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Cosmic dawn: First stars formed 250-350 million years after beginning of the universe, researchers at Cambridge and UCL discover



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The very first stars formed 250 million to 350 million years after the beginning of the universe, a new study has found, and it is believed that the new James Webb Space Telescope will be sensitive enough to enable us to witness this cosmic dawn directly.

The work, led by researchers at the University of Cambridge and UCL, examined six of the most distant galaxies currently known. Light from these galaxies has taken most of the universe’s lifetime to reach us.

The formation and evolution of the first stars and galaxies in a virtual universe similar to our own. Picture: Dr Harley Katz, Beecroft fellow, Department of Physics, University of Oxford
The formation and evolution of the first stars and galaxies in a virtual universe similar to our own. Picture: Dr Harley Katz, Beecroft fellow, Department of Physics, University of Oxford

The distance of these galaxies from Earth gave them a “look back” time of more than 13 billion years, when the universe was only 550 million years old.

The researchers then analysed images from the Hubble and Spitzer Space Telescopes and calculated the age of the galaxies as ranging from 200 to 300 million years. This enabled an estimate of when their stars first formed.

Hubble’s successor, the NASA-led James Webb Space Telescope is scheduled to launch in November and has been dubbed the ‘world’s most magnificent time machine’.

The largest, most powerful and complex space telescope ever built, it will help researchers observe light from the most distant objects in the universe, enabling them to peer back to the early universe.

James Webb Space Telescope artist conception. Pictrue: Northrop Grumman (48636491)
James Webb Space Telescope artist conception. Pictrue: Northrop Grumman (48636491)

Lead author Dr Nicolas Laporte, at Cambridge’s Kavli Institute for Cosmology, said: “Theorists speculate that the universe was a dark place for the first few hundred million years, before the first stars and galaxies formed.

“Witnessing the moment when the universe was first bathed in starlight is a major quest in astronomy.

“Our observations indicate that cosmic dawn occurred between 250 and 350 million years after the beginning of the universe, and, at the time of their formation, galaxies such as the ones we studied would have been sufficiently luminous to be seen with the James Webb Space Telescope.”

For the study, researchers examined starlight from galaxies as it was recorded by the Hubble and Spitzer Space Telescopes. They studied a marker in their energy distribution that indicated the presence of atomic hydrogen in their stellar atmospheres, which in turn provides an estimate of the age of the stars they contain.

That is because the hydrogen signature increases in strength as the stellar population ages, but diminishes when the galaxy is older than a billion years.

That reflects the fact that massive stars that contribute to this signal burn their nuclear fuel more rapidly and die first.

The James Webb Space Telescope's Near Infrared Spectrograph (NIRSpec) is mounted onto a stand in NASA Goddard's cleanroom. Picture: NASA/Chris Gunn (48636541)
The James Webb Space Telescope's Near Infrared Spectrograph (NIRSpec) is mounted onto a stand in NASA Goddard's cleanroom. Picture: NASA/Chris Gunn (48636541)

Co-author Dr Romain Meyer, of UCL physics and astronomy and the Max Planck Institute for Astronomy in Heidelberg, Germany, said: “This age indicator is used to date stars in our own neighbourhood in the Milky Way but it can also be used to date extremely remote galaxies, seen at a very early period of the universe.

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

The researchers estimated the “redshift” of each galaxy - the changing wavelength of the light - to derive their cosmological distance, which gave them the look-back time at which they were being observed.

They did this using spectroscopic measurements from the world’s most powerful ground-based telescopes – the Chilean Atacama Large Millimetre Array (ALMA), the European Very Large Telescope, the twin Keck telescopes in Hawaii and Gemini-South telescope.

These measurements confirmed that they were looking back to a time when the universe was 550 million years old.

Co-author Professor Richard Ellis (UCL), who has spent his career tracking ever more distant galaxies, said: “Over the last decade, astronomers have pushed back the frontiers of what we can observe to a time when the universe was only four per cent of its present age. However, due to the limited transparency of Earth’s atmosphere and the capabilities of the Hubble and Spitzer Space Telescopes, we have reached our limit.

“We now eagerly await the launch of the James Webb Space Telescope, which we believe has the capability to directly witness cosmic dawn.

“The quest to see this important moment in the universe’s history has been a holy grail in astronomy for decades. Since we are made of material processed in stars, this is in some sense the search for our own origins.”

The Jame Webb Space Telescope, with its diamond-shaped sunshield and huge 6.5-metre mirror, will be the premier observatory over the next decade. The infrared observatory features four instruments, including NIRSpec (near-infrared spectrograph), to which researchers at the Kavli Institute for Cosmology in Cambridge and UCL scientists at the Mullard Space Science Laboratory have contributed.

Also involved in the study were astronomers at the University of California-Santa Cruz, the University of California and the University of Texas.

The research was supported by the Kavli Foundation, the European Research Council, NASA and the National Science Foundation (NSF) in the United States.

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Cambridge astronomers help develop James Webb Space Telescope - the ‘world’s most magnificent time machine’

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