APOD: M100: A Grand Design Spiral Galaxy (2015 Feb 11)

[APOD Robot]

M100: A Grand Design Spiral Galaxy

Explanation: Majestic on a truly cosmic scale, M100 is appropriately known as a grand design spiral galaxy. It is a large galaxy of over 100 billion stars with well-defined spiral arms that is similar to our own Milky Way Galaxy. One of the brightest members of the Virgo Cluster of galaxies, M100 (alias NGC 4321) is 56 million light-years distant toward the constellation of Berenice's Hair (Coma Berenices). This Hubble Space Telescope image of M100 was made in 2006 and reveals bright blue star clusters and intricate winding dust lanes which are hallmarks of this class of galaxies. Studies of variable stars in M100 have played an important role in determining the size and age of the Universe. If you know exactly where to look, you can find a small spot that is a light echo from a bright supernova that was recorded a few months before the image was taken.

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[Ann]

Nice work, Geck!

Tell me, is the supernova echo the small ring-like shape below and slightly to the right of the brightest yellow foreground star slightly below center of the picture?

Ann

[Boomer12k]

It appears to have two cores....a main brighter one, and the other next to it....


This is a slendid shot...but wish it was a tad wider....

:---[===] *

[BillBixby]

Judy S - You've brought out an image in blue that rocks. Ann had to like it!!! So do I. I love the talent attracted to APOD

[Case]

If you know exactly where to look, you can find a small spot that is a light echo from a bright supernova that was recorded a few months before the image was taken.

A light echo with a radius of approximately 3 pixels or more in the 4060px image. Is “a few light months” really that big a distance in the image? I didn't think the echo could grow that big in such a short time span.

Tell me, is the supernova echo the small ring-like shape?

There is an annotated version with the location at http://www.geckzilla.com/astro/SN2006X_light_echo.jpg

[geckzilla]

Yes, Case is on point. Thanks for that. My internet connection was out having midnight snack and I couldn't connect earlier.

[Nitpicker]

If you know exactly where to look, you can find a small spot that is a light echo from a bright supernova that was recorded a few months before the image was taken.

A light echo with a radius of approximately 3 pixels or more in the 4060px image. Is “a few light months” really that big a distance in the image? I didn't think the echo could grow that big in such a short time span.

The radius of the apparent light echo, a few months after the supernova, might be a lot bigger than a few light months. It depends on the radius of the material (previously surrounding the star before it popped) that is illuminated by the echo.

Edit: And great APOD! (Where are my manners?)

[geckzilla]

You are both right to be dubious about the use of "a few months" unless you are willing to accept 46 months as a few. Years is indeed a more appropriate word.

[Xyrcesfenol]

If you know exactly where to look, you can find a small spot that is a light echo from a bright supernova that was recorded a few months before the image was taken.

A light echo with a radius of approximately 3 pixels or more in the 4060px image. Is “a few light months” really that big a distance in the image? I didn't think the echo could grow that big in such a short time span.

The radius of the apparent light echo, a few months after the supernova, might be a lot bigger than a few light months. It depends on the radius of the material (previously surrounding the star before it popped) that is illuminated by the echo.

Edit: And great APOD! (Where are my manners?)

If the radius is bigger than the light months of the time that has passed since the star popped, it would have to tavel faster than light...?

[Nitpicker]

The radius of the apparent light echo, a few months after the supernova, might be a lot bigger than a few light months. It depends on the radius of the material (previously surrounding the star before it popped) that is illuminated by the echo.

Edit: And great APOD! (Where are my manners?)

If the radius is bigger than the light months of the time that has passed since the star popped, it would have to tavel faster than light...?

Not at all. The light moves at the speed of light. According to geck, the light echo we see in the APOD is closer to 4 years after the star popped. Now imagine a spherical shell of (comparatively) stationary dust around the star, existent beforehand. Imagine this sphere to have a radius of 10 light years, say. With such a sphere, the expanding parabolic light echo would be visible for 20 years, as it illuminated different parts of the spherical dust shell. At year zero it would appear like a dot (from in front of the star). The echo would expand to a circle, with the maximum radius of 10 light years being visible at year 10. The echo would then contract back down to a dot (from behind the star) over the next 10 years. But the apparent circle of illuminated dust we observe, does not expand and contract at uniform speed. At year 4, the circle would appear with a radius of about 7 or 8 light years.

[geckzilla]

At year 4, the circle would appear with a radius of about 7 or 8 light years.

Diameter?

[Nitpicker]

At year 4, the circle would appear with a radius of about 7 or 8 light years.

Diameter?

No, radius. The maximum radius is 10 light years at year 10. A radius of 5 light years would be seen around year 3.

[Nitpicker]

I've now gone through the actual mathematics of intersecting expanding paraboloids (star at the focus, vertex moving away from us at half the speed of light), with a static, spherical dust shell of radius 10 light years (surrounding the star), and the apparent echo radius we'd observe is summarised as follows (only a little different from my initial estimations):

hypothetical_parabolic_echo.PNG (7.33 KiB) Viewed 87236 times

Note: I've assumed paraboloids rather than ellipsoids, due to the practically infinite distance between M100 and Earth. The numbers are practically the same either way.

[kindness]

The center of the galaxy doesn't appear to be barred. As mentioned above there is a large concentrated mass off to the right of the 'center' in this galaxies image. Is that a very dense star cluster close to the center or does this galaxy have two black holes at it's center?

