APOD: M13: The Great Globular Cluster in... (2020 Mar 19)

[APOD Robot]

M13: The Great Globular Cluster in Hercules

Explanation: In 1716, English astronomer Edmond Halley noted, "This is but a little Patch, but it shews 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 and reveals three subtle dark lanes forming the apparent shape of a propeller just below and slightly left of center. Distant background galaxies in the medium-wide field of view include NGC 6207 at the upper left.

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[christianhoffmann]

I am a mathematician and would like to estimate/compute the brightness in the interior/middle of a globular cluster, given eht number of 'normal' stars of teh entire cluster, e.g. M13.https://apod.nasa.gov/apod/image/2003/M ... mColes.jpg

[orin stepanek]

Very nice! That's a lot of stars in a small area!

[sillyworm 2]

This propeller...is it dust? Less/more populated areas? Why is there such a nearly equal mixture of young and old stars?

[Chris Peterson]

This propeller...is it dust? Less/more populated areas? Why is there such a nearly equal mixture of young and old stars?

The "propeller" is nothing but our brain finding a transient pattern. It has no dynamical significance. Globular clusters are largely free of dust and gas... and all the stars are the same age.

[sillyworm 2]

Thanks..I always confuse color with age.Color is eventually more a size element?

[Chris Peterson]

Thanks..I always confuse color with age.Color is eventually more a size element?

Color is temperature. And temperature is highly determined by mass, as well as position along the stellar evolution curve.

[CuriousChimp]

The remarkable range of brightness recorded in this image follows stars into the dense cluster core and reveals three subtle dark lanes forming the apparent shape of a propeller just below and slightly left of center. Distant background galaxies in the medium-wide field of view include NGC 6207 at the upper left.

A propellor? Really? With my brain working its pareidolia to the maximum I can "see" a stick-figure of my wife just out of the shower, complete with towel on head and several Starships but I see no propellor.

Sorry. Maybe I'm not programmed properly?

The overwhelming feeling I get from images like this, apart from absolute awe and joy of course, is deep, deep sadness. Millions of stars and few, if any will have useful, rocky worlds, even fewer, probably none, will have Life and Man will most likely never visit any of them.

Worse, I will never get to see the skies full of stars from a world near the centre of a Cluster. That's just tragic.

[Chris Peterson]

The remarkable range of brightness recorded in this image follows stars into the dense cluster core and reveals three subtle dark lanes forming the apparent shape of a propeller just below and slightly left of center. Distant background galaxies in the medium-wide field of view include NGC 6207 at the upper left.

A propellor? Really? With my brain working its pareidolia to the maximum I can "see" a stick-figure of my wife just out of the shower, complete with towel on head and several Starships but I see no propellor.

Sorry. Maybe I'm not programmed properly?

The overwhelming feeling I get from images like this, apart from absolute awe and joy of course, is deep, deep sadness. Millions of stars and few, if any will have useful, rocky worlds, even fewer, probably none, will have Life and Man will most likely never visit any of them.

Worse, I will never get to see the skies full of stars from a world near the centre of a Cluster. That's just tragic.

It''s unlikely that any stars near the center of a globular cluster have worlds from which to view things. But I imagine there are countless stars outside of clusters that have worlds on which life might exist. But you're right- we'll never visit them.

[CuriousChimp]

The remarkable range of brightness recorded in this image follows stars into the dense cluster core and reveals three subtle dark lanes forming the apparent shape of a propeller just below and slightly left of center. Distant background galaxies in the medium-wide field of view include NGC 6207 at the upper left.

A propellor? Really? With my brain working its pareidolia to the maximum I can "see" a stick-figure of my wife just out of the shower, complete with towel on head and several Starships but I see no propellor.

Sorry. Maybe I'm not programmed properly?

The overwhelming feeling I get from images like this, apart from absolute awe and joy of course, is deep, deep sadness. Millions of stars and few, if any will have useful, rocky worlds, even fewer, probably none, will have Life and Man will most likely never visit any of them.

