APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

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APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by APOD Robot » Sat Aug 24, 2019 4:07 am

Image Millions of Stars in Omega Centauri

Explanation: Globular star cluster Omega Centauri, also known as NGC 5139, is some 15,000 light-years away. The cluster is packed with about 10 million stars much older than the Sun within a volume about 150 light-years in diameter. It's the largest and brightest of 200 or so known globular clusters that roam the halo of our Milky Way galaxy. Though most star clusters consist of stars with the same age and composition, the enigmatic Omega Cen exhibits the presence of different stellar populations with a spread of ages and chemical abundances. In fact, Omega Cen may be the remnant core of a small galaxy merging with the Milky Way.

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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by MarkBour » Sat Aug 24, 2019 5:18 am

Looks like one APOD has used before. Which is fine, it's so beautiful.
Anyone want to wager on whether there's a black hole in the middle of it?
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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by OB1Kubota » Sat Aug 24, 2019 5:27 am

What is the relative moment of the stars within a globular cluster? And referring to the question from Mark Bour, if there were a black hole what would it's movement be if any and how would it be affecting the stars around it? Would the mass of a star position it a certain way within the cluster? Is the comment "that roam the halo of our Milky Way galaxy mean they move independently of the rotation of the Milky Way?

Circpro

Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by Circpro » Sat Aug 24, 2019 6:05 am

This image was just shot in July in Chile. It’s not a repeat.

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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by Ann » Sat Aug 24, 2019 6:32 am

MarkBour wrote:
Sat Aug 24, 2019 5:18 am
Looks like one APOD has used before. Which is fine, it's so beautiful.
Anyone want to wager on whether there's a black hole in the middle of it?
My guess, for what it's worth, is that there just may be a small black hole somewhere inside it, with a mass of perhaps ten solar masses.

But I've always thought that Omega Centauri looks "fluffy". The stars don't seem to get more densely packed towards the center.

It has been said that Omega Centauri may be the remnant of the core of a dwarf galaxy that has been absorbed by the Milky Way. If that is the case, then Omega Centauri doesn't necessarily contain an (at least intermediate-mass) central black hole, because dwarf galaxies don't always do that. Other globulars may be the remnants of tremendous bursts of star formation which gave birth to huge numbers of massive stars in close proximity, and such massive and dense clusters may more easily form black holes. Or at least that seems more reasonable to my amateur mind.

Wikipedia wrote that a 2008 study suggested that Omega Centauri does contain a central intermediate-mass black hole, but:
However, more recent work has challenged these conclusions, in particular disputing the proposed location of the cluster center.[26] [27] Calculations using a revised location for the center found that the velocity of core stars does not vary with distance, as would be expected if an intermediate-mass black hole were present. The same studies also found that starlight does not increase toward the center but instead remains relatively constant. The authors noted that their results do not entirely rule out the black hole proposed by Noyola and colleagues, but they do not confirm it, and they limit its maximum mass to 1.2 x 104 solar masses.
To me, centrally concentrated globular 47 Tucanae looks like a more promising intermediate black hole candidate. However, according to Wikipedia, no solid evidence for such a black hole in 47 Tuc has been found.
Wikipedia wrote:

It is not yet clear whether 47 Tucanae hosts a central black hole. Hubble Space Telescope data constrain the mass of any possible black hole at the cluster's center to be less than approximately 1,500 solar masses.[8] However, in February, 2017, astronomers announced that a black hole of some 2,200 solar masses may be located in the cluster; the researchers detected the black hole's signature from the motions and distributions of pulsars in the cluster.[10] However, a recent analysis of an updated and more extensive timing data set on these pulsars provides no solid evidence in favor of the existence of a black hole.
Fluffy globular Omega Centauri.
NASA, ESA and the Hubble Heritage Team
Centrally concentrated globular 47 Tucanae.
Photo: Don Goldman.
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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by orin stepanek » Sat Aug 24, 2019 12:30 pm

This cluster looks to be a hodgepodge of white; gold; & blue stars, so I agree with the statement about the age differential in it's population! I don't know it has many planets there; but if there are; Space travel would probably be highly probable! :D :wink:
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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by Leon1949Green » Sat Aug 24, 2019 1:03 pm

Would it be now possible with data from Gaia to identify which stars were originally part of this cluster/mini-galaxy?

