Born-again planetary nebula

July 28, 2015, European Space Agency
Credit: ESA/XMM-Newton/J.A. Toalá et al. 2015

Beneath the vivid hues of this eye-shaped cloud, named Abell 78, a tale of stellar life and death is unfolding. At the centre of the nebula, a dying star – not unlike our Sun – which shed its outer layers on its way to oblivion has, for a brief period of time, come back to echo its past glory.

Releasing their outer shells is the usual fate for any star with a mass of 0.8–8 times that of the Sun. Having exhausted the nuclear fuel in their cores after burning for billions of years, these stars collapse to become dense, hot white dwarf stars. Around them, the ejected material strikes the ambient gas and dust, creating beautiful clouds known as 'planetary nebulas'. This curious name was adopted by 18th-century astronomers who discovered these 'puffing' stars and thought their round shape similar to that of planets.

However, the resurgence to life seen in this image is an exceptional event for a planetary nebula. Only a handful of such born-again stars have been discovered, and here the intricate shape of the cloud's glowing material gives away its turbulent history.

Although nuclear burning of hydrogen and helium had ceased in the core of the , causing it to collapse under its own weight and its envelope to expand into a bubble, some of the star's outer layers became so dense that fusion of helium resumed there.

The renewed nuclear activity triggered another, much faster wind, blowing more material away. The interplay between old and new outflows has shaped the cloud's complex structure, including the radial filaments that can be seen streaming from the collapsing star at the centre.

The interaction between slow and fast winds gusting in the environment of Abell 78 heated the gas to over a million degrees, making it shine brightly in X-rays. Astronomers detected this hot gas with ESA's XMM-Newton space observatory, revealing striking similarities with another born-again , Abell 30.

This three-colour image combines X-ray data collected in 2013 by XMM-Newton (blue) with optical observations obtained using two special filters that reveal the glow of oxygen (green) and helium (red). The optical data were gathered in 2014 with the Andalusian Faint Object Spectrograph and Camera at the Nordic Optical Telescope on La Palma, in the Canary Islands. A study of the X-ray emission from Abell 78 is presented in a paper by J.A. Toalá et al. 2015.

Explore further: Image: XMM-Newton and Hubble view of Jupiter's ghost

More information: "The Born-Again Planetary Nebula A78: An X-Ray Twin Of A30." 2015 ApJ 799 67 DOI: 10.1088/0004-637X/799/1/67

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14 comments

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cantdrive85
2.3 / 5 (6) Jul 29, 2015
Plasma ball complete with the radial filaments.
Returners
1 / 5 (3) Jul 29, 2015
I'll never understand why a cooling star should expand more/more rapidly than a hot one.
Uncle Ira
3.1 / 5 (7) Jul 29, 2015
I'll never understand why a cooling star should expand more/more rapidly than a hot one.


Maybe you are looking at him backwards Cher. I am not the scientist so I might be getting it wrong me. Maybe the expanding star is cooling more rapidly than the not expanding star.
Enthusiastic Fool
4 / 5 (8) Jul 29, 2015
Plasma ball complete with the radial filaments.


Well, a star is a sphere of plasma...
https://en.wikipe...iki/Star
and the article does say radial filaments... but knowing you it's tough to not think you are implying filaments are electrical filaments like in light bulbs attempting to undermine the current understanding of stellar mechanics.

But for now I'll 5 you as it seems to be the most reasonably factual thing I've seen you post related to cosmology. Everyone deserves the benefit of the doubt. Welcome to the team?
Enthusiastic Fool
3.3 / 5 (7) Jul 29, 2015
I'll never understand why a cooling star should expand more/more rapidly than a hot one.


I'm not an expert but it seems to me that helium fusion starting back up in the now denser outer layers is not ideal for hydrostatic equilibrium and with less material "above" it wieghing down on it there's less buffering of the energy by convective outer layers allowing for a faster stellar wind and thus faster expansion of the bubble of material around it. Maybe I'm completely wrong but since helium burning under normal circumstances is signalled by the start of the red giant phase for many stars it makes sense to me that the wind/rate of expansion would be faster if He fusion was happening near the "surface". If I've misaprehended your question or led you astray here I'm sorry.
Uncle Ira
3.3 / 5 (7) Jul 29, 2015
I'll never understand why a cooling star should expand more/more rapidly than a hot one.


I'm not an expert but it seems to me that helium fusion starting back up in the now denser outer layers is not ideal for hydrostatic equilibrium and with less material "above" it wieghing down on it there's less buffering of the energy by convective outer layers allowing for a faster stellar wind and thus faster expansion of the bubble of material around it. Maybe I'm completely wrong but since helium burning under normal circumstances is signalled by the start of the red giant phase for many stars it makes sense to me that the wind/rate of expansion would be faster if He fusion was happening near the "surface". If I've misaprehended your question or led you astray here I'm sorry.


You get my karma points because I like your style. You thought about a maybe and didn't need to call all the professionals idiots and morons. More peoples should try to do the same.
cantdrive85
1.8 / 5 (5) Jul 29, 2015
Plasma ball complete with the radial filaments.


Well, a star is a sphere of plasma...
and the article does say radial filaments... but knowing you...