Worse, I will never get to see the skies full of stars from a world near the centre of a Cluster. That's just tragic.

It''s unlikely that any stars near the center of a globular cluster have worlds from which to view things. But I imagine there are countless stars outside of clusters that have worlds on which life might exist. But you're right- we'll never visit them.

Yerp, and that last just makes all of that glorious wondrousness ever so much sadder. What a waste of a huge, beautiful, magical cosmos when no one and nothing is ever going to see the best bits.

About not having a planet inside the Cluster from which to view stuff, well, that's what Engineers are for. We can build stuff. It's sort of what Homo Sap. is famous for.

Given FTL and a lack of government oversight building bases, colony O'Neil cylinders and even useful worlds is only a matter of effort. There's nothing magic about it. The Romans could have done it. House, City, roads, worlds, it's all just engineering.

Getting out there may be a bit of a deal-breaker but the rest is easy.

[donaldbullock]

Can you explain;
Why with such a huge number of stars within very close proximity, has gravity not coalesced them into a super star.
Thanks

[Ann]

I am a mathematician and would like to estimate/compute the brightness in the interior/middle of a globular cluster, given eht number of 'normal' stars of teh entire cluster, e.g. M13.https://apod.nasa.gov/apod/image/2003/M ... mColes.jpg

A view from the outskirts of 47 Tucanae, the second brightest globular of the Milky Way. The core of 47 Tuc is seen at 4 o'clock, and another globular, either NGC 121 or NGC 362, can be seen at 11 o'clock. The reddish dust lanes of the Milky Way are seen at left. Image: William Harris and Jeremy Webb.

---

Another picture of a world inside a globular cluster. Note how the mountains are lit up by the light of the stars. Illustration: I don't know.

---

I am very much a non-mathematician, so I can't help you, but at least I can post two interesting illustrations of what a view from a planet inside a globular cluster might look like. Judging from the presence of blue horizontal branch stars in the globular in the picture at right, we might guess that that globular might be either M13 or Omega Centauri.

Ann

[Ann]

Thanks..I always confuse color with age.Color is eventually more a size element?

As Chris said, color means temperature. We are talking about the temperature of the photosphere, the outermost visible layer of a star.

The Herzsprung-Russell diagram of stars. When stars are on the main sequence, they fuse hydrogen to helium in their cores. The more massive the stars are, they faster they fuse their hydrogen, and the hotter and bluer they are. The more lightweight the stars are, the slower they fuse their hydrogen, and the cooler and redder they are. When stars have used up their core hydrogen, they swell into giants. Red supergiants like Betelgeuse become tremendously big, whereas blue, white and even yellow supergiants are somewhat smaller. Medium-mass stars like the Sun will eventually turn into red giants, but they will never be as big as Betelgeuse. In many globular clusters, red giants can shrink and become blue horizontal branch stars before swelling into red asymtotic branch giants. Illustration: Astronomy magazine.

---

Massive young stars are blue (Chris would say blue-white), because they fuse hydrogen to helium in their cores at a furious rate. Medium-mass stars like the Sun have never been blue, because they have never produced enough energy in their cores to look blue. They don't need that much energy to keep themselves from collapsing, unlike the stellar heavyweights. And small stars like Proxima Centauri need even less energy to "hold themselves up", and they are yellow-orange in color.

When massive stars have used up their supply of energy in their cores, they start expanding. At first it doesn't affect their color that much. An example of a star that has used up its core hydrogen and started expanding without losing its blue color is Alnilam, the middle star in Orion's Belt. But another star in Orion, Betelgeuse, started out as a hot blue star, and it has since expanded so mightily that its outer layers have cooled to a yellow-orange color. Note that the core of Betelgeuse is still very hot, but we can't see it.

In globular clusters the brightest stars are red giants. The outer layers of the red giants have expanded mightily (though not as much as Betelgeuse) and they have cooled to an orange-yellow color. But there are blue stars in many globular clusters, too. These stars are always fainter than the brightest red giants, but they are relatively bright anyway.

