Researchers discover the universe's oldest stars in our own galactic backyard (2024)

MIT researchers, including several undergraduate students, have discovered three of the oldest stars in the universe, and they happen to live in our own galactic neighborhood.

The team spotted the stars in the Milky Way's "halo" -- the cloud of stars that envelopes the entire main galactic disk. Based on the team's analysis, the three stars formed between 12 and 13 billion years ago, the time when the very first galaxies were taking shape.

The researchers have coined the stars "SASS," for Small Accreted Stellar System stars, as they believe each star once belonged to its own small, primitive galaxy that was later absorbed by the larger but still growing Milky Way. Today, the three stars are all that are left of their respective galaxies. They circle the outskirts of the Milky Way, where the team suspects there may be more such ancient stellar survivors.

"These oldest stars should definitely be there, given what we know of galaxy formation," says MIT professor of physics Anna Frebel. "They are part of our cosmic family tree. And we now have a new way to find them."

As they uncover similar SASS stars, the researchers hope to use them as analogs of ultrafaint dwarf galaxies, which are thought to be some of the universe's surviving first galaxies. Such galaxies are still intact today but are too distant and faint for astronomers to study in depth. As SASS stars may have once belonged to similarly primitive dwarf galaxies but are in the Milky Way and as such much closer, they could be an accessible key to understanding the evolution of ultrafaint dwarf galaxies.

"Now we can look for more analogs in the Milky Way, that are much brighter, and study their chemical evolution without having to chase these extremely faint stars," Frebel says.

She and her colleagues have published their findings today in the Monthly Notices of the Royal Astronomical Society (MNRAS). The study's co-authors are Mohammad Mardini, at Zarqa University, in Jordan; Hillary Andales '23; and current MIT undergraduates Ananda Santos and Casey Fienberg.

Stellar frontier

The team's discoveries grew out of a classroom concept. During the 2022 fall semester, Frebel launched a new course, 8.S30(Observational Stellar Archaeology), in which students learned techniques for analyzing ancient stars and then applied those tools to stars that had never been studied before, to determine their origins.

"While most of our classes are taught from the ground up, this class immediately put us at the frontier of research in astrophysics," Andales says.

The students worked from star data collected by Frebel over the years from the 6.5-meter Magellan-Clay telescope at the Las Campanas Observatory. She keeps hard copies of the data in a large binder in her office, which the students combed through to look for stars of interest.

In particular, they were searching ancient stars that formed soon after the Big Bang, which occurred 13.8 billion years ago. At this time, the universe was made mostly of hydrogen and helium and very low abundances of other chemical elements, such as strontium and barium. So, the students looked through Frebel's binder for stars with spectra, or measurements of starlight, that indicated low abundances of strontium and barium.

Their search narrowed in on three stars that were originally observed by the Magellan telescope between 2013 and 2014. Astronomers never followed up on these particular stars to interpret their spectra and deduce their origins. They were, then, perfect candidates for the students in Frebel's class.

The students learned how to characterize a star in order to prepare for the analysis of the spectra for each of the three stars. They were able to determine the chemical composition of each one with various stellar models. The intensity of a particular feature in the stellar spectrum, corresponding to a specific wavelength of light, corresponds to a particular abundance of a specific element.

After finalizing their analysis, the students were able to confidently conclude that the three stars did hold very low abundances of strontium, barium, and other elements such as iron, compared to their reference star -- our own sun. In fact, one star contained less than 1/10,000 the amount of iron to helium compared to the sun today.

"It took a lot of hours staring at a computer, and a lot of debugging, frantically texting and emailing each other to figure this out," Santos recalls. "It was a big learning curve, and a special experience."

"On the run"

The stars' low chemical abundance did hint that they originally formed 12 to 13 billion years ago. In fact, their low chemical signatures were similar to what astronomers had previously measured for some ancient, ultrafaint dwarf galaxies. Did the team's stars originate in similar galaxies? And how did they come to be in the Milky Way?

On a hunch, the scientists checked out the stars' orbital patterns and how they move across the sky. The three stars are in different locations throughout the Milky Way's halo and are estimated to be about 30,000 light years from Earth. (For reference, the disk of the Milky Way spans 100,000 light years across.)

As they retraced each star's motion about the galactic center using observations from the Gaia astrometric satellite, the team noticed a curious thing: Relative to most of the stars in the main disk, which move like cars on a racetrack, all three stars seemed to be going the wrong way. In astronomy, this is known as "retrograde motion" and is a tipoff that an object was once "accreted," or drawn in from elsewhere.

"The only way you can have stars going the wrong way from the rest of the gang is if you threw them in the wrong way," Frebel says.

The fact that these three stars were orbiting in completely different ways from the rest of the galactic disk and even the halo, combined with the fact that they held low chemical abundances, made a strong case that the stars were indeed ancient and once belonged to older, smaller dwarf galaxies that fell into the Milky Way at random angles and continued their stubborn trajectories billions of years later.

Frebel, curious as to whether retrograde motion was a feature of other ancient stars in the halo that astronomers previously analyzed, looked through the scientific literature and found 65 other stars, also with low strontium and barium abundances, that appeared to also be going against the galactic flow.

