Starship Asterisk*

Globular Cluster M15 from Hubble

Explanation: Stars, like bees, swarm around the center of bright globular cluster M15. This ball of over 100,000 stars is a relic from the early years of our Galaxy, and continues to orbit the Milky Way's center. M15, one of about 150 globular clusters remaining, is noted for being easily visible with only binoculars, having at its center one of the densest concentrations of stars known, and containing a high abundance of variable stars and pulsars. This sharp image, taken by the Earth-orbiting Hubble Space Telescope, spans about 120 light years. It shows the dramatic increase in density of stars toward the cluster's center. M15 lies about 35,000 light years away toward the constellation of the Winged Horse (Pegasus). Recent evidence indicates that a massive black hole might reside as the center of M15.

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Wow! swarm alright... is that a blue planetary to the left of center?

Attention APOD detractors & naysayers:
Have you been waiting for a day with an image that is completely, totally, absolutely, 100% astronomy-related?
A day when the image shows both 'spiky' foreground stars and multi-colored 'gemstone' stars floating in a cluster-y 'jewelbox'?
A day when you find the wallpaper of a lifetime?

Well, wait no more: because today is that day!!!!!



Absolutely gorgeous image!

lol, Indigo!

This is certainly a very pretty cluster. I like M13 a lot, too.

atalas wrote:Wow! swarm alright... is that a blue planetary to the left of center?

I guess it could be. Here is another Hubble image of M15, which shows a hydrogen-rich pink planetary nebula in M15:
Note the pink planetary at the upper left. The blue object in today's APOD could be the same planetary, if a hydrogen alpha filter was not used to produce today's APOD.

Ann

Beautiful APOD!

I globular clusters.

Rob

[ That doesn't work very well. We need a heart Smily. ]

Absolutely beautiful.
I wish I could see it with my own two eyes.
Maybe one day.

I'm familiar with the idea that galaxies can/may have black holes at their center as is thought that our own galaxy does - but today's APOD suggests the possibility that a galaxy can contain more than one black hole! I wonder if any interaction could be discerned between the two black holes?

It is beautiful.
But I still can't fathom, with a massive black hole in the center, and the density of stars centrally, how the thing doesn't gravitationally collapse quickly (it's ancient, apparently) without any rotational "centrifugal" force. And if it were rotating substantially (enough to help prevent collapse) then it would have polar symmetry, instead of radial/spherical.
Is there no physicist out there to crunch the Newtonian numbers????

cabellasus wrote: Is there no physicist out there to crunch the Newtonian numbers????

I have the willingness, just not the brains.

Ailean4321 wrote:Absolutely beautiful.
I wish I could see it with my own two eyes.

Why can't you? It is large and bright- visible with the naked eye, remarkable through binoculars, and stunning with a small telescope, which will show it to your eye looking almost identical to this HST image.

cabellasus wrote:But I still can't fathom, with a massive black hole in the center, and the density of stars centrally, how the thing doesn't gravitationally collapse quickly (it's ancient, apparently) without any rotational "centrifugal" force. And if it were rotating substantially (enough to help prevent collapse) then it would have polar symmetry, instead of radial/spherical.

A globular cluster isn't a rigid body- there is really nothing like an object that could rotate. It is a collection of millions of stars, each in its own orbit. And it is those individual orbits that maintain the global stability of a globular. If you could look at this thing sped up to thousands of years a second, it would look like a swarm of bees- the stars are not fixed in position with respect to each other.

Chris Peterson wrote:A globular cluster isn't a rigid body- there is really nothing like an object that could rotate. It is a collection of millions of stars, each in its own orbit. And it is those individual orbits that maintain the global stability of a globular. If you could look at this thing sped up to thousands of years a second, it would look like a swarm of bees- the stars are not fixed in position with respect to each other.

Chris - thanks. i know it's not rigid. But neither is a galaxy, and yet a galaxy rotates. solar systems rotate, and if the planets didn't, they would crash into the sun, as would the ISS around earth. I know there must be relative motion between the clusters stars. But IF they rotated/orbited the cluster's center fast enough to count (centrifugal-wise), then they would have a discernable axis, instead of such perfect radial symmetry.

casabellasus wrote:Chris - thanks. i know it's not rigid. But neither is a galaxy, and yet a galaxy rotates.

