APOD: Omega Centauri: The Brightest... (2013 May 01)

APOD Robot · Post by **APOD Robot** » Wed May 01, 2013 4:07 am

Omega Centauri: The Brightest Globular Cluster

Explanation: This huge ball of stars predates our Sun. Long before humankind evolved, before dinosaurs roamed, and even before our Earth existed, ancient globs of stars condensed and orbited a young Milky Way Galaxy. Of the 200 or so globular clusters that survive today, Omega Centauri is the largest, containing over ten million stars. Omega Centauri is also the brightest globular cluster, at apparent visual magnitude 3.9 it is visible to southern observers with the unaided eye. Cataloged as NGC 5139, Omega Centauri is about 18,000 light-years away and 150 light-years in diameter. Unlike many other globular clusters, the stars in Omega Centauri show several different ages and trace chemical abundances, indicating that the globular star cluster has a complex history over its 12 billion year age.

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owlice · Post by **owlice** » Wed May 01, 2013 4:33 am

Ah, what a lovely image! I love globular clusters, and hope to see this one with mine own eyes someday.

Kalulu · Post by **Kalulu** » Wed May 01, 2013 4:39 am

Amazing cluster - what would the sky look like from the centre of the cluster? How bright would it be?

starsurfer · Post by **starsurfer** » Wed May 01, 2013 6:44 am

This is actually quite a mysterious object, there is a possibility it might be the remains of a dwarf galaxy that was canibalized by the Milky Way in the past. Also I believe it contains a black hole at its centre!!

ta152h0 · Post by **ta152h0** » Wed May 01, 2013 8:32 am

maybe I will get flamed for this, boiled to a crisp but I don't believe there bis a " black hole " within this complex but quite possibly held in confinement by outside gravitational forces pushing this thing in from all sides equally....Ok, start the fireworks

Boomer12k · Post by **Boomer12k** » Wed May 01, 2013 9:33 am

ta152h0 wrote:maybe I will get flamed for this, boiled to a crisp but I don't believe there bis a " black hole " within this complex but quite possibly held in confinement by outside gravitational forces pushing this thing in from all sides equally....Ok, start the fireworks

Wolf...you seem to have an odd impression of Gravity....Gravity SUCKS...it does not "PUSH"....In fact...gravity does not "PULL" either....Say What???? Gravity is different than most people think. Gravity is not an attracting force. Gravity is not an Electro-magnetic field. Gravity is not an emanating radiation. Or ray, like light. It is not a particle...
(Well, then Boomer...just what the HELLO is it then????)
It is a SLIDE....Things....FALL....the truth is...and Galileo would point this out too...that all the objects around you...regardless of their mass....fall at the SAME RATE...that means that gravity cannot be magnetism...or electro-magnetic...as a more massive object would "PULL" the other object a little more than a lesser massive object...but this is not the case...
So...all the objects in your surrounding, EVEN THOUGH STOPPED BY THE FLOOR, are in fact still IN FREE-FALL...like weightlessness....but are STOPPED BY THE FLOOR...causing pressure that we measure with a scale as weight....it is the pressure of the FALL being stopped, that is measured.
So...STARS FALL AROUND EACH OTHER....The are not PUSHED...or PULLED.....regardless of their MASSES.... They FALL through the WARPED SPACETIME that is a creation of their mass's...EFFECT...on Spacetime....the PROOF of this ON THE EARTH IS.....TIME.....Time runs slower on the Earth, than up in Space....because SPACE is STRETCHED, LIKE A SLIDE....to the Earth, by ITS MASS....like a cannon ball on a trampoline. Thus showing that SPACE ITSELF IS drawn into the Earth, because as Einstein showed...space and time are ONE.....so, if one is warped...ergo...the other is warped...we fall in the warp....
You are not Pulled to the Earth...you Fall in the Warped Spacetime of the Earth...THUS....the Stars in the Cluster...FALL in the warped spacetime around all of them.
A black hole, there may or may not be, at the heart of the globular cluster....Ten million stars, tightly bound gravitationally, may not need a black hole to hold them, there maybe that much warp of the space around them. It can be only around 100 light years in diameter for some Globulars.

