Starship Asterisk*

bay area john wrote:So what would be the effect on Earth if a moderately nearby star in our galaxy went supernova? It would seem the light and maybe radiation would be significant issues.

Ann wrote:Today's APOD is very good, but I would like to know more about the picture itself.

bystander wrote:

Ann wrote:Today's APOD is very good, but I would like to know more about the picture itself.

http://www.martinpughastrophotography.i ... GC1365.htm

ChrisK wrote:Hi there,
I was looking at some pictures of the pinwheel galaxy, and in particular the SN2011fe supernova. It occured to me, that pictures taken just one day apart, showed a supernova flash which looks to be a few light years in diameter. If the speed of light is constant, how could the light have travelled so far in such a short period of time?

Regards,
Chris

Ann wrote:

bay area john wrote:
So what would be the effect on Earth if a moderately nearby star in our galaxy went supernova?
It would seem the light and maybe radiation would be significant issues.

I have also read somewhere, perhaps here at Starship Asterisk, that the "safety distance" to a supernova type II (the Betelgeuse kind) is about 30 light-years. If that is true, then we are quite safe from any possible supernova type II explosion. There is absolutely no star massive enough to build up an iron core within 30 light-years, and not within 100 light-years, either. Not within 200 light-years, either. But the stars that will explode as supernovae Ia are extremely faint, and if their "safety distance" is considerably greater than 30 light-years, then maybe a tiny little "death star" is lurking somewhere too close for comfort.

http://en.wikipedia.org/wiki/IK_Pegasi wrote:

<<IK Pegasi (or HR 8210) is a binary star system in the constellation Pegasus. It is just luminous enough to be seen with the unaided eye, at a distance of about 150 light years from the Solar System. The primary (IK Pegasi A) is a main sequence, A-class star that displays minor pulsations in luminosity. It is categorized as a Delta Scuti variable star and it has a periodic cycle of luminosity variation that repeats itself about 22.9 times per day. Its companion (IK Pegasi B) is a massive white dwarf—a star that has evolved past the main sequence and is no longer generating energy through nuclear fusion. They orbit each other every 21.7 days with an average separation of about 31 million kilometres, or 19 million miles, or 0.21 astronomical units (AU). This is smaller than the orbit of Mercury around the Sun. IK Pegasi B is the nearest known supernova progenitor candidate. When the primary begins to evolve into a red giant, it is expected to grow to a radius where the white dwarf can accrete matter from the expanded gaseous envelope. When the white dwarf approaches the Chandrasekhar limit of 1.38 solar masses, it may explode as a Type Ia supernova.>>

http://en.wikipedia.org/wiki/Near-Earth_supernova wrote:

[color=#0000FF]The Crab Nebula is a pulsar wind nebula associated with the 1054 supernova. It is located about 6,500 light-years from the Earth. In 2009, researchers have found nitrates in ice cores from Antarctica at depths corresponding to the known supernovae of 1006 and 1054 CE, as well as from around 1060 CE. The nitrates were apparently formed from nitrogen oxides created by gamma rays from the supernovae.[/color]

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<<A near-Earth supernova is an explosion resulting from the death of a star that occurs close enough to the Earth (roughly less than 100 light-years away) to have noticeable effects on its biosphere.

On average, a supernova explosion occurs within 10 parsecs (33 light-years) of the Earth every 240 million years. Gamma rays are responsible for most of the adverse effects a supernova can have on a living terrestrial planet. In Earth's case, gamma rays induce a chemical reaction in the upper atmosphere, converting molecular nitrogen into nitrogen oxides, depleting the ozone layer enough to expose the surface to harmful solar and cosmic radiation. Phytoplankton and reef communities would be particularly affected, which could badly deplete the base of the marine food chain.

