Starship Asterisk*

owlice wrote:Chris, thank you! Magnetic poles, I assume, yes?

owlice wrote:How does something that is spherical point right at us?

wonderboy wrote:http://www.theinsider.org/news/article.asp?id=2769

Is the end of the world imminent?, The Insider, 10 April 2010

• Supernova
  
  Various cosmic phenomena are capable of destroying most or all life on Earth, and the most obvious example is a supernova. (I will not discuss solar flares, but these could fall within the general category of common cosmic events.) Supernovae each release a burst of the most powerful energies in the universe (ten times more energy than our sun releases over its entire lifetime). Long after the initial explosion, there is a pair of directional beams of extremely high energy radiation pointing opposite directions. The Gamma Rays alone are capable of sterilising the surface of the Earth, instantly eliminating all life on land and in the sea. Less severe exposure will expose all life to dangerous radiation, and change the world's climate significantly for a long period. The fossil record shows that this has happened before, e.g. causing the extinction of trilobites. Ironically in less severe cases, the mutations caused by Gamma Rays, X-Rays and other forms of radiation from a supernova may accelerate the rate of evolution, increasing the chances of new species emerging that can survive under the new conditions.
  
  E.g. The star WR104 is about to die, is within range (8,000 light years) and appears to be pointing right at us! It could already have exploded, but of course we won't see it until the light and radiation reaches us 8,000 years later. It could hit us tomorrow, or the next day, and there will be no warning.

I spend a lot of time in my upcoming book Death from the Skies! making the case that for the most part, astronomical dangers to life on Earth — especially from explosions called gamma-ray bursts — are incredibly rare, and not worth fretting over too much.

I may — may — have to change my mind.
...
Up until now, I hadn’t heard of WR 104. This is a binary star located 8000 light years away, more or less toward the center of our galaxy. The two stars are both whoppers; one is a massive O star, which will someday detonate in a tremendous supernova. However, at that great distance, it won’t do anything more than be a bright light in the sky.

The other star in the system is a bit of a worry, though. It’s what’s called a Wolf Rayet star, a massive, luminous star that is on the brink of exploding as well. In general, these also blow up as supernovae and, from 8000 light years away (80 quadrillion kilometers) it wouldn’t pose much of a threat.

But what if it explodes as a gamma-ray burst?
...
To wrap up: WR 104 is an interesting system. Both stars are guaranteed to explode one day. If they are just regular old supernovae, then we are in no danger at all, because they are way way too far away to hurt us (a regular supernova has to be about 25 light years or closer to hurt us, and WR 104 is 300 times farther away than that). It is possible that one of the stars may explode as a GRB, and it’s possible it’s aimed at us, but we don’t know. And we don’t know exactly what effects it would have on us. So if it’s less than 10,000 years from exploding and if it blows up as a GRB and if it’s aimed at us and if there isn’t much junk between us and it, then yeah, we may have a problem. But that’s an awful lot of ifs.

Given all these uncertainties, and having researched the dangers of GRBs extensively for my book, I won’t be losing any sleep over WR 104. For now, this is just an extraordinarily cool object, and it’s worth keeping an eye on — certainly for its astronomical interest alone! But as for it being a Death Star, I think it’s way way too early to tell.

Early last year, concern was growing for a Wolf-Rayet star named WR 104 that appeared to be aiming right at Earth (see Looking Down the Barrel of A Gamma Ray Burst). A Wolf-Rayet star is a highly unstable star coming to the end of its life, possibly culminating in a powerful, planet-killing gamma-ray burst (GRB). GRBs are collimated beams of high energy gamma-rays, projected from the poles of a collapsing Wolf-Rayet star. It was little wonder that we were concerned when a dying Wolf-Rayet star was found to be pointing right at us! Today, at the AAS in Long Beach, one scientist (Dr. Grant Hill) working at the Keck Telescope has taken a keen interest in WR 104 and shared new findings that show our Solar System may not be bathed in deadly gamma-rays after all…

Interview: Dr. Grant Hill, a researcher at the Keck Observatory, tells Discovery News whether we are staring down the barrel of a potential GRB gun...

The scoop: Last year, a star called WR 104 caused a stir. This massive Wolf-Rayet star is reaching the end of its life and astrophysicists believe it may explode as a supernova some time in the near future (in astronomical terms, this means tens to hundreds of thousands of years, so don't bet on anything happening soon).

