APOD: M13: The Great Globular Cluster in... (2010 May 27)

[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 it self to the naked Eye, when the Sky is serene and the Moon absent." Of course, M13 is now modestly recognized as the Great Globular Cluster in Hercules, one of the brightest globular star clusters in the northern sky. Telescopic views 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, but 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. Along with the cluster's dense core, the outer reaches of M13 are highlighted in this sharp color image. The cluster's evolved red and blue giant stars show up in yellowish and blue tints.

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[Beyond]

NICE!

[nstahl]

It seems to me any planets that had formed about one of those stars would have long since been jarred out of its orbit and eventually fallen into one of those. Maybe a planet could survive way out around the edges but even that seems chancy.

And it always seemed amazing to me that those stars, which all have to orbit the center of mass, wouldn't have mostly crashed into each other long since too. And surely a lot have. What do we know about the orbits of stars in a cluster like that?

[orin stepanek]

I'm thinking that the night sky on a planet in this cluster would be lit up almost as bright as day. Considering the planet had an atmosphere of course.

[biddie67]

Wow!! Incredible ...

[p1gnone]

Comparing the 3ly on a side at the center of the cluster to 4ly to the alpha centauri system:
place the Sun at cube center with the centauri system at a vertex, a corner, gives the smallest cube with side length computed:

4^2= sqrt(8)^2 + sqrt(8)^2 for half side length 2sqrt(2), side length 4sqrt(2)

[rstevenson]

I'm thinking that the night sky on a planet in this cluster would be lit up almost as bright as day. Considering the planet had an atmosphere of course.

Orin, have a look at the "crowd" and "approaching" links in the APOD text. Together they will give you the best approximation of what such a night sky would look like that I've come across so far.

Rob

[Mike999]

Has there been observed a cluster of older stars, where one went nova or supernova which then touched off the other stars in the cluster causing a chain reaction of enormous extent? Is this mathematically possible?

[orin stepanek]

I'm thinking that the night sky on a planet in this cluster would be lit up almost as bright as day. Considering the planet had an atmosphere of course.

Orin, have a look at the "crowd" and "approaching" links in the APOD text. Together they will give you the best approximation of what such a night sky would look like that I've come across so far.

Rob

so the sky would be filled with 100,000 stars each brighter than the star Sirius,

Even so They are probably just as big of bigger than Sirius; and yet, a lot closer. We would have a pretty well lit sky. Away from city lights; it still gets pretty well lit here at night. I'll bet it would be beautiful at night.

[neufer]

It seems to me any planets that had formed about one of those stars would have long since been jarred out of its orbit and eventually fallen into one of those. Maybe a planet could survive way out around the edges but even that seems chancy.

And it always seemed amazing to me that those stars, which all have to orbit the center of mass, wouldn't have mostly crashed into each other long since too. And surely a lot have. What do we know about the orbits of stars in a cluster like that?

Because globular clusters have an overall spherical symmetry one can be sure that many near collisions have taken place in order to have randomized the velocity profile. Fewer collisions are close enough to actually disrupt solar systems and far fewer still have resulted in an actual physical collisions (since almost all globular cluster stars normal [i.e., main sequence]).

<<Globular clusters have a very high star density, and therefore close interactions and near-collisions of stars occur relatively often. Due to these chance encounters, some exotic classes of stars, such as blue stragglers, millisecond pulsars and low-mass X-ray binaries, are much more common in globular clusters. A blue straggler is formed from the merger of two stars, possibly as a result of an encounter with a binary system. The resulting star has a higher temperature than comparable stars in the cluster with the same luminosity, and thus differs from the main sequence stars formed at the beginning of the cluster.

http://antwrp.gsfc.nasa.gov/apod/ap020220.html
http://antwrp.gsfc.nasa.gov/apod/ap971104.html

The reason for the low abundance of unusual blue straggler stars in M13 remains unknown.

