Starship Asterisk*

starsurfer wrote:The other interesting thing about M15 is that it is one of four globular clusters in the Milky Way known to contain a planetary nebula. The one in M15 is called Pease 1 and would have been visible if exposures taken through an OIII filter had been included (that is if it lies in the field of view of this particular image).

alter-ego wrote:

starsurfer wrote:The other interesting thing about M15 is that it is one of four globular clusters in the Milky Way known to contain a planetary nebula. The one in M15 is called Pease 1 and would have been visible if exposures taken through an OIII filter had been included (that is if it lies in the field of view of this particular image).

The nebula is visible in this field. The 2004 APOD (one of the links) shows it more clearly as a nebula, and I've overlapped the old APOD with the new. (The hover utility works funny now )

Assuming the larger image is 120 ly x 120 ly, the earlier Hubble M15 photo (inset) is ~68 ly x 47 ly

Click to view full size image 1 or image 2

Juwie wrote:Seeing images like this I always wonder if there mustn't happen some star collisions. Or do they happen in a globular cluster - and if yes - how often?

Juwie wrote:Seeing images like this I always wonder if there mustn't happen some star collisions. Or do they happen in a globular cluster - and if yes - how often?

A stellar collision is the coming together of two stars, which through the force of gravity merge into one larger unit. Astronomers predict that events of this type occur in the globular clusters of our galaxy about once every 10,000 years.

http://en.wikipedia.org/wiki/Messier_14 wrote:
<<Messier 14 (also known as M14 or NGC 6402) is a globular cluster in the constellation Ophiuchus. It was discovered by Charles Messier in 1764. At a distance of about 30,000 light-years, M14 contains several hundreds of thousands of stars. At an apparent magnitude +7.6 it can be easily observed with binoculars. Medium-sized telescopes will show some hint of the individual stars of which the brightest is of magnitude +14. The total luminosity of M14 is in the order of 400,000 times that of the Sun corresponding to an absolute magnitude of -9.12. The shape of the cluster is decidedly elongated. M14 is about 100 light-years across. A respectable total of 70 variable stars is known in M14, many of the W Virginis variety common in globular clusters. In 1938, a nova appeared although this was not discovered until photographic plates from that time were studied in 1964. It is estimated that the nova reached a maximum brightness of magnitude +9.2, over five times brighter than the brightest 'normal' star in the cluster.>>

tomatoherd wrote:I hate to beat a dead horse ( i've asked this before) but these clusters still seem to defy gravity to me. Since they have a spherical symmetry instead of an axial symmetry (like galaxies), they must not have an organiized rotation to amount to anything, and therefore lack much in way of centrifugal forces to counteract gravity. So I don't know, after billions of years especially, why they don't collapse together. They appear much denser than the universe, which until relatively recent times, was thought could eventually collapse under its own mass attractions.
They certainly MUST NOT contain any dark matter (which I don't believe in), or this conundrum would be even more flagrant. Pardon my use of lay-persons physics, etc. Thanks.

tomatoherd wrote:
I hate to beat a dead horse ( i've asked this before) but these clusters still seem to defy gravity to me. Since they have a spherical symmetry instead of an axial symmetry (like galaxies), they must not have an organiized rotation to amount to anything, and therefore lack much in way of centrifugal forces to counteract gravity. So I don't know, after billions of years especially, why they don't collapse together. They appear much denser than the universe, which until relatively recent times, was thought could eventually collapse under its own mass attractions.
They certainly MUST NOT contain any dark matter (which I don't believe in), or this conundrum would be even more flagrant. Pardon my use of lay-persons physics, etc. Thanks.

Markus Schwarz wrote:Why are the diffraction spikes of the red stars different in size than the ones from the blue stars? Are there separate cameras mounted differently, or is it due to the different wavelengths?

tomatoherd wrote:I hate to beat a dead horse ( i've asked this before) but these clusters still seem to defy gravity to me. Since they have a spherical symmetry instead of an axial symmetry (like galaxies), they must not have an organiized rotation to amount to anything....

alter-ego wrote: (The hover utility works funny now )

dwainwilder wrote:I've wondered something along a parallel line of thought: how could so many stars accumulate without any angular momentum? If there is angular momentum among the members of the cluster, would there not be an "aggregate effective center of rotation," to perhaps coin a term? And in that case, would the individual stars not begin to behave as a galaxy does, effectively generating whirlpools in the galactic maelstrom?

geckzilla wrote:

alter-ego wrote: (The hover utility works funny now :?: )

My bad, I just fixed it. I was messing with linked image display last week and neglected to realize my changes would affect the hover CSS.

Chris Peterson wrote:

Markus Schwarz wrote:Why are the diffraction spikes of the red stars different in size than the ones from the blue stars? Are there separate cameras mounted differently, or is it due to the different wavelengths?

An interesting question. I think it is mainly just because more light in those bands reached the detector, both because the sources are brighter at longer wavelengths, and because the sensors are more responsive there. The orange stars correspond with visible and IR bands. Also, most of the signal we see there was captured with the ACS camera, not the WFC. Different sensors and optics (although the same primary optics, of course).

Chris Peterson wrote:Maybe trying to get the system to support hover images with attachments that don't need to be elsewhere in the post, as well? That's an annoyance.

tomatoherd wrote:Nevertheless, they seem too stable. maybe it's a matter of gravity's extreme weakness compared to the other fundamental forces, I dunno.

No, my disbelief in dark matter is not 'religious'. But I think time and history will confirm that present day astrophysicists are just using dark matter as a gigantic fudge-factor for current deficiencies in the standard model.

But I am curious: do these same fudging a-physicists figure these clusters have or lack dark matter?

tomatoherd wrote:Thanks, Chris. I do have lots of respect for you and everyone here. I have learned a lot from your replies over the years.
I may BE irrational. And I don't aim to be a troll. But to me, dark matter and energy is a case of an emperor without clothes, whom everyone genuflects to. If it is 90% of the universe, send me a piece of it.
And for anyone to imply that the standard model, current cosmology, and gravitation theory are neatly unified and things are 'almost figured out already' would be disingenuous.