New Way to Measure Dark Energy

Researchers have discovered a method to potentially detect and measure dark energy by examining the motion between the Milky Way and Andromeda galaxies. This technique, still in its early stages, can estimate the upper value of the cosmological constant, a simple model of dark energy, which is five times higher than values determined from the early universe.




Researchers from the University of Cambridge have discovered a new way to measure dark energy – the mysterious force that makes up more than two-thirds of the universe and is responsible for its accelerating expansion – in our own cosmic backyard.

The researchers found that it may be possible to detect and measure dark energy by studying Andromeda, our galactic next-door neighbor that is on a slow-motion collision course with the Milky Way.


Since it was first identified in the late 1990s, scientists have used very distant galaxies to study dark energy but have yet to directly detect it. 

However, the Cambridge researchers found that by studying how Andromeda and the Milky Way are moving toward each other given their collective mass, they could place an upper limit on the value of the cosmological constant, which is the simplest model of dark energy. 

The upper limit they found is five times higher than the value of the cosmological constant that can be detected from the early universe.

Although the technique is still early in its development, the researchers say that it could be possible to detect dark energy by studying our own cosmic neighborhood. The results are reported in The Astrophysical Journal Letters.

Everything we can see in our world and in the skies – from tiny insects to massive galaxies – makes up just five percent of the observable universe. 

The rest is dark: scientists believe that about 27% of the universe is made of dark matter, which holds objects together, while 68% is dark energy, which pushes objects apart.  READ MORE...

Dark Energy

This diagram reveals changes in the rate of expansion since the universe’s birth nearly 15 billion years ago. The more shallow the curve, the faster the rate of expansion. The curve changes noticeably about 7.5 billion years ago when objects in the universe began flying apart at a faster rate. Astronomers theorize that the faster expansion rate is due to a force called “dark energy” that is pulling galaxies apart. Credit: NASA/STSci/Ann Feild






Dark Energy Was Always Present, Everywhere and at Every Time


The Force is with us, according to cosmologists working to understand a mysterious “something” that’s making the universe expand. Its name? Dark energy. And, it turns out that it’s been present everywhere throughout cosmic history.

Astronomers have known since the 1920s that the universe is expanding. That understanding began with Edwin Hubble’s groundbreaking observation of a Type I supernova in the Andromeda Galaxy. 

And, astronomy trucked along for many years, using that expansion to measure distances and other parameters in the cosmos. Then, in 1998, something happened. Astronomers discovered that the cosmic expansion is speeding up.

The culprit? This completely not-at-all-understood dark energy force which can’t be seen, but with effects that can be detected. Some explain it as a property of space that causes the universe to expand faster and faster. 

Others suggest that it’s some kind of new energy fluid or a field that fits throughout space, but has an effect on the expansion of the Universe. It could also be something that doesn’t fit our current theories about gravity, and that a new theory of gravity could account for dark energy’s effects.

There’s no consensus yet about which of these theories is correct. However, its discovery immediately raised a bunch of questions, such as, when did the expansion rate accelerate? Will that change, too? Was it the same rate throughout the universe across all time?

Dark Energy, eROSITA, and Galaxy Clusters

To answer those, a group of researchers used something called eROSITA to look at a specific subset of galaxy clusters across time. eROSITA is the main X-ray-sensitive instrument aboard the Spectrum-ROENTGEN-GAMMA (SRG) mission launched in 2019. (Currently, it is shut down due to the ongoing conflict between Russia and Ukraine.) 

One of its jobs is to do a complete all-sky survey in the medium energy X-ray range (up to 10 keV). The data it returns should help probe the nature and ubiquity of dark energy by studying up to 100,000 galaxy clusters and the material between them. It also studies obscured black holes in galaxies and looks at X-ray sources ranging from young stars and supernova remnants to X-ray binaries.

Astronomers I-Non Chieu of Taiwan’s National Cheng Kung University and Matthias Klein, Sebastian Bocquet, and Joseph Mohr at Ludwig Maximilians-Universitat in Munich used eROSITA Final Equatorial Depth Survey (eFEDS) data taken before the shutdown to characterize about 500 low-mass galaxy clusters. 

It’s one of the largest such samples and it “saw” them over the past ten billion years. That’s around 3/4 of the age of the Universe.  READ MORE...