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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by giorgiomacellari@gmail.com » Sat Aug 24, 2019 1:41 pm

10 million stars in Omega Centauri spanning 150 light-years means about 1 star like our sun every 1.500.000 kilometers. Is this correct? If so, any civilized people possibly living on a planet around one sun should easily reach many planets around another one. Is this true? Thank a lot, giorgio macellari, Piacenza, Italy

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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by Fred the Cat » Sat Aug 24, 2019 3:05 pm

Not only did the astrophotographer image Omega Centauri with a hole in one. He also makes them. :wink:
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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by BobinBend » Sat Aug 24, 2019 3:33 pm

If the earth was orbiting around a star in the center of Omega Centauri similar to ours, what would the night sky look like?

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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by ralph.couey@gmail.com » Sat Aug 24, 2019 4:05 pm

I wonder what the night sky would look like on a planet inside a globular star cluster?

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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by Psnarf » Sat Aug 24, 2019 5:28 pm

giorgiomacellari@gmail.com wrote:
Sat Aug 24, 2019 1:41 pm
10 million stars in Omega Centauri spanning 150 light-years means about 1 star like our sun every 1.500.000 kilometers.
Lessee, now where'd I put my slide rule?...

F = GMm/r^2

Units
m^3/kg-s^2 X kg^2/m^2 = kg-m/s^2 == N

Slide Rule
(1.99x10^30)^2 x 6.67x10^-11 = 2.69x10^50
(1.5X10^9)^2 = 2.25X10^18
2.69x10^50 / 2.25X10^18 = 1.17x10^32

Sew! the force between each star is approximately 1.17x10^32 N. Is that sufficient to hold the cluster together? Are they moving toward each other? Is each orbiting the galaxy independently? If a small black hole is in the center, are the stars swirling around it, eventually falling into it?

Czerno O

Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by Czerno O » Sat Aug 24, 2019 6:58 pm

giorgiomacellari@gmail.com wrote:
Sat Aug 24, 2019 1:41 pm
10 million stars in Omega Centauri spanning 150 light-years means about 1 star like our sun every 1.500.000 kilometers. Is this correct?
Sorry, Giorgio, I don' think you got the math correct. The cluster is a three-dimentional volume, see? The linear distance between a star and its nearest neighbors , in other word the diameter of an individual star's niche or its lebensraum is in inverse proportion to the cubic root of the total number of stars, N=10 million, cubic root (N) ~ = 215,
hence the distance between stars must be on the order of 150 / 215 = 0.55 l.y.

zendae1

Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by zendae1 » Sat Aug 24, 2019 7:00 pm

giorgiomacellari@gmail.com wrote:
Sat Aug 24, 2019 1:41 pm
10 million stars in Omega Centauri spanning 150 light-years means about 1 star like our sun every 1.500.000 kilometers. Is this correct? If so, any civilized people possibly living on a planet around one sun should easily reach many planets around another one. Is this true? Thank a lot, giorgio macellari, Piacenza, Italy
I am not even an amateur, but as no one else has replied directly to your distance question, perhaps my incorrect answer will inspire a good reply!
We are talking about some 450 trillion miles in all directions of the starry sphere from the center. As such, I think your guesstimate is too dense. If it was a 2D plane that the 10 million stars were squeezed into, the nearest stars would be about the same distance as the Sun is to us now, and there is far more area in a sphere where all points go out 450 trillion miles. Well, let the corrections begin! lol.....

