APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

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APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by APOD Robot » Wed Oct 17, 2018 4:06 am

Image M15: Dense Globular Star Cluster

Explanation: Messier 15 is an immense swarm of over 100,000 stars. A 13 billion year old relic of the early formative years of our galaxy it's one of about 170 globular star clusters that still roam the halo of the Milky Way. Centered in this sharp telescopic view, M15 lies about 35,000 light years away toward the constellation Pegasus, well beyond the spiky foreground stars. Its diameter is about 200 light-years. But more than half its stars are packed into the central 10 light-years or so, one of the densest concentrations of stars known. Hubble-based measurements of the increasing velocities of M15's central stars are evidence that a massive black hole resides at the center of dense globular cluster M15.

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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by Boomer12k » Wed Oct 17, 2018 7:51 am

Awesome...I looked at it tonight...though only with my 6" Celestron...not as impressive.

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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by frankhummer113@hotmail.com » Wed Oct 17, 2018 8:04 am

I did a rough calculation. I think those 50,000 stars occupying the central 10 light years would still be able to have about a quarter of a light year between them, on average. This is not quite as congested as if first sounds.

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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by BDanielMayfield » Wed Oct 17, 2018 10:39 am

frankhummer113@hotmail.com wrote:
Wed Oct 17, 2018 8:04 am
I did a rough calculation. I think those 50,000 stars occupying the central 10 light years would still be able to have about a quarter of a light year between them, on average. This is not quite as congested as if first sounds.
Nice calculation Frank, but all those stars aren't evenly distributed in that volume. According to the links the increasing of the consentration of stars continues all the way down to about .06 light years or about 100 AU of the center. And at the very center, the presence of an approximately 4,000 sun massed black hole is inferred by stellar velocities.

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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by lasersam » Wed Oct 17, 2018 11:07 am

Someone should do a 3D simulation of the stellar paths in the innermost light year or two, it's hard to imagine how a densely populated core of a spherical globular cluster can be a stable configuration where star interaction is rare.

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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by Chris Peterson » Wed Oct 17, 2018 2:01 pm

lasersam wrote:
Wed Oct 17, 2018 11:07 am
Someone should do a 3D simulation of the stellar paths in the innermost light year or two, it's hard to imagine how a densely populated core of a spherical globular cluster can be a stable configuration where star interaction is rare.
Stellar collisions are extremely rare. But all of the stars interact, all of the time, and orbits are chaotic- which is why globular clusters evaporate over time.
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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by starsurfer » Wed Oct 17, 2018 2:26 pm

The really cool thing about this one is that it contains the planetary nebula Pease 1.

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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by Ann » Wed Oct 17, 2018 3:30 pm

Chris Peterson wrote:
Wed Oct 17, 2018 2:01 pm
lasersam wrote:
Wed Oct 17, 2018 11:07 am
Someone should do a 3D simulation of the stellar paths in the innermost light year or two, it's hard to imagine how a densely populated core of a spherical globular cluster can be a stable configuration where star interaction is rare.
Stellar collisions are extremely rare. But all of the stars interact, all of the time, and orbits are chaotic- which is why globular clusters evaporate over time.
I'm sure I've read someplace that it is primarily the small lightweight stars that are being expelled due to gravitational interactions, which should mean that age-old, dense globular clusters should display a (relative) deficit of small red stars. In other words, young (and sparse) clusters should be more "bottom-heavy" - that is, contain a larger percentage of - small red stars than old populous globulars do.

Does this also mean that planets in globular clusters run a comparatively high risk of being expelled?

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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by neufer » Wed Oct 17, 2018 4:53 pm

Ann wrote:
Wed Oct 17, 2018 3:30 pm

I'm sure I've read someplace that it is primarily the small lightweight stars that are being expelled due to gravitational interactions, which should mean that age-old, dense globular clusters should display a (relative) deficit of small red stars. In other words, young (and sparse) clusters should be more "bottom-heavy" - that is, contain a larger percentage of - small red stars than old populous globulars do.
If you think of it as a gas "in thermal equilibrium" the lightest gas particles will have the highest average velocity & be ejected first.
Ann wrote:
Wed Oct 17, 2018 3:30 pm

Does this also mean that planets in globular clusters run a comparatively high risk of being expelled?
Certainly planets are somewhat more likely to be ejected from their solar systems.
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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by Chris Peterson » Wed Oct 17, 2018 5:16 pm

