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Fraser
2005-Aug-11, 05:35 PM
SUMMARY: Galaxies are actually much larger than they appear in most telescopes. Astronomers working with the Gemini Observatory in Hawaii have found stars associated with galaxy NGC 300 at twice the previously estimated radius. These old, dim stars would have blazed brilliantly billions of years ago, but now it takes a powerful telescope to be able to see them. And if NGC 300 is probably twice as large as previously estimate, our own Milky Way galaxy could extend as much as 200,000 light-years across.

View full article (http://www.universetoday.com/am/publish/gemini_uncovers_lost_city_of_stars.html)

What do you think about this story? Post your comments below.

galacsi
2005-Aug-11, 09:09 PM
Originally posted by fraser@Aug 11 2005, 05:35 PM
SUMMARY: Galaxies are actually much larger than they appear in most telescopes. Astronomers working with the Gemini Observatory in Hawaii have found stars associated with galaxy NGC 300 at twice the previously estimated radius. These old, dim stars would have blazed brilliantly billions of years ago, but now it takes a powerful telescope to be able to see them. And if NGC 300 is probably twice as large as previously estimate, our own Milky Way galaxy could extend as much as 200,000 light-years across.

View full article (http://www.universetoday.com/am/publish/gemini_uncovers_lost_city_of_stars.html)

What do you think about this story? Post your comments below.
Hello

i am very impressed by this kind of discovery . No fancy incomprehensible theory but fine observation of the real universe. 3 hourras for the observers.

anyway it is very important to determine what type they are these dim stars.

If they are white dwarves , one may think they are very old stars . But why young stars are not born any more in this régions ?

But if they are population II stars it a great discovery because these stars are suppose to inhabit galaxy core and globular clusters.

If they are red dwarves , how they have been born ,?

It make me think , if there is some truth in the electric sun theory may there are low powered stars far away from the high tension wires !


Thanks to Harrap's compact dictionnaire , but all mistakes are mine . . .

TBaker
2005-Aug-11, 09:11 PM
When we say galaxies are twice as large as previously thought, do we mean they are more massive, or just of greater spatial extent? If the former, does this account for some of the mssing matter?

Guest
2005-Aug-11, 09:32 PM
Suggests the universe is much older than the 15 billion years or so, often given as consequence of Big Bang theory which (theory) in my view is wrong.

mcpayne
2005-Aug-12, 01:53 AM
It'd be interesting to observe these stars for a while to find their orbital motion, it could tell us a lot about the dark matter surrounding this galaxy.

Also, do you think that its possible that, rather than these stars forming in their current orbit 10 billion years ago, they actually formed further in and were later slingshot out by the galaxy's core black hole?

Cheers
Martin

Greg
2005-Aug-12, 03:30 AM
This galaxy is indeed quite interesting. I would think that faint stars such as these would not be so faint in the outskirts of our galaxy from our vantage point, considering for a moment that something like this is common to all galaxies. To explain this, I would not look towards extremes like the electric universe theory. Recall that this galaxy is a member of the Sculptor cluster. Most galaxies withing clusters have had close encounters with other galaxies at some point. These close encounters commonly strip gas away from galaxies while leaving stars in place. I suspect that early on in this gaalxy's history (10 billion years ago) it ran through a larger galaxy or group of galaxies, an encounter that stripped its outer half of gas by which new stars could be formed.

cran
2005-Aug-12, 06:48 AM
All good questions so far...and I'm sure the answers will soon follow...? :unsure:

suitti
2005-Aug-12, 05:30 PM
Its time to put a new notice on your Newtonian telescope:
Objects in Mirror are Larger Than They Appear


Suggests the universe is much older than the 15 billion years or so
How do you figure that? All it says to me is that, like an atmosphere, there's no hard edge. NASA says 100 km makes you an astronaut. So that's where the atmosphere ends, right? Then why does the ISS need periodic boosting, even though it orbits at something like 400 km? What a drag. My atmosphere expert talks about Earth's atmosphere up to 1100 km. In some ways, Voyager I is just about to, or has just left the Sun's atmosphere. The outer parts of atmospheres can do a good imitation of hard vacuum.

Stars are really bright, but even nearby galaxies are really, really far away. The brightest stars are some 10,000 times brighter than the Sun. The dimmest stars are some 10,000 times dimmer than the Sun. So, you may be able to see individual Cepheid variables out that far, but red dwarfs like Proxima Centuri will not show up. It does not surprise me that it takes a telescope with a primary mirror the size of a house to image the outskirts of nearby galaxies. Stars aren't much like the Windows Starfield screensaver, after all.