Not to FLAME you...to help you understand....because it took ME SIX MONTHS TO GET MY HEAD AROUND THE FACT THAT MASS DOES NOT ATTRACT MASS, AND THERE IS A VERY GOOD REASON THAT IS SO.....go lean on the WALL....

:---[===] *

neufer · Post by **neufer** » Wed May 01, 2013 10:03 am

Click to play embedded YouTube video.

casus · Post by **casus** » Wed May 01, 2013 12:38 pm

Art:
but for all intents and purposes, mass DOES attract mass - the result is the same, semantics aside.
But i have a different problem: i just can't fathom that 10 million stars in a 150 light year space haven't collapsed together after 12 billion years due to gravity. It's a weak force, for sure, but it aint that weak, especially with no significant spin or "cetrifugal" force from rotation. Wouldnt the earth accelerate to the sun if it had no orbital velocity? of course, indeed technically we're falling to the sun constantly, just happens to be at the same rate we're also flying out tangentially into space. But clusters don't seem to have an orbital axis.
i agree with you- they don't need a black hole! indeed they probably can't have dark matter either. something has to lack, mass has to be as little a 'visibly' possible, and i still can't grasp how it has stayed 'fluffy' for 12 billion years. would love to see some physicists figures on it.

Chris Peterson · Post by **Chris Peterson** » Wed May 01, 2013 12:53 pm

casus wrote:But i have a different problem: i just can't fathom that 10 million stars in a 150 light year space haven't collapsed together after 12 billion years due to gravity. It's a weak force, for sure, but it aint that weak, especially with no significant spin or "cetrifugal" force from rotation. Wouldnt the earth accelerate to the sun if it had no orbital velocity? of course, indeed technically we're falling to the sun constantly, just happens to be at the same rate we're also flying out tangentially into space. But clusters don't seem to have an orbital axis.

Clusters don't have an overall orbital axis. But each star in a cluster is in orbit around the cluster's center of gravity. That's why clusters don't collapse. In fact, it's just the opposite: clusters eventually fall apart, losing their stars to intergalactic space. That happens because the complex, multiple body orbits inside a cluster are fundamentally chaotic, and as stars perturb each other in their orbits, they transfer orbital angular momentum. This results in stars occasionally being knocked into hyperbolic orbits, meaning their velocities exceed the cluster escape velocity. Over billions of years, globular clusters evaporate.

neufer · Post by **neufer** » Wed May 01, 2013 1:41 pm

Chris Peterson wrote:
casus wrote:
i just can't fathom that 10 million stars in a 150 light year space haven't collapsed together after 12 billion years due to gravity. It's a weak force, for sure, but it aint that weak, especially with no significant spin or "cetrifugal" force from rotation. Wouldnt the earth accelerate to the sun if it had no orbital velocity? of course, indeed technically we're falling to the sun constantly, just happens to be at the same rate we're also flying out tangentially into space. But clusters don't seem to have an orbital axis.
Clusters don't have an overall orbital axis. But each star in a cluster is in orbit around the cluster's center of gravity. That's why clusters don't collapse. In fact, it's just the opposite: clusters eventually fall apart, losing their stars to intergalactic space. That happens because the complex, multiple body orbits inside a cluster are fundamentally chaotic, and as stars perturb each other in their orbits, they transfer orbital angular momentum. This results in stars occasionally being knocked into hyperbolic orbits, meaning their velocities exceed the cluster escape velocity. Over billions of years, globular clusters evaporate.

