National Geographic News
An optical image of the star SDSS J0018-0939.

Star SDSS J0018-0939 is a small, second-generation star bearing the chemical imprint of one of the universe's first stars. Seen as white here, the star would appear orange to human eyes.

Photograph by SDSS/NAOJ

Nadia Drake

For National Geographic

Published August 21, 2014

After digging around in the light from an old, orange star, astronomers have found possible remnants of one of the universe's first stars: a giant that may have been more than 140 times as massive as the sun.

The finding, reported Thursday in the journal Science, marks the first time astronomers have made observations suggesting that such massive stars populated the early universe, despite decades of theories proposing that some of those first stars must have been huge.

Billions of years ago, when that primordial star exploded in a spectacular supernova, it blasted its guts into space and seeded the cloud that eventually formed the orange star, which is now about 1,000 light-years from Earth.

Knowing the mass of these first stars—or the range of masses—is crucial for understanding how quickly the lights turned on in the very early universe and shifted it from a dark, gassy place to one filled with nascent galaxies and stars.

"How the cosmic Dark Ages ended—that really depends on the mass of the first stars," says University of Texas at Austin astrophysicist Volker Bromm, who calls the new findings "an important data point."

Ancient Fingerprints

The universe's first stars were born several hundred million years after the big bang, Bromm says, when hydrogen, helium, and dark matter were mixed into a thin soup that flooded space. At that time, irregular clumps of dark matter began to collapse, creating dense mixtures of gases that eventually ignited and became stars, lighting the universe and bringing an end to what astronomers call the cosmic Dark Ages.

Many of these first stars, called population III stars, were relatively small, several tens of times as massive as Earth's sun. But astronomers think that some must have been huge-hundreds of solar masses. Formed from large clouds of slowly collapsing gas, these giant stars were energetic enough to reshape their surroundings, helping to form early galaxies and star clusters and burning away a long-standing cosmic fog.

But large stars live fast and die young. After a few million years, the primordial giants exploded in supernovae so spectacular they could destroy galaxies.

The chemical elements flung from these dying stars into the infant universe seeded the surrounding gas clouds, leaving patterns that astronomers can now read like fingerprints. Those elements helped gas clouds cool and condense more quickly and form a second generation of smaller stars, some of which still survive and can be mined for ancient stellar imprints.

Explaining an Oddball

A team led by astronomer Wako Aoki from the National Astronomical Observatory in Japan began its search for the fingerprints of ancient massive stars by looking for small, long-lived stars with low metal content. These might be stars that formed early in the universe and hadn't been contaminated by the splatters from eons of supernovae.

"A low-metallicity star clearly records the products of a single supernova," Aoki says. "We can estimate the mass of the progenitor star from the chemical abundances of the products."

In other words, they were looking for the second-generation stars that might bear fingerprints from first-generation ancestors.

One of the stars in the survey, a small, orange star called J0018-0939, stood out. It had low levels of carbon, magnesium, and cobalt (all considered "metals" in astronomy) but a peculiarly high level of iron. Normally, that high iron reading would have been enough to exclude the star from the survey. But scientists were intrigued.

The team pointed the Subaru Telescope in Hawaii at the star and took a closer look at its chemical profile, making careful measurements of the abundance of chemical elements. It didn't look like anything anyone had ever seen before.

"They took a risk and it paid off," Bromm says.

Then, astronomers compared the fingerprint to computer simulations of the chemicals that are created and chucked out by various types of supernovae. According to the team, the explosion model that best fits the chemical profile is what's called a pair-instability supernova, a spectacular type of explosion that can be a hundred times more powerful than the supernovae seen today.

And the only way to get a pair-instability supernova and produce that much iron is by exploding a giant star at least 140 times as massive as the sun, Aoki says.

Not all the elements in the chemical profile fit the bill for this type of explosion, a result that astronomer Anna Frebel of MIT quibbles with. But Frebel notes that simulating what would happen in supernovae that have not been observed is incredibly difficult.

"I'm still a little bit on the fence about whether I believe these [primordial giant stars] existed," says Frebel, who has observed a handful of other second-generation stars.