"Interestingly they're all quite fast -- hundreds of kilometers per second, going the wrong way," Frebel says. "They're on the run! We don't know why that's the case, but it was the piece to the puzzle that we needed, and that I didn't quite anticipate when we started."

The team is eager to search out other ancient SASS stars, and they now have a relatively simple recipe to do so: First, look for stars with low chemical abundances, and then track their orbital patterns for signs of retrograde motion. Of the more than 400 billion stars in the Milky Way, they anticipate that the method will turn up a small but significant number of the universe's oldest stars.

Frebel plans to relaunch the class this fall, and looks back at that first course, and the three students who took their results through to publication, with admiration and gratitude.

"It's been awesome to work with three women undergrads. That's a first for me," she says. "It's really an example of the MIT way. We do. And whoever says, 'I want to participate,' they can do that, and good things happen."

This research was supported, in part, by the National Science Foundation.

Researchers discover the universe's oldest stars in our own galactic backyard (2024)


Researchers discover the universe's oldest stars in our own galactic backyard? ›

MIT researchers, including several undergraduate students, have discovered three of the oldest stars in the universe, and they happen to live in our own galactic neighborhood. The team spotted the stars in the Milky Way's “halo” — the cloud of stars that envelopes the entire main galactic disk.

Where can the oldest stars in our galaxy be found? ›

Some of the oldest stars in the universe found hiding near the Milky Way's edge — and they may not be alone. Astronomers reanalyzed the chemical composition of three stars in the Milky Way's halo and found that they are between 12 and 13 billion years old. They may have also been stolen from other galaxies.

Where are the oldest stars in the Milky Way _______________? ›

About 13 billion years old, the stars, given the “endearing” name SASS, Small Accreted Stellar System stars, formed in small dwarf galaxies and are now located in the outer limits of the Milky Way, called the “halo,” which starts at about 10,000 light-years from Earth and extends to a million light-years away, Frebel ...

Where are the oldest individual stars found? ›

Milky Way halo

What is the oldest star in the cosmos? ›

The oldest star in the known universe is the Methuselah star, also known as HD 140283, a subgiant star. Methuselah is located in the constellation Libra, close to the Milky Way galaxy's Ophiuchus border, and around 190 light-years away from the Earth.

What is the oldest thing in our galaxy? ›

The earliest known celestial object that formed within our Galaxy is a star called HD 140283, also known as the Methuselah star. It is a metal-poor star, meaning that it has a low abundance of elements heavier than hydrogen and helium.

What are the oldest stars in our solar system? ›

HE 1523-0901 is the oldest known star in our galaxy, the Milky Way. The star's estimated age is about 13.2 billion years.

Is there something older than the universe? ›

One study suggested that the “Methuselah Star” is older than the Universe itself. The Universe is thought to be 13.797 billion years old, with an uncertainty of ±0.023 billion years. In 2013, a measurement of the “Methuselah Star” suggested that it is 14.45 billion years old — older than the age of the Universe.

What is the oldest thing in the universe? ›

GRB 090423 was also the oldest known object in the Universe, apart from the Methuselah star. As the light from the burst took approximately 13 billion years to reach Earth.

Where are the youngest and oldest stars in the galaxy? ›

Young stars lie in the thin disk, are rich in metals, and orbit the Galaxy's center at high speed. The stars in the halo are old, have low abundances of elements heavier than hydrogen and helium, and have highly elliptical orbits randomly oriented in direction (see Figure 1).

Who was the first person to find a star? ›

The discovery of stars dates back to prehistoric times, as humans have been observing and studying the stars for thousands of years. However, the exact individuals who first discovered stars are unknown, as it likely occurred before recorded history.

How long do the oldest stars live? ›

In other words, of the stars that exist right now, the longest-lived ones will survive for tens to hundreds of trillions of years, with a maximum possible lifetime of around 380 trillion years.

Do the first stars still exist? ›

Based on what we know about physics, we know that if any of the earliest stars were smaller than 0.9 times the mass of the Sun, they should still be shining today. But if they were very massive, they would have had extremely short lifetimes, burning up their fuel quickly and dying within a few million years of forming.

What was before the universe? ›

The universe materialized literally out of nothing, at a tiny but finite size, and expanded thereafter. There were no moments before the moment of smallest size because there was no “before.” Likewise, there was no “creation” of the universe, since that concept implies action in time.

Is there anything older than the Methuselah star? ›

Since HD 140283 is a Population II star, it is older. In fact, it is the oldest star with a well-determined age. Because of this, astronomers colloquially call the star “the Methuselah star.” Initial estimates of its age were in excess of 14 billion years.

Which galaxy is powerful? ›

Quasars are the most luminous type of active galaxy. They emit light across the electromagnetic spectrum, produce powerful particle jets, and can radiate thousands of times the energy emitted by a galaxy like the Milky Way.

How do you find the oldest star? ›

Astronomers can figure out the ages of some of the oldest stars in the Universe by studying globular clusters. A globular cluster is a dense collection of close to a million stars, all of which formed at roughly the same time. The density of stars near the center of a globular cluster is enormous.

Which galaxies have older stars? ›

Instead of spiral arms, elliptical galaxies are just big clumps of stars. There is very little gas and dust. Because there is not much gas and dust, there's not enough material to make new stars. In general, the stars in elliptical galaxies are old, red stars.


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