Gravity shapes the clusters and voids made by galaxies (Image: 6DF Galaxy Survet/AAO)
We’re on the verge of being able to see the structure of the entire universe. That could help us go beyond Einstein’s masterwork, says Pedro Ferreira
AS WE near the centenary of Einstein’s general theory of relativity, a quiet revolution is under way. A number of groups around the world are attempting to test the validity of general relativity on the scale of the universe. So far the tests are inconclusive, yet they herald a striking shift in the way that Einstein’s theory is perceived. And testing general relativity is rapidly becoming one of the core endeavours for some of the most powerful satellite and ground-based experiments being developed.
Einstein’s general theory of relativity has served us well. Yet what if he was off the mark? Don’t get me wrong, the theory is remarkably successful at explaining many different phenomena: it allows us to calculate the orbits of all the planets of the solar system with extraordinary accuracy. It also enables us to work out how light is deflected by the deformed space-time around stars and planets. But could we have taken general relativity too far in attempting to predict the evolution of the universe?
It is a striking fact that general relativity has remained unchanged since Einstein first proposed it in 1915. At its heart is our understanding of the force of gravity. Einstein put forward the idea that there is no force of gravity per se. Instead, what we perceive as gravity results from the geometry of space-time. If we place an object – a…
![Astronomers have long known that understanding how star clusters come to be is key to unlocking other secrets of galactic evolution. Stars form in clusters, created when clouds of gas collapse under gravity. As more and more stars are born in a collapsing cloud, strong stellar winds, harsh ultraviolet radiation and the supernova explosions of massive stars eventually disperse the cloud, and their light can bear down on other star-forming regions in the galaxy. This process is called stellar feedback, and it means that most of the gas in a galaxy never gets used for star formation. Researching how star clusters develop can answer questions about star formation at a galactic scale. Now, the state of the art has been further developed with both Hubble and Webb working together to provide a broad-spectrum view of thousands of young star clusters. An international team of astronomers has pored over images of four nearby galaxies from the FEAST observing programme (#1783), trying to solve this mystery. Their results show that it is the most massive star clusters that clear away their gaseous shroud the fastest, and begin lighting their galaxy the earliest. The team identified nearly 9000 star clusters in the four galaxies in different evolutionary stages: young clusters just starting to emerge from their natal clouds of gas, clusters that had partially dispersed the gas (both from Webb images), and fully unobstructed clusters visible in optical light (found in Hubble images). With Webb???s ability to peer inside the gas clouds, they were able to then estimate the mass and age of each cluster from its light spectrum. This image shows a section of one of the spiral arms of Messier 51 (M51), one of the four galaxies studied in this work, as seen by Webb???s Near-Infrared Camera (NIRCam). The thick clumps of star-forming gas are shown here in red and orange, representing infrared light emitted by ionised gas, dust grains, and complex molecules such as polycyclic aromatic hydrocarbons (PAHs). Within these gas complexes, each tens or hundreds of light years across, Webb reveals the dense, extremely bright clusters of massive stars that have just recently formed. The countless stars strewn across the arm of the galaxy, many of which would be invisible to our eyes behind layers of dust, are also laid bare in infrared light. [Image description: A large, long portion of one of the spiral arms in galaxy M51. Red-orange, clumpy filaments of gas and dust that stretch in a chain from left to right comprise the arm. Shining cyan bubbles light up parts of the gas clouds from within, and gaps expose bright star clusters in these bubbles as glowing white dots. The whole image is dotted with small stars. A faint blue glow around the arm colours the otherwise dark background.]](https://images.newscientist.com/wp-content/uploads/2026/05/13114322/SEI_296271016.jpg)
