APOD: M13: The Great Globular Cluster in... (2012 Jun 14)

[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 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.

<< Previous APOD

Discuss Any APOD

Next APOD >>

[/b]

[Ernest]

Does the density of the cluster make it impossible for Kepler to detect any planets orbiting the core stars? What would they look like, showered with radiation?

[Skytreker]

Does the density of the cluster make it impossible for Kepler to detect any planets orbiting the core stars? What would they look like, showered with radiation?

This reminds me of the great story by Isaac Asimov - Nightfall. A Planet with 7 suns inside a globular cluster. When night falls, there were 30 000 bright stars shining across the sky. 10 times as much as one can see under dark skies on Earth. What a glorious sight to behold!!

[Lordcat Darkstar]

Does the density of the cluster make it impossible for Kepler to detect any planets orbiting the core stars? What would they look like, showered with radiation?

I would think kepler is sensitive enough to detect planets orbiting the core stars. The problem is that current models predict that globular clusters are far to chaotic for planets to form in stable orbits around their host stars. That's why kepler isn't pointed at a globular cluster

[owlice]

I love this; it's my favorite glob!

[neufer]

This reminds me of the great story by Isaac Asimov - Nightfall. A Planet with 7 suns inside a globular cluster. When night falls, there were 30 000 bright stars shining across the sky. 10 times as much as one can see under dark skies on Earth. What a glorious sight to behold!!

. http://www.cita.utoronto.ca/~dubinski/G ... htfall.mov

<<Asimov was approached in 1953 by Twayne Press editor Fletcher Pratt with a story proposal: a scientist would create a world, and then he, Poul Anderson and Virginia Kidd would write novellas set in that world. The three novellas would then be published as a book, together with an essay by the scientist who created the scenario. This formula, which Pratt called a Twayne Triplet, had already resulted in the 1952 book The Petrified Planet.

The scenario created was that of a binary star system in the Messier 13 globular cluster with an Earthlike planet called Troas (or more informally, Junior) located at one of the system's Lagrangian points. An earlier expedition to Troas had suffered some mysterious disaster, and a second expedition was being mounted to determine if the planet was suitable for colonization, and to find out what happened to the first expedition.

Asimov finished his story, and Anderson finished a story called "Question and Answer", but Kidd never completed the third story, and the proposed book never saw print. Asimov, anticipating just such an eventuality, confirmed that he held first serial rights on the story, and sold Sucker Bait to Astounding (where it appeared a few months before "Question and Answer").

The story concerns the starship George G. Grundy, or Triple G., which has been chartered by the Confederacy of Worlds to investigate Junior. The only nonscientist among the Triple G.'s passengers is 20-year-old Mark Annuncio of the Mnemonic Service, who has been trained from the age of five to memorize and correlate vast amounts of information.

Over a century earlier, an attempt to colonize Junior had failed; after nearly two years on the planet, all 1,337 colonists had died for reasons unknown. The Triple G.'s scientists and Annuncio have to find out what killed them. For the first two weeks after landing, everyone remains aboard while the scientists take readings. After Rodriguez, the expedition's microbiologist, declares the local life forms noninfectious, a handful of scientists, plus Annuncio, travel to the original colony site.

Relations between the scientists and Annuncio deteriorate rapidly. Mnemonics are loners by nature, and their training makes them even more so. The scientists, on the other hand, as specialists, tend to be contemptuous of a professional generalist like Annuncio. When Annuncio asks Rodriguez to explain how he came to a conclusion, the microbiologist regards the request as an affront to his professional reputation, and refuses to answer. The other scientists manage to offend Annuncio in various ways.

When Annuncio finally realizes that the abnormally high concentration of beryllium in Junior's crust was what killed the colonists, and that they all have to leave immediately, he does not trust the scientists to deal with it. He returns to the ship and persuades the crew to mutiny and take the ship off the planet. The captain is barely able to convince the crew to stop at the colony site to pick up the scientists. When Annuncio is put on trial for fomenting the mutiny, he explains his actions, is acquitted, and the ship returns to Earth to seek treatment.>>

[BillLee]

What would the night sky look like on a planet around a sun within a cluster like that? Would there even BE a "night sky"?

[neufer]

Does the density of the cluster make it impossible for Kepler to detect any planets orbiting the core stars?

I would think kepler is sensitive enough to detect planets orbiting the core stars. The problem is that current models predict that globular clusters are far to chaotic for planets to form in stable orbits around their host stars. That's why kepler isn't pointed at a globular cluster

Even Hubble doesn't have the resolving power to clearly distinguish most core stars from one another.

A five meter mirror using 100x the magnification of Kepler might work though.

[rstevenson]

Art, what does "Sucker Bait" have to do with "Nightfall"?

