At the beginning of our last episode, I mentioned that we’d just learned that new work by the Dark Energy Spectroscopic Instrument, or DESI, had provided hints that our universe has a changing density of dark energy, but I needed time to look over the research. Well, I’ve looked, and the news is kind of cool, especially if you like mysteries.
As the story goes, back in 1998 two different supernovae research teams did a fit to their brightness versus velocity data and found the expansion rate of our universe, which is the source of that measured velocity, appears to be growing over time. This was unexpected, and in a moment of lack of creativity, that thing causing the universe to expand was named Dark Energy.
Initial results seemed to indicate that the amount of Energy in every cubic meter of space is about the same as a few protons, and this density is constant with time, but trying to measure what’s going on in the distant universe isn’t all that easy, and better data would require new instruments.
And those new instruments are starting to get us results. First on the scene is DESI. This instrument is very carefully documenting where galaxies and cold neutral clouds of gas are located by looking for the galaxies light and then looking for how those cold clouds are absorbing that light from some galaxies emission lines. By mapping out the evolving distribution of our universe’s mass, they are able to compare what we see with the expected distribution based on what we see in the cosmic microwave background – that wall of light that was produced when our universe cooled enough to form neutral atoms. The slight temperature variations we see in this light reflects the distribution of mass at that moment, and the distribution of galaxies and cold gas we see closer to us reflect the distribution of mass at the times when light was emitted or absorbed.
When the DESI team combined their early results with other data, they found evidence that the changing distribution of mass is best matched by models that have Dark Energy may be weakening over time, or that its energy density – the amount of energy per cubic meter – may be decreasing over time.
These are still preliminary results. Within error, the data can also be fit by models with constant amounts of dark energy… just not quite as well.
More data from DESI is coming, and now all of us have even more reason to be excited by this instrument.
And other data sets are also on the horizon. ESA’s Euclid mission is starting to return its own maps of galaxies and more, with its first data release coming mid March. So far they’ve classified 380,000 galaxies and 500 gravitational lens candidates. We also saw the launch of SphereX, a small NASA space telescope that will be mapping the first galaxies to light up the universe. While it hasn’t completed calibration yet, early, uncalibrated images demonstrate its ability to make out faint, distant galaxies.
If I were a betting person, I’d be putting down money on the evolution of Dark Energy getting sorted this decade. As new information is published, we’ll bring it to you right here on EVSN.