Does it? I'd argue otherwise. Galaxies appear to rotate, but in fact we are seeing nothing but the aggregate motion of their member stars. There is no rotational force preventing a galaxy from collapsing, any more than there is for a globular cluster.

solar systems rotate, and if the planets didn't, they would crash into the sun, as would the ISS around earth.

And I'd argue against the idea that solar systems rotate, as well. Planets revolve around the central star. Individually.

I know there must be relative motion between the clusters stars. But IF they rotated/orbited the cluster's center fast enough to count (centrifugal-wise), then they would have a discernable axis, instead of such perfect radial symmetry.

Why? The stars in a globular cluster orbit on random inclinations, so there is no preferred axis. A sphere is the lowest energy state for a system like that, so that type of symmetry is to be expected.

I'm not sure what you mean by "centrifugal-wise". The stars are orbiting around the cluster's center of mass. The orbital velocity is what it must be, as determined by (mainly) Keplerian dynamics.

Chris Peterson wrote:

Ailean4321 wrote:Absolutely beautiful.
I wish I could see it with my own two eyes.

Why can't you? It is large and bright- visible with the naked eye, remarkable through binoculars, and stunning with a small telescope, which will show it to your eye looking almost identical to this HST image.

Good point!
I really meant up close and personal.

Ann wrote:

atalas wrote:Is that a blue planetary to the left of center?

I guess it could be. Here is another Hubble image of M15, which shows a hydrogen-rich pink planetary nebula in M15:
Note the pink planetary at the upper left. The blue object in today's APOD could be the same planetary, if a hydrogen alpha filter was not used to produce today's APOD.

It is the same planetary nebula, named 'Pease 1', after Francis Gladheim Pease, who first identified it as a PN in 1928.
SEDS.org has some nice close-ups of the nebula.
Blackskies.org has helpful finder charts for stargazers up for a challenge.

Chris-
thank you, that does help. And I concede all your points.
But, nonetheless, IF a planet lost all of its angular momentum, it would move and accelerate towards the sun, no question.
All I'm wondering is, that there must be so much mass near the center of these clusters, that the stars must have to have tremendous angular momentums (and therefore velocities) and that these individual orbits would eventually disclose a majority axis of symmetry. How can they all have formed at about the same time, and yet have individual planes of orbit as you say, and these be so random as to betray no majority pole/disc ??????????

Cabellasus,
Spiral galaxies have large (net) angular momentum. Spherical galaxies do not (due to the random orbital inclinations of the stars). Elliptical galaxies fall in between these two extremes. That seems to be their major difference. As to how or why such differences originate I wonder. I would like to think that such differences themselves are random, but I have no basis for that.

cabellasus wrote:But, nonetheless, IF a planet lost all of its angular momentum, it would move and accelerate towards the sun, no question.

Yes, and if pigs could fly...

All I'm wondering is, that there must be so much mass near the center of these clusters, that the stars must have to have tremendous angular momentums (and therefore velocities) and that these individual orbits would eventually disclose a majority axis of symmetry. How can they all have formed at about the same time, and yet have individual planes of orbit as you say, and these be so random as to betray no majority pole/disc ??????????

It is difficult to seriously consider this in the absence of any compelling theory describing how globular clusters formed. My own view is that disc-like rotating systems are a special case, and occur when a rotating system forms under viscous conditions that favor a single axis for angular momentum. But in lower density systems, there is no reason to expect disc formation, and in the long term I expect disc-like systems to evolve to elliptical and ultimately spherical systems. Globular clusters are currently in high entropy states, and I see no mechanism to lower that entropy and produce a more ordered or symmetrical structure.

Hello,

My first post. Apod has been my daily homepage for years. I'm a glass artist that enjoys trying to capture space-time and spirit in fusion glass. My question is that I'd like to find images of objects without foreground or background stars. For instance, are there a lot of foreground stars in this image of M15? Thanks.

