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"The Great Silence" -Are Supernovas Destroyers of Life in the Universe?

6a00d8341bf7f753ef0120a7b37085970b-500wi The physicist Enrico Fermi once asked referring to visits to Earth by extraterrestrial civilizations: Where are they?The accurate answer might well be: destroyed by radiation from supernova explosions.

A massive white dwarf star in our galaxy may become a supernova several million years from now, and could possibly destroy life on Earth. 

Most astronomers today believe that one of the plausible reasons we have yet to detect intelligent life in the universe is due to the deadly effects of local supernova explosions that wipe out all life in a given region of a galaxy.
While there is, on average, only one supernova per galaxy per century, there is something on the order of 100 billion galaxies in the observable Universe. Taking 10 billion years for the age of the Universe (it's actually 13.7 billion, but stars didn't form for the first few hundred million), Dr. Richard Mushotzky of the NASA Goddard Space Flight Center, derived a figure of 1 billion supernovae per year, or 30 supernovae per second in the observable Universe!

Certain rare stars -real killers -type 11 stars, are core-collapse hypernova that generate deadly gamma ray bursts (GRBs). These long burst objects release 1000 times the non-neutrino energy release of an ordinary "core-collapse" supernova. Concrete proof of the core-collapse GRB model came in 2003.

It was made possible in part to a fortuitously "nearby" burst whose location was distributed to astronomers by the Gamma-ray Burst Coordinates Network (GCN). On March 29, 2003, a burst went off close enough that the follow-up observations were decisive in solving the gamma-ray burst mystery. The optical spectrum of the afterglow was nearly identical to that of supernova SN1998bw. In addition, observations from x-ray satellites showed the same characteristic signature of "shocked" and "heated" oxygen that's also present in supernovae. Thus, astronomers were able to determine the "afterglow" light of a relatively close gamma-ray burst (located "just" 2 billion light years away) resembled a supernova.

It isn't known if every hypernova is associated with a GRB. However, astronomers estimate only about one out of 100,000 supernovae produce a hypernova. This works out to about one gamma-ray burst per day, which is in fact what is observed.

What is almost certain is that the core of the star involved in a given hypernova is massive enough to collapse into a black hole (rather than a neutron star). So every GRB detected is also the "birth cry" of a new black hole.

Scientists at the American Astronomical Society's 215th meeting, in Washington DC, said earlier this week that new observations of T Pyxidis in the constellation Pyxis (the compass) using the International Ultraviolet Explorer satellite, indicate the white dwarf is part of a close binary system with a sun, and the pair are 3,260 light-years from Earth and much closer than the previous estimate of 6,000 light-years.

Hs-1997-29-c-web The white dwarf in the T Pyxidis system is a recurrent nova, which means it undergoes nova (thermonuclear) eruptions around every 20 years. The most recent known events were in 1967, 1944, 1920, 1902, and 1890. These explosions are nova rather than supernova events, and do not destroy the star, and have no effect on Earth. The astronomers do not know why the there has been a longer than usual interval since the last nova eruption.

Astronomers believe the nova explosions are the result of an increase of mass as the dwarf siphons off hydrogen-rich gases from its stellar companion. When the mass reaches a certain limit a nova is triggered. It is unknown whether there is a net gain or loss of mass during the siphoning/explosion cycle, but if the mass does build up the so-called Chandrasekhar Limit could be reached, and the dwarf would then become a Type 1a supernova. In this event the dwarf would collapse and detonate a massive explosion resulting in its total destruction. This type of supernova releases 10 million times the energy of a nova.

Observations of the white dwarf during the nova eruptions suggest its mass is increasing, and pictures from the Hubble telescope of shells of material expelled during the previous explosions support the view. Models estimate the white dwarf's mass could reach the Chandrasekhar Limit in around 10 million years or less.

