Sterrekunde

Is kosmiese straal-sterrekunde iets?

Is kosmiese straal-sterrekunde iets?


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Histories was die sterrekunde die sigbare lig, kyk na voorwerpe in die sigbare spektrum en neem later foto's in die sigbare spektrum.

In die afgelope eeu was radiosterrekunde, infrarooi sterrekunde en die ondersoek na ander bande in die elektromagnetiese spektrum haalbaar.

In die afgelope dekade kon ons neutrino-sterrekunde begin doen en die afstand van neutrino-bronne identifiseer.

Is daar enige rede dat dit nie na ander deeltjies kan vorder nie, I.E. algemene kosmiese straalsterrekunde?

'N Gespesialiseerde teleskoop (dit moet in 'n satelliet wees) kan oorweeg word wat slegs muone opspoor en beelde vorm van muonopsporing, of miskien 'n protonteleskoop. Die idee is om inkomende deeltjies op pixels in 'n beeld te karteer en 'n helderheid toe te ken afhangende van die deeltjiesfrekwensie.


Ja, kosmiese straal-sterrekunde is iets, en dit was al 'n rukkie.

Meer algemeen is daar multi-boodskapper sterrekunde aangesien daar nou verskeie vensters is waardeur ons die heelal kan waarneem deur direkte waarneming:

  1. elektromagnetiese (dws ligstrale, fotone)
  2. neutrino
  3. kosmiese strale (dws hoë-energie protone en atoomkerne wat teen relativistiese snelhede beweeg)
  4. gravitasiestraling

Natuurlik het ons eers teleskope gebou om lig waar te neem. Galileo het 'n optiese teleskoop gebruik en dit was baie vrugbaar vir hom, en dit het van daar af opgestyg. Lensvervaardiging het 'n kuns geword wat intiem gekoppel was aan die vordering van sterrekunde tot in die 20ste eeu, waar die ontdekking van kwantummeganika die wêreld van deeltjiefisika oopgemaak het. Neutrino's afkomstig van kernreaksies in die son, prosesse elders in die melkweg en in ander sterrestelsels kom by die aarde aan en word al sedert die 1960's opgespoor (hoewel 'n groot fraksie ekstra-galaktiese neutrino's in supernovas gegenereer word, is dit interessant om daarop te let dat geoneutrino's afkomstig is van die verval van radionukliede in die binneland van die aarde, wat gehelp het om die radiogeniese teorie van die verhitting van die aarde te bevestig).

In die afgelope dekade kon ons neutrino-sterrekunde begin doen en die afstand van neutrino-bronne identifiseer. Is daar enige rede dat dit nie na ander deeltjies kan vorder nie, I.E. algemene kosmiese straal-sterrekunde?

Daar is talle verklikkers regoor die wêreld wat ontwerp is om kosmiese strale op te spoor. Daar is direkte (met inbegrip van ballonne of satelliete in die atmosfeer wat metings maak) en indirekte (waarby grondgebaseerde detektore op soek is na die stort van deeltjies wat deur die verval van kosmiese strale in die atmosfeer stroom of soek na fotone wat uit die kaskade geskep word, beweeg deur die atmosfeer) opsporingsmetodes. Ek veralgemeen, daar is ander metodes en dit is 'n aktiewe navorsingsgebied (soos Benny baie voorbeelde in hul opmerking genoem het).

Muons is byvoorbeeld oorspronklik in kosmiese strale ontdek kort nadat antimaterie ontdek is. Muon-detektors is van baie soorte (dit wil sê Cherenkov-stralingswatertenk-detektor) en kan vir allerlei interessante doeleindes gebruik word. Om byvoorbeeld die binnekant van piramides en vulkane te ondersoek sonder dat mense seerkry.

Die onlangse direkte opsporing van swaartekragstraling deur die LIGO / Maagd-samewerking onthul dat dele van die heelal wat ons voorheen gedink het dat ons afgesluit is van waarneming, nou sigbaar is (of moontlik binnekort sal wees), byvoorbeeld in die vroeë heelal voor die kosmiese-mikrogolf-agtergrondstraling, en die binnekant van kompakte voorwerpe soos wit dwerge en neutronsterre.

Daar kan ook ander onontdekte vensters in die heelal wees, byvoorbeeld as daar 'n 'donker krag' is en dus 'n 'donker foton' wat verband hou met donker materie, maar dit is spekulatief. Oor die algemeen het ons redes nodig om te vermoed dat daar iets bestaan ​​voordat ons detektore maak om dit te sien, maar die vroeë voël kan die wurm kry, of soms nie (soos Joseph Weber !!).

Voor die koms van groot deeltjieversnellers, oftewel 1950's, het deeltjiefisici op kosmiese straalwaarnemings staatgemaak. Hierdie groot versnellers, soos by Fermilab of die LHC, is gebou om deeltjies te ontdek, en hulle het uiteenlopende sukses behaal wat ook gehelp het met die ontwikkeling van moderne kosmiese straalopsporings wat u as 'algemene kosmiese straalteleskope' sou kon beskou.


Observatory ontdek 'n dosyn PeVatrons en fotone wat meer as 1 PeV is, begin die gamma-sterrekunde-era met 'n baie hoë energie

Lugfoto van LHAASO. Krediet: IHEP

In China se Large High Altitude Air Shower Observatory (LHAASO) - een van die belangrikste nasionale wetenskaplike en tegnologiese infrastruktuurfasiliteite in die land - is 'n dosyn kosmiese versnellers met ultra-hoë energie (UHE) in die Melkweg gevind. Dit het ook fotone opgespoor met energie wat meer is as 1 peta-elektronvolt (kwadriljoen elektronvolt of PeV), insluitend een teen 1,4 PeV. Laasgenoemde is die hoogste energie-foton wat nog ooit waargeneem is.

Hierdie bevindings omverwerp die tradisionele begrip van die Melkweg en open 'n era van UHE-gamma-sterrekunde. Hierdie waarnemings sal mense aanspoor om weer te dink oor die meganisme waardeur hoë-energie deeltjies in die Melkweg gegenereer en vermeerder word, en sal mense aanmoedig om dieper gewelddadige hemelse verskynsels en hul fisiese prosesse te ondersoek, asook om basiese fisiese wette onder uiterste toestande te toets.

Hierdie ontdekkings is in die tydskrif gepubliseer Aard op 17 Mei. Die LHAASO International Collaboration, wat gelei word deur die Institute of High Energy Physics (IHEP) van die Chinese Akademie vir Wetenskappe, het hierdie studie voltooi.

Die LHAASO-sterrewag is nog in aanbou. Die kosmiese versnellers - bekend as PeVatrons omdat hulle deeltjies na die PeV-reeks versnel - en PeV-fotone is ontdek met behulp van die eerste helfte van die opsporingsreeks, wat aan die einde van 2019 voltooi is en in 2020 11 maande lank bedryf word.

Fotone met energie wat meer is as 1 PeV is in 'n baie aktiewe stervormende streek in die sterrebeeld Cygnus bespeur. LHAASO het ook 12 stabiele gammastraalbronne opgespoor met energie tot ongeveer 1 PeV en die betekenis van die foton dui op sewe standaardafwykings wat groter is as die omliggende agtergrond. Hierdie bronne is geleë op posisies in ons sterrestelsel wat met 'n akkuraatheid beter as 0,3 ° gemeet kan word. Dit is die helderste gammastraalbronne van die Melkweg in die gesigsveld van LHAASO.