However, WR 104 has a sinister side... it could erupt as the most energetic explosion observed in the cosmos: a gamma-ray burst (GRB).

As it's in our galaxy, and looks as if it's pointing right at us, there's concern that it could cause damage to Earth's biosphere should it explode as a GRB. With this in mind, Dr. Grant Hill, a researcher at the Keck Observatory on Big Island, Hawaii, has been investigating whether we are actually staring down the barrel of a potential GRB gun...

wonderboy wrote:Anywho, this author suggests that a star 8000 light years away could have exploded and the radiation may in fact be able to steralise the earth, I assume this is poppycock, but then again it may not be, I want an answer

jle666 wrote:I've seen images such as that presented on 8/1/09 of SN 1006 Supernova Remnant and have always been curious about one point. Its states that this remnant, as viewed from earth, is some 60 ly across (ie, 30 ly radius). Given that this event was observed to have occured 1000 years ago, then one can trivially calculate that the outer edge of this expanding shell has a radial velocity of only 3% of the speed of light or about 9000 km/sec. This is admittedly very fast but I have often heard it stated that such supernova explosions accelerate material to "close to the speed of light". Perhaps I'm misinterpreting the meaning of the word "close" in this context but it seems to me that 3% does not really qualify. Or perhaps material other than that responsible for the shell structure seen in the image is what gets accelerated to nearly light speeds, I don't know.

Can anybody offer any insight to this seeming conundrum? Just curious, I've been curious about this for literally many years.

• 1) The stellar material, itself, gets ejected at a few percent the speed of light.
  
  2) This expanding stellar material then collides with surrounding circumstellar
  or interstellar gas to form a shock wave (visible in radio & X-rays).
  
  3) This shock wave then accelerates external (cosmic ray?) particles
  to relativistic velocities by "Fermi Mechanism" processes.

http://en.wikipedia.org/wiki/Supernova_remnant wrote:
A supernova expels much or all of the stellar material with velocities [a few percent] the speed of light. When this material collides with the surrounding circumstellar or interstellar gas, it forms a shock wave that can heat the gas up to temperatures as high as 10 million K, forming a plasma.
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Summary of stages

An SNR passes through the following stages as it expands:

1. Free expansion of the ejecta, until they sweep up their own weight in circumstellar or interstellar medium. This can last tens to a few hundred years depending on the density of the surrounding gas.

2. Sweeping up of a shell of shocked circumstellar and interstellar gas. This begins the Sedov-Taylor phase, which can be well modeled by a self-similar analytic solution. Strong X-ray emission traces the strong shock waves and hot shocked gas.

3. Cooling of the shell, to form a thin (< 1 pc), dense (1-100 million atoms per cubic metre) shell surrounding the hot (few million kelvin) interior. This is the pressure-driven snowplow phase. The shell can be clearly seen in optical emission from recombining ionized hydrogen and ionized oxygen atoms.

4. Cooling of the interior. The dense shell continues to expand from its own momentum, in a momentum-driven snowplow. This stage is best seen in the radio emission from neutral hydrogen atoms.

5. Merging with the surrounding interstellar medium. When the supernova remnant slows to the speed of the random velocities in the surrounding medium, after roughly a million years, it will merge into the general turbulent flow, contributing its remaining kinetic energy to the turbulence.
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Origin of cosmic rays

<<Supernova remnants are considered the major source of Galactic cosmic rays. The connection between cosmic rays and supernovas was first suggested by Walter Baade and Fritz Zwicky in 1934. Vitaly Ginzburg and Sergei Syrovatskii in 1964 remarked that if the efficiency of cosmic ray acceleration in supernova remnants is about 10 percent, the cosmic ray losses of the Milky Way are compensated. This hypothesis is supported by a specific mechanism called "shock wave acceleration" based on Enrico Fermi's ideas, which is still under development. Indeed, Enrico Fermi proposed in 1949 a model for the acceleration of cosmic rays through particle collisions with magnetic clouds in the interstellar medium. This process, known as the "Second Order Fermi Mechanism", increases particle energy during head-on collisions, resulting in a steady gain in energy. A later model to produce Fermi Acceleration was generated by a powerful shock front moving through space. Particles that repeatedly cross the front of the shock can gain significant increases in energy. This became known as the "First Order Fermi Mechanism". Supernova remnants can provide the energetic shock fronts required to generate ultra-high energy cosmic rays. Observation of the SN 1006 remnant in the X-ray has shown synchrotron emission consistent with it being a source of cosmic rays.>>

emc wrote:Perhaps the enlarged light in the 1006 AD night sky was taken as a sign
by the natives of “Vinland/Newfoundland” to kick the invading Viking butt??

