Cosmic Event: The first "Super-Kilonova" in human history – The explosion that generates gold and silver

A phenomenon that until today existed only in the realm of theoretical astrophysics appears to have become a reality. The collision of two neutron stars produces an explosion in the form of a perfect sphere called a kilonova, and for the first time, astronomers report the detection of a "super-kilonova."

The AT2025ulz signal and observatory mobilization

The discovery, published in The Astrophysical Journal Letters, began with the detection of gravitational waves on August 18, 2025.

• The "Hearing": The LIGO observatories and their European partner, Virgo, "heard" signal AT2025ulz.

• Initial Thought: It was first considered the second confirmed detection of a neutron star merger since the historic 2017 event (GW170817).

• Global Alert: The alert was immediately sent to astronomers worldwide.

• First Sighting: The Zwicky Transient Facility at the Palomar Observatory in California identified a red object fading rapidly, located 1.3 billion light-years away.

The mystery of "transformation": Kilonova or Supernova?

Professor of Astronomy at Caltech, Mansi Kasliwal, explained that for the first three days, the explosion looked identical to the 2017 kilonova. However, the situation became complex:

1. Brightening: The object began to get brighter and turned blue.

2. Spectral Lines: It displayed hydrogen emissions—typical characteristics of a supernova.

3. The Paradox: A supernova at that distance (1.3 billion light-years) could never produce gravitational waves strong enough for LIGO to detect.

The team realized this was a super-kilonova: a kilonova born within a supernova explosion, which initially obscured the astronomers' view.

Anatomy of the "Forbidden" Stars

Analysis of the gravitational waves revealed something shocking: one of the neutron stars involved had a mass smaller than that of the Sun. Normally, neutron stars are $1.2$ to $2$ times the mass of the Sun. Scientists proposed two scenarios:

• Fission: A rapidly rotating star explodes (supernova), and its core splits into two smaller neutron stars.

• Disk Formation: A neutron star forms from a supernova and is surrounded by a disk of matter that eventually condenses into a second, smaller neutron star.

In both cases, these twin stars spiral toward each other and merge, ejecting heavy elements such as gold and silver.

Confirmation and the Future of Research

Further research from the W. M. Keck Observatory in Hawaii and the Fraunhofer telescope in Germany showed that the initial red glow was the result of heavy elements blocking blue light. This view was eventually "drowned out" by the expanding shell of debris from the supernova.

According to Brian Metzger of Columbia University, this is the only way to explain the existence of these "forbidden" stars. Moving forward, scientists will search for similar events using:

• The Vera Rubin Observatory

• NASA’s Nancy Roman Space Telescope

• The UVEX and Cryoscope (Antarctica) programs

"This event is revelatory," Kasliwal concluded, as it shows that many future kilonovae might be mistaken for simple supernovae, hiding their true nature.

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