Talk:UDFy-38135539

Timeline?

The article says "The galaxy's image was first captured in the Hubble Ultra Deep Field, the most detailed deep space picture ever taken,[1] by the Hubble telescope's recently-attached Wide Field Camera 3 (WFC3) in August and September of 2009.[3][4]" But HUDF was created in 2003 and 2004, using the Advanced Camera for Surveys put up in March 2002. Wide Field Camera 3 wasn't installed until 2009 on SM4. So which is it? Did they go back over the same field with the new camera, or something else? Somedaypilot (talk) 21:37, 21 October 2010 (UTC)

Yes - astronomers used the infrared channel of the new WFC3 camera to image the HUDF. When combined with existing HUDF data from the previous campaign, astronomers were able to identify a new list of potentially very distant galaxies. —Preceding unsigned comment added by 98.233.136.22 (talk) 14:12, 24 October 2010 (UTC)

Fallacy

"...a galaxy which, as of October 2010, is the most distant object from Earth known to exist in the universe to date."

Isn't there something slightly fallacious in suggesting that this galaxy "exists" in the universe? If it's 13 billion light years away then surely all we can verify is that it existed 13 billion years ago. - filelakeshoe 22:10, 21 October 2010 (UTC)

How about: "...a galaxy which, as of October 2010, is the most distant object in the universe observed from Earth"? -- Black Falcon ^(talk) 22:37, 21 October 2010 (UTC)

Filelakeshoe makes a good point,and I think Black Falcon's revision comes as close as possible to remedying the problem. AGradman / talk / how the subject page looked when I made this edit 23:04, 21 October 2010 (UTC)

Yep, that sounds a lot better. - filelakeshoe 23:43, 21 October 2010 (UTC)

Seriously? So in every single article about astronomy, we have to say something "exists or used to exist, in case it has stopped existing since the time its most recently perceived-on-earth photons were emitted or at any time after that but less than the time since its very last photons were emitted, which we don't know because it is in our future as observers but in the past from the point of view of its immediate environment"? REALLY? And if THAT level of specificity isn't enough, why not do away with the word "object," since no "object" at a distance of billions of light years is likely to be the same "object" "now"?63.17.51.20 (talk) 04:04, 24 October 2010 (UTC)

Yeah, seems over-pedantic. Anyway, if "the universe" is understood to include all of spacetime, then "exists in our universe" is true regardless of whether it exists "now". The very concept "exists now" has no objective meaning in relativity anyway, thanks to the relativity of simultaneity. Hypnosifl (talk) 08:36, 24 October 2010 (UTC)

Not in every single article, just those concerning things of great distances or those verifiably likely not to exist any more (like Rho Cassiopeiae). And I was NOT suggesting an overcomplicated explanation, just avoiding using the term "exists". Wikipedia articles should be written plainly to explain whatever to people without knowledge of the topic as well, and I daresay the majority of people haven't heard of the relativity of simultaneity, thus would interpret "exists in the universe" to mean "exists now". I notice we don't claim that GRB 090423 "exists" in the universe, because it quite obviously doesn't any more - it was a flash of light that happened billions of years ago. Using Black Falcon's wording is simpler and less ambiguous, that's all. - filelakeshoe 11:02, 25 October 2010 (UTC)

Sorting out the Dark Ages; microwave background transmission from a transparent universe

The article currently says:

The universe's first stars, blue giants, were born out of the once-ubiquitous hydrogen fog, and burned bright but had short lifespans. Their existence created the first heavy elements, and intense ultraviolet radiation split atoms into protons and electrons, clearing the hydrogen fog and producing plasma still detectable between closely neighboring stars. The period of opaque space between the Big Bang and this event is referred to as the Dark Ages. The era of star birth which followed is known as the reionization epoch, and lasted from somewhere around 150 million to 800 million years after the Big Bang. Astronomers are trying to pin down when and how the Dark Ages ended. The transparent "bubble" which surrounds UDFy-38135539 proves that 600 million years after the Big Bang, stars in galaxies had almost completed the process of hydrogen reionization which resulted in the end of the Dark Ages, by creating the magnetic field that shaped subsequent galaxies and spurred more star formation.