Conservation of Energy

http://en.wikipedia.org/wiki/Virial_theorem wrote:
<<In mechanics, the virial theorem provides a general equation that relates the average over time of the total kinetic energy,, of a stable system consisting of N particles, bound by potential forces, with that of the total potential energy, , where angle brackets represent the average over time of the enclosed quantity. If the force between any two particles of the system results from a potential energy V(r) = αrⁿ that is proportional to some power n of the inter-particle distance r, the virial theorem takes the simple form: . Thus, twice the average total kinetic energy equals n times the average total potential energy . Whereas V(r) represents the potential energy between two particles, VTOT represents the total potential energy of the system, i.e., the sum of the potential energy V(r) over all pairs of particles in the system. A common example of such a system is globular star cluster, where n equals −1 (i.e., the total kinetic energy of a globular star cluster amounts to only half the negative total potential energy.>>

http://en.wikipedia.org/wiki/Globular_cluster#Mass_segregation.2C_luminosity_and_core_collapse wrote:
[b][color=#0000FF][size=150]A[n evolved] core-collapsed globular: M15[/size][/color][/b]
<<In measuring the luminosity curve of a given globular cluster as a function of distance from the core, most clusters in the Milky Way increase steadily in luminosity as this distance decreases, up to a certain distance from the core, then the luminosity levels off. Typically this distance is about 1–2 parsecs from the core. However about 20% of the globular clusters have [already] undergone a process termed "core collapse". In this type of cluster, the luminosity continues to increase steadily all the way to the core region. An example of a core-collapsed globular is M15.

Core-collapse is thought to occur when the more massive stars in a globular cluster encounter their less massive companions. Over time, dynamic processes cause individual stars to migrate from the center of the cluster to the outside. This results in a net loss of kinetic energy from the core region, leading the remaining stars grouped in the core region to occupy a more compact volume. When this gravothermal instability occurs, the central region of the cluster becomes densely crowded with stars and the surface brightness of the cluster forms a power-law cusp. (Note that a core collapse is not the only mechanism that can cause such a luminosity distribution; a massive black hole at the core can also result in a luminosity cusp.) Over a lengthy period of time this leads to a concentration of massive stars near the core, a phenomenon called mass segregation.

The dynamical heating effect of binary star systems works to prevent an initial core collapse of the cluster. When a star passes near a binary system, the orbit of the latter pair tends to contract, releasing energy. Only after the primordial supply of binaries are exhausted due to interactions can a deeper core collapse proceed. In contrast, the effect of tidal shocks as a globular cluster repeatedly passes through the plane of a spiral galaxy tends to significantly accelerate core collapse.

The different stages of core-collapse may be divided into three phases. During a globular cluster's adolescence, the process of core-collapse begins with stars near the core. However, the interactions between binary star systems prevents further collapse as the cluster approaches middle age. Finally, the central binaries are either disrupted or ejected, resulting in a tighter concentration at the core. The interaction of stars in the collapsed core region causes tight binary systems to form. As other stars interact with these tight binaries, they increase the energy at the core, which causes the cluster to re-expand. As the mean time for a core collapse is typically less than the age of the galaxy, many of a galaxy's globular clusters may have passed through a core collapse stage, then re-expanded.

The Hubble Space Telescope has been used to provide convincing observational evidence of this stellar mass-sorting process in globular clusters. Heavier stars slow down and crowd at the cluster's core, while lighter stars pick up speed and tend to spend more time at the cluster's periphery. The globular star cluster 47 Tucanae, which is made up of about 1 million stars, is one of the densest globular clusters in the Southern Hemisphere. This cluster was subjected to an intensive photographic survey, which allowed astronomers to track the motion of its stars. Precise velocities were obtained for nearly 15,000 stars in this cluster.

