{"id":2043,"date":"2018-01-01T20:01:02","date_gmt":"2018-01-01T20:01:02","guid":{"rendered":"https:\/\/www.mrsphysics.co.uk\/higher\/?p=2043"},"modified":"2025-11-25T07:37:57","modified_gmt":"2025-11-25T07:37:57","slug":"what-is-the-biggest-ever-redshift","status":"publish","type":"post","link":"https:\/\/mrsphysics.co.uk\/index.php\/2018\/01\/01\/what-is-the-biggest-ever-redshift\/","title":{"rendered":"What is the Biggest Ever Redshift?"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">A discussion on the Physics\nTeachers\u2019 Network requested advice on \u201cWhat is the biggest ever redshift\ndetected?\u201d<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Research shows it was a\nredshift, z = 11.09 for galaxy GN-z11; and the measurements were &nbsp;taken in the near infra red using Hubble&#8217;s\nWide Field Camera.&nbsp;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This is a big question because\neffectively we are seeing the furthest galaxy back in time.&nbsp; It is 32.2\nbillion years away and came into existence 400 million years after big bang. &nbsp;So if the Universe is only 13.8 billion years\nold then how come we can see something so far away?<\/p>\n\n\n\n<figure class=\"wp-block-embed-youtube wp-block-embed is-type-video is-provider-youtube wp-embed-aspect-16-9 wp-has-aspect-ratio\"><div class=\"wp-block-embed__wrapper\">\n<iframe title=\"If the universe is only 14 billion years old, how can it be 92 billion light years wide?\" width=\"751\" height=\"422\" src=\"https:\/\/www.youtube.com\/embed\/vIJTwYOZrGU?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen><\/iframe>\n<\/div><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">During this time the Universe was\nopaque and full of neutral atoms. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Professor Martin Hendry supplied an interesting reply.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In\nsome cases we can determine the redshift of a galaxy by measuring the\nwavelength of a particular spectral line that corresponds to a particular\ntransition of an electron in a hydrogen atom.&nbsp; For example the Lyman alpha\nemission line is the result of an electron dropping down from the n=2 energy\nlevel to the n=1 energy level, and the presence of this spectral line is often\nseen as an indicator of a recent burst of new stars forming as one might expect\nto see in a very young, recently formed galaxy.&nbsp; (This line was proposed\nas a tell-tale sign of a very young galaxy by Bruce Partridge and Jim Peebles \u2013\nawarded the Nobel Prize for physics this week: see e.g.&nbsp;<a href=\"https:\/\/en.wikipedia.org\/wiki\/Lyman-alpha_emitter\" target=\"_blank\" rel=\"noreferrer noopener\">https:\/\/en.wikipedia.org\/wiki\/Lyman-alpha_emitter<\/a>).&nbsp; This line has a wavelength of\n121.567 nm in the rest frame of the hydrogen atom.&nbsp; If a galaxy is a\nstrong Lyman alpha emitter, and the line is observed at wavelength lambda, then\nby comparing the observed wavelength with the 121nm at which it was emitted we\ncan measure the redshift of the galaxy.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">(Of course if this spectral line is redshifted then how do you know it\u2019s a Lyman alpha line?\u00a0 Likewise for any other spectral line.\u00a0 Often it\u2019s the combination of several spectral lines and their relative spacing that gives the game away \u2013 a bit like a bar code in the supermarket.\u00a0 You could imagine enlarging the image of a bar code in a photocopied and, generally, it\u2019d still be recognisable as the overall pattern would still be the giveaway).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In\nfact for this record-holding galaxy, the redshift was determined a slightly\ndifferent way, from the Lyman series but not the Lyman alpha line and not from\nan emission line but an *<strong>absorption<\/strong>* line: specifically it was\ndetermined from the \u201cLyman break\u201d \u2013 i.e. the limiting wavelength that\ncorresponds to the amount of photon energy you need to absorb to allow an\nelectron in the n=1 energy level to escape from its hydrogen atom\naltogether.&nbsp; &nbsp;That is a higher energy (and so a higher frequency, and\na shorter wavelength) than the Lyman alpha line, and in fact corresponds to\nabout 91 nm in the rest frame of the hydrogen atom.&nbsp; &nbsp;Any photons\nthat have even higher energies (and thus even shorter wavelengths) than this\nget absorbed by the (lots of) neutral hydrogen that is around in the Universe\nat that time; these photons thus *<strong>ionise<\/strong>* that neutral hydrogen.