Rob

[neufer]

Art, what does "Sucker Bait" have to do with "Nightfall"?

It is an Asimov story specifically about the Messier 13 globular cluster.

[rstevenson]

Art, what does "Sucker Bait" have to do with "Nightfall"?

It is an Asimov story specifically about the Messier 13 globular cluster.

Ah! Got it.

Rob

[dlw]

There's an interesting looking galaxy in the lower right corner of the image. Looks like 2 galaxies merging and there's a significant halo around it/them. Is this particular object being studied?

[Case]

There's an interesting looking galaxy in the lower right corner of the image. Looks like 2 galaxies merging and there's a significant halo around it/them. Is this particular object being studied?

"Nearby, about 40 arc minutes north-east of M13, is the faint (mag 11) galaxy NGC 6207, visible in many large- and medium-size-field photographs of M13, e.g., in the DSSM image. This galaxy has recently produced a type II supernova (SN 2004A)."

The HST did have a look at it: image 1, image 2

[Chris Peterson]

Even Hubble doesn't have the resolving power to clearly distinguish most core stars from one another.

I don't think that's true. At the core, the typical separation of the stars is around 0.9 arcsec; resolving that requires only a 150mm objective. It also requires very good seeing, or better, a space telescope. Hubble has imaged the core of M13, and easily resolves the individual stars.

Of course, this is just an optical problem. In reality, M13 is essentially empty space. Looking at just the core, in projection (as we see it), the area of empty space is about one trillion (10¹²) times greater than the area of the stars. You could zip back and forth throughout the cluster billions of times before you ever hit a star. But optically, diffraction makes the stars appear huge. If they weren't emitting light, we'd never know that M13 was there- it wouldn't block enough light from the background to be detectable, even against something like a glowing gas cloud.

[Boomer12k]

One of my favs to look at with my 10" Meade LX200 GPS....and my Deep Sky Imager 2....hope to get out soon as the weather permits. Been nice, but cloudy. Right now, it is clear, and hopefully night is the night!!!!

One thing I have done is hook up my DSI to my laptop, and use the VGA output to my Epson 705 HD projector, and have objects projected to a 72" screen....awesome!!!!! But there can't be any WIND!!!!! Blows over the screen.

That is Jupiter the size of my CAR DOOR!!!

PEOPLE STOPPED AND WERE AWESTRUCK!!!

Screen and Z...

Screen, laptop and Z...

Star map on garage...door is open on right, and you can see roof line and roses on the left side....

:---[===] *

[owlice]

Field trip to Boomer's house! Who's with me?

[orin stepanek]

Globular clusters just don't do it for me! I mean they're interesting; but I like open clusters better! Like the Sisters; also galaxies; nebulae; comets and planets.

[Mactavish]

Even Hubble doesn't have the resolving power to clearly distinguish most core stars from one another.

I don't think that's true. At the core, the typical separation of the stars is around 0.9 arcsec; resolving that requires only a 150mm objective. It also requires very good seeing, or better, a space telescope. Hubble has imaged the core of M13, and easily resolves the individual stars.

Of course, this is just an optical problem. In reality, M13 is essentially empty space. Looking at just the core, in projection (as we see it), the area of empty space is about one trillion (10¹²) times greater than the area of the stars. You could zip back and forth throughout the cluster billions of times before you ever hit a star. But optically, diffraction makes the stars appear huge. If they weren't emitting light, we'd never know that M13 was there- it wouldn't block enough light from the background to be detectable, even against something like a glowing gas cloud.

I wonder. . . Perhaps it could be globular clusters of dead stars emitting no light that might be the evasive “dark matter” that can’t be seen.

[Chris Peterson]

I wonder. . . Perhaps it could be globular clusters of dead stars emitting no light that might be the evasive “dark matter” that can’t be seen.

The stars would have to be just the right size... much smaller than the Sun, and they'd not have time to stop buring; much larger and they'd have exploded. Any sort of stellar remnant besides a black hole would still be glowing in infrared, and an entire globular cluster of IR emitters would show up to our instruments.

For the most part, ordinary matter has been eliminated as a dark matter candidate because in nearly any form people can come up with, it would glow in the IR- something we don't see.

[henrystar]

How I miss Arthur C. Clarke and Isaac Asimov! Those were the days, my friend, we thought they'd never end, those were the days!

[saturno2]

M 13 is a Globular Cluster very compact.
As the center of an atom

[geckzilla]

Even Hubble doesn't have the resolving power to clearly distinguish most core stars from one another.

I don't think that's true. At the core, the typical separation of the stars is around 0.9 arcsec; resolving that requires only a 150mm objective. It also requires very good seeing, or better, a space telescope. Hubble has imaged the core of M13, and easily resolves the individual stars.

