Starship Asterisk*

Messier 109

Explanation: Beautiful barred spiral galaxy M109, 109th entry in Charles Messier's famous catalog of bright Nebulae and Star Clusters, is found just below the Big Dipper's bowl in the northern constellation Ursa Major. In telescopic views, its striking central bar gives the galaxy the appearance of the Greek letter "theta", θ, a common mathematical symbol representing an angle. Of course M109 spans a very small angle in planet Earth's sky, about 7 arcminutes or 0.12 degrees. But that small angle corresponds to an enormous 120,000 light-year diameter at the galaxy's estimated 60 million light-year distance. The brightest member of the now recognized Ursa Major galaxy cluster, M109 (aka NGC 3992) is joined by three spiky foreground stars strung out across this frame. The three small, fuzzy bluish galaxies also on the scene, identified left to right as UGC 6969, UGC 6940 and UGC 6923, are possibly satellite galaxies of the larger M109.

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If those small blue galaxies are satellites of M 109, then they are dominated by stars that are much younger than the stars that dominate M 109.

The mass-to-light ratio is much higher for old yellow stars than for young blue ones: in other words, you get a lot of "oomph" for the mass of young blue stars, whereas old yellow stars glow dimly for their mass.

There are billions and billions and billions of small yellow stars in the bulge, bar and lens of M 109. But the small blue companions are made up of only a fraction of that number of stars, but the stars themselves shine brilliantly.

Ann

Really nice picture...very clear...

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It's nice to see this underrated galaxy get some love from the astroimaging scene! One of the most ignored Messier galaxies in my opinion.

Whenever I look at an image like this - of any galaxy that looks similar to our own - I always imagine a small star somewhere towards the outer edge, that has a few planets orbiting it.. and on one of these sits a being gazing at an image taken by one of their astronomers of a far-away galaxy that looks just like theirs........

Ann wrote:If those small blue galaxies are satellites of M 109, then they aredominated by stars that are much younger than the stars that dominate M 109.

The mass-to-ligt ratio is much higher for old yellow stars than for young blue ones: in other words, you get a lot of "oomph" for the mass of young blue stars, whereas old yellow stars glow dimly for their mass.

There are billions and billions and billions of small yellow stars in the bulge, bar and lens of M 109. But the small blue companions are made up of only a fraction of that number of stars, but the stars themselves glow comparatively brilliantly.

Ann

Wouldn't that make the "mass-to-light ratio" much lower for old yellow stars than for young blue ones?

flash wrote:

Ann wrote:If those small blue galaxies are satellites of M 109, then they aredominated by stars that are much younger than the stars that dominate M 109.

The mass-to-ligt ratio is much higher for old yellow stars than for young blue ones: in other words, you get a lot of "oomph" for the mass of young blue stars, whereas old yellow stars glow dimly for their mass.

There are billions and billions and billions of small yellow stars in the bulge, bar and lens of M 109. But the small blue companions are made up of only a fraction of that number of stars, but the stars themselves glow comparatively brilliantly.

Ann

Wouldn't that make the "mass-to-light ratio" much lower for old yellow stars than for young blue ones?

I often have to double check myself around things regarding things like higher/lower, more/less, left/right, etc. When I took algebra in high school and calculus in college (back in those days we did our calculations by scratching burnt sharpened sticks on flat rocks) I would often solve equations correctly except that somewhere along the way I had made a positive number negative, or vice versa, so I would get no credit!

With that disclaimer in mind, Ann's statement makes sense to me. In an old yellow star there is a high mass and a low light output. So there is a high mass to light ratio.

By the way, when I was looking at this lovely picture of M109 I was appreciating the rich golden color in M109's central bulge and bar and the blue speckles in the outer spiral arms and the other little galaxies. Thanks Ann for helping me understand the colors of stars and galaxies.

Anthony Barreiro wrote:I often have to double check myself around things regarding things like higher/lower, more/less, left/right, etc. When I took algebra in high school and calculus in college (back in those days we did our calculations by scratching burnt sharpened sticks on flat rocks) I would often solve equations correctly except that somewhere along the way I had made a positive number negative, or vice versa, so I would get no credit!

A pretty crummy teacher who wouldn't see a trivial sign error in the middle of perfectly correct reasoning. An error like that should barely reduce your credit at all!

With that disclaimer in mind, Ann's statement makes sense to me. In an old yellow star there is a high mass and a low light output. So there is a high mass to light ratio.

The way I think of it is that the mass is pretty much constant, be it an individual star over most of its life, or an entire galaxy. But the light output certainly isn't- old stars (that is, stars that have moved off the main sequence) are cooler, and not only does that shift their spectral output, but also reduces their intensity. So- constant mass, decreasing intensity means an increase in the mass-to-light ratio.

http://csep10.phys.utk.edu/astr162/lect ... sslum.html

The way I read it, doubling the mass of a star results in more than an order of magnitude increase in luminosity. (11.3)
This applies to main sequence stars.
Considering the stars as one homogeneous mass won't work.

stephen63 wrote:
. http://csep10.phys.utk.edu/astr162/lect ... sslum.html

The way I read it, doubling the mass of a star results in more than an order of magnitude increase in luminosity. (11.3)
This applies to main sequence stars.
Considering the stars as one homogeneous mass won't work.

http://en.wikipedia.org/wiki/Mass%E2%80 ... y_relation

It's an excellent picture. On examining it closer (particularly when enlarging the image) many probable galaxies can be seen, some faint but others less so. There is a nice spiral galaxy near the bottom right corner at about 7:30 from the brightest star there.

This is such a beautiful image. Not only is the galaxy Messier 109 lovely, the addition of it's two satellites in the photo gives a clear idea of how vast and isolating distances of space are. Thank you APOD.

Chris Peterson wrote:

Anthony Barreiro wrote:I often have to double check myself around things regarding things like higher/lower, more/less, left/right, etc. When I took algebra in high school and calculus in college (back in those days we did our calculations by scratching burnt sharpened sticks on flat rocks) I would often solve equations correctly except that somewhere along the way I had made a positive number negative, or vice versa, so I would get no credit!

A pretty crummy teacher who wouldn't see a trivial sign error in the middle of perfectly correct reasoning. An error like that should barely reduce your credit at all!

On further reflection, I probably did get partial credit for these equations. I passed the classes after all, although not at the top of the class. In my youthful narcissism, partial credit probably felt like no credit.

Chris Peterson wrote:

Anthony Barreiro wrote:With that disclaimer in mind, Ann's statement makes sense to me. In an old yellow star there is a high mass and a low light output. So there is a high mass to light ratio.

The way I think of it is that the mass is pretty much constant, be it an individual star over most of its life, or an entire galaxy. But the light output certainly isn't- old stars (that is, stars that have moved off the main sequence) are cooler, and not only does that shift their spectral output, but also reduces their intensity. So- constant mass, decreasing intensity means an increase in the mass-to-light ratio.

Well said.