why is the record of something so small, a singularity for an instant, all around us? I never got that, even after a modest education in astronomy in college as well as my work in the hobby. Maybe you can explain that to me.

4:24 AM  
Bruce Dorminey said...

While theories of standard cosmology state that the big bang stemmed from an infinite singularity and the space time continuum we experience in our own little solar system is a product of all that evolution some 13.7 billion years later; then the usual analogy given is that the expansion was isotropic, in all directions, somewhat akin to an inflating balloon, with earth on the edge of that balloon looking back into the center. That works on one level, but I believe your real question is if this is so, then why does the CMB appear to be isotropic? How can earth just happen to appear to be at the center of it all? I believe I'm correct in saying that it's a function of our own observational bias. That if we were able to see beyond our limited field of view to the whole of the universe in one fell swoop, then the CMB would not appear to us as inherently isotropic. If you have further questions, I can refer this to David Koo, the cosmologist quoted in this story.
Thanks for your comment.

1:00 AM  

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