Far out cosmology: finding first stars (Introduction)

by David Turell , Monday, January 30, 2023, 19:10 (453 days ago) @ David Turell

New Webb telescope sightings and theories:

https://www.quantamagazine.org/astronomers-say-they-have-spotted-the-universes-first-st...

"Agroup of astronomers poring over data from the James Webb Space Telescope (JWST) has glimpsed light from a rare isotope of helium in a distant galaxy, which could indicate the presence of the universe’s very first generation of stars.

"These long-sought, inaptly named “Population III” stars would have been ginormous balls of hydrogen and helium sculpted from the universe’s primordial gas. Theorists started imagining these first fireballs in the 1970s, hypothesizing that, after short lifetimes, they exploded as supernovas, forging heavier elements and spewing them into the cosmos. That star stuff later gave rise to Population II stars more abundant in heavy elements, then even richer Population I stars like our sun, as well as planets, asteroids, comets and eventually life itself.

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"About 400,000 years after the Big Bang, electrons, protons and neutrons settled down enough to combine into hydrogen and helium atoms. As the temperature kept dropping, dark matter gradually clumped up, pulling the atoms with it. Inside the clumps, hydrogen and helium were squashed by gravity, condensing into enormous balls of gas until, once the balls were dense enough, nuclear fusion suddenly ignited in their centers. The first stars were born.

"The German astronomer Walter Baade categorized the stars in our galaxy into types I and II in 1944. The former includes our sun and other metal-rich stars; the latter contains older stars made of lighter elements. The idea of Population III stars entered the literature decades later. In a 1984 paper that raised their profile, the British astrophysicist Bernard Carr described the vital role this original breed of star may have played in the early universe. “Their heat or explosions could have reionized the universe,” Carr and his colleagues wrote, “… and their heavy-element yield could have produced a burst of pregalactic enrichment,” giving rise to later stars richer in heavier elements.

"Carr and his co-authors estimated that the stars could have grown to immense sizes, measuring anywhere between a few hundred and 100,000 times more massive than our sun, because of the large volume of hydrogen and helium gas available in the early universe.

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"Windhorst leads a JWST program that is attempting the technique. “I’m pretty confident that in a year or two we will have seen some,” he said. “We already have some candidates.” Similarly, Eros Vanzella, an astronomer at the National Institute for Astrophysics in Italy, is leading a program that’s studying a clump of 10 or 20 candidate Population III stars using gravitational lensing. “We are just playing with the data now,” he said.

"And there remains the tantalizing possibility that some of the unexpectedly bright galaxies already seen by JWST in the early universe could owe their brightness to massive Population III stars. “These are exactly the epochs where we expect the first stars are forming,” Vanzella said. “I hope … that in the next weeks or months, the first stars will be detected.”

"Those at the heavier end of the range, so-called supermassive stars, would have been relatively cool, red and bloated, with sizes that could encompass almost our entire solar system. Denser, more modestly sized variants of Population III stars would have shone blue hot, with surface temperatures of some 50,000 degrees Celsius, compared to just 5,500 degrees for our sun.

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"Their immense proportions meant the stars were short-lived, lasting a few million years at most. (More massive stars burn through their available fuel more quickly.) As such, Population III stars wouldn’t have lasted long in the history of the universe — perhaps a few hundred million years as the last pockets of primordial gas dissipated.

"There are many uncertainties. How massive did these stars really become? How late into the universe did they exist? And how abundant were they in the early universe? “They’re completely different stars to the stars in our own galaxy,” Bowler said. “They’re just such interesting objects.”

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"...in 1999, astronomers at the University of Colorado, Boulder predicted that the stars should produce a telltale signature: a specific frequency of light from helium-2."

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"Windhorst leads a JWST program that is attempting the technique. “I’m pretty confident that in a year or two we will have seen some,” he said. “We already have some candidates.” Similarly, Eros Vanzella, an astronomer at the National Institute for Astrophysics in Italy, is leading a program that’s studying a clump of 10 or 20 candidate Population III stars using gravitational lensing. “We are just playing with the data now,” he said.

"And there remains the tantalizing possibility that some of the unexpectedly bright galaxies already seen by JWST in the early universe could owe their brightness to massive Population III stars. “These are exactly the epochs where we expect the first stars are forming,” Vanzella said. “I hope … that in the next weeks or months, the first stars will be detected.'”

Comment: in a matter time those theoretical stars will be seen