First look
The idea, in plain words
This building stands on the ice at the South Pole, and the telescope it belongs to is underneath it. It does not collect light from the sky. It waits for particles called neutrinos that have come up through the whole Earth. Light is still how nearly everything about space is learnt, but three other messengers now arrive as well.
Neutrinos are the hardest to stop. They are made wherever atoms are being built or broken, in the middle of the Sun above all, and they go through rock as if it were not there. Tens of billions of them from the Sun pass through every square centimetre of you each second, by night as well as by day, because at night they simply come up through the ground.
Catching one takes a huge detector and a lot of patience. Under that building, 5,160 light sensors hang on 86 cables frozen into the ice, between about one and a half and two and a half kilometres down. Together they watch a cubic kilometre of clear ice. Once in a long while a neutrino hits an atom in it and makes a faint streak of light, and the sensors record the streak.
Neutrinos bring news from places light cannot get out of. When this star blew up in 1987, three detectors caught 25 neutrinos from its collapsing core. They were recorded before anyone saw the light, because light has to work its way out through the star and neutrinos do not.
Cosmic rays are the second messenger. They are the bare centres of atoms, mostly hydrogen, flung across space at nearly the speed of light. When one hits the top of the air it breaks into a shower of smaller particles miles long, and it is the shower that is caught. In 1991 one single particle arrived carrying as much energy as a hard tennis serve.
The third messenger is a ripple in space itself, set off when very heavy things collide. On 17 August 2017 the ripples from two neutron stars crashing together reached the Earth, and 1.7 seconds later so did a flash of gamma rays. Telescopes then found this fading glow in a galaxy 130 million light years away. It was the first event caught by ripples and by light together.
Go deeper
That was the idea. The same subject is written again below for readers who want more, each on a page of its own.
Words used here
- Neutrino
- A particle with almost no mass that passes through ordinary matter nearly untouched.
- Gravitational wave
- A ripple in space itself, sent out when very heavy things move violently.
- Supernova
- The explosion of a star. For a few weeks it can outshine a whole galaxy.
- Neutron star
- The crushed core left by an exploded star: more than the Sun's mass in a ball about 20 km across.
- Blazar
- An active galaxy with a jet pointing almost straight at the Earth.
- Magnetic field
- The region round a magnet, or round moving electric charge, in which other magnets and charges feel a force.
- Speed of light
- 299,792,458 metres per second in empty space, the fastest that anything can carry news from one place to another.
Where this comes from
- IceCube Neutrino Observatory, The detector
- USGS, The IceCube lab in the South Pole (photograph, public domain)
- Nobel Prize in Physics 2002 (neutrinos from the Sun and from a supernova)
- IceCube, Neutrinos point to long-sought cosmic ray accelerator (2018)
- Panagia 2004, SN 1987A: the unusual explosion of a normal Type II supernova
- NASA Imagine the Universe, Cosmic rays
- Bird and others 1995, Detection of a cosmic ray with measured energy well beyond the expected cutoff
- Abbott et al. 2017, The Astrophysical Journal Letters 848, L12
The words are written for this site. The pictures are drawn by the page from the figures in the lesson, and each one says underneath what it is based on.