Well I am "attempting" to undermine the current understanding of stellar mechanics, due to the fact they are incorrect. The plasma ball I am referring to is like the novelty ball you get at Spencer's.
https://www.googl...sma+ball

Plasma filaments are by definition electrical, the only way to confine the plasma is via magnetism created by the movement of charge, i.e. electricity. One of these days the idiotic moronic astrophysicists will finally understand plasma for what it really is...
Returners
1.8 / 5 (5) Aug 01, 2015
EF:

Helium fusion supposedly requires more heat and pressure to get started and remain in progress than Hydrogen fusion. Moreover, there is less energy per unit mass in Helium fusion than there is in Hydrogen fusion. From that perspective, the helium fusion cycle requires a denser star to start burning than the proton-proton chain. The star expelling 1/3rd of its mass does not improve its chances of burning or continuing to burn helium. In fact, with the luminosity formula scientists use, losing 1/3rd of its mass should cool the star to about 1/5th the luminosity.

If you were to plot the continuous mass of the star on the X axis, and have this X axis represent mass decreasing with time (as the star allegedly burns off fuel) its luminosity(y-axis) should decrease with time, and therefore the likelihood of expelling gas into space actually decreases.

For this reason, the standard model of the red giant phase is flawed.

Whatever causes that phase, it is not helium fusion.
Returners
2 / 5 (4) Aug 01, 2015
There is a reason for this, sort of like tropical cyclone classification names, classifications are a man-made abstraction. The real star, just like a tropical cyclone, doesn't suddenly become "something different" just because you change from say 25% Helium to 30% helium by mass as it ages.

In a star of the right mass (about the same as our Sun) Helium actually starts fusing long before the star finishes consuming its core hydrogen. The Sun has been fusing Helium throughout its lifetime, and it is even provably hot enough to be burning the CNO cycle right now.

In stars which don't have a certain "critical mass", the "stage" transitions are very smooth. They are not this distinct "pow catastrophic change in a few days/years time" the way Supernovas can be. The Sun happens to be at exactly the right mass and initial composition so that it will never have this catastrophic phase change, because it burns core Helium as fast as it is made.
Returners
1.8 / 5 (5) Aug 01, 2015
The standard mode of the so-called "Red Giant" phase of stars is that core hydrogen runs out, and the core suddenly begins to collapse to a denser state until Helium starts burning, and this supposedly heats the star up even more and blows off the outer shells of the star forming a Red Giant, with a white dwarf remnant inside.

This sudden transitional stage does not make sense, because the equilibrium point of the star is still going to be the same, it will just need to burn helium faster than it was burning before in order to keep up with the old equilibrium point. That is to say Helium fusion should not blow the atmosphere off any more than hydrogen fusion.

When a star exhausts the heaviest fuel it can generate the appropriate temperature and pressure to fuse, then it should shrink (not expand) until it gets to a density where the nuclear force breaks even with gravity, and in this condition it will gradually cool for the remainder of time, unless it collide w something.
Returners
1.8 / 5 (5) Aug 01, 2015
The faint young sun paradox is faulty, because the Sun was not faint when it was young.

When a star starts burning, there should be a certain amount of time where the temperature of its entire mass must warm up to equilibrium with the reaction in its core, this would be represented by a steep temperature line vs time as the entire volume and surface of the star warm up. Then after this equilibrium is reached, as fuel and mass decrease with time, the luminosity of the star should continually decrease until it runs out of fuel.

That is what you get when you plot the luminosity formula with mass decreasing with time, as the star burns off some of its mass in the form of released nuclear bonds, and some in the form of winds and coronal mass ejections.

The nuclear model does not predict the behavior seen in :lanetary Nebula, even though that has been the textbook explanation for a century.
Returners
2 / 5 (4) Aug 01, 2015
I'll continue to oppose false sciences where ever I find them, in every nook and cranny of standard, accepted models which are self-contradictory.

And EXPANDING cloud is NOT "more dense" than a smaller cloud of the same mass, you louts.

Just read the article people. It's full of self-contradictions that you guys are so brainwashed into believing that you don't even question it any more.
Enthusiastic Fool
3 / 5 (2) Aug 01, 2015
@Returners

Correct, the proton-proton chain is dominant in sun-like dwarf stars...to a point. Once most of Hydrogen in the core is expended the core is made up of inert helium just sitting there, pressed on all sides by a shell of p-p chain fusing Hydrogen. This slowly heats up the helium while also producing... more helium. As less and less H burns the outward thermal pressure is not strong enough to counter gravitational contraction to degeneracy. The He core is at this point 40% of the mass of the star. He fusion can occur at "1×10^8 K". This causes thermal runaway and a helium flash wherein 60–80% of the helium core is suddenly burned to Be and then C12. From this point on the triple-alpha process is dominant in the core and the p-p chain occurs in the shell around the core.
https://en.wikipe...um_flash
https://en.wikipe..._process
tbc
Enthusiastic Fool
1 / 5 (2) Aug 01, 2015
cont.
I should mention that the helium flash actually occurs at the end of the red giant branch not the beginning as I earlier mispoke. The red giant expansion is caused by the temperature increase in the dense core increasing the reaction rate/energy production from the pp chain.

From the triple alpha process article: "The power released by the reaction is approximately proportional to the temperature to the 40th power, and the density squared.[4] Contrast this to the PP chain which produces energy at a rate proportional to the fourth power of temperature and directly with density."

I'm going to go out on a limb and guess that you already knew all this and are trolling. A wispy expanding cloud surrounding a massive dense core is more dense in the area where reactions take place than the same mass during pp chain H burning because the density is more stratified.

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