Alhoewel die opgehoopte data van die eerste 11 maande van die operasie slegs mense in staat gestel het om daardie bronne waar te neem, stuur hulle almal sogenaamde UHE-fotone uit, dit wil sê gammastrale bo 0,1 PeV. Die resultate toon dat die melkweg vol PeVatrons is, terwyl die grootste versneller op aarde (LHC by CERN) slegs deeltjies tot 0,01 PeV kan versnel. Wetenskaplikes het reeds vasgestel dat kosmiese straalversnellers in die Melkweg 'n energielimiet het. Tot dusver was die voorspelde limiet ongeveer 0,1 PeV, wat gelei het tot 'n natuurlike afsnyding van die gammastraal-spektrum daarbo.

Maar die ontdekking van LHAASO het hierdie 'limiet' verhoog, aangesien die spektra van die meeste bronne nie afgekap word nie. Hierdie bevindings begin 'n era vir astronomiese waarneming van UHE-gamma. Hulle toon aan dat nie-termiese stralingshemels, soos jong massiewe sterretrosse, supernovareste, pulsêre windnewels, ensovoorts - wat deur Cygnus-stervormende streke en die krapnevel voorgestel word - die beste kandidate is om UHE-kosmiese strale in die Melk te vind. Manier.

Deur UHE-gamma-sterrekunde kan 'n eeu-oue raaisel - die oorsprong van kosmiese strale - binnekort opgelos word. LHAASO sal wetenskaplikes aanspoor om die meganismes van hoë-energie kosmiese straalversnelling en voortplanting in die Melkweg te heroorweeg. Dit sal ook wetenskaplikes in staat stel om ekstreme astrofisiese verskynsels en hul ooreenstemmende prosesse te ondersoek, wat die basiese wette van fisika onder uiterste toestande kan ondersoek.


Sterrekunde en astrofisika vir die 1980 & # 039's, Deel 2: Verslae van die panele (1983)

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Hieronder is die ongekorrigeerde teks van die masjien gelees van hierdie hoofstuk, wat bedoel is om ons eie soekenjins en eksterne enjins uiters ryk, hoofstuk-verteenwoordigende soekbare teks van elke boek te voorsien. Aangesien dit ONGEREGREERDE materiaal is, beskou u die volgende teks as 'n nuttige, maar onvoldoende volmag vir die gesaghebbende boekeblaaie.

55 4. Ondersteuning van navorsing en ontwikkeling 'n wesenlike doelwit van die 1980 & # 039's is die ontwikkeling van kragtiger instrumentele tegnieke wat groot verbeterings in sensitiwiteit en spektrale en hoekoplossings sal behaal. Tegniese konsepte bestaan ​​reeds om hierdie doelwitte te bereik, maar dit moet uitgebrei word voordat dit gereed is vir ruimtevlug. 'N Kragtige navorsings- en ontwikkelingsprogram met ontwikkelingsvlugte op ballonne en die Shuttle is dus 'n wesenlike deel van die strategie vir gammastraalsterrekunde in die 1980 & # 039's. VI I. KOSMIEKSTRAALASTRONOMIE A. Inleiding Kosmiese strale vorm 'n supraterale gas van energiek gelaaide deeltjies wat deur die hele Melkweg versprei. Bestaande uit protone, alfa-deeltjies en ander kaal kerne van die elemente met individuele deeltjie-energieë van 106 eV tot minstens 102 ° eV, is dit die enigste voorbeeld van materie uit gebiede ver buite die sonnestelsel wat ons kan ondersoek. volledig. Elektrones met 'n hoë energie, die bron van Galaktiese sinchrotron-radiogeraas, vorm ongeveer 1 persent van die totale kosmiese straalstroom. Positrone en antiprotons wat geproduseer word in botsings van kosmiese strale met interstellêre materie, is ook waargeneem. Die astrofisiese betekenis van kosmiese strale spruit uit twee oorwegings. Enersyds dra hulle die besonderhede van hul samestelling en energiespektrum interessante en unieke inligting oor hul bronne en die gebiede waarin hulle gereis het, in, andersyds is dit 'n belangrike astrofisiese entiteit op sigself. , met 'n energiedigtheid wat vergelykbaar is met die van die Galaktiese magnetiese veld en van die onstuimige beweging van die interstellêre gas. Die druk van die kosmiese straalgas en die verhitting van die interstellêre medium beïnvloed die prosesse van stervorming en beïnvloed die struktuur en evolusie van die Melkweg. Waarnemings van kosmiese strale word gedoen met 'n wye verskeidenheid instrumente wat elkeen aangepas is vir die kenmerke van 'n bepaalde komponent en energieregime. Onder die belangrikste tegniese ontwikkelings in die afgelope jaar is instrumente wat individuele elemente en isotope kan oplos, en meet die oorvloed van die

56 uiters seldsame swaar kerne tot by uraan, waarnemende hoë-energie elektrone en positrone, en op soek na deeltjies antimaterie. Klein satelliete en ruimtesonders het klein detektors gevlieg om die eienskappe van kosmiese strale met lae energie in die sonnestelsel te ondersoek vanaf die wentelbaan van Mercurius tot buite die baan van Saturnus. Groot en swaar instrumente is op groot hoogtes tydens ballonvlugte en in die aarde om die HEAD-3-satelliet gebruik om die samestelling en spektra van kosmiese strale tot energieë van 101 te meet.

eV. Baie groot deteksies op die grond is gebruik om kosmiese strale met energie tot 1012 eV te bestudeer deur die waarneming van buie van sekondêre deeltjies wat in die atmosfeer geproduseer word. Daar word geglo dat die meeste kosmiese strale hul oorsprong het in prosesse wat verband hou met supernovas en word miljoene jare in die Melkweg beperk deur die Galaktiese magneetveld. Sommige kosmiese strale met lae energie word in die sonnestelsel geproduseer in sonfakkels, in planetêre magnetosfere en in skokgolwe in die interplanetêre medium. Die seldsame kosmiese strale met energie bo 1019 eV kom waarskynlik buite ons Melkweg. Magnetiese krag draai die bane van kosmiese strale in helieke om die lyne van die magneetveld en vernietig daardeur enige eenvoudige verband tussen die verspreiding van hul aankomsrigtings en die ligging van hul bronne. Inligting oor die bronne van kosmiese strale word dus hoofsaaklik verkry deur metings van hul samestelling en energiespektra. Die teenwoordigheid in die ultra-swaar (Z groter as 28) kosmiese strale van kerne wat slegs geproduseer kan word deur vinnige opeenvolgende absorpsie van vrye neutrone, kan aandui dat dit tydens die kernfase van 'n supernova-ontploffing gesintetiseer word. Die isotopiese samestellings van die kerne van individuele elemente soos neon, magnesium, silikon, swael en yster kan verband hou met die temperatuur, digtheid en vermenging tydens nukleosintese. - Die bestaan ​​van 'n wesenlike verskil tussen die samestellings van kosmiese strale met energie onder en onder die kritieke waarde naby 1017 eV vir magnetiese bevalling in die Melkweg, sou die hipotese ondersteun dat kosmiese strale van baie hoë energie 'n ander, en waarskynlik buitegalaktiese, het. , oorsprong. Die ondubbelsinnige opsporing van enige kerne van antimaterie met Z wat groter is as eenheid, sou oortuigend wees vir die bestaan ​​van sterre van antimaterie en het diepgaande implikasies vir die ontstaan ​​van die heelal en die aard van die fundamentele kragte.