These blue stars, called horizontal branch stars, are former red giants which have "turned on" their helium fusion. As they did so, they shrunk a lot and turned blue precisely because they became relatively small. Their outer layers are relatively close to their hot interiors, and the outer layers are therefore hot enough to be blue.

Ann

[sillyworm 2]

Thanks Chris & Ann.I do read up daily but I still miss some details.I did not know that a Red Giant could turn blue.I thought that stars ,toward their end time,expanded and turned red..then went supernova or collapsed.I'll have to do more reading.Chris..I know in all likelihood we will never teach other Galaxies.Time and radiation our enemies.I do believe we may someday figure out quick space travel....Is it not space radiation that will not allow this even if we do?

[TheOtherBruce]

Can you explain;
Why with such a huge number of stars within very close proximity, has gravity not coalesced them into a super star.
Thanks

As a wise man* once said, “Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space.”

In comparison, stars — even the biggest super-giants — are very not-big. Even in the crowded conditions in the middle of a globular cluster, there's lots of room between them for any number of nearly-but-not-quite close passes. Collisions aren't impossible, they happen occasionally in a normal galaxy, but on a human timescale, they'll be few and far between.

FWIW, "coalescing into a super star" generally isn't a thing colliding stars do. Instead, they tend to go boom. Very boom. All the boom.

* I don't think I need to give a name, we've got some hoopy froods here.

[Chris Peterson]

Can you explain;
Why with such a huge number of stars within very close proximity, has gravity not coalesced them into a super star.
Thanks

They are all in orbit. They don't coalesce for the same reason our solar system doesn't.

[CuriousChimp]

Can you explain;
Why with such a huge number of stars within very close proximity, has gravity not coalesced them into a super star.
Thanks

They are all in orbit. They don't coalesce for the same reason our solar system doesn't.

Though, like elliptical galaxies and utterly unlike the Solar System, a Galactic Cluster's components seem to move more like a bee swarm than a sensible planetary system. Stars orbit in 3D, sometimes in exceedingly thin, long ellipses and in chaotic ones heavily influenced by all of the millions of other stars whirling nearby.

Clusters are complicated dances of tiny, bright diamonds around a theoretical centre that may never be occupied by anything for very long. They are examples of the Many Body Problem written very, very large.

They are fun.

[CuriousChimp]

I am a mathematician and would like to estimate/compute the brightness in the interior/middle of a globular cluster, given eht number of 'normal' stars of teh entire cluster, e.g. M13.https://apod.nasa.gov/apod/image/2003/M ... mColes.jpg

I am very much a non-mathematician, so I can't help you, but at least I can post two interesting illustrations of what a view from a planet inside a globular cluster might look like. Judging from the presence of blue horizontal branch stars in the globular in the picture at right, we might guess that that globular might be either M13 or Omega Centauri.

Ann

Thank you, lady, those are pretty but also so sad.


When I was very much younger than I am now, I saw the beginning of Man's great adventure into the deep black between the stars and I dreamed of one day touching their worlds. It was a hard thing to learn that neither I nor Man himself ever will and that the dream has gone, forever.

In a way, APoD is a small hurty thing. It brings to us the little, tiny flicker of hope of seeing the beauties and wonders of our home, the cosmos, before the reality snatches away that flicker. SF movies, TV and books sometimes do similarly.

We can read Dr. Asimov's lovely "Nightfall" and we can dream but we'll never see.

We are blessed and cursed by wanderlust.

[TheOtherBruce]

We can read Dr. Asimov's lovely "Nightfall" and we can dream but we'll never see.

I just realised — the planet in Nightfall was in the middle of a big globular cluster. But the people there didn't know, because with (I think) six suns, it was never night. Until suddenly it was...

Also going back to the classics, Poul Anderson had a short story, Starfog, about the problem of navigating through a large region of stars at ridiculously close distances. Can't remember whether the term "globular cluster" was actually used, but the description does fit very closely.

[TheZuke!]

Sorry to get theological on you great folks...

But, I think, someday in Eternal Life, I may get to view, if not travel, this vast beautiful universe!

