Free Astronomy Magazine July-August 2020

JULY-AUGUST 2020 Field Camera 3 and Advanced Camera for Surveys, as part of the Hubble Frontier Fields pro- gramme. This programme (which observed six distant galaxy clusters from 2012 to 2017) produced the deepest obser- vations ever made of galaxy clusters and the galaxies located behind them which were magnified by the gravitational lens- ing effect, thereby revealing galaxies 10 to 100 times fainter than any previously ob- served. The masses of foreground galaxy clusters are large enough to bend and magnify the light from the more distant ob- jects behind them. This allows Hubble to use these cosmic magnifying glasses to study objects that are beyond its nominal opera- tional capabilities. Bhatawdekar and her team devel- oped a new technique that removes the light from the bright fore- ground galaxies that constitute these gravitational lenses. This al- lowed them to discover galaxies with lower masses than ever previ- ously observed with Hubble, at a dis- tance corresponding to when the Universe was less than a billion years old. At this point in cosmic time, the lack of evidence for exotic stellar populations and the identification T his image from the NASA/ESA Hubble Space Telescope shows the galaxy cluster MACS J0416. This is one of six clusters that was studied by the Hubble Frontier Fields programme, which yielded the deepest images of gravita- tional lensing ever made. Scientists used intracluster light (visible in blue) to study the distribution of dark matter within the cluster. [NASA, ESA, and M. Montes (University of New South Wales, Sydney, Australia)] of many low-mass galaxies supports the suggestion that these galaxies are the most likely candidates for the reionisation of the Universe. This period of reionisation in the early Universe is when the neutral inter- galactic medium was ionised by the first stars and galaxies. “These results have profound astro- physical consequences as they show that galaxies must have formed much earlier than we thought,” said Bhatawdekar. “This also strongly supports the idea that low-mass/ faint galaxies in the early Universe are responsible for reionisation.” These results also suggest that the earliest formation of stars and gal- axies occurred much earlier than can be probed with the Hubble Space Telescope. This leaves an exciting area of fur- ther research for the upcoming NASA/ESA/CSA James Webb Space Telescope — to study the Universe’s earliest galaxies. !