Podcaster: Richard Drumm

Title: Space Scoop: Mystery Solved: Ghost Particles Come From Blazing Galaxies

Organization: 365 Days Of Astronomy

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Description: Space scoop, news for children. 

The South Pole is a hostile environment; it’s a frozen desert where temperatures can drop below -80°C.

Yet scientists have been flocking there for the last 8 years, because it’s one of the best places to go to answer a mystery: What shoots beams of tiny, almost undetectable particles at Earth?

Bio: Richard Drumm is President of the Charlottesville Astronomical Society and President of 3D – Drumm Digital Design, a video production company with clients such as Kodak, Xerox and GlaxoSmithKline Pharmaceuticals. He was an observer with the UVa Parallax Program at McCormick Observatory in 1981 & 1982. He has found that his greatest passion in life is public outreach astronomy and he pursues it at every opportunity.

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This is the 365 Days of Astronomy Podcast. Today we bring you a new episode in our Space Scoop series. This show is produced in collaboration with Universe Awareness, a program that strives to inspire every child with our wonderful cosmos.

Mystery Solved: Ghost Particles Come From Blazing Galaxies

The South Pole is a hostile environment; it’s a frozen desert where temperatures can drop below -80°C.

Yet scientists have been flocking there for the last 8 years, because it’s one of the best places to go to answer a mystery: What shoots beams of tiny, almost undetectable particles at Earth?

These particles, called neutrinos, are extremely difficult to catch. Tens of billions of these so-called “ghost particles” pass through your body every second without you even noticing. 

If you shine a flashlight at a wall the light will hit the wall but won’t travel through it. Something shining neutrinos would shine straight through the wall like the wall wasn’t even there!.

Heck, like the planet wasn’t even there!

However, every once in a while astronomers get a lucky break and one of these neutrinos is caught by a detector. 

To be more specific, in this case, the neutrinos hit a facility called the IceCube Neutrino Observatory, which is buried deep under the ice at the Amundsen-Scott South Pole Station.

Now, you might think that this observatory can only see half the sky from way down there, and with an optical observatory that’d be the case. But remember, neutrinos can pass right through the Earth, so this is one observatory that can see the whole sky at once! 

The neutrinos in today’s story came from a place that was 5.7° below the horizon when the neutrino event happened!

This detector has 5,160 sensors in an array a cubic kilometer in size, placed deep in the antarctic ice.

When this detection happened, back on September 22, 2017, computers at the site were able to quickly work out the rough direction from which the neutrino came. 

An automated system sent out a real-time alert 43 seconds after the event and asked telescopes around the world to hunt for the cosmic source.

A set of more accurate directional coordinates was distributed about 4 hours after the event which further improved accuracy.

Only .1° away from the predicted spot was a known gamma-ray source that was previously catalogued by a team using the Fermi LAT, or Large Area Telescope, part of the Fermi Gamma-ray Space Telescope.

The gamma-ray source was a blazar designated TXS 0506+056 in the constellation Orion. It had started shining three times brighter than normal in April of 2017, just 5 months before the neutrino detection event.

Now, a blazar is what we call an AGN, an active galactic nucleus, which has its jet pointed at us. Many AGNs have such jets of ionized matter spewing out along the axis of their rotation. 

When the jet is pointed toward us the AGN appears much brighter than it would otherwise, so we call it a blazar.

The chance that the neutrino detection event and the blazar both happening by random chance to be coming from the same part of the sky and that this was just a freak occurrence, that they are unrelated, is vanishingly low.

We can now say for the first time that gamma-ray emitting blazars are likely sources for at least some of the high energy neutrinos that astronomers have observed.

Hey Here’s A Cool Fact:The IceCube array doesn’t directly detect neutrinos. It detects secondary particles that are emitted when the neutrinos collide with the water molecules in the ice.

The collision of a neutrino with a water molecule produces electrons, muons or tau particles that emit the blue light of Cherenkov radiation. This happens when the particles are moving through the ice faster than the speed of light through that ice.

We know from Einstein’s equations that the speed of light in a vacuum is the ultimate speed limit in the Universe, that nothing with mass can ever be accelerated to or beyond that speed.

But the speed of light in a material – air, water, ice, whatever – is slower than its speed in a vacuum.

The speed of light in ice is 76% of the speed of light in a vacuum. Thus it’s quite possible to have particles move faster than light in ice, but still be slower than the Universe’s ultimate speed limit.

This creates Cherenkov radiation, which is analogous to the sonic boom that’s created when an airplane travels faster than the speed of sound. The sound of the airplane piles up in a shock wave off to the side of the plane.

The Cherenkov radiation’s blue light is similarly piled up to the side of the speeding muon, tau particle or electron. And it’s this blue light that IceCube detects.

Thank you for listening to the 365 Days of Astronomy Podcast!

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365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by Planetary Science Institute. Audio post-production by Richard Drumm. Bandwidth donated by and wizzard media. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at or email us at This year we will celebrates the Year of Everyday Astronomers as we embrace Amateur Astronomer contributions and the importance of citizen science. Join us and share your story. Until tomorrow! Goodbye!