Last night we completed our observations for the Supernova Legacy Survey. This was a five year program to study supernovae using a 4-meter telescope in Hawaii in combination with several of the largest optical telescopes in the world.

The project was headed by a group at a university in Toronto and a group at a university in Paris. Canada and France sponsor the 4-meter telescope that is used to discover and observe the supernovae from the point of explosion to the final days when the supernova fades from view. We call this the imaging part of the program. This data constrains the apparent brightness and life cycle of the supernova, and eventually the absolute distance to the supernova.

Our contribution to the project was primarily through our affiliation with Keck Observatory. We were typically awarded four nights a year to observe recently discovered supernovae spectroscopically. The data is used to determine the redshift and the kind of supernova explosion.

The supernovae are used to study the rate of expansion of the universe. It was this type of experiment that was first used to discover that the universe is actually dominated by dark energy.

No one really suspected the presence of dark energy for almost the entirety of the 20^th century. Now, we not only know it exists but are actually trying to understand it in the same way we understand gravity, protons, and electrons. That is where projects like the Supernova Legacy Survey come in. With projects like this, we work to collect enormous samples of well-studied supernovae that can improve our understanding of dark energy.

We use a certain type of supernova as yardsticks to measure distances in the universe. We then model the affects of dark energy on the expansion history of the universe by comparing distances and rates of expansion. This comparison is typically represented in a Hubble Diagram.

The Supernova Legacy Survey has been very successful in its attempts thus far. On the right, I show the Hubble Diagram from the first year of data. This is less than 20% of the full sample. The dotted line outlines the expectations of the 1990’s cosmology crowd. The solid line shows the prediction from the more sophisticated cosmologists of the 21^st century. As you can see, the original expectations were pretty far off the mark - the supernovae just don’t lie on top of the dotted line.

Now that this program is finishing up, we should be seeing similar figures that are teeming with supernovae. Future programs should do an even better job of making these measurements. Someday we may actually understand this dark energy thing, it may turn out to be something else completely new and unexpected!

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.

The Forest

Venus Landing. Credit:
Soviet Planetary Exploration ProgramIt’s time to get back to some of the reader’s questions. Over the last couple of months I’ve focused on the easy ones like “how big is the universe?”. Now, people are asking the tough ones, like that from Mike:

“There’s been a recent debate in our local papers regarding Venus’ high planetary temperature being related to the dearth of carbon dioxide on the planet. Apparently Venus is much, much hotter than Mercury, even though Venus is twice as far from the sun. Could you explain a bit about our system’s planets and how they differ compositionally? What is it about the Earth’s composition of elements that makes it just right for 99% of the life on the planet? I say 99% because it seems 1% of the life is strange enough to exist in all sorts of harsh conditions.”

When it comes to the landscape of our own neighborhood, it gets a little more complicated for me. I have a tendency to look right past the solar system in my research of the distant Universe. I’m sure there’s an explanation for this in the cliché of missing the forest for the trees. I just do it in reverse.

The Trees

Hubble Deep Field. Credit:
R. Williams, The HDF Team (STScI), NASATruth is, the trees are quite intriguing in their own right. I think people are more impressed with the observations of our solar system because the proximity lends to very detailed images and observations. Compare an image of the surface of Venus to one of the deepest images from Hubble Space Telescope. The image of Venus fits within our sense of scale that we established in our time here on Earth. You can even see familiar rocks and the feet of the Soviet robot. The Hubble Deep Field… needs a bit of explanation.

For the rest of the year, I am going to pull back from the farthest reaches of the universe and focus on Venus and the other planets. It will give me a chance to learn a little about what the Solar System actually looks like. It will also give me a chance to explore some of the most breath-taking images that NASA has created. I’m just going to have to do a little research to get it right.

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.

latitude: 37.6797, longitude: -121.698