JimBeemer wrote:In the explanation for APOD Aug 1, 2009 the author of the explanation states that SN 1006 is

Part of a binary star system, the compact white dwarf gradually captured material from its companion star. The buildup in mass finally triggered a thermonuclear explosion that destroyed the dwarf star.

I know that explanations need to be kept short but wouldn't it be more informative if the explanation explained that the star imploded and then exploded in the thermonuclear explosion? Furthermore, if there is enough space the explanation could go on to mention that the heavier elements are synthesized by supernovae as a result of supernovae implosions.

http://www.saudiaramcoworld.com/issue/200604/the.scholar.s.supernova.htm wrote:
<<The ambitious son of a poor baker, Ibn Ridwan had just begun his education in medicine, but he was already an astrologer accomplished enough to support himself by casting horoscopes. [When Ibn Ridwan was 18 years old] the “new star,” today simply called SN1006, first appeared on the evening of April 30, 1006. It persisted through the summer, but by mid-August the sun had moved so close to it that, from Cairo, it was above the horizon only during the daylight hours, making further observation difficult. According to Chinese accounts, within two years it was no longer visible at all. It appeared low in the southern sky, in the sign of Scorpio, which Ibn Ridwan interpreted as a portent of ill fortune. For young Ibn Ridwan, however, good fortune also beckoned. The year before the supernova appeared, Al-Hakim had founded the Dar al-‘Ilm, “the House of Knowledge.” This was a sort of informal public university where anyone who wished might come to read and copy books, study, or attend lectures in theology, grammar, philology, medicine and astronomy. Astrology was excluded, for a distinction had emerged between the empirical discipline of astronomy and what many, including Al-Hakim, regarded as its less respectable, interpretive counterpart.



No other observer has described [SN1006] with the scientific precision of Ibn Ridwan: "The sun on that day was 15 degrees in Taurus and the spectacle in the 15th degree of Scorpio. This spectacle was a large circular body, two and a half to three times as large as Venus. The sky was shining because of its light. The intensity of its light was a little more than a quarter of that of moonlight. It remained where it was and it moved daily with its zodiacal sign until the sun was in sextile with it in Virgo, when it disappeared at once.">>

Vivian wrote:It seemed that Chinese austronomers always did a lot for the world's astronomy...

It is said that the image includes three parts. Which one could we see using our eyes?

Part of a binary star system, the compact white dwarf gradually captured material from its companion star. The buildup in mass finally triggered a thermonuclear explosion that destroyed the dwarf star.

http://en.wikipedia.org/wiki/Walpurgis_Night wrote:
<<Walpurgisnacht is a traditional religious holiday of pre-Christian origin, celebrated today by Christian and non-Christian communities as well, on April 30 or May 1 in large parts of Central and Northern Europe. Historically Walpurgisnacht is derived from various pagan spring customs. Bonfires were built to keep away the dead and chaotic spirits that were said to walk among the living then. This is followed by the return of light and the sun as celebrated during May Day. The current festival is in most countries celebrating it named after Saint Walpurga, born in Devon about 710. Walpurga was honored in the same way that Vikings had celebrated spring and as they spread throughout Europe, the two dates became mixed together and created the Walpurgis Night celebration. Early Christianity had a policy of 'Christianising' pagan festivals so it is perhaps no accident that St. Walpurga's day was set to May 1.>>

• ----------------------------------------------------
  <<Son of Erik the Red, Leif Erikson discovered and settled Vinland/Newfoundland around the year 1003 AD. The settlement which is now known as L’Anse aux Meadows. Conflicts with the natives arose around 1006 AD. The natives eventually drove the Vikings off.>>
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http://en.wikipedia.org/wiki/SN_1006 wrote:
<<SN 1006 was a supernova, widely seen on Earth beginning in the year 1006 CE; Earth was about 7200 light-years away from the supernova. It was the brightest apparent magnitude stellar event in recorded history. First appearing in the constellation of Lupus between April 30 and May 1 of that year, this "guest star" was described by observers in China, Egypt, Iraq, Japan, Switzerland, and possibly North America.

