APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

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APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by APOD Robot » Sat Dec 07, 2013 5:06 am

Image Naked Eye Nova Centauri 2013

Explanation: Brightest stellar beacons of the constellation Centaurus, Alpha and Beta Centauri are easy to spot from the southern hemisphere. For now, so is new naked eye Nova Centauri 2013. In this night skyscape recorded near Las Campanas Observatory in the Chilean southern Atacama desert on December 5, the new star joins the old in the expansive constellation, seen at early morning hours through a greenish airglow. Caught by nova hunter John Seach from Australia on December 2 as it approached near naked eye brightness, Nova Cen 2013 has been spectroscopically identified as a classical nova, an interacting binary star system composed of a dense, hot white dwarf and cool, giant companion. Material from the companion star builds up as it falls onto the white dwarf's surface triggering a thermonuclear event. The cataclysmic blast results in a drastic increase in brightness and an expanding shell of debris. The stars are not destroyed, though. Classical novae are thought to recur when the flow of material onto the white dwarf eventually resumes and produces another outburst.

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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by Beyond » Sat Dec 07, 2013 5:14 am

Naked eye Nova :?: Well, at least put a monocle on it :!:
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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by Chris Peterson » Sat Dec 07, 2013 5:45 am

Beyond wrote:Naked eye Nova :?: Well, at least put a monocle on it :!:
"Naked" is a high value keyword in lots of nanny filters of the sort used by libraries and schools. It's crazy, but today's APOD is probably going to be blocked at a lot of sites.
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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by Beyond » Sat Dec 07, 2013 5:57 am

Not only that, but it would probably get an 'R' rating for violence, also. They are the most violent happenings we know of in the universe, aren't they :?:
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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by Chris Peterson » Sat Dec 07, 2013 6:19 am

Beyond wrote:Not only that, but it would probably get an 'R' rating for violence, also. They are the most violent happenings we know of in the universe, aren't they :?:
Novas? They're wimpy little things, less luminous than lots of stars. Not violent at all in terms of what the Universe is capable of.
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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by Beyond » Sat Dec 07, 2013 6:43 am

Huh!
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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by Ann » Sat Dec 07, 2013 7:38 am

It would be interesting to know just how wimpy or violent this explosion is. (Yes, we already know that it is no supernova.) :wink:

But how wimpy is it? How far away is this system? How bright is it when it is not in its nova state?

White dwarfs can be bright when they are very young, many times brighter than the Sun (or so I think), but they just keep fading. According to wikipedia, the brightness of Sirius B, the white dwarf, is just 0.026 times the Sun. (Wikipedia also says that Sirius B became a white dwarf about 120 million years ago.)

So the white dwarf in this nova system could very well be very faint. What about its companion? If the companion is itself a red dwarf, which is possible, it too will be very faint, much fainter than the Sun. But if the companion is a red giant it can be quite bright, a hundred times brighter than the Sun or more. (Or less.) In any case, if the companion is a red dwarf, then the system could be quite nearby and the explosion could be a mere puff. But if the companion is a red giant, then the system could be far away, and the explosion could be respectable in its magnitude.

I note that the color of the nova appears to be bluish. (Please note that I'm not trying to guess at the dominant wavelength of what is seen as blue in the photograph.) But anyway, if the nova is bluish, then the light from the explosion is totally overpowering the light from the red companion. Just maybe the companion isn't a mighty red giant. (Or maybe it is. Oh well.)

(An interesting possibility is that the nova in Centaurus might be a system somewhat reminiscent of binary star Algol. The current Algol primary, a B-type main sequence star about a hundred times brighter than the Sun, has been cannibalizing its red giant companion (the former primary of the system) and whittled it down to a puny luminosity just 4.5 times the Sun. That's not a lot for a red giant, to be sure, and the same thing could possibly have happened to the red star in Nova Centauri 2013.)

