Shortly after the Big Bang, deep space was totally dark. Stars and galaxies, which offer the Universe with light, had actually not yet formed, and deep space consisted of a primitive soup of neutral hydrogen and helium atoms and invisible ‘dark matter’. Throughout these cosmic dark ages, which lasted for several hundred million years, the very first stars and galaxies emerged. Sadly, observations of this era are challenging due to the fact that dark-age galaxies are incredibly faint 1 Writing in Nature, Willis et al. 2 provide a glimpse of what occurred throughout the dark ages by doing some stellar archaeology. By determining the ages of stars in among the most distant clusters of galaxies understood, the authors situated galaxies that formed stars in the dark ages, near the earliest possible time that stars might emerge.
A galaxy cluster is a group of countless galaxies that orbit each other at speeds 3 of about 1,000 kilometres per second. They are avoided from flying apart by the gravitational pull of the accompanying dark matter, which has the comparable total mass of about one hundred trillion Suns 4 Astronomers use these clusters as labs for lots of experiments in astrophysics, such as measuring the structure of the Universe, testing theories of gravity and figuring out how galaxies form. Willis et al. used among the most remote clusters understood to study when the most huge galaxies in deep space started to produce stars.
Although close-by clusters, such as the Coma cluster, are simpler to observe than those farther away, we can not measure their ages exactly due to the fact that the galaxies are exceptionally old. It is tough to separate between, for example, a galaxy that is 7 billion years old and one that is 13 billion years old 5 Therefore, to obtain an exact date for when clusters first formed their stars, Willis and colleagues utilized NASA’s Hubble Area Telescope to look at one of the most remote clusters they might discover.
Due to the fact that light travels at a finite speed, the most remote clusters we can see are likewise those in the earliest phases of the Universe that we can see. The light from the cluster taken a look at by Willis et al. has actually been travelling for 10.4 billion years prior to it reaches Earth, which indicates that we are looking at a cluster as it was simply 3.3 billion years after the Big Bang. As a result, this cluster serves as a keyhole through which we can peer into the early Universe (Fig. 1).
Willis and coworkers found that the cluster consists of numerous galaxies that have comparable red colours. The colour of a galaxy can be utilized to estimate its age since more youthful stars are bluer than their older, redder equivalents. As an outcome, galaxies that have red colours formed their stars a long period of time ago 5 By comparing the colours of the cluster galaxies with those of models, the authors estimated that the stars of these galaxies began to emerge when deep space was only 370 million years old. This epoch is when we expect the first stars to have actually formed in the cosmic dark ages 6
One particularly interesting point is that Willis et al. identified a minimum of 19 galaxies in the cluster that have similar colours, which indicates that the galaxies have comparable ages. At the time when these galaxies formed their stars, they would have been well expanded, so it is a conundrum regarding why they all began producing stars at approximately the very same time. Were they affected by their environment? Additionally, did the star formation in one galaxy somehow activate a chain response, leading to star development in close-by gas clouds? We do not presently have the response, however what is clear from the authors’ work is that these distant clusters have lots of the oldest galaxies in the Universe.
In my opinion, Willis and colleagues’ age quotes are the very best ones possible, given the restricted data that the authors have from the Hubble telescope. However, identifying ages from the colours of galaxies is a relatively unrefined approach that goes through large uncertainties. For instance, a young galaxy which contains a lot of astronomical dust can have the exact same colour as an old galaxy containing little dust. For that reason, although the authors’ outcomes are enticing, they should be treated with caution until NASA’s James Webb Space Telescope (JWST) is introduced in the next couple of years.
The JWST will measure spectra of the light given off by these galaxies. A comparison of the spectra with models will be a far more accurate way to figure out the ages of the stars than utilizing the colours of galaxies. Additionally, due to the fact that it is simpler to determine the ages of earlier galaxies than those of more current ones 5, it makes good sense to target galaxies in the progenitors of these galaxy clusters in the early Universe. Willis and coworkers’ results make a strong case for these distant clusters being some of the very first targets that the JWST should observe.