Blazar glory

For the first time ever, a high- en­ergy neu­trino has been tracked to its source – a galaxy four bil­lion light years away.

Cosmos - - Digest -

Ev­ery sec­ond 100 tril­lion neu­tri­nos pass through your body. Th­ese ghostly par­ti­cles are among the most abun­dant in the uni­verse, but apart from the Sun and a su­per­nova in 1987, we’ve never known pre­cisely where they are com­ing from.

Now Ice­cube, a neu­trino de­tec­tor buried un­der the Antarc­tic ice, has pin­pointed a source: a vi­o­lent galaxy four bil­lion light years away that is spew­ing a jet of plasma in our di­rec­tion, ac­cord­ing to a pa­per pub­lished in Science by as­tronomers from the Ice­cube col­lab­o­ra­tion. Neu­tri­nos are the small­est fun­da­men­tal par­ti­cles – more than a mil­lion times lighter than an elec­tron – and very dif­fi­cult to de­tect. Ice­cube has de­tected only sev­eral hun­dred high­en­ergy neu­tri­nos since it be­gan op­er­at­ing in 2010.

Un­til now, none of those neu­tri­nos could be traced back to a spe­cific source. How­ever, when Ice­cube clocked a neu­trino last Septem­ber with the whop­ping en­ergy of nearly 300 ter­a­elec­tron­volts, a mes­sage went out to ob­ser­va­to­ries around the globe.

As tele­scopes swiv­elled in the di­rec­tion in­di­cated by Ice­cube, as­tronomers re­alised the source was an ul­tra-com­pact type of quasar, or “blazar”, called TXS 0506+056, in a galaxy four bil­lion light years away. Among the bright­est ob­jects in the uni­verse, quasars are jets of plasma re­leased as ga­lac­tic mat­ter is sucked into a black hole. In this case, one of the jets was aimed straight at the Earth.

As they stud­ied the blazar more closely they re­alised that de­spite its bright­ness, it was fur­ther away than they had thought, says Gary Hill, a mem­ber of the Ice­cube col­lab­o­ra­tion based at the Univer­sity of Ade­laide. “This neu­trino could have been trav­el­ling to us since around the for­ma­tion of the Earth.”

The Ice­cube team also went back through their data to see if other high­en­ergy neu­tri­nos had come from the same part of the sky. With care­ful sift­ing, they found some likely can­di­dates be­tween Septem­ber 2014 and March 2015.

The ev­i­dence seems to add up to a link be­tween high-en­ergy neu­tri­nos and TXS 0506+056, but Hill says we will need to see more flares from the blazar to put the is­sue beyond doubt.


Antarc­tica’s Ice­cube de­tec­tor has pin­pointed the in­ter­ga­lac­tic source of en­er­getic neu­tri­nos.

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