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Neutron Stars' Collision May Have Created The Lightest Known Black Hole Yet

Jun 03, 2018 10:15 PM EDT
Gravitational Wave Event Likely Signaled Creation of a Black Hole
Two neutron stars collided in a massive astronomical event — and then history's smallest ever black hole emerged.
(Photo : NASA | CXC | M.Weiss)

When two neutron stars collide, what happens? Scientists say a recent collision resulted in the creation of the lowest mass black hole in known history.

Count this as a good couple of months for science. Witnessing two neutron stars crash together is already an extraordinary event for astronomers, and now they find that the result is also quite extraordinary.

In a paper published in the Astrophysical Journal Letters, researchers suggest that the crash between the stars produced a black hole that's the smallest one ever found.

The Collision, Black Hole Event

According to a report from NASA, two neutron stars were observed to have collided in August 2017. The event generated gravitational waves and also gamma rays that were detected by astronomers and then analyzed by NASA's Chandra X-ray Observatory in the following months.

The findings included the surprising mass of this mysterious object, projected at roughly 2.7 times larger than the Sun's mass. This is a strange size, as it becomes either the tiniest black hole that's ever been discovered or the most massive neutron star known to man.

If the object that resulted from the collision — now called GW170817 — were another neutron star, it would have given off a bright X-ray emission due to rapid spinning and high-energy particles in an increasingly massive bubble. Instead, the X-ray levels were observed to be far lower than what's expected of a star, so astronomers suggest a black hole — albeit, a small one — was formed from the crash.

What It Means

"We may have answered one of the most basic questions about this dazzling event: what did it make?" coauthor Pawan Kumar explains. "Astronomers have long suspected that neutron star mergers would form a black hole and produce bursts of radiation, but we lacked a strong case for it until now."

Both black holes and neutron stars are still relatively big mysteries even to astronomers, and these new findings shed some light on the subjects.

For one, the creation of black holes can be very complicated. After all, for GW170817 to have formed, it took two supernova explosions that resulted in two neutron stars that are orbiting closely enough for gravitational wave radiation to pull the two stars into a massive collision.

"We are learning so much about the astrophysics of the densest known objects from this one event," coauthor J. Craig Wheeler says, calling the new object an event that just keeps on giving.

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