APOD: Omega Centauri: The Brightest Star... (2016 Apr 27)

Comments and questions about the APOD on the main view screen.
BillT
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Re: APOD: Omega Centauri: The Brightest Star... (2016 Apr 27)

Post by BillT » Thu Apr 28, 2016 3:31 am

Rob v. wrote:
That's really interesting to know. Going forward I will need to look a little more critically at the distances published in Astronomy related articles. It would be nice if quoted distances were accompanied in brackets by some form of abbreviation which would define either the measurement technique used, the estimated accuracy (±xxxx units) or statistical probability indicating the estimated measurement error. I appreciate your patience.

Regards, Rob v.
Things will improve a lot when the Gaia mission is completed and all the data reduced.

https://en.wikipedia.org/wiki/Gaia_%28spacecraft%29

The observation part of the mission is a couple of months away from halfway point (2.5 years) and they are planning to release a preliminary catalogue towards the end of this year. At the end of the mission they will have collected about 200 tb of data. The full results are expected around 2020.

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Re: APOD: Omega Centauri: The Brightest Star... (2016 Apr 27)

Post by Chris Peterson » Thu Apr 28, 2016 4:33 am

BillT wrote:
Rob v. wrote: That's really interesting to know. Going forward I will need to look a little more critically at the distances published in Astronomy related articles. It would be nice if quoted distances were accompanied in brackets by some form of abbreviation which would define either the measurement technique used, the estimated accuracy (±xxxx units) or statistical probability indicating the estimated measurement error. I appreciate your patience.
Things will improve a lot when the Gaia mission is completed and all the data reduced.
Yes, but only for a very limited range- stars in our region of the Milky Way. Gaia won't improve our distance estimates for Omega Centauri (where its ~5% error will be similar to the present error with other methods).
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Re: APOD: Omega Centauri: The Brightest Star... (2016 Apr 27)

Post by alter-ego » Thu Apr 28, 2016 4:43 am

Chris Peterson wrote:
BillT wrote:
Rob v. wrote: That's really interesting to know. Going forward I will need to look a little more critically at the distances published in Astronomy related articles. It would be nice if quoted distances were accompanied in brackets by some form of abbreviation which would define either the measurement technique used, the estimated accuracy (±xxxx units) or statistical probability indicating the estimated measurement error. I appreciate your patience.
Things will improve a lot when the Gaia mission is completed and all the data reduced.
Yes, but only for a very limited range- stars in our region of the Milky Way. Gaia won't improve our distance estimates for Omega Centauri (where its ~5% error will be similar to the present error with other methods).
Yes, and ironically, it won't measure Deneb either. Stars brighter that 5th to 6th magnitude will saturate the sensors so they are not candidate targets.

Edit: There is disagreement amongst the literature. This description may be the most accurate for the brightness range of stars for astrometry:
Gaia Science Performance wrote: ... G - in the range 3-20 mag - denotes the broad-band, white-light, Gaia magnitude (see below). All stars brighter than G = 3 mag will be observed with a special mode. Depending on how well this mode can be calibrated, end-of-mission parallax standard errors at the level of a few dozen μas could potentially be achieved for these stars. This remains the topic of further work.
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Re: APOD: Omega Centauri: The Brightest Star... (2016 Apr 27)

Post by BillT » Thu Apr 28, 2016 9:36 am

The Gaia data will also improve many of the other methods. For example, they will get accurate parallax measurements of a considerable number of Cepheid variables allowing improved calibration of that method.

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Re: APOD: Omega Centauri: The Brightest Star... (2016 Apr 27)

Post by Ann » Thu Apr 28, 2016 10:06 am

I look forward to the resolution of the Pleiades controversy!

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Re: APOD: Omega Centauri: The Brightest Star... (2016 Apr 27)

Post by neufer » Thu Apr 28, 2016 7:35 pm

geckzilla wrote:
RocketRon wrote:
Do they spin, or otherwise rotate ?
The stars of a globular cluster are said to be in chaotic orbits around the gravitational center. The motion has been likened to bees circling a beehive.
I've often wondered why globular clusters have so little overall rotation.

