Starship Asterisk*

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 reprocessed Hubble image, M15 lies some 35,000 light-years away toward the constellation Pegasus. Its diameter is about 200 light-years, but more than half its stars are packed into the central 10 light-years or so, making 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 the dense cluster. M15 is also known to harbour a planetary nebula. Called Pease 1 (aka PN Ps 1), it can be seen in this image as a small blue blob below and just right of center.

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There are maybe 10 stars within 10 lightyears from Earth. Imagine it being 50,000! The night sky would never be black, but instead have a ‘milky’ glow, perhaps even perpetual daylight, and be absolutely covered with stars that could shine as bright as a full moon. But (inter)stellar radiation might be way too high for any life to evolve in such clusters… still, impressive

M15 and NGC 46 are the only clusters I know of that contain a planetary nebula. And NGC 2436 isn't even a member of NGC 2436 but a line-of-sight foreground object!

It's strange that planetary nebulas are so rare in rich clusters, isn't it? Because the way I understand it, all hydrogen-fusing stars will eventually turn into white dwarfs. Then surely they should go through a planetary nebula phase, too? Or maybe the smallest stars will not get extremely hot inside, so they won't do a good job of ionizing the fairly small amounts of gas they will expel when they shrug off their outer layers? Still though, that sounds weird. Surely the core of a puny little M-type dwarf is at least as hot as the photosphere of a mighty O-star?

I said that planetary nebula NGC 2436, which appears to belong to M46, is actually only a foreground object. Yes, but there is another planetary nebula that is really inside M46, or rather, this particular object that is inside M46 is a proto-planetary nebula!


Read about the Calabash Nebula in M46 here, and read about Pease 1 in globular cluster M15 here.

And don't even get me started on mapped color!!!

Ann

Locutus76 wrote: ↑Thu Jun 15, 2023 9:44 am There are maybe 10 stars within 10 lightyears from Earth. Imagine it being 50,000! The night sky would never be black, but instead have a ‘milky’ glow, perhaps even perpetual daylight, and be absolutely covered with stars that could shine as bright as a full moon. But (inter)stellar radiation might be way too high for any life to evolve in such clusters… still, impressive

That would be quite a sight indeed! I always like to Imagine what the sky would look like if we lived right next to or inside any given awesome cosmic object. - As for the challenges of life evolving in M15, in addition to the constant intense radiation, some ten neutron stars have been identified in there, so life would have had to survive ten nearby supernovae! Good luck with that.

Nightfall
short story - Asimov
novel - Asimov & Silverberg

Chris Alex wrote: ↑Thu Jun 15, 2023 12:13 pm

Locutus76 wrote: ↑Thu Jun 15, 2023 9:44 am There are maybe 10 stars within 10 lightyears from Earth. Imagine it being 50,000! The night sky would never be black, but instead have a ‘milky’ glow, perhaps even perpetual daylight, and be absolutely covered with stars that could shine as bright as a full moon. But (inter)stellar radiation might be way too high for any life to evolve in such clusters… still, impressive

That would be quite a sight indeed! I always like to Imagine what the sky would look like if we lived right next to or inside any given awesome cosmic object. - As for the challenges of life evolving in M15, in addition to the constant intense radiation, some ten neutron stars have been identified in there, so life would have had to survive ten nearby supernovae! Good luck with that.

There was an APOD about this very long ago.
https://apod.nasa.gov/apod/ap011005.html

Well, I know this APOD's been made with birds shining, but still a hilarious sight!

Rauf wrote: ↑Thu Jun 15, 2023 2:47 pm

Chris Alex wrote: ↑Thu Jun 15, 2023 12:13 pm

Locutus76 wrote: ↑Thu Jun 15, 2023 9:44 am There are maybe 10 stars within 10 lightyears from Earth. Imagine it being 50,000! The night sky would never be black, but instead have a ‘milky’ glow, perhaps even perpetual daylight, and be absolutely covered with stars that could shine as bright as a full moon. But (inter)stellar radiation might be way too high for any life to evolve in such clusters… still, impressive

That would be quite a sight indeed! I always like to Imagine what the sky would look like if we lived right next to or inside any given awesome cosmic object. - As for the challenges of life evolving in M15, in addition to the constant intense radiation, some ten neutron stars have been identified in there, so life would have had to survive ten nearby supernovae! Good luck with that.

There was an APOD about this very long ago.
https://apod.nasa.gov/apod/ap011005.html

Well, I know this APOD's been made with birds shining, but still a hilarious sight!

Nice find!

Possible views from inside a globular cluster:

Ann

So many stars in only one cluster!

So would those central stars with "increasing velocities" be falling inward toward the black hole on a straight course, or circling in toward it in a spiral pattern?

Avalon wrote: ↑Fri Jun 16, 2023 3:10 am So would those central stars with "increasing velocities" be falling inward toward the black hole on a straight course, or circling in toward it in a spiral pattern?

if toward the black hole on a straight course means passing at tidal rapture distance than the chances are zero.
All they mean are high velocities of stars at their perimelasma (peribothron? perinigricon? pericenter?)

Avalon wrote: ↑Fri Jun 16, 2023 3:10 am So would those central stars with "increasing velocities" be falling inward toward the black hole on a straight course, or circling in toward it in a spiral pattern?