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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by Ann » Sat Aug 24, 2019 7:33 pm

BobinBend wrote:
Sat Aug 24, 2019 3:33 pm
If the earth was orbiting around a star in the center of Omega Centauri similar to ours, what would the night sky look like?
A view from inside a globular cluster (47 Tuc?)
Illustration: Jeremy Webb and William E. Harris.
Jeremy Webb wrote:
For the July 2014 issue of Astronomy Magazine, Professor William E. Harris and I were asked to submit an article describing what life would be like if Earth was orbiting a star that lived within a globular cluster. For the article, we took dynamical simulations of globular clusters and placed our theoretical planet at various locations within the model. Not only were we able to determine what life would be like for astronomers on such a planet, but we used our simulations to generate images of what the night sky would look like for anyone living inside a globular cluster.
More recently, with the help of UITS Research Technologies at Indiana University, we developed a 3D visualization of what the nighy sky would look like if you lived on such a planet.
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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by neufer » Sat Aug 24, 2019 7:43 pm

ralph.couey@gmail.com wrote:
Sat Aug 24, 2019 4:05 pm

I wonder what the night sky would look like on a planet inside a globular star cluster?
There would be dozens of Venus, Jupiter, Mars & Saturn bright stars in the sky
such that the total sky brightness would approximate that of a full moon.
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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by sillyworm 2 » Sat Aug 24, 2019 9:35 pm

I am puzzled as to why,if a globular cluster might be a dwarf galaxy merge remnant, the merge would not have completely absorbed the dwarf galaxy.

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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by BDanielMayfield » Sun Aug 25, 2019 3:13 am

sillyworm 2 wrote:
Sat Aug 24, 2019 9:35 pm
I am puzzled as to why,if a globular cluster might be a dwarf galaxy merge remnant, the merge would not have completely absorbed the dwarf galaxy.
These mergers take time. Wait about a billion years, give or take 500 million.
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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by BDanielMayfield » Sun Aug 25, 2019 4:36 am

Leon1949Green wrote:
Sat Aug 24, 2019 1:03 pm
Would it be now possible with data from Gaia to identify which stars were originally part of this cluster/mini-galaxy?
Yes that should be possible. But even prior to Gaia we had good indications about some stars that are thought to have been pulled out from Omega Centauri. A nearby example is this;
Kapteyn's Star is a class M1 red subdwarf about 12.76 light years from Earth in the southern constellation Pictor; it is the closest halo star to the Solar System. With a magnitude of nearly 9 it is visible through binoculars or a telescope.[2]

Its diameter is 30% of the Sun's, but its luminosity just 1.2% that of the Sun. It may have once been part of the globular cluster Omega Centauri, itself a likely dwarf galaxy swallowed up by the Milky Way in the distant past. The discovery of two planets — Kapteyn b and Kapteyn c — was announced in 2014.

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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by Ann » Sun Aug 25, 2019 6:41 am

sillyworm 2 wrote:
Sat Aug 24, 2019 9:35 pm
I am puzzled as to why,if a globular cluster might be a dwarf galaxy merge remnant, the merge would not have completely absorbed the dwarf galaxy.
M31, the Andromeda Galaxy. Photo: YURIY_KULIK/ISTOCK
M32, satllite galaxy of M31. Photo: Wikisky.

















Take a look at the picture of the Andromeda galaxy at left. Andromeda is anything but a dwarf galaxy, but the picture underscores the fact that the core of Andromeda is much more luminous than the disk, because the stars of the core and bulge of M31 are comparatively densely packed. The disk, by contrast, is so much fainter, because the stars in the disk are at much larger distances from one another.

Now take a look at the picture at right, which shows M32, the compact satellite galaxy of M31.
Wikipedia wrote:

The structure and stellar content of M32 are difficult to explain by traditional galaxy formation models. Theoretical arguments[14] and some simulations suggest a scenario in which the strong tidal field of M31 can transform a spiral galaxy or a lenticular galaxy into a compact elliptical. As a small disk galaxy falls into the central parts of M31, much of its outer layers will be stripped away. The central bulge of the small galaxy is much less affected and retains its morphology.
So maybe M32 was a normal disk galaxy before it came too close to the powerful tidal field of M31 and had its disk stripped away from it.

