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Most distant Galaxy discovered.,

barkis

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barkis

barkis

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A small dot on a Hubble picture, was examined and measured by the Very Large Telescope in Chile, and found to be at a distance of 13 Billion Light Years. It's estimated to have been formed 600 million years after the Big Bang.

Ron.

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barkis

barkis

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Here's the link from the BBC news website: BBC News - Galaxy is most distant object yet

The equipment they used looks pretty impressive. Especially to capture something so faint.

Impressive Indeed. Thanks for the Link to the Article.

I saw the report on Teletext this morning.

The James Webb Telescope is an exciting prospect.

Ron.:)

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George Jones

George Jones

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The light from this galaxy took 13 billion years to reach us. Where were we then (when the light we now see left the galaxy)? 3.2 billion light-years away from the galaxy. Where is the galaxy now? 30.3 billion light-years away from us.

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ollypenrice

ollypenrice

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The light from this galaxy took 13 billion years to reach us. Where were we then (when the light we now see left the galaxy)? 3.2 billion light-years away from the galaxy. Where is the galaxy now? 30.3 billion light-years away from us.

I'm glad to hear you say this, George, because without your serious grasp of things this is, none the less, the gist of my understanding. However, a recently visiting string theorist (a little over my head) seemed to say that only the light travel time had any validity. I may be misrepresenting him since he was not a native English speaker. Oh dear, I will happily stick with your version. Am I right in thinking that your figures do not rely on inflation but simply on the post inflationary expansion of the universe?

Olly

Olly

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George Jones

George Jones

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Yes, all of this is after inflation. The universe has grown by about the same factor after inflation that it grew by during inflation. So, in comparison with today's size, the size of the universe after inflation was almost infinitesimal. The growth after inflation, however, took place over a much, much greater period of time than did the growth during inflation.

Lookback time/distance is a good physical measure. The distances that I gave require a convention for the concept of simultaneity; both galaxies at the same time then, and both galaxies at the same now. what does "same time" mean? The homogeneity and isotropy of the universe picks out this notion of simultaneity.

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George

George

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The light from this galaxy took 13 billion years to reach us. Where were we then (when the light we now see left the galaxy)? 3.2 billion light-years away from the galaxy. Where is the galaxy now? 30.3 billion light-years away from us.

If the universe is only 13.6 billion years old how can a galaxy be 30.3 billion light years away ?:)

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ollypenrice

ollypenrice

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If the universe is only 13.6 billion years old how can a galaxy be 30.3 billion light years away ?:)

My amateur explanation would be this; the universe is expanding during the 13.6 billion years of the light's flight time so the point from which it set out is getting pushed further away from us (by this expansion) during the flight.

I'll always stand corrected...

Olly

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661-pete

661-pete

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Anybody know the visual magnitude of this object, just for grins?
The faintest the HUDF could reach was, apparently, mag. 30, so it won't be fainter than that. Some terrestrial telescopes can beat the Hubble though - if the 100m OWL ever gets built (unlikely :)), it's predicted to get down to mag. 38. More wonders await us no doubt...
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themos

themos

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If the universe is only 13.6 billion years old how can a galaxy be 30.3 billion light years away ?:)

Today's light year is "devalued" by "inflation"compared to the good old times. The light we actually see left the galaxy when it was only 3.2 billion light years away (if George Jones's calculations are correct). By the time the light got to us, inflation had devalued the light year so it's now at 30.3 billion.

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FraserClarke

FraserClarke

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The faintest the HUDF could reach was, apparently, mag. 30, so it won't be fainter than that.

That's the detection limit of HUDF -- but this object is undetected in all the visible bands. It's at redshift ~8.5, which means the visual band (~550nm) corresponds to a rest frame wavelength of 57.8nm (far-UV). This is below the lyman-limit, so any neutral Hydrogen gas between us and the object will absorb these photons. It's also far enough back in the Universe's history that it is in the epoch before most of the Hydrogen in universe was re-ionised, so the Universe would have been effectively opaque to this radiation... So, there will be effectively no visible radiation from this galaxy at all...

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661-pete

661-pete

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That's the detection limit of HUDF -- but this object is undetected in all the visible bands. It's at redshift ~8.5, which means the visual band (~550nm) corresponds to a rest frame wavelength of 57.8nm (far-UV). This is below the lyman-limit, so any neutral Hydrogen gas between us and the object will absorb these photons. It's also far enough back in the Universe's history that it is in the epoch before most of the Hydrogen in universe was re-ionised, so the Universe would have been effectively opaque to this radiation... So, there will be effectively no visible radiation from this galaxy at all...
Yes, but the hydrogen in the universe at the time this galaxy emitted the light we see it by, would have 'seen' the galaxy in visible light - it wouldn't have been receding from the hydrogen. So it would have let it through...

I think the question was, more simply, what magnitude is the galaxy at whichever IR wavelength the HUDF recorded it at. It must have recorded it, else we wouldn't know it's there!

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FraserClarke

FraserClarke

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Yes, but the hydrogen in the universe at the time this galaxy emitted the light we see it by, would have 'seen' the galaxy in visible light - it wouldn't have been receding from the hydrogen. So it would have let it through...

Yes of course, but that light is now at 5-microns, in the infrared.

My understanding was 'how bright is the galaxy in the visible now?'. Depends on how (when) one defines "visible" :)

I think the question was, more simply, what magnitude is the galaxy at whichever IR wavelength the HUDF recorded it at. It must have recorded it, else we wouldn't know it's there!

No detection below J band (1.25 microns). Magnitude in J is 28.3 (on the AB system; ~29.1 on the Vega system most people here will use).

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dph1nm

dph1nm

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No detection below J band (1.25 microns). Magnitude in J is 28.3 (on the AB system; ~29.1 on the Vega system most people here will use).
30th mag in H-band, according to one of the authors of the paper, who works just down the corridor from me! There is an interesting question as to why it is visible at all, as at the time we see it, it should have been obscured by neutral hydrogen, and it is too feeble a galaxy (about 1/100 of the mass of the Milky Way) to have cleared the neutral hydrogen on its own.

NigelM

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George Jones

George Jones

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The light we actually see left the galaxy when it was only 3.2 billion light years away (if George Jones's calculations are correct).

I was going to use a fairly realistic model to calculate this number myself, but then I decided to use Ned Wright's (a very good professional cosmologist) even more realistic on-line calculator

Ned Wright's Javascript Cosmology Calculator

to do almost all of the work. I calculated the above number as follows.

According to articles, the galaxy's redshift is z = 8.55. On the left in Wright's calculator, replace the 3 in the z field by 8.55, and click on "General". After doing this, the line

The comoving radial distance, which goes into Hubble's law, is 9302.1 Mpc or 30.340 Gly.

should appear on the right. This means that the galaxy is now 30.340 light-years from us. (This is true only if the galaxy still exists, and if the galaxy has not been affected by cluster or supercluster dynamics. Probably bad assumptions.)

Now find the distance when the light left. Call the scale of the universe now a2, and call the scale of the universe when the light left a1. Then, the redshift z is defined by

1 + z = a2/a1.

This, with z = 8.55, gives

a1 = a2/9.55,

and the distance then is

30.34/9.55 = 3.18 (billion light-years).

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