Absolute Beginner

Scientists have found where a tiny particle came from. The particle is called a neutrino. It came from a very faraway galaxy called the Shadow Blaster.

The Shadow Blaster is 11 billion light-years away from Earth. It is a galaxy full of new stars being born. A light-year is the distance light travels in one year.

Scientists used a special detector called IceCube to find the neutrino. IceCube is in Antarctica, under the ice. It detected the particle in 2021.

This is an important discovery. Scientists want to understand where these tiny particles come from in space. Now they know one source is a very distant, busy galaxy.

neutrino

a tiny particle with almost no mass that travels at nearly the speed of light

galaxy

a very large group of billions of stars held together by gravity

light-year

the distance that light travels in one year, about 9.5 trillion kilometres

telescope

a tool scientists use to observe distant objects in space

Antarctica

the frozen continent at the South Pole of the Earth

detect

to discover or find something using special instruments

particle

a very small piece of matter, much smaller than an atom

distant

very far away

Elementary

Astronomers have traced a high-energy neutrino to a distant galaxy called the Shadow Blaster. The galaxy is located about 11 billion light-years from Earth. A neutrino is a tiny subatomic particle that rarely interacts with matter and can travel across the universe almost without stopping.

The neutrino, identified as IceCube event IC 210922A, was detected by the IceCube Neutrino Observatory in Antarctica in September 2021. IceCube is buried more than two kilometres under the Antarctic ice and uses sensors to detect neutrinos passing through the Earth.

Scientists used the ALMA radio telescope and the Gemini North telescope to identify the Shadow Blaster as the source. The galaxy is a starburst galaxy, meaning it is forming new stars extremely rapidly. It appears brighter than it really is because another galaxy between us and the Shadow Blaster bends and magnifies its light, acting as a gravitational lens.

The discovery was published in Nature Astronomy in June 2026. Scientists believe that dense starburst galaxies like the Shadow Blaster may be responsible for a large portion of the high-energy neutrinos that arrive at Earth from all directions in space.

neutrino

an extremely small subatomic particle with almost no mass that can pass through almost any material

starburst galaxy

a galaxy that is forming new stars at a very high rate

gravitational lens

a massive object whose gravity bends and magnifies the light from objects behind it

subatomic

smaller than an atom; referring to particles that make up atoms

observatory

a building or instrument system used to observe astronomical objects

magnify

to make something appear larger or brighter than it really is

sensor

a device that detects and measures physical properties such as light, heat, or particles

cosmic

relating to the universe or outer space beyond Earth

Intermediate

A paper published in Nature Astronomy in June 2026 has identified the source of a high-energy astrophysical neutrino detected by the IceCube Neutrino Observatory in September 2021. The neutrino, designated IC 210922A, has been traced to a gravitationally lensed starburst galaxy known as the Shadow Blaster, located approximately 11 billion light-years from Earth at a redshift of roughly 2.4.

The identification relied on follow-up observations with the ALMA radio interferometer in Chile and the Gemini North telescope in Hawaii. A foreground galaxy between Earth and the Shadow Blaster acts as a gravitational lens, bending and amplifying the light from the more distant starburst. The Shadow Blaster has an extremely dense compact core, estimated at roughly 3,000 light-years across, with a molecular hydrogen column density greater than ten to the power of 25 per square centimetre.

Neutrinos from the Shadow Blaster are thought to be produced through hadronic processes: high-energy protons collide with other protons in the dense interstellar medium, producing charged pions that then decay into neutrinos. This mechanism is distinct from the neutrino production associated with active galactic nuclei powered by supermassive black holes, suggesting a broader class of sources for the cosmic neutrino background.

Of the approximately 82 IceCube events with energies above 100 teraelectronvolts, around 40 percent remain unattributed to a confirmed source. The Shadow Blaster result strengthens the case that dense starburst galaxies at high redshift may account for a significant fraction of this unresolved population. The finding has implications for next-generation observatories including IceCube-Gen2 and the SKA-Mid radio telescope.

redshift

the stretching of light to longer wavelengths as an object moves away, used to measure cosmic distances

hadronic process

a particle physics process involving protons or other heavy particles colliding and producing secondary particles

pion

a subatomic particle produced in high-energy collisions that can decay into neutrinos

active galactic nucleus

the extremely bright central region of a galaxy powered by material falling into a supermassive black hole

column density

the total number of atoms or molecules along a line of sight through a cloud or medium

interferometer

an instrument that combines signals from multiple telescopes to achieve very high resolution

teraelectronvolt

a unit of energy equal to one trillion electron volts, used to describe very high-energy particles

cosmic neutrino background

the diffuse flux of high-energy neutrinos arriving at Earth from all directions across the universe

Advanced

A June 2026 paper in Nature Astronomy presents the identification of IceCube event IC 210922A's astrophysical origin as a gravitationally lensed compact starburst galaxy at redshift z approximately 2.4, designated the Shadow Blaster following its NOIRLab press-release branding. The source was localised through multi-wavelength follow-up combining ALMA continuum and CO-line observations with Gemini North optical and near-infrared imaging, enabled by lensing magnification from an intervening galaxy that amplifies the background starburst's flux by an estimated factor of several. The Shadow Blaster's delensed core subtends approximately 3,000 light-years and exhibits a molecular hydrogen column density N(H2) exceeding 10^25 per square centimetre, placing it among the most gas-opaque systems known.

Neutrino production in the Shadow Blaster is attributed to hadronic pp interactions in the dense interstellar medium, followed by charged pion decay through the chain pi-plus to muon-neutrino plus muon, which further decays to electron-neutrino plus muon-antineutrino plus muon-neutrino. The absence of an identified active galactic nucleus in the system's spectral energy distribution distinguishes this mechanism from the AGN-dominated paradigm that has historically been favoured for explaining high-energy astrophysical neutrinos. The result instead implicates the collective action of massive stellar winds, supernova remnant shocks, and starburst-driven galactic superwinds as the hadronic accelerator.

The IceCube collaboration's catalogue of 82 astrophysical events exceeding 100 TeV retains roughly 40 percent without counterpart identification. The Shadow Blaster association, if representative, suggests that populations of compact, heavily obscured starburst galaxies at z between 2 and 3, broadly coincident with the cosmic star formation rate peak, may account for a substantial fraction of this unresolved component. This implies a physical coevolution between the cosmic infrared background and the diffuse astrophysical neutrino background at redshifts where both signals are observationally constrained but mechanistically underexplained.

The implications for detector design are significant. IceCube-Gen2's projected sensitivity improvement by a factor of five to ten in effective volume, combined with SKA-Mid's capacity to resolve radio continuum morphology in obscured starburst systems at cosmological distances, creates a synergistic programme: neutrino directional reconstruction at Gen2 with sub-degree precision could cross-correlate against SKA catalogues of high-redshift starbursts to statistically confirm or refute the population-level association hypothesised here. The Shadow Blaster thus transitions from an individual detection to the anchor point of a broader observational strategy for mapping the hadronic universe.

delensed

corrected for the magnifying effect of gravitational lensing to reveal the true properties of a background object

spectral energy distribution