Maybe the dwarf galaxy whose core was the progenitor of Omega Centauri was somewhat - somewhat! - similar to M32. Maybe it had a fluffy disk, which was easily absorbed as the dwarf galaxy fell into the strong tidal field of the Milky Way. But maybe the dwarf galaxy's core was sufficiently densely packed to retain its shape and most of its stars. Maybe the now "naked" core settled into a wide orbit around the Milky Way where it is relatively "undisturbed" most of the time.

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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by Chris Peterson » Sun Aug 25, 2019 1:53 pm

Psnarf wrote:
Sat Aug 24, 2019 5:28 pm
Sew! the force between each star is approximately 1.17x10^32 N. Is that sufficient to hold the cluster together? Are they moving toward each other? Is each orbiting the galaxy independently? If a small black hole is in the center, are the stars swirling around it, eventually falling into it?
Each star is in orbit around the center of mass of the entire cluster. It's a complex gravitational environment, of course, so stars are frequently perturbed by interacting with other stars passing nearby. But all that does is shift their orbital elements. The overall orbits remain Keplerian. A central black hole, representing as it does only a small fraction of the entire mass, would have little effect on the motion of the stars, except for those quite close to it. Collisions of stars with that black hole, given its very small physical size, would be very rare.
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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by neufer » Sun Aug 25, 2019 2:58 pm

Chris Peterson wrote:
Sun Aug 25, 2019 1:53 pm

Each star is in orbit around the center of mass of the entire cluster. It's a complex gravitational environment, of course, so stars are frequently perturbed by interacting with other stars passing nearby. But all that does is shift their orbital elements. The overall orbits remain Keplerian.
Basically they are harmonic elliptical orbits centered on the center of the cluster.
Kepler's 3 laws of planetary motion:

1) The orbit of a planet is an ellipse with the Sun at one of the two foci.
The orbit of a star is an ellipse centered on the center of the cluster.
2) A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.
A line segment joining a star and the center of the cluster
sweeps out equal areas during equal intervals of time.
3) The square of the orbital period of a planet is
directly proportional to the cube of the semi-major axis of its orbit.
The square of the orbital period of all stars is the same
and is inversely proportional to the mass density of the cluster.

For Omega Centauri with a mass ~4 million Suns & a radius ~5 million AU
the orbital period for all stars ~ 6 million years.
Art Neuendorffer

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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by Psnarf » Mon Aug 26, 2019 2:10 pm

Thank you for your kind explanation to an obvious dummy, that'd be me. Of course my force figgers were merely an amusing exercise, since the interstellar distance is wrong, too far apart for much gravitational interaction. Sew! the cluster behaves like a miniature galaxy with the center of mass orbiting within the Milky Way?

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Re: APOD: Millions of Stars in Omega Centauri (2019 Aug 24)

Post by MarkBour » Mon Aug 26, 2019 4:15 pm

MarkBour wrote:
Sat Aug 24, 2019 5:18 am
Looks like one APOD has used before. Which is fine, it's so beautiful.
Anyone want to wager on whether there's a black hole in the middle of it?
Circpro wrote:
Sat Aug 24, 2019 6:05 am
This image was just shot in July in Chile. It’s not a repeat.
Thanks for the correction, Circpro. My apologies to Michael Miller and Jimmy Walker !

I was fooled by the near-identical caption on the APOD of 29 May 2014. And of course, at first glance, the images are similar, but this one has an amazing resolution, detail, and coloring. It's interesting to compare the two images. Today's has a smaller field of view than the one posted at 29 May 2014. Hopefully, in the future, I will be more careful about assuming that a matching APOD caption implies the same image.
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