The oldest supernovae in the universe ejected by powerful jets, say astronomers | Astronomy

A team of MIT astronomers has observed evidence of the explosion of the first stars of the Universe as an asymmetric supernova, strong enough to disperse heavy elements in the primitive universe. The results appear in the Astrophysical Journal.

Several hundred million years after the Big Bang, the very first stars have invaded the Universe in the form of extremely bright accumulations of hydrogen and helium. In the nuclei of these stars, thermonuclear reactions forged the first heavy elements, notably carbon, iron and zinc.

These first stars were probably huge and short-lived fireballs, and the astrophysicists assumed that they had exploded in the form of a supernovae of the same sphere.

But now, astronomers from MIT and elsewhere have discovered that these stars may have exploded in a more powerful and asymmetrical way, throwing jets strong enough to eject heavy elements into nearby galaxies. These elements eventually served as seeds for the second generation of stars, some of which can still be seen today.

"When a star explodes, some of that star is sucked into a black hole like a vacuum," said Dr. Anna Frebel of MIT.

"It's only when you have a mechanism, such as a jet that can extract a material, that you can observe later in a new generation of stars." . "

In 2005, Dr. Frebel and his colleagues discovered that a star called HE 1327-2326 is an old surviving star that is part of the second generation of stars in the Universe.

At that time, the star was the lowest metal star ever observed, that is, it had extremely low concentrations of heavier elements than hydrogen and helium – indicating that it was formed as part of the second generation of stars, at a time when heavy element content of the universe had not yet been wrought.

"The first stars were so massive that they had to explode almost immediately," said Dr. Frebel.

"The smaller stars that formed the second generation are still available today and preserve the old materials left by these first stars. Our star has just a pinch of heavier elements than hydrogen and helium, so we know that she had to be part of the second generation of stars. "

In 2016, the team used the Cosmic Origins spectrograph aboard the NASA / ESA Hubble Space Telescope to observe the star.

Astronomers have compiled a list of heavy elements they suspected of being in such an ancient star, which they planned to search for in Hubble's data, including silicon, iron, phosphorus, and zinc.

"We found that whatever we measure, we get a very high zinc supply," said Dr. Rana Ezzeddine of MIT.

The researchers then performed more than 10,000 simulations of supernovae and secondary stars that formed as a result.

They found that while most spherical supernova simulations were capable of producing a secondary star with elemental compositions observed in HE 1327-2326, none of them reproduced the zinc signal.

It turned out that the only simulation that could explain the composition of the star, including its high zinc abundance, was that of an aspheric supernova with jet ejection of a first star.

Such a supernova would have been extremely explosive, with a power equivalent to about a thousand times that of a hydrogen bomb.

"We discovered that this first supernova was much more energetic than people thought before, about 5 to 10 times more," said Dr. Ezzeddine.

"In fact, the previous idea of ​​the existence of a dimmer supernova to explain the stars of the second generation may have to be removed soon."

The results could lead scientists to a better understanding of reionization, a pivotal period in which the Universe gas, which was completely neutral, became ionized – a state that allowed galaxies to take shape.

"After the first sightings, people thought that the first stars were neither so bright nor energetic, so when they exploded, they did not participate much in reionization. universe, "said Dr. Frebel.

"We're sort of rectifying this picture and showing, maybe the first stars had enough punch when they exploded, and maybe now they're strong opponents to help reionization and for to wreak havoc in their own small dwarf galaxies. "

These first supernovae could also have been powerful enough to project heavy elements into neighboring "virgin galaxies", which have not yet formed any star.

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Rana Ezzeddine et al. 2019. Evidence on the explosion of a supernova in an aspheric population III deduced from the star deficient in hyper-metals HE 1327-2326. ApJ 876, 97; doi: 10.3847 / 1538-4357 / ab14e7