Astronomers: 2017 Neutron Star Explosion Was Perfectly Round

Neutron stars are extreme stellar objects. With magnetic fields billions of times more intense than Earth’s and density second only to black holes, these dead stars push the bounds of physical laws we are only beginning to grasp. Things get even wilder when two neutron stars meet up. A neutron star collision, known as a kilonova, is one of the most energetic events in the known universe, and new research suggests these explosions are perfectly spherical. And they shouldn’t be. So far, that has astrophysicists baffled.

A neutron star is what’s left over after a massive star runs out of nuclear fuel. The largest stars become black holes when they die, and smaller ones, like the sun, become white dwarfs. Without the energy from fusion, the star collapses inward to become an ultra-dense relic of what once was. Neutron stars, so-named because they are composed almost entirely of neutrons, are only a few kilometers across, but they have more mass than the sun.

When two of these objects collide, they create “the most extreme physical conditions in the universe,” according to University of Copenhagen researchers. Kilonovae are believed responsible for creating heavy elements like gold, platinum, and uranium, but we know surprisingly little about these events. In 2017, a kilonova was detected 140 million light-years away, allowing scientists to gather detailed data for the first time ver. The team from the University of Copenhagen analyzing the data has found that current kilonovae models don’t match the observations.

Illustration of spherical explosion in space.

As the stars spiral toward each other, they might orbit each other more than 100 times per second. Based on that, scientists believed a kilonova would produce a flattened, asymmetrical explosion. And yet, the 2017 kilonova appears to have produced a spherical explosion. The researchers say the most likely reason for the unanticipated shape is that kilonovae produce a massive energy release from the center of the explosion. This would effectively “even out” the asymmetrical explosion, but the source of this energy is unclear. The team speculates that the collapse of the two neutron stars into a black hole triggers a kind of “magnetic bomb.” Whatever the cause, it suggests we’re missing some of the physics involved.

Scientists will need to examine more kilonovae to unravel the mystery, which could lead to other important discoveries. These perfectly spherical explosions could be an ideal distance marker for measuring the size and rate of expansion of the universe. That could nail down the universe’s exact age, which varies by about a billion years depending on which current techniques are used.

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