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A team of observatories, including NASA’s Swift satellite,
recently joined forces to trace a hard-to-detect cosmic particle

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back to its dramatic origin.

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The particle, called a high-energy neutrino,
was likely produced by a tidal disruption event,

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which occurs when a star passes too close to a black hole.

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There, extreme gravity causes the star to bulge
and break apart into a stream of gas,

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with some of the material swinging around to form an accretion disk.

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Neutrinos vastly outnumber all the atoms in the universe,
but they have almost no mass and rarely interact with other matter,

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so they’re very hard to pin down.

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However, scientists have detected them coming from
extreme objects like exploding stars.

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High-energy neutrinos come from even more bizarre places,

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like super-fast particle jets driven by supermassive black holes.

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Scientists suspected that tidal disruptions could also produce
high-energy neutrinos.

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But they weren’t sure where or when in the process
the particles might appear.

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Some suggested powerful jets would create these neutrinos.

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Regardless of how they’re made, though, astronomers expected
they’d appear early on, when the event is brightest.

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However, a high-energy neutrino arriving from a tidal disruption
called AT2019dsg offered new insights.

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An observatory called the Zwicky Transient Facility in California
discovered the event in April 2019,

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but it wasn’t until October that the IceCube Neutrino Observatory in Antarctica
detected a high-energy neutrino astronomers linked to this event.


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Measurements by Swift and other observatories show that the tidal disruption’s
visible and ultraviolet light peaked and appeared to plateau,

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and its X-rays dimmed quickly.

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However, radio telescopes saw its emission steadily increase.

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This meant some particles were being accelerated
even though super-fast particle jets were never detected.

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So, AT2019dsg had the right environment to accelerate particles
and produce high-energy neutrinos --

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and maintained it for a longer period than scientists expected.

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Astronomers think the neutrino may have come from one of three regions:

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in the disk close to the black hole, where particles colliding with
X-rays could produce neutrinos;

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further out in the disk, where particles could interact with UV light;

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or in broad outflows where particles could collide with each other.

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This is only the second time a high-energy neutrino
has been tied to a source beyond our galaxy.

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Scientists are searching for links between
previous tidal disruptions and other high-energy neutrinos.

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And, as observatories discover new events, they now have a better idea
of where and when they might find these elusive particles.

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