. Historic description

The Chinese and Arabic astronomers have left the most complete historical descriptions of the supernova.

The Egyptian Arabic astronomer and astrologer Ali ibn Ridwan, writing in a commentary on Ptolemy's Tetrabiblos, said that the object was 2.5 to three times as large as the disc of Venus, and about one-quarter the brightness of the Moon; like all other observers, says that the star was low on the southern horizon. Monks at the Benedictine abbey at St. Gallen broadly corroborate bin Ridwan's observations as to magnitude and location in the sky, additionally writing that "n a wonderful manner this was sometimes contracted, sometimes diffused, and moreover sometimes extinguished." This last is often taken as proof that the supernova was of Type Ia. Some sources state that the star was bright enough to cast shadows; it was certainly seen during daylight hours for some time, and the modern-day astronomer Frank Winkler has said that "in the spring of 1006, people could probably have read manuscripts at midnight by its light."

The reports from Switzerland are particularly noteworthy, as the supernova would have been very low in the sky there, rising to at most 5 degrees above the southern horizon and being visible for only 4-5 hours at a time. Atmospheric extinction and the need to find a site with a clear southern horizon make seeing even bright objects this low difficult; the "sometimes contracted, diffused, extinguished" remarks quoted above hint at atmospheric effects caused by the low apparent altitude of the object.

According to Songshi in the section of 56 and 461, the star was seen on May 1, 1006 which appeared to the south of constellation Di, east of Lupus and one degree to the west of Centaurus. The size of the visual explosion was half that of the moon, and shone so brightly that objects on the ground could be seen at night. By December, it was again sighted in the constellation Di. The Chinese astrologer Zhou Keming, who was on his return to Kaifeng from his duty in Guangdong, interpreted the star to the emperor on May 30 as an auspicious star, yellow in color and brilliant in its brightness, that would bring great prosperity to the state over which it appeared.

There appear to have been two distinct phases in the early evolution of this supernova. There was first a three-month period at which it was at its brightest; after this period it diminished, then returned for a period of about eighteen months. Most astrologers interpreted the event as a portent of warfare and famine.

A petroglyph by the Hohokam has been discovered in White Tank Mountain Regional Park which may be the first known North American representation of the supernova.

. Remnant

The associated supernova remnant from this explosion was not identified until 1965, when Doug Milne and Frank Gardner used the Parkes radio telescope to demonstrate that the previously known radio source PKS 1459-41, near the star Beta Lupi, had the appearance of a 30-arcminute circular shell.

Over the next few years, both X-ray and optical emission from this remnant were also detected. The supernova remnant of SN 1006 has an estimated distance of 2.2 kiloparsecs, making it approximately 20 parsecs in diameter. As expected for the remnant of a Type Ia supernova, no associated neutron star or black hole has been found.>>

http://en.wikipedia.org/wiki/Lupus_(constellation) wrote:

<<Lupus is a constellation in the southern sky. Its name is Latin for wolf. In ancient times, the constellation was considered an asterism within Centaurus, and was considered to have been an arbitrary animal, killed, or about to be killed, on behalf of, or for, Centaurus. It was not separated from Centaurus until Hipparchus of Bithynia named it Therion (meaning beast) in the 200s BC. No particular animal was associated with it until the Latin translation of Ptolemy's work identified it with the wolf.

Most of the brightest stars in Lupus are massive members of the nearest OB association: Scorpius-Centaurus. Towards the north of the constellation are globular clusters NGC 5824 and NGC 5986, and close by the dark nebula B 228. Two open clusters are to the south of the constellation, NGC 5822 and NGC 5749. On the western border are two spiral galaxies and the Wolf-Rayet planetary nebula IC 4406, containing some of the hottest stars in existence. Another planetary nebula, NGC 5882, is towards the centre of the constellation. The transiting exoplanet Lupus-TR-3b lies in this constellation.>>