The Oldest Stars: How Did These Ancient Stars Form?

When the stars come out at night, it’s hard to imagine they’re anything more than small twinkles in the sky. However, those seemingly little lights are actually huge, ancient balls of gas burning thousands of miles away. How did they get there, and how long have they lasted? Here’s a list of the oldest stars in the universe, as well as how they came to be.

1. HD 140283

HD 140283 — also referred to as Methuselah — is commonly thought of as the oldest star in the universe and is located in the constellation Libra. However, its age is up for debate. The first estimate was 16 billion years, which was a significant discrepancy with the age of the universe, which is commonly considered to be 13.8 billion years.

This naturally piqued a lot of interest, as if this estimate was accurate, it changed either the age of the universe or how scientists thought it formed. Other research has lowered that number from 14.27-14.46 billion to 12 billion years, with the former still possible with the margin of error. Either way, this star is incredibly old.

2. 2MASS J22132050-5137385

2MASS J22132050‑5137385 within the constellation Grus is the next contender for the most ancient star. Astronomers have determined its approximate age to be 13.6 billion years, with a margin of error of 2.6 billion years. This was only the eighth rapid neutron-capture process-enhanced star that contained uranium and thorium, and they evaluated the age based on the radioactive isotope decay.

3. SMSS J031300.36-670839.3

SMSS J031300.36-670839.3 was found in 2014 within the constellation Hydrus. It is the oldest star with an accurately determined age, which sits at 13.6 billion years. This is also likely one of the oldest second-generation stars, which are metal-poor stars within a galaxy’s galactic halo and bulge.

4. 2MASS J18082002-5104378 B

Next on the roundup of the oldest stars in the universe is 2MASS J18082002-5104378 B. It is 2,000 light-years away in the constellation Ara, and scientists believe it is at least 13.53 billion years old. They were able to establish this approximation based on the makeup of the star.

When the universe first formed, it was around 75% hydrogen, 25% helium, and small amounts of beryllium and lithium. The older the star, the closer its composition should match the components and ratio of the Big Bang. 2MASS J18082002-5104378 B meets these requirements almost exactly, so it likely formed a few hundred million years after the beginning of the universe.

5. TOI-157

TOI-157 is another one of the oldest stars at 12.82 billion years old, with an error margin of an additional 0.73 billion or minus 1.4 billion years. This is the first star on this list with an exoplanet — TOI 157 b, which was discovered in 2020. The planet is huge, taking 2.1 days to complete its orbit with a size that equals 1.18 Jupiters.

6. PSR B1620-26

At 12.2 billion years old, PSR B1620-26 is another incredibly ancient star. Despite being much smaller than the sun, it burns 467% hotter than it at 26,727° Celsius. Its exoplanet PSR B1620-26 b is one of the oldest found, at 12.7 billion years old. Some call it “the Genesis planet” or also call it “Methuselah” due to its incredibly old age.

7. Gliese 414 A

Gliese 414 is a binary system, with 414 A being the older of the two components. Estimates place it at 12.4 billion years old, with a margin of error of 5.2 billion years. The star has two exoplanets orbiting it.

How Do Stars Form?

Stars start out as clouds of gas and dust astronomers call molecular clouds. They can get huge — some span as many as hundreds of light-years and be 1,000 to 10 million times the mass of the Sun. As they move around in space, some of them merge or hit each other, which strengthens their gravitational force as their masses grow.

Once a molecular cloud can no longer support itself, it collapses, causing friction that heats it up and develops a baby star or protostar. Most of its energy comes from the warmth it produced while collapsing, but after millions of years, pressure and temperature at the star’s core start creating helium through nuclear fusion. This process releases more energy that heats the star and halts any further collapse. At this point, it is a main sequence star.

The main sequence phase is the longest phase of a star’s life. The larger it is in mass, the faster it will burn through the gases that make it up to heat itself, eventually leading to a collapse in its core.

How Can Scientists Tell the Ages of Ancient Stars?

After finding new stars, there are multiple ways astronomers can attempt to measure how old they are:

• Metallicity: The oldest stars contain only hydrogen and helium, while newer ones contain heavier metals that formed from previous star collapses, like oxygen, iron or carbon. Scientists can study the absorption lines in a star’s spectrum to analyze what materials it is made of and judge its age based on those results.
• The Hertzprung-Russell diagram: This technique plots stars by their surface temperatures — which humans see as colors — and brightness. These help estimate how much fuel they have already burned and how much longer they have until they “turn off.”
• Asteroseismology: Like how Earth scientists use seismology to understand what the Earth is made of, astronomers can use asteroseismology to assess a star’s brightness fluctuations to measure its internal structure and density. With this science, they can guess its age within about 10%.

The Incredible Origins of the Oldest Stars

The stars didn’t just come out of nowhere. Like the known universe, they formed billions of years ago from clouds of dust and gases. Though this process is still happening today, the oldest stars in the universe can teach scientists a lot about the origins of themselves and life itself.