The good news is that you can sleep easy tonight, because this scenario would not happen. Life on Earth is safe from such an event. Superluminous supernovae \u2013 up to 100 times as powerful as any stellar explosion previously known \u2013 are not only very rare, but appear to detonate in galaxies quite a bit different from our own.<\/p>\n
In 1931, Fritz Zwicky<\/a> and Walter Baade, working at the California Institute of Technology in Pasadena, made an astonishing claim about exploding stars, or \u2018novae\u2019. Their work built on a discovery made eight years earlier by Edwin Hubble, who had used what was then the biggest telescope in the world (the 2.5m Hooker Telescope on Mount Wilson, which overlooks Caltech) to show that the mysterious spiral nebulae were in fact galaxies \u2013 great islands of stars separate from the Milky Way and millions of light-years away.<\/p>\n Zwicky and Baade noticed that sometimes such galaxies hosted stellar explosions, capable of outshining 100 billion normal stars. Knowing that such explosions were enormously further away than ones in our Galaxy, the two astronomers concluded that they belonged to a new class they called \u2018supernovae\u2019, around 10 million times more luminous than standard novae.<\/p>\n Read more about supernovae:<\/strong><\/p>\n The latest leap in luminosity is not as big as a factor of 10 million, but it is still impressive. A superluminous supernovae is about 10 times as luminous as a Type Ia supernova, which is powered by a star-shattering explosion of a white dwarf \u2013 a compact stellar remnant about the size of Earth \u2013 that has been swamped by matter from a companion star. And it\u2019s about 100 times as powerful as a Type II supernova, the other main type of supernova, which is powered by the implosion of the core of a massive star at the end of its life.<\/p>\n The first superluminous supernova was discovered in 2005 and they were widely recognised as a distinct class of stellar explosion in 2011, principally by the work of Prof Robert Quimby of San Diego State University.<\/p>\n Their existence has come as a big shock to the astronomical community. \u201cWe thought we\u2019d discovered all classes of exploding stars,\u201d says Dr Matt Nicholl<\/a> of the University of Birmingham. \u201cHow in the world did we miss the brightest ones?\u201d<\/p>\n One reason superluminous supernovae went unnoticed until the 21st Century is they\u2019re extremely rare, accounting for only about one in every 10,000 supernovae. The other reason is that supernova searches with telescopes tended to concentrate on big galaxies, with astronomers \u2013 quite understandably \u2013 reasoning that the more stars in a galaxy, the greater the chance of one going supernova.<\/p>\n Nature, however, had other ideas: it put superluminous supernovae into dwarf galaxies. \u201cOnly with the advent of robotic telescopes with wide fields of view were dwarf galaxies caught in our net,\u201d explains Nicholl. \u201cOnce that started happening, we spotted superluminous supernovae. So far about 100 have been found.\u201d<\/p>\n What kind of stars are detonating as such cosmic mega-explosions? The biggest clue comes from the explosions\u2019 spectra \u2013 the way in which the light varies with energy, or equivalent frequency. Astronomers can see the spectral fingerprint of heavy elements such as carbon, oxygen and neon, but not of the lightest two elements: hydrogen and helium. To grasp what this means, it\u2019s necessary to understand something about the evolution of stars.<\/p>\n A star like the Sun fuses together the cores, or nuclei, of atoms of hydrogen to make helium, with the by-product being sunlight. But in stars that are between 8 and 25 times as massive as the Sun, conditions in the core can become dense enough and hot enough to fuse helium into carbon, carbon into oxygen, oxygen into neon, and so on. Potentially, such fusion reactions can proceed all the way up to iron, at which point they cease to generate any more heat (the hot gas of the core, no longer able to stop gravity from crushing it, promptly implodes).<\/p>\n The result is a star with an onion-like structure: the heaviest elements are in the core with each successive layer containing lighter elements, culminating in helium and finally hydrogen in the outer mantle. \u201cSomehow the stars that detonate as superluminous supernovae have lost this hydrogen and helium,\u201d says Nicholl.<\/p>\n The obvious way for a star to be stripped of its outer mantle of hydrogen and helium is via a stellar wind, similar to but far more powerful than the 1,000,000mph solar wind that blows from the Sun.<\/p>\n The problem is that stellar winds are stronger in stars that have a smattering of heavy elements mixed in with their hydrogen and helium mantle. Yet the low-mass galaxies in which the precursors of superluminous supernovae are located are deficient in such elements. This is basically because the galaxies\u2019 weak gravities haven\u2019t been\u00a0able to hang on to any heavy elements forged in earlier generations of stars and blasted into space by ordinary supernova.<\/p>\n Another way for a star to be stripped of its mantle of hydrogen and helium is if it\u2019s in a close binary star system and the gravity of a massive companion star has stripped it off. \u201cThis seems the most likely possibility,\u201d says Nicholl.<\/p>\n The $64,000 question is of course: what powers these mega stellar explosions? An obvious possibility is that they\u2019re merely souped-up versions of standard supernovae, whose power source is ultimately gravitational energy.