According to the scientists the supernova would result in gamma radiation with an energy equivalent to 1,000 solar flares simultaneously - enough to threaten Earth by production of nitrous oxides that would damage and perhaps destroy the ozone layer. The supernova would be as bright as all the other stars in the Milky Way put together. One of the astronomers, Dr Edward Sion, from Villanova University in Pennsylvania, said the supernova could occur "soon" on the timescales familiar to astronomers and geologists, but this is a long time in the future in human terms.

Astronomers think supernova explosions closer than 100 light years from Earth would be catastrophic, but the effects of events further away are unclear and would depend on how powerful the supernova is. The research team postulate it could be close enough and powerful enough to damage Earth, possibly severely, although other researchers, such as Professor Fillipenko of the Berkeley Astronomy Department, disagree with the calculations and believe the supernova, if it occurred, would be unlikely to damage the planet.

Who ever said science is boring!

The image at the top is a composite Chandra X-ray (blue) and Palomar infrared (red and green) image of the supernova remnant W49B -a barrel-shaped nebula consisting of bright infrared rings around a glowing bar of intense X-radiation along the axis. W49B was created when a massive star formed from a dense cloud of dust and gas, shone brightly for a few million years while spinning off rings of gas and pushing them away to form a nearly empty cavity around the star. The star then exhausted its nuclear fuel and its core collapsed to form a black hole. Much of the gas around the black hole was pulled into it, but some, including material rich in iron and nickel was flung away in oppositely directed jets of gas traveling near the speed of light. When the jet hit the dense cloud surrounding the star, it flared out and drove a shock wave into the cloud.

An observer aligned with one these jets would have seen a gamma-ray burst, a blinding flash in which the concentrated power equals that of ten quadrillion Suns for a minute or so. The view perpendicular to the jets would be a less astonishing, although nonetheless spectacular supernova explosion. For W49B, the jet is tilted out of the plane of the sky by about 20 degrees, but the remains of the jet are visible as a hot X-ray emitting bar of gas.

W49B is about 35 thousand light years away, whereas the nearest known gamma-ray burst to Earth is several million light years away - most are billions of light years distant. And safe to Earthlings.

Casey Kazan.Adapted from NASAJPL materials. 

http://imagine.gsfc.nasa.gov/docs/science/know_l1/why_hyper.html 

Comments

I think that the reason for the absence of evidence of life is actually much simpler.

First, it takes time to travel long distances. Andromeda is 2,5 million light-years away. With achievable travel speeds that means perhaps 2,5 billion years for space travellers. That is 2 500 million years of exposure to pretty strong radiation.

The Milky Way is 100 000 light years cross, or perhaps 100 million years in travel time.

The nearest star (which has no planets), Proxima Centauri, is 4,5 light years, or 4500 years of travel.

The second reason is that possible radio signals generated by advanced life would be so weak as to be undetectable by the time they reach us.

Thus, for all practical purposes, we are alone in this universe, although there surely must be life, even intelligent life, elsewhere.

Accelerate a spacecraft at 1 g for 1 year and you get almost to the speed of light.
The return journey to anywhere in the universe is 4 years or so.

It's articles like this one that make me realize how tiny tiny tiny we really are.

Why would aliens want to pollute this wonderful little laboratory / ecosystem called Earth if they found it? I'm sure they would rather sit back, study it and in so doing, enhance their own understanding about the origins of their own indusrial, technological and electronic revolutions...

I would speculate that there are an enormous amounts of civilizations dispersed throughout the universe. To get anywhere from here would take a very large leap of technology. Civilizations are a quirk of nature in a broader picture. We are carbon based. What if there are others that have a similar element base.

The future of propulsion of a craft lies with matter/anti-matter integration much like Roddenbury's dream of Star-Trek. Their research is getting very close. There is a projecct that uses Lithium Dioxide plasma for propulsion. Now if they can only combine very carefully matter/anti-matter in a safe configuration.

View "The Privileged Planet". Highly UNlikely, statistically, for intelligent carbon based life elsewhere in the universe. Of course, not impossible.

supernovas that far will have no way to reach us like what the fuck

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