Physicists spot potential source of OhMyGod particles

Sign up for our daily newsletter Get more great content like this delivered right to you! Country For decades, physicists have sought the sources of the most energetic subatomic particles in the universe—cosmic rays that strike the atmosphere with as much energy as well-thrown baseballs. Now, a team working with the Telescope Array, a collection of 507 particle detectors covering 700 square kilometers of desert in Utah, has observed a broad “hotspot” in the sky in which such cosmic rays seem to originate. Although not definitive, the observation suggests the cosmic rays emanate from a distinct source near our galaxy and not from sources spread all over the universe.Physicists have been down a similar road before. In 2007, researchers with the Pierre Auger Observatory, an even bigger array in Argentina, reported that ultra–high-energy cosmic rays appeared to spring from the fiery hearts of certain galaxies—only to see that correlation weaken with more data. However, the Telescope Array team has taken a more catholic approach, looking only for evidence that cosmic rays do not arrive in equal numbers in all directions. “It’s simpler and more direct, and therefore more robust,” says Glennys Farrar, a theorist at New York University (NYU) in New York City, who was not involved in the work.Nobody knows how ultra–high-energy cosmic rays—mainly protons or heavier atomic nuclei—acquire energies millions of times higher than have been achieved with humanmade particle accelerators. (Physicists dubbed one of the first ones observed the “Oh-My-God particle.”) Lower energy cosmic rays are thought to spring from the lingering remnants of stellar explosions called supernovas. But such clouds are far too small to produce the highest energy cosmic rays. Instead, theorists generally expect that the most energetic cosmic rays rev up over millions of years in unidentified accelerators the size of galaxies. The Telescope Array aims to help solve that mystery. When a high-energy cosmic array strikes the atmosphere, it disappears in an avalanche of lower  energy particles. Those particles trigger the detectors in the array, enabling researchers to deduce the direction and energy of the original cosmic ray. From 2008 to 2013, researchers spotted 72 cosmic rays with energies above 57 exaelectron volts—15 million times the highest energy achieved with a particle accelerator. And 19 of them appear to cluster in a hotspot in the sky about 20° in radius, as Hiroyuki Sagawa, a co-representative for the Telescope Array team from the University of Tokyo, reported today in a press conference at the university.The signal isn’t strong enough for scientists to claim a discovery, cautions Pierre Sokolsky of the University of Utah in Salt Lake City, one of 125 members of the Telescope Array team. “It’s an enhancement at a statistical level that raises eyebrows,” he says. By running millions of simulations in which they dot the sky with 72 random points, researchers estimate the chances that random cosmic rays could produce such a hotspot at one in 2700, the Telescope Array team explains in a paper in press at The Astrophysical Journal Letters.But analyzing such sparse data is tricky, says Karl-Heinz Kampert, a physicist at the University of Wuppertal in Germany and spokesman for the 500-member Auger team. The Telescope Array researchers have no reason to expect that a hotspot would be 20° in radius, he says, so they can’t be sure they haven’t adjusted that width to inadvertently emphasize a random clustering. Still, he says, it’s plausible that the team is seeing a real signal, all the more so because Auger has long seen similar clustering in the direction of active galaxy Centaurus A. “We have what you might you might call a warm spot,” he says.But if the Telescope Array is starting to see a source of ultra–high-energy cosmic rays, then its identity remains unclear. Physicists think that the highest energy cosmic rays cannot come from more than 500 million light-years away, as interactions with lingering radiation from the big bang ought to snuff out cosmic rays from more distant sources. But no obvious