Emette raggi X ed è vicino alla Terra

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15 novembre 2010. Conferenza stampa internazionale della NASA. Grazie all’Osservatorio a raggi X Chandra, è stato scoperto il più giovane buco nero esploso nell’Universo più prossimo alla Terra. È nato dall’esplosione della supernova SN1979C, ha 30 anni luce e si trova nella galassia M100, a circa 50 milioni di anni luce dal nostro pianeta. Gli astrofisici stanno osservando che SN1979C, contrariamente alla maggior parte delle supernove finora osservate, emette raggi X e non raggi gamma. Questa caratteristica suggerisce anche una seconda ipotesi: che SN1979C non abbia prodotto un buco nero, bensì una pulsar, una stella di neutroni, la più piccola mai osservata fino ad oggi.

L’SN1979C fu scoperto inizialmente da un astronomo amatoriale del Maryland, il prof. Gus Johnson, nel 1979 (da qui il nome della supernova, ndr.), quando una stella circa venti volte più grande del sole collassò.

Queste le parole di Daniel Patnaude del Harvard-Smithsonian Center for Astrophysics: “In looking at this supernova, we actually went all the way back to the Einstein era and looked at the data from 1980 all the way up until now. This included data from Einstein, ROSAT (osservatorio tedesco, ndr.), Chandra, SWIFT (satellite ndr.) and XMM-Newton (telescopio spaziale a raggi X dell’Agenzia Spaziale Europea, ndr.). Now Einstein didn’t actually see the supernova, but ROSAT was able to observe it. When you compare the data from ROSAT moving forward, you actually see that this supernova is remarkably constant in its brightness. Now you don’t expect this from a supernova. Generally, when a star explodes, it expands out into the circumstellar medium (or its surrounding material) and the X-ray emission and all of the other emission drops with time. So this is actually rather remarkable. What we interpreted this as was the formation of a black hole in the center of the supernova. If this is the case then this would be evidence for the youngest and the nearest newly-formed black hole known to date. What makes this exceptional is that we haven’t actually ever directly observed a black hole inside of a supernova. It’s thought that they are formed in some type of supernova, but we’ve never actually observed them to date, so to actually see this would be remarkable. The other alternative besides it being possibly a black hole that’s accreting supernova material is that instead of a black hole forming, a neutron star formed at the center of this supernova. What happens in this case is that the neutron star is spinning rapidly and what we’re actually observing is a so-called Wind Nebula from this rapidly-spinning neutron star. It’s called a Pulsar Wind Nebula, and an example of this would be the Crab. Interestingly enough, this particular supernova is only one of three at the time which was observed when it was going off. It was discovered in 1979 by a schoolteacher, Gus Johnson, who lived in Maryland, and he was observing M100, which is something he liked to do, and what he noticed was that there was this bright star, this new bright star in the field, and it turned out that this was Supernova 1979C”.

I risultati delle osservazioni sono state pubblicate nel New Astronomy Journal (autori: Daniel Patnaude, Abraham Loeb e Christine Jones, ndr.).

Clicca qua per leggere l’articolo del Chandra X-ray Observatory.

Matteo Vitiello

Leggi anche:

Buco nero esplode al centro della Via Lattea

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