APOD: M13: A Great Globular Cluster of Stars (2016 Jul 27)

[APOD Robot]

M13: A Great Globular Cluster of Stars

Explanation: M13 is one of the most prominent and best known globular clusters. Visible with binoculars in the constellation of Hercules, M13 is frequently one of the first objects found by curious sky gazers seeking celestials wonders beyond normal human vision. M13 is a colossal home to over 100,000 stars, spans over 150 light years across, lies over 20,000 light years distant, and is over 12 billion years old. At the 1974 dedication of Arecibo Observatory, a radio message about Earth was sent in the direction of M13. The featured image in HDR, taken through a small telescope, spans an angular size just larger than a full Moon, whereas the inset image, taken by Hubble Space Telescope, zooms in on the central 0.04 degrees.

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[Chris Peterson]

Visible with binoculars...

And to the naked eye under good observing conditions.

The featured image in HDR, taken through a small telescope...

A kind of marginal usage of "HDR". This is just a stacked astronomical image.

[Joe Stieber]

Visible with binoculars...

And to the naked eye under good observing conditions.

The featured image in HDR, taken through a small telescope...

A kind of marginal usage of "HDR". This is just a stacked astronomical image.

Yes -- I've seen M13 many times with unaided eyes, even here in the Pines of Southern New Jersey! Just a faint, slightly fuzzy "star," but it can be seen.

The featured image page at Astrobin indicates a combination of three different exposures, 40 x 8 min, 55 x 20 seconds and 45 x 5 seconds. That sounds like HDR to me, and indeed, the central part of the cluster is not "blown out" (saturated) as is often the case with amateur images of M13.

[somebodyshort]

Couple of thoughts
1) With that many stars in that volume, at the center stars must be light months apart, if not closer. That would make interstellar travel a possibility.
2) At over 12 billion years old, that puts it early in the life of the universe. I'm surprised it's held together through all that our galaxy has been through.
3) At that age stars in the cluster must have gone through complete life cycles. There must be white dwarfs, brown dwarfs, neutron stars and black holes.
4) At those densities I would expect that planets have been swapped between stars, along with much other material.

[ShaileshS]

Are we seeing some galaxy in yellow color at 7/7:30pm (hour hand in clock) position ? If yes, how far is it and how come we are able to see it so clearly through binoculars ? The nearest one (Andromeda) is seen pale while glowing small blob/patch .. then how come this one is seen much better ? Am I missing something ?

[geckzilla]

Are we seeing some galaxy in yellow color at 7/7:30pm (hour hand in clock) position ? If yes, how far is it and how come we are able to see it so clearly through binoculars ? The nearest one (Andromeda) is seen pale while glowing small blob/patch .. then how come this one is seen much better ? Am I missing something ?

The globular cluster can be seen with binoculars, but not with this much detail. The little background galaxy would not be discernible with binoculars.

[ShaileshS]

Are we seeing some galaxy in yellow color at 7/7:30pm (hour hand in clock) position ? If yes, how far is it and how come we are able to see it so clearly through binoculars ? The nearest one (Andromeda) is seen pale white glowing small blob/patch .. then how come this one is seen much better ? Am I missing something ?

The globular cluster can be seen with binoculars, but not with this much detail. The little background galaxy would not be discernible with binoculars.

But then what is that object ? It's the only one in whole image that seems to be shaped like a galaxy. And, the main image is said to be through binoculars. Thanks.

[ShaileshS]

Are we seeing some galaxy in yellow color at 7/7:30pm (hour hand in clock) position ? If yes, how far is it and how come we are able to see it so clearly through binoculars ? The nearest one (Andromeda) is seen pale white glowing small blob/patch .. then how come this one is seen much better ? Am I missing something ?

The globular cluster can be seen with binoculars, but not with this much detail. The little background galaxy would not be discernible with binoculars.

Sorry, my bad, I thought the main image was taken by binoculars. Now I read it, it was through a small telescope. In-set was through Hubble. So ignore my above question/comment.

[Ann]

Click to view full size image

Widefield image of IC 4617.
Photo: SDSS.

I believe the little galaxy is IC 4617. It is a faint 15th magnitude galaxy, and my software has very little information on it, other than that it is an Sb-type galaxy. I agree, a Hubble classification of Sb was my own guess when I looked at it.


Ann

[Coil_Smoke]

Do these clusters rotate? Does the lack of rotation allow them to keep their uniform shape. Do they lack a central gravitational singularity?