Like J0018-0939, Frebel's stars bear signatures of the universe's first stars. But unlike this one, those signatures don't reveal the presence of bulked-up behemoths. "But I would be absolutely thrilled if it turns out to be correct."

Follow Nadia Drake on Twitter.

15 comments
David Theil
David Theil

" After a few million years, the primordial giants exploded in supernovae so spectacular they could destroy galaxies."

I want to see a citation for that line.  Makes very little sense. Even at 140 M_sun you still are not getting more than  a few times 10^53 ergs out even if you include neutrino flux.  How does that compare to the gravitational binding energy of a galaxy?

I can imagine a slew of these going off in short time scale blowing all the gas out of the galaxy...maybe...

Does Nadia Drake care to comment?

Ryan Karl
Ryan Karl

Soooo on "How the Universe Works" this week, Michio Kaku and other renowned astrophysicists were saying super-massive black holes likely came first, from the direct collapse of very massive clumps of hot gas, before star and galaxy formation. This is due to observations of quasars in the VERY early universe and the presence of super-massive black holes being at the center of 100+ observed dwarf galaxies. I just feel we have gotten to a point to where we are just chasing our tales and really do not know how any of this happened because this is in direct objection to so many other prominent theories of the universe. Which came first: the chicken or the egg? Stars and galaxies or black holes? Its all very intriguing but its just frustrating that it changes every time I read a scientific article on the universe.

digital beachbum
digital beachbum

In the beginning every thing was small and close together. Eventually every thing became mega larger, but as the Universe expanded and those mega stars exploded things got smaller and further away. As the Universe continues to expand things will get smaller again and further away. Eventually the Universe will dissipate as the outer membrane of the Universe breaks open and then the end will start. 

Nikki Smallwood
Nikki Smallwood

Not to be a negative Nancy, but have you looked at the size of VY Canis Majoris? It is approx a billion times larger than our sun. I'm struggling with the description of these primordial stars as 'huge'. 

Tony Edgin
Tony Edgin

@Ryan Karl These results aren't contradictory.  It is possible that large gas clouds ~140 solar masses collapse into these very short lived, very large stars, after very large gas clouds collapse directly into super massive black holes.  

Michael Busby
Michael Busby

@Ryan Karl  You have to take it on faith that they are right. Know what else you have to take on faith? Religion. BTW, it is "tails," not "tales." that people "chase." And if it bothers you so much, don't read any more scientific articles.

Doc Holiday
Doc Holiday

@Ryan Karl science continually tweaks existing theories as more information is discovered. It's a learning process to go from one side of understanding to the other.

Ranger Dan Parsons
Ranger Dan Parsons

@Mik Lopz  I just love the way Digital Beachbum's prose gives way to your major announcement.  It's a miracle of the universe.  I wouldn't dare click on your link.  It might reveal a wormhole.

Patrick Lueck
Patrick Lueck

@Nikki Smallwood 

Wiki:  --  University of Minnesota Professor Roberta M. Humphreys originally estimated the radius of VY CMa at 1,800 to 2,100 solar radii,[17] which would make it the largest known star by radius. However, a more recent VLTI direct measurement[8] gives a radius of 1420 ± 120 solar radii.

w

Aayush Saxena
Aayush Saxena

@Nikki Smallwood Stars being 'huge' is more about the mass, rather than the volume. VY CMa is roughly 15 solar masses, which is nothing compared to what primordial stars are expected to be. VY CMa is a hypergiant and its size by nature will be quite large. But not necessarily its mass.

Paul Heco
Paul Heco

@Michael Busby @Ryan Karl The truth (they won't admit) is we'll never know for sure - Big Bang, God did it, the universe is really in the eye of a big newt.... who knows?

They may come back and say 8 billion years is way short - maybe it's 100 billion or 200 billion years.  It's the journey that's fascinating.


George Campbell
George Campbell

@Ryan Karl

The Scientific method has humility which is a strength as it allows our collective knowledge to move further towards the truth, changing constantly. Look at scientific history and see the progress change allows. Then look at religion where changing of ideas is seen as a bad thing, e.g. Evolution, and you never get closer to the truth with that kind of thinking. This is the bleeding edge of astronomy and physics, ofcourse there will be contradicting theories, this is a good thing.

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