Ann wrote:
Wed Oct 17, 2018 3:30 pm
Chris Peterson wrote:
Wed Oct 17, 2018 2:01 pm
lasersam wrote:
Wed Oct 17, 2018 11:07 am
Someone should do a 3D simulation of the stellar paths in the innermost light year or two, it's hard to imagine how a densely populated core of a spherical globular cluster can be a stable configuration where star interaction is rare.
Stellar collisions are extremely rare. But all of the stars interact, all of the time, and orbits are chaotic- which is why globular clusters evaporate over time.
Does this also mean that planets in globular clusters run a comparatively high risk of being expelled?
Most models I've seen suggest that planetary systems in globular clusters or galactic bulges are likely to be short lived.
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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by MarkBour » Wed Oct 17, 2018 8:52 pm

Chris Peterson wrote:
Wed Oct 17, 2018 5:16 pm
Most models I've seen suggest that planetary systems in globular clusters or galactic bulges are likely to be short lived.
Sounds reasonable. Nonetheless, with so many smaller stars that should be on the periphery or should have been ejected by now, and with the extreme age they have attained, perhaps the region near a globular is an above-average place to look for signs of life.

Besides, these images are quite beautiful. Like gazing at a jeweled chandelier.
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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by Chris Peterson » Wed Oct 17, 2018 10:23 pm

MarkBour wrote:
Wed Oct 17, 2018 8:52 pm
Chris Peterson wrote:
Wed Oct 17, 2018 5:16 pm
Most models I've seen suggest that planetary systems in globular clusters or galactic bulges are likely to be short lived.
Sounds reasonable. Nonetheless, with so many smaller stars that should be on the periphery or should have been ejected by now, and with the extreme age they have attained, perhaps the region near a globular is an above-average place to look for signs of life.

Besides, these images are quite beautiful. Like gazing at a jeweled chandelier.
The problem is that planetary systems are chaotic. It doesn't take much of a perturbation to shake things up. It's possible that's even happened to our own system early on. But it would be much more common in any dense star environment. It's not that all that many planets would necessarily be ejected, but orbits get tweaked. And if you're looking for life, especially complex life, that's a big problem. Those Goldilocks zones are pretty narrow, and if a planet with life gets knocked out of one, it's probably game over. So we might find simple life of the sort that flourished on Earth for a few billion years, but complex life- multicellular organisms and animals- seem much more unlikely. The necessary stability is missing.
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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by neufer » Thu Oct 18, 2018 3:08 am


Chris Peterson wrote:
Wed Oct 17, 2018 10:23 pm

The problem is that planetary systems are chaotic. It doesn't take much of a perturbation to shake things up. It's possible that's even happened to our own system early on. But it would be much more common in any dense star environment. It's not that all that many planets would necessarily be ejected, but orbits get tweaked. And if you're looking for life, especially complex life, that's a big problem. Those Goldilocks zones are pretty narrow, and if a planet with life gets knocked out of one, it's probably game over. So we might find simple life of the sort that flourished on Earth for a few billion years, but complex life- multicellular organisms and animals- seem much more unlikely. The necessary stability is missing.
Besides... we already sent a radio message to M13 and have yet to get a reply.
https://en.wikipedia.org/wiki/Arecibo_message wrote:
<<The Arecibo message is a 1974 interstellar radio message carrying basic information about humanity and Earth sent to globular star cluster M13 in the hope that extraterrestrial intelligence might receive and decipher it. The message consisted of 1,679 binary digits transmitted at a frequency of 2,380 MHz and modulated by shifting the frequency by 10 Hz, with a power of 450 kW. The "ones" and "zeros" were transmitted by frequency shifting at the rate of 10 bits per second. The number 1,679 was chosen because it is a semiprime (the product of two prime numbers), to be arranged rectangularly as 73 rows by 23 columns. The message forms the image shown on the left, or its inverse, when translated into graphics, characters, and spaces.>>
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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by Ann » Thu Oct 18, 2018 3:25 am

neufer wrote:
Thu Oct 18, 2018 3:08 am

Besides... we already sent a radio message to M13 and have yet to get a reply.
Sure! :D

We sent a message in 1974, 44 years ago, towards the globular cluster M13. This globular, according to a quick googling, is about 22,000 light-years away. So the fact that our message hasn't yet been received by and replied to by the "Em-thirteen-eans", and that their reply hasn't yet reached us... yes, it's troubling, isn't it? :wink:

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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by khh » Thu Oct 18, 2018 5:24 am

Hubble-based measurements of the increasing velocities of M15's central stars are evidence that a massive black hole resides at the center of dense globular cluster M15.
Will the black hole eventually swallow the stars in the cluster?

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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by BDanielMayfield » Thu Oct 18, 2018 12:05 pm

khh wrote:
Thu Oct 18, 2018 5:24 am
Hubble-based measurements of the increasing velocities of M15's central stars are evidence that a massive black hole resides at the center of dense globular cluster M15.
Will the black hole eventually swallow the stars in the cluster?
No, or at most just a very, very small number of them. Just like the super massive black holes at the center of galaxies hardly ever swallow any of their galaxy's stars. The star's orbits may be a bit chaotic due to close encounters with each other, but their orbits are still stable enough to keep them from ever passing through the relatively tiny destructive zones around black holes.