When we say galaxies are twice as large as previously thought, do we mean they are more massive, or just of greater spatial extent?
Mostly just more volume.

If the former, does this account for some of the missing matter?
Certainly not. The mass of a galaxy has to do with its rotation rate and size. One does not need to see more than a few bright stars to determine these things. The Dark Side of the force (dark matter) is still required to explain the observed rotation rates.

It'd be interesting to observe these stars for a while to find their orbital motion, it could tell us a lot about the dark matter surrounding this galaxy.
Yes, but for some galaxies, rotation speeds can be quickly determined with spectroscopy. Presumably, other galaxies have this kind of structure too. VLBI radio can detect proper motion over the course of a few years. This is new. We're talking detection of 10 microarcseconds of movement. A picture of, M31 - Andromeda taken just after launch (or when corrective optics was installed) with the Hubble Space Telescope is not different from one taken at the end of its life. Even using the Fine Guidance Sensors for 20 hours, and achieving 200 microarcseconds. It wouldn't be good enough.

RUF
2005-Aug-12, 06:13 PM
Didn't the story relate that not all galaxies have this outer halo of stars? Though I saw that the stars in some galaxies taper off like was always thought, but some don't seem to.

I love the possibility that this in some way explains the "Dark matter" mystery. I don't remember who the astronomer was, but she found that the outer stars in a galaxy seemed to travel around the galaxy core faster than the ones closer to the core. The mass from these darker halo stars could explain that faster rotation.

I like the idea of Dark Matter being more mundane that exotic.

cran
2005-Aug-12, 09:52 PM
It was Vera Rubin... plug that name into a search engine, you'll get plenty of info... :)

cran
2005-Aug-12, 10:04 PM
Originally posted by RUF@Aug 13 2005, 02:13 AM
I love the possibility that this in some way explains the "Dark matter" mystery. I don't remember who the astronomer was, but she found that the outer stars in a galaxy seemed to travel around the galaxy core faster than the ones closer to the core. The mass from these darker halo stars could explain that faster rotation.

I like the idea of Dark Matter being more mundane that exotic.
Actually, the outer stars (in the disc) don't rotate faster than some in core (bulge), but faster than Keplerian mechanics would allow.

From the centre of the galaxy to the edge of the central bulge - rotation velocity increases with distance; beyond that, rotation velocity appears to be constant, so the formulae and calculations that apply to solar systems (like ours) simply cannot explain the dynamics in a spiral galaxy ... and because Keplerian mechanics is based on Newtonian physics (the one we tend to favour for gravitational dynamics at less than relativistic velocities) something is required to plug into the equation to explain the observations and measurements... :unsure:

wstevenbrown
2005-Aug-13, 07:15 PM
Be a little careful in your use of terms quoted from other sources:

1) There are two common types of rotation velocities in common use for disk galaxies. HI (un-ionized hydrogen atomic gas) rotation is measured at radio frequency. Stellar rotation velocities are measured in the visible range. They can be very different. By analogy, rotating a bucket of silty water immediately shows you that the water and the silt move at different speeds-- sometimes, in different directions!

2) Mass: Total mass = gas + dust + stars + dark matter + photon mass-equivalent. Very often people are only talking about one component of this mix, but people generalize from that, or select from it only what they wish to hear.

3) Redshifts use the same two common methods of measurement-- optical and radio, and they can be very different. I had my nose rubbed in this recently. One database said that a particular galaxy had a radial velocity of 400 km/sec (HI). Another database said the same galaxy was receding at 12000 km/sec.! The second one was the optical measure, which was correct. The radio signal was being swamped by the outer HI disk of a foreground galaxy-- but the point being measured was WAY outside the visible disk of the foreground galaxy-- 2.5 times as far away as the visible 'edge'.

We are deeply conditioned to only look where we expect to see something. The underlying assumption about the galactic outskirts is that if there was any matter there, it would be visible. It is. But we have to look.

Best regards-- Steve

xelasnave
2005-Aug-15, 07:52 AM
Does not a trace of hydrogen stretch from our Gallaxy to M 31? (and by implication such a situation should be found elsewhere?)
Does that mean then (along the lines expressed re depth of atmosphere) that our Gallaxy is approx 1 million light year across? (at one point).
Space seems (for me) to be "filling up" with previously undiscovered matter.
Will undiscoved matter beocme "dark matter" ever or is there more to it than that??
alex

cran
2005-Aug-20, 04:06 AM
1) as far as I know, primordial hydrogen is being found in many places between galaxies...

2) only if it can be established that the gas is gravitationally bound to our galaxy...

3) yes...

4) still has a long long long way to go to account for nearly 90% of missing matter...

:unsure: