Physicists are quite literally in the dark about most of the universe. There is more matter in the universe than we can see—nearly 5 times more. Visible matter only accounts for a small fraction, about 4%, of the universe. The other 96% is composed of so-called dark energy (~73%) and dark matter (~23%).
Astronomers and astrophysicists have long grappled with gravity’s unexplained effects on galaxies, such as galaxy rotational velocity curves and gravitational lensing. These and other types of physical evidence have led to the search for dark matter, which has been ranked as among the most important mission goals of the Department of Energy’s High Energy Physics (HEP) program. Decades of searching have yet to yield dark matter signals. Responding to the need to expand that search, the HEP program initiated a second-generation search that both deepens and broadens the search horizon. PNNL scientists are involved in both aspects of this expanded search.
Axions and WIMPS
One dark matter candidate is the axion, a light, electrically neutral hypothetical particle. It’s at the center of the Axion Dark Matter Experiment (ADMX), which aims to convert axions into microwave photons using a strong magnet. Axions are thought to interact with matter in a way that may be detected using an axion haloscope, which is designed to convert dark matter axions to detectable microwave photons using a strong magnetic field.
Weakly interacting massive particles (WIMPs) would be detected when they bounce off a liquid or solid-state detector such as a silicon crystal. In the search for WIMPS, PNNL scientists contribute to the SuperCDMS (Cryogenic Dark Matter Search) Collaboration, an international research effort based on experiments that deploy detectors highly sensitive to ionization and phonon signals from collisions of dark matter with atomic nuclei in silicon and germanium crystals.
Wanafizikia hawajui chochote kuhusu sehemu kubwa ya ulimwengu. Kuna vitu vingi katika ulimwengu kuliko tunavyoweza kuona - karibu mara tano zaidi. Vitu vinavyoonekana vina sehemu ndogo tu ya ulimwengu, karibu asilimia nne. "Nayo sehemu nyingine 96% ni ya ""nishati nyeusi"" (~ 73%) na ""mali nyeusi"" (~ 23%)."" Wataalamu wa nyota na fizikia ya nyota wamekuwa wakijishughulisha kwa muda mrefu na athari zisizoelezeka za nguvu ya uvutano kwenye galaksi, kama vile curves za mwendo wa mzunguko wa galaksi na lensi za uvutano. "Hizi na aina nyingine za ushahidi wa kimwili zimeongoza kwenye utafutaji wa ""dutu nyeusi,"" ambayo imeorodheshwa kama moja ya malengo muhimu zaidi ya mradi wa Wizara ya Nishati ya Fisika ya Nishati ya Juu (HEP)." Miongo mingi ya utafutaji bado haijatoa ishara za vitu vyeusi. Ili kukabiliana na mahitaji ya kupanua utafutaji huo, programu ya HEP ilianzisha utafutaji wa kizazi cha pili ambao huongeza na kupanua upeo wa utafutaji. Wanasayansi wa PNNL wanahusika katika mambo yote mawili ya utafutaji huu uliopanuliwa. Axion ni chembe ndogo ya nyenzo nyeusi inayoitwa WIMPS, ambayo ni chembe ndogo ya nyenzo nyeusi inayoitwa axion. Ni katika kituo cha Axion Dark Matter Experiment (ADMX), ambayo inalenga kubadilisha axions katika photons microwave kwa kutumia sumaku nguvu. Axons huingiliana na vitu kwa njia ambayo inaweza kugunduliwa kwa kutumia haloscope ya axon, ambayo imeundwa kubadilisha axons za vitu vya giza kuwa photons za microwave zinazoweza kugunduliwa kwa kutumia uwanja mkubwa wa sumaku. Chembe ndogo za WIMP (Weakly Interacting Massive Particles) zinapatikana wakati zinapopiga detector ya hali ya kioevu au imara kama vile kioo cha silicon. WIMP ni sehemu ya Super-CDMS (Cryogenic Dark Matter Search) mradi wa utafiti wa kimataifa unaohusisha vifaa vya kugundua nyenzo za ionization na phonon kutoka kwa mgongano wa nyenzo nyeusi na nyuklia za atomu katika fuwele za silicon na germanium.