57 Sonfakkels en planetêre magnetosfere is bronne van uiters veranderlike vloed van kosmiese strale met lae energie binne die sonnestelsel. Metings van hul elementêre en isotopiese oorvloed gee direkte inligting oor die samestelling van materiaal in ander liggame in ons sonnestelsel en oor die aard van die versnellingsmeganismes. Laaide deeltjies word versnel deur elektriese velde wat veroorsaak word deur veranderende magnetiese velde. Laasgenoemde word op hul beurt veroorsaak deur kollektiewe bewegings van plasma of ander geleiers, soos roterende sterre en planete, waarin die huidige bronne van die magneetveld geleë is. Die noodsaaklike toestand vir hierdie proses om kosmiese strale te produseer, is dat die digtheid van plasma in die versnellingsgebied laag genoeg is sodat die deeltjies vinniger energie kry uit die geïnduseerde elektriese veld as wat hulle dit verloor tydens botsings. Hierdie toestand kom blykbaar dwarsdeur die heelal onder verskillende omstandighede voor. Baie bespreekde gevalle is die buitenste lae van 'n ontploffende supernova-oorblyfsel en interstellêre skokgolwe. Inligting oor die versnellingsmeganismes kan verkry word uit metings van die energiespektrum van individuele komponente van kosmiese strale. Spesiaal belangrik is die reeks bokant 1011 eV / nukleon waarin die spektra wat op die aarde waargeneem word, nie merkbaar verdraai word deur die effekte van die sonwind nie en die relatiewe oorvloed blykbaar baie min verander deur interaksies met interstellêre materie. Meer spesifieke inligting kan verkry word uit metings van die isotopiese samestelling. Die gemiddelde tyd tussen die nukleosintese van kosmiese straalkerne en hul versnelling tot relatiwistiese energieë kan byvoorbeeld afgelei word van metings van die oorvloed radioaktiewe nukliede wat verval deur K-elektronopvang. Slegs die nukliede is aanwesig wat deur Coulomb-botsings versnel en van hul K-elektrone gestroop is voordat dit verval het. Kosmiese strale is interaksie met interstellêre materie, met die magnetiese veld wat hul bewegings beheer, en met fotone van sterlig en die mikrogolfagtergrond. Die gemiddelde dikte, of padlengte, van die materie wat deurkruis word voordat dit uit die Melkweg ontsnap, word bepaal aan die hand van metings van die relatiewe oorvloed van die sekondêre kosmiese strale wat in hierdie interaksies geproduseer word, soos die kerne wat geproduseer word deur fragmentasie van swaarder kerne in botsings met interstellêre saak. As 'n mens ook die gemiddelde insluitingstyd bepaal, byvoorbeeld deur die hoeveelhede van verskillende radioaktiewe isotope te meet,

58 kan 'n mens die gemiddelde digtheid van die materie vind in die streke wat deur kosmiese strale deurkruis word. Kosmiese stralingselektrone met energieë bo 1013 eV, wat langs magnetiese veldlyne in die Galaktiese skyf spiraal, verloor die grootste deel van hul energie binne enkele honderd parsek as gevolg van synchrotron-emissie en omgekeerde Compton-verspreiding met die agtergrondstraling van die mikrogolfoond. Die vorm van die energiespektrum van elektrone in hierdie energiebereik is dus 'n sensitiewe aanduiding van die verspreiding in afstand van die bronne van kosmiese straalelektrone. Soortgelyke oorwegings is van toepassing op die interpretasie van die energiespektrum van kosmiese straalkern bo die drempel vir fotodisintegrasie deur botsings met fotone van die mikrogolfagtergrond. m is drempel is naby 1019 eV. Alhoewel kosmiese straalkerne met energie bo hierdie dorspunt ongetwyfeld hul oorsprong het buite die Melkweg, is hul gemiddelde vrye pad voor fotodisintegrasie kort vergeleke met die Hubble-afstand, sodat die vorm van hul spektrum beïnvloed moet word deur die ruimtelike verspreiding van hul bronne. Interstellêre materie word geïoniseer en verhit deur kosmiese strale wat energie verloor deur Coulomb-botsings. Dit kan beduidende effekte hê op die evolusie van molekulêre wolke en stervorming. Die belangrikheid van hierdie effek hang krities af van die stroom van Galaktiese kosmiese strale teen baie lae energie. Hierdie vloed is nog onbekend, omdat kosmiese strale met lae energie uit die sonnestelsel gevee word deur die sonmagnetiese veld wat met die sonwind na buite beweeg. 'N Direkte meting kan slegs gedoen word deur 'n diep ruimtesonde wat die sonholte verlaat. B. Vordering gedurende die 1970 & # 039's 1. Instrumentasie en voertuie. Gedurende die 1970's was balloneksperimente die belangrikste en byna eksklusiewe bron van nuwe inligting oor die samestelling en energiespektrum van Galaktiese kosmiese strale by energiee bo 1 GeV per nukleon. By laer energie kan die opname en produksie van sekondêre in die aarde se atmosfeer die bruikbaarheid van ballonwaarnemings beperk. Balloneksperimente het ook 'n wesenlike rol gespeel in die ontwikkeling van instrumentasie vir daaropvolgende waarnemings vanuit ruimtevoertuie. Aansienlike vordering is gemaak met die vergroting van die vermoëns van ballonvoertuie ten opsigte daarvan

59 tot betroubaarheid en # 039 vragte, en duur en om die kwaliteit van ondersteuningsfasiliteite en dataherstel te verbeter. Gewone vlugte het ongeveer 1 dag laai vragte van 1000 of 2000 kg na hoogtes bo 40 km vervoer. Ruimte-eksperimente het die omvang van kosmiese straalmetings uitgebrei tot laer energieë en het data van 'n presisie opgelewer wat slegs deur statistieke getel is. Die interplanetêre moniteringsplatform (IMP) -5, -6, -7 en -8, die Orbitale geofisiese sterrewag (OGO) -5 en -6 en die International Sun Earth Explorer (ISEE) -1 en -3 het instrumente buite die aarde gedra & # 039s magnetosfeer om die elementêre en isotopiese samestelling en die energiespektrum van lae-energie (E minder as 109 eV / nukleon) kosmiese strale van Galaktiese en sonnestelselbronne te meet. Instrumente op sonsatelliete en diep ruimtesondes, wat Pioneer-10 en -11, Mariner-10, Helios-1 en -2 en Voyager-1 en -2 insluit, het die samestelling en spektra van kosmiese strale oor 'n wye reeks gemeet. van heliosentriese afstande en die deeltjiepopulasies en versnellingsverskynsels in die magnetosfere van Jupiter en Saturnus ondervra. Skylab het aan die begin van die dekade plastiese spoorsnyers in die Aarde-baan gedra om die samestelling van die seldsame ultra-swaar kerne te meet. Aan die einde van die dekade is die derde van die hoë-energie astronomiese sterrewag, HEAD-3, met swaar instrumente gelanseer om die gemiddelde isotopiese samestelling van die kosmiese straalkerne tot by yster en die elementêre samestelling buite yster te meet. Soortgelyke metings is onderneem met die Britse Explorer-satelliet, Ariel VI. In verskeie lande is groot lugstortdetektore op die grond bedien om die energiespektrum, rigting en samestelling van die baie seldsame kosmiese strale in die gebied bokant 1017 eV te meet, waar 'n oorgang van Galaktiese na ekstragalaktiese bronne kan plaasvind. Nuwe benaderings tot die meting van ultra-hoë-energie kosmiese strale is geneem om die & quotFly & # 039s Eye & quot detector te ontwikkel, wat ontwerp is om die fluoresserende lig wat op die baan van 'n lugstort in die atmosfeer uitgestraal word, op te neem, en die Homestake-myninstallasie, wat opspoor hoë-energie muone wat geproduseer word deur interaksies van primêre kosmiese straalkerne met lugatome naby die top van die atmosfeer.

