APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

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APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by APOD Robot » Thu Aug 04, 2022 4:05 am

Image M13: The Great Globular Cluster in Hercules

Explanation: In 1716, English astronomer Edmond Halley noted, "This is but a little Patch, but it shows itself to the naked Eye, when the Sky is serene and the Moon absent." Of course, M13 is now less modestly recognized as the Great Globular Cluster in Hercules, one of the brightest globular star clusters in the northern sky. Sharp telescopic views like this one reveal the spectacular cluster's hundreds of thousands of stars. At a distance of 25,000 light-years, the cluster stars crowd into a region 150 light-years in diameter. Approaching the cluster core upwards of 100 stars could be contained in a cube just 3 light-years on a side. For comparison, the closest star to the Sun is over 4 light-years away. The remarkable range of brightness recorded in this image follows stars into the dense cluster core. Distant background galaxies in the medium-wide field of view include NGC 6207 at the upper left.

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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by sym666 » Thu Aug 04, 2022 7:35 am

I wonder how the sky would look like from an hypothetical planet orbiting one of the star near the center, where, as the caption says, there are some a 100 stars in 3 light years.

Edit: Of course, someone already asked the same question and someone tried to answer: https://gizmodo.com/what-the-night-sky- ... 1589324556

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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by Ann » Thu Aug 04, 2022 7:44 am

sym666 wrote: Thu Aug 04, 2022 7:35 am I wonder how the sky would look like from an hypothetical planet orbiting one of the star near the center, where, as the caption says, there are some a 100 stars in 3 light years.

Maybe it would look something like this?

Explanation: The brilliant light at lower right is the crowded center of 47 Tuc, and the bright but fainter light at upper left is another, nearby globular cluster, whose designation I'm too lazy to google now. The reddish, brownish "veins" seen in the left part of the image are dust lanes in the background Milky Way. Not sure you would see the Milky Way from inside a globular cluster, though!

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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by sym666 » Thu Aug 04, 2022 7:57 am

Ann wrote: Thu Aug 04, 2022 7:44 am
sym666 wrote: Thu Aug 04, 2022 7:35 am I wonder how the sky would look like from an hypothetical planet orbiting one of the star near the center, where, as the caption says, there are some a 100 stars in 3 light years.

Maybe it would look something like this?

Explanation: The brilliant light at lower right is the crowded center of 47 Tuc, and the bright but fainter light at upper left is another, nearby globular cluster, whose designation I'm too lazy to google now. The reddish, brownish "veins" seen in the left part of the image are dust lanes in the background Milky Way. Not sure you would see the Milky Way from inside a globular cluster, though!

Ann
I think it could be in the ballpark. In the article I quoted, the author tough, says that it could be a countinous sort of "grainy" (because of the incredible amount of visible stars) twilight, so maybe the background should be brighter instead of the pitch black we are used to:

"At the center, our planet would be surrounded by a few hundred stars per cubic light-year (several thousand stars per cubic pc), which is thousands of times the stellar density of the Sun's neighborhood in the Milky Way's suburbs. The typical distance from our hypothetical planet to the closest star, however, still would be substantial — about 0.05 light-year (0.015 pc). In our solar system, this would place it beyond the inner edge of the Oort Cloud of comets.

Unless the closest stars happen to be red giants, none of them would have angular diameters large enough to resolve with the human eye, so all the stars still would appear as points of light. Across the entire sky, inhabitants of our hypothetical world would see 10,000 stars brighter than 1st magnitude — compared with just 29 in Earth's sky — and more than a thousand brighter than Earth's most brilliant nighttime star, Sirius. The brightest suns would blaze at apparent magnitudes brighter than –9, or 100 times more luminous than Venus appears from Earth. More than 130,000 stars would shine brighter than 6th magnitude, the naked-eye limit, compared with 6,000 from Earth.

Although it might sound like lots of empty space still exists at the cluster's center, the prospects for doing astronomy from there would be discouraging. The biggest problem would be the sheer amount of light from all those stars. The cluster's suns would combine to give an average sky brightness some 20 times brighter than Earth's night sky at Full Moon (or about 16.7 magnitudes per square arcsecond). In other words, the darkest night our viewers would ever see would be a strange sort of twilight that possesses a kind of grainy texture unlike the uniform sheet of light we see on Earth. The galaxy's disk — already hard to see from Earth at Full Moon except from isolated locations — would be visible in the background but hard to study. Astronomers on our hypothetical planet likely would favor telescopes with small fields of view and excellent baffling against scattered light."

Very interesting anyway, thanks for your insight! :ssmile:

P.S.: Is your picture located in a accessible site?...Disregard that, I found it!

