Early this year, scientists at the IceCube experiment reported an exciting connection. A neutrino, a tiny fundamental particle, has been detected with incredible energy, much higher than we can produce in our particle accelerators. The culprit they suspected was one of the most dramatic events in the universe: a star being ripped apart. Other scientists are not so sure.
In a galaxy 750 million light-years away, a supermassive black hole devoured a star that got too close. The tidal disruption event (TDE) is known as AT2019dsg. This gruesome happening released an outflow of energy equivalent to what the Sun produces in 30 million years. That’s a lot. But researchers say that it’s not enough to link it to the neutrino.
A neutrino that energetic, as reported in The Astrophysical Journal, would require an event 1,000 times more powerful. The team believed that the neutrinos spewed by the end as the black hole messily ate the stars were quite ordinary. Nothing of extraordinary level like that one.
"Instead of seeing the bright jet of material needed for this, we see a fainter radio outflow of material," co-author Dr. Kate Alexander, a study co-author and postdoctoral fellow at Northwestern University said in a statement. "Instead of a powerful firehose, we see a soft wind."
Such winds are similar to those observed in the Type Ib and Type Ic (pronounced One-b and One-c) supernovae, where stars collapse under their own weight once they run out of fuel to fuse, and so internal radiation can’t push against the gravity any longer. And they go boom. Releasing light and matter (including neutrinos) into the universe.
"If this neutrino somehow came from AT2019dsg, it begs the question: Why haven't we spotted neutrinos associated with supernovae at this distance or closer? They are much more common and have the same energy velocities," explained lead author Dr Yvette Cendes, from Harvard & Smithsonian Center for Astrophysics.
The work uses radio observations of the event from the Karl G. Jansky Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA). The data allowed them to better understand how this TDE is panning out and have a better model for the kind of energies that are being released.
And while the paper makes a compelling case for this neutrino not being from AT2019dsg, the team points out that there’s plenty more to learn about TDEs and this event in particular.
"We're probably going to check-in on this one again," Cendes added. "This particular black hole is still feeding."
And the question now is, if the neutrino is not from a TDE then where did it come from?
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