Season 17, Episode 51: 3 Ways We’re Hunting Dark Energy, Explained

Hey StarTalkians! Episode 51 of season 17 welcomed Dr. Jason Rhodes, who sat down with Neil and Paul to discuss the new Nancy Grace Roman Space Telescope and the hunt for dark energy. This took up most of the podcast, but particularly the first half:

The Hunt for Dark Energy with Jason Rhodes - StarTalk Radio

Dr. Rhodes mentions three ways the telescope will be looking for dark energy, but as is often the case, it was easy to get lost in the meandering discussion. So here’s a briefer, clearer list.

Method 1: Type 1a Supernovae

This was discussed early on in the history of this board, but the short version is: these supernovae are “standard candles,” which are used to fix cosmic distances. If you fix the distances of many of these across different redshifts, you can tell how fast space appears to be expanding.

Method 2: Baryon Acoustic Oscillations

Baryon acoustic oscillations are a little like frozen sound waves, spread out over the universe. Back when the universe was a hot, electron-baryon plasma, photons were basically trapped. They continually interacted with the plasma, until the universe cooled enough for the particles to form into the first atoms. At this point, the photons could finally escape, leading to the well-known cosmic microwave background radiation (CMB).

But at the same time, the ripples of what happened in the plasma phase spread out too. Denser regions of the early plasma universe were pulled together by gravity, but pushed back apart by the interacting photons. This led to oscillations – like sound waves – which travelled through the plasma until the universe cooled.

These waves were released along with the CMB, and form another key relic of the early universe. A distinctive signal of this has been detected.

Like type 1a supernovae, these can be used to establish a distance scale, and any distance scale can be used to probe dark energy.

Method 3: Weak Lensing

Gravitational lensing is usually discussed in the dramatic cases, like a galaxy cluster magnifying and warping an ancient galaxy behind it. But it also operates on much smaller scales, and this type is useful in the hunts for dark matter and dark energy. This gets especially technical, but the short version is: weak lensing is useful in combination with the other two methods, and by helping to map the distribution of dark matter.