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| Yousuf Khan... |
 Posted: Tue Nov 03, 2009 8:08 am |
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The article is about the "Cosmic Web" structure, which is pretty
interesting by itself. But what I found more interesting was that they
seemed to have used the parallax between two different telescopes to
distinguish 3D data from groups of galaxies 7 billion light-years away!
Last I read about parallax, it was only sensitive enough for measuring
the nearby stars within our own galaxy out to maybe 70 light-years, let
alone 7 billion! The influx of computer technology is just making
impossible things possible now. We see it in the discovery of
exoplanets, and now out into the cosmological realm too.
Yousuf Khan
The Cosmic 'Skeleton' Revealed - Matter is not distributed uniformly -
Softpedia
"According to the team, the previously unknown assembly of galaxies that
made the target of the new research is located almost seven billion
light-years away from the Earth. Because of the spatial disposition of
the two telescopes, the images that were obtained – when combined – were
three-dimensional. This was owed to the fact that they were taken from
two different perspectives, and then superimposed. The accomplishment
allowed the astronomers to identify several groups of galaxies around
the main cluster, something that had not been noticed before. "
http://news.softpedia.com/news/The-Cosmic-Skeleton-Revealed-125972.shtml |
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| Dan Birchall... |
| Posted: Wed Nov 04, 2009 7:07 pm |
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bbbl67 at (no spam) spammenot.yahoo.com (Yousuf Khan) wrote:
[quote]The article is about the "Cosmic Web" structure, which is pretty
interesting by itself. But what I found more interesting was that they
seemed to have used the parallax between two different telescopes to
distinguish 3D data from groups of galaxies 7 billion light-years away!
Last I read about parallax, it was only sensitive enough for measuring
the nearby stars within our own galaxy out to maybe 70 light-years, let
alone 7 billion! The influx of computer technology is just making
impossible things possible now. We see it in the discovery of
exoplanets, and now out into the cosmological realm too.
[/quote]
Nice! I hadn't noticed that in the article previously. I imagine the
"3D effect" was very slight, but enough for computers to pick it out.
-Dan
--
djb at (no spam) | Dan Birchall, Night Operation Assistant, Subaru Telescope/NAOJ.
naoj | Views I express are my own, certainly not those of my employer.
..org | Oh wicked, bad, naughty, _evil_ Dan! He is a _naughty_ person. |
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| YKhan... |
| Posted: Wed Nov 04, 2009 7:53 pm |
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On Nov 4, 7:07 pm, Dan Birchall <d... at (no spam) naoj.org.REMOVE_TO_REPLY> wrote:
[quote]Nice! I hadn't noticed that in the article previously. I imagine the
"3D effect" was very slight, but enough for computers to pick it out.
[/quote]
In the past, I think they even needed the parallax effect of the Earth
as it traveled from one side of its orbit around the Sun to the other
side, just to pick out star parallaxes. Here they're simply using the
diameter of the Earth to pick out parallaxes half way across the
Universe!
Yousuf Khan |
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| Steve Willner... |
| Posted: Thu Nov 05, 2009 8:26 am |
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On Nov 3, 8:08 am, Yousuf Khan <bbb... at (no spam) spammenot.yahoo.com> wrote:
[quote]But what I found more interesting was that they
seemed to have used the parallax between two different telescopes to
distinguish 3D data from groups of galaxies 7 billion light-years away!
[/quote]
The news article makes it sound like that, but it seems to be wrong.
The paper appears to be the one by Tanaka et al. (2009 A&A 505, L9),
and distances come from redshift, as usual. I've quoted the abstract
below.
As far as I've seen, direct trigonometric parallaxes via radio VLBI
are now possible within the Local Group of galaxies (given suitable
maser sources to look at) but not beyond. Direct physical distance
measures are possible in special cases such as NGC 4258 out to
somewhat larger distances.
Once again, everyone: please don't take news articles and press
releases seriously. If at all possible, look for the actual research
paper or astro-ph preprint.
Tanaka et al. abstract:
We report on the spectroscopic confirmation of a huge cosmic structure
around the CL0016 cluster at z=0.55. We made wide-field imaging
observations of the surrounding regions of the cluster and identified
more than 30 concentrations of red galaxies near the cluster redshift.
The follow-up spectroscopic observations of the most prominent part of
the structure confirmed 14 systems close to the cluster redshift,
roughly half of which have a probability of being bound to the cluster
dynamically. We also made an X-ray follow-up, which detected extended
X-ray emissions from 70% of the systems in the X-ray surveyed region.
The observed structure is among the richest ever observed in the
distant Universe. They will be an ideal site for quantifying
environmental variations in the galaxy properties and effects of large-
scale structure on galaxy evolution. |
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| YKhan... |
| Posted: Thu Nov 05, 2009 12:51 pm |
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On Nov 5, 1:26 pm, Steve Willner <will... at (no spam) cfa.harvard.edu> wrote:
[quote]The news article makes it sound like that, but it seems to be wrong.
The paper appears to be the one by Tanaka et al. (2009 A&A 505, L9),
and distances come from redshift, as usual. I've quoted the abstract
below.
[/quote]
Oh, that's too bad, but it would've been really cool if it were true.
Maybe once we're dead, they might be able to take computerized
parallax measurements out to the edge of the visible Universe, using
just the parallax spacing of two eyes in an average human. :-)
[quote]As far as I've seen, direct trigonometric parallaxes via radio VLBI
are now possible within the Local Group of galaxies (given suitable
maser sources to look at) but not beyond. Direct physical distance
measures are possible in special cases such as NGC 4258 out to
somewhat larger distances.
Once again, everyone: please don't take news articles and press
releases seriously. If at all possible, look for the actual research
paper or astro-ph preprint.
[/quote]
What do you mean by "direct physical distance measures" to NGC 4258?
Does that mean you can measure its distance without parallax? If so,
how?
Yousuf Khan |
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| Steve Willner... |
| Posted: Fri Nov 06, 2009 11:49 am |
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In article <d5ce01e2-13d4-4acb-8fec-f044da5ff867 at (no spam) m35g2000vbi.googlegroups.com>,
YKhan <yjkhan at (no spam) gmail.com> writes:
[quote]What do you mean by "direct physical distance measures" to NGC 4258?
Does that mean you can measure its distance without parallax?
[/quote]
Yes, without trigonometric parallax. The method is basically the
same as used for binary stars that are both visual and spectroscopic
binaries. The imaging information gives you the orbit size in
angular units, and the spectroscopy gives you the orbit size in
meters, and combining them gives you the distance. You also get
stellar masses, which makes these binaries especially important for
calibrating stellar models.
For NGC 4258, the "secondary stars" are H2O masers orbiting the
central black hole. VLBI gives angular positions, and spectroscopy
gives velocites, and there you are. The most recent paper I found
(Humphreys et al. 2008, ApJ 672, 800) is on the road to distance
accuracy of 3% but isn't there quite yet because some of the fine
details of the orbits still need to be modeled.
I think there are around half a dozen galaxies for which this method
can be applied. So it's no good for large statistical samples, but
it's great for calibrating other distance measures (or will be, when
the required suite of measurements is in hand).
--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123 swillner at (no spam) cfa.harvard.edu
Cambridge, MA 02138 USA |
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