It is difficult to seriously consider this in the absence of any compelling theory describing how globular clusters formed. My own view is that disc-like rotating systems are a special case, and occur when a rotating system forms under viscous conditions that favor a single axis for angular momentum. But in lower density systems, there is no reason to expect disc formation, and in the long term I expect disc-like systems to evolve to elliptical and ultimately spherical systems. Globular clusters are currently in high entropy states, and I see no mechanism to lower that entropy and produce a more ordered or symmetrical structure.

Ah, so I'm not crazy. There "is no compelling theory describing how globular clusters form" ???
Mentally, certainly, i cannot picture how globular clusters OR spherical galaxies form, if they form by accretion (and not capture, which g.c.'s certainly do not, given relative uniformity of star types/ages). Picture a sphere of randomly moving particles. How would they accrete? And when they did, there would be coalescence into non-random flows, giving a predominate vector or vectors. IOW, i can only picture accretion occuring in a disc (relatively two-dimensional) despite being in three dimensions (or more, granted).
One must admit, that if a planetary system was spherical, without an ecliptic plane , and whose planets had random orbits, then astronomers would argue it formed by capture, not accretion. Right? So how the h*ll do they explain globular clusters or galaxies, the former with matching (not random) stars, so to speak???

cabellasus wrote: Ah, so I'm not crazy. There "is no compelling theory describing how globular clusters form" ???

Nope.

Mentally, certainly, i cannot picture how globular clusters OR spherical galaxies form, if they form by accretion (and not capture, which g.c.'s certainly do not, given relative uniformity of star types/ages). Picture a sphere of randomly moving particles. How would they accrete?

Yet that is precisely how a stellar system begins- a spherical region of randomly moving particles. If the density is high enough, and the materials can interact electromagnetically, an accretion disc will form. Angular momentum will transfer in ways that favor a particular axis, and other material will simply be ejected. But the resulting system is at best metastable. In the long run, it will evolve to a spherically symmetric system, not a disc.

Galaxies are fundamentally spherical structures- even spiral galaxies. 80% or more of their mass is found in a spherical halo of dark matter. It never collapsed into a disc because it doesn't interact with radiation.

One must admit, that if a planetary system was spherical, without an ecliptic plane , and whose planets had random orbits, then astronomers would argue it formed by capture, not accretion. Right?

There is good evidence that many of the recently discovered planetary systems found around other stars contain planets which orbit at very different inclinations. I don't think anybody is arguing that the planets are captured, just that accretion exists in more complex forms than previously believed. Even in our own system, the Oort cloud is believed to be a huge spherical structure around the disc-like inner part of the Solar System.

The Galactic Center and a Globular Cluster are very similar in orbital mechanics since the Former has orbital prameters flowing around a stationary fixed highly dense object, the central black hole, and the latter has orbital parameters flowing around a barycenter.
This video demonstrates the actual observed orbits of stars around the Milky Way's central black hole and comes from 16 years of observations. The orbital paths would be similar in a globular cluster.
Pay close attention to the central point of orbit and you will notice what appears to be some gravitational lensing as the stars pass behind the Black Hole
http://www.brighthub.com/science/space/ ... 13435.aspx
See also This APOD
http://apod.nasa.gov/apod/ap020730.html
and Here http://www.noao.edu/outreach/aop/observers/nbody.html

For the visually-oriented among us, some fun links. I couldn't find any done really, really well in HD though... Sounds like it could be a fun simulation project for someone.

Hope you've got good internet bandwidth!

http://www.sns.ias.edu/~starlab/animations/
http://www.sns.ias.edu/~starlab/research/BHeject/

http://www.noao.edu/outreach/aop/observers/nbody.html

http://www.rkm.com.au/animations/Globular-Cluster.html

http://www.youtube.com/watch?v=3NgCBqlBYbk

http://www.youtube.com/watch?v=GQgjmE5oBS0

http://www.spacetelescope.org/videos/heic0809h/

I encourage anyone who knows of any other good globular cluster animations to post links!

-Noel