Now the Dark Ages can't have reached all the way back to the Big Bang, because at 380,000 years the microwave background radiation was emitted at about 3000K. So the Dark Ages have a beginning, which should be explained. (it'd also be interesting to hear how the not-yet-microwaves made it through the Dark Ages, but maybe not relevant. What frequency was it down to by the time the Dark Ages started?)

Also, my impression from the other articles was that the transparency of the universe at this early time was due to the emergence of neutral matter. So wouldn't reionization make it opaque again?

A last detail is that, as I understand from the little section linked, the Dark Ages were actually a "foggy" age, and people are hunting for 21-cm radiation from it. This should come from some sort of "wall" representing something less than 600 million years after the Big Bang. Is there a current consensus about where that wall of 21-cm emission should be, i.e. how much space is "behind" this galaxy, if any (from the article it looks like it may actually be in a sort of cranny in the wall!) Wnt (talk) 23:08, 21 October 2010 (UTC)

"have a light travel time of 13 billion light years" - it makes no sense. Light years are units of distance not time. Besides, the sentence is a bit circular. —Preceding unsigned comment added by 128.146.238.235 (talk) 21:35, 22 October 2010 (UTC)

References

Accuracy of distance

This article states in the Characteristics section that, "It has a light travel distance of more than 4 billion parsecs from our planet[10] (over 13 billion light years), and a luminosity distance of 86.9 billion parsecs (about 283 billion light years)" Neither source 10 or 11 stated the luminosity distance and a distance of 86.9 billion parsecs would put it well beyond the current accepted diameter of the observable Universe (93 billion LY). Given that figure the furthest it could be would be 46.5 billion LY. It seems the media still does not understand the concept of expansion and its effect on spacetime as almost every source lists the distance as 13 billion LY due to the mistaken idea that this is the furthest that light could travel in 13 billion years. That being said I can't find a source that gives a real figure for distance to UDFy-38135539 in parsecs or LY. —Preceding unsigned comment added by 71.226.131.15 (talk) 01:43, 22 October 2010 (UTC)

The source after the comment about luminosity distance does give a value of 86.9 billion parsecs, just look at the first paragraph in the right-hand column on the first page. There are many different measures of "distance" in cosmology—see Distance measures (cosmology)— and the figure for the size of the observable universe, about 46-47 billion LY, is expressed in terms of comoving distance or proper distance, which are defined to be equal at the present time. Unfortunately no sources give the comoving distance/proper distance of the galaxy, but it's easy to calculate: the luminosity distance page mentions that the luminosity distance $D_{L}$ is related to something called the "comoving transverse distance" $D_{M}$ by the equation $D_{L}=(1+z)D_{M}$, where z is the redshift, so with $D_{L}$ = 86.9 billion parsecs and z=8.55 this gives $D_{M}$ = 86.9/9.55 = 9.1 billion parsecs. The page also mentions that $D_{M}$ is equal to the radial comoving distance $D_{C}$ in a spatially flat universe (which ours appears to be), so 9.1 billion parsecs would also be the radial comoving distance, i.e. the comoving distance between us and the galaxy at present. This is equal to about 30 billion light years, within the radius of the observable universe.

