APOD: MyCn18: An Hourglass Planetary Nebula (2015 May 10)

[APOD Robot]

MyCn18: An Hourglass Planetary Nebula

Explanation: The sands of time are running out for the central star of this hourglass-shaped planetary nebula. With its nuclear fuel exhausted, this brief, spectacular, closing phase of a Sun-like star's life occurs as its outer layers are ejected - its core becoming a cooling, fading white dwarf. In 1995, astronomers used the Hubble Space Telescope (HST) to make a series of images of planetary nebulae, including the one above. Here, delicate rings of colorful glowing gas (nitrogen-red, hydrogen-green, and oxygen-blue) outline the tenuous walls of the hourglass. The unprecedented sharpness of the HST images has revealed surprising details of the nebula ejection process that are helping to resolve the outstanding mysteries of the complex shapes and symmetries of planetary nebulas.

<< Previous APOD

This Day in APOD

Next APOD >>

[/b]

[Ann]

The Eye in the Sky. I'm just saying.

What is it about this planetary nebula that makes it look like a green eye surrounded by two sets of red rings?

Ann

[RocketRon]

Indeed. Here's looking at you, kid.

[geckzilla]

What is it about this planetary nebula that makes it look like a green eye surrounded by two sets of red rings?

The center is a place dominated by emissions from Ha (656nm) and [OIII] (502nm). [NII] (658nm) here in red is noticeably less prominent in the center, which results in a somewhat cyan appearance since the green and blue channels are much brighter.

The rings are simply rings but rather they are the contours of an hourglass as seen at a significant inclination. At a 0° inclination, the hourglass would be seen in profile and be easy for one to interpret. The higher the inclination, the less it looks like an hourglass. If it were at a perfect 90° inclination, we would have a very hard time telling what shape it really is since the dimensions of the two lobes would be totally overlapping one another. Then again, maybe then we'd be able to see what's going on with that bright, inner structure better. As it is, it's pretty difficult to even distinguish the foreground lobe from the background lobe.

[daddyo]

Heeeerrrss Sauron!

[alex_space]

I suppose the dying star is the white dot inside the green region. Why is it not centered in the dark part of the green region ? For what reason symmetry is broken ?

[Dad is watching]

this brief, spectacular, closing phase of a Sun-like star

Relative to our solar system, what would the dimensions of this nebula be? (diameter, height, width, etc?) Also, what controls the general shape of the ejected material? Does it align with the axis of rotation of the star, the magnetic field of the star, or the plane of an (assumed) accretion disk/planetary system, or is some other natural force in control?

[starsurfer]

This image strongly evokes my childhood, I remember being gobsmacked when I used to see that image in astronomy books published in the late 90's. I love astronomy and everyone involved in it! Big hugs to the universe!

[Craine]

The Eye in the Sky. I'm just saying.

What is it about this planetary nebula that makes it look like a green eye surrounded by two sets of red rings?

Ann

It's the illuminati.

[Chris Peterson]

Relative to our solar system, what would the dimensions of this nebula be? (diameter, height, width, etc?)

The object subtends about 25 arcseconds. At a distance of 8000 light years, that makes its size about one light year. Of course, it's asymmetrical, so that figure just gives a sense of dimension. But what it means is that the object is about the size of our solar system.

Also, what controls the general shape of the ejected material? Does it align with the axis of rotation of the star, the magnetic field of the star, or the plane of an (assumed) accretion disk/planetary system, or is some other natural force in control?

Presumably, the spin and magnetic axes of the progenitor, as well as orbit of any possible companion star. The effect of any planetary system components is probably insignificant.

[Craine]

this brief, spectacular, closing phase of a Sun-like star

Relative to our solar system, what would the dimensions of this nebula be? (diameter, height, width, etc?) Also, what controls the general shape of the ejected material? Does it align with the axis of rotation of the star, the magnetic field of the star, or the plane of an (assumed) accretion disk/planetary system, or is some other natural force in control?