60 2. Wetenskaplike prestasies a. Elementêre samestelling en energiespektra (Z tot en met 28): Nauwkeurige metings van die elementêre samestelling is gemaak tot energieë van ongeveer 10 GeV / nukleon, en verkennende samestellingsmetings is uitgevoer tot ongeveer 100 GeV / nukleon. Hierdie metings het gelei tot die ontdekking dat die elementêre samestelling van kosmiese strale opvallend soortgelyk is aan die materiaal van die sonnestelsel. Aan die ander kant is daar verskeie kenmerkende afwykings van die sonnestelsel-oorvloed gevind, en hierdie afwykings het tot hierdie belangrike gevolgtrekkings gelei: (i) Die oorvloed van die sekondêre kosmiese strale rondom 1 GeV / nukleon impliseer 'n gemiddelde padlengte in interstellêre materie van 7 g / cm voor ontsnap uit die Melkweg. (ii) Die gemiddelde padlengte, en miskien die insluitingstyd, neem af met toenemende energie. Ongeveer 100 GeV / nucleon kan die gemiddelde padlengte so klein soos l g / cm2 wees, 'n verrassendste resultaat waarvan die interpretasie tans 'n onderwerp van intense studie is. (iii) Swaar elemente kom relatief meer voor in kosmiese strale as in die sonnestelsel, moontlik as gevolg van die groter gemak waarmee hoë atome voor die versnelling geïoniseer kan word. 'N & quotanomale komponent & quot van kosmiese strale met baie lae energieë van ongeveer 10 MeV / nukleon of minder is ontdek. Die waarskynlikste oorsprong daarvan is neutrale atome van interstellêre materie, gefotografeer in die omgewing van die son en versnel deur magnetohydrodinamiese onstuimigheid in die sonholte. Die samestelling van kosmiese strale bo 1012 eV is in wese onbekend. Die metings van die energiespektrum is egter uitgebrei tot ongeveer 1012 eV. Bo 3 X 10 eV begin die spektrum vinniger afval, moontlik as gevolg van 'n hoër lekkasie uit die Melkweg. Bo 1019 eV draai hierdie tendens om, en daar is blykbaar 'n klein, maar beduidende anisotropie in die verspreiding van aankomsrigting. Dit is waarskynlik dat die oorsprong van die deeltjies bo 1019 ekstra-galakties is, maar die aard en ligging van hul bronne is onbekend. b. Ultraheavy Nuclei met Z Groter as 28 Voor 1979 was daar slegs baie beperkte data beskikbaar oor die uiters skaars ultraheavy nuclei. Die situasie het verander nadat HEAD-3 en Ariel VI van stapel gestuur is. Die in-

61 strumente aan boord van hierdie ruimtetuig kon vir die eerste keer die meer oorvloedige elemente met kernlading tot by die aktinide-elemente oplos. Die voorlopige gegewens was onvoldoende om vas te stel of daar 'n oorvloed van swaar herwerkingselemente soos platinum en die aktiniede bestaan, soos verwag word vir supernovamateriaal. In die omgewing van laer kernladings (Z tot 40) word die elementêre samestelling duidelik nie oorheers deur die produkte van die herverwerkende nukleosintese nie, en die verskil tussen kosmiese straal- en sonnestelsel-oorvloed is ongeveer gekorreleer met die waardes van die eerste ionisasiepotensiale. c. Isotopiese samestelling Onlangse ondersoeke na kosmiese strale met lae energie-energie het individuele isotope van die elemente van waterstof tot yster opgelos en het inligting opgelewer wat nie uit metings van elementêre oorvloed alleen afgelei kan word nie. Die neutronryke isotope van neon, magnesium en silikon is byvoorbeeld aansienlik oorvloedig in vergelyking met materiaal in die sonnestelsel. Dit is 'n duidelike bewys dat kosmiese straalstof 'n nukleosintetiese geskiedenis het wat verskil van dié van sonnestelselmateriaal. Nog 'n voorbeeld is die lae voorkoms van die radioaktiewe isotoop 1OBe (halfleeftyd = 1-5 X 106 jaar) rondom 200 MeV / nukleon, wat impliseer dat die kosmiese straaltydperk ongeveer 10 jaar is, baie langer as wat voorheen aanvaar is. Dit en die bekende gemiddelde padlengte impliseer dat kosmiese strale beperk word in streke met lae digtheid van die interstellêre ruimte (met ongeveer 0,2 atoom / cm3) of miskien die galaktiese stralekrans. d. Kosmiese stralingselektrone en positrone Die waarnemings van kosmiese stralingselektrone en posisies lei tot die volgende gevolgtrekkings: (i) Die energiespektrum van elektrone bo ongeveer 30 GeV is steiler as dié van alle kosmiese straalkerne. As ons hierdie effek toeskryf aan die invloed van Compton- en synchrotronenergieverliese in die interstellêre ruimte, is die insluitingstyd van kosmiese stralingselektrone in die Melkweg van 107 jaar, in ooreenstemming met die insluitingstyd van kosmiese straalkern afkomstig van die metings van 1OBe. (ii) In die energiebereik 1-30 GeV het positrone 'n intensiteit wat baie kleiner is as dié van negatiewe elektrone. Aangesien positrone en negatiewe elektrone in byna gelyke getalle geproduseer word as gevolg van hoë-energie inter

62 waarnemings van kosmiese straalkerne met interstellêre materie, wys hierdie waarneming dat slegs 'n klein fraksie van die kosmiese straalelektrone ontstaan ​​uit sulke interaksies. (iii) Elektrone wat naby die aarde waargeneem word met lae energieë (minder as 50 MeV), bevat nie net deeltjies van intersterre en sonkrag nie, maar ook, en miskien meestal, deeltjies wat in die magnetosfeer van Jupiter ontstaan. Wetenskaplike doelwitte vir die 1980 & # 039s-navorsing oor kosmiese strale het die stadium bereik waar dit nou moontlik is om definitiewe metings te maak wat verband hou met die oorsprong van kosmiese strale en die wisselwerking tussen kosmiese strale, interstellêre materie en velde. Die volgende waarnemings is die belangrikste doelwitte van die 1980 & # 039's. 1. Isotopiese samestelling van waterstof deur nikkel 'n Gedetailleerde vergelyking van die oorvloed kosmiese straal-isotope met die oorvloed van die sonnestelsel, bied kritiese inligting oor die nukleosintetiese geskiedenis van die materiaal wat kosmiese strale word, en, ter vergelyking, 'n nuwe perspektief op die oorsprong van die sonnestelsel. Veral belangrik is die oorvloed van die neutronryke isotope van neon, magnesium, silikon, swael, yster en nikkel, wat almal sensitief is vir omstandighede in die beginfase van 'n supernova-ontploffing. Inligting oor die galaktiese insluitingstyd van kosmiese strale kan verkry word uit metings van die relatiewe oorvloed radioaktiewe isotope. Dit is belangrik dat die oorvloed van 'n wye verskeidenheid isotope ondersoek word om te besluit of alle kosmiese straalspesies dieselfde voortplantingsgeskiedenis ervaar. Die metings moet 'n groot energiebereik dek wat ooreenstem met 'n wye verskeidenheid relativistiese tydverwidings. 2. Elementêre samestelling van die ultra-swaar kern Die elementêre samestelling in die aantal atoomgetalle bo Z = 26 gee leidrade vir die prosesse van nukleosintese en versnelling van kosmiese strale. Presiese oorvloedmetings moet gemaak word van individuele elemente, insluitend die seldsame onewe elemente. Nog meer waardevol

