- 3697 - OLDEST GALAXIES - the start of the Universe? Ancient galaxy , first-generation star, was so massive that its final explosion blasted every single atom of the star’s mass into space, leaving nothing behind except the star’s chemical fingerprint, smeared across the center of its host galaxy.
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------------------ 3697 - OLDEST GALAXIES - the start of the Universe?
- 13,100,000,000 years ago before I was born one of the universe’s first stars exploded. When this massive star dies, the supernova explosion typically blows the outer layers of the star into space, leaving the star’s collapsed core behind as either a neutron star or, for the most massive stars, a black hole.
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- Astronomers analyzing data from the Gemini North radio telescope in Hawai’ say they have identified that chemical fingerprint for the first time. Gemini North measured the bright infrared glow of gas falling into the oldest supermassive black hole ever discovered. The spiraling disk of gas around an actively feeding supermassive black hole is always bright, but the ones that release the most energy are called “quasars“. This quasar “ ULAS J1342+0928“, is thousands of times brighter than our Milky Way Galaxy galaxy.
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- This quasar is ancient even in astronomical terms. It is 13.1 billion light years away, so astronomers see it as it looked 13.1 billion years ago, or about 700 million years after the Big Bang. It is the second-oldest quasar that astronomers have discovered so far. The oldest is called “P172+18“.
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- Most of the chemical ingredients that make up our current universe were forged in the cores of massive stars, or in the tremendous pressure of their final collapse. Each new generation of stars contained a slightly different mix of elements than the last, so the chemical fingerprint of the universe’s first stars should look very different from that of a star like our Sun. And comparing the two can tell scientists something about how the universe evolved, and, in the very long run, how we got here.
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- Gemini North’s instruments measured the spectrum of infrared light coming from that distant quasar. They split the quasar’s light into the individual wavelengths that make it up. They can tell what an object is made of based on the wavelengths of light it absorbs and emits.
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- The quasar contained an unusually large amount of iron, compared to an unusually small amount of magnesium. This was extremely unusual. In fact, it seems to match what computer simulations predict you’d end up with if a first-generation star about 300 times the mass of our Sun exploded. This is a type of supernova so rare that no one’s ever seen it happen or found direct evidence of it.
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- Any star more than 150 times the mass of our Sun will meet an especially violent end. At the core of such a gargantuan star, the heat and pressure are so intense that they actually convert photons into electrons and their antimatter rivals, “positrons“. The pressure of all those photons pushing their way upward from the center is all that keeps the star from collapsing under its own tremendous gravity. With photons getting squished into matter, gravity takes over, and the star collapses.
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- When astronomers say that massive stars go supernova at the end of their lifespans, they’re talking about stars more than 8 times the mass of our Sun. When a star that size collapses, it triggers an explosion that blows most of the star’s outer layers into space as a glowing cloud of superheated gas, leaving behind a super-dense core. But for really, really massive stars, more than 150 times the mass of our Sun, the explosion is so powerful and so destructive that it leaves nothing intact in its wake.
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- Astrophysicists call this a “pair-instability supernova“. They are so rare because the incredibly enormous stars that cause them are so rare that the odds of astronomers ever actually seeing one happen are vanishingly small. The best evidence of one of these epic supernovae is in the chemical fingerprint of the star, scattered all over interstellar space by the explosion.
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- The spectrum of the quasar “ULAS J1342+0928” is the chemical fingerprint of one of the first stars in the universe, which formed about 100 million years after the Big Bang, and later collapsed and exploded in a pair-instability supernova when the universe was still just a tiny fraction of its current age.
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- The period when the first stars flared to life is still a mystery to physicists, at least when it comes to specific details. Even with an extremely powerful telescope like the James Webb Space Telescope, the universe’s oldest stars are nearly impossible targets. They’re distant, relatively faint, and hidden behind thick clouds of hydrogen. But if it’s possible to find their chemical fingerprints on objects that astronomers can see, that could open up a whole new way to study the distant past
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- A globular cluster is a densely-packed group of thousands or even millions of stars, held together by their mutual gravity in a sparkling sphere. Webb’s First Deep Field contained a stunning image of the distant universe. Five of the oldest globular clusters were discovered, dancing like fireflies around a far-away galaxy.
