Science. The cosmic dawn was 250 to 350 million years after the Big Bang

2021-06-25 Galaxies in the distant universe. The cosmic dawn, when stars first formed, occurred between 250 million and 350 million years after the beginning of the universe. UCL Research and Technology Policy

Madrid, 25 years old (Europe Press)

The cosmic dawn, when stars first formed, occurred between 250 million and 350 million years after the beginning of the universe.

A new study led by researchers at University College London (UCL) and University of Cambridge, published in the Monthly Notices of the Royal Astronomical Society, suggests that NASA’s James Webb Space Telescope (JWST), due to launch in November, will be sensitive enough to directly observe the birth of galaxies.

The UK-led research team examined six of the most distant galaxies currently known, the light of which took most of the universe’s life to reach us. They found that the distance between these galaxies and Earth corresponds to a time of more than 13 billion years, when the universe was only 550 million years old.

By analyzing images from the Hubble and Spitzer space telescopes, the researchers calculated the age of these galaxies in the range of 200 to 300 million years, which allowed an estimate of when their stars first formed.

Lead author Dr Nicolas Laporte (University of Cambridge), who started the project while at the University of California, said in a statement: “Theorists believe that the universe was a dark place for the first hundreds of millions of years, before the first stars and galaxies formed.

“Watching the moment the universe was first bathed in starlight is an important task in astronomy. Our observations indicate that the cosmic dawn occurred between 250 and 350 million years after the universe began, at a time when galaxies like the ones we studied would be bright enough to appear with James Webb Telescope”.

The researchers analyzed the starlight of galaxies as recorded by the Hubble and Spitzer Space Telescopes, and examined a sign in their energy distribution for the presence of atomic hydrogen in the stellar atmosphere. This provides an estimate of the age of the stars that contain them.

The strength of this hydrogen signature increases as stars age, but decreases when the galaxy is more than a billion years old. Age dependence arises because more massive stars that contribute to this signal burn their nuclear fuel faster and therefore die first.

Co-author Dr Romain Meyer (UCL Physics & Astronomy and the Max Planck Institute for Astronomy in Heidelberg, Germany) said: “This age indicator is used to date stars in our region in the Milky Way, but it can also be used to date very distant galaxies. , was seen in a very early period of the universe.

“Using this indicator we can conclude that even at these early times, our galaxies are between 200 and 300 million years old.”

By analyzing the Hubble and Spitzer data, the researchers needed to estimate each galaxy’s “redshift,” which indicates their cosmic distance, and thus the time at which they were observed in retrospect. To achieve this, they made spectroscopic measurements using an entire arsenal of powerful ground-based telescopes: the Atacama Large Millimeter Array in Chile (ALMA), the European Very Large Telescope, the Keck Dual Telescopes in Hawaii, and the Gemini-South Telescope.

These measurements allowed the team to confirm that looking at these galaxies is consistent with looking back at a time when the universe was 550 million years old.

Co-author Professor Richard Ellis (UCLA Physics and Astronomy), who has tracked increasingly distant galaxies throughout his career, said: “Over the past decade, astronomers have pushed the boundaries of what we can observe back to a time when the universe was only 4%. of its current age, but due to the limited transparency of Earth’s atmosphere and the capabilities of the Hubble and Spitzer space telescopes, we’ve come to the limit.

“We are now eagerly awaiting the launch of the James Webb Space Telescope, which we believe has the ability to watch the cosmic sunrise live. The quest to see this important moment in the history of the universe has been the holy grail of astronomy for decades. stars, then this is in a sense the search for our own origins.”

NASA’s James Webb Space Telescope, the successor to the Hubble Observatory, is scheduled to launch into space in November. It will be the main observatory for the next decade, serving thousands of astronomers around the world. It consists of an infrared observatory, a huge mirror with a width of 6.5 meters and a diamond-shaped canopy. UCL scientists at Mullard Space Science Laboratory have built and tested key instrument components for the NIRSpec (Near Infrared Spectrometer), one of the telescope’s four instruments.

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