[heehaw]

2) At over 12 billion years old, that puts it early in the life of the universe. I'm surprised it's held together through all that our galaxy has been through.

Someone please explain to me why globular clusters don't have dark matter concentrations. Everything else does. And there's "galaxies" with few stars but LOTS of dark matter. I don't think this is understood at all!

[geckzilla]

Do these clusters rotate? Does the lack of rotation allow them to keep their uniform shape. Do they lack a central gravitational singularity?

Simulations have shown the orbits of stars in globular clusters to be chaotic. They do not necessarily stay moving on nice, elliptical paths. Here's a video I like that's not really a globular cluster, but it is easier to track individual stars when there are fewer. (Much easier in HD at fullscreen, very hard in the forum window)

Click to play embedded YouTube video.

Presumably if a globular cluster had any kind of overall rotation it would exhibit this property by becoming a disc.

[Knight of Clear Skies]

Nice illustration geckzilla.

Couple of thoughts
1) With that many stars in that volume, at the center stars must be light months apart, if not closer. That would make interstellar travel a possibility.

Yes, I believe the distances are as low as a few light days in the cores of some clusters, those that have undergone core collapse. However, the closer the stars the less chance of finding planets in stable orbits I'd have thought, and such an old 'metal' poor cluster may have little in the way of rocky planets. It might be more feasible in a younger glob perhaps, but I couldn't guess how likely this is.

[Chris Peterson]

A kind of marginal usage of "HDR". This is just a stacked astronomical image.

The featured image page at Astrobin indicates a combination of three different exposures, 40 x 8 min, 55 x 20 seconds and 45 x 5 seconds. That sounds like HDR to me, and indeed, the central part of the cluster is not "blown out" (saturated) as is often the case with amateur images of M13.

Agreed. I missed that reference on the imager's page.

[Chris Peterson]

Do these clusters rotate?

Consider what it would even mean for a cluster to rotate, given that it's not a solid body, but merely a collection of loosely bound stars. What would be happening around the poles? Would you have stars that weren't moving at all?

Do they lack a central gravitational singularity?

Some globulars apparently do have supermassive black holes at their centers. But as is the case with galaxies, those probably play a minor role in the structure and gravitational dynamics of the body. The stars of a globular cluster are in orbit around the center of mass of the cluster itself, which is largely defined by its individual stars.

[Asterhole]

Do these clusters rotate?

Consider what it would even mean for a cluster to rotate, given that it's not a solid body, but merely a collection of loosely bound stars. What would be happening around the poles? Would you have stars that weren't moving at all?

Do they lack a central gravitational singularity?

Some globulars apparently do have supermassive black holes at their centers. But as is the case with galaxies, those probably play a minor role in the structure and gravitational dynamics of the body. The stars of a globular cluster are in orbit around the center of mass of the cluster itself, which is largely defined by its individual stars.

The question crossed my mind as well - what is at the centers of these clusters? If it were supermassive black holes, wouldn't we be able to detect some evidence of such, like jets streaming away at opposite directions, gamma radiation, etc.?

[JimWWhite@aol.com]

I can only imagine what the night time sky would be like on a world somewhere in M13. Does anyone know of a simulation of what it might look like? I'd also imagine it would be a fairly hostile environment with all the radiation sources in relatively close proximity. Amazing!

[Chris Peterson]

Some globulars apparently do have supermassive black holes at their centers. But as is the case with galaxies, those probably play a minor role in the structure and gravitational dynamics of the body. The stars of a globular cluster are in orbit around the center of mass of the cluster itself, which is largely defined by its individual stars.

The question crossed my mind as well - what is at the centers of these clusters? If it were supermassive black holes, wouldn't we be able to detect some evidence of such, like jets streaming away at opposite directions, gamma radiation, etc.?

Like all black holes, supermassive ones (or intermediate mass ones, which seem to be what is found in globulars) are generally invisible. They only become apparent when they have matter falling into them, which heats up and radiates. But that doesn't happen very often, and that should be especially true in globular clusters, where almost all of the mass is in the form of stars, not free gas and dust. I think that all of the black holes identified in globular clusters have been found by studying the dynamics of stellar orbits.

[rstevenson]

For those who'd like a short, not too technical read, there's A Thousand Blazing Suns: The Inner Life of Globular Clusters, a 1999 article by Brian W. Murphy of Butler University. It briefly touches on stellar orbits within a globular cluster, and mentions the possibility of black holes at their centers and why we think there's not many of them there.

