Starship Asterisk*

Posted: **Thu May 09, 2019 4:05 am**

Messier 5

Explanation: "Beautiful Nebula discovered between the Balance [Libra] & the Serpent [Serpens] ..." begins the description of the 5th entry in 18th century astronomer Charles Messier's famous catalog of nebulae and star clusters. Though it appeared to Messier to be fuzzy and round and without stars, Messier 5 (M5) is now known to be a globular star cluster, 100,000 stars or more, bound by gravity and packed into a region around 165 light-years in diameter. It lies some 25,000 light-years away. Roaming the halo of our galaxy, globular star clusters are ancient members of the Milky Way. M5 is one of the oldest globulars, its stars estimated to be nearly 13 billion years old. The beautiful star cluster is a popular target for earthbound telescopes. Even close to its dense core, the cluster's red and blue giant stars, and rejuvenated blue stragglers stand out with yellowish and blue hues in this sharp color image.

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Posted: **Thu May 09, 2019 11:45 am**

Like a sparkler in the dark!

Posted: **Thu May 09, 2019 12:38 pm**

I counted 103,041 stars.

Posted: **Thu May 09, 2019 12:49 pm**

mjsakers wrote: ↑Thu May 09, 2019 12:38 pm I counted 103,041 stars.

Check again. You're off by two.

Posted: **Thu May 09, 2019 1:00 pm**

Chris Peterson wrote: ↑Thu May 09, 2019 12:49 pm
mjsakers wrote: ↑Thu May 09, 2019 12:38 pm I counted 103,041 stars.
Check again. You're off by two.

I think you've both included stars behind, and not part of M5, in your counts, or are you including the brown dwarfs?

Posted: **Thu May 09, 2019 1:09 pm**

Does night exist In the middle of a star cluster?

Posted: **Thu May 09, 2019 1:29 pm**

Tszabeau wrote: ↑Thu May 09, 2019 1:09 pm Does night exist In the middle of a star cluster?

Well, it might look like a brightly moonlit night, or maybe even a bit brighter than that. But there will still be many orders of magnitude difference between day and night. (That said, it's unlikely that stars near the center of clusters like this have any planets to experience night and day.)

Posted: **Thu May 09, 2019 2:01 pm**

What keeps them from forming a tight lump - black hole perhaps?

Posted: **Thu May 09, 2019 2:06 pm**

sunson wrote: ↑Thu May 09, 2019 2:01 pm What keeps them from forming a tight lump - black hole perhaps?

They are all in orbit. They don't form a clump for the same reason that all of the planets in the Solar System don't end up in the Sun.

Posted: **Thu May 09, 2019 2:13 pm**

sunson wrote: ↑Thu May 09, 2019 2:01 pm What keeps them from forming a tight lump - black hole perhaps?

Conservation of momentum. But really, the centers do tend to tighten up over time as the most massive stars exchange momentum with less massive stars. The net result is that on average massive stars' orbits become smaller while less massive stars can get thrown toward the outside of the cluster.

Bruce

Posted: **Thu May 09, 2019 2:20 pm**

BDanielMayfield wrote: ↑Thu May 09, 2019 2:13 pm
sunson wrote: ↑Thu May 09, 2019 2:01 pm What keeps them from forming a tight lump - black hole perhaps?
Conservation of momentum. But really, the centers do tend to tighten up over time as the most massive stars exchange momentum with less massive stars. The net result is that on average massive stars' orbits become smaller while less massive stars can get thrown toward the outside of the cluster.

And over a very long time scale, all the stars get ejected and the cluster evaporates.

Posted: **Thu May 09, 2019 5:58 pm**

Chris Peterson wrote: ↑Thu May 09, 2019 2:20 pm
BDanielMayfield wrote: ↑Thu May 09, 2019 2:13 pm
sunson wrote: ↑Thu May 09, 2019 2:01 pm What keeps them from forming a tight lump - black hole perhaps?
Conservation of momentum. But really, the centers do tend to tighten up over time as the most massive stars exchange momentum with less massive stars. The net result is that on average massive stars' orbits become smaller while less massive stars can get thrown toward the outside of the cluster.
And over a very long time scale, all the stars get ejected and the cluster evaporates.