Speculation as to the effects of a nearby supernova on Earth often focuses on large stars as Type II supernova candidates. Several prominent stars within a few hundred light years from the Sun are candidates for becoming supernovae in as little as a millennium. One example is Betelgeuse, a red supergiant about 640 light-years from Earth. Though spectacular, these "predictable" supernovae are thought to have little potential to affect Earth.

Recent estimates predict that a Type II supernova would have to be closer than eight parsecs (26 light-years) to destroy half of the Earth's ozone layer. Such estimates are mostly concerned with atmospheric modeling and considered only the known radiation flux from SN 1987A, a Type II supernova in the Large Magellanic Cloud. Estimates of the rate of supernova occurrence within 10 parsecs of the Earth vary from 0.05-0.5 per Ga (for gigaannum = billion years) to 10 per Ga. Several authors have based their estimates on the idea that supernovae are concentrated in the spiral arms of the galaxy, and that supernova explosions near the Sun usually occur during the ~10 million years that the Sun takes to pass through one of these regions (we are now in or entering the Orion arm). The relatively recent paper by Gehrels et al. uses a value of 3 supernovae less than 10 parsecs away per Ga. The frequency within a distance D is proportional to D³ for small values of D, but for larger values is proportional to D² because of the finite thickness of the galactic disk (at intergalactic distances D³ is again appropriate). Examples of relatively near supernovae are the Vela Supernova Remnant (~800 ly, ~12,000 years ago) and Geminga (~550 ly, ~300,000 years ago).

Type Ia supernovae are thought to be potentially the most dangerous if they occur close enough to the Earth. Because Type Ia supernovae arise from dim, common white dwarf stars, it is likely that a supernova that could affect the Earth will occur unpredictably and take place in a star system that is not well studied. One theory suggests that a Type Ia supernova would have to be closer than 10 parsecs (33 light-years) to affect the Earth. The closest known candidate is IK Pegasi. It is currently estimated, however, that by the time it could become a threat, its velocity in relation to the Solar System would have carried IK Pegasi to a safe distance.

Evidence from daughter products of short-lived radioactive isotopes shows that a nearby supernova helped determine the composition of the Solar System 4.5 billion years ago, and may even have triggered the formation of this system. Supernova production of heavy elements over astronomic periods of time ultimately made the chemistry of life on Earth possible.

In 1996, astronomers at the University of Illinois at Urbana-Champaign theorized that traces of past supernovae might be detectable on Earth in the form of metal isotope signatures in rock strata. Subsequently, iron-60 enrichment has been reported in deep-sea rock of the Pacific Ocean by researchers from the Technical University of Munich. [⁶⁰Fe is an extinct radionuclide of long half-life (2.6 million years). It is not found on Earth, but its ultimate decay product is the stable nuclide nickel-60.] 23 atoms of this iron isotope were found in the top 2 cm of crust, and these date from the last 13 million years or so. It is estimated that the supernova must have occurred in the last 5 million years or else it would have had to have happened very close to the solar system to account for so much iron-60 still being here. A supernova occurring as close as would have been needed would have probably caused a mass extinction, which didn't happen in that time frame. The quantity of iron seems to indicate that the supernova was less than 30 parsecs away. On the other hand, the authors estimate the frequency of supernovae at a distance less than D (for reasonably small D) as around (D/10 pc)³ per Ga, which gives a probability of only around 5% for a supernova within 30 pc in the last 5 million years. They point out that the probability may be higher because we are entering the Orion arm of the Milky Way.

Adrian L. Melott et al. estimated that gamma ray bursts from "dangerously close" supernova explosions occur two or more times per billion years, and this has been proposed as the cause of the end Ordovician extinction, which resulted in the death of nearly 60% of the oceanic life on Earth.

