dme depicted a swarm of stars with a trifling flare that i had to put close to my face to see。
this； evans told me； was a star in a constellation called fornax from a galaxy known toastronomy as ngc1365。 （ngc stands for new general catalogue； where these things arerecorded。 once it was a heavy book on someone’s desk in dublin； today； needless to say； it’sa database。） for sixty million silent years； the light from the star’s spectacular demise traveledunceasingly through space until one night in august of 2001 it arrived at earth in the form ofa puff of radiance； the tiniest brightening； in the night sky。 it was of course robert evans onhis eucalypt…scented hillside who spotted it。
“there’s something satisfying； i think；” evans said； “about the idea of light traveling formillions of years through space and just at the right moment as it reaches earth someonelooks at the right bit of sky and sees it。 it just seems right that an event of that magnitudeshould be witnessed。”
supernovae do much more than simply impart a sense of wonder。 they e in severaltypes （one of them discovered by evans） and of these one in particular； known as a iasupernova； is important to astronomy because it always explodes in the same way； with thesame critical mass。 for this reason it can be used as a standard candle to measure theexpansion rate of the universe。
in 1987 saul perlmutter at the lawrence berkeley lab in california； needing more iasupernovae than visual sightings were providing； set out to find a more systematic method ofsearching for them。 perlmutter devised a nifty system using sophisticated puters andcharge…coupled devices—in essence； really good digital cameras。 it automated supernovahunting。 telescopes could now take thousands of pictures and let a puter detect thetelltale bright spots that marked a supernova explosion。 in five years； with the new technique；perlmutter and his colleagues at berkeley found forty…two supernovae。 now even amateursare finding supernovae with charge…coupled devices。 “with ccds you can aim a telescope atthe sky and go watch television；” evans said with a touch of dismay。 “it took all the romanceout of it。”
i asked him if he was tempted to adopt the new technology。 “oh； no；” he said； “i enjoy myway too much。 besides”—he gave a nod at the photo of his latest supernova and smiled—“ican still beat them sometimes。”
the question that naturally occurs is “what would it be like if a star exploded nearby？” ournearest stellar neighbor； as we have seen； is alpha centauri； 4。3 light…years away。 i hadimagined that if there were an explosion there we would have 4。3 years to watch the light ofthis magnificent event spreading across the sky； as if tipped from a giant can。 what would itbe like if we had four years and four months to watch an inescapable doom advancing towardus； knowing that when it finally arrived it would blow the skin right off our bones？ wouldpeople still go to work？ would farmers plant crops？ would anyone deliver them to the stores？
weeks later； back in the town in new hampshire where i live； i put these questions to johnthorstensen； an astronomer at dartmouth college。 “oh no；” he said； laughing。 “the news ofsuch an event travels out at the speed of light； but so does the destructiveness； so you’d learnabout it and die from it in the same instant。 but don’t worry because it’s not going to happen。”
for the blast of a supernova explosion to kill you； he explained； you would have to be“ridiculously close”—probably within ten light…years or so。 “the danger would be varioustypes of radiation—cosmic rays and so on。” these would produce fabulous auroras；shimmering curtains of spooky light that would fill the whole sky。 this would not be a goodthing。 anything potent enough to put on such a show could well blow away themagnetosphere； the magnetic zone high above the earth that normally protects us fromultraviolet rays and other cosmic assaults。 without the magnetosphere anyone unfortunateenough to step into sunlight would pretty quickly take on the appearance of； let us say； anovercooked pizza。
the reason we can be reasonably confident that such an event won’t happen in our cornerof the galaxy； thorstensen said； is that it takes a particular kind of star to make a supernova inthe first place。 a candidate star must be ten to twenty times as massive as our own sun and“we don’t have anything of the requisite size that’s that close。 the universe is a mercifully bigplace。” the nearest likely candidate he added； is betelgeuse； whose various sputterings havefor years suggested that something interestingly unstable is going on there。 but betelgeuse isfifty thousand light…years away。
only half a dozen times in recorded history have supernovae been close enough to bevisible to the naked eye。 one was a blast in 1054 that created the crab nebula。 another； in1604； made a star bright enough to be seen during the day for over three weeks。 the mostrecent was in 1987； when a supernova flared in a zone of the cosmos known as the largemagellanic cloud； but that was only barely visible and only in the southern hemisphere—andit was a fortably safe 169；000 light…years away。
supernovae are significant to us in one other decidedly central way。 without them wewouldn’t be here。 you will recall the cosmological conundrum with which we ended the firstchapter—that the big bang created lots of light gases but no heavy elements。 those camelater； but for a very long time nobody could figure out how they came later。 the problem wasthat you needed something really hot—hotter even than the middle of the hottest stars—toforge carbon and iron and the other elements without which we would be distressingly immaterial。 supernovae provided the explanation； and it was an english cosmologist almostas singular in manner as fritz zwicky who figured it out。
he was a yorkshireman named fred hoyle。 hoyle； who died in 2001； was described in anobituary in nature as a “cosmologist and controversialist” and both of those he most certainlywas。 he was； according to nature ’s obituary； “embroiled in controversy for most of his life”
and “put his name to much rubbish。” he claimed； for instance； and without evidence； that thenatural history museum’s treasured fossil of an archaeopteryx was a forgery along the linesof the piltdown hoax； causing much exasperation to the museum’s paleontologists； who had tospend days fielding phone calls from journalists from all over the world。 he also believed thatearth was not only seeded by life from space but also by many of its diseases； such asinfluenza and bubonic plague； and suggested at one point that humans evolved projectingnoses with the nostrils underneath as a way of keeping cosmic pathogens from falling intothem。
it was he who coined the term “big bang；” in a moment of facetiousness； for a radiobroadcast in 1952。 he pointed out that nothing in our understanding of physics could accountfor why everything； gathered to a point； would suddenly and dramatically begin to expand。
hoyle favored a steady…state theory in which the universe was constantly expanding andcontinually creating new matter as it went。 hoyle also realized that if stars imploded theywould liberate huge amounts of heat—100 million degrees or more； enough to begin togenerate the heavier elements in a process known as nucleosynthesis。 in 1957； working withothers； hoyle showed how the heavier elements were formed in supernova explosions。 forthis work； w。 a。 fowler； one of his collaborators； received a nobel prize。 hoyle； shamefully；did not。
according to hoyle’s theory； an exploding star would generate enough heat to create all thenew elements and spray them into the cosmos where they would form gaseous clouds—theinterstellar medium as it is known—that could eventually coalesce into new solar systems。
with the new theories it became possible at last to construct plausible scenarios for how wegot here。 what we now think we know is this：
about 4。6 billion years ago； a great swirl of gas and dust some 15 billion miles acrossaccumulated in space where we are now and began to aggregate。 virtually all of it—99。9percent of the mass of the solar system—went to make the sun。 out of the floating materialthat was left over； two microscopic grains floated close enough together to be joined byelectrostatic forces。 this was the moment of conception for our planet。 all over the inchoatesolar system； the same was happening。 colliding dust grains formed larger and larger clumps。
eventually the clumps grew large enough to be called planetesimals。 as these endlesslybumped and collided； they fractured or split or rebined in endless random permutations；but in every encounter there was a winner； and some of the winners grew big enough todominate the orbit around which they traveled。
it all happened remarkably quickly。 to grow from a tiny cluster of grains to a baby planetsome hundreds of miles across is thought to have taken only a few tens of thousands of years。
in just 200 million years； possibly less； the earth was essentially formed； though still moltenand subject to constant bombardment from all the debris that remained floating about。
at this point； about 4。5 billion