63 inligting kan afgelei word van metings van hul isotopiese oorvloed, maar die tegniese probleme van sulke metings is erg. Die relatiewe oorvloed van interstellêre sekondêre ultra-swaar kerne (Z-waardes in die reekse 41-49 en 67-75) bied 'n besonder sensitiewe maatstaf vir die verspreiding van die padlengte van kosmiese strale op kort padlengtes, aangesien hul interaksie-dwarsdeursnee baie groter is as dié van die ligter kosmiese strale. Die radioaktiewe aktiniedelemente is potensieel nuttig as chronometers om die tyd wat verloop het sedert hul nukleosintese te bereken. 3. Elementêre samestelling by hoë energieë Die samestelling en die individuele energiespektra van die belangrikste kosmiese straalkomponente moet in direkte metings tot energieë van ten minste 104 GeV / nukleon bepaal word. Soos hierbo opgemerk, is die gemiddelde padlengte van kosmiese straalkerne by hierdie hoë energieë waarskynlik minder as 1 g / cm2. Dus is oorvloedveranderings as gevolg van interstellêre spallasie byna weglaatbaar, en die metings lewer direkte inligting oor die elementêre samestelling op die versnellingsterrein. Hierdie metings sal ook onthul hoe die gemiddelde padlengte van energie afhang en sodoende nuwe lig werp op die beperking van kosmiese strale in die Melkweg. Die reeks direkte metings moet die ultra-hoë-energie-reeks lugmetings oorvleuel om 'n effektiewe kruiskalibrasie van die meettegnieke te bewerkstellig. 4. Energiespektrum van elektrone by hoë energieë Die energiespektrum van kosmiese straalelektrone moet tot ten minste 104 GeV gemeet word. Sulke metings sal inligting verskaf oor die moontlike bestaan ​​van kosmiese straalbronne nader aan ongeveer 1 kiloparsek. Hulle sal ook meer presiese inligting oplewer oor die insluitingstyd van Galaktiese kosmiese stralingselektrone. Meting van die positron-spektrum is van besondere belang omdat die inset-spektrum van positrone bereken kan word uit kennis van die interstellêre kernbotsings waarin dit ontstaan. Tans beskikbare positron-data dek nog nie die energiestreek bo 30 GeV nie, waar stralingsenergieverliese beduidend is.

64 5. Die samestelling en oorsprong van kosmiese strale met ultra-hoë energie Die oorsprong van kosmiese straaldeeltjies met energie bo 1018 eV bly 'n sentrale probleem van hoë-energie astrofisika wat slegs benader kan word deur die opsporing en analise van die baie groot storte wat sulke deeltjies in die atmosfeer produseer. Beter kennis van stortontwikkeling en akkurate kalibrasies van detektore is nodig om die betroubaarheid waarmee die energie en samestelling van die ultra-hoë-energie primêre afgelei word, uit waarnemings van storte te verbeter. Jare se blootstellingstyd met detektore van die grootste bereikbare effektiewe versamelareas is nodig om voldoende statistiese akkuraatheid in die meting van die spektrum en die verspreiding in aankomingsrigtings te verkry. 6. Kosmiese strale met lae energie (& lt300 MeV / kern) in die interstellêre ruimte Die bydrae van kosmiese strale met lae energie tot die verhitting van die interstellêre gas en die effekte wat dit op die struktuur van die Melkweg het, moet bestudeer word deur metings buite die heliosfeer. Direkte metings kan slegs gedoen word met 'n diep ruimtesonde wat die sonnestelsel verlaat. 7. Kosmiese strale van die sonnestelsel Metings van energieke deeltjies wat in die sonnestelsel ontstaan, is van fundamentele belang in die poging om 'n beter begrip te kry van die prosesse van deeltjieversnelling en voortplanting in minder toeganklike streke van die kosmos. Sulke metings kan ook subtiele verskille in die isotopiese samestelling tussen kosmiese sonstrale en aardse materiaal openbaar en sodoende nuwe lig werp op die oorsprong en geskiedenis van die sonnestelsel. Om duidelik te kan onderskei tussen tydelike en ruimtelike variasies, moet die metings gelyktydig op verskillende plekke in die sonnestelsel en oor verskillende sonsiklusse gedoen word.

65 D. Inventory of Present or Approved Resources 1. Small Satellites and Space Probes Several spacecraft or deep-space probes with small cosmic-ray detectors aboard are expected to remain active into the 1980's. Detectors on ISEE-1 and -3 will con- tinue to measure the low-energy elemental composition and low-energy electrons in interplanetary space and provide the isotopic composition of the more abundant nuclides. Detectors on the deep-space probes Pioneer-10 and -11, and Voyager-1 and -2 will measure Galactic, solar, and planetary cosmic rays at very large distances from the Sun, and thereby probe the particle population and the solar modulation mechanisms in regions not pre- viously explored. During the next decade, these missions will reach distances out to 30 astronomical units (AU). The International Solar Polar Mission (ISPM), as originally approved, would be the first spacecraft to carry cosmic-ray and energetic-particle detectors far outside the ecliptic plane and over the poles of the Sun. It would thus explore fluxes and composition of particles from interstellar space and from the Sun in those parts of the solar system where no direct measure- ments could ever before be made. 2. Large Spacecraft HEAD-3 carried two large cosmic-ray detectors to measure the elemental composition of the more abundant ultraheavy cosmic rays and to measure the mean mass, i.e., the iso- topic mix of the elements around a few GeV/nucleon. This mission ceased operation in 1981. 3. Space Shuttle m e Space Shuttle can carry very large and heavy detec- tors. Unfortunately, the exposure times will be limited initially to only about 1 week. Nonetheless, experiments approved for Spacelab flights in the early 1980's will address key questions of cosmic-ray astrophysics. They will extend measurements of the elemental composition and energy spectra of the more abundant cosmic-ray species into the TeV/nucleon range, and they will provide informa- tion on the interactions of high-energy heavy nuclei at

66 energies far above those currently attainable at accel Orators. 4. Balloons High-altitude balloons have been important vehicles for cosmic-ray measurements and will continue to be vitally important to development of the field. The balloon pro- gram is, however, severely underfunded. Its full poten- tial could be realized with an increase in funds in amounts that are small compared with the costs of space missions. 5. Air-Shower Detectors Ground-based observations of the extremely energetic cos- mic radiation will be pursued at several installations. In particular, the first phases of the Fly's Eye project is nearly completed and will provide pioneering data during the next few years. E. Recommendations for the 1980's Broad progress in cosmic-ray astronomy requires a wide variety of observations. Of central importance to the field in the 1980's are long exposures of large instru- ments in near-Earth orbit and high-sensitivity isotopic composition measurements on spacecraft beyond the inter- ference of the Earth's magnetosphere. Experiments on cur- rently active satellites and space probes should be fully utilized, and future planetary missions should be equipped with appropriate particle detectors. Instrumentation development and exploratory measurements on balloon vehi- cles must be continued. Progress at the highest energies requires the further development of air-shower installations. 1. The Cosmic-RaY Platform Definitive measurements in several important areas of cosmic-ray astronomy require exposures of massive (1000- 5000 kg) detectors with large collection areas (1-30 m2 sr) in Earth orbit for periods of at least 1 year. Such

