M55 (globular) & star clusters (APOD 02 Apr 2008)

[Anthraquinone]

Does anyone know of a link to a site that has any information or prefably an image of what the night sky woubd look like if you inhabited a planet in the centre of one of these clusters.

AQ

[Indigo_Sunrise]

Maybe you could try:
http://www.shatters.net/celestia/

[neufer]

Does anyone know of a link to a site that has any information or prefably an image of what the night sky would look like if you inhabited a planet in the centre of one of these clusters.

http://www.utahskies.org/image_library/ ... uriHSt.jpg
http://terpsichore.stsci.edu/~summers/v ... z/spz.html
http://www.physorg.com/news75043316.html

[neufer]

http://antwrp.gsfc.nasa.gov/apod/ap000922.html
http://antwrp.gsfc.nasa.gov/apod/ap010223.html
http://antwrp.gsfc.nasa.gov/apod/image/ ... ka_big.jpg

• <<This color "picture" of globular star cluster M55 may not look like any star cluster you've ever seen. Still, it shows a most fundamental view for students of stellar astronomy. In the picture, a Color Magnitude Diagram (CMD), M55's individual stars are represented as dots whose color indicates relative temperature, red (cool) to blue (hot). Position in the CMD does not correspond to a star's location in the sky, though. Instead, it corresponds to a measured astronomical color, (B-V color) read off the bottom scale, and a brightness in magnitudes (M) on the left hand scale. The temperature for each star can also be found by reading the equivalent scale at the top, where the Sun would have a temperature of 6,000 kelvins (K). Brightness relative to the Sun's luminosity (Sun = 1) is given on the scale at the right. The globular cluster stars clearly fall into distinct groups dramatically visible in this CMD. The broad swath extending diagonally from the lower right is the cluster's main sequence. A sharp turn toward the upper right hand corner follows the red giant branch while the blue giants are found grouped in the upper left. M55's stars were formed at the same time and at first were all located along the main sequence by mass, lower mass stars at the lower right. Over time, higher mass stars have evolved off the main sequence into red, then blue giants and beyond. The exact position of the sharp turn-off from the main sequence to the red giant branch measures the cluster's age.>>

[bystander]

http://www.shatters.net/celestia/

http://terpsichore.stsci.edu/~summers/v ... z/spz.html

Nice Links Thanx

[ChrisO]

There is an interesting red object at approx. 2o'clock just outside of the "denser" area of the cluster. Is this perhaps a background galaxy, maybe seen side-on?

Thanks!
-Chris O

"Do astronauts ever bump their heads on Dark Matter during space walks?" Probably not wise to talk off your space helmet in space...

[coldbeer]

So how close are stars in the center of a cluster like this?

Is there any reason why stars in a cluster could not have planets around them?

I wonder what it would be like to look up into the sky if you on a planet inside a cluster? Would the stars look bigger? Would the night sky ever be dark?

[Case]

Isaac Asimov wrote a short story about that, "Nightfall", first published in Astounding Science Fiction, September 1941.

There, an astronomer on a planet with multiple suns where it is always day learns through his N-body calculations that all of the suns will soon set for the first time in thousands of years. The last time this happened civilization collapsed because of the mass insanity that followed when night fell. As the last sun sets and mass hysteria ensues, the astronomer looks up into the sky and perceives the fantastic view of a sky filled with tens of thousands of stars for he lives on a planet at the heart of a globular cluster!

"Through it shone the Stars! Not Earth's feeble thirty-six hundred Stars visible to the eye; Lagash was in the center of a giant cluster. Thirty thousand might suns shone down in a soul-searing splendor that was more frighteningly cold in its awful indifference than the bitter wind that shivered across the cold horribly bleak world."

[Phil G]

I wonder if dense star clusters, such as M55, might be the remnants of a [probably much smaller] galaxy that the Milky Way absorbed [correct terminology?] many millions of years ago.

