​The oldest stars act like fossils from the universe’s childhood. By studying their light and chemistry, we can reconstruct a narrative that runs from the Big Bang, through the first stars, to the galaxies we see today. After the Big Bang, the universe was a hot, dense plasma, then cooled enough for neutral hydrogen and helium to form about 380,000 years later. After that, it entered a long dark age with no stars. At some point between that time and roughly 400 million years after the Big Bang, gravity pulled the primordial gas into the first dense clumps, where the very first stars ignited and ended the dark ages with their ultraviolet light, beginning the era of reionization.
 
Theory predicts that the very first generation, called Population III stars, formed purely from hydrogen and helium, with essentially no heavier elements (metals). Because they were probably very massive, they burned fast and died in a few million years, so none of them should survive today, but their brief lives created the first carbon, oxygen, and heavier elements and seeded the next generations. Recent James Webb Space Telescope observations of a distant galaxy (LAP1‑B) about 13 billion light‑years away show signatures of extremely low metal content and very intense ultraviolet light, matching expectations for regions dominated by, or just emerging from, Population III stars, giving us our first indirect glimpse of that primordial era.
 
The oldest surviving stars that we can actually observe directly are not Population III, but the next generations (Population II), which formed from gas lightly enriched by those first explosions. They are metal‑poor: their spectra show extremely small amounts of iron and other heavy elements, and because the universe’s metal content grows over time as stars live and die, that metal deficiency acts like a clock telling us they were born very early. One record-holder, SMSS J031300.36‑670839.3 in the Milky Way’s halo, has less than one millionth the Sun’s iron content and likely formed about 13.6 billion years ago, from gas that existed before the Milky Way itself was assembled. Such stars show that tiny protogalactic clouds formed, birthed stars, and later merged hierarchically to build large galaxies like our own, so each ancient star preserves the chemistry of one of these early fragments.
 
Nearby examples like HD 140283, the Methuselah star, about 200 light‑years away, are also extremely metal‑poor subgiants dominated by hydrogen and helium. Detailed modeling of its composition and evolution shows it is roughly 12–13 billion years old, confirming that some stars in our immediate cosmic neighborhood date back to within the first billion years after the Big Bang. These ages, combined with cosmological measurements of the universe’s expansion and the cosmic microwave background, mutually constrain the timeline: the universe must be just old enough to accommodate such ancient stars, and the stars’ properties must fit that global age. Where early estimates appeared to make Methuselah older than the universe, refinements in both stellar models and cosmological parameters brought them into agreement, tightening our picture of cosmic history.
 
Taken together, the oldest stars tell a coherent creation story in several chapters. Their extreme metal‑poverty says the first heavy elements were forged very quickly after the Big Bang, in short‑lived massive stars. Their locations in extended galactic halos and streams show that big galaxies were built from many smaller building blocks that merged over billions of years. Their ages bracket when star formation began, anchoring the transition from a dark, neutral universe to a luminous, structured cosmos. Their detailed chemical patterns (which elements, and in what ratios) encode how the first supernovae exploded and how efficiently they mixed their products into surrounding gas.
 
In that sense, each ancient star is a small, long‑lived archive. By reading its spectrum, we reconstruct a page in the universe’s early history and watch a formless, nearly featureless cosmos give rise to complexity, structure, and the ingredients for planets and life.
 
References
Crookes, D. (2022, March 7). Methuselah: The Oldest Star in the Universe. Space.Com.
 
Malik, T. (2013, March 8). The Methusaleh Star: Oldest Known Star Revealed. Space.Com.
 
(2026, March 1). HD 140283. In Wikipedia: https://en.wikipedia.org/wiki/HD_140283
 
(2025, August 28). First Stars: Timeline of the Universe. NASA. https://science.nasa.gov/asset/webb/first-stars-timeline-of-the-universe/