<\/p>\n To understand gravitational energy, think of slate falling off a roof onto the ground. The slate\u2019s gravitational potential energy (the energy it has due its height in Earth\u2019s gravitational field) is converted into the energies of motion, sound and heat. Similarly, when the core of a star implodes, it\u2019s like countless quadrillion slates falling, and results in a tremendous amount of gravitational energy that\u2019s converted into a tremendous amount of heat. It is implosion, ironically, that drives explosion!<\/p>\n In a superluminous supernova, the spectrum reveals that between 5 and 20 solar masses of oxygen are ejected. In comparison, two to four solar masses of oxygen are ejected in a Type Ic supernova, which occurs in a standard star stripped of hydrogen and helium.<\/p>\n The implication is that the stars are only a few times bigger than the stars responsible for normal supernovae, and so a standard explosion is unlikely to make them 10 times as luminous.<\/p>\n The clincher for why superluminous supernovae are not simply souped-up versions of standard supernovae is that a normal supernova stays bright for a month or so because it\u2019s powered by the radioactive decay of nickel-56 and cobalt-56, forged in the fury of the initial explosion. \u201cHowever, something like 20 solar masses of such elements are needed to power a superluminous supernovae,\u201d says Nicholl. \u201cThough we see about 20 solar masses of oxygen, we don\u2019t see an equivalent amount of nickel and cobalt.\u201d<\/p>\n Another possible mechanism for a superluminous supernova involves the blast wave, expanding through space at about 10,000 kilometres a second, slamming into a slow-moving circumstellar shell of matter ejected by the star some time before the explosion. The rapid slowdown of the blast wave would shock heat the ejecta very efficiently, converting its energy of motion into prodigious amounts of heat and light.<\/p>\n \u201cThe problem is we don\u2019t see any evidence of slow-moving stuff in the spectra of superluminous supernovae,\u201d says Nicholl.<\/p>\n This leaves a final candidate for the engine of superluminous supernova. When the core shrinks, the endpoint is a highly compact object, such as a neutron star. Such an object, with a mass comparable to the Sun, but merely the size of Mount Everest, would be expected to be spinning fast, for the same reason that an ice skater who pulls in their arms spins faster: conservation of angular momentum. In fact, such an object could be spinning as fast as 1,000 times a second!<\/p>\n \u201cSuch an extraordinary flywheel has more than enough rotational energy to energise a superluminous supernova, if there is some way to transfer that energy outwards,\u201d says Nicholl. \u201cFortunately, there is.\u201d<\/p>\n When the core of a star implodes catastrophically, any magnetic field that the star possessed is enormously concentrated and amplified. The neutron star may end up with a prodigious magnetic field \u2013 these neutron stars are known as \u2018magnetars\u2019. The magnetic field of such a magnetar could be in the range 1012<\/sup> (a trillion) to 1015<\/sup> (1,000 trillion) gauss (a unit that measures magnetic fields). For comparison, even the minimal field is 100 billion times stronger than a fridge magnet.<\/p>\n The problem is that the bigger the magnetic field, the more it interacts with surrounding material and the faster this interaction \u2018brakes\u2019 the magnetar\u2019s rotation. \u201cTo keep a supernova bright for the month or so observed, a lower magnetic field is necessary,\u201d says Nicholl. \u201cThere is a sweet spot at about 1013<\/sup> to 1014<\/sup> gauss.\u201d<\/p>\n The precise mechanism by which the magnetar supplies energy to the material ejected by the star is not yet known. But Nicholl says there\u2019s a way to prove or disprove the idea of a magnetar-as-central-engine. Its magnetic field is so strong it will conjure electron-positron pairs out of the surrounding vacuum, and their subsequent annihilation should create a distinctive spike of high-energy light, or gamma rays. \u201cThe falloff of gamma rays should precisely track the spin down of the magnetar,\u201d says Nicholl.<\/p>\n \u201cI think the magnetar model is the odds-on favourite for powering most superluminous supernovae,\u201d says Quimby. \u201cSome supernovae mark the births of neutron stars, and tapping just a small fraction of the energy from such beasts ought to be enough to produce some remarkable fireworks.\u201d<\/p>\n But not everyone agrees that magnetars are the engines of superluminous supernovae. \u201cI favour a mechanism where the ejecta from energetic supernova collide with massive circumstellar matter and the supernova kinetic energy is efficiently converted into radiation,\u201d says Dr Takashi Moriya<\/a> of the National Astronomical Observatory of Japan. But he concedes: \u201cThere may not be a single mechanism that makes supernovae extremely bright.\u201d<\/p>\n Although it has taken almost two decades to find the first 100 superluminous supernovae, the discovery rate will soon be boosted by the Vera C Rubin Observatory when it begins operating in Chile in October 2023. The telescope will observe the whole sky, night after night. \u201cThis ability will utterly transform the field,\u201d says Nicholl. \u201cInstead of 100 in 15 years, we\u2019re expecting to discover 1,000 superluminous supernovae every year!\u201d<\/p>\n An even more mouthwatering prospect will be provided by NASA\u2019s James Webb Space Telescope<\/a>, the successor to Hubble. With its 6.5m mirror (4.5 times the collecting area of Hubble), it will be able to detect superluminous supernovae at greater distances, which because of the finite speed of light, means at earlier cosmic times.