2023-06-17 14:25:26
There was a time when our entire Universe was shrouded in thick fog. Then the veil lifted. Thanks to the stars that shone in the heart of the first galaxies, today show data returned by the James-Webb space telescope.
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First, there was the Big Bang. And in those early moments, our Universe bore little resemblance to the one we know today. It was filled with an incredibly dense and hot gas. A gas that took hundreds of millions of years to cool. It was then completely opaque. Then, as if ” someone “ pressed the button « repeat », the gas began to heat up again. He ionized. And it finally became transparent.
For a long time, researchers wondered who this could be. ” someone “ who pressed the button « repeat ». Now, new data returned from the James-Webb Space Telescope (JWST) sheds light on this mysterious period that astronomers call the reionization epoch.
To trace the culprit, [O iii]-emitting Galaxies at 5.3 < z < 6.9 and Direct Evidence for Local Reionization by Galaxies" target="_blank">researchers of the’Swiss Federal Institute of Technology Zurich (ETH, Switzerland) have targeted a moment in the life of the Universe located just before the end of this epoch of reionization. A moment when he wasn’t quite transparent yet, but no longer quite opaque either. By pointing the JWST at a distant quasar, they got information about the gas sitting between us and this active supermassive black hole that’s so bright it acts like a huge flashlight. Its light was sometimes absorbed by an opaque gas, sometimes transmitted through a transparent gas. And this provided researchers with detailed information about the composition and state of said gas.
An incredible quasar to shed light
In a second step, astronomers again relied on the James-Webb Space Telescope to identify galaxies close to their line of sight. And they weren’t disappointed. Where they hoped to find a few dozen, it finally appeared to them nearly 120! Galaxies that were restless and actively forming stars. And which, for the most part, were surrounded by transparent regions about 2 million light-years in radius — roughly the distance that separates our Milky Way from the nearest galaxy, Andromeda. As if they had literally cleared the space around them at the end of the reionization epoch.
Thus, the first relatively tiny galaxies in the Universe and the stars they contained seem to have been those which, by emitting quantities of light and heat, “pressed the repeat button” to drive reionization, releasing ” bubbles “ transparent around them. Bubbles that continued to expand over the millions of years that followed, until they merged and made our Universe completely transparent. A scenario that astronomers hope to confirm a little more soon by studying five other regions, each lit by a different quasar.
But in the meantime, the ETH team points to another result obtained using JWST data. The confirmation of the colossal mass of the quasar which allowed them to reach these conclusions. The object would weigh no less than 10 billion times more than our Sun. Making it the most massive black hole known in the early Universe. One more puzzle. Because astronomers are unable to date to explain how quasars could have become so large so early in our history.
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