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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by sym666 » Thu Aug 04, 2022 8:18 am

The article I quoted also says at the end: "Astronomy will be making the simulation available next month, where you can position yourself from anywhere inside the cluster. So cool."

I suppose it refers to Astronomy.com site, but I can't find that simulation! :cry:

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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by AVAO » Thu Aug 04, 2022 8:41 am

sym666 wrote: Thu Aug 04, 2022 8:18 am The article I quoted also says at the end: "Astronomy will be making the simulation available next month, where you can position yourself from anywhere inside the cluster. So cool."

I suppose it refers to Astronomy.com site, but I can't find that simulation! :cry:
2014 as source is old. https://www.physicsforums.com/attachmen ... -pdf.79520

In my opinion, the simulations are too short-sighted. If there were stars with planets with life, they would have developed other organs of perception and their eyes would work differently than ours...

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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by sym666 » Thu Aug 04, 2022 9:25 am

AVAO wrote: Thu Aug 04, 2022 8:41 am
sym666 wrote: Thu Aug 04, 2022 8:18 am The article I quoted also says at the end: "Astronomy will be making the simulation available next month, where you can position yourself from anywhere inside the cluster. So cool."

I suppose it refers to Astronomy.com site, but I can't find that simulation! :cry:
2014 as source is old. https://www.physicsforums.com/attachmen ... -pdf.79520

In my opinion, the simulations are too short-sighted. If there were stars with planets with life, they would have developed other organs of perception and their eyes would work differently than ours...
Right, besides today as I was wandering thru these articles I read somewhere that such a planetary system could survive on average 3k years or such.
Anyway we were just wondering about the aspect of the sky in such a place.
Thanks for the article!

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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by zeecatman » Thu Aug 04, 2022 9:28 am

M13, a favorite telescope target of mine! I highly recommend anyone with a telescope to view this amazing cluster through the eyepiece. With a bit of focus on a nice clear night, it isn't difficult to pick out individual stars surrounding the central blob. This picture, of course, is much more detailed and stunning.

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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by Redbone » Thu Aug 04, 2022 10:44 am

A little research into why these clusters don't collapse resulted in:

This means that over time, the massive stars will tend to slow down, and the light stars will tend to speed up. If a star is slowing down, then gravity gets to take over, and does indeed pull that star down, closer to the core of the cluster. You wind up with some globular clusters collecting all their high mass stars in their very centers, with the lightest stars zooming around the outskirts, going much faster. This pattern of energy allows the cluster to sort itself from heaviest to lightest. (The technical term for this end result is called ‘mass segregation’.)

Source: https://medium.com/starts-with-a-bang/a ... 2c4b985ec2

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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by orin stepanek » Thu Aug 04, 2022 12:24 pm

M13_final2_sinfirma1024.jpg
Star clusters amaze me! I wonder why they don't just drift apart;
but they are beautiful little gems in the universe! 8-)
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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by Chris Peterson » Thu Aug 04, 2022 1:52 pm

sym666 wrote: Thu Aug 04, 2022 9:25 am
AVAO wrote: Thu Aug 04, 2022 8:41 am
sym666 wrote: Thu Aug 04, 2022 8:18 am The article I quoted also says at the end: "Astronomy will be making the simulation available next month, where you can position yourself from anywhere inside the cluster. So cool."

I suppose it refers to Astronomy.com site, but I can't find that simulation! :cry:
2014 as source is old. https://www.physicsforums.com/attachmen ... -pdf.79520

In my opinion, the simulations are too short-sighted. If there were stars with planets with life, they would have developed other organs of perception and their eyes would work differently than ours...
Right, besides today as I was wandering thru these articles I read somewhere that such a planetary system could survive on average 3k years or such.
Anyway we were just wondering about the aspect of the sky in such a place.
Thanks for the article!
Planetary systems are always unstable, and the greater the stellar density, the greater the instability. In a globular, in a galactic core... the only planets are going to be ones that orbit very, very close to their stars. Not places you'd find life. Other planets will have been long since tossed out of their parent systems. So in a globular... no observers.
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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by Chris Peterson » Thu Aug 04, 2022 1:53 pm

Redbone wrote: Thu Aug 04, 2022 10:44 am A little research into why these clusters don't collapse resulted in:

This means that over time, the massive stars will tend to slow down, and the light stars will tend to speed up. If a star is slowing down, then gravity gets to take over, and does indeed pull that star down, closer to the core of the cluster. You wind up with some globular clusters collecting all their high mass stars in their very centers, with the lightest stars zooming around the outskirts, going much faster. This pattern of energy allows the cluster to sort itself from heaviest to lightest. (The technical term for this end result is called ‘mass segregation’.)

