Half hour exposure of star trails
above the Keck Telescopes taken by yours truly
The dark matter that I discussed in my last post is quite bizarre, but makes up only a small fraction of the universe. The dominant material in the universe actually appears to be some kind of “dark energy“.

Since no one has any idea what dark energy actually is, I can’t really write a whole lot about it. All I can say is that something is out there, and it’s really weird.

Dark energy presents itself to us as a mysterious force, counteracting gravity over enormous cosmological distances. The effects of this force were first observed through observations of very distant supernovae.

Given the right conditions (any idea what these conditions may be?), an old star can explode as a supernova. The explosion is so bright that it can be seen from across the universe. All of these explosions are very similar, enabling us to estimate the distance to the supernova from its apparent brightness.

Observations of supernovae are used to measure the rate at which space is expanding. Measurements show that supernovae are much fainter than expected. It appears that there must be a new force at work, caused by a previously unknown material. We call this material dark energy.

As this NASA chart indicates,
the dominant material in the universe is “dark energy”
This week I’m actually observing supernovae (and dark energy) using the Keck Observatory on Hawai’i. We discovered a little over 30 of these supernovae in the last year using the Hubble Space Telescope. We use large ground-based telescopes to measure the speed at which they are moving away from us.

Combining the brightness from the Hubble data with the speed from the Keck data, we get a measure of this dark energy. But it’s not all fun and games there in the beautiful Hawaiian islands– I get to spend 16 hours a day in front of a computer screen watching data come while my girlfriend scuba dives nearby with a pod of dolphins. Well, you can’t have your poi and eat it too.

Kyle S. Dawson is engaged in post-doctorate studies of distant supernovae and
development of a proposed space-based telescope at Lawrence Berkeley National Laboratory

Why does it … matter? Part II 6 July,2011Kyle S. Dawson
  • Barry Starr

    So dark energy is invoked to explain supernovae being dimmer than we think they should be? Are there any alternative explanations? Maybe we don’t really understand supernovae…

  • Kyle Dawson

    Alternative explanations have been proposed, including a new type of grey dust that is uniformly spread throughout the universe and absorbing SN light. It has also been suggested that dust from the galaxies that host supernovae may evolve and change its behavior as it ages. It has also been suggested that supernovae may change as their host galaxy ages. However, none of these explanations adequately describes the effect that is observed.

    It is also true that more recent observations of other cosmological effects appear consistent with the dark energy scenario. Supernovae were the first measurement technique to reveal this supposed dark energy, but now several other experiments show similar results.

    That being said, the dark energy explanation is not very satisfying, and we are still looking for alternative explanations. Maybe we just don’t know what gravity is?

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Kyle S. Dawson

Kyle Dawson is engaged in post-doctorate studies of distant supernovae and development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.

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