May 29, 2023
Ghost particles falling in Antarctica reveal invisible heart of nearby galaxy

Why ghost particles falling in Antarctica could change astronomy forever

About 47 million light-years from where you sit, the center of a black hole-laden galaxy called NGC 1068 is spewing streams of enigmatic particles. They’re neutrinos — otherwise known as the elusive “ghost particles” that haunt our universe while leaving little trace of their existence.

Immediately after their creation, bundles of these invisible pieces sink into the cosmic expanse. They zip past bright stars we can see and zip through pockets of space filled with wonders we’ve yet to discover. They fly and fly and fly until, occasionally, they reach the Earth’s South Pole and burrow underground. Neutrino travel is seamless.

But scientists are patiently waiting for them to arrive.

Nestled in about 1 billion tons of ice, more than 2 kilometers (1.24 miles) below Antarctica, is the IceCube Neutrino Observatory. Neutrino hunter, you might say. And when any neutrino takes its party to the frozen continent, IceCube remains alert.

In a paper published Friday in the journal Science, the international team behind this ambitious experiment confirmed that it has found evidence of 79 “high-energy neutrino emissions” coming from where NGC 1068 is located, opening the door for innovative — and endlessly fascinating — kinds of physics. “Neutrino astronomy”, scientists call it.

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 laboratory at twilight, with a starry sky showing a glimpse of the Milky Way and sunlight lingering on the horizon.

Martin Wolf, IceCube/NSF

Before today, physicists had only shown neutrinos coming from either the sun. our planet’s atmosphere. a chemical mechanism called radioactive decay. supernova; and — thanks to IceCube’s first major discovery in 2017 — a blazar, or ravenous supermassive black hole pointed directly at Earth. An empty compiled TXS 0506+056.

With this new neutrino source, we are entering a new era in the particle’s history. In fact, according to the research team, it is possible that the neutrinos coming from NGC 1068 have up to millions, billions, maybe even trillions the amount of energy held by neutrinos originating in the sun or supernovae. These are amazing figures, because, in general, such ghosts are so powerful, but pointless, that every second, trillions of trillions of neutrinos move directly into your body. You just can’t tell.

And if you wanted to stop a neutrino in its tracks, you’d have to fight it with a block of lead a light-year wide — though even then, there’d be a fractional chance of success. So harnessing these particles, NCG 1068 version or not, could allow us to penetrate areas of the universe that would normally be inaccessible.

And now what?

Not only is this moment huge because it gives us more evidence of a strange particle that wasn’t even announced to exist until 1956, but also because neutrinos are like keys to the background of our universe.

They have the ability to reveal phenomena and solve puzzles that we are unable to tackle by any other means, and this is the main reason scientists are trying to develop neutrino astronomy in the first place.

“The universe has many ways of communicating with us,” Denise Caldwell of the National Science Foundation and a member of the IceCube team told reporters Thursday. “Electromagnetic radiation, which 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 local sources.

“One of those elementary particles was neutrinos that permeate the universe, but unfortunately, neutrinos are very difficult to detect.”

In fact, even the galaxy NGC 1068 and its supermassive black hole are usually hidden by a thick veil of dust and gas, making them difficult to analyze with standard optical telescopes and equipment — despite years of scientists trying to pierce its curtain . NASA’s James Webb Space Telescope could have a leg up in this case because of its infrared eyes, but neutrinos might be an even better way to get in.

These particles, expected to be created behind such opaque screens that filter our universe, can carry cosmic information behind these screens, zoom across great distances while interacting virtually with no other matter, and deliver pristine, untouched information. to humanity for elusive corners of space.

“We are very lucky, in a sense, because we can access an amazing understanding of this object,” Elisa Resconi, of the Technical University of Munich and a member of the IceCube team, said of NGC 1068.

ice cube

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


It is also notable that there are many (many) more galaxies similar to NGC 1068 — categorized as Seyfert galaxies — than there are blazars similar to TXS 0506+056. That means IceCube’s latest discovery is arguably a bigger step forward for neutrino astronomers than the observatory’s sperm.

Perhaps most of the neutrinos scattered throughout the universe have their origins in NGC 1068 doppelgangers. But in the grand scheme of things, there is much more to the value of neutrinos than just their sources.

These ghosts, as Justin Vandenbroucke of the University of Wisconsin-Madison and a member of the IceCube team put it, are apt to solve two big mysteries in astronomy.

First of all, a wealth of galaxies in our universe have gravitationally massive voids at their centers, black holes reaching masses millions to billions of times that of our sun. And these black holes, when active, shoot jets of light from their guts — emitting enough light to outshine every star in the galaxy itself. “We don’t understand how this happens,” Vandenbrouke said simply. Neutrinos could provide a way to study the regions around black holes.

The second is the general, but persistent, enigma of cosmic rays.

We don’t really know where cosmic rays come from, but these arrays of particles reach energies up to and beyond millions of times higher than we can reach here on Earth with man-made particle accelerators like the one at CERN.

“We think neutrinos have a role to play,” Vandenbroucke said. “Something that can help us answer these two mysteries of black holes powering very bright galaxies and the origin of cosmic rays.”

A decade to catch a handful

To be clear, IceCube doesn’t exactly trap neutrinos.

Basically, this observatory tells us every time a neutrino interacts with the ice covering it. “Neutrinos hardly interact with matter,” Vandenbrouke pointed out. “But they interact sometimes.”

As millions of neutrinos are blasted into the frozen region where the IceCube is set up, at least one tends to hit a chunk of ice, which then shatters and produces a flash of light. IceCube sensors record this flash and send the signal to the surface, alerts that are then analyzed by hundreds of scientists.


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

IceCube Collaboration/NSF

Ten years of light flare data allowed the team to map roughly where each neutrino appears to be coming from in the sky. It soon became clear that there was a dense neutrino emission region right where the galaxy NGC 1068 is located.

But even with such evidence, Resconi said the team knew “it’s not time to pop the champagne, because we still have a fundamental question to answer. How many times did this alignment happen by chance? How can we be sure that the neutrinos are does it actually come from such an object?”

A chart of the latest IceCube sky results.  It shows where neutrinos from around the universe seem to come from and pinpoints the densest locations as sources.

A sky map of the scan for point sources in the Northern Hemisphere, showing where neutrinos from across the universe appear to come from. NGC 1068’s cycle also coincides with the overall hottest spot in the northern sky.

IceCube collaboration

So to make things as specific as possible, and really, really prove that this galaxy is spewing ghosts, “we created 500 million times the same experiment,” Resconi said.

Upon which, I can only imagine, a bottle of Veuve was finally popped. Although the hunt is not over.

“We are just beginning to scratch the surface in terms of finding 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 much deeper than NGC 1068, hiding somewhere to be found.”

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