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Astronomers discover coldest ever white dwarf - an ancient diamond the size of the Earth The galactic oddity is 11 billion years old - the same age as the Milky Way James Vincent James Vincent is Science and Technology Reporter for The Independent online, and his work appears in print too. In the past he has written freelance for Wired, the New Statesman and the Financial Times. Wednesday 25 June 2014 Astronomers have identified what might be one of the strangest stars in our galaxy: an incredibly cold, ancient and faint white dwarf that has crystallized into a diamond the size of Earth. “It’s a really remarkable object,” said Professor David Kaplan of the University of Wisconsin-Milwaukee in a press release. “These things should be out there, but because they are so dim they are very hard to find.” White dwarfs are stars at the end of their life span when the fusion reaction that has pumped out heat and energy during has all but stopped, leaving the remaining carbon and oxygen to compact into an incredibly dense and cold state. In the case of this recently discovered white dwarf, astronomers believe that it has cooled and crystallized all the way to diamond, estimating that the once-fiery star is 11 billion years old – making it the same age as the Milky Way. Stars like this aren’t rare (around 97 per cent of stars are thought to turn into white dwarfs and we've even discovered planets made of diamond) but they are incredibly difficult to find – simply because their light is too faint to make its way through the cosmos to telescopes on Earth. Thankfully, this particular white dwarf had a partner that gave away its presence to astronomers on Earth: a companion pulsar star dubbed PSR J2222-0137. Read more: The weiredest planets discovered by Nasa Newly discovered 'super-Earth' is made of diamonds Earth's 'underground oceans' three times size of surface Pulsars are superdense neutron stars that spin incredibly quickly, shooting beams of radio waves into the cosmos like supercharged lighthouses. However, with PSR J2222-0137 astronomers noticed that the radio beams were regularly obstructed by an unknown object. The team from the National Radio Astronomy Observatory in the US suspected it was a white dwarf, but were still unable to see the object after further observation. Their explanation? That this is one of the coldest white dwarf ever discovered. “Our final image should show us a companion 100 times fainter than any other white dwarf orbiting a neutron star and about 10 times fainter than any known white dwarf, but we don’t see a thing,” said University of North Carolina graduate student Bart Dunlap. “If there's a white dwarf there, and there almost certainly is, it must be extremely cold." However, this is cold in an astronomical sense and despite being 5,000 times cooler than the center of the Sun, the diamond white dwarf is still thought to be 2,700 degrees Celsius (or 4,892 degrees Fahrenheit). 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'Ovo je stvarno izuzetno tijelo', rekao je David Kaplan, profesor na University of Wisconsin-Milwaukee. 'Takve stvari bi trebale postojati u svemiru, međutim budući da su jako blijede, vrlo ih je teško otkriti', dodao je. U istraživanju zvjezdanog dragulja Kaplan i njegovi suradnici koristili su više teleskopa, među kojima i Green Bank Telescope (GBT) te Very Long Baseline Array (VLBA). Bijeli patuljci su ekstremno gusta tijela koja predstavljaju posljednju fazu u razvoju zvijezda sličnih našem Suncu. Na kraju svojeg života, kada izgube gotovo svu nuklearnu energiju, one se urušavaju do veličine slične Zemljinoj. Sastoje se uglavnom od ugljika i kisika, hlade se milijardama godina i postupno gube sjaj. Novootkriveni bijeli patuljak vjerojatno je star koliko i Mliječna staza – oko 11 milijardi godina. Svemirski dijamant, udaljen oko 900 svjetlosnih godina, otkriven je u zviježđu Vodenjaka tijekom istraživanja njegova kompanjona pulsara PSR J2222-0137. Već prva promatranja pokazala su da se pulsar okreće više od 30 puta u sekundi te da je gravitacijski vezan uz neko drugo tijelo. Pulsari su neutronske zvijezde izuzetno brze rotacije, ostaci golemih zvijezda koje su eksplodirale kao supernove. Dok se okreću, u svemir odašilju snopove radiovalova poput svjetionika. Kada neki od njih prijeđe preko Zemlje, radioteleskopi ga registriraju kao snažan signal. U svojoj studiji američki je tim na analize podataka primijenio Einsteinovu teoriju relativnosti kako bi utvrdio na koji način i u kolikoj mjeri gravitacija kompanjona iskrivljuje prostor te uzrokuje kašnjenje radio signala kada pulsar prolazi iza njega. Kalkulacijama je utvrđeno da je masa pulsara oko 1,2 puta, a bijelog patuljka oko 1,05 puta veća od Sunčeve. Rezultati su jasno pokazali da kompanjon pulsara ne može biti neutronska zvijezda – njihove su orbite bile previše uredne za par neutronskih zvijezda. Pretpostavivši da bi kompanjon mogao biti bijeli patuljak, znanstvenici su par istražili moćnim teleskopima, SOAR-om u Čileu i Keckom na Havajima. No niti jedan od njih nije uspio zabilježiti sjaj manjeg tijela. Stoga su zaključili da je ono mora biti izuzetno hladno – da mu temperatura ne može biti veća od 2.700 °C. Za usporedbu, naše je Sunce u središtu čak 5.000 puta toplije. Astronomi su uvjereni da bi se tako hladna, urušena zvijezda uglavnom morala sastojati od kristaliziranog ugljika sličnog dijamantu. Ovakve zvijezde se ne smatraju posebno rijetkima, međutim zbog vrlo slabog sjaja jako ih je teško otkriti. Studija je objavljena u novom broju časopisa Astrophysical Journal.