67 instruments can be developed and tested and will yield important preliminary results in Spacelab flights. How- ever, the long exposures required for definitive measure- ments could be provided by a relatively simple Cosmic-Ray Platform (CRP) that is launched, maintained, and refur- bished by the Shuttle Transportation System. The CRP does not need accurate celestial pointing. It should be able to carry one or two instruments and should be usable in either near-equatorial or high-inclination orbits. In typical missions, each individual instrument will be developed and supported by a group of invest) gators and institutions. Launch opportunities should exist at 1- to 2-year intervals, starting in the mid-1980's. The following investigations promise the most impor- tant scientific returns and should therefore be given highest priority: (a) Measurements of the composition of cosmic rays up to very high energies (104-105 GeV/nucleon). (b) Detailed composition measurements of ultraheavy cosmic rays, with resolution of individual elements and, perhaps, isotopes. (c) Precise measurements of the isotopic composition from hydrogen to iron at energies up to several GeV/nucleon. The experimental techniques to perform these measure- ments are currently available. In several cases, they have been verified on balloons or on HEA0-3 or are under development for Spacelab flights. 2. Missions outside the Magnetosphere We recommend that an Advanced Interplanetary Explorer be launched in the mid-1980's and that opportunities be made available to fly cosmic-ray instruments on this and other interplanetary spacecraft. Such spacecraft provide long- term (about 3 years) exposures outside the magnetosphere for detectors of modest size and cost. Highest priority should be given to detailed measurements of the isotopic composition of cosmic rays at low energies (1 GeV/nucleon) and of solar-flare-accelerated particles. Other scien- tific objectives include measurement of the elemental composition at low energies, detailed studies of the anomalous component, and investigations of particles of interplanetary origin. Simultaneous measurements at different locations in the heliosphere and over a long period of time are necessary. These measurements will

68 require detectors with geometrical factors of about 100 cm2 sr (1 to 2 orders of magnitude larger than previous instruments) and good mass resolution (0.2 AMU) over the energy region from well below 1 MeV/nucleon to 1000 MeV/nucleon. The appropriate technology is at hand, and the expected scientific return is large. 3. Deep-Space Missions The study of the low-energy interstellar cosmic rays requires the operation of detectors outside the solar system to avoid the perturbing effects of the solar wind. During the 1980's Pioneer-10 will be beyond 20 AU from the Sun, Pioneer-ll will have passed Saturn, and the Voyagers will be traveling between 10 AU and 30 AU. The ISPM probes will be passing over both polar regions of the Sun at distances somewhat over 1 AU. In order to realize the astronomy objectives of these investigations, it is vital that collection of data from these missions by the Deep Space Network continue through 1990. Fur- thermore, in order to distinguish temporal from spatial variations, simultaneous measurements are needed near 1 AU. Opportunities for deep-space observations on future outer planetary missions should be utilized in order to enhance the probability that a properly functioning spacecraft will eventually leave the region of solar modulation, even though the time required for the journey significantly exceeds nominal mission and spacecraft design lifetimes. 4. Balloons High-altitude balloons have been exceedingly successful carriers of cosmic-ray instrumentation in the past, and they will continue to be important in the 1980's. They provide the means to develop and optimize innovative experimental approaches at relatively low cost and with rapid turnaround. Techniques to fly heavy payloads for weeks or months have been proposed. Their development should be supported along with the conventional balloon program. It is extremely important that adequate suppor be made available not only for the development of new instrumentation techniques but also for a broad range of basic experimental and theoretical studies.


Is Cosmic Ray Astronomy a thing? - Sterrekunde

Bruno Rossi is considered one of the fathers of modern physics, being also a pioneer in virtually every aspect of what is today called high-energy astrophysics. At the beginning of 1930s he was the pioneer of cosmic ray research in Italy, and, as one of the leading actors in the study of the nature and behavior of the cosmic radiation, he witnessed the birth of particle physics and was one of the main investigators in this fields for many years. While cosmic ray physics moved more and more towards astrophysics, Rossi continued to be one of the inspirers of this line of research. When outer space became a reality, he did not hesitate to leap into this new scientific dimension. Rossi's intuition on the importance of exploiting new technological windows to look at the universe with new eyes, is a fundamental key to understand the profound unity which guided his scientific research path up to its culminating moments at the beginning of 1960s, when his group at MIT performed the first in situ measurements of the density, speed and direction of the solar wind at the boundary of Earth's magnetosphere, and when he promoted the search for extra-solar sources of X rays. A visionary idea which eventually led to the breakthrough experiment which discovered Scorpius X-1 in 1962, and inaugurated X-ray astronomy.


Is Cosmic Ray Astronomy a thing? - Sterrekunde

It is our great pleasure and honor to extend a warm welcome to all of you to the 38th International Cosmic Ray Conference (ICRC2023), which will be held at Osaka International Convention Center (Grand Cube Osaka) in Osaka, Japan.

The ICRC conference series has been held biennially since 1947 by Commission C4 (Astroparticle Physics) of the International Union of Pure and Applied Physics (IUPAP). The main topics covered by this conference are Cosmic Ray Physics, Gamma-Ray Astronomy, Neutrino Astronomy & Neutrino Physics, Dark Matter Physics, Solar and Heliospheric Physics, Multi-messenger Astronomy, and an additional new topic in the 2023 conference is Gravitational Wave Astronomy. ICRC2023 will provide an excellent forum for you to refresh your knowledge base and explore innovations. We hope that at the end of the conference, participants will feel that they have collected the latest information available in the field of Astroparticle Physics.

The Local Organizing Committee (LOC), the International Scientific Program Committee (ISPC), and the International Advisory Committee (IAC) are jointly organized for ICRC2023. The members of the LOC are very proud to host the ICRC2023 and look forward to welcoming you to our city and country.

Osaka was the capital of Japan in ancient times and later developed into the commercial center of Japan. Today, it is the center of economic activity in western Japan. The Osaka metropolitan area, formed by Osaka and the surrounding areas of Kyoto, Nara, and Kobe, is a wonderful place to visit. The modern and developed city, the old capital with its history and traditions, and the rich nature of the sea and mountains surrounding it will fill you with excitement and joy as you experience nature, culture, and nightlife. And best of all, Osaka is a very safe area.

Although we are currently under the severe situation of the COVID-19 pandemic, the LOC of ICRC2023 is preparing to hold the international conference in person. We are looking forward to seeing you all in Osaka in 2023!

Prof. Shoichi OGIO (Osaka City University)
Chair of the Local Organizing Committee


Abstrak

Seven years data from underground muon telescopes are analyzed for components of 24h00m, 23h56m, 23h52m, 24h04m, and 24h08m mean solar time. Repeatable daily time-count profiles are obtained for the first two periods. Their count amplitudes are respectively 0.187 and 0.098 per cent. Both components have standard errors of 0.002 per cent. The last three periods gave amplitudes less than 0.02 per cent. The 24h00m period has a sharp maximum near 16 hour local time. The 23h56m period has a broad maximum at about 0700 right ascension which is split into two peaks at 0430 RA and 0900 RA. Suggestions are outlined for future development. It is recommended that the harmonic dial representation be abandoned in favor of true celestial surveying.