In 1998 a supernova remnant, RX J0852.0-4622, was found in front (apparently) of the larger Vela Supernova Remnant. Gamma rays from the decay of titanium-44 (half-life about 60 years) were independently discovered coming from it, showing that it must have exploded fairly recently (perhaps around 1200 CE), but there is no historical record of it. The flux of gamma rays and x-rays indicates that the supernova was relatively close to us (perhaps 200 parsecs or 660 ly). If so, this is a surprising event because supernovae less than 200 parsecs away are estimated to occur less than once per 100,000 years.>>

sunlitho wrote:
if you could image the galaxy every day over the current period, wouldn't you notice differences in the supernova?

I thought they went off very rapidly.

• They do & they don't:

http://en.wikipedia.org/wiki/Supernova_1987A#Neutrino_emissions wrote:
<<SN 1987A was a [type II] supernova in the outskirts of the Tarantula Nebula in the Large Magellanic Cloud, a nearby dwarf galaxy. It occurred approximately 51.4 kiloparsecs from Earth, approximately 168,000 light-years, close enough that it was visible to the naked eye. Voyager 2, then en route to Neptune, was able to observe the supernova with its cameras.

Approximately two to three hours before the visible light from SN 1987A reached the Earth, a burst of neutrinos was observed at three separate neutrino observatories. This is likely due to neutrino emission (which occurs simultaneously with core collapse) preceding the emission of visible light (which occurs only after the shock wave reaches the stellar surface). At 7:35 a.m. Universal time, Kamiokande II detected 11 antineutrinos; IMB, 8 antineutrinos; and Baksan, 5 antineutrinos; in a burst lasting less than 13 seconds. The observations were consistent with theoretical supernova models in which 99% of the energy of the collapse is radiated away in neutrinos. The observations are also consistent with the models' estimates of a total neutrino count of 10⁵⁸ with a total energy of 10⁴⁶ joules.>>

http://en.wikipedia.org/wiki/Supernova#Light_curves wrote:

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<<The visual light curves of the different supernova types vary in shape and amplitude, based on the underlying mechanisms of the explosion, the way that visible radiation is produced, and the transparency of the ejected material. The light curves can be significantly different at other wavelengths. For example, at UV and shorter wavelengths there is an extremely luminous peak lasting just a few hours, corresponding to the shock breakout of the initial explosion, which is hardly detectable at longer wavelengths.

The light curves for type Ia are mostly very uniform, with a consistent maximum absolute magnitude and a relatively steep decline in luminosity. The energy output is driven by radioactive decay of nickel-56 (half life 6 days), which then decays to radioactive cobalt-56 (half life 77 days). These radioisotopes from material ejected in the explosion excite surrounding material to incandescence. The initial phases of the light curve decline steeply as the effective size of the photosphere decreases and trapped electromagnetic radiation is depleted. The light curve continues to decline in the B band while it may show a small shoulder in the visual at about 40 days, but this is only a hint of a secondary maximum that occurs in the infra-red as certain ionised heavy elements recombine to produce infra-red radiation and the ejecta become transparent to it. The visual light curve continues to decline at a rate slightly greater than the decay rate of the radioactive cobalt (which has the longer half life and controls the later curve), because the ejected material becomes more diffuse and less able to convert the high energy radiation into visual radiation. After several months, the light curve changes its decline rate again as positron emission becomes dominant from the remaining cobalt-56, although this portion of the light curve has been little-studied.

Type Ib and Ic light curves are basically similar to type Ia although with a lower average peak luminosity. The visual light output is again due to radioactive decay being converted into visual radiation, but there is a much lower mass of nickel-56 produced in these types of explosion. The peak luminosity varies considerably and there are even occasional type Ib/c supernovae orders of magnitude more and less luminous than the norm. The most luminous type Ic supernovae are referred to as hypernovae and tend to have broadened light curves in addition to the increases peak luminosity. The source of the extra energy is thought to be relativistic jets driven by the formation of a rotating black hole, which also produce gamma-ray bursts.

