Space is basically a giant time machine. When you look up at the night sky, you aren't seeing things as they are right now; you’re seeing ghost images of the past. But some ghosts are much, much older than others. For decades, astronomers have been hunting for a specific holy grail: the very first objects to ever flicker into existence after the Big Bang. If you've ever wondered what is the oldest star in the universe, you’ve probably stumbled upon a name that sounds like it belongs in a Sunday school lesson: Methuselah.
Formally known as HD 140283, this star is a bit of a headache for physicists. Why? Because for a long time, it looked like it was actually older than the universe itself. That’s obviously impossible. You can't be older than your own mother. Yet, the math kept pointing to an age that made scientists sweat. It’s a subgiant star sitting about 190 light-years away in the constellation Libra, and it has been cruising through our neighborhood at a blistering speed.
The Star That Broke the Math
The Methuselah star isn't some flickering candle on the edge of the observable universe. It’s relatively close. We can see it through a decent pair of binoculars. But its chemistry is weird. It’s "metal-poor." In astronomy-speak, "metal" means anything heavier than hydrogen and helium. Since the early universe was almost entirely hydrogen and helium, the first stars had no heavy elements. Methuselah has a tiny, tiny fraction of the iron content found in our Sun. That tells us it was born in an era when the cosmos was still a toddler.
Initially, estimates based on its luminosity and temperature suggested Methuselah was roughly 16 billion years old. There’s just one tiny problem: the Big Bang happened 13.8 billion years ago.
This discrepancy nearly broke cosmology. Scientists like Howard Bond of Pennsylvania State University had to dig deeper into the data from the Hubble Space Telescope to figure out where they went wrong. It turns out the error bars were the savior. After refining the distance measurements and accounting for things like the rate of helium diffusion into the core, the age was revised down to about 14.46 billion years, plus or minus 800 million years. If you take the lower end of that margin, it lands at 13.66 billion years. That fits. Barely.
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Why We Can't Find "Population III" Stars
The real answer to what is the oldest star in the universe might be something we haven't even seen yet. Astronomers categorize stars into "Populations."
- Population I: These are the youngsters, like our Sun. They are rich in metals because they were formed from the recycled guts of dead stars.
- Population II: Older stars like Methuselah. They have some metals, but not many.
- Population III: The mythical first stars.
We have never actually seen a Population III star. Not once. These were the monsters that formed about 100 million years after the Big Bang. They were likely massive—hundreds of times the size of the Sun—and they lived fast and died young. Because they were so huge, they burned through their fuel in a few million years and exploded as supernovae. They seeded the universe with the first heavy elements. To find a "living" oldest star, we have to look for the smaller ones that survived.
Small stars are the tortoises of the cosmos. A star with 10% of the Sun's mass can live for trillions of years. If a low-mass Population III star was ever born, it's still out there somewhere, lurking in the dark.
The Contender in Our Own Backyard: SMSS J031300.36-670839.3
While Methuselah gets all the press, there’s another star with a much less catchy name that might actually hold the title. Discovered by researchers at the Australian National University using the SkyMapper telescope, SMSS J031300.36-670839.3 (let's just call it SMSS J0313) is roughly 6,000 light-years away.
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Its iron levels are so low they are almost unmeasurable. We’re talking less than one ten-millionth of the iron in the Sun. This suggests it formed from the debris of a single, low-energy supernova from one of the very first stars. It is essentially a direct descendant of the beginning of time.
How we measure these relics
We use spectroscopy. By splitting the light of a star into a rainbow, we can see dark lines where specific elements absorb light. If the iron lines are missing or incredibly faint, we know the star is ancient. It’s like carbon dating, but with light and heavy metals.
The James Webb Factor
The James Webb Space Telescope (JWST) changed the game. It isn't just looking for individual stars; it’s looking for the first galaxies. In 2023 and 2024, JWST began spotting galaxies like JADES-GS-z14-0, which existed only 290 million years after the Big Bang.
These galaxies are surprisingly bright. This suggests that the stars inside them were either much bigger or formed much faster than our current models predicted. When we ask about the oldest star, we are really asking: how quickly can gravity pull gas together to start a fire? The answer, according to JWST, is "way faster than you thought."
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Misconceptions About Stellar Age
People often think "oldest" means "furthest." That's not always true. You can have a very old star right next door in the Milky Way's halo. The halo is like a cosmic retirement home. It’s filled with ancient, metal-poor stars that were kicked out of the galactic center or absorbed from smaller galaxies billions of years ago.
Another misconception is that the oldest star must be the biggest. It's the opposite. The big ones die in the blink of an eye. The oldest stars are almost always dim, red, or yellowish subgiants that just happen to be extremely efficient with their fuel.
The Irony of Cosmic Chemistry
It’s kind of wild to think that you are made of the "pollution" of these ancient stars. Every carbon atom in your DNA and the calcium in your bones came from a star that lived and died billions of years ago. The oldest stars like Methuselah are basically the original ancestors. They are the reason the universe isn't just a boring cloud of hydrogen anymore.
Practical Steps for Interested Observers
If you want to dive deeper into the hunt for the universe’s oldest residents, you don't need a PhD, but you do need to know where to look.
- Track the JWST Pipeline: Follow the "JADES" (JWST Advanced Deep Extragalactic Survey) releases. This is where the newest records for the oldest objects are being set.
- Explore the Sloan Digital Sky Survey (SDSS): Their public data contains the spectral signatures of millions of stars. You can actually look up the "metallicity" of stars yourself.
- Learn to Spot the Halo: If you’re an amateur astronomer, learn to identify the Milky Way's halo stars. Use apps like Stellarium to find the coordinates for HD 140283. You won't see much—just a dot—but knowing that dot is nearly 14 billion years old changes how you feel about a Tuesday night.
- Monitor ArXiv.org: Search for "Population III" or "Extremely Metal-Poor (EMP) stars." This is where the raw, peer-reviewed papers drop before they hit the news cycle.
The search for the oldest star is really a search for our own origins. We are trying to find the "Point Zero" of chemistry. Whether it’s Methuselah or a yet-to-be-named smudge in a JWST deep-field image, these stars are the only witnesses we have to the moment the lights turned on in the dark.
Actionable Insight: To stay truly updated on this evolving record, focus on "metallicity" reports rather than "age" reports. Age is an estimate based on models that change, but the chemical composition (metallicity) of a star is a physical fact that tells its true history. Keep an eye on the Australian National University’s SkyMapper project, as they are currently leading the charge in finding metal-poor relics in our own galaxy.