My guess it it's a cluster but that is just a guess.

[RJN]

You are both right to be dubious about the use of "a few months" unless you are willing to accept 46 months as a few. Years is indeed a more appropriate word.

OK. Indeed. (Oops.) I changed the text now to "years". Thanks!

- RJN

[Ann]

The center of the galaxy doesn't appear to be barred. As mentioned above there is a large concentrated mass off to the right of the 'center' in this galaxies image. Is that a very dense star cluster close to the center or does this galaxy have two black holes at it's center?

My guess it it's a cluster but that is just a guess.

No, this galaxy isn't obviously barred. But galaxy photographer and classifier James D Wray wrote about M100 in his book, The Color Atlas of Galaxies:

In the galaxy, note among other things the pattern of dust lanes in the lens. This pattern is actually characteristic of dust lanes associated with bars. The tendency for spiral arms to form outside a bar region may also be relevant here. The implication is that this system contains an incipient barred structure. It is conceivable that this system may actually be in dynamical transition into a fully developed barred galaxy.

Ann

[Visual_Astronomer]

Nice work, Geck!

Tell me, is the supernova echo the small ring-like shape below and slightly to the right of the brightest yellow foreground star slightly below center of the picture?

Ann

Yes. I remember seeing this supernova back in 2006. It's very cool to actually catch the light expanding into the surrounding galaxy!

[bystander]

Tell me, is the supernova echo the small ring-like shape below and slightly to the right of the brightest yellow foreground star slightly below center of the picture?

http://www.geckzilla.com/astro/SN2006X_light_echo.jpg

[Ron-Astro Pharmacist]

The orbital mechanics of two stars interacting must be a complicated, dynamic process. I think most would assume gravity is supplying most of the energy of their motions. Yesterday's APOD showed our suns magnetic fields in action. A highlight of today's APOD is the captured image of two stars initiating a supernova.

How much is realistically known about the mechanisms of gravito-magnetic interaction which leads to the various types of supernovae?

http://en.wikipedia.org/wiki/Gravitoelectromagnetism

Specifically, what prevents a (-) pole to (+) pole attraction between two stars? In asking this before (in reference to magnetars), I believe it was just stated an unlikely event.

Type 1a supernova involving white dwarf and companion or two white dwarfs (with significant magnetic fields) are much more common events. What keeps these strong magnet interactions from occurring in nature? I expect others have dispelled the notion of this common physical effect happening between stars. Is it radial velocity or field alignment or something quite different that overcomes magnet attraction?

As an addendum - some mechanisms for a core-collapse supernova are discussed in this paper (including magneto-hydrodynamic) but it's a bit much for me to decipher. It's very interesting despite its complexity.

http://arxiv.org/pdf/1206.2503v1.pdf

[Nitpicker]

Regarding the little light echo again, if we make the rough approximation on the full resolution image that 4000 pixels span 100,000 light years, then the outer radius of the little light echo is about 150 light years. Based on the APOD echo being four years old, this means that it is illuminating dust that is almost 3000 light years closer to us than the supernova. So, this dust probably wouldn't have originated from the star, but is more likely to be inter-stellar, galactic dust.

[geckzilla]

At year 4, the circle would appear with a radius of about 7 or 8 light years.

Diameter?

No, radius. The maximum radius is 10 light years at year 10. A radius of 5 light years would be seen around year 3.

Yeah, I am just not getting this light echo thing.

[Nitpicker]

Yeah, I am just not getting this light echo thing.

The light of the light echo we see in the APOD (outer radius ~150 light years), took 4 years longer to reach us than the original supernova burst. This is because the light that bounced off the illuminated dust we see, had to travel 4 light years further, because it did not travel in a straight line to us.

[geckzilla]

Yeah, I am just not getting this light echo thing.

The light of the light echo we see in the APOD (outer radius ~150 light years), took 4 years longer to reach us than the original supernova burst. This is because the light that bounced off the illuminated dust we see, had to travel 4 light years further, because it did not travel in a straight line to us.

Haha, you're making it worse. 150 light years? How'd it get so big in four years? And still struggling with the radius being twice as wide as expected... I need to tell Universe Sandbox developers to please add a light echo function to its light pulse feature so I can see this happening. My poor brain is just failing left and right on this.

[Nitpicker]

Perhaps I confused matters by initially discussing a hypothetical, spherical dust shell around the star. I invented the dust sphere to demonstrate a point (which I've clearly failed to do). Please forget the hypotheticals.

By measuring 12 pixels across the outer diameter of the light echo, in the full resolution APOD, I (roughly) estimate its apparent radius to be about 150 light years (or ~300 light years diameter). Based purely on the geometry of parabolas, and the knowledge that the light echo is about four years old, one can determine that the illuminated dust is almost 3000 light years closer to us than the supernova. You have to think in 3-D.

When we see an initial pulse of light from afar, we are also seeing anything that it illuminated along the way, in the direct line of sight. As time progresses, anything else illuminated by the initial pulse, that is not in our direct line of sight with the initial light source, will also appear to us, based on how much further the reflected light has to travel to us, and how long that takes.

[geckzilla]

I'm most certainly thinking in 3D (plus time) but my intuition is betraying me and I'm not following you. Or maybe you're wrong. I can't tell. Ha.