Unfortunately no references actually state the comoving distance or proper distance, google "UDFy-38135539" and "comoving distance" to see...I wonder, would it violate the Wikipedia:No original research rule to put a straightforward calculation like this in the article? Many science articles on wikipedia include basic calculations without giving references, and in astrophysics articles it's pretty common practice to put the distance in light years in parentheses after the distance in parsecs, even if the source being referenced only gives the distance in parsecs. Hypnosifl (talk) 05:59, 22 October 2010 (UTC)

Hmm, there seems to be some disagreement about whether simple manipulation of equations constitutes "original research", see Wikipedia_talk:No_original_research/Archive_16#Equations:_Original_research_and_verifiability. See also the policies at Wikipedia:SCG#Examples.2C_derivations_and_restatements and Wikipedia:ATT#What_is_not_original_research.3F which are linked to from that discussion. I think a calculation of the comoving distance would be acceptable under these guidelines so I'll add it to the article, if others think this goes too far in the direction of "original research" we can discuss it here and try to form a consensus. Hypnosifl (talk) 06:34, 22 October 2010 (UTC)

I see now the reference to luminosity distance and and yes there are several distance measures in cosmology. I should have been more specific and asked what the comoving distance would be since this is the figure that would best describe how much space is currently between us and this galaxy. This would be the best figure to use for an audience of non-experts since it is about as close as you can come to saying how far away is it in the same frame of reference as expressing the distance from here to the Sun.

Nice work on the calculation BTW, this is the first time I have seen the actual comoving distance to this galaxy expressed. I found the Newsweek article especially troublesome because it listed the current distance at 13.7 billion LY. This highly inaccurate figure was also listed in nearly all of the main stream media sources on this story. This clearly shows how wiki style editing is superior to traditional edits by one person or media source.

I think the best way to avoid the argument that using there equation constitutes original research would be to simply show the calculation in the article and reference the source. I realize their whitepaper was intended for cosmology experts but I was surprised that a paper on the new furthest observable object failed to list its current comoving distance anywhere. —Preceding unsigned comment added by 71.226.131.15 (talk) 13:16, 22 October 2010 (UTC)

I think your last edit is very well done and is the clearest explanation I have seen of just how far away this galaxy is since this story broke. —Preceding unsigned comment added by 71.226.131.15 (talk) 13:22, 22 October 2010 (UTC)

"Characteristics" not current, perhaps misleading

"According to Lehnert (of the Observatoire de Paris), it is forming the same number of stars per year as our galaxy, but they are much smaller and less massive, making it "intensely star forming".

Isn't this somewhat misleading, given that we are currently observing photons emitted 13 billion years ago? Any reader not up on cosmology (and I certainly include myself in that group) could take that to mean that we know what the galaxy is currently like and what's currently happening there.

Maybe "13 billion years ago, the galaxy was forming the same number of stars per year as our galaxy is now, but..." And this could perhaps lead into a discussion on why star formation was so different at that time, compared to now, which could lead nicely into the "Significance" section.

Or not. I don't pretend to be well-versed in the issues, and am not about to try an edit, but thought I'd bring it up for discussion amongst editors with more knowledge. 209.217.221.162 (talk) 02:04, 22 October 2010 (UTC)

I've made the edit. Feel free to revert me if I'm wrong and Lehnert is correct[1]. See also the #Fallacy section above. -- Jeandré, 2010-10-22t09:25z

Abell 2218

Abell 2218 — location of the previous record holder for most distant galaxy

That's factually incorrect. Abell 2218 is very close by in comparison to IOK-1 and this galaxy. The claim is for a pair of galaxies gravitationally lensed by the cluster, which is not the same thing, since they are not in the same location, they are only coincidentally in the same line of sight.

Abell 2218's lensing of galaxies at redshift 7 is also unsourced at Abell 2218, and there is no reference given that it was ever confirmed.

The see also section here is therefore containing WP:OR claims.

76.66.198.128 (talk) 04:51, 22 October 2010 (UTC)

JKCS 041

JKCS 041 — location of the record holder for most distant galaxy until the announcement of IOK-1

That's just plain wrong. JKCS 041 is a galaxy cluster, and holds the record for most distant galaxy cluster, a totally different beast than an galaxy.

76.66.198.128 (talk) 04:55, 22 October 2010 (UTC)

So how far away is it?

