The highest-energy photon ever seen from a cosmic blast should have been absorbed en route, and quantum gravity may explain why it wasn’t.<\/p>\n
Deep space is not empty. At these energies, a photon crossing billions of years of it should collide with the faint glow left over from the Big Bang. It stops existing long before it gets here.<\/p>\n
One photon from the brightest cosmic explosion on record arrived anyway. Two physicists now say a small break in one of Einstein\u2019s rules could be why.<\/p>\n
Giorgio Galanti of Italy\u2019s National Institute for Astrophysics and Marco Roncadelli of the INFN<\/a>, the country\u2019s nuclear physics institute, laid out the case in a paper published on September 8. <\/p>\n It\u2019s an interpretation of someone else\u2019s measurement, not a new observation, and both say it needs more sightings to become a discovery.<\/p>\n Galanti said they started from one question: how did a photon survive a trip that known physics should have made fatal? Their answer, if it holds, makes space itself change at extreme energies.<\/p>\n One detector caught the photon<\/p>\n The explosion, GRB 221009A, went off on October 9, 2022, roughly 2 billion light-years away.<\/p>\n NASA\u2019s Swift<\/a> satellite and the Fermi<\/a> Gamma-ray Burst Monitor both caught it. Astronomers nicknamed it the BOAT<\/a>, for brightest of all time.<\/p>\n At the Baksan Observatory in the Russian Caucasus, a cosmic-ray array called Carpet logged one photon-like shower pointing back at the burst. An early look at part of the detector put its energy near 251 TeV.<\/p>\n The Carpet team then reworked a full day of data from the whole array and moved the figure to 300 TeV, give or take about 40. That is the highest energy ever reported for a photon from a gamma-ray burst.<\/p>\n An unrelated shower lining up with the burst in direction and time has roughly a 9 in 1,000 chance. A proton or another nucleus faking a photon has about a 3 in 10,000 chance.<\/p>\n Neither number is airtight, and the whole argument rests on that single shower. Two larger observatories missed it: the burst sat at the edge of LHAASO<\/a>\u2018s field of view, and below HAWC\u2019s horizon.<\/p>\n Deep space is not empty<\/p>\n The sky everywhere carries the cosmic microwave background, the afterglow of the Big Bang. <\/p>\n It\u2019s the oldest light there is, and under standard physics, a photon this energetic can\u2019t slip past it.<\/p>\n When two photons meet with enough energy between them, they convert into an electron and its antimatter twin, and the high-energy one is gone. <\/p>\n That background is the main obstacle at the top of the scale, with starlight from every galaxy adding to it lower down.<\/p>\n So Galanti and Roncadelli worked out how many such photons ordinary physics predicts for a detector like Carpet. Their answer is about 10\u207b\u2079\u2076 of an event: a decimal point, 95 zeros, then a one.<\/p>\n That\u2019s not a long shot. It\u2019s a number that means never.<\/p>\n A lighter particle could not explain it<\/p>\n Physicists already had a candidate fix. Some theories predict a very light, neutral particle that a photon can turn into and back again along the way. In that other form nothing absorbs it, so more of the beam survives.<\/p>\n Those particles have a name, axion-like particles, and they double as dark matter<\/a> candidates. <\/p>\n The same two physicists had already used them to explain eight photons above 10 TeV that LHAASO recorded from this burst.<\/p>\n The idea doesn\u2019t stretch far enough. Across the full range of masses and couplings that keeps their earlier explanation standing, the expected count of Carpet events lands at about 1 in 10,000 or lower.<\/p>\n Seeing a single photon at 95% confidence takes roughly 0.05. That\u2019s short by a factor of about 100.<\/p>\n A small break in relativity fits<\/p>\n So they turned to the other option. Many attempts to fold gravity into quantum mechanics predict that at extreme energies, space-time<\/a> stops behaving like the smooth stage special relativity assumes. <\/p>\n One possible casualty is the rule that every photon travels at exactly the same speed<\/a>.<\/p>\n In the version that works here, a very energetic photon moves a shade slower than a weak one. <\/p>\n That shifts which background photons it can react with: it now needs ones carrying more energy, and those are rarer. The universe turns more transparent, and the photon has a route through.<\/p>\n Their job was to pin down how sharp the break would be. Fitted to the Carpet event, the simplest form of it comes in below 1.22 \u00d7 10\u00b2\u00b9 GeV, about 100 times the scale where quantum gravity is expected to appear. <\/p>\n A steeper version lands below 2.03 \u00d7 10\u00b9\u00b3 GeV.<\/p>\n The delay was predicted too<\/p>\n A second thing falls out, and nobody put it there on purpose. If the most energetic photons run slightly slow, the 300 TeV one should also have shown up late.<\/p>\n It did. The LHAASO photons above 10 TeV arrived within about 15 minutes of the trigger, while Carpet\u2019s event was recorded 4,536 seconds after it, or roughly 75 minutes.<\/p>\n Ofengeim and Piran, working the same puzzle, recently put a number on it. A gap of more than an hour is what the steeper version predicts, at a scale near 1.59 \u00d7 10\u00b9\u00b2 GeV. <\/p>\n That sits under the ceiling the pair derived from the photon\u2019s survival alone.<\/p>\n One idea covers two facts: a photon that exists when it should not, and a photon that runs late.<\/p>\n Confirmation depends on future bursts<\/p>\n What nobody has is a second case. Every number here comes from one shower in one detector, from the brightest gamma-ray burst<\/a> on record. <\/p>\n The same effect has not been seen anywhere else, and the authors are plain that future observations have to decide it.<\/p>\n Ordinary explanations aren\u2019t finished either. Other groups have tried building the burst\u2019s highest-energy output out of protons or neutrons, and Galanti and Roncadelli said neither model holds together in a realistic setup.<\/p>\n Roncadelli said the interesting part is that the work joins two ideas developed separately. <\/p>\n If it survives, he said, the universe becomes a natural laboratory for quantum gravity, at energies past any accelerator built here.<\/p>\n Settling it takes another burst that hard, and another detector to catch the shower. Until then the case rests on one air shower, recorded on a single day in the Caucasus.<\/p>\n The full study was published in the journal Physical Review Letters<\/a>.<\/p>\n \u2014\u2013<\/p>\n Like what you read? Subscribe to our newsletter<\/a> for engaging articles, exclusive content, and the latest updates.<\/p>\n Check us out on EarthSnap<\/a>, a free app brought to you by Eric Ralls<\/a> and Earth.com.<\/p>\n \u2014\u2013<\/p>\n","protected":false},"excerpt":{"rendered":"The highest-energy photon ever seen from a cosmic blast should have been absorbed en route, and quantum gravity…\n","protected":false},"author":2,"featured_media":906223,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[24],"tags":[64,63,292,128],"class_list":["post-906222","post","type-post","status-publish","format-standard","has-post-thumbnail","category-physics","tag-au","tag-australia","tag-physics","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts\/906222","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/comments?post=906222"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts\/906222\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/media\/906223"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/media?parent=906222"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/categories?post=906222"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/tags?post=906222"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}