Astronomers have searched for black holes within globular clusters since the 1970s. The resolution requirements for this task, however, are exacting, and it is only with the Hubble space telescope that the first confirmed discoveries have been made. In independent programs, a 4,000 solar mass intermediate-mass black hole has been suggested to exist based on HST observations in the globular cluster M15 and a 20,000 solar mass black hole in the Mayall II cluster in the Andromeda Galaxy. Both x-ray and radio emissions from Mayall II appear to be consistent with an intermediate-mass black hole.

http://antwrp.gsfc.nasa.gov/apod/ap981017.html

http://antwrp.gsfc.nasa.gov/apod/ap980117.html
http://antwrp.gsfc.nasa.gov/apod/ap011210.html
http://antwrp.gsfc.nasa.gov/apod/ap010920.html

These are of particular interest because they are the first black holes discovered that were intermediate in mass between the conventional stellar-mass black hole and the supermassive black holes discovered at the cores of galaxies. The mass of these intermediate mass black holes is proportional to the mass of the clusters, following a pattern previously discovered between supermassive black holes and their surrounding galaxies.

Claims of intermediate mass black holes have been met with some skepticism. The densest objects in globular clusters are expected to migrate to the cluster center due to mass segregation. These will be white dwarfs and neutron stars in an old stellar population like a globular cluster. As pointed out in two papers by Holger Baumgardt and collaborators, the mass-to-light ratio should rise sharply towards the center of the cluster, even without a black hole, in both M15 and Mayall II.>>

[nstahl]

Art, thanks for the extensive reply. Perhaps then things aren't quite as close as I thought, but still over billions of years with things coming at each other from all directions it seems to me solar systems would have been severely disrupted.

[Beyond]

nstahl; perhaps there are no solar systems??

[neufer]

Art, thanks for the extensive reply. Perhaps then things aren't quite as close as I thought, but still over billions of years with things coming at each other from all directions it seems to me solar systems would have been severely disrupted.

But stars stripped of their planets may also be more likely to adopt planets stripped from other stars.

Ergo: planetary solar systems in globular clusters may have adopted planets with cometary like orbits.

Comet 96P/Machholz or 96P/Machholz 1 is a short-period comet discovered on May 12, 1986 by amateur astronomer Donald Machholz in Loma Prieta, California. Machholz 1 is unusual among comets in several respects. Its highly eccentric 5.2 year orbit has the smallest perihelion distance known among regular short-period comets, bringing it considerably closer to the Sun than the orbit of Mercury. It is also the only known short period comet with both high orbital inclination and high eccentricity.

http://antwrp.gsfc.nasa.gov/apod/ap020111.html

Most short-period comets are thought to originate in the Kuiper belt, but this radically modified orbit implies a different and possibly extrasolar origin. Machholz 1 was also recently found to be both carbon-depleted and cyanogen-depleted, a chemical composition nearly unique among comets with known compositions. The only comet previously seen with similar depletion both in carbon-chain molecules and cyanogens is Yanaka (1988r), but it has a substantially different orbit. A leading hypothesis for the difference is that Machholz 1 comes from outside the Solar System and was captured by the Sun.>>

Is Halley's comet an alien interloper?
New Scientist 10 May 2010 by David Shiga

<<OUR sun may have stolen the vast majority of its comets from other stars. The theft could explain the puzzling profusion of objects in a huge reservoir surrounding the sun called the Oort cloud.

The Oort cloud is a collection of comets thought to orbit the sun in a roughly spherical halo about 50,000 times as far from the sun as Earth - at the outer edge of the solar system. How did the comets get there? In the standard picture, they formed much closer to the sun, then migrated outward in a two-stage process.

First, the gravity of the giant planets flung them into elongated orbits to form a population called the scattered disc. Objects in the scattered disc come about as close to the sun as Neptune, but venture dozens of times further out, to more than 1000 times the Earth-sun distance. That far from the sun, the gravitational pull of the galaxy becomes significant, so many of the scattered-disc objects get pulled out to populate the Oort cloud.