I'm not an astrophycisist, which seems to be a requirement for understanding this article. I just wanted to find out what the actual distance was from Earth. With the Front page ITN blurb reading "The discovery of the galaxy UDFy-38135539 (pictured), the most remote object ever observed from Earth, is announced", I would expect to find this in the lede section, and in layman's terms. But no such luck! In the third section I find the phrase "The galaxy's light photons now observable on Earth were emitted 13 billion years ago". Now, does this constitute the distance from Earth? As I read on there is mention of "light travel distance", "luminosity distance", "comoving distance" as well as "proper distance". I understamd this is complicated. Still, with most (at least very many) people checking out this page from the Main page link, probably wanting to see how far away is it, this should be adequately addressed in the lede, even though it is exceedingly complicated. __meco (talk) 08:18, 22 October 2010 (UTC)

I added a recommendation to check out Uses of the proper distance, which discusses the physical meaning of the comoving distance; I don't think it's possible to get much simpler than that without being misleading, the notion of "distance" is complicated in relativity. You might also check out the observable universe article which is also linked from this article. Hypnosifl (talk) 08:37, 22 October 2010 (UTC)

@Meco I am not a astrophysicist, but I think experts would agree that once distances get this vast (into the billions of light years), methods of measurement (which are built on a chain of less and less accurate methods as the distance increases, from parallax to redshift) can differ by as much as a factor of 2! Commonly quoted distances may become the norm, but it is always wise to remember the uncertainty involved...--Novus Orator 08:41, 22 October 2010 (UTC)

Comments from a skeptic

Just because they give it a complicated name doesn't make it worth anything scientifically. There are so many details that are wrong about this "discovery" that I don't know where to begin...

1. appears as an "incredibly faint" smudge in the Hubble image
2. It is estimated to have contained roughly a billion stars

So if it's a smudge, then how can you estimate that it contains a billion stars? What if it only contains let's say a million? How can you determine how many stars are in an incredibly faint smudge??

1. it was forming the same number of stars per year as our galaxy, but they were much smaller and less massive

Again, how do you know this?

1. Light from the galaxy that we now observe on Earth was emitted 13 billion years ago, only 600 million years after the Big Bang

So this galaxy is 13 billion light-years from us. Nothing can travel faster than the speed of light. If the Big Bang happened 600 million years before this light was emitted, then it means that, in 600 million years, particles travelled 13 billion light-years to get into position when they emitted that light which we now received. So how can you travel 13 billion light-years in 600 million years? Let's take that we are travelling in the opposite direction of this galaxy, then it would still need to make at minimum 6.5 billion light-years in 600 years!

1. The light that we now observe from the galaxy was emitted during a time when the universe was filled with hydrogen fog and not fully transparent

How do we know this? If it's just a hypothesis, then it's not a good explanation and this is also bs: ‘Scientists therefore suspect that other neighboring galaxies, which we have not yet detected, helped to clear out a bubble of transparent space around UDFy-38135539’

Anyway, it's really sad to see that these people get paid to make up this kind of stories, and they're even too lazy to think of something more creative. I've no idea why this got on the front page of Wikipedia. You might as well publish that Grandma Lilly the town witch ate two children this morning, the claim is just as valid...

--Gcsaba2 (talk) 20:19, 22 October 2010 (UTC)

"If the Big Bang happened 600 million years before this light was emitted, then it means that, in 600 million years, particles travelled 13 billion light-years to get into position when they emitted that light which we now received."

First of all, it's not exactly true that nothing can travel faster than the speed of light in general relativity, "speed" is defined in terms of distance/time and the rule that nothing can travel faster than the speed of light c, and that light itself only moves at c, only applies if you are talking about an inertial frame of reference, and no coordinate system in a large region of expanding spacetime can really qualify as "inertial", although in a small region of spacetime where the effects of expansion are negligible you can still define a "local inertial frame" in which nothing moves faster than c, thanks to the equivalence principle (see this article for a good summary). I recommend reading Comoving distance#Uses of the proper distance (especially the third paragraph) for more on this point. As stated in the first paragraph, proper distance represents the distance that would be measured between ourselves and a distant object if we had a row of observers in a line from us to the object, and each one used a ruler to make a local measurement of the distance between themselves and the next one in the line, all making their measurements at the same moment in cosmological time; then if you sum up all these local measurements, you get the proper distance. As stated in "uses of the proper distance", if you look at the proper distance from us to some distant galaxy at different moments, it can actually be increasing much faster than c! The proper distance to this galaxy now is actually about 30 billion light years despite the fact that the universe has only been around for about 13.75 billion years (and the size of the observable universe, whose edge is defined by the current proper distance of the furthest objects we can see in the past, is even larger, about 46 billion light years).