And if you take a look at the FITS data, they are even easier to distinguish without the processing which was done for aesthetically pleasing contrast.

[Ann]

Martin Pugh's image is a very fine one. Do compare it, however, with the ESA/HEIC Hubble Picture of the Week | 2012 Jun 11, showing the Compact Blue Dwarf galaxy UGC 5497. The galaxy and the globular look extremely similar, but thanks to Martin Pugh's excellent color data we can tell that the object in his image is a globular. The brightest stars in his picture are red giants, and the very brightest and most orange of them are so called Asymptotic Giant Branch stars, which have just reached their greatest luminosity before expelling their outer atmospheres and turning into white dwarfs. There is a large number of obviously blue stars, which are fainter than the red giants but brighter than an even larger population of neutral-colored stars. The blue stars are blue horizontal branch stars, which represents an intermediate stage between "normal" red giants and Asymptotic Branch Giants in metal-poor stellar populations. The neutral-colored stars are hydrogen-fusing dwarfs at about the same temperature as the Sun.

The color information of the UGC 5497 image is poor, however, since the picture was produced from exposures through only two filters, an optical or clear one centered at 606 nm, and an infrared one centered at 814 one.

http://www.spacetelescope.org/static/ar ... w1224a.jpg wrote:

The object is a compact blue dwarf galaxy that is infused with newly formed clusters of stars. The bright, blue stars that arise in these clusters help to give the galaxy an overall bluish appearance that lasts for several million years until these fast-burning stars explode as supernovae.

If you look at a better-resolved version of the ESA/HEIC image of UGC 5497, you can see that there really appears to be a brightish population of marginally orange stars in this dwarf galaxy as well as a number of faint blue stars. Personally I can't spot any bright blue stars at all in this object, however, and no clusters, either. I can see a few small, faint, extended, neutral-colored objects in or or next to UGC 5497 which may be emission nebulae, since they ought to be redder in color if they were background galaxies. Actually, though, I'm not sure they aren't galaxies.

We can clearly see how unfavorable the use of one clear optical filter and one infrared filter is, if you want to extract color information from a nearby, relatively dust-free object.

For another comparison, take a look at this ESA/HEIC picture of globular cluster M53. This image, too, is made from exposures through the clear filter at 606 nm and the infrared one at 814 nm. You can see how hard it is to extract good color information from this image. There really are a number of bright orange objects in M53, but nothing in this picture looks more orange than anything in the Hubble picture of UGC 5497. If anything, the most orange stars in UGC 5497 look more orange than anything in M53, while the blue stars in M53 look every bit as blue the blue population of UGC 5497, even though the latter object is certainly bluer overall. Not that you can tell.

Thank you so much, Martin Pugh, for producing pictures with such great color information!

(By the way, don't miss Martin's picture of the heart of M13, showing a greenish star at about 2 o'clock!)

Ann

[neufer]

Even Hubble doesn't have the resolving power to clearly distinguish most core stars from one another.

I don't think that's true. At the core, the typical separation of the stars is around 0.9 arcsec; resolving that requires only a 150mm objective. It also requires very good seeing, or better, a space telescope. Hubble has imaged the core of M13, and easily resolves the individual stars.

And if you take a look at the FITS data, they are even easier to distinguish without the processing which was done for aesthetically pleasing contrast.

[color=#0000FF]The Crowded Heart of the Hercules Cluster in Hubble[/color]

---

With it's pixel size resolution of 0.13 arcsec Hubble is probably capable of transit monitoring a few tens of thousands of M13 central core stars for planets.

However, I doubt that it could do a very adequate "Keplerian" job for over 145,000 central core stars.

You can observe many apparently isolated stars but not the more numerous fainter ones that are hidden behind the overexposed Airy disks of their brighter neighbors.

Kepler's only instrument is a photometer that continually monitors the brightness of over 145,000 main sequence stars in a fixed field of view.

[Chris Peterson]

With it's pixel size resolution of 0.13 arcsec Hubble is probably capable of transit monitoring a few tens of thousands of M13 central core stars for planets.

However, I doubt that it could do a very adequate "Keplerian" job for over 145,000 central core stars.

You can observe many apparently isolated stars but not the more numerous fainter ones that are hidden behind the overexposed Airy disks of their brighter neighbors.

But they aren't. Do the math. I assumed the core is about 50 ly across, and contains 250,000 stars. Change the numbers a bit if you want, but I think these are pretty close. Flatten this to a 2D projection. The odds of two stars having significantly overlapping Airy disks (assuming an optical resolution better than 1 arcsec) is low. Almost all the stars are resolvable, even to a small telescope.