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- Amid the thousands of galaxies in Webb’s First Deep Field 9 billion light years away was surrounded by small, sparkly yellow and red dots of light. They nicknamed it the “Sparkler Galaxy” and took a closer look at 12 of its “sparkles.” Five of them turned out to be the oldest and most distant globular clusters ever seen, home to stars that may have formed just half a billion years after the Big Bang.
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- The ages of the individual clusters was estimated from their relative brightness at different wavelengths. Older, cooler stars tend to emit most of their light at longer wavelengths, so the spectrum of light from a cluster of elderly stars will be mostly reddish, compared to the bright blue glow of younger, hotter stars.
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- Each chemical element absorbs or emits different wavelengths of light, so a detailed spectrum of light can reveal what an object is made of. The Sparkler Galaxy’s globular clusters showed no trace of oxygen, which usually shows up in younger star clusters, where new stars are still being born. That suggested that these five clusters were mostly full of old, fading stars.
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- All the evidence suggests that the star clusters were around 4 billion years old when the light we see left them. And since the Sparkler Galaxy is about 9 billion light years away, that means the stars that make up its “sparkler” globular clusters formed just a few hundred million years after the Big Bang.
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- The Hubble Space Telescope had imaged the Sparkler Galaxy before, but it couldn’t see the galaxy’s much smaller “sparklers,” which turned out to be incredibly ancient star clusters. At such a huge distance, even these bright balls of hundreds of thousands of stars would have been too small for Webb to see, either without the help of a nearby cluster of galaxies and a technique called gravitational lensing.
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- Galaxy cluster “SMACS 0723“, which sits at the center of Webb’s First Deep Field, is so dense that its gravity actually bends spacetime. Light from objects on the far side of the galaxy cluster follows the curve of spacetime around it instead of shining straight through. It's like what happens when light passes through a curved lens, but on a cosmic scale, a natural telescope that magnified the Sparkler Galaxy up to 100 times.
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- The Sparkler’s was a serendipitous combination of JWST’s incredible angular resolution that allows us to clearly see the individual sparkles, and 10x to 100x magnification of the Sparkler due to gravitational lensing caused by the massive foreground galaxy cluster.
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- In our own Milky Way galaxy, most of the 150 known globular clusters are deep within the bulk of the galaxy itself. But for astronomers looking at a distant galaxy like the Sparkler Galaxy, clusters on the edges of the galaxy are much easier to see and study. They also tend to last longer than globular clusters in the inner region of a galaxy, where the pull of tidal forces would eventually rips them apart.
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- These ancient star clusters could eventually shed light on how galaxies form and even how dark matter behaves. The fact that they’re so far away may actually make that process easier. Most of the globular clusters astronomers have studied so far are much closer to home, which also means they’re part of the fairly recent universe.
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- Astronomers looking at globular clusters in the Milky Way are seeing light that left the stars sometime between 12 billion and 13.5 billion years after the Big Bang. Because the universe is evolving more slowly than it did in the distant past, it can be hard to pinpoint an exact age for something so recent.
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- In a distant galaxy like the Sparkler Galaxy astronomers are seeing light from just 2 to 4 billion years after the Big Bang, and it’s much easier to guess the age of a star cluster from back when the universe was so young.
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- Globular clusters from the very early universe, like the ones in the Sparkler Galaxy, could help physicists piece together the still mysterious connection between dark matter and how galaxies form. Even though they don’t contain dark matter themselves, globular clusters are directly related to the individual dark matter halos of the galaxies they orbit around. Galaxies with more massive haloes of dark matter also tend to have more globular clusters.
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- Webb’s “NIRISS” instrument to study five more deep fields, with help from five massive galaxy clusters and their gravitational lensing.
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- Astronomers hope to use another Webb instrument, the “Near Infrared Spectrograph” (NIRSpec) to get a higher-resolution look at the spectrum of light from each of the Sparkler Galaxy’s globular clusters. That will help narrow down the clusters’ ages more precisely and reveal more about the types of stars in the clusters, their chemical makeup, and other properties.
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September 30, 2022 OLDEST GALAXIES 3697
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