I wonder if a quasar jet condenses into a string of blobs of matter that form into globular clusters.
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Re: APOD: Omega Centauri: The Brightest Star... (2016 Apr 27)

Post by geckzilla » Thu Apr 28, 2016 8:08 pm

I would guess that the little overall rotation might have something to do with their age, sort of like how spiral galaxies are thought to evolve into elliptical galaxies. Maybe they used to be flat, but they're not anymore.
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Re: APOD: Omega Centauri: The Brightest Star... (2016 Apr 27)

Post by neufer » Thu Apr 28, 2016 8:38 pm

geckzilla wrote:
I would guess that the little overall rotation might have something to do with their age, sort of like how spiral galaxies are thought to evolve into elliptical galaxies. Maybe they used to be flat, but they're not anymore.
I didn't think that spiral galaxies were thought to evolve into elliptical galaxies (or vice versa).
https://en.wikipedia.org/wiki/Elliptical_galaxy wrote:
<<Originally Edwin Hubble hypothesized that elliptical galaxies evolved into spiral galaxies, which was later discovered to be false. Stars found inside of elliptical galaxies are much older than stars found in spiral galaxies. Most elliptical galaxies are composed of older, low-mass stars, with a sparse interstellar medium and minimal star formation activity, and they tend to be surrounded by large numbers of globular clusters.>>
I'm thinking that quasar jets evolve into non-rotating globular clusters...
which then cluster into elliptical galaxies or the cores of future spiral galaxies.
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Re: APOD: Omega Centauri: The Brightest Star... (2016 Apr 27)

Post by Chris Peterson » Thu Apr 28, 2016 8:42 pm

neufer wrote:I didn't think that spiral galaxies were thought to evolve into elliptical galaxies (or vice versa).
I think that's the dominant theory on the origin of most ellipticals. Most galaxies form as spirals, and subsequent collisions and interactions turn those into ellipticals.
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Re: APOD: Omega Centauri: The Brightest Star... (2016 Apr 27)

Post by neufer » Fri Apr 29, 2016 2:40 am

Chris Peterson wrote:
neufer wrote:
I didn't think that spiral galaxies were thought to evolve into elliptical galaxies (or vice versa).
I think that's the dominant theory on the origin of most ellipticals. Most galaxies form as spirals, and subsequent collisions and interactions turn those into ellipticals.
Reference :?:
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Re: APOD: Omega Centauri: The Brightest Star... (2016 Apr 27)

Post by geckzilla » Fri Apr 29, 2016 2:56 am

You know, I don't have any particular reference for that one. I think I was watching some cosmology lectures when I first learned about that. Since I like Brian Koberlein I'm just gonna reference him.
https://briankoberlein.com/2014/04/25/h ... ning-fork/
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Re: APOD: Omega Centauri: The Brightest Star... (2016 Apr 27)

Post by neufer » Fri Apr 29, 2016 12:53 pm

geckzilla wrote:
You know, I don't have any particular reference for that one. I think I was watching some cosmology lectures when I first learned about that. Since I like Brian Koberlein I'm just gonna reference him.
https://briankoberlein.com/2014/04/25/hubbles-tuning-fork wrote:
It is now thought that elliptical galaxies are the result of mergers between galaxies.
"It is now thought that elliptical galaxies are the result of mergers between" what kinds of galaxies :?:
  • Dwarf, irregular, spiral ... all kinds :?:
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Re: APOD: Omega Centauri: The Brightest Star... (2016 Apr 27)

Post by Chris Peterson » Fri Apr 29, 2016 2:15 pm

neufer wrote:"It is now thought that elliptical galaxies are the result of mergers between" what kinds of galaxies :?:
  • Dwarf, irregular, spiral ... all kinds :?:
All kinds. Ellipticals are the endpoint of loss of organization. Most galaxies have a high degree of organization when they formed, but are randomized by subsequent collisions and interactions.
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Re: APOD: Omega Centauri: The Brightest Star... (2016 Apr 27)

Post by neufer » Fri Apr 29, 2016 2:54 pm

Chris Peterson wrote:
neufer wrote:
"It is now thought that elliptical galaxies are the result of mergers between" what kinds of galaxies :?:
  • Dwarf, irregular, spiral ... all kinds :?:
All kinds. Ellipticals are the endpoint of loss of organization. Most galaxies have a high degree of organization when they formed, but are randomized by subsequent collisions and interactions.
Well, that might explain why elliptical galaxies have so little overall rotation
but not necessarily why they have so many globular clusters ...
nor why globular clusters themselves have so little overall rotation.
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Re: APOD: Omega Centauri: The Brightest Star... (2016 Apr 27)

Post by Chris Peterson » Fri Apr 29, 2016 3:04 pm

neufer wrote:
Chris Peterson wrote:
neufer wrote:
"It is now thought that elliptical galaxies are the result of mergers between" what kinds of galaxies :?:
  • Dwarf, irregular, spiral ... all kinds :?:
All kinds. Ellipticals are the endpoint of loss of organization. Most galaxies have a high degree of organization when they formed, but are randomized by subsequent collisions and interactions.
Well, that might explain why elliptical galaxies have so little overall rotation
but not necessarily why they have so many globular clusters ...
nor why globular clusters themselves have so little overall rotation.
Indeed. Theories about galaxy formation and evolution are not yet well developed. There's a great deal of uncertainty about many factors.
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