If I read this correctly:
http://iopscience.iop.org/1538-3881/119/1/315/fulltext/
then the widest part of the hourglass has a diameter of about 1/3 light-year. But frankly, there is a pretty good chance I am not reading that correctly. Any of the boffin types on here want to comment?

[neufer]

I suppose the dying star is the white dot inside the green region.
Why is it not centered in the dark part of the green region ?
For what reason symmetry is broken ?

• It might be part of a binary star system but is >10,000 more luminous than it's companion:

[b][color=#0000FF]Hertzsprung-Russell(HR) diagram, showing the evolutionary phase of a low mass star towards the planetary nebulae phase. (Credit: Swinburne)[/color][/b]

---

• SAO astro news

<<Planetary nebulae (PNe) come in a wide variety of shapes, with complex morphologies including asymmetries, bipolar jets and high-velocity outflows. The origin of their complex structure has been debated for many years – how can a spherical star produce such an asymmetric structure? The resulting asymmetry is likely due to processes that occurred during the main mass-loss phase of the star and are thought to result from a central binary system, or structure in the local stellar magnetic field, or both.>>

[MDB]

There is another star at the 5 o'clock position relative to the central star. Is it part of a two star system or an unrelated star?

Mike

[Boomer12k]

Hubble.... A true scientist.... Went out, used his intrument, took his data, got measurements... Made obsevations, did his calculations, came to his conclusions, and repeated, and got new, and more observations, and measurements, etc....even though he was not always correct, as he kept finding farther away objects...

Did not rely on theory, and conjecture, smashed the limited theories....changed Einstein's view, and changed Astronomy forever... And the instrument named after him has done a slendid job of continueing that legacy....

:---(===) *

[Ann]

[b][color=#0000FF]Hertzsprung-Russell(HR) diagram, showing the evolutionary phase of a low mass star towards the planetary nebulae phase. (Credit: Swinburne)[/color][/b]

---

• SAO astro news

<<Planetary nebulae (PNe) come in a wide variety of shapes, with complex morphologies including asymmetries, bipolar jets and high-velocity outflows. The origin of their complex structure has been debated for many years – how can a spherical star produce such an asymmetric structure? The resulting asymmetry is likely due to processes that occurred during the main mass-loss phase of the star and are thought to result from a central binary system, or structure in the local stellar magnetic field, or both.>>

Judging from that diagram, it looks like the planetary nebula phase starts when the parent star has a temperature of about 3,500 K. The stellar corpse then gets hotter until it hits a temperature of about 7,000 - 10,000 K. Obviously that is not correct. In order to ionize an emission nebula, a star has to have a temperature of at least 20,000 K.

Ann

[Chris Peterson]

Hubble.... A true scientist....

Did not rely on theory, and conjecture, smashed the limited theories....changed Einstein's view, and changed Astronomy forever... And the instrument named after him has done a slendid job of continueing that legacy....

Say what? Hubble totally relied on theory. He totally utilized conjecture. That's exactly what scientists do!

[neufer]

Judging from that diagram, it looks like the planetary nebula phase starts when the parent star has a temperature of about 3,500 K. The stellar corpse then gets hotter until it hits a temperature of about 7,000 - 10,000 K. Obviously that is not correct. In order to ionize an emission nebula, a star has to have a temperature of at least 20,000 K.

• The rest of the Story

The planetary nebula phase starts when the parent star has a temperature of about 3,500 K.
The planetary nebula phase ends when the parent star has a temperature of about 35,000 K.

But the total luminosity (from core burning) remains constant!

[neufer]

Hubble.... A true scientist....

Did not rely on theory, and conjecture, smashed the limited theories....changed Einstein's view, and changed Astronomy forever... And the instrument named after him has done a splendid job of continuing that legacy....

Say what? Hubble totally relied on theory. He totally utilized conjecture. That's exactly what scientists do!

