Scientists, by scrutinizing an unusually prolonged gamma-ray burst (GRB), confirmed its origin in the collision of dense neutron stars, validating their role in gold creation. Using the James Webb Space Telescope (JWST) and Hubble Space Telescope, researchers observed the forging of gold and heavy elements, providing insight into the tumultuous environments spawned by neutron star mergers.
The discovery of a kilonova thrilled the research team, including Eleonora Troja, a University of Rome astrophysicist, emphasizing the groundbreaking verification of metals heavier than iron and silver freshly produced before their eyes.
Challenging Beliefs on Neutron Star Mergers and High-Energy Bursts
GRBs, the most powerful energy bursts in the universe, were linked to neutron star mergers, but a recent discovery challenges this. GRBs fall into two categories: long ones lasting over 2 seconds and short ones under 2 seconds. While short GRBs are linked to neutron star mergers, long GRBs were believed to arise from massive star collapses, opposing traditional views.
In March 2023, NASA's Fermi mission detected an extraordinarily bright and extended burst, labeled GRB 230307A, lasting 200 seconds, making it the second most energetic GRB ever recorded.
This event appeared linked to a kilonova, named AT2017gfo, and a neutron star merger situated approximately 8.3 million light-years away. This discovery challenges established ideas about the origins of high-energy radiation bursts and defies conventional theories.
Yu-Han Yang, the leader of the research team and a postdoctoral astrophysicist at the University of Rome, remarked on the challenge posed by the duration of GRBs originating from compact binary mergers, expressing skepticism about the conventional understanding.
Stars serve as cosmic forges, fusing elements from hydrogen to iron. Massive stars, 7-8 times the sun's mass, create elements until supernova explosions. Neutron stars, remnants of supernovae, contribute to heavier element creation through binary collisions.
Merging neutron stars generates gravitational waves, causing gamma-ray bursts and releasing neutron-rich material, forming heavier elements. These collisions produce superheavy "lanthanides" that decay into lighter elements, emitting radiation visible as kilonovas.
Studying kilonovas unveils insights into synthesizing precious elements like gold and silver, shedding light on the complex nucleosynthesis during neutron star mergers. Understanding these mergers reveals previously obscured aspects of nucleosynthesis, according to Yang.
Binary Neutron Stars Unveil Gold Production in Kilonova
New research titled "A lanthanide-rich kilonova in the aftermath of a long gamma-ray burst" published in the journal Nature, reveals binary neutron stars, like those in the GRB and kilonova AT2017gfo, contribute gold to the universe's elemental building blocks.
Kilonovas exhibit diverse behaviors over weeks to months, influenced by ejected material composition and the remnant at the merger site's center. While most kilonova observations lack late-time data, AT2017gfo's observations faced limitations from the Spitzer Space Telescope, offering weak signals tainted by the host galaxy and insufficient wavelength coverage.
Troja explained that the early behavior of kilonovas remains unaffected by chemical composition, requiring extended observation to reveal forged metals.
Observing kilonovas is challenging, hindering a deeper understanding of their formation. Despite JWST and Hubble enabling extended observation of AT2017gfo, confirming neutron star mergers forge elements beyond gold and can cause long GRBs, the mystery persists on why this specific merger resulted in an unusually prolonged GRB.
Yang emphasized that the confirmation implies that long-duration GRBs from compact binary mergers are not random, raising numerous questions. He anticipates future joint observations of gamma-ray bursts, kilonovas, and gravitational waves to unravel mysteries.
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