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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by neufer » Thu Oct 18, 2018 2:14 pm

https://en.wikipedia.org/wiki/Globular_cluster#Mass_segregation,_luminosity_and_core_collapse wrote:
<<In measuring the luminosity curve of a given globular cluster as a function of distance from the core, most clusters in the Milky Way increase steadily in luminosity as this distance decreases, up to a certain distance from the core, then the luminosity levels off. Typically this distance is about [5 lyrs] from the core. However about 20% of the globular clusters have undergone a process termed "core collapse". In this type of cluster, the luminosity continues to increase steadily all the way to the core region. An example of a core-collapsed globular is M15.

Core-collapse is thought to occur when the more massive stars in a globular cluster encounter their less massive companions. Over time, dynamic processes cause individual stars to migrate from the center of the cluster to the outside. This results in a net loss of kinetic energy from the core region, leading the remaining stars grouped in the core region to occupy a more compact volume. When this gravothermal instability occurs, the central region of the cluster becomes densely crowded with stars and the surface brightness of the cluster forms a power-law cusp. (Note that a core collapse is not the only mechanism that can cause such a luminosity distribution; a massive black hole at the core can also result in a luminosity cusp.) Over a lengthy period of time this leads to a concentration of massive stars near the core, a phenomenon called mass segregation.

The dynamical heating effect of binary star systems works to prevent an initial core collapse of the cluster. When a star passes near a binary system, the orbit of the latter pair tends to contract, releasing energy. Only after the primordial supply of binaries is exhausted due to interactions can a deeper core collapse proceed. In contrast, the effect of tidal shocks as a globular cluster repeatedly passes through the plane of a spiral galaxy tends to significantly accelerate core collapse.

The different stages of core-collapse may be divided into three phases. During a globular cluster's adolescence, the process of core-collapse begins with stars near the core. However, the interactions between binary star systems prevents further collapse as the cluster approaches middle age. Finally, the central binaries are either disrupted or ejected, resulting in a tighter concentration at the core.

The interaction of stars in the collapsed core region causes tight binary systems to form. As other stars interact with these tight binaries, they increase the energy at the core, which causes the cluster to re-expand. As the mean time for a core collapse is typically less than the age of the galaxy, many of a galaxy's globular clusters may have passed through a core collapse stage, then re-expanded.

The Hubble Space Telescope has been used to provide convincing observational evidence of this stellar mass-sorting process in globular clusters. Heavier stars slow down and crowd at the cluster's core, while lighter stars pick up speed and tend to spend more time at the cluster's periphery.

A 2008 study by John Fregeau of 13 globular clusters in the Milky Way shows that three of them have an unusually large number of X-ray sources, or X-ray binaries, suggesting the clusters are middle-aged. Previously, these globular clusters had been classified as being in old age because they had very tight concentrations of stars in their centers, another test of age used by astronomers. The implication is that most globular clusters, including the other ten studied by Fregeau, are not in middle age as previously thought, but are actually in 'adolescence'.>>
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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by Spectrumtacular » Thu Oct 18, 2018 4:12 pm

Ann wrote:
Thu Oct 18, 2018 3:25 am
neufer wrote:
Thu Oct 18, 2018 3:08 am

Besides... we already sent a radio message to M13 and have yet to get a reply.
Sure! :D

We sent a message in 1974, 44 years ago, towards the globular cluster M13. This globular, according to a quick googling, is about 22,000 light-years away. So the fact that our message hasn't yet been received by and replied to by the "Em-thirteen-eans", and that their reply hasn't yet reached us... yes, it's troubling, isn't it?

Ann
Ann wrote:
Thu Oct 18, 2018 3:25 am
neufer wrote:
Thu Oct 18, 2018 3:08 am

Besides... we already sent a radio message to M13 and have yet to get a reply.
Sure! :D

We sent a message in 1974, 44 years ago, towards the globular cluster M13. This globular, according to a quick googling, is about 22,000 light-years away. So the fact that our message hasn't yet been received by and replied to by the "Em-thirteen-eans", and that their reply hasn't yet reached us... yes, it's troubling, isn't it?

