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Ghost particles crashing into Antarctica reveal the unseen heart of a nearby galaxy

Ghost particles crashing into Antarctica reveal the unseen heart of a nearby galaxy
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About 47 million light-years from where you are seated, the center of a black-hole-laden galaxy called NGC 1068 spews out streams of mysterious particles. These “neutrinos”, also known as the notoriously elusive “ghost particles”, haunt our universe leave little trace of their existence.

Immediately upon their formation, bundles of these invisible parts tumble across the cosmic expanse. They whiz past bright stars for us to see and hurtle past pockets of space filled with wonders we have yet to discover. They fly and fly and fly, until they occasionally collide with a detector deep beneath the earth’s surface.

The journey of the neutrinos is seamless. But scientists are patiently awaiting their arrival.

Nestled in approximately 1 billion tons of ice more than 2 kilometers (1.24 miles) below Antarctica lies the IceCube Neutrino Observatory. You could call it a neutrino hunter. If any neutrinos transfer their party to the cold continent, IceCube is ready.

in a paper published Friday in the journal Science, the international team behind this ambitious experiment confirmed that they found evidence of 79 “high-energy neutrino emissions” originating from around NGC 1068, opening the door to novel – and endlessly fascinating – types of physics. Scientists call it “neutrino astronomy”.

It would be a branch of astronomy that can do what existing branches simply cannot.

A starry sky shows the heart of the Milky Way.  On the ground is the snowy surface of Antarctica, on which a structure rests.

Front view of the IceCube Lab at dusk, with a starry sky showing a glimpse of the Milky Way and sunlight lingering on the horizon.

Martin Wolf, IceCube/NSF

To date, physicists had only shown neutrinos that either came from the sun; the atmosphere of our planet; a chemical mechanism called radioactive decay; supernova; and — thanks to IceCube’s first Breakthrough 2017 — a blazar, or voracious supermassive black hole, aimed straight at Earth. A Void named TXS 0506+056.

With this newly discovered neutrino source, we are entering a new era in particle history. In fact, according to the research team, neutrinos originating from NGC 1068 are likely to have in the millions, billions, maybe even trillion the amount of energy contained in neutrinos rooted in the sun or supernovae. Those are staggering numbers, because generally such spooky bits are so powerful yet evasive that every second, Trillions upon trillions of neutrinos move right through your body. You just can’t tell.

And if you wanted to stop a neutrino, you would have to fight it with a block of lead a light-year away – although even then there would only be a fractional chance of success. So, harnessing these particles, NCG 1068 version or not, could allow us to penetrate areas of the cosmos that are normally beyond our reach.

What now?

This moment is not only powerful because it gives us further evidence of a strange particle that was not even announced existed until 1956but also because neutrinos are like keys to the backstage of our universe.

They have the ability to uncover phenomena and solve mysteries that we cannot solve any other way, which is the main reason scientists try to develop neutrino astronomy in the first place.

“The universe has multiple ways of communicating with us,” Denise Caldwell of the National Science Foundation and a member of the IceCube team told reporters Thursday. “Electromagnetic radiation that we see as light from stars, gravitational waves that shake the fabric of space — and elementary particles such as protons, neutrons and electrons that are ejected from localized sources.

“One of these elementary particles were neutrinos, which permeate the universe, but unfortunately, neutrinos are very difficult to detect.”

In fact, even the galaxy NGC 1068 and its gigantic black hole are usually obscured by a thick veil of dust and gas, making it difficult to analyze with standard optical telescopes and equipment – despite years of attempts by scientists to penetrate its curtain. NASA’s James Webb Space Telescope could have a leg up in this case because of that infrared eyesbut neutrinos might be an even better way in.

Expected to be generated behind such opaque screens that filter our universe, these particles can carry cosmic information behind those screens, zoom great distances while interacting with essentially no other matter, and present humanity with pristine, pristine information about elusive ones deliver corners of space.

“In a way, we’re very fortunate because we have access to an amazing understanding of this object,” said Elisa Resconi of the Technical University of Munich and a member of the IceCube team about NGC 1068.

ice cubes

In this artist’s rendering, based on a real image of the IceCube laboratory at the South Pole, a distant source emits neutrinos that are detected by IceCube sensors called DOMs beneath the ice.

IceCube/NSF

It’s also worth noting that there are many (many) more galaxies similar to NGC 1068 – categorized as Seyfert galaxies — then there are blazars similar to TXS 0506+056. This means IceCube’s latest discovery arguably represents a bigger step forward for neutrino astronomers than the observatory’s groundbreaking discovery.

Perhaps most of the neutrinos diffusing through the universe are rooted in NGC 1068 doubles. But on the whole, neutrinos have much more to offer than just their sources.

These ghosts, as Justin Vandenbroucke of the University of Wisconsin-Madison and an IceCube team member put it, are capable of solving two of astronomy’s great mysteries.

For starters, a plethora of galaxies in our Universe have gravitationally monstrous cavities at their centers, black holes that reach masses millions to billions of times larger than that of our Sun. And these black holes, when active, shoot out beams of light from their bowels — emitting enough light to outshine every single star in the galaxy itself. “We don’t understand how this happens,” said Vandenbrouke simply. Neutrinos could offer a way to study the regions around black holes.

Second, the general, but persistent, Mystery of cosmic rays.

We also don’t really know where cosmic rays come from, but these chains of particles reach energies millions of times higher than we can reach here on Earth with human-built particle accelerators those at CERN.

“We think neutrinos play a role,” said Vandenbroucke. “Something that may help us answer both of these mysteries of black holes powering very bright galaxies and the origins of cosmic rays.”

A decade to catch a handful

To be clear: IceCube doesn’t exactly capture neutrinos.

Basically, this observatory tells us every time a neutrino happens to interact with the ice that encases it. “Neutrinos rarely interact with matter,” emphasized Vandenbrouke. “But they interact sometimes.”

When millions of neutrinos shoot into the icy region where IceCube is placed, at least one tends to hit an ice atom, which then shatters and produces a flash of light. IceCube sensors capture this flash and send the signal to the surface, notifications that are then analyzed by hundreds of scientists.

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A representation of the IceCube detector shows the interaction of a neutrino with an ice molecule.

IceCube Collaboration/NSF

Ten years of flash data allowed the team to map fairly accurately where each neutrino appears to be coming from in the sky. It soon became clear that there was a dense region of neutrino emissions right where galaxy NGC 1068 is stationed.

But even with such evidence, Resconi said the team knows “it’s not time to open the champagne because we still have a fundamental question to answer. How many times has this alignment just happened by accident? How can we be sure that these are actually neutrinos coming from such an object?”

A graph of IceCube's latest sky results.  It shows where neutrinos appear to come from across the Universe and identifies the densest locations as sources.

A sky map from the Northern Hemisphere point source scan, showing where neutrinos appear to come from across the Universe. NGC 1068’s circle also coincides with the overall hottest spot in the northern sky.

IceCube collaboration

To make things as concrete as possible and really prove that this galaxy is spewing ghosts, “we ran the same experiment 500 million times,” Resconi said.

Which, as I can only imagine, was finally popped with a bottle of Veuve. Although the hunt is not over yet.

“We’re just beginning to scratch the surface of the search for new neutrino sources,” said Ignacio Taboada of the Georgia Institute of Technology and a member of the IceCube team. “There must be many other sources far deeper than NGC 1068 hiding somewhere to be found.”

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