Scientists involved in discovery of origins of ghost particles in space

Scientists from our University have played a key role in a momentous discovery about the origins of ‘ghostly’ particles from the distant universe that bombard Earth from billions of light years away.

The Leicester team from the Department of Physics & Astronomy are part of a global network of researchers that have helped to resolve a more than century-old riddle about what sends subatomic particles such as neutrinos and cosmic rays speeding through the universe.

Since they were first detected over one hundred years ago, cosmic rays—highly energetic particles that continuously rain down on Earth from space—have posed an enduring mystery: What creates and launches these particles across such vast distances? Where do they come from?

In this illustration, based on an aerial view near the South Pole, an artistic rendering of the IceCube detector shows the interaction of a neutrino with a molecule of ice. Credit: IceCube Collaboration/NSF
Because most cosmic rays are charged particles, their paths cannot be traced directly back to their sources due to the magnetic fields that fill space and warp their trajectories. But the powerful cosmic accelerators that produce them will also produce neutrinos. Neutrinos are uncharged particles, unaffected by even the most powerful magnetic field. Because they rarely interact with matter and have almost no mass—hence their sobriquet “ghost particle”—neutrinos travel nearly undisturbed from their accelerators, giving scientists an almost direct pointer to their source.

Two papers published this week in the journal Science have for the first time provided evidence for a known blazar as a source of high-energy neutrinos detected by the US National Science Foundation-supported IceCube observatory. A blazar is a giant elliptical galaxy with a massive, rapidly spinning black hole at its core. This blazar, designated by astronomers as TXS 0506+056, was first singled out following a neutrino alert sent by IceCube on Sept. 22, 2017.

Equipped with a nearly real-time alert system—triggered when a very high-energy neutrino collides with an atomic nucleus in the Antarctic ice in or near the IceCube detector—the observatory broadcast coordinates of the Sept. 22 neutrino alert to telescopes worldwide for follow-up observations.  Scientists from Leicester were involved in the observations by the Neil Gehrels Swift Observatory in orbit and the H.E.S.S. gamma-ray telescope in Namibia. The Swift observations confirmed the contemporary flaring of the blazar.

• Leicester is the UK’s leading space city, home to the National Space Centre, Space Park Leicester and the University of Leicester’s #outofthisworld space research.

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