Ann
If M13ers had developed non local technology they could have received our message and sent one back a few minutes after we sent ours (although understanding of how they could possibly do this has not reached the consideration stage yet in many scientifically inclined minds.) We would have missed their return message, though, because non locality itself was not generally considered a possibility until the past several years. M13ers would, however, know by our use of what they would consider ancient technology that we are in an era in which we would not recognize non-local technology, so they would probably just plan on sending a message, say perhaps, 50 years from now when we may have developed non-local technology capable of receiving and sending messages. Perhaps they are 'televising' 'live from Planet Earth' programs on their home planets in which we are The Flintstones, much as we CERTAINLY enjoyed Fred, Wilma and BamBam, Barney, Betty and Pebbles, Dino, etc. They would certainly enjoy those of us fortunate enough not to be involved in the catastrophes around us as we bumble humorously through our daily lives using what they consider stone age technology. :b:

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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by Ann » Thu Oct 18, 2018 4:53 pm

"Non local technology" is another word for science fiction.

Or wishful thinking.

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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by Chris Peterson » Thu Oct 18, 2018 4:55 pm

Spectrumtacular wrote:
Thu Oct 18, 2018 4:12 pm
If M13ers had developed non local technology they could have received our message and sent one back a few minutes after we sent ours...
Sure. Although it might be easier if they just used their time machine to jump to the future and fetch Jean-Luc Picard to pass their message on to us.
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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by BDanielMayfield » Thu Oct 18, 2018 9:29 pm

Chris Peterson wrote:
Wed Oct 17, 2018 10:23 pm
MarkBour wrote:
Wed Oct 17, 2018 8:52 pm
Chris Peterson wrote:
Wed Oct 17, 2018 5:16 pm
Most models I've seen suggest that planetary systems in globular clusters or galactic bulges are likely to be short lived.
Sounds reasonable. Nonetheless, with so many smaller stars that should be on the periphery or should have been ejected by now, and with the extreme age they have attained, perhaps the region near a globular is an above-average place to look for signs of life.

Besides, these images are quite beautiful. Like gazing at a jeweled chandelier.
The problem is that planetary systems are chaotic. It doesn't take much of a perturbation to shake things up. It's possible that's even happened to our own system early on. But it would be much more common in any dense star environment. It's not that all that many planets would necessarily be ejected, but orbits get tweaked. And if you're looking for life, especially complex life, that's a big problem. Those Goldilocks zones are pretty narrow, and if a planet with life gets knocked out of one, it's probably game over. So we might find simple life of the sort that flourished on Earth for a few billion years, but complex life- multicellular organisms and animals- seem much more unlikely. The necessary stability is missing.
An additional problem with having planets in and around globulars would be the extremely low metal content of the material that created these star systems. Way back when these star systems were forming there wasn't hardly any heavy elements yet, so forming rocky planets would have been much harder.

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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by neufer » Fri Oct 19, 2018 3:12 am

BDanielMayfield wrote:
Thu Oct 18, 2018 9:29 pm

An additional problem with having planets in and around globulars would be the extremely low metal content of the material that created these star systems. Way back when these star systems were forming there wasn't hardly any heavy elements yet, so forming rocky planets would have been much harder.
There wasn't hardly any heavy elements yet :?:
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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by BDanielMayfield » Fri Oct 19, 2018 3:29 pm

neufer wrote:
Fri Oct 19, 2018 3:12 am
BDanielMayfield wrote:
Thu Oct 18, 2018 9:29 pm

An additional problem with having planets in and around globulars would be the extremely low metal content of the material that created these star systems. Way back when these star systems were forming there wasn't hardly any heavy elements yet, so forming rocky planets would have been much harder.
There wasn't hardly any heavy elements yet :?:
Some, but not nearly as much as when our solar system formed. M15's metal content is now found to be -2.37 dec, or only 10^-2.37 = 0.00427 times the sun's value. My inference would be that it might well have been much harder for rocky planets to have formed out of material so thinly enriched with metals. It takes a lot of rocks to make rocky planets.

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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by BDanielMayfield » Fri Oct 19, 2018 3:46 pm

And my common sense intuition about this planets in globulars question isn't far fetched. From the wikipedia article on globular clusters:
Astronomers are searching for exoplanets of stars in globular star clusters.[92]

In 2000, the results of a search for giant planets in the globular cluster 47 Tucanae were announced. The lack of any successful discoveries suggests that the abundance of elements (other than hydrogen or helium) necessary to build these planets may need to be at least 40% of the abundance in the Sun. Terrestrial planets are built from heavier elements such as silicon, iron and magnesium. The very low abundance of these elements in globular clusters means that the member stars have a far lower likelihood of hosting Earth-mass planets, when compared to stars in the neighborhood of the Sun. Hence the halo region of the Milky Way galaxy, including globular cluster members, are unlikely to host habitable terrestrial planets.
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Re: APOD: M15: Dense Globular Star Cluster (2018 Oct 17)

Post by coffeesippin » Fri Oct 19, 2018 6:24 pm

I hope the NASA National Security Advisors are more up to date than a couple of participants here .. the Chinese are set to get non-local communication going soon. https://www.sciencemag.org/news/2017/06 ... d-distance