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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by Boomer12k » Sat Dec 07, 2013 11:52 am

Why do all the interesting things happen in the Southern Hemisphere????? OR in the dead of a cold wave the likes of which has not been seen for a decade???

Man....WELL....that is why we have APOD...at least I get to view it here, and read up about it. THANKS!!!!!!!!!!

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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by Boomer12k » Sat Dec 07, 2013 11:57 am

Cannibalizing another star....and then having "gas".....bad digestion....and then doing it again....sounds like an eating disorder... you could say his disorder.."Flares up" every now and then...


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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by neufer » Sat Dec 07, 2013 1:35 pm

Chris Peterson wrote:
Beyond wrote:
Not only that, but it would probably get an 'R' rating for violence, also. They are the most violent happenings we know of in the universe, aren't they :?:
Novas? They're wimpy little things, less luminous than lots of stars. Not violent at all in terms of what the Universe is capable of.

  • Remember that supernovas are just a subset of novas.
http://en.wikipedia.org/wiki/Nova wrote:
<<A nova (plural novae or novas) is a cataclysmic nuclear explosion in a white dwarf star. A nova is a sudden brightening of a star. The most luminous type of nova is called a supernova and luminous red novae have also been distinguished. It is caused by the accretion of hydrogen on to the surface of the star, which ignites and starts nuclear fusion in a runaway manner. Novae are thought to occur on the surface of a white dwarf star in a binary system. If these two stars are close enough, material from one star can be pulled off the companion star's surface and onto the white dwarf.

Novae in M31 are relatively common. There are roughly a couple dozen novae discovered (brighter than about absolute magnitude -4) in M31 each year. There are ten known galactic recurrent novae. The recurrent nova typically brightens by about 8.6 magnitude, whereas a classic nova brightens by more than 12 magnitude.>>
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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by BDanielMayfield » Sat Dec 07, 2013 2:42 pm

Boomer12k wrote:Why do all the interesting things happen in the Southern Hemisphere?????
Boomer, you are suffering from H.L.E. (Hemispherical Location Envy), which is caused by being on the wrong side of the planet whenever something amazing is happening that can only be seen from the other side. Beware, for this can lead to spending vast sums on travel, which can result in H.L.E.P. (Hemispherical Location Envy Poverty), causing one to need help. :lol2:

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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by BDanielMayfield » Sat Dec 07, 2013 3:12 pm

It’s interesting that a “runaway thermonuclear event” involving hydrogen burning can happen on or near the surface of a white dwarf, while in the cores of stars hydrogen is fused at such a slow pace that stars can stay on the main sequence for millions, billions and in the case of the lightest stars, trillions of years.

How can the same nuclear reaction produce such differing effects?

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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by Chris Peterson » Sat Dec 07, 2013 3:38 pm

BDanielMayfield wrote:It’s interesting that a “runaway thermonuclear event” involving hydrogen burning can happen on or near the surface of a white dwarf, while in the cores of stars hydrogen is fused at such a slow pace that stars can stay on the main sequence for millions, billions and in the case of the lightest stars, trillions of years.

How can the same nuclear reaction produce such differing effects?
It's not necessarily the same nuclear reaction. Inside stellar mass main sequence stars, the primary reaction is normally the p-p chain. What occurs on the surface of a white dwarf- at a higher temperature and pressure- is normally the CNO cycle, a different reaction that is the one driving high mass stars.

Fundamentally, I think the difference is that the fusion on the surface of a white dwarf is occurring in a very different temperature-pressure space than the fusion that occurs in a stellar core.
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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by Ann » Sat Dec 07, 2013 4:11 pm

BDanielMayfield wrote:It’s interesting that a “runaway thermonuclear event” involving hydrogen burning can happen on or near the surface of a white dwarf, while in the cores of stars hydrogen is fused at such a slow pace that stars can stay on the main sequence for millions, billions and in the case of the lightest stars, trillions of years.

How can the same nuclear reaction produce such differing effects?

