The star that DIED TWICE

This su­per­nova “breaks ev­ery­thing we thought we knew”

Sky at Night Magazine - - BULLETIN -

Like a ce­les­tial hor­ror vil­lain, an ex­ploded star has burst back to life af­ter 50 years. This su­per­nova, which ex­ploded in 2014 but only re­cently faded, may be the re­vived rem­nant of a pre­vi­ous ex­plo­sion wit­nessed in 1954.

In Septem­ber 2014, the in­ter­me­di­ate Palo­mar Tran­sient Fac­tory team at the Univer­sity of Cal­i­for­nia, Santa Bar­bara (USCB) dis­cov­ered a new su­per­nova in a dis­tant galaxy named iPTF14hls. At first it ap­peared to be a run-of-the-mill Type II-P su­per­nova, one caused by the rapid col­lapse of a mas­sive star, and should have dimmed af­ter 100 days or so. In­stead, af­ter a few months it be­gan to grow in bright­ness, and re­mained bright for around 600 days.

“Su­per­nova iPTF14hls may be the most mas­sive stel­lar ex­plo­sion ever seen,” says Lars Bild­sten, di­rec­tor of USBC’s Kavli In­sti­tute for The­o­ret­i­cal Physics. “For me, the most re­mark­able as­pect of this su­per­nova was its long du­ra­tion, some­thing we have never seen be­fore. It cer­tainly puz­zled all of us as it just con­tin­ued shin­ing.”

When con­sult­ing archival data, the team found that a su­per­nova had pre­vi­ously been seen in 1954 in the same lo­ca­tion. Some­how, the star had sur­vived to ex­plode again 50 years later. This ear­lier ex­plo­sion could be an im­por­tant clue to the su­per­nova’s true iden­tity.

Some re­searchers sug­gest that this is the first ob­served ex­am­ple of a pul­sa­tional pairin­sta­bil­ity su­per­nova. These oc­cur when mas­sive stars be­come hot enough to con­vert en­ergy into mat­ter and an­ti­mat­ter, cre­at­ing an ex­plo­sion that blows off the star’s outer lay­ers while leav­ing the core in­tact. The process could re­peat it­self for decades.

“These ex­plo­sions were only ex­pected to be seen in the early Uni­verse and should be ex­tinct to­day,” says Andy How­ell who leads the su­per­nova group at the Las Cum­bres Ob­ser­va­tory. “This is like find­ing a di­nosaur still alive to­day. If you found one, you would ques­tion whether it truly was a di­nosaur.”

How­ever, it could be that iPTF14hls is a com­pletely new type of su­per­nova.

“This su­per­nova breaks ev­ery­thing we thought we knew about how they work,” says Iair Ar­cavi from UCSB, the study’s lead au­thor. “It’s the big­gest puz­zle I’ve en­coun­tered in al­most a decade of study­ing stel­lar ex­plo­sions.”

The su­per­nova was sup­posed to fade away; that it hasn’t has sur­prised astronomer­s

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