The Small Magellanic Cloud (SMC) is one of the Milky Way's closest galactic neighbours, a small, gas-rich galaxy visible to the naked eye from the southern hemisphere, and bound to our galaxy by gravity, alongside its companion, the Large Magellanic Cloud (LMC). It is dwarf irregular galaxy, a satellite of the Milky Way, and a key laboratory for studying star formation and galaxy evolution. All three galaxies have been interacting for hundreds of millions of years; they are linked by extended gaseous structures (the Magellanic Bridge and Stream), tracing their gravitational interactions over giga-year timescales. The SMC lies at a distance of roughly 60–65 kpc, about 200,000 light‑years from the Milky Way, spanning on the order of 18–20 thousand light‑years in diameter and contains several hundred million to a few billion stars, with a total mass of around a few billion solar masses. On the sky it covers about 4 degrees and is visible to the naked eye from dark southern latitudes as a hazy patch in Tucana and Hydrus. The SMC is also one of the most studied galaxies in the sky. Astronomers have catalogued its stars, mapped its gas and tracked its motion for more than half a century. Yet a basic question about it has remained. The galaxy's stars do not orbit around its centre the way stars in most galaxies do, and it has been challenging to explain why.
 
In a study published in The Astrophysical Journal, University of Arizona astronomers have traced the lack of rotation in stars to a direct collision between the SMC and its larger companion, the LMC. The findings also raise questions about how scientists use the SMC as a reference point for understanding galaxies across the history of the universe. "We are seeing a galaxy transforming in live action," said Himansh Rathore, a graduate student at Steward Observatory and the lead author of the paper. "The SMC gives us a unique, front-row view of something very transformative of a process that is critical to how galaxies evolve."
 
The SMC contains more mass in gas than in stars. Gas cools, contracts under gravity and settles into a rotating disk, the same process that shaped the spinning plane of our solar system. But when researchers, including those at U of A, previously measured the motion of the SMC's stars using the Hubble Space Telescope and the Gaia satellite of the European Space Agency, the SMC's stars were not orbiting around the galaxy's centre the way stars in most galaxies do. The possible reason, Rathore said, is a collision. A few hundred million years ago, the SMC crashed directly through the LMC's disk. The LMC's gravity disrupted the SMC's internal structure and sent its stars into random, disordered motion. Also, the LMC's gas applied a tremendous amount of pressure to the SMC's gas and destroyed its gas rotation. "Imagine sprinkling water droplets on your hand and moving it through the air, as the air rushes past, the droplets get blown off because of the pressure it exerts. Something similar happened to the SMC's gas as it punched through the LMC," Rathore said. The collision accounts for a decades-old puzzle about the SMC's gas, said Gurtina Besla, an astronomy professor at Steward Observatory and the study's senior author. For decades, telescope observations suggested that the gas inside the SMC was rotating. But stars form out of gas and inherit its motion, which means that if the gas were spinning, the stars would typically be too. The researchers now show that the rotation was an illusion of viewing angle, the collision is stretching the SMC, and gas moving toward and away from Earth along that stretch looks like rotation from certain perspectives.
 
For decades, the SMC served as a benchmark for understanding how galaxies form stars and evolve across cosmic time, a status this study now puts in question. "The SMC went through a catastrophic crash that injected a lot of energy into the system. It is not a 'normal' galaxy by any means," Besla said.
 
The team used computer simulations tailored to match the known properties of the SMC and the LMC, their gas contents, total star masses, and positions relative to the Milky Way. They paired the simulations with theoretical calculations of how the SMC's gas was affected as it ploughed through the LMC's dense gas environment during the collision. They also developed new methods for reading the scrambled star motions in a post-collision galaxy, tools that can now be used to properly interpret what telescopes actually measure in the SMC. That matters because the SMC is small, gas-rich and low in heavy elements, which are properties that made it a standard yardstick for the kinds of galaxies that existed early in the universe. A galaxy still reeling from a collision may not be a clean reference point, Besla said.
 
Another study published by the team in 2025 showed that the collision also left a physical mark on the LMC that could help scientists probe dark matter. The LMC has a bar-shaped structure at its centre, and that bar is tilted out of the plane of the galaxy because of the collision. Rathore, the 2025 study's lead author, said the degree of the tilt is tied to how much dark matter the SMC contains, giving researchers a new way to measure a substance that has never been directly detected, only inferred from its gravitational effects. "We are used to thinking of astronomy as a snapshot in time," Rathore said. "But these two galaxies have come very close together, gone right through one another, and transformed into something different."
 
Reference
Rajalakshmi, N. (2026, March 16). A Galaxy Next Door is Transforming and Astronomers Can See It Happening. Phys.Org.