Bruce
The utter non-mathematician that is me should not even attempt to answer that. Nevertheless, this is how I think of it.

Inside main sequence stars, hydrogen fusion takes place at a slow pace because the stellar core is not strongly compressed and the temperature of the core is not exceedingly high. When a star leaves the main sequence and core hydrogen fusion ceases, the stellar core shrinks and its temperature rises. Although this very greatly affects the star, whose outer layers expand mightily, there is no danger at this stage of the star being destroyed.

When the core has been sufficiently compressed, and the temperature in the core has risen sufficiently, core helium fusion will take place. Core helium fusion will be the end of the line for our own Sun. When the Sun, several billion years into the future, has used up its core helium, its core will be inert. It will shrink and heat, but the mass of the core (and the layers of the Sun weighing down on the core) will not be enough to heat the core to the sort of temperature where other kinds of fusion can take place. Similarly, the mass of the core and the layers of the Sun weighing down on the core will not be nearly enough to compress the core to the point where it can become a black hole. The core of the Sun will have reached the end of the line.

Yes, but for a while the Sun will still keep both helium fusion and hydrogen fusion going in shells around its core. But the way that the helium-fusing and hydrogen-fusing shells of the Sun will interact with each other is going to make the Sun unstable. This instability will lead to worse and worse convulsions in the Sun, until the Sun casts off its outer layer and becomes first a planetary nebula and then a cooling white dwarf. And that will be the end of the line for the Sun.

Okay. But now imagine that the Sun had been more massive than it is. Imagine that it had been "teetering on the brink" as to whether or not it would be able to get carbon fusion and oxygen fusion going. It almost got there. But not quite.

Now image that the inert core that almost got more fusion going in itself has a stellar companion. And imagine that this stellar companion dumps matter on the inert core. And imagine that suddenly a large enough helping of gas is dumped on the core to start a "runaway thermonuclear event". How can this happen?

This is how I understand it. I believe that the core is relatively homogeneous. All of it is quite tightly packed, and all of it is made up of more or less the same elements. And all of it, mind you, is prime "fuel". All it takes to turn this inert core into a super-duper amazing super-bomb is to add a smidgen of mass. Remember that the only thing that prevented this core from getting another round of fusion going while the core was inside a functioning star was just a bit more mass coming into the core. Now the core is naked, but it is still able to get a brand new round of fusion going if only it gets a sufficient helping of new mass. And if this mass is coming, from a companion star, then every part of this previously inert core is ready to start turning itself into another kind of matter and also into pure energy. Remember that there is no "stellar envelope" to absorb the shock of the onset of this fusion. Every part of the core is turning itself into matter and pure energy almost simultaneously. Remember that the core is its own fuel, and remember that the core is so closely packed that every part of it has its own fuel right at hand.

Okay. That's how I understand a Type Ia supernova. I have probably missed some very important aspects of it, and I would be grateful to anyone who can set me straight! :D

And as for why most novae just involve the outer parts of the white dwarf, and not the whole star, well, that is something that I'd appreciate some information about! :wink:

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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by eltodesukane » Sat Dec 07, 2013 4:43 pm

Chris Peterson wrote:
Beyond wrote:Naked eye Nova :?: Well, at least put a monocle on it :!:
"Naked" is a high value keyword in lots of nanny filters of the sort used by libraries and schools. It's crazy, but today's APOD is probably going to be blocked at a lot of sites.
Just like me not able to access my Hotmail account from the public library, because hot sites are censored.

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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by BDanielMayfield » Sat Dec 07, 2013 5:19 pm

Chris Peterson wrote:
BDanielMayfield wrote:It’s interesting that a “runaway thermonuclear event” involving hydrogen burning can happen on or near the surface of a white dwarf, while in the cores of stars hydrogen is fused at such a slow pace that stars can stay on the main sequence for millions, billions and in the case of the lightest stars, trillions of years.