• Hubble mostly relied & utilized the hard work of others:

<<Edwin Hubble is commonly incorrectly credited with discovering the redshift of galaxies; these measurements and their significance were understood before 1917 by James Edward Keeler (Lick & Allegheny), Vesto Melvin Slipher (Lowell), and William Wallace Campbell (Lick) at other observatories. Combining his own measurements of galaxy distances with Vesto Slipher's measurements of the redshifts associated with the galaxies, Hubble and Milton Humason discovered a rough proportionality of the objects' distances with their redshifts. This redshift-distance correlation, nowadays termed Hubble's law, was formulated by Hubble and Humason in 1929 and became the basis for the modern model of the expanding universe.>>

• . https://telescoper.wordpress.com/2012/0 ... s-slipher/

[Chris Peterson]

• Hubble mostly relied & utilized the hard work of others:

<<Edwin Hubble is commonly incorrectly credited with discovering the redshift of galaxies; these measurements and their significance were understood before 1917 by James Edward Keeler (Lick & Allegheny), Vesto Melvin Slipher (Lowell), and William Wallace Campbell (Lick) at other observatories. Combining his own measurements of galaxy distances with Vesto Slipher's measurements of the redshifts associated with the galaxies, Hubble and Milton Humason discovered a rough proportionality of the objects' distances with their redshifts. This redshift-distance correlation, nowadays termed Hubble's law, was formulated by Hubble and Humason in 1929 and became the basis for the modern model of the expanding universe.>>

I wouldn't say that the correct significance was understood in 1917. Even Hubble incorrectly believed that the redshift was caused by recession of distant galaxies.

FWIW, another aspect of science is depending heavily on the previous work of others.

[Boomer12k]

I stand corrected.... Did not mean to make it sound like he did it alone....of course he did not...
Did not say he discovered red shifts... Only meant his work changed things...and if he relied on the work and conjecture of others... It did not stop him...after all... If everything is known to be true by conjecture.... Why look?

He got out there...and looked...

:---(===) *

[Chris Peterson]

If everything is known to be true by conjecture.... Why look?

I don't really understand what that means. Every single piece of scientific knowledge we have starts with conjecture. It is critical to the scientific method.

[geckzilla]

My own personal conjecture about this nebula is that it is not off-center from its star at all. Of course, every astronomical paper I've looked at regarding it disagrees with what I think, so that's not a good sign, but I haven't given up quite yet. Either I will be convinced or I will convince others. I need to learn some more stuff first. Preplanetary nebulae are definitely my favorite topic.

[geckzilla]

Here's an image that shows the individual filters. Compare to the APOD which has been darkened in the center to make those central structures easier to discern, but that process also removed the dynamic range natural to the nebula. It's actually very bright in the center.

I've put emphasis on the 502nm channel to make it easier to see. You should see clearly that the [OIII] is more concentrated centrally and comparatively diffuse. Ha is assigned to green and [NII] shown as red. The assignment of colors results in something very typical of planetary nebulae, but you'd find it more familiar if you looked at the famous Helix Nebula, which is inclined to us in a way that makes the separation of colors very easy to notice. Blue-green on the inside, yellow between, and red on the outside corresponding to energy levels of the ions surrounding the star. It's profoundly beautiful.

[RocketRon]

Relative to our solar system, what would the dimensions of this nebula be? (diameter, height, width, etc?)

The object subtends about 25 arcseconds. At a distance of 8000 light years, that makes its size about one light year. Of course, it's asymmetrical, so that figure just gives a sense of dimension. But what it means is that the object is about the size of our solar system.

The size of our solar System is an interesting comment.
When Pluto is 'only' 5 or 6 light hours away, presumeably you are extending the Solar System limits far into space ??
Or does 'the object' signify something other than the whole nebula ?

[neufer]

Relative to our solar system, what would the dimensions of this nebula be? (diameter, height, width, etc?)

The object subtends about 25 arcseconds. At a distance of 8000 light years, that makes its size about one light year. Of course, it's asymmetrical, so that figure just gives a sense of dimension. But what it means is that the object is about the size of our solar system.

The size of our solar System is an interesting comment.

When Pluto is 'only' 5 or 6 light hours away, presumeably you are extending the Solar System limits far into space ??

Chris is extending the Solar System limits into the Oort Cloud.