Rob

[zoomer]

I can only imagine what the night time sky would be like on a world somewhere in M13. Does anyone know of a simulation of what it might look like? I'd also imagine it would be a fairly hostile environment with all the radiation sources in relatively close proximity. Amazing!

If some of estimates of distace between stars actually is "light days", this concentration at the cluster's core might mean there is no night at all.

[zeroglobular]

Is a globular cluster a galaxy without a black hole in the center? Are they common?

[Chris Peterson]

Is a globular cluster a galaxy without a black hole in the center? Are they common?

A globular cluster and a galaxy are very different. Globular clusters (which sometimes have black holes at the center) are found in orbit around galaxies (which don't always have central black holes). Most galaxies have many globular clusters around them.

[Fred the Cat]

It doesn't say, "If you intercept this and it's the Earth year 2016 please re-evaluate your visit. In November part of our world could be about to elect the man depicted with a large head and even bigger hair. He will either re-define chaos theory so that large changes make absolutely no difference or build a wall that you might see coming in. If you see that "other" wall - build a Dyson Sphere around the Earth so we can't get out to cause the universe any extra problems."

I suspect it didn't. Any way to get it back?

[geckzilla]

I can only imagine what the night time sky would be like on a world somewhere in M13. Does anyone know of a simulation of what it might look like? I'd also imagine it would be a fairly hostile environment with all the radiation sources in relatively close proximity. Amazing!

Many artists have attempted to depict such worlds. I did so myself, once, using Stellarium and some Hubble data. It's not M13, though.

[Ann]

Is a globular cluster a galaxy without a black hole in the center? Are they common?

Click to view full size image

[c]Fornax dwarf galaxy. Photo:
ESO/Digitized Sky Survey 2 - http://www.eso.org/public/images/eso1007a/[/c]

There are interesting differences between galaxies and globulars. In the case of the Fornax dwarf galaxy, the globulars have a much, much higher surface brightness than the faint, scattered galaxy. Read about the galaxy and its globulars here, where you can also see the picture at left at much higher resolution.

Another example of a fluffy galaxy and a bright, concentrated globular apparently (but not really) right next to one another is the Small Magellanic Cloud and globular cluster 47 Tucanae.

Click to view full size image

Globular clusters M53 and NGC 5053. Photo:Frank Zierhut, via
http://www.nightviews.de/cluster/m53.html.

I'd say that globular clusters were probably all formed after tremendous bursts of concentrated star formation, which led to the formation of massive, highly concentrated clusters. They are, as far as I know, practically always spherical, although some might be elongated or flattened. They are never disk-shaped, and they never have spiral arms.

Source: http://apod.nasa.gov/apod/ap010223.html

Globulars can evaporate over time. The picture of globulars M53 and NGC 5053 shows one dense, massive globular (M53) and one fluffy one (NGC 5053). The latter was shown to be a globular only after it was made clear that it followed the typical globular cluster Hertszprung-Russell color-magnitude diagram, which meant that it was as old as other Milky Way globular clusters.

Galaxies, by contrast, are not the product of a single burst of star formation. They are typically far, far more extended than globular clusters. In the relatively few cases where galaxies are small, highly concentrated and extremely bright for their size, they have typically been "bullied" by a much larger neighboring galaxy. But even those small compact galaxies are larger than globular clusters.

Click to view full size image

The Bullet Cluster. Chandra X-Ray Observatory: 1E 0657-56
NASA/CXC/M. Weiss

Why do globular clusters lack dark matter?

I don't know, but I do know that dark matter and baryonic matter ("ordinary matter") can separate from one another. The most famous example of this is the Bullet Cluster, where dark matter (blue) has separated from the baryonic matter, the hot hydrogen gas (red). The Bullet Cluster is the result of two massive cluster colliding with one another, and the dark matter doesn't seem able to "keep up" with the baryonic matter.

I believe that globular clusters typically survive for ten billion years of more because they have been flung away from their busy birthplaces, the crowded disks or molecular clouds of starburst galaxies. Most likely, they have been flung away when their parent galaxies interacted with other galaxies, like mini-versions of the colliding Bullet cluster. The globular clusters were likely "flung away" in such a way that the dark matter was left behind. At least that is my personal amateur hypothesis.

Ann