We’re scientists with the IceCube Neutrino Observatory, which just announced new evidence for a source of high-energy neutrinos and cosmic rays. Ask Us Anything!
It's now after 3 p.m. ET and we are all going to sign off for now. Thanks for joining us for this AMA! Your questions have been great and we're really glad we could share our excitement and enthusiasm for this discovery with you. We do hope to come back later and answer some of those we couldn't get to during the AMA. IceCube has a lot more information on their website if you still have a question you need answered: https://icecube.wisc.edu/news/view/586 and you can find more here, too: https://news.wisc.edu/cosmic-rays/.
We’re posting this AMA early so people can follow along with our live press conference –https://www.youtube.com/c/VideosatNSF/live – and begin asking questions. We will start answering questions around 12:30 p.m. ET.
We’re Justin Vandenbroucke and Ali Kheirandish, two scientists at the Wisconsin IceCube Particle Astrophysics Center (WIPAC) and members of the IceCube Collaboration, an international project using a cubic kilometer of South Pole ice to detect and study neutrinos, some of the universe’s most mysterious particles.
Our team at IceCube, along with our partners at about 20 observatories on Earth and in space – including the Fermi Gamma-ray Space Telescope and the Major Atmospheric Gamma Imaging Cherenkov Telescope, or MAGIC – just announced today news of some of the first good evidence for a source of astrophysical neutrinos, and therefore, of cosmic rays. We are excited about these new results!
Cosmic rays were discovered more than a century ago and have been a mystery ever since. Earth is constantly being pelted by these extremely energetic particles, and we don’t know where most of them come from. But, we use neutrinos to help track them and now, we know more!
In September 2017, IceCube detected an extremely energetic neutrino coming from the direction of the Orion constellation. Automated systems immediately sent an alert to other telescopes around the world, and Fermi and MAGIC saw gamma rays coming from the same place.
That place was a blazar, a galaxy with a supermassive black hole that absorbs new material and shoots out galaxy-sized jets of energy and matter. These jets point toward Earth and the coincident observations of high-energy neutrinos and gamma rays indicate that these objects are almost certainly accelerating cosmic rays to high energies.
Cosmic rays are hard to pin down because they’re charged particles, which means their paths through the universe get distorted by magnetic fields. But objects that produce high-energy cosmic rays must also produce neutrinos, which have no charge and rarely interact with matter. This means they can travel in straight lines for billions of years.
At IceCube, we use a billion tons of ice to try to catch neutrinos. All this mass makes it more likely a neutrino is snared; otherwise it will continue on its straight path, undetected. On average, we catch only one neutrino for every million that cross IceCube, but when they do collide with a molecule of ice, this creates charged particles that travel faster than the speed of light in ice. This gives off Cherenkov radiation (the same effect that gives nuclear reactors their eerie blue glow) and thousands of light detectors one mile beneath the South Pole watch for this light.
We’d love to answer your questions about this discovery and about cosmic rays, IceCube, working at the South Pole, or what it’s like to collaborate with scientists all over the world. Thousands of our colleagues around the world are celebrating today, and we’d like to celebrate a bit with you, too.
Justin Vandenbroucke (JV) - University of Wisconsin–Madison professor of physics and astronomy. In addition to his work on neutrinos and gamma rays with IceCube and the Cherenkov Telescope Array, Justin runs the Distributed Electronic Cosmic-Ray Observatory, DECO, a citizen science project lets people around the world detect cosmic rays with their cell phones and tablets.
Ali Kheirandish (AK) - a postdoc in physics at UW–Madison. His research focuses on particle astrophysics with high-energy neutrinos – identifying the sources of cosmic neutrinos and searching for physics beyond the Standard Model of Particle Physics.
We are joined by Nahee Park (NP), a researcher focused on very high energy gamma-ray measurements as part of the VERITAS collaboration. She is currently a Bahcall Fellow at WIPAC, using IceCube data to study hadronic accelerators in the universe and working to develop future neutrino detectors.
We are also joined by colleagues from the Fermi telescope, here as /u/NASA, including:
Elizabeth Ferrara (EF) - deputy lead scientist, Fermi Science Support Center at NASA’s Goddard Space Flight Center
Tonia Venters (TV) - multimessenger theorist, Astroparticle Physics Laboratory at NASA’s Goddard Space Flight Center
Joseph Eggen (JE) - astrophysicist, Fermi Science Support Center at NASA’s Goddard Space Flight Center
Here’s more information about the discovery: https://news.wisc.edu/cosmic-rays/
And the two papers that were published today in Science: http://science.sciencemag.org/cgi/doi/10.1126/science.aat1378 and http://science.sciencemag.org/cgi/doi/10.1126/science.aat2890