The Journal publishes, from time to time, contributions by distinguished recipients of awards by The Franklin Institute. These may be original research papers, review or tutorial articles. The present author was awarded an Elliot Cresson Medal in 1963, for his pioneering achievements in the field of radio astronomy.


The existence of cosmic rays has been known for more than a century. They were first found by physicist Victor Hess. He launched high-accuracy electrometers aboard weather balloons in 1912 to measure the ionization rate of atoms (that is, how quickly and how often atoms are energized) in upper layers of Earth's atmosphere. What he discovered was that the ionization rate was much greater the higher you rise in the atmosphere — a discovery for which he later won the Nobel Prize.

This flew in the face of conventional wisdom. His first instinct on how to explain this was that some solar phenomenon was creating this effect. However, after repeating his experiments during a near solar eclipse he obtained the same results, effectively ruling out any solar origin for, Therefore, he concluded that there must be some intrinsic electric field in the atmosphere creating the observed ionization, though he could not deduce what the source of the field would be.

It was more than a decade later before physicist Robert Millikan was able to prove that the electric field in the atmosphere observed by Hess was instead a flux of photons and electrons. He called this phenomenon "cosmic rays" and they streamed through our atmosphere. He also determined that these particles weren't from Earth or the near-Earth environment, but rather came from deep space. The next challenge was to figure out what processes or objects could have been creating them.


Highest radiation observed so far

In ultra-high-energy gamma astronomy, the energy shoots past 1014 electronic volts. It is the highest electromagnetic radiation window in the universe that has ever been observed so far.

Detecting ultra-high-energy gamma rays has always been a tough task, as the amount of rays is very small and they are a part of big cosmic ray background. The observatory that made the study is situated in the mountains of the eastern Qinghai-Tibet Plateau and continuously observes cosmic rays.

Recently, an international team of scientists found methanol-ijs inside the warm part of a planet-forming disk. It’s impossible that the methanol was produced there, so it could be coming from the cold gas clouds that form stars and disks. It could be a breakthrough discovery if this process is a common phenomenon. The findings will be published in Nature Astronomy.


Is Cosmic Ray Astronomy a thing? - Sterrekunde

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LHAASO Discovers a Dozen PeVatrons and Photons Exceeding 1 PeV and Launches Ultra-high-energy Gamma Astronomy Era

China's Large High Altitude Air Shower Observatory (LHAASO)—one of the country's key national science and technology infrastructure facilities—has found a dozen ultra-high-energy (UHE) cosmic accelerators within the Milky Way. It has also detected photons with energies exceeding 1 peta-electron-volt (quadrillion electron-volts or PeV), including one at 1.4 PeV. The latter is the highest energy photon ever observed .

These findings overturn the traditional understanding of the Milky Way and open up an era of UHE gamma astronomy. These observations will prompt people to rethink the mechanism by which high-energy particles are generated and propagated in the Milky Way, and will encourage people to explore more deeply violent celestial phenomena and their physical processes as well as test basic physical laws under extreme conditions.

These discoveries are published in the journal Aard on May 17. The LHAASO International Collaboration, which is led by the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences, completed this study.

The LHAASO Observatory is still under construction. The cosmic accelerators—known as PeVatrons since they accelerate particles to the PeV range—and PeV photons were discovered using the first half of the detection array, which was finished at the end of 2019 and operated for 11 months in 2020.

Photons with energies exceeding 1 PeV were detected in a very active star-forming region in the constellation Cygnus. LHAASO also detected 12 stable gamma ray sources with energies up to about 1 PeV and significances of the photon signals seven standard deviations greater than the surrounding background. These sources are located at positions in our galaxy that can be measured with an accuracy better than 0.3°. They are the brightest Milky Way gamma ray sources in LHAASO's field of view.

Although the accumulated data from the first 11 months of operation only allowed people to observe those sources, all of them emit so-called UHE photons, i.e., gamma rays above 0.1 PeV. The results show that the Milky Way is full of PeVatrons, while the largest accelerator on Earth (LHC at CERN) can only accelerate particles to 0.01 PeV. Scientists have already determined that cosmic ray accelerators in the Milky Way have an energy limit. Until now, the predicted limit was around 0.1 PeV, thus leading to a natural cut-off of the gamma-ray spectrum above that.

But LHAASO's discovery has increased this “limit,” since the spectra of most sources are not truncated. These findings launch an era for UHE gamma astronomic observation. They show that non-thermal radiation celestials, such as young massive star clusters, supernova remnants, pulsar wind nebulas and so on—represented by Cygnus star-forming regions and the Crab nebula—are the best candidates for finding UHE cosmic rays in the Milky Way.

Through UHE gamma astronomy, a century-old mystery-—the origin of cosmic rays—may soon be solved. LHAASO will prompt scientists to rethink the mechanisms of high energy cosmic ray acceleration and propagation in the Milky Way. It will also allow scientists to explore extreme astrophysical phenomena and their corresponding processes, thus enabling examination of the basic laws of physics under extreme conditions.

Extended Materials:

LHAASO and Its Core Scientific Goals

LHAASO is a major national scientific and technological infrastructure facility focusing on cosmic ray observation and research. It is located 4,410 meters above sea level on Mt. Haizi in Daocheng County, Sichuan Province. When construction is completed in 2021, LHAASO’s particle detector arrays will comprise 5,195 electromagnetic particle detectors and 1,188 Muon detectors located in the square-kilometer complex array (KM2A), a 78,000 m 2 water Cherenkov detector array (WCDA), and 18 wide-field-of-view Cherenkov telescopes (WFCTA). Using these four detection techniques, LHAASO will be able to measure cosmic rays omnidirectionally with multiple variables simultaneously. The arrays will cover an area of about 1.36 km 2 .

LHAASO's core scientific goal is to explore the origin of high-energy cosmic rays and study related physics such as the evolution of the universe, the motion and interaction of high-energy astronomical celestials, and the nature of dark matter. LHAASO will extensively survey the universe (especially the Milky Way) for gamma ray sources. It will precisely measure their energy spectra over a broad range—from less than 1 TeV (trillion electron-volts or tera-electron-volts) to more than 1 PeV. It will also measure the components of diffused cosmic rays and their spectra at even higher energies, thus revealing the laws of the generation, acceleration and propagation of cosmic rays, as part of the exploration of new physics frontiers.

PeVatrons and PeV Photons

The signal of UHE photons around PeVatrons is so weak that just one or two photons at PeV energy can be detected using 1 km 2 of detectors per year even when focusing on the Crab Nebula, known as the “standard candle for gamma astronomy.” What's worse, those one or two photons are submerged in tens of thousands of ordinary cosmic rays. The 1,188 muon detectors in LHAASO's KM2A are designed to select photon-like signals, making LHAASO the most sensitive UHE gamma ray detector in the world. With its unprecedented sensitivity, in just 11 months, the half-sized KM2A detected one photon around 1 PeV from the Crab Nebula. In addition, KM2A found 12 similar sources in the Milky Way, all of which emit UHE photons and extend their spectra continuously into the vicinity of 1 PeV. Even more important, KM2A has detected a photon with energy of 1.4 PeV—the highest ever recorded. It is clear that LHAASO's scientific discoveries represent a milestone in identifying the origin of cosmic rays. To be specific, LHAASO's scientific breakthroughs fall into the following three areas:

1) Revealing the ubiquity of cosmic accelerators capable of accelerating particles to energies exceeding 1 PeV in the Milky Way. All the gamma ray sources that LHAASO has effectively observed radiate photons in the UHE range above 0.1 PeV, indicating that the energy of the parent particles radiating these gamma rays must exceed 1 PeV. As a matter of convention, these sources must have significances of photon signals five standard deviations greater than the surrounding background. The observed energy spectrum of these gamma rays has not truncated above 0.1 peV, demonstrating that there is no acceleration limit below PeV in the galactic accelerators.