There is a problem with this picture, however. Simulations have long predicted that this process could only populate the Oort cloud with 10 times as many comets as are currently in the scattered disc, while estimates based on observed comets suggest the ratio is more like 700 to 1.

"This nice, beautiful picture we have been developing for the last 25 years or so just crashes and burns," Hal Levison of the Southwest Research Institute in Boulder, Colorado, said at a meeting of the American Astronomical Society's Division on Dynamical Astronomy in Boston last week.
This nice picture we have been developing of how the Oort cloud formed just crashes and burns

Levison and his colleagues say many of the Oort-cloud objects may have been stolen from other stars born in the same stellar nursery as the sun. Most stars like the sun form in clusters of between 10 and 1000 members. According to the team's simulations, encounters between stars in this crowded environment tend to disturb their scattered discs and detach objects from them, creating a reservoir of free-floating comets.

When stars later leave the cluster, some of these objects move along with them, getting captured into wide, Oort cloud-like orbits. "They head off in the same direction together and eventually become bound," says Levison. That could explain the high number of Oort-cloud objects in our solar system. If most of the cloud's members were captured from other stars, then famous comets like Halley and Hale-Bopp, whose trajectories suggest they once resided in the Oort cloud, probably were too, Levison says.

Brian Marsden of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, who was not involved in the study, says it is too soon to tell whether there really is an overabundance of Oort-cloud objects, since observations are not good enough to provide very precise estimates of the population there. But if the overabundance persists with better observations, the capture scenario could explain it, he says. "It's a very interesting idea and it might work.">>

[nstahl]

Thanks again Art. There's a heck of a Sci Fi story there in the right hands.

[ta152h0]

I am totally in awe, just thinking what this would look like if it was possible for a humble human in the middle of this looking up from a mountain location ( eternal daylight )

[neufer]

[list] Great green globs of greasy, grimy gopher guts
Mutilated monkey feet
Chopped up baby parakeet
Great green globs of greasy, grimy gopher guts
And me without my spoon [/list]

[ta152h0]

reality sucks

[Beyond]

I don't know about reality, but this realm does!!

[DavidLeodis]

Marvellous image. I have trouble seeing more than just a few stars from my very light polluted location!

I have a query. The explanationn implies that M13 was discovered in 1716 but when I have been looking up further information about M13 the discovery year was always given as 1714. Is 1716 a typographical error or is that the correct year? I will appreciate any help.

[neufer]

I have a query. The explanation implies that M13 was discovered in 1716 but when I have been looking up further information about M13 the discovery year was always given as 1714. Is 1716 a typographical error or is that the correct year? I will appreciate any help.

Edmond Halley; Phil. Trans. XXIX, 390-392 (1716)
I. An Account of several Nebulae or lucid Spots like Clouds, lately discovered among the Fixt Stars by help of the Telescope.

<<In our last [contribution] we gave short Account of the several New-Stars that have appeared in the Heavens, within the last 150 Years, some of which afford very surprising Phaenomena. But not less wonderful are certain luminous Spots or Patches, which discover themselves only by the Telescope, and appear to the naked Eye like small Fixt Stars; but in reality are nothing else but Light coming from an extraordinary great Space in the Ether; through which a lucid Medium is diffused, that shines with its own proper Lustre. This seems fully to reconsile that Difficulty which some have moved against the Description Moses gives of the Creation, alledging that Light could not be created without the Sun. But in the following Instances the contrary is manifest; some of these bright Spots discover no sign of a Star in the middle of them; and the irregular Form of those that have, shews them not to proceed from the Illumination of a Central Body. These are, as the aforesaid New Stars, Six in Number, all which we will describe in the order of time, as they were discovered; giving their Places in the Sphere of Fixt Stars, to enable the Curious, who are furnished with good Telescopes, to take the Satisfaction of contemplating them.