[jcbaty]

Phil G, since the stars that make up M55 are much older than the stars around it, it must have come from an extra-Milky Way source.

One thing I've always wondered is how the stars in these dense clusters keep from combining and creating one gigantic star, since they are so close to each other. It seems like over time, their gravity would draw them crashing together.

[neufer]

One thing I've always wondered is how the stars in these dense clusters keep from combining and creating one gigantic star, since they are so close to each other. It seems like over time, their gravity would draw them crashing together.

Globular cluster
http://en.wikipedia.org/wiki/Globular_cluster
-----------------------------------------------
<<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.

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.

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>>
-----------------------------------------------
<<The results of N-body simulations have shown that the stars can follow unusual paths through the cluster, often forming loops and often falling more directly toward the core than would a single star orbiting a central mass. In addition, due to interactions with other stars that result in an increase in velocity, some of the stars gain sufficient energy to escape the cluster. Over long periods of time this will result in a dissipation of the cluster, a process termed evaporation. The typical time scale for the evaporation of a globular cluster is 10^10 years.

Binary stars form a significant portion of the total population of stellar systems, with up to half of all stars occurring in binary systems. Numerical simulations of globular clusters have demonstrated that binaries can hinder and even reverse the process of core collapse in globular clusters. When a star in a cluster has a gravitational encounter with a binary system, a possible result is that the binary becomes more tightly bound and kinetic energy is added to the solitary star. When the massive stars in the cluster are sped up by this process, it reduces the contraction at the core and limits core collapse>>
-----------------------------------------------

[jcbaty]

Thanks neufer

[Boner]

Do stars exist outside of galaxies? I've often wondered if stars are something that can exist in space outside of a galaxy, or do they have to be part of a galaxy?

[akwaugh]

An "outside looking in" sort of question here!

Regarding M55 and how "busy" it seems from the APOD picture.

Are we fortunate that our solar system is on the edge of our local galaxy?

Does this give us an advantage in terms of seeing much of the known universe without the clutter that would be present in, say, M55, or from deeper within a galaxy? Or is it just a matter of having the necessary technical ability to separate the wood from the trees?

[Nereid]

Do stars exist outside of galaxies? I've often wondered if stars are something that can exist in space outside of a galaxy, or do they have to be part of a galaxy?

Yes they do; there are many such that have been observed, both in the space between galaxies in our Local Group and in nearby clusters such as Virgo.

I think there are even some older APODs on just this topic; maybe another reader can give us some links?

[Arramon]

Stars do get ejected from galaxies I've read... I don't think they can 'form' outside of a galaxy though. The ingredients for star-life are found within the hotbeds of nurseries for infant stars to grow like in Orion nebula.

Links links links?

[BMAONE23]

Do stars exist outside of galaxies? I've often wondered if stars are something that can exist in space outside of a galaxy, or do they have to be part of a galaxy?

Yes they do; there are many such that have been observed, both in the space between galaxies in our Local Group and in nearby clusters such as Virgo.

I think there are even some older APODs on just this topic; maybe another reader can give us some links?

Here is the quick search results
http://antwrp.gsfc.nasa.gov/cgi-bin/apo ... CTIC+STARS

[neufer]

Do stars exist outside of galaxies? I've often wondered if stars are something that can exist in space outside of a galaxy, or do they have to be part of a galaxy?

Yes they do; there are many such that have been observed, both in the space between galaxies in our Local Group and in nearby clusters such as Virgo.

I think there are even some older APODs on just this topic; maybe another reader can give us some links?

Here is the quick search results
http://antwrp.gsfc.nasa.gov/cgi-bin/apo ... CTIC+STARS

http://antwrp.gsfc.nasa.gov/apod/ap020119.html
-----------------------------------
Beckham on target as Galaxy net first win
ESPNsoccernet April 4, 2008

<<David Beckham scored his first goal of the Major League Soccer season to help the Los Angeles Galaxy to a 2-0 win over the San Jose Earthquakes. >>