How can the same nuclear reaction produce such differing effects?
It's not necessarily the same nuclear reaction. Inside stellar mass main sequence stars, the primary reaction is normally the p-p chain. What occurs on the surface of a white dwarf- at a higher temperature and pressure- is normally the CNO cycle, a different reaction that is the one driving high mass stars.

Fundamentally, I think the difference is that the fusion on the surface of a white dwarf is occurring in a very different temperature-pressure space than the fusion that occurs in a stellar core.
Right, and thanks for making those points Chris. Differing temps and pressures are key to the differing effects, as I was aware. But there is much more to the story, as you obviously know too.

A point that I’d like to see discussed for the benefit of all is how and why, since these p-p and CNO cycle nuclear fusion reactions produce more heat than what is required to cause them, runaway chain reactions don’t happen in the cores of hydrogen burning MS stars. This is fundamental to stellar longevity, without which life in the universe would be impossible.

The fusing of two deuterium (heavy hydrogen) nuclei is part of the p-p reaction that causes the sun-like stars to be able to shine for such enormous time spans. While mankind has learned how to fuse deuterium in a runaway chain reaction (an H-bomb), but as yet we haven’t learned how to harness the stars’ enormous power source in a controlled, sustainable way.

Figuring out how to harness nuclear fusion for energy generation could be extremely important. We can compare our present situation with nuclear fusion to man’s early experiences with fire. We might be in or near the Bronze Age as far as nuclear “fire” is concerned. We know how to burn and blow things up and even fuse some atoms in the lab, but that’s about it. The fusion equivalent of the internal combustion engine hasn’t been invented yet, but if or when it is, things could really take off.

Self edit: "The fusing of two deuterium" directly together rarely happens. For the reactions that do in the proton-proton or p-p chain see:http://en.wikipedia.org/wiki/P-p_chain
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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by BDanielMayfield » Sat Dec 07, 2013 6:46 pm

Ann wrote:Inside main sequence stars, hydrogen fusion takes place at a slow pace because the stellar core is not strongly compressed and the temperature of the core is not exceedingly high. When a star leaves the main sequence and core hydrogen fusion ceases, the stellar core shrinks and its temperature rises. Although this very greatly affects the star, whose outer layers expand mightily, there is no danger at this stage of the star being destroyed.
Yes Ann, but all things are relative.
Wikipedia wrote:The core of the Sun is considered to extend from the center to about 0.2 to 0.25 solar radius.[1] It is the hottest part of the Sun and of the Solar System. It has a density of up to 150 g/cm³ (150 times the density of liquid water) and a temperature of close to 15,000,000 kelvin, or about 15,000,000 degrees Celsius; by contrast, the surface of the Sun is close to 6,000 kelvin. The core is made of hot, dense gas in the plasmic state. The core, inside 0.24 solar radius, generates 99% of the fusion power of the Sun.
But the question remains, since fusion reactions produce more heat than is needed to cause them, why doesn’t the temperature continue to rise in cores once fusion starts? Why is there no runaway chain reaction?
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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by Paul Barrett » Sat Dec 07, 2013 7:13 pm

I would just like to note that the secondary in a cataclysmic variable (CV), i.e., the binary that produces a nova, is almost always a red dwarf, typically with a mass of <0.3 solar masses and an orbital period of <6 hours. I am aware of only one CV that has a red subgiant as a companion. It has the variable star designation of GK Per (see APOD 2011 Nov 05) and has an orbital period of 1.9 days. There is also a subclass of CVs that have a white dwarf companion. They have orbital periods of <30 minutes.