• ...[M13] The Sixth and last was accidentally hit upon by M. Edm. Halley in the Constellation of Hercules, in the Year 1714. It is nearly in a Right Line with Zeta and Eta of Bayer, somewhat nearer to Zeta than to Eta: and by comparing its Situation among the Stars, its Place is sufficiently near in [Scorpio] 26 deg 1/2 with 57 deg 00. North. Lat. This is but a little Patch, but it shews it self to the naked Eye, when the Sky is serene and the Moon absent.

There are undoubtedly more of these which have not yet come to our Knowledge, and some perhaps bigger but though all these Spots are in Appearance but little, and most of them but a few Minutes in Diameter; yet since they are among the Fixt Stars, that is, since they have no Annual Parallax, they cannot fail to occupy Spaces immensely great, and perhaps not less than our whole Solar System. In all these so vast Spaces it should seem that there is perpetual uninterrupted Day, which may furnish Matter of Speculation, as well to the curious Naturalist as to the Astronomer.>>

[DavidLeodis]

Thanks for your very prompt reply neufer. It seems that 1714 is the correct discovery date, not the 1716 implied in the explanation.

I like the style of the text in the report. The "But not less wonderful are certain luminous Spots or Patches, which discover themselves only by the Telescope, and appear to the naked Eye like small Fixt Stars; but in reality are nothing else but Light coming from an extraordinary great Space in the Ether; through which a lucid Medium is diffused, that shines with its own proper Lustre" is particularly wonderful.

[epitalon]

Hi,

as a geologist, I am used to detect the trace of a fault in the landscape : discontinuity caused by the fault appears in the relief, vegetation, ...
A fault usually follows a straight line.

It seems to me that I can see such a straight line of discontinuities accross the top part of M13 globular cluster :
from a point at 9 o clock at left of the picture to 2 o clock at right.

Can anybody confirm that ? Is this discontinuity caused by patch of photographs ? Or is it natural ?

[neufer]

Hi,

as a geologist, I am used to detect the trace of a fault in the landscape : discontinuity caused by the fault appears in the relief, vegetation, ...
A fault usually follows a straight line.

It seems to me that I can see such a straight line of discontinuities accross the top part of M13 globular cluster :
from a point at 9 o clock at left of the picture to 2 o clock at right.

Can anybody confirm that ? Is this discontinuity caused by patch of photographs ? Or is it natural ?

Hi epitalon,

Welcome to The Asterisk.

I think that no one has responded thus far because no one quite knows what to say.

Perhaps you could use your geologist's eye and tell us if you see this discontinuity in other images of M13. If you do then it is probably not an artifact. However, it could still simply be a random linear feature in what is basically a spherically symmetric cluster.

There is the possibility that a collision between two stars in the cluster has produced a spectacular linear jet but other than that I really have no ideas.

[epitalon]

Thanks, Art, for your quick reponse.

I am able to see the same characteristic in some other images of M13, not all.
I marked the images with pointers to the discontinuity that I see.
I don't want to pollute this forum with images. If you want to see them, just ask.

It is probably a simple alignment of stars. I t could be that these stars are aligned because they move around in a synchronised fashion ?

[Chris Peterson]

I am able to see the same characteristic in some other images of M13, not all.
I marked the images with pointers to the discontinuity that I see.
I don't want to pollute this forum with images. If you want to see them, just ask.

By all means, "pollute" away. Your question depends on what you see in an image, and providing a marked up example is the best way to get some opinions expressed.

It is probably a simple alignment of stars. I t could be that these stars are aligned because they move around in a synchronised fashion ?

I agree that any alignment you are seeing is likely a matter of chance. But the stars will not be moving in any kind of synchronized way. Stars in a globular cluster are in orbits of random inclination and radius, and are constantly being perturbed. You can essentially consider the orbit of any one star randomized with respect to any other star.