The Universe's First Stars Exploded, Sending Out Powerful Jets That Produced New Ones

The universe's first stars were immense, very short-lived fireballs of hydrogen and helium gas, which formed a few hundred million years after the big bang. Scientists have long thought that their lives quickly came to end in cataclysmic explosions known as supernovae that were spherical in shape.

But according to a study published in the Astrophysical Journal, these early stars may have blown up in a more violent, asymmetric fashion, shooting out vast jets which transported the first heavy elements—such as carbon, iron and zinc—into neighboring galaxies.

MIT researchers say that these elements provided the raw material for the formation of a second generation of stars, some of which survive to this day.

The team came to their conclusions after observing one of these ancient surviving stars—known as HE 1327-2326—with NASA's Hubble Space Telescope for two weeks in 2016. With the help of an instrument which can measure the abundance of various elements within a star, they noticed that HE 1327-2326 contained high amounts of zinc, which could have originated from an asymmetric explosion of one of the very first stars.

"When a star explodes, some proportion of that star gets sucked into a black hole like a vacuum cleaner," Anna Frebel, an author of the study from MIT, said in a statement. "Only when you have some kind of mechanism, like a jet that can yank out material, can you observe that material later in a next-generation star. And we believe that's exactly what could have happened here."

According to the team, this is the first observational evidence that such an asymmetric supernova occurred in the early universe.

"This changes our understanding of how the first stars exploded," Rana Ezzeddine, lead author of the study, said in the statement.

When HE 1327-2326 was first discovered in 2005, scientists noticed something intriguing: The star had extremely low concentrations of elements heavier than hydrogen and helium. This suggested that it was part of the second generation of stars, given that when it formed, most heavy elements had yet to be created.

"The first stars were so massive that they had to explode almost immediately," Frebel said. "The smaller stars that formed as the second generation are still available today, and they preserve the early material left behind by these first stars. Our star has just a sprinkle of elements heavier than hydrogen and helium, so we know it must have formed as part of the second generation of stars."

In an attempt to explain the unusual composition of HE 1327-2326, the team conducted thousands of computer simulations of supernovae explosions. These tests revealed that the only scenario that could explain its makeup was an asymmetrical supernova of an early star shooting out jets of material.

A supernova of this type would have been unimaginably explosive, blowing up with a nonillion times more power than a hydrogen bomb, the researchers say. (A nonillion is 1 with 30 zeroes following.)

"We found this first supernova was much more energetic than people have thought before, about five to 10 times more," Ezzeddine said. "In fact, the previous idea of the existence of a dimmer supernova to explain the second-generation stars may soon need to be retired."

In fact, the team think these supernovae were so powerful that they shot heavy elements into neighboring "virgin" galaxies" which contained no fully-formed stars.

"Once you have some heavy elements in a hydrogen and helium gas, you have a much easier time forming stars, especially little ones," Frebel said. "The working hypothesis is, maybe second generation stars of this kind formed in these polluted virgin systems, and not in the same system as the supernova explosion itself, which is always what we had assumed, without thinking in any other way. So this is opening up a new channel for early star formation."