Astronomers have made the largest and best map yet of the large-scale structure of our universe: a map of 1.2 million galaxies that sheds some light on the mystery of dark energy.
The Sloan Digital Sky Survey is a collaboration between astronomers from around the world which makes use of a 2.5 meter telescope, located at Apache Point Observatory in New Mexico, to survey a large portion of the observable Universe. This new result is from the Baryon Oscillation Spectroscopic Survey (BOSS) which uses a spectrograph attached to the telescope to determine the distances to millions of galaxies. The distribution of distances to these galaxies in a 3D volume of the Universe allows astronomers to better understand how dark energy works over time.
BOSS is looking to measure the expansion rate of the Universe. When the Universe was very young (less than 400,000 years old) there were pressure waves traveling through it. As it continued to expand at an accelerated rate, these pressure waves imprinted a signature on it in the form of baryon acoustic oscillations (BAO) which determined how matter was distributed. By measuring the clusters and voids of galaxies between then and now, we can see how the expansion of the Universe changes over time. We can’t actually see (or map) galaxies over the range of the full age of the Universe yet (13.8 billion years), so BOSS focused on galaxies between 7 million and 2 million years old. Within that distance range, they found 1.2 million galaxies in a volume of 650 cubic billion light years.
The resolution with which they determine the distances and positions of galaxies within this volume was akin to measuring this distance between two grains of sand 100 yards apart in a cubic mile. What they found was that the clustering of galaxies at various distances (and hence various times) was consistent with Einstein’s cosmological constant (essentially the dark energy component) to within 5%. The map also showed the gravity component to be inline with the predictions of general relativity on smaller scales where dark energy doesn’t dominate yet.
While confirming things we already know might not sound important, it is. So many theories and experiments in physics and astronomy rely on our ability to accurate model and measure cosmological parameters such as these. We make observations, come up with theories based on those observations, make predictions to what else those theories might produce, and then go look to see if we can observe what was prediction. And then we do it all again, each time learning a little bit more and learning what questions to ask next.
You can read more about this result from several of the teams involved: Max Planck Institute for Extraterrestrial Physics, Lawrence Berkeley National Laboratory, and the Sloan Digital Sky Survey itself. Here’s some more geek from the week: Keep on geeking! @Summer_Ash, In-house Astrophysicist
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