I wondered about how long that time scale might be, and came up with this from the Globular Cluster article in wikipedia:

The results of N-body simulations have shown that the stars can follow unusual paths through the cluster, often forming loops and often falling more directly toward the core than would a single star orbiting a central mass. In addition, due to interactions with other stars that result in an increase in velocity, some of the stars gain sufficient energy to escape the cluster. Over long periods of time this will result in a dissipation of the cluster, a process termed evaporation.[83] The typical time scale for the evaporation of a globular cluster is 10¹⁰ years.[62]

And yet, our galaxy and others still have GCs like M5 that are still holding it together magnificently after 13 x 10^9 years, already longer that the simulation based estimate. Are there any examples of nearly completely evaporated Globulars?

Bruce

Posted: **Thu May 09, 2019 6:30 pm**

I calculate that the stars are on average about 3.6 light-years apart. That means some are much closer together. I am wondering if some intelligent life form has been able to travel to nearby stars.

Posted: **Thu May 09, 2019 6:43 pm**

BDanielMayfield wrote: ↑Thu May 09, 2019 5:58 pm
Chris Peterson wrote: ↑Thu May 09, 2019 2:20 pm
BDanielMayfield wrote: ↑Thu May 09, 2019 2:13 pm
Conservation of momentum. But really, the centers do tend to tighten up over time as the most massive stars exchange momentum with less massive stars. The net result is that on average massive stars' orbits become smaller while less massive stars can get thrown toward the outside of the cluster.
And over a very long time scale, all the stars get ejected and the cluster evaporates.
I wondered about how long that time scale might be, and came up with this from the Globular Cluster article in wikipedia:
The results of N-body simulations have shown that the stars can follow unusual paths through the cluster, often forming loops and often falling more directly toward the core than would a single star orbiting a central mass. In addition, due to interactions with other stars that result in an increase in velocity, some of the stars gain sufficient energy to escape the cluster. Over long periods of time this will result in a dissipation of the cluster, a process termed evaporation.[83] The typical time scale for the evaporation of a globular cluster is 10¹⁰ years.[62]
And yet, our galaxy and others still have GCs like M5 that are still holding it together magnificently after 13 x 10^9 years, already longer that the simulation based estimate. Are there any examples of nearly completely evaporated Globulars?

It's complicated. The evaporation rate isn't linear, and it becomes less so for clusters closer to the galactic plane and closer to the galactic center. Models suggest that clusters may have already lost 50-90% of their original stars. At this point their mass loss rate and their stellar populations are both decreasing much slower than they were in their first few billion years.

It isn't clear what a nearly evaporated cluster might look like, given poor knowledge of initial mass and the wide range of different cluster sizes. Certain clusters, such as Palomar 13, seem to generally be regarded as highly evolved and mostly evaporated, a process accelerated by tidal interactions with the galaxy.

Posted: **Thu May 09, 2019 8:08 pm**

Thanks Chris. Palomar 13

fits the bill as an evaporated cluster.

Posted: **Thu May 09, 2019 11:00 pm**

1. How close together are the closest stars in this cluster?

2. How did this cluster of stars "break away" from the Milky Way? Seems like the Milk Way's gravitation forces would have kept the star cluster as part of our galaxy?

Posted: **Fri May 10, 2019 12:48 am**

https://www.syfy.com/syfywire/what-is-the-milky-ways-most-distant-globular-cluster wrote:
What is the Milky Way’s most distant globular cluster?
Bad Astronomy

My very hearty thanks to Judy Schmidt, aka @SpaceGeck, who is amazing at taking raw Hubble data and creating color images from them. I contacted her about this cluster, figuring she’d get a kick out of it, and she grabbed the observations from Hubble and produced the image used here the very same day! She’s aces.

Posted: **Fri May 10, 2019 3:36 am**

BDanielMayfield wrote: ↑Thu May 09, 2019 5:58 pm
Chris Peterson wrote: ↑Thu May 09, 2019 2:20 pm
BDanielMayfield wrote: ↑Thu May 09, 2019 2:13 pm
Conservation of momentum. But really, the centers do tend to tighten up over time as the most massive stars exchange momentum with less massive stars. The net result is that on average massive stars' orbits become smaller while less massive stars can get thrown toward the outside of the cluster.
And over a very long time scale, all the stars get ejected and the cluster evaporates.
I wondered about how long that time scale might be, and came up with this from the Globular Cluster article in wikipedia:
The results of N-body simulations have shown that the stars can follow unusual paths through the cluster, often forming loops and often falling more directly toward the core than would a single star orbiting a central mass. In addition, due to interactions with other stars that result in an increase in velocity, some of the stars gain sufficient energy to escape the cluster. Over long periods of time this will result in a dissipation of the cluster, a process termed evaporation.[83] The typical time scale for the evaporation of a globular cluster is 10¹⁰ years.[62]
And yet, our galaxy and others still have GCs like M5 that are still holding it together magnificently after 13 x 10^9 years, already longer that the simulation based estimate. Are there any examples of nearly completely evaporated Globulars?