&nbsp;\nThis is sometimes referred to as \u201cre-ionisation\u201d in the sense that the universe\nwas fully ionised when it was much younger, because it was much hotter, then it\ncools enough for neutral hydrogen to form \u2013 i.e. when the CMBR was emitted \u2013\nand now it\u2019s being ionised again.&nbsp; Where are the high-energy photons\ncoming from to do this ionising (being absorbed in the process)?&nbsp; They are\nbelieved to come from hot young stars \u2013 i.e. the newly formed stars in these\nyoung galaxies.&nbsp; (Remember, the more massive the star the hotter their\nsurface temperature, so massive blue stars emit lots more of these energetic\nphotons than cooler red stars do).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">So,\nin summary, the spectrum of light from a galaxy as a whole drops off at the\nLyman break, like a \u201ccliff edge\u201d because at shorter wavelengths than the Lyman\nbreak these photons get absorbed, ionising the hydrogen gas in their\nenvironments.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">You\ncan then play the same game as with an emission line: look for where this\n\u201ccliff edge\u201d appears in the observed spectrum and then use that observed\nwavelength (which will be much longer than 91nm) to estimate the redshift.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The\nresearch paper on GN-z11 is at&nbsp;<a href=\"https:\/\/arxiv.org\/pdf\/1603.00461.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">https:\/\/arxiv.org\/pdf\/1603.00461.pdf<\/a>,\nand is actually pretty readable I think\u2026<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Other references:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><a href=\"https:\/\/www.youtube.com\/watch?v=vIJTwYOZrGU\">https:\/\/www.youtube.com\/watch?v=vIJTwYOZrGU<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><a href=\"https:\/\/www.space.com\/32150-farthest-galaxy-smashes-cosmic-distance-record.html\">https:\/\/www.space.com\/32150-farthest-galaxy-smashes-cosmic-distance-record.html<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Another clear explanation from Prof. Hendry, who never makes us teachers feel silly for asking questions. Thanks to Mr Thomson and his student for the original question.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>A discussion on the Physics Teachers\u2019 Network requested advice on \u201cWhat is the biggest ever redshift detected?\u201d Research shows it was a redshift, z = 11.09 for galaxy GN-z11; and the measurements were &nbsp;taken in the near infra red using Hubble&#8217;s Wide Field Camera.&nbsp; This is a big question because effectively we are seeing the&#8230;<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[603],"tags":[698,699,700,602,701,702,613,614,70,703,704],"ppma_author":[1267],"class_list":["post-2043","post","type-post","status-publish","format-standard","hentry","category-ourdynamicuniverse","tag-cmbr","tag-galaxy","tag-galaxy-gn-z11","tag-higher","tag-largest-redshift","tag-martin-hendry","tag-odu","tag-our-dynamic-universe","tag-physics","tag-prof-hendry","tag-red-shift","vs-blog blog-single wow fadeInUp"],"acf":[],"authors":[{"term_id":1267,"user_id":3,"is_guest":0,"slug":"n5","display_name":"Mrs Physics","avatar_url":"https:\/\/mrsphysics.co.uk\/wp-content\/uploads\/2025\/12\/OK-scaled.png","author_category":"","first_name":"Mrs","last_name":"Physics","user_url":"","job_title":"","description":""}],"_links":{"self":[{"href":"https:\/\/mrsphysics.co.uk\/index.php\/wp-json\/wp\/v2\/posts\/2043","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mrsphysics.co.uk\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mrsphysics.co.uk\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mrsphysics.co.uk\/index.php\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/mrsphysics.co.uk\/index.php\/wp-json\/wp\/v2\/comments?post=2043"}],"version-history":[{"count":1,"href":"https:\/\/mrsphysics.co.uk\/index.php\/wp-json\/wp\/v2\/posts\/2043\/revisions"}],"predecessor-version":[{"id":8347,"href":"https:\/\/mrsphysics.co.uk\/index.php\/wp-json\/wp\/v2\/posts\/2043\/revisions\/8347"}],"wp:attachment":[{"href":"https:\/\/mrsphysics.co.uk\/index.php\/wp-json\/wp\/v2\/media?parent=2043"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mrsphysics.co.uk\/index.php\/wp-json\/wp\/v2\/categories?post=2043"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mrsphysics.co.uk\/index.php\/wp-json\/wp\/v2\/tags?post=2043"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/mrsphysics.co.uk\/index.php\/wp-json\/wp\/v2\/ppma_author?post=2043"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}