'King' of star explosions seen
May 11,2007 00:00 by Bend_Weekly_News_Sources

As­tro­no­mers have de­tected the bright­est stel­lar ex­plo­sion, or su­per­no­va, on rec­ord. They say it may be a new type of su­per­no­va that may also oc­cur be­fore long in our own ga­l­axy—what one re­search­er said would be his­to­ry’s most awe­some star show.

The find­ing comes from ob­ser­va­tions by NASA’s Chan­dra X ray Ob­serv­a­to­ry and ground-based tele­scopes. It in­di­cates vi­o­lent ex­plo­sions of ex­treme­ly mas­sive stars were fair­ly com­mon in the ear­ly uni­verse, sci­en­tists said.

“This was a tru­ly mon­strous ex­plo­sion, a hun­dred times more en­er­get­ic than a typ­i­cal su­per­no­va,” said Na­than Smith of the Uni­ver­si­ty of Cal­i­for­nia at Berke­ley, who led a team of as­tro­no­mers in the re­search. 

“That means the star that ex­plod­ed might have been as mas­sive as a star can get, about 150 times [the weight] of our sun. We’ve nev­er seen that be­fore.” 

As­tro­no­mers think many of the first gen­er­a­tion of stars were this mas­sive, and this new su­per­no­va may thus pro­vide a rare glimpse of how the first stars died.

The top pan­el is an artist's il­lus­tra­tion that shows what SN 2006gy may have looked like if viewed from near­by. The bot­tom left pan­el is an in­fra­red im­age from the Lick Ob­serv­a­to­ry, of NGC 1260, the gal­axy con­tain­ing SN 2006gy. The pan­el to the right shows Chan­dra's X-ray im­age of the same field of view, again show­ing the core of the gal­axy and SN 2006gy. (Image cre­dits: Il­lus­t­ra­tion: NA­SA/CXC/M. Weiss; X-ray: NA­SA/CXC/UC Ber­ke­ley/N. Smith et al.; IR: Lick/UC Ber­ke­ley/J. Bloom & C. Han­sen)

The su­per­no­va, known as SN 2006gy, pro­vides ev­i­dence that the death of such mas­sive stars is fun­da­men­tal­ly dif­fer­ent from the­o­ret­i­cal pre­dic­tions, re­search­ers claimed.

“Of all ex­plod­ing stars ev­er ob­served, this was the king,” said Al­ex Fil­ip­penko, lead­er of the ground-based ob­ser­va­tions at the Lick Ob­serv­a­to­ry at Mt. Ham­il­ton, Calif., and the Keck Ob­serv­a­to­ry in Mauna Kea, Ha­waii. 

“We were as­ton­ished to see how bright it got, and how long it last­ed.” The Chan­dra ob­ser­va­tion al­lowed the team to rule out the most like­ly al­ter­na­tive ex­pla­na­tion for the su­per­no­va, the as­tro­no­mers said: that a white dwarf star on­ly slight­ly heav­i­er than the sun ex­plod­ed in­to a dense, hydrogen-rich en­vi­ron­ment. In that event, SN 2006gy should have been 1,000 times brighter in X-ray light than what Chan­dra de­tected, they said.

“This pro­vides strong ev­i­dence that SN 2006gy was, in fact, the death of an ex­treme­ly mas­sive star,” said Dave Poo­ley of the Uni­ver­si­ty of Cal­i­for­nia at Berke­ley, who led the Chan­dra ob­ser­va­tions.

The star that pro­duced SN 2006gy ap­par­ent­ly blew off a large amount of mass be­fore ex­plod­ing, as­tro­no­mers said. This large mass loss is si­m­i­lar to that seen from Eta Cari­nae, a mas­sive star in our gal­axy, rais­ing sus­pi­cion that Eta Cari­nae may be poised to ex­plode as a su­per­no­va. Al­though SN 2006gy is in­trin­si­cal­ly the bright­est su­per­no­va ev­er, it is in the gal­axy NGC 1260, some 240 mil­lion light years away. Howev­er, Eta Cari­nae is on­ly about 7,500 light years away in our own Milky Way gal­axy. A light year is the dis­tance light travels in a year.

“We don’t know for sure if Eta Cari­nae will ex­plode soon, but we had bet­ter keep a close eye on it just in case,” said Ma­rio Livio of the Space Tel­e­scope Sci­ence In­sti­tute in Bal­ti­more, who was not in­volved in the re­search. “Eta Cari­nae’s ex­plo­sion could be the best star-show in the his­to­ry of mod­ern civ­i­liza­tion.” 

Su­per­novas usu­al­ly oc­cur when mas­sive stars ex­haust their fu­el and col­lapse un­der their own grav­i­ty. In the case of SN 2006gy, as­tro­no­mers think some­thing else may have trig­gered the blast. Un­der some con­di­tions, a mas­sive star’s co­re could pro­duce so much ra­di­a­tion in the form of gam­ma rays that some of the en­er­gy from the ra­di­a­tion con­verts in­to mat­ter. This takes the form of par­t­i­cles paired up with en­ti­ties that are in a sense their evil twins, called anti-par­t­i­cles. This leads to a drop in en­er­gy that causes the star to col­lapse un­der its own mighty grav­i­ty.

Next, runa­way ther­mo­nu­cle­ar re­ac­tions en­sue and the star ex­plodes, spew­ing the re­mains in­to space. The SN 2006gy da­ta sug­gest that it may have been more com­mon than pre­vi­ously be­lieved for the first stars to die in spec­tac­u­lar su­per­no­vas, ast­ro­nom­ers said. An alternative fate theo­rized for these ob­jects is to col­lapse into black holes, ob­jects so com­pact that their gra­vi­ta­tion­al force runs out of cont­rol and they start to suck in everything near­by, in­clud­ing light.

“In terms of the ef­fect on the ear­ly uni­verse, there’s a huge dif­fer­ence be­tween these two pos­si­bil­i­ties,” said Smith. “One pol­lutes the gal­axy with large quan­ti­ties of new­ly made el­e­ments and the oth­er locks them up for­ev­er in a black hole.” The find­ings  are to ap­pear in a forth­com­ing issue of the re­search pub­li­ca­tion As­t­ro­phys­i­cal Jour­nal.




Courtesy NASA Marshall Space Flight Center and World Science staff