Why ghost particles crashing into Antarctica could change astronomy forever

About 47 million light-years from where you’re sitting, the center of a black hole-laden galaxy named NGC 1068 spews streams of enigmatic particles. These are neutrinos – otherwise known as the elusive “ghost particles” that haunt our universe while leaving little trace of their existence.

Immediately after coming into existence, beams of these invisible pieces plunge through the cosmic expanse. They pass bright stars we can see and pass pockets of space full of wonders we have yet to discover. They fly and fly and fly until, occasionally, they reach the South Pole of the Earth and bore underground. Neutrino travel is continuous.

But scientists are patiently awaiting their arrival.

Nestled in about 1 billion tons of ice, more than 2 kilometers (1.24 miles) below Antarctica, is the IceCube Neutrino Observatory. A neutrino hunter, you might say. And when neutrinos transfer their group to the freezing continent, IceCube remains vigilant.

In a paper published Friday in the journal Science, the international team behind the ambitious experiment confirmed they had found evidence of 79 “high-energy neutrino emissions” from where NGC is located. 1068, opening the door to novel — and infinitely fascinating — types of physics. “Neutrino astronomy”, scientists call it.

It would be a branch of astronomy capable of doing what existing branches simply cannot do.

A starry sky shows the heart of the Milky Way.  On the ground is the snow-covered 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 overhead and sunlight lingering on the horizon.

Martin Wolf, IceCube/NSF

Before today, physicists had only shown neutrinos from either the sun; the atmosphere of our planet; a chemical mechanism called radioactive decay; supernovae; and – thanks to IceCube’s first breakthrough in 2017 – a blazar, or voracious supermassive black hole pointed directly at Earth. A void named TXS 0506+056.

With this new source of neutrinos, we are entering a new era in the history of the particle. In fact, according to the research team, it’s likely that neutrinos from NGC 1068 have up to millions, billions, maybe even trillion the amount of energy held by neutrinos rooted in the sun or supernovae. These are jaw-dropping numbers because, in general, these ghostly fragments are so powerful, yet elusive, that every second billions and billions of neutrinos are moving through your body. You can’t tell.

And if you wanted to stop a neutrino in its tracks, you’d need to fight it with a light-year block of lead – although even then there would be a fraction of a chance of success. Thus, exploiting these particles, NCG 1068 version or not, could allow us to penetrate into areas of the cosmos that would usually be out of reach.

Now what?

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

They have the ability to reveal phenomena and solve puzzles that we cannot solve by any other means, which is the main reason why scientists are trying 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 member of the IceCube team told reporters Thursday. “Electromagnetic radiation, which we see as starlight, gravitational waves that shake the fabric of space – and elementary particles, such as protons, neutrons and electrons spewed out from localized sources.

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

In fact, even galaxy NGC 1068 and its gargantuan black hole are mostly obscured by a thick veil of dust and gas, making them difficult to analyze with standard telescopes and optical equipment – ​​despite years of scientists trying to break through. its curtain. NASA’s James Webb Space Telescope might have a head start in this case due to its infrared eyes, but neutrinos might be an even better way in.

Intended to be generated behind such opaque screens filtering our universe, these particles can carry cosmic information behind these screens, zoom great distances while interacting with virtually no other matter, and provide humanity with pristine and untouched information about the elusive corners of outer space.

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

ice Cube

In this artistic rendering, based on an actual image from the IceCube lab at the South Pole, a distant source emits neutrinos that are detected under the ice by IceCube sensors, called DOMs.


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

Perhaps the bulk of neutrinos scattering in the universe are rooted in NGC 1068 lookalikes. But in the grand scheme of things, neutrino merit is not limited to their sources.

These ghosts, as Justin Vandenbroucke of the University of Wisconsin-Madison and a member of the IceCube team have said, are adept at solving two major mysteries in astronomy.

First, a host of galaxies in our universe have gravitationally monstrous voids at their centers, black holes reaching masses millions to billions of times greater than our sun. And these black holes, when active, blast jets of light from their innards – emitting enough illumination to dwarf 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.

Second, there is the general, but persistent, cosmic ray conundrum.

We don’t really know where cosmic rays come from either, but these strings of particles reach energies up to and beyond millions of times greater than what we can reach here on Earth with particle accelerators built by man like that of 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 whenever a neutrino interacts with the ice that envelops it. “Neutrinos barely interact with matter,” Vandenbrouke pointed out. “But they sometimes interact.”

As millions of neutrinos shoot into the icy region where IceCube is installed, at least one tends to collide with a grain of ice, which then shatters and produces a flash of light. IceCube sensors capture this flash and send the signal to the surface, notifications which are then analyzed by hundreds of scientists.


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

IceCube/NSF Collaboration

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

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

A diagram of the latest IceCube results on the sky.  It shows where neutrinos appear to come from across the universe and identifies the densest places as sources.

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

IceCube Collaboration

So to make it as concrete as possible and to really, really prove that this galaxy spits out ghosts, “we generated the same experiment 500 million times,” Resconi said.

Whereupon, I can only imagine, a bottle of Widow finally popped. Although the hunt is not over.

“We are only beginning to scratch the surface when it comes to finding new sources of neutrinos,” 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, hidden somewhere to be found.”

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