This observation violates the prevailing theoretical model. According to current theory, cosmic rays with energies in the PeV range can produce gamma rays of 0.1 PeV by interacting with surrounding gases in the accelerating region. Detecting gamma rays with energies greater than 0.1 PeV is an important way to find and verify PeV cosmic ray sources. Since previous international mainstream detectors work below this energy level, the existence of PeV cosmic ray accelerators had not been solidly confirmed before. But now LHAASO has revealed a large number of PeV cosmic acceleration sources in the Milky Way, all of which are candidates for being UHE cosmic ray generators. This is a crucial step toward determining the origin of cosmic rays.

2) Beginning an era of “UHE gamma astronomy.” In 1989, an experimental group at the Whipple Observatory in Arizona successfully discovered the first object emitting gamma radiation above 0.1 TeV, marking the onset of the era of “very-high-energy” gamma astronomy. Over the next 30 years, more than 200 “very-high-energy” gamma ray sources were discovered. However, the first object emitting UHE gamma radiation was not detected until 2019. Surprisingly, by using a partly complete array for less than a year, LHAASO has already boosted the number of UHE gamma ray sources to 12.

With the completion of LHAASO and the continuous accumulation of data, we can anticipate to find an unexplored “UHE universe” full of surprising phenomena. It is well known that background radiation from the Big Bang is so pervasive it can absorb gamma rays with energies greater than 1 PeV. Even if gamma rays were produced beyond the Milky Way, we wouldn't be able to detect them. This makes LHAASO's observational window so special.

3) Photons with energies greater than 1 PeV were first detected from the Cygnus region and the Crab Nebula. The detection of PeV photons is a milestone in gamma astronomy. It fulfills the dream of the gamma astronomy community and has long been a strong driving force in the development of research instruments in the field. In fact, one of the main reasons for the explosion of gamma astronomy in the 1980s was the challenge of the PeV photon limit. The star-forming region in the direction of Cygnus is the brightest area in the northern territory of the Milky Way, with a large number of massive star clusters. Massive stars live only on the order of one million years, so the clusters contain enormous stars in the process of birth and death, with a complex strong shock environment. They are ideal “particle astrophysics laboratories,” i.e., places for accelerating cosmic rays.

The first PeV photons found by LHAASO were from the star-forming region of the constellation Cygnus, making this area the best candidate for exploring the origin of UHE cosmic rays. Therefore, much attention has turned to LHAASO and multi-wavelength observation of this region, which could offer a potential breakthrough in solving the “mystery of the century.”

Extensive observational studies of the Crab Nebula over the years have made the celestial body almost the only standard gamma ray source with a clear emission mechanism. Indeed, precise spectrum measurements across 22 orders of magnitude clearly reveal the signature of an electron accelerator. However, the UHE spectra measured by LHAASO, especially photons at PeV energy, seriously challenge this “standard model” of high-energy astrophysics and even the more fundamental theory of electron acceleration.

Technology Innovations

LHAASO has developed and/or improved: 1) clock synchronization technology over long distances that ensures timing synchronization accuracy to the sub-nanosecond level for each detector in the array 2) multiple parallel event trigger algorithms and their realization, with the help of high-speed front-end signal digitization, high-speed data transmission and large on-site computing clusters and advanced detection technologies include 3) silicon photo multipliers (SiPM) and 4) ultra-large photocathode micro-channel plate photomultiplier tubes (MCP-PMT). They are being employed at LHAASO on a large scale for the first time. They have greatly improved the spatial resolution of photon measurements and lowered the detection energy threshold. These features allow detectors to achieve unprecedented sensitivity in exploring the deep universe at a wide energy range. LHAASO provides an attractive experimental platform for conducting interdisciplinary research in frontier sciences such as atmosphere, high-altitude environment and space weather. It will also serve as a base for international cooperation on high-level scientific research projects.

History of Cosmic Ray Research in China

Cosmic ray research in China has experienced three stages. LHAASO represents the third generation of high-altitude cosmic ray observatories. High-altitude experiments are a means of making full use of the atmosphere as a detector medium. In this way, scientists can observe cosmic rays on the ground, where the size of the detector can be much larger than in a space-borne detector outside the atmosphere. This is the only way to observe cosmic rays at very high energy.

In 1954, China's first cosmic ray laboratory was built on Mt. Luoxue in Dongchuan, Yunnan Province, at 3,180 meters above sea level. In 1989, the Sino-Japanese cosmic ray experiment ASg was built at an altitude of 4,300 meters above sea level at Yangbajing, Tibet Autonomous Region.

In 2006, the joint Sino-Italian ARGO-YBJ experiment was built at the same site.


Neutrinos: Silent messengers

Neutrinos also rain down on Earth in staggering numbers each second. However, these odd particles, which have no electric charge and are almost massless, can pass through entire galaxies without any interaction. When scientists detect a neutrino, its path leads right back to its origin.

This proved to be a boon for astronomers, because processes that accelerate protons to the energy levels seen in cosmic rays are known to generate high-energy neutrinos. This is precisely the type of neutrino the IceCube Neutrino Observatory, located at the Amundsen-Scott South Pole Station, detected on Sept. 22, 2017.

Within minutes of detecting the particle, IceCube automatically alerted other observatories, which then focused their observations toward the region where the neutrino had come from, according to a statement from the Deutsches Elektronen-Synchrotron, a particle-accelerator research center in Hamburg, Germany.

The cascade of activity mirrors the efforts made following the gravitational-wave detection last year. A speedy alert sent from one type of observatory — in this case, a gravitational-wave detector — enabled others to follow up on the observation across a wide range of different signals. The events led to the first multimessenger observation of merging neutron stars, which provided a wealth of information about these superdense celestial objects. [Did a Neutron-Star Collision Make a Black Hole?]

In the recent discovery, electromagnetic signals from gamma rays to radio waves revealed the neutrino came from a spinning supermassive black hole at the center of a galaxy some 4 billion light-years away. It just so happens that one of the jets of high-energy particles shooting away from the black hole points directly toward Earth. Astronomers call these objects blazars, and although they are not the most powerful phenomena in the universe, they certainly have the energy to accelerate a proton to the speeds seen in cosmic rays.

"It is interesting that there was a general consensus in the astrophysics community that blazars were unlikely to be sources of cosmic rays, and here we are," IceCube lead scientist Francis Halzen, aprofessor of physics at the University of Wisconsin-Madison, said in a statement. "Now, we have identified at least one source that produces high-energy cosmic rays because it produces cosmic neutrinos."

Combining information from different messengers promises to provide scientists with even more insights in the future.

"We have not identified neutrinos in connection with gravitational-wave events, yet," Olga Botner, an astrophysicist and former spokesperson for the IceCube experiment, said during yesterday's news conference. "But we believe this is a discovery waiting for us just around the corner."


Kyk die video: Practicum Sterrenkunde (November 2022).