<\/p>\n At the dawn of the Universe, there were many more dwarf galaxies in existence than now because they had not had time to merge to form the giant galaxies, such as the Milky Way, that we see today. They were also depleted in heavy elements because stars had not had time since the Big Bang<\/a> to synthesise them. And there are theoretical reasons to believe that the first generation of stars to form after the Big Bang were monsters \u2013 possibly more than 100 solar masses. \u201cSuperluminous supernovae could easily have been more common at the beginning of time,\u201d says Nicholl.<\/p>\n This raises an interesting possibility. The iron in your blood, the calcium in your bones, the oxygen that fills your lungs each time you take a breath\u2026 all of these were forged inside stars that lived and died, blowing themselves to smithereens, before Earth and the Sun were born. Perhaps superluminous supernova contributed a significant fraction of the heavy elements in the Universe. In which case, you may not need to look far to see the fruits of the superluminous supernovae. Just hold up your hand!<\/p>\n The first exploding stars were recorded by Chinese astronomers about 2,000 years ago. But it was not until 1931 that astronomers realised there was a class of super-explosions and not until 2005 a class of super-super explosions. The obvious question is: are there even bigger stellar explosions out there that we have so far missed? \u201cI wouldn\u2019t bet against it,\u201d says Nicholl.<\/p>\n \u201cSuperluminous supernovae may mark the limit of what is possible for supernovae \u2013 at least locally,\u201d says Quimby. \u201cThe big exceptions are the hypothetical pair-instability supernovae thought to exist only in the early Universe.\u201d<\/p>\n In a pair-instability supernova, expected to occur in a star of between 130 and 250 solar masses, the interior gets so hot that gamma rays inside conjure into existence electron-positron pairs. These reduce the thermal pressure opposing gravity A pair-instability supernova would shine 100 times brighter than even a superluminous supernova. Such supernovae might be detected by the James Webb Space Telescope. \u201cAs a hunter of exotic explosions,\u201d says Quimby, \u201cI like to think there are more surprises left to find in the Universe.\u201d<\/p>\n Read more about space:<\/strong><\/p>\n By Marcus Chown Published: Thursday, 17 February 2022 at 12:00 am Thirty light-years away, a star explodes. For several months, it shines 10,000 times brighter than the full Moon. It\u2019s so bright that, during the day, it looks as if the Sun has been joined by another sun, pumping out a hundredth as much heat […]<\/p>\n","protected":false},"author":24,"featured_media":6204,"template":"","categories":[54],"acf":{"readingTimeMinutes":"12"},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/02\/superluminous-supernovae-how-well-find-the-most-powerful-explosions-in-the-universe.jpg",1200,800,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/02\/superluminous-supernovae-how-well-find-the-most-powerful-explosions-in-the-universe-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/02\/superluminous-supernovae-how-well-find-the-most-powerful-explosions-in-the-universe-300x200.jpg",300,200,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/02\/superluminous-supernovae-how-well-find-the-most-powerful-explosions-in-the-universe-768x512.jpg",768,512,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/02\/superluminous-supernovae-how-well-find-the-most-powerful-explosions-in-the-universe-1024x683.jpg",800,534,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/02\/superluminous-supernovae-how-well-find-the-most-powerful-explosions-in-the-universe.jpg",1200,800,false],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/02\/superluminous-supernovae-how-well-find-the-most-powerful-explosions-in-the-universe.jpg",1200,800,false]},"uagb_author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/author\/importmanagerhubsprylab-com\/"},"uagb_comment_info":0,"uagb_excerpt":"By Marcus Chown Published: Thursday, 17 February 2022 at 12:00 am Thirty light-years away, a star explodes. For several months, it shines 10,000 times brighter than the full Moon. It\u2019s so bright that, during the day, it looks as if the Sun has been joined by another sun, pumping out a hundredth as much heat…","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/rss_feed\/6203"}],"collection":[{"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/rss_feed"}],"about":[{"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/types\/rss_feed"}],"author":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/users\/24"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/media\/6204"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/media?parent=6203"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/categories?post=6203"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}What is a superluminous supernova?<\/h2>\n
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<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>What causes superluminous supernovae?<\/h2>\n
Where does the power come from?<\/h2>\n
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<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>Searching for superluminous supernovae<\/h2>\n
![\""James\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/4\/2022\/02\/James-Webb-Space-Telescope-6019844.jpg?quality=90&resize=620%2C620"\" "\\"\"James\\"\/")
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