Bruce

: Click to view full size image

NGC 5053 (left) and M53 (right). Photo: Jonas Grinde.

I really don't know if NGC 5053 has evaporated much at all, or if it was more or less born low-mass, large and distended, but faint globular NGC 5053 and bright globular M53 do make a striking pair. Particularly so since they are not only close to one another in the sky, but they are also at relatively comparable distances from us.

Wikipedia wrote:

NGC 5053 is a relatively low mass cluster with a low core concentration factor of 1.32. It sports a stream of tidal debris to the west with a projected length of 1.7 kpc. This stream may have been created through shock-induced processes.[10] The cluster is located less than 3° from Messier 53 and the two have nearly the same distance modulus, which corresponds to a spatial separation of around 2 kpc. There is a tidal bridge joining M53 to NGC 5053, suggesting the pair may have interacted in the past.

But NGC 5053 may not be a "true" Milky Way globular:

Wikipedia wrote:

The chemical abundances of the stars in NGC 5053 are more similar to those in the dwarf galaxy Sagittarius Dwarf Spheroidal Galaxy than to the Milky Way halo. Along with the kinematics of the globular cluster, this suggests that NGC 5053 may have been stripped from the dwarf galaxy.

Ann

Posted: **Fri May 10, 2019 3:42 am**

neufer wrote: ↑Fri May 10, 2019 12:48 am
https://www.syfy.com/syfywire/what-is-the-milky-ways-most-distant-globular-cluster wrote:
What is the Milky Way’s most distant globular cluster?
Bad Astronomy

My very hearty thanks to Judy Schmidt, aka @SpaceGeck, who is amazing at taking raw Hubble data and creating color images from them. I contacted her about this cluster, figuring she’d get a kick out of it, and she grabbed the observations from Hubble and produced the image used here the very same day! She’s aces.

Fantastic. Geck, we don't give you enough credit here.

And the cluster that Geck produced an image of from raw Hubble data is pretty fascinating too.

Ann

Posted: **Fri May 10, 2019 3:44 am**

rghjes wrote: ↑Thu May 09, 2019 11:00 pm 1. How close together are the closest stars in this cluster?

2. How did this cluster of stars "break away" from the Milky Way? Seems like the Milk Way's gravitation forces would have kept the star cluster as part of our galaxy?

The cluster is orbiting the Milky Way. It is a part of it, and presumably formed outside the main body of stars, where it remains.

Posted: **Fri May 10, 2019 6:18 am**

rghjes wrote: ↑Thu May 09, 2019 11:00 pm 1. How close together are the closest stars in this cluster?

I'd guess that in a cluster with as many close pairs as M5 must have that there would be at least one contact binary. These are pairs of stars that are so close that their surfaces overlap and they share a common envelope.

Bruce

Starship Asterisk*

APOD: Messier 5 (2019 May 09)

APOD: Messier 5 (2019 May 09)

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Re: APOD: Messier 5 (2019 May 09)

Re: APOD: Messier 5 (2019 May 09)

Re: APOD: Messier 5 (2019 May 09)

Re: APOD: Messier 5 (2019 May 09)

Re: APOD: Messier 5 (2019 May 09)

Re: APOD: Messier 5 (2019 May 09)

Re: APOD: Messier 5 (2019 May 09)

Re: APOD: Messier 5 (2019 May 09)

Re: APOD: Messier 5 (2019 May 09)

Re: APOD: Messier 5 (2019 May 09)

Re: APOD: Messier 5 (2019 May 09)

What is the Milky Way’s most distant globular cluster?

Re: APOD: Messier 5 (2019 May 09)

Re: What is the Milky Way’s most distant globular cluster?

Re: APOD: Messier 5 (2019 May 09)

Re: APOD: Messier 5 (2019 May 09)