Recently acquired evidence has significant astrophysical implications on how we look at the early universe
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An artist's impression of the early universe. - Image Credits: ESA/Hubble, M. Kornmesser and NASA / HDR tune by Universal-Sci
Unraveling the earliest galaxies and stars in the universe is very difficult. It is still not known how, or even when the earliest galaxies began to take shape. However, the Hubble Space Telescope remains a very potent tool as it is capable of observing the universe as it was just half a billion years old.
European astronomers started studying the earliest generation of stars after the big bang. These types of stars are also known as 'Population III stars.' Population III stars have not yet been observed, but their existence is inferred from physical cosmology. Secondary evidence for their existence has been discovered in a gravitationally lensed galaxy in a remote part of the universe.
Shortly after the big bang, the universe contained no heavy elements like, for example, nitrogen, iron and oxygen. The only elements available for star formation were hydrogen, helium and lithium. Population III stars should, therefore, have been made exclusively out of these three elements.
Possible glow of Population III stars imaged by NASA's Spitzer Space Telescope - Image Credit:NASA/JPL-CALTECH/A. KASHLINSKY (GSFC) via Wikimedia Commons
Using the Hubble Space Telescope, the ESO Very Large Telescope and the Spitzer Space Telescope, lead researcher Rachana Bhatwdeka from the European Space Agency and her team investigated the early universe as it was from approximately half a billion to a billion years after the big bang.
The team was able to look so far back in time by making cunning use of Hubble's Wide Field Camera 3 combined with the ACS, which previously was capable of generating the deepest observations ever made of galaxy clusters. The magnifying characteristics of the gravitational lensing effect caused by these immensely massive clusters uncovered galaxies 10 to 100 times fainter than ever witnessed before. The masses of foreground galaxy clusters are significant enough to actually bend and magnify light from the more remote objects in the background.
Bhatawdekar and her team developed a new technique that removes the light from the bright foreground galaxies that constitute these gravitational lenses. This allowed them to discover galaxies with lower masses than ever previously observed with Hubble, at a distance that matches to a time when the universe was less than a billion years old.
To their surprise, the team witnessed no evidence of actual Population III stars during this period in time. At this moment in cosmic time, the absence of exotic stellar populations and the identification of many low-mass galaxies sustains the suspicion that these galaxies are the most likely candidates for the reionization of the universe.
A timeline of the universe, showing where the period of reionize fits within the grand scheme of cosmic history - Image Credit: NASA via Wikimedia Commons - Edited by Universal-Sci (click on image to enlarge)
Reionization is the process that caused the matter in the universe to reionize after the lapse of the so-called "dark ages."
According to Batawdekar, these results have significant astrophysical consequences because they reveal that galaxies must have formed much earlier than previously believed. It also firmly establishes the concept of low-mass/faint galaxies in the early universe being responsible for reionization.
This new discovery raises excitement for the upcoming James Webb Space Telescope (JWST) that is supposed to have even greater capabilities than the Hubble Space Telescope when it comes to observing distant and early objects. The JWST is expected to be the biggest and most capable space telescope ever built and is set to launch in March of 2021. We can't wait!
If you're interested in the subject, be sure to check out the further reading section below in addition to a forthcoming paper that will soon release in the MNRAS.
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