At the time the light was emitted the distance was shorter, however. The ratio between proper distance now and proper distance at time of emission is the same as the ratio of the scale factor then and now, and as mentioned near the bottom of Redshift#Mathematical_derivation this ratio is given by $1+z={\frac {a_{\mathrm {now} }}{a_{\mathrm {then} }}}$. So with a redshift of z=8.55, the universe now must be about 9.55 times larger than it was at the time of emission, meaning the proper distance at the time of emission was only (30 billion)/9.55 = 3.14 billion light years, a lot less than today although larger than 600 million light years. Hypnosifl (talk) 22:12, 22 October 2010 (UTC)

Blue giants

The universe's first stars, which were blue giants, were born out of the once-ubiquitous hydrogen fog, and burned bright but had short lifespans.

That seems wrong. I know it came from the BBC article used as a source, but Population III stars are supposed to be beyond hypergiant in size, and power. 76.66.199.238 (talk) 06:43, 23 October 2010 (UTC)

Coordinates?

IP 187.17.137.13 claims that the galaxy is located at 03 32 38.13 -27 45 53.9. Wikisky shows this location is in Fornax, but does someone have a reliable reference and does someone know the apparent magnitude of the galaxy? -- Kheider (talk) 11:58, 25 October 2010 (UTC)

Checking the paper should have been the first place to look. It gives the optical photometry as 'B <29.8, V <30.2, i <29.8, z <29.1, all 2-sigma limits', and references the Bouwens paper for the rest of the catalogue info. That paper in turn gives coordinates of 03:32:38.13 −27:45:53.9 (exactly as the IP had), H = 28.1+-0.1, Y-J > 2.1 (1 sigma), J-H = 0.2+-0.2. I'd incorporate those numbers myself, but should sleep instead. Modest Genius ^talk 02:19, 26 October 2010 (UTC)

Orphaned references in UDFy-38135539

I check pages listed in Category:Pages with incorrect ref formatting to try to fix reference errors. One of the things I do is look for content for orphaned references in wikilinked articles. I have found content for some of UDFy-38135539's orphans, the problem is that I found more than one version. I can't determine which (if any) is correct for this article, so I am asking for a sentient editor to look it over and copy the correct ref content into this article.

Reference named "Bunker2013":

• From List of the most distant astronomical objects: VLT/XSHOOTER and Subaru/MOIRCS spectroscopy of HUDF.YD3: no evidence for Lyman alpha emission at z = 8.55[2]
• From List of the most distant astronomical objects: VLT/XSHOOTER and Subaru/MOIRCS spectroscopy of HUDF.YD3: no evidence for Lyman alpha emission at z = 8.55

I apologize if any of the above are effectively identical; I am just a simple computer program, so I can't determine whether minor differences are significant or not. AnomieBOT⚡ 18:57, 11 July 2014 (UTC)

Galaxy shape of UDFy-38135539

Since UDFy-38135539 contains 1 billion stars and is one-tenth of the diameter of our own galaxy (i.e. 10,000 light years), the Milky Way, is it in spiral or elliptical in shape?

Dantescifi 09:54, 13 June 2015 (UTC)

Importance

Should the oldest and most distant known object in the universe really be considered of 'low importance?' That doesn't seem right. 2620:0:2820:A0D:7409:5BDC:D85F:552D (talk) 18:28, 11 February 2016 (UTC)