Jump to content

Narrowband

?? Why can we see "inside" the Ring Nebula?


m_j_lyons

Recommended Posts

I've observed the beautiful Ring Nebula (M57) many times and am always in live with the view. But after viewing a particularly detailed APOD graphic I was left with a question - why can we seeded inside the nebula? Why can we see the central star? I'd the start exploded it should form a sphere of debris/gas -right? What am I missing? It appears the stars explode in only 2 dimensions...which means that i'm missing some fundamental knowledge.

Anyone?

Sent from my Xoom using Tapatalk

Link to comment
Share on other sites

Good question.

From what I was reading the Ring nebula might not actually be a ring when viewed from a different angle to the earth.

Some have suggested its actually dumbbell shaped and we are looking at the top of it.

I suspect that the reason we can see the central star is that the explosion was so large that all its mass ejected nearly instantaneously forming a ring devoid of material in between which has now expanded away from its dying star.

Just my thoughts. :)

Link to comment
Share on other sites

Because for whatever reason it exploded to form a torus, and we are at the right position, above or below it, to be able to see it as a torus.

If we had been on the same plane then we would see a "bar" and would be asking why do we see it as a bar.

They do not have to explode as a sphere.

Perhaps the star from which it came was spinningg fast and so the explosion exited mainly in the equitorial band of the star.

Link to comment
Share on other sites

I would guess this stems from rotation. As the star rotates, material is expelled more in the equatorial plane than along the axis of rotation (simply because it has a higher velocity component in the plane than perpendicular to it). The reverse seems to happen in accretion disks, where matter is expelled more along the axis of rotation (the mechanisms of that are not fully understood, I think).

The gas is not opaque, by the way. Though it might absorb hydrogen and oxygen lines quite well (the same lines it emits) many other wavelengths may well pass through unhindered.

Link to comment
Share on other sites

Is it not a case of when we look straight at it we're only looking through a small amount of material but around the 'edges' we're looking through a much greater amount of material - a bit like looking straight up through the atmosphere versus looking near the horizon?

Of course, it'd be far more interesting if it is a strange shape and we happen to have a good vantage point :)

James

Link to comment
Share on other sites

I've always assumed it was due to the rotation as Michael says. The ring nebula we look at effectively from along the axis of rotation and more material is thrown off radially from this line, forming the ring.

Something like the dumbbell, we are looking at perpendicular to the axis of rotation so are seeing it more as a cylinder from the side, if that makes sense

Link to comment
Share on other sites

Is the term 'explosion' really the right one in this case? The Ring is a planetary nebula formed by fast stellar winds but not a supernova.

Olly

That would be me using the wrong term not understanding the nature of how these planetary nebula are formed more assuming they are formed by a method similar to supernovas.

Best brush up on my cosmology :)

Link to comment
Share on other sites

'Explosion' was the term used in the original post. I noted your choice of 'expelled,' Michael. I was just trying to clarify the difference between a planetary and a supernova. Mind you, the stellar winds from dying solar mass(ish) stars like this one are close to lightspeed which is faster than the bits flying off an exploding hand grenade!

Olly

Link to comment
Share on other sites

I have just checked definitions for explosion, and one option is....

' A violent expansion in which energy is transmitted outwards as a shock wave'

This doesn't seem too far from what's happening perhaps, although most descriptions I've seen use words like 'expelled' or ' thrown off' by pulsations in the star and fast stellar winds.

Either way I suppose it's better to be observing from a safe distance....

Stu

Link to comment
Share on other sites

Of course there are explosions, and then there are supernovae. There is nothing in our earthly experience which has allowed us to coin a different word for the magnitude of violence involved. Even setting of the entire nuclear arsenal of the entire world in a single blast is so many orders of magnitude below a supernova, that we are simply lost for words.

Link to comment
Share on other sites

Some very interesting replies :)

One thing is they are intriguing and one of my favourite targets in the night sky coming a close second to globular clusters.

I have had the Hubble image of M57, Ring Nebula as my PC wallpaper for a while now.

http://upload.wikimedia.org/wikipedia/commons/1/13/M57_The_Ring_Nebula.JPG

Wasn't there a big debate about the material which at the edge of the ring on the inner most edge from the perspective that we see it from? some weird steller activity in the shape of pillars? Cant remember what it was called :)

Link to comment
Share on other sites

Quote from webpage Messier Object 57

"Recent research has confirmed that it is, most probably, actually a ring (torus) of bright light-emitting material surrounding its central star, and not a spherical (or ellipsoidal) shell, thus coinciding with an early assumption by John Herschel. Viewed from this equatorial plane, it would thus more resemble the Dumbbell Nebula M27 or the Little Dumbbell Nebula M76 than its appearance we know from here: We happen to view it from near one pole. This is contrary to the belief expressed e.g. in Kenneth Glyn Jones' book. There are even indications from investigations of deep observations such as George Jacoby's deep photos obtained at Kitt Peak National Observatory that the overall shape might be more that of a cylinder viewed along the direction of the axis than that of a ring, i.e., we are looking down a tunnel of gas ejected by a star at the end of its nuclear-burning life. Eventually, these observations have given evidence that the equatorial ring or cylinder has lobe-shaped extensions in polar directions, similar to those found in deep images of M76, but even more resembling other planetaries like NGC 6302, see e.g. the review by Sun Kwok (2000)."

The shapes of planetary nebulae are hypothesized to be related to magnetic fields: there are various articles and papers online, e.g.

Magnetic Dynamo Appears To Shape Planetary Nebulae

http://www.staff.alfvenlab.kth.se/hanna.dahlgren/seminars/filaments.pdf

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.