Neither. They mostly don't even feel the effects of the black hole. All of the stars are simply orbiting the common center of mass of the cluster. Those closer to the center are in shorter, faster orbits... just like the planets on the Solar System.

Chris Peterson wrote: ↑Fri Jun 16, 2023 3:54 am

Avalon wrote: ↑Fri Jun 16, 2023 3:10 am So would those central stars with "increasing velocities" be falling inward toward the black hole on a straight course, or circling in toward it in a spiral pattern?

Neither. They mostly don't even feel the effects of the black hole. All of the stars are simply orbiting the common center of mass of the cluster. Those closer to the center are in shorter, faster orbits... just like the planets on the Solar System.

Hmm, so if the black hole were to suddenly vanish, along with it's mass, would the stars know? I wonder how big the central black hole is. It's described as having "intermediate mass" in the linked paper, and Wikipedia says those are in the range of 100 - 100000 solar masses. The cluster as a whole is said to have about 100000 stars. If the black hole were only a few thousand solar masses, that would be pretty insignificant compared to the overall mass, and it's sudden vanishing might not have much of an effect.

johnnydeep wrote: ↑Fri Jun 16, 2023 9:12 pm

Chris Peterson wrote: ↑Fri Jun 16, 2023 3:54 am

Avalon wrote: ↑Fri Jun 16, 2023 3:10 am So would those central stars with "increasing velocities" be falling inward toward the black hole on a straight course, or circling in toward it in a spiral pattern?

Neither. They mostly don't even feel the effects of the black hole. All of the stars are simply orbiting the common center of mass of the cluster. Those closer to the center are in shorter, faster orbits... just like the planets on the Solar System.

Hmm, so if the black hole were to suddenly vanish, along with it's mass, would the stars know? I wonder how big the central black hole is. It's described as having "intermediate mass" in the linked paper, and Wikipedia says those are in the range of 100 - 100000 solar masses. The cluster as a whole is said to have about 100000 stars. If the black hole were only a few thousand solar masses, that would be pretty insignificant compared to the overall mass, and it's sudden vanishing might not have much of an effect.

It's far from certain that there even is a BH in the center. And the model used to offer it as a possibility suggests a mass of about 2000 solar masses to be consistent with the orbital dynamics of the innermost stars.

Chris Peterson wrote: ↑Fri Jun 16, 2023 9:56 pm

johnnydeep wrote: ↑Fri Jun 16, 2023 9:12 pm

Chris Peterson wrote: ↑Fri Jun 16, 2023 3:54 am

Neither. They mostly don't even feel the effects of the black hole. All of the stars are simply orbiting the common center of mass of the cluster. Those closer to the center are in shorter, faster orbits... just like the planets on the Solar System.

Hmm, so if the black hole were to suddenly vanish, along with it's mass, would the stars know? I wonder how big the central black hole is. It's described as having "intermediate mass" in the linked paper, and Wikipedia says those are in the range of 100 - 100000 solar masses. The cluster as a whole is said to have about 100000 stars. If the black hole were only a few thousand solar masses, that would be pretty insignificant compared to the overall mass, and it's sudden vanishing might not have much of an effect.

It's far from certain that there even is a BH in the center. And the model used to offer it as a possibility suggests a mass of about 2000 solar masses to be consistent with the orbital dynamics of the innermost stars.

Ok. And if such a 2000 solar mass BH vanished, would the stars in the cluster care? Perhaps only the very close ones, for some value of "close"?

johnnydeep wrote: ↑Sat Jun 17, 2023 8:38 pm

Chris Peterson wrote: ↑Fri Jun 16, 2023 9:56 pm

johnnydeep wrote: ↑Fri Jun 16, 2023 9:12 pm

Hmm, so if the black hole were to suddenly vanish, along with it's mass, would the stars know? I wonder how big the central black hole is. It's described as having "intermediate mass" in the linked paper, and Wikipedia says those are in the range of 100 - 100000 solar masses. The cluster as a whole is said to have about 100000 stars. If the black hole were only a few thousand solar masses, that would be pretty insignificant compared to the overall mass, and it's sudden vanishing might not have much of an effect.

It's far from certain that there even is a BH in the center. And the model used to offer it as a possibility suggests a mass of about 2000 solar masses to be consistent with the orbital dynamics of the innermost stars.

Ok. And if such a 2000 solar mass BH vanished, would the stars in the cluster care? Perhaps only the very close ones, for some value of "close"?

The impact would depend on where they were. The closer, the more it would matter. But broadly, the BH isn't what's determining the dynamics of the stars in the cluster.

Chris Peterson wrote: ↑Sat Jun 17, 2023 9:05 pm

johnnydeep wrote: ↑Sat Jun 17, 2023 8:38 pm

Chris Peterson wrote: ↑Fri Jun 16, 2023 9:56 pm

It's far from certain that there even is a BH in the center. And the model used to offer it as a possibility suggests a mass of about 2000 solar masses to be consistent with the orbital dynamics of the innermost stars.

Ok. And if such a 2000 solar mass BH vanished, would the stars in the cluster care? Perhaps only the very close ones, for some value of "close"?

The impact would depend on where they were. The closer, the more it would matter. But broadly, the BH isn't what's determining the dynamics of the stars in the cluster.

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