Okay, neufer, your turn to put me down!

[Chris Peterson]

Sorry to get theological on you great folks...

But, I think, someday in Eternal Life, I may get to view, if not travel, this vast beautiful universe!

Okay, neufer, your turn to put me down! :)

Maybe it's all the Matrix. Get out, and you can inspect the code that is used to create globular clusters.

[MarkBour]

...
When I was very much younger than I am now, I saw the beginning of Man's great adventure into the deep black between the stars and I dreamed of one day touching their worlds. It was a hard thing to learn that neither I nor Man himself ever will and that the dream has gone, forever.

In a way, APoD is a small hurty thing. It brings to us the little, tiny flicker of hope of seeing the beauties and wonders of our home, the cosmos, before the reality snatches away that flicker. SF movies, TV and books sometimes do similarly.

We can read Dr. Asimov's lovely "Nightfall" and we can dream but we'll never see.

We are blessed and cursed by wanderlust.

Got a planetarium nearby?

You realize that you're just purposely making yourself feel bad, don't you? Actually, based on your last statement, I'm thinking you understood this already.

I'm not sure I can explain myself, but what I feel I've come to realize lately is a paradox. There are lots of things in this universe that are inutterably sad. And I mean sad in reality, truly tragic. But then, after a longer reflection, it turns into a matter of perspective. Perhaps the greatest gift given to mankind is the ability to change our perspective, at will, with just a bit of effort. (Take the coronavirus COVID-19, for example. It's pure, pure badness, right?)

[Chris Peterson]

...
When I was very much younger than I am now, I saw the beginning of Man's great adventure into the deep black between the stars and I dreamed of one day touching their worlds. It was a hard thing to learn that neither I nor Man himself ever will and that the dream has gone, forever.

In a way, APoD is a small hurty thing. It brings to us the little, tiny flicker of hope of seeing the beauties and wonders of our home, the cosmos, before the reality snatches away that flicker. SF movies, TV and books sometimes do similarly.

We can read Dr. Asimov's lovely "Nightfall" and we can dream but we'll never see.

We are blessed and cursed by wanderlust.

Got a planetarium nearby?

You realize that you're just purposely making yourself feel bad, don't you? Actually, based on your last statement, I'm thinking you understood this already.

I'm not sure I can explain myself, but what I feel I've come to realize lately is a paradox. There are lots of things in this universe that are inutterably sad. And I mean sad in reality, truly tragic. But then, after a longer reflection, it turns into a matter of perspective. Perhaps the greatest gift given to mankind is the ability to change our perspective, at will, with just a bit of effort. (Take the coronavirus COVID-19, for example. It's pure, pure badness, right?)

Quibble, utterly unrelated to your comment: the virus is actually SARS-CoV-2. COVID-19 is the disease caused by that virus.

[MarkBour]

FWIW, "coalescing into a super star" generally isn't a thing colliding stars do. Instead, they tend to go boom. Very boom. All the boom.

Loved this description. Maybe it's a reference, too. It sounds familiar, but I don't recognize it.

[Chris Peterson]

Can you explain;
Why with such a huge number of stars within very close proximity, has gravity not coalesced them into a super star.
Thanks

They are all in orbit. They don't coalesce for the same reason our solar system doesn't.

Though, like elliptical galaxies and utterly unlike the Solar System, a Galactic Cluster's components seem to move more like a bee swarm than a sensible planetary system. Stars orbit in 3D, sometimes in exceedingly thin, long ellipses and in chaotic ones heavily influenced by all of the millions of other stars whirling nearby.

Clusters are complicated dances of tiny, bright diamonds around a theoretical centre that may never be occupied by anything for very long. They are examples of the Many Body Problem written very, very large.

They are fun.

Yes, the orbits are highly perturbed. But even in the densest parts, the distance between the stars is huge compared with the diameter of the stars, which is why collisions are extremely rare.

I once did an analysis of a dense globular cluster by projecting lines with a stellar cross section through a model cluster. Less than one in a million ended up intersecting a star.