Source: https://medium.com/starts-with-a-bang/a ... 2c4b985ec2
Globulars don't collapse for the same reason our solar system doesn't collapse.
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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by De58te » Thu Aug 04, 2022 4:23 pm

Makes me wonder with Halley's comment about a little patch being M13, what this looked like to Edmond Halley? The information says that this photo was taken by an 8 inch Newtonian. Now Newton had already invented the Newtonian by the turn of the century, they were small. Research told me that the first 6 inch Newtonian wasn't created until 1721. Halley had to see this through a smaller scope. I would find it interesting to compare this side by side to a telescope image that Halley would have seen in 1716.

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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by Ann » Thu Aug 04, 2022 5:16 pm

Chris Peterson wrote: Thu Aug 04, 2022 1:53 pm
Redbone wrote: Thu Aug 04, 2022 10:44 am A little research into why these clusters don't collapse resulted in:

This means that over time, the massive stars will tend to slow down, and the light stars will tend to speed up. If a star is slowing down, then gravity gets to take over, and does indeed pull that star down, closer to the core of the cluster. You wind up with some globular clusters collecting all their high mass stars in their very centers, with the lightest stars zooming around the outskirts, going much faster. This pattern of energy allows the cluster to sort itself from heaviest to lightest. (The technical term for this end result is called ‘mass segregation’.)

Source: https://medium.com/starts-with-a-bang/a ... 2c4b985ec2
Globulars don't collapse for the same reason our solar system doesn't collapse.

Globular clusters don't collapse, but they may evaporate. That means that some stars, particularly small lightweight stars, get kicked out of the cluster, never to return.


Click to play embedded YouTube video.
Star cluster simulation.


And take a look at these two neighboring clusters, M53 and NGC 5053. M53 is a rich cluster, whereas NGC 5053 is comparatively poor in stars. How did NGC 5053 get like this? Perhaps it was born with relatively few stars, but perhaps it has lost a large number of them due to evaporation.


M53 NGC 5053 Bob Franke.png
NGC 5053 (lower left) and M53 (top right). Photo: Bob Franke.

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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by Chris Peterson » Thu Aug 04, 2022 5:29 pm

Ann wrote: Thu Aug 04, 2022 5:16 pm
Chris Peterson wrote: Thu Aug 04, 2022 1:53 pm
Redbone wrote: Thu Aug 04, 2022 10:44 am A little research into why these clusters don't collapse resulted in:

This means that over time, the massive stars will tend to slow down, and the light stars will tend to speed up. If a star is slowing down, then gravity gets to take over, and does indeed pull that star down, closer to the core of the cluster. You wind up with some globular clusters collecting all their high mass stars in their very centers, with the lightest stars zooming around the outskirts, going much faster. This pattern of energy allows the cluster to sort itself from heaviest to lightest. (The technical term for this end result is called ‘mass segregation’.)

Source: https://medium.com/starts-with-a-bang/a ... 2c4b985ec2
Globulars don't collapse for the same reason our solar system doesn't collapse.

Globular clusters don't collapse, but they may evaporate. That means that some stars, particularly small lightweight stars, get kicked out of the cluster, never to return.
Actually, evaporation is also accompanied by collapse. Ejected stars carry away angular momentum and energy, which results in other stars moving inward.
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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by FLPhotoCatcher » Thu Aug 04, 2022 10:57 pm

Are there globular clusters in inter-galactic space? It seems that they are always near, or in galaxies. Why would that be? How do they form?

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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by Chris Peterson » Fri Aug 05, 2022 1:10 am

FLPhotoCatcher wrote: Thu Aug 04, 2022 10:57 pm Are there globular clusters in inter-galactic space? It seems that they are always near, or in galaxies. Why would that be? How do they form?
Nobody knows. But they are closely associated with galaxies. It's likely that they both form together.
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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by Ann » Fri Aug 05, 2022 3:29 am

Chris Peterson wrote: Thu Aug 04, 2022 5:29 pm
Ann wrote: Thu Aug 04, 2022 5:16 pm
Chris Peterson wrote: Thu Aug 04, 2022 1:53 pm

Globulars don't collapse for the same reason our solar system doesn't collapse.

Globular clusters don't collapse, but they may evaporate. That means that some stars, particularly small lightweight stars, get kicked out of the cluster, never to return.
Actually, evaporation is also accompanied by collapse. Ejected stars carry away angular momentum and energy, which results in other stars moving inward.

Indeed. But so far globular clusters have never collapsed into one mid-sized black hole, at least.

Or so I believe anyway.

