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deSitter
Still in Old School


Reged: 12/09/04

Re: New Hubble X-treme deep field photo new [Re: deSitter]
      #5445912 - 09/28/12 09:55 PM Attachment (15 downloads)

Quote:


Oh, here's another knots-and-blue-dude object...





This object is also visible on the not-so-deep Ultra Deep Field - see pic. Thanks for linking to this, it's interesting to compare them in detail.

-drl


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brentwood
Carpal Tunnel
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Reged: 11/04/05

Loc: BC Canada
Re: New Hubble X-treme deep field photo new [Re: deSitter]
      #5446205 - 09/29/12 03:00 AM

There appears to be only two or three actual stars with diffraction spikes visible. I'm wondering how many of those very faint dots are very faint red dwarf stars in our galaxy.
Do they actually get spectra on all the objects visible to verify the red shift & therefore the distance?


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deSitter
Still in Old School


Reged: 12/09/04

Re: New Hubble X-treme deep field photo new [Re: brentwood]
      #5446229 - 09/29/12 03:50 AM

A small planet will produce short stubby spikes. So you can't be sure those are stars. They could be bright AGN.

I'm not sure how "low they can go" but I'd estimate mag 26 for direct reliable measurement of spectral lines. Photometric spectra (by inference) can go much deeper. This one is mag 30!

http://jcconwell.wordpress.com/2010/10/21/extreme-universe-the-most-distant-object-measured-in-the-universe/

-drl


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Ira
Carpal Tunnel
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Reged: 08/22/10

Loc: Mitzpe Ramon, Israel
Re: New Hubble X-treme deep field photo new [Re: deSitter]
      #5447338 - 09/29/12 07:40 PM

"These red galaxies are the remnants of dramatic collisions between galaxies and are in their declining years."
>> I thought the tidal forces unleashed in galactic collisions started bursts of new star formation.

"Peppered across the field are tiny, faint, more distant galaxies that were like the seedlings from which today's striking galaxies grew."
>>Which galaxies are these in the photo?

"The youngest galaxy found in the XDF existed just 450 million years after the universe's birth in the big bang."
>>Seems like an awfully short time for a galaxy to form.

/Ira


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deSitter
Still in Old School


Reged: 12/09/04

Re: New Hubble X-treme deep field photo new [Re: Ira]
      #5447343 - 09/29/12 07:41 PM

I don't think you can take this sort of boilerplate too seriously. It's just a mantra that gets recited. The subject of low surface brightness galaxies and selection effects is very complex.

-drl


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Ira
Carpal Tunnel
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Reged: 08/22/10

Loc: Mitzpe Ramon, Israel
Re: New Hubble X-treme deep field photo new [Re: Mister T]
      #5447349 - 09/29/12 07:45 PM

Quote:

could some one check my math. (peer review):

posted this on another forum:


FYI some quick math:

area of the night sky sphere = 41,253 square degrees

times (60 arc minutes per degree) squared = 41253 x3600=148,510,800 square arc minutes in entire sky.

divided by 4.6 arc minutes area of Hubble XDF Image x approximately 5,500 galaxies in this picture=

177,567,260,750 Galaxies potentially resolvable by HST in the visible universe!!




This is so cool, thanks. People are always asking me how many galaxies there are in the universe. And I always have to answer "Uncountably many". Now I have a real number. And if you estimate that each galaxy has on average 1,000,000,000 ( 1 billion) stars than you get

177,567,260,750,000,000,000 stars in the observable universe! (What is that number???)

/Ira


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deSitter
Still in Old School


Reged: 12/09/04

Re: New Hubble X-treme deep field photo new [Re: Ira]
      #5447528 - 09/29/12 09:13 PM

Nice! Good deal!

-drl


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Jarad
Postmaster
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Reged: 04/28/03

Loc: Atlanta, GA
Re: New Hubble X-treme deep field photo new [Re: Ira]
      #5447566 - 09/29/12 09:32 PM

Quote:

177,567,260,750,000,000,000 stars in the observable universe! (What is that number???)





I think that's 177 quintillion. (millions, billions, trillions, quadrillions, quintillions).

Or, as my daughters like to call it, a bazillion.

Jarad


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Ira
Carpal Tunnel
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Reged: 08/22/10

Loc: Mitzpe Ramon, Israel
Re: New Hubble X-treme deep field photo new [Re: Jarad]
      #5447614 - 09/29/12 10:10 PM

A bazillion sounds about right to me.

/Ira


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Ira
Carpal Tunnel
*****

Reged: 08/22/10

Loc: Mitzpe Ramon, Israel
Re: New Hubble X-treme deep field photo new [Re: Ira]
      #5447621 - 09/29/12 10:14 PM

BTW, does anyone know the size of the XTM field in colloquial terms? I seem to remember that the deep field was the size of a grain of sand held at arm's length.

/Ira


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deSitter
Still in Old School


Reged: 12/09/04

Re: New Hubble X-treme deep field photo [Re: Ira]
      #5447844 - 09/30/12 01:49 AM

It's about 3 arcminutes on a side - 180 arcseconds, 4 Jupiters. So you could fit 16 Jupiters onto the frame.

-drl


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Mister T
Pooh-Bah


Reged: 02/01/08

Loc: Upstate NY
Re: New Hubble X-treme deep field photo new [Re: deSitter]
      #5448008 - 09/30/12 07:59 AM

The 4.6 square arc minutes I use came from the Hubble site.

the Image they posted is 2.3x2.0 arc minutes


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deSitter
Still in Old School


Reged: 12/09/04

Re: New Hubble X-treme deep field photo new [Re: brentwood]
      #5448228 - 09/30/12 10:55 AM

Quote:

There appears to be only two or three actual stars with diffraction spikes visible. I'm wondering how many of those very faint dots are very faint red dwarf stars in our galaxy.
Do they actually get spectra on all the objects visible to verify the red shift & therefore the distance?




I seem to remember there were no stars at all in the UDF, which is why that area of the sky got selected for this. Some of those objects have two sets of diffraction spikes. I would imagine that's the difference in the HST cameras, one being the infrared version they used to accomplish the XDF.

-drl


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