Cosmic dawn: scientists hope to go back in time to see the birth of stars

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Cosmic dawn: scientists hope to go back in time to see the birth of stars


It is often said that looking through a telescope is like stepping back in time, due to the millions of years it takes for light from distant cosmic objects to reach Earth. Now, scientists have calculated that they may be able to see far enough to observe the birth of the very first stars – the first images may be available as early as next year. They also specified when this momentous event occurred.

Observing the moment when the universe was first bathed in light, the cosmic dawn, is a major pursuit of astronomy.

“All of the chemical elements that make us up are synthesized in the stars, so in a sense the cosmic dawn is our own birth,” said Professor Richard Ellis of University College London, who participated in the research. “It was a holy grail for astronomers not only to predict when it happened, but to actually witness it. “

The universe is thought to have started with the big bang 13.8 billion years ago, but for the first hundreds of millions of years it was a dark, starless expanse of hydrogen gas. flooded with radiation, known as the diffuse cosmic background. Gradually, these clouds of hydrogen gas began to clump together under gravity and heat up, reaching temperatures equivalent to the center of the sun, where nuclear fusion could occur. This is how the first stars were born.

Attending the event directly is beyond the reach of our current telescopes, but it could be possible with the launch of the James Webb Space Telescope, scheduled for November. “We predict from our measurements that he will have the sensitivity to witness this cosmic dawn, possibly as early as next year,” said Ellis.

However, to achieve this, astronomers must first know where to look. Ellis, working with an international team of researchers, used images from the Hubble and Spitzer telescopes to examine six of the most distant galaxies known, the light of which took most of the life of the universe to reach us.

This meant pushing the capabilities of these telescopes to their limits, but combining these images with spectroscopic measurements from powerful ground-based telescopes – the Atacama Large Millimeter Array (ALMA) and the Very Large European Telescope in Chile, and Gemini South and Telescopes Keck twins in Hawaii – they calculated that the distance of these galaxies from Earth corresponded to a “look back” time of over 13 billion years, when the universe was only 550m away. years.

By analyzing the light from the stars in these galaxies, by observing a hydrogen signature that allows astronomers to date stars, they were also able to calculate the age of stars in these galaxies. “Our observations indicate that the cosmic dawn occurred between 250 and 350m years after the start of the universe and, at the time of their formation, galaxies such as the ones we studied would have been bright enough to be seen with the James Webb Space Telescope, ”said Dr Nicolas Laporte of the University of Cambridge, who led the study.

The research, published in the Monthly Notices of the Royal Astronomical Society, also suggests that the “lighting” of these early stars was a gradual process, rather than a single coordinated burst of light.

“We found that the ages of the six galaxies we looked at were slightly different, so they didn’t all light up at the same time,” Ellis said. “We are now looking forward to the launch of the James Webb Space Telescope. It has seven times the light-gathering power of Hubble and extends further in the infrared, which is crucial for traveling further back in time.

The NASA-led telescope is the successor to the Hubble Observatory, comprising an infrared observatory, a huge 6.5-meter-wide mirror and a diamond-shaped sunshade. Assuming its launch goes as planned, it will become the premier space observatory over the next decade, serving thousands of astronomers around the world.

Still, this is a high-risk mission, as the telescope’s mirror and solar panels have to deploy into space and it is sent into a solar orbit beyond the moon, which means there is unlikely to fix it if there is a problem. “Our hearts will be in our mouths when the James Webb goes up, because everything has to work,” Ellis said.

We may also need to temper our expectations of what the Cosmic Dawn will look like, assuming the telescope can observe it directly. “If you were there, there would be plenty of little stars that would light up. And over a period of 100 million years, many more of them would light up, so that would be a dramatic event, ”Ellis said. “The problem is that with a telescope, you will only see a handful of objects that could be candidates for Cosmic Dawn, then we will have to examine them in detail and see if they are free of elements. heavy chemicals, which would be consistent with a first generation star.

On the cinematographic level then, it may be an anticlimax. But as a scientific achievement, it could be capital.

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