Some of the oldest stars yet to come to light were seen in one of the first images from the James Webb Space Telescope.
Stars live in dense balls called globules formed about 1,800 million years ago and are surrounded by a distant galaxy called the Sparkler, astronomers report on Oct. 1. Literary Journal of Astrophysics. Globular clusters are often some of the oldest stars in modern galaxies such as ours, but the exact age is difficult to tell. The new discovery could help researchers pinpoint when such bonds began to form.
Globular clusters are tiny compared to galaxies, which makes them difficult to see from across the globe. But this time, a gargantuan natural lens is helping in space. Sparkler is one of thousands of galaxies that lie far behind the massive, much closer galaxy cluster called SMACS 0723, which is the subject of the first publicly released science image from the James Webb Space Telescope, or JWST (SN: 7/11/22). The cluster distorts space in such a way that the light from the more distant galaxies behind it is magnified.
For all those distant galaxies, that extra magnification brings out details that have never been seen before. One elongated galaxy surrounded by yellow blobs caught the attention of astronomers Lamiya Mowla and his colleagues.
“When we first saw it, we noticed all these little ridges around it that we called sparks,” says Mowla, of the University of Toronto. The team wondered if they could be clustered with sparklers, the closest families of stars that are thought to be born together and stay close to each other throughout their lives.SN: 10/15/20).
“The outstanding question is still, how did the globular clusters themselves come to be?” Mowla says. Were they born before the “cosmic noon” 10 billion years ago, when the formation of stars in the universe bisected? Or they form four billion years ago before the “cosmic dawn,” when stars could form at all for the first time.SN: 3/4/22)?
The light from the Sparkler reached Earth about 9 billion years ago, so if the sparks are clustered in clusters that once sparkled, they help astronomers answer that question.
Mowla and his colleagues used data from the JWST to analyze the fluctuations in the light coming from the sparks. Some of them appear to form stars when the light leaves the clusters. But some had made their stars long before all.
“When we see them, the stars are already about 4 billion years old,” says astrophysicist Kartheik Iyer, also of the University of Toronto.
This means that the oldest stars could have formed in sparks about 13 billion years ago. Since the universe is 13.8 billion years old, “there is a short period of time after the Big Bang when these things could have formed,” he says.
That is, these clusters were born in the early morning, not at noon.
Searching for more globular clusters around ancient galaxies could help determine if such early clusters were common or rarer in the history of the universe. They can also help reconstruct the history of galaxy formation, say Mowla and Iyer. Their team proposed that observations should be made in the first year of JWST that could be done in this way.
Being able to pick out small structures such as globular clusters so far away was almost impossible before JWST, says astronomer Adelaïde Claeyssens of Stockholm University. She was not involved in the new work, but she led a similar study earlier this year of multiple galaxies magnified by the clusters of SMACS 0723.
“We have shown for the first time that, with James Webb, we will be able to observe many of these galaxies with very small structures,” said Claeyssens. “James Webb will be a game changer in this field.”
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