A 2008 study by John Fregeau of 13 globular clusters in the Milky Way shows that three of them have an unusually large number of X-ray sources, or X-ray binaries, suggesting the clusters are middle-aged. Previously, these globular clusters had been classified as being in old age because they had very tight concentrations of stars in their centers, another test of age used by astronomers. The implication is that most globular clusters, including the other ten studied by Fregeau, are not in middle age as previously thought, but are actually in 'adolescence'.>>

Ron-Astro Pharmacist · Post by **Ron-Astro Pharmacist** » Wed May 01, 2013 3:21 pm

In that Vera Rubin and many others have measured that most stars in spiral galaxies orbit at roughly the same speed relative from the distance to their centers, have others quantified this effect relative to clusters? Art just mentioned that lighter stars tend to speed around the periphery of clusters.

Just curious in regard to an earlier statement that clusters may not be influenced or contain what’s identified as “dark matter.” Ron

Chris Peterson · Post by **Chris Peterson** » Wed May 01, 2013 3:35 pm

Ron-Astro Pharmacist wrote:In that Vera Rubin and many others have measured that most stars in spiral galaxies orbit at roughly the same speed relative from the distance to their centers, have others quantified this effect relative to clusters? Art just mentioned that lighter stars tend to speed around the periphery of clusters.

Just curious in regard to an earlier statement that clusters may not be influenced or contain what’s identified as “dark matter.” Ron

Numerical simulations show that globular clusters work fine without requiring dark matter. Observational evidence leans towards globular clusters lacking their own dark matter halos, although they clearly exist within the dark matter halos of their parent galaxies. Put slightly differently, the stars inside globulars seem to follow classically Newtonian orbital mechanics.

Ron-Astro Pharmacist · Post by **Ron-Astro Pharmacist** » Wed May 01, 2013 4:53 pm

Interesting. Makes one wonder if that is related to the relative flatness of a spiral galaxy and the speroidal shape of a cluster? Of course aren't clusters mostly found in the halo of our galaxy? Wow too many questions to expect to be answered.

Thanks Chris!!

vonhaase189 · Post by **vonhaase189** » Wed May 01, 2013 5:33 pm

I often wounder what the sky would look like if you were on a planet orbiting a star in a globular cluster, or if there any planets in a globular cluster.

emc · Post by **emc** » Wed May 01, 2013 5:55 pm

Maybe we should look for signs of intelligent life… i.e., are there too many cars causing globular warming…?

Chris Peterson · Post by **Chris Peterson** » Wed May 01, 2013 5:56 pm

vonhaase189 wrote:I often wounder what the sky would look like if you were on a planet orbiting a star in a globular cluster, or if there any planets in a globular cluster.

It would depend a lot on where you were in the cluster. They actually have a very strong density gradient, with the central star density several orders of magnitude greater than the edge. Certainly, if you were central, there could be hundreds of stars as bright as Venus appears to us (or even brighter), so you'd never have any real darkness.

Planets around stars in globulars are probably uncommon, because the many near passes between individual stars would be disruptive to planetary systems.

Boomer12k · Post by **Boomer12k** » Wed May 01, 2013 6:48 pm

Chris Peterson wrote:
casus wrote:But i have a different problem: i just can't fathom that 10 million stars in a 150 light year space haven't collapsed together after 12 billion years due to gravity. It's a weak force, for sure, but it aint that weak, especially with no significant spin or "cetrifugal" force from rotation. Wouldnt the earth accelerate to the sun if it had no orbital velocity? of course, indeed technically we're falling to the sun constantly, just happens to be at the same rate we're also flying out tangentially into space. But clusters don't seem to have an orbital axis.
Clusters don't have an overall orbital axis. But each star in a cluster is in orbit around the cluster's center of gravity. That's why clusters don't collapse. In fact, it's just the opposite: clusters eventually fall apart, losing their stars to intergalactic space. That happens because the complex, multiple body orbits inside a cluster are fundamentally chaotic, and as stars perturb each other in their orbits, they transfer orbital angular momentum. This results in stars occasionally being knocked into hyperbolic orbits, meaning their velocities exceed the cluster escape velocity. Over billions of years, globular clusters evaporate.