candidate for a nearby cosmic accelerator lies directly in line with the hotspot, Sokolsky says. He notes, however, that in that region a filament of galaxies kinks toward Earth and speculates that magnetic fields in that string might help rev up particles.That’s not surprising, NYU’s Farrar says. Over the past decade, physicists have developed much more detailed maps of the magnetic field within the galaxy, which can deflect charged particles such as protons and nuclei. Those fields can deflect the path of a high-energy proton by tens of degrees—even more for heavy atomic nuclei. Still, Farrar says, “I wouldn’t be surprised if within 5 years we could predict the deflection to within a few degrees”—at least for protons.In the meantime, the Telescope Array team hopes to prove whether the hotspot is real. The $25 million array was built primarily with funding from the Japanese government and is run mainly by the U.S. National Science Foundation. Sokolsky and colleagues hope to expand the array—doubling the number of detectors and quadrupling its area—in a proposed $6.4 million upgrade. The upgrade would enable them to collect five times more data in a few years and really settle the matter. Click to view the privacy policy. Required fields are indicated by an asterisk (*) Country * Afghanistan Aland Islands Albania Algeria Andorra Angola Anguilla Antarctica Antigua and Barbuda Argentina Armenia Aruba Australia Austria Azerbaijan Bahamas Bahrain Bangladesh Barbados Belarus Belgium Belize Benin Bermuda Bhutan Bolivia, Plurinational State of Bonaire, Sint Eustatius and Saba Bosnia and Herzegovina Botswana Bouvet Island Brazil British Indian Ocean Territory Brunei Darussalam Bulgaria Burkina Faso Burundi Cambodia Cameroon Canada Cape Verde Cayman Islands Central African Republic Chad Chile China Christmas Island Cocos (Keeling) Islands Colombia Comoros Congo Congo, the Democratic Republic of the Cook Islands Costa Rica Cote d’Ivoire Croatia Cuba Curaçao Cyprus Czech Republic Denmark Djibouti Dominica Dominican Republic Ecuador Egypt El Salvador Equatorial Guinea Eritrea Estonia Ethiopia Falkland Islands (Malvinas) Faroe Islands Fiji Finland France French Guiana French Polynesia French Southern Territories Gabon Gambia Georgia Germany Ghana Gibraltar Greece Greenland Grenada Guadeloupe Guatemala Guernsey Guinea Guinea-Bissau Guyana Haiti Heard Island and McDonald Islands Holy See (Vatican City State) Honduras Hungary Iceland India Indonesia Iran, Islamic Republic of Iraq Ireland Isle of Man Israel Italy Jamaica Japan Jersey Jordan Kazakhstan Kenya Kiribati Korea, Democratic People’s Republic of Korea, Republic of Kuwait Kyrgyzstan Lao People’s Democratic Republic Latvia Lebanon Lesotho Liberia Libyan Arab Jamahiriya Liechtenstein Lithuania Luxembourg Macao Macedonia, the former Yugoslav Republic of Madagascar Malawi Malaysia Maldives Mali Malta Martinique Mauritania Mauritius Mayotte Mexico Moldova, Republic of Monaco Mongolia Montenegro Montserrat Morocco Mozambique Myanmar Namibia Nauru Nepal Netherlands New Caledonia New Zealand Nicaragua Niger Nigeria Niue Norfolk Island Norway Oman Pakistan Palestine Panama Papua New Guinea Paraguay Peru Philippines Pitcairn Poland Portugal Qatar Reunion Romania Russian Federation Rwanda Saint Barthélemy Saint Helena, Ascension and Tristan da Cunha Saint Kitts and Nevis Saint Lucia Saint Martin (French part) Saint Pierre and Miquelon Saint Vincent and the Grenadines Samoa San Marino Sao Tome and Principe Saudi Arabia Senegal Serbia Seychelles Sierra Leone Singapore Sint Maarten (Dutch part) Slovakia Slovenia Solomon Islands Somalia South Africa South Georgia and the South Sandwich Islands South Sudan Spain Sri Lanka Sudan Suriname Svalbard and Jan Mayen Swaziland Sweden Switzerland Syrian Arab Republic Taiwan Tajikistan Tanzania, United Republic of Thailand Timor-Leste Togo Tokelau Tonga Trinidad and Tobago Tunisia Turkey Turkmenistan Turks and Caicos Islands Tuvalu Uganda Ukraine United Arab Emirates United Kingdom United States Uruguay Uzbekistan Vanuatu Venezuela, Bolivarian Republic of Vietnam Virgin Islands, British Wallis and Futuna Western Sahara Yemen Zambia Zimbabwe Email read more