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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by Cousin Ricky » Sat Dec 07, 2013 7:49 pm

Boomer12k wrote:Why do all the interesting things happen in the Southern Hemisphere????? OR in the dead of a cold wave the likes of which has not been seen for a decade???
Or at the wrong time? It would be visible from my latitude (in the southern part of the northern hemisphere), except that it doesn't rise until after the start of civil twilight. :(

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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by Nitpicker » Sat Dec 07, 2013 8:08 pm

Chris Peterson wrote:"Naked" is a high value keyword in lots of nanny filters of the sort used by libraries and schools. It's crazy, but today's APOD is probably going to be blocked at a lot of sites.
On the other hand, if a few porn-addled minds inadvertently stumble upon this APOD, they might just see the light.

Quite out of character, I woke up at 3:30am today and the clouds parted with perfect timing to reveal the light of this nova to my naked eyes (and fully clothed body). I got a few shots of it with Crux and the Pointers in frame, too.

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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by rstevenson » Sat Dec 07, 2013 8:49 pm

BDanielMayfield wrote:... But the question remains, since fusion reactions produce more heat than is needed to cause them, why doesn’t the temperature continue to rise in cores once fusion starts? Why is there no runaway chain reaction?
By definition, a runaway nuclear reaction in a stellar core produces a supernova. So your question becomes, why aren't all stars turning into supernovas. The answer, as I'm sure you know, is there is not enough mass in most stars. How does that prevent runaway nuclear reactions in most stars? Two words: hydrostatic equilibrium. The lesser amount of pressure (from gravity) in smaller stars means that as the reaction heats up, it is able to push material away from the reaction, slowing it down. This natural damping effect keeps the core reaction in balance, just hot enough to keep burning for very long periods of time.

edit: Here's a link that explains that better than I did.

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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by BDanielMayfield » Sun Dec 08, 2013 1:43 am

Yes Rob, it is very true that the cores of stable stars are in hydrostatic equilibrium. A very important factor here is heat transfer. Since heat always flows from hotter to cooler areas, heat is always moving out from the core into the cooler regions toward the coolest region of all at its surface, where heat is radiated away into space. Thus even though heat is being continuously generated, and hotter temps would cause more reactions, the rate of heat flow away from the core maintains a stable core temperature, and the reaction rate stays constant as well.

Our sun, a rather ordinary main sequence star, currently converts about 620 million metric tons of hydrogen into helium each second.
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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by Anthony Barreiro » Sun Dec 08, 2013 4:49 am

Nitpicker wrote: Quite out of character, I woke up at 3:30am today and the clouds parted with perfect timing to reveal the light of this nova to my naked eyes (and fully clothed body). I got a few shots of it with Crux and the Pointers in frame, too.
Good show! I hope you'll post a link to your pictures.

It still seems very odd to me that a nuclear explosion can happen on the surface of a white dwarf in a binary system, shining very brightly, but leaving the system intact to repeat the whole show at some time in the future.

And then there's electron degeneracy. Who really understands that?
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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by Nitpicker » Sun Dec 08, 2013 5:01 am

Anthony Barreiro wrote:
Nitpicker wrote: Quite out of character, I woke up at 3:30am today and the clouds parted with perfect timing to reveal the light of this nova to my naked eyes (and fully clothed body). I got a few shots of it with Crux and the Pointers in frame, too.
Good show! I hope you'll post a link to your pictures.
Thanks Anthony. Here are my pics:
http://asterisk.apod.com/viewtopic.php? ... 00#p215495

I didn't think mine were quite good enough to post in the same topic as today's APOD. I might try and get a slightly deeper telescopic shot soon, but doing that sort of thing before dawn is a challenge for me.

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Re: APOD: Naked Eye Nova Centauri 2013 (2013 Dec 07)

Post by Chris Peterson » Sun Dec 08, 2013 5:37 am

Anthony Barreiro wrote:It still seems very odd to me that a nuclear explosion can happen on the surface of a white dwarf in a binary system, shining very brightly, but leaving the system intact to repeat the whole show at some time in the future.
What is there to destroy the system? Even in the case of a supernova, releasing orders of magnitude more energy, it is possible that orbiting planets could survive, still gravitationally bound to the remnant parent star.
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