Far away secrets unveiled
Even the most distant galaxies cannot escape astronomers’ reach. The images obtained thanks to the Hubble and Spitzer space telescopes have contributed to a better understanding of the process of galaxy genesis. A team made of members from EPFL and the University of Geneva, associated with French, American and Spanish researchers, reports its initial findings.
What did our galaxy look like less than a billion years after the Big Bang? Thanks to the deep sky images taken by the Hubble Space Telescope at the end of last year, researchers have been able to characterize the most distant galaxies ever seen. One of these galaxies, located close to the limit of visibility from Earth, is seen the way it looked when the universe was merely 650 million years old –since the image detected by the telescope took more than 13 billion years to reach us.
"At this stage of formation, galaxies are very dense and function as nurseries for extremely active stars. This is the first time we are able to observe such faint and distant galaxies" said Hakim Atek, researcher at EPFL’s Astrophysics Laboratory (LASTRO) and first author of one of the two papers published on this subject. * "Our partners at the Institute of Astrophysics at the Canary Islands (IAC) were interested in the most distant galaxy observed. They measured its dimensions and determined that its size is about 30 times smaller than our Milky Way, yet it produces stars at a rate at least 10 times superior", he continued. These calculations were possible thanks to the models developed by Daniel Schaerer from the University of Geneva, expert on the first galaxies.
A natural telescope located billions of light-years from Earth
By itself, the Hubble telescope’s performance is not able to clarify much about these entities at the edge of the observable world. The researchers increased the telescope’s capacity through the optical phenomenon of "gravitational lensing": the colossal mass of distant galaxy clusters has the effect of augmenting and multiplying the image of the objects behind them.
Researchers use this phenomenon to amplify up to 100 times the amount of light received from a distant galaxy. "We have developed an advanced knowledge in modeling the distribution of mass within these galaxy clusters, which allows us to know exactly the way they affect the rays of light passing within their reach, and therefore to precisely reconstruct the image of a galaxy behind them, "explained Jean- Paul Kneib, head of the ERC research team "Light on the Dark" at LASTRO.
Thanks to this knowledge, astronomers identified six "frontier fields" of galaxy clusters acting as natural telescopes capable of delivering new information on the most distant galaxies. Then, they obtained NASA authorization to use an important share of the Hubble and Spitzer telescopes’ working time to observe these fields. Their study, which began in November last year, will last three years in total. As for the images, they are available to the global scientific community, which is engaged in a race against the clock to get the most of this opportunity.
These extremely promising initial results will be further refined in the coming months thanks to the new images that the Hubble will take by using a second sensor in the visible range. Within a few years, the James Webb telescope, much more powerful than the Hubble, will also provide a lot of data to process. Thus, the work on these" frontier fields" at the edge of the Universe has only just begun.