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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by Ann » Fri Aug 05, 2022 3:46 am

Chris Peterson wrote: Fri Aug 05, 2022 1:10 am
FLPhotoCatcher wrote: Thu Aug 04, 2022 10:57 pm Are there globular clusters in inter-galactic space? It seems that they are always near, or in galaxies. Why would that be? How do they form?
Nobody knows. But they are closely associated with galaxies. It's likely that they both form together.

So, Chris, what's the difference between a globular cluster and a small spheroidal galaxy?

A small spheroidal galaxy has been discovered behind globular cluster NGC 6752:

heic1903c[1].jpg
Globular cluster NGC 6752 and a small dwarf galaxy (near top left)
seen right through it. ESA/Hubble, NASA, Bedin et al.

Are globular clusters different from dwarf spheroidal galaxies because of their metal content and their stellar populations? Or what?

And by the way, NGC 6752 is one of those globulars that has undergone core collapse.

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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by Chris Peterson » Fri Aug 05, 2022 4:26 am

Ann wrote: Fri Aug 05, 2022 3:46 am
Chris Peterson wrote: Fri Aug 05, 2022 1:10 am
FLPhotoCatcher wrote: Thu Aug 04, 2022 10:57 pm Are there globular clusters in inter-galactic space? It seems that they are always near, or in galaxies. Why would that be? How do they form?
Nobody knows. But they are closely associated with galaxies. It's likely that they both form together.

So, Chris, what's the difference between a globular cluster and a small spheroidal galaxy?

A small spheroidal galaxy has been discovered behind globular cluster NGC 6752:

Are globular clusters different from dwarf spheroidal galaxies because of their metal content and their stellar populations? Or what?
Heck if I know. Looking at stellar populations seems to be up your alley. Globulars do seem to have a rather distinctive stellar population, though. Does the spherical galaxy look anything like it?
And by the way, NGC 6752 is one of those globulars that has undergone core collapse.
That's a term that could be misleading or confusing, of course. It really just reflects a change in the stellar distribution within the cluster. There's still no collapse in the sense of stars colliding and coalescing into a black hole. (Nobody understands the origin of massive black holes thought to exist in a small number of globulars.)
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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by Ann » Fri Aug 05, 2022 5:41 am

Chris Peterson wrote: Fri Aug 05, 2022 4:26 am
Ann wrote: Fri Aug 05, 2022 3:46 am
Chris Peterson wrote: Fri Aug 05, 2022 1:10 am

Nobody knows. But they are closely associated with galaxies. It's likely that they both form together.

So, Chris, what's the difference between a globular cluster and a small spheroidal galaxy?

A small spheroidal galaxy has been discovered behind globular cluster NGC 6752:

Are globular clusters different from dwarf spheroidal galaxies because of their metal content and their stellar populations? Or what?
Heck if I know. Looking at stellar populations seems to be up your alley. Globulars do seem to have a rather distinctive stellar population, though. Does the spherical galaxy look anything like it?
Heck if I know! All I think I understand about globular clusters is that the largest ones in the Milky Way are very old, some ~12 billion years old, and they are metal-poor. Many of them, but not all, contain a special kind of evolved giant stars that are blue in color, blue horizontal branch stars. The globulars that contain these blue stars are also the globulars that contain RR Lyrae variables, whose pulsations make it possible to determine the distance to the globulars that contain them.

I don't know of anything else that sets globular clusters apart from galaxies. Admittedly though, I think that globular clusters in most cases are one-generation clusters, which is to say that all their stars formed in one single enormous starburst. But there are a few globulars that show signs of more than one generation of stars.

Perhaps, in dwarf spheroidal galaxies, there have almost always been multiple generations of stars, even if star formation stopped billions of years ago? And the first burst of star formation was not so tremendous? Or the dwarf spheroidals formed "alone", not close to a larger galaxy?

I really don't know, which is why I asked.


I agree that neither dwarf spheroidal galaxy NGC 147 nor the Fornax Dwarf galaxy look like globular clusters. Their red giants are far too faint, so that they don't stand out, the way the red giants do in globulars.

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Re: APOD: M13: The Great Globular Cluster in... (2022 Aug 04)

Post by Rauf » Wed Aug 17, 2022 11:18 am

sym666 wrote: Thu Aug 04, 2022 7:35 am I wonder how the sky would look like from an hypothetical planet orbiting one of the star near the center, where, as the caption says, there are some a 100 stars in 3 light years.

Edit: Of course, someone already asked the same question and someone tried to answer: https://gizmodo.com/what-the-night-sky- ... 1589324556
Umm, I don't know if you have heard of this, but I found this simulator very helpful.
https://spaceengine.org/
You can download it for free, and it gives you a good enough simulation of the universe, and I found it very entertaining. You can travel inside galaxies, clusters, move around neutron stars and feel the surface of unknown planets.
I recommend you give it a try!!