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from the there's-supposed-to-be-an-earth-shattering-kaboom dept.
There are a few known ways that black holes could be created. First way: start with a very massive star, watch it burn through all its nuclear fuel, and wait for the core to collapse in a violent supernova explosion, leaving a black hole behind. Second way: start with a neutron star, and let it accumulate enough mass to push it over the edge, either by accretion or by colliding with something like another neutron star. There was long theorised to be a third way: for a star to collapse directly into a black hole with no supernova. Astronomers using the Large Binocular Telescope, and the Hubble and Spitzer Space Telescopes have observed just such a thing happening to a star in the nearby galaxy NGC 6946, 22 million light years away. They saw a star of 25 solar masses, given the designation N6946-BH1, quietly wink out into a black hole.
Astronomers have watched as a massive, dying star was likely reborn as a black hole. It took the combined power of the Large Binocular Telescope (LBT), and NASA's Hubble and Spitzer space telescopes to go looking for remnants of the vanquished star, only to find that it disappeared out of sight.
It went out with a whimper instead of a bang.
The star, which was 25 times as massive as our sun, should have exploded in a very bright supernova. Instead, it fizzled out — and then left behind a black hole.
"Massive fails" like this one in a nearby galaxy could explain why astronomers rarely see supernovae from the most massive stars, said Christopher Kochanek, professor of astronomy at The Ohio State University and the Ohio Eminent Scholar in Observational Cosmology.
As many as 30 percent of such stars, it seems, may quietly collapse into black holes —no supernova required.
"The typical view is that a star can form a black hole only after it goes supernova," Kochanek explained. "If a star can fall short of a supernova and still make a black hole, that would help to explain why we don't see supernovae from the most massive stars."
He leads a team of astronomers who published their latest results in the Monthly Notices of the Royal Astronomical Society.
The original paper (paywalled) appears to be "The search for failed supernovae with the Large Binocular Telescope: confirmation of a disappearing star" (DOI: 10.1093/mnras/stx816) but it is not linked in the JPL press release. Also available as arXiv:1609.01283.
(Score: 1, Informative) by Anonymous Coward on Tuesday May 30 2017, @04:16PM (3 children)
A Dyson sphere still emits radiation. If it didn't, its inside would quickly overheat. It's just that the Dyson sphere emits radiation at a lower temperature than the star. You simply can't beat the laws of thermodynamics, even if you are an alien.
Now you might say that the aliens might decide to have that emission only on one side of the Dyson sphere, the one which we don't see. But while this might be technically possible, it would mean a lot of wasted energy, which would be against the very purpose of a Dyson sphere, which is to get as much useful energy from the star as possible. And what would be the purpose of that directional emission?
(Score: 0) by Anonymous Coward on Tuesday May 30 2017, @04:55PM (2 children)
To hide. Obviously they're not hiding from us -- we can't make it to the planet next door! -- so we should be looking behind us to see what alien menace is so terrible that an older and wiser civilization sees it coming a galaxy a way, and shutters their very sun to hide. I'm afraid it's already too late for us.
(Score: 2) by ragequit on Wednesday May 31 2017, @11:24AM
There has to have been a novel about that. If there isn't, there should be.
The above views are fabricated for your reading pleasure.
(Score: 2) by Bot on Thursday June 01 2017, @09:48AM
They are hiding from us. Reason: their SETI stations picked up the presidential race. In fact the star didn't need a dyson sphere yet.
Account abandoned.