Hundreds of millions of years after the Big Bang, the first stars flared up in the universe as massive light accumulations of hydrogen and helium. Within the nuclei of these first stars, extreme thermonuclear reactions falsified the first heavier elements, including carbon, iron, and zinc.
These first stars were probably huge, short-lived fiery balls, and scientists assumed they exploded like similar spherical supernovae.
But now astronomers at MIT and elsewhere discovered that these first stars could be torn apart more forcefully, asymmetrically, to eject planes that were violent enough to drive out heavy elements in neighboring galaxies. These elements eventually served as seed for the second generation of stars, some of which can still be seen today.
In an article published today in the Astrophysical Journal, researchers report a strong abundance of zinc in NE 1327-2326, an ancient, surviving star that is among the second generation of stars in the universe. They believe that the star could only get as much zinc as the asymmetric explosion of one of the first stars enriched the cloud from birth.
"When the star explodes, part of that star is planted in a black hole like a vacuum cleaner," said Anna Frebel, an associate professor of physics at MIT and a member of the Kali Institute for Astrophysics and Space Research at MIT. "Only when you have a mechanism, such as a plane that can extract material, you can observe that material later in a star of the next generation. And we believe that this is exactly what can happen here."
"This is the first observation evidence that such an asymmetric supernova occurred in the early universe," added MIT's post-war Rana Ezededine, lead author of the study. "This changes our understanding of how the first stars exploded."
HE 1327-2326 was discovered by Frebel in 2005. At that time, the star was the weakest star of most metals, which means that it has extremely low concentrations of elements heavier than hydrogen and helium – an indication that it is formed as part of the second generation of stars at a time when the majority of the content of the heavy element the universe had yet to be forged.
"The first stars were so massive that they had to explode immediately," said Frebel. "The smaller stars that are formed as the second generation are still available and retain the early material that left these first stars. Our star has only the sprinkling of elements heavier than hydrogen and helium, so we know it must be formed as part of the second generation of stars. "
In May 2016, the team was able to observe a star that orbits close to Earth, only 5,000 light-years away. The researchers took the time of the Hubble Space Telescope at NASA for two weeks and captured stellar light over multiple orbits. They used the Cosmic Origin Spectrograph telescope to measure the minute abundance of various elements within the star.
The spectrograph is designed with high precision to raise a weak ultraviolet light. Some of these wavelengths are absorbed by certain elements, such as zinc. The researchers made a list of tough elements that they suspected might be in such an ancient star that they were planning to search for UV data, including silicon, iron, phosphoric, and zinc.
"I remember getting data and seeing this line of zinc and I could not believe it, so we re-analyzed the analysis," Ezededine recalls. "We found that, no matter how we measured it, we got this really strong abundance of zinc."
A star channel is open
Frebel and Ezzeddine then contacted their associates in Japan who specialize in developing simulations of supernovae and secondary stars that are formed in their consequences. The researchers had over 10,000 simulations of supernovae, each with different explosive energies, configurations, and other parameters. They found that although most of the spherical supernova simulations were able to produce a secondary star with elementary compositions, the researchers noted in HE 1327-2326, none of them reproduced the zinc signal.
As it turns out, the only simulation that could explain the make-up of the star, including its large amount of zinc, was one of the first aspherical, jet-epigasic supernovae. Such a supernova would be extremely explosive, with a power that is equivalent to non-hygienic times (that is, 10 with 30 zeros per second) of the hydrogen bomb.
"We found that this first supernova is much more energetic than people thought earlier, about five to ten times as much," Ezededine said. "In fact, the previous idea of the existence of a darker supernova for explaining the stars of the second generation may need to retire."
The team's results can shift scientists into understanding the reionization, the key period in which the gas in the universe turned into a completely neutral, ionized state that allowed galaxies to shape.
"People thought from the early observations that the first stars were not so bright or energetic, so when they exploded, they did not have much to participate in the re-ionization of the universe," said Frebel. "We are in a sense correcting this picture and displaying, maybe the first stars had enough sexual explosion when they exploded, and maybe now they are strong candidates to contribute to reionization and chaos in their own small dwarf galaxies."
These first supernovae could also be strong enough to shoot heavy elements in the neighboring "virgin galaxies" that had yet to form their own stars.
"Once you have some heavy elements in hydrogen and helium gas, you have a much easier time to form stars, especially small ones," says Frebel. "The working hypothesis is, perhaps, of second-generation stars of this kind formed in these polluted virgins, and not in the same system as the supernova explosion itself, which is always what we have assumed, without thinking otherwise. So this opens a new channel for the formation of early stars ".