Since light always travels at a constant speed (the speed of light), looking out further into space is equivalent to looking back in time ... which is what Carilli and his team did. Looking at the galaxies 13.7 billion years ago, when they were first forming, they found that the ratio of black holes to the bulges in the center of galaxies was different in the early galaxies. The black holes appeared to be more massive, and in turn drew more stars together, forming the bulges.
Most galaxies seem to settle on a ratio where the massive black hole at the center of the galaxy is about 0.1 percent the mass of the galaxy (in the case of a spiral galaxy, like our Milky Way, the "arms" don't count in determining this ratio). Even these new findings don't indicate why the universe seems to somehow optimize for this relationship of black hole to galaxy size.
The finding itself may also be in question, as Tod Lauer suggests there might be selection bias at work. The methods used by the team might be over-examining smaller galaxies (because there are more of them), so their study wouldn't be representative of the entire ancient universe.
Artistic rendering of a black hole
Source: NASA
Related Articles:
- Scientific American - Which came first - galaxies or black holes?
- Science News - In the young universe, black holes may have formed first
- BBC News - Black holes 'preceded galaxies'
- Space.com - Black Holes Preceded Galaxies, Discovery Suggests
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