Kind of like the Earth and the Moon...the Earth used to rotate faster...the Moon used to be closer. The Earth imparted its rotational speed into momentum for the Moon, and the Earth slowed, and the Moon sped up, and moved farther away. It is moving away at around 1 inch per year. In the far flung future, we will have longer days, and Solar Eclipses will be "less Moon, more Sun".

I guess Globulars do the same...it is a transfer of the orbital energies.

This MAY, also explain the source of "dark energy"...it could be that as the matter in the Universe contracts, and condenses into lesser, closer quarters, the Energy is being transferred to the Space around it...thus fueling expansion, much as lesser mass stars are given momentum and move to the edge of Globulars. This would be a Universal effect, as the Universe looks very much like a gigantic globular cluster. A ball of Galactic Clusters and Super Clusters...with a few stragglers, and voids spread between.

:---[===] *

ta152h0 · Post by **ta152h0** » Wed May 01, 2013 8:04 pm

Thumbs up to APOD ! Toasting an ice cold one for you all !!!!!

kopernik · Post by **kopernik** » Wed May 01, 2013 8:16 pm

Chris Peterson wrote:
casus wrote:But i have a different problem: i just can't fathom that 10 million stars in a 150 light year space haven't collapsed together after 12 billion years due to gravity. It's a weak force, for sure, but it aint that weak, especially with no significant spin or "cetrifugal" force from rotation. Wouldnt the earth accelerate to the sun if it had no orbital velocity? of course, indeed technically we're falling to the sun constantly, just happens to be at the same rate we're also flying out tangentially into space. But clusters don't seem to have an orbital axis.
Clusters don't have an overall orbital axis. But each star in a cluster is in orbit around the cluster's center of gravity. That's why clusters don't collapse. In fact, it's just the opposite: clusters eventually fall apart, losing their stars to intergalactic space. That happens because the complex, multiple body orbits inside a cluster are fundamentally chaotic, and as stars perturb each other in their orbits, they transfer orbital angular momentum. This results in stars occasionally being knocked into hyperbolic orbits, meaning their velocities exceed the cluster escape velocity. Over billions of years, globular clusters evaporate.

At least two forces keep Omega Centauri from collapsing toward the center -
multiple sources of stellar radiation;
outflow (winds) of dark energy.

Chris Peterson · Post by **Chris Peterson** » Wed May 01, 2013 8:20 pm

kopernik wrote:At least two forces keep Omega Centauri from collapsing toward the center -
multiple sources of stellar radiation;
outflow (winds) of dark energy.

Stellar radiation is not a significant force, and dark energy doesn't operate at all over such a small region of space.

Globular clusters don't collapse for the same reason that the Solar System doesn't collapse. Nothing more is required than simple Newtonian mechanics.

Anthony Barreiro · Post by **Anthony Barreiro** » Wed May 01, 2013 11:16 pm

Chris Peterson wrote:
kopernik wrote:At least two forces keep Omega Centauri from collapsing toward the center -
multiple sources of stellar radiation;
outflow (winds) of dark energy.
Stellar radiation is not a significant force, and dark energy doesn't operate at all over such a small region of space.

Globular clusters don't collapse for the same reason that the Solar System doesn't collapse. Nothing more is required than simple Newtonian mechanics.

Don't forget the hamsters.

Beyond · Post by **Beyond** » Wed May 01, 2013 11:37 pm

Squeek Power

Yeah

It's the little things that keep the big things going.

kopernik · Post by **kopernik** » Thu May 02, 2013 4:51 pm

[This is completely unacceptable to conventional scientists -]

owlice · Post by **owlice** » Thu May 02, 2013 4:57 pm

kopernik wrote:[This is completely unacceptable to conventional scientists -]

Then you shouldn't have posted it; I've removed it. Please read and follow the rules.

Starship Asterisk*