The light curves for type II supernovae are characterised by a much slower decline than type I, on the order of 0.05 magnitudes per day, excluding the plateau phase. The visual light output is dominated by kinetic energy rather than radioactive decay for several months, due primarily to the existence of hydrogen in the ejecta from the atmosphere of the supergiant progenitor star. In the initial explosion this hydrogen becomes heated and ionised. The majority of type II supernovae show a prolonged plateau in their light curves as this hydrogen recombines, emitting visible light and becoming more transparent. This is then followed by a declining light curve driven by radioactive decay although slower than in type&bnsp; supernovae due to the efficiency of conversion into light by all the hydrogen.>>

Jack Johnson wrote:
As a meteorologist i have always notices similarities that exist between spiral galaxies and some of the principles of atmospheric circulations. NGC 1365 is no exception where there appears to be great zones of mass convergence along discrete lines known as spiral arms. In an earth bound tropical cyclone these lines of convergence are called "spiral bands". Indeed, the convergence in a hurricane turns inward toward the center and causes the much fabled "eye" which is a singular point just as is the "black hole" of a galaxy. Any thoughts?

• There is no convergence taking place in spiral galaxies
  but both types of spirals could be primarily the result of density waves:

http://en.wikipedia.org/wiki/Density_wave_theory wrote:

Density wave theory or the Lin-Shu density wave theory is a theory proposed by C.C. Lin and Frank Shu in the mid-1960s to explain spiral arm structure of spiral galaxies. Their theory introduces the idea of long-lived quasistatic density waves (also called heavy sound), which are sections of the galactic disk that have greater mass density (about 10–20% greater). The theory has also been successfully applied to Saturn's rings.>>

Peeratz wrote:This APOD picture is a perfect example of a question I have been wanting to ask for a long time. Are there any sites/people that take the time to "drop" stars out of our local galaxy when showing pictures of other galaxies, or even to exclude all stars but those in a specific area (like a cluster of stars) within our galaxy? For example, in this supernova picture, taking out all of the local stars would seem to better express how large this supernova is compared to its neighbor stars, not ours. Or for example, a picture showing several galaxy groupings, but with our local stars removed to clear up any questions as to what is a faint galaxy and not a "nearby" star that might questionably be a far off galaxy if you didn't know otherwise. I know it would be easy to just photoshop out the stars (which I have wanted to do on several occasions when trying to explain pictures to others that aren't so understanding of pictures of our universe), but I'm in no way expert enough to be sure I'm not removing the wrong things out of some of the more complex pictures.

DavidLeodis wrote:I am unsure if the image used in the APOD of November 24 2012 is a recently taken one or if it is the same image that was the used in the APOD of August 20 2010 but onto which the position of the recent supernova has been superimposed.

Ann wrote:

bystander wrote:

Ann wrote:Today's APOD is very good, but I would like to know more about the picture itself.

http://www.martinpughastrophotography.i ... GC1365.htm

Thanks for the link, bystander. However, it takes me to a site which doesn't seem to contain a high-resolution image of today's APOD, and no information about when the exposures for today's APOD were made.

DavidLeodis wrote:I am unsure if the image used in the APOD of November 24 2012 is a recently taken one or if it is the same image that was the used in the APOD of August 20 2010 but onto which the position of the recent supernova has been superimposed. :?:

http://www.universetoday.com/#ixzz2DUUXhTg3 wrote:

[b][color=#0000FF](Image credit: NASA/JPL/Space Science Institute)[/color][/b]

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Incredible Raw Image of Saturn’s Swirling North Pole
by Jason Major, Universe Today, November 28, 2012

<<Ok, are you ready for this?

I know… WOW.

This swirling maelstrom of clouds is what was seen over Saturn’s north pole earlier today, November 27, by NASA’s Cassini spacecraft. This is a raw image, acquired in polarized light, from a distance of 238,045 miles (383,097 kilometers)… all I did was remove some of the hot pixels that are commonly found on Cassini images taken with longer exposures.

Again… WOW.

I’ll let this sink in a bit until more information is available.>>

geckzilla wrote:The connection is the spiral.