Search results for "tähdet"
showing 9 items of 9 documents
Morphological and molecular analysis of Henricia Gray, 1840 (Asteroidea: Echinodermata) from the Northern Atlantic Ocean
2017
Studies of Tz= -3/2 nuclei of astrophysical interest
2011
This thesis presents a summary of experimental studies of -decaying Tz = 3=2 nuclei 23Al and 31Cl. The properties of these nuclei and the respective -decay daughters, 23Mg and 31S, have an in uence on the end products of ONe nova outbursts. The experiments were carried out at the IGISOL facility in the Accelerator laboratory of University of Jyväskylä and at the Cyclotron institute of Texas A&M University. The mass excess of 23Al was determined with Penning trap mass spectrometry by using the JYFLTRAP setup at IGISOL facility. The new mass excess is two orders of magnitude more precise than the previous value. A good agreement between theory and experimental values was found when applying…
PBH assisted search for QCD axion dark matter
2022
The entropy production prior to BBN era is one of ways to prevent QCD axion with the decay constant $F_{a}\in[10^{12}{\rm GeV},10^{16}{\rm GeV}]$ from overclosing the universe when the misalignment angle is $\theta_{\rm i}=\mathcal{O}(1)$. As such, it is necessarily accompanied by an early matter-dominated era (EMD) provided the entropy production is achieved via the decay of a heavy particle. In this work, we consider the possibility of formation of primordial black holes during the EMD era with the assumption of the enhanced primordial scalar perturbation on small scales ($k>10^{4}{\rm Mpc}^{-1}$). In such a scenario, it is expected that PBHs with axion halo accretion develop to ultracomp…
Progress on nuclear reaction rates affecting the stellar production of 26Al
2023
Abstract The radioisotope 26Al is a key observable for nucleosynthesis in the Galaxy and the environment of the early Solar System. To properly interpret the large variety of astronomical and meteoritic data, it is crucial to understand both the nuclear reactions involved in the production of 26Al in the relevant stellar sites and the physics of such sites. These range from the winds of low- and intermediate-mass asymptotic giant branch stars; to massive and very massive stars, both their Wolf–Rayet winds and their final core-collapse supernovae (CCSN); and the ejecta from novae, the explosions that occur on the surface of a white dwarf accreting material from a stellar companion. Several r…
Maailmankaikkeuden rakenne sekä tähdet ja planeetat Plinius vanhemman Naturalis historia -teoksen toisessa kirjassa
2003
Fainomena Aratea : tähtiä ja tähdistöjä kuvaavat adjektiivit Ciceron, Germanicuksen ja Avienuksen käännöksissä
2002
Kreikkalainen Aratos Soloslainen kirjoitti tähtitaivasta kuvailevan heksametri-mittaisen Fainomena-opetusrunoelman n. 270 eKr. Teos oli tunnettu kautta koko antiikin ajan, ja sitä käytettiin pohjana useissa muissa tähtitiedettä käsittelevissä teoksissa. Kreikankielisen alkuperäistekstin lisäksi antiikin ajalta on säilynyt sen kolme latinankielistä käännösversiota: Ciceron, Germanicuksen ja Avienuksen Fainomena-käännökset. Cicero julkaisi omansa ensimmäisellä vuosisadalla eKr., Germanicus ensimmäisellä vuosisadalla jKr. ja Avienus neljännellä vuosisadalla jKr. Tässä pro gradu -työssä tarkastellaan, millaisin adjektiivein tähtiä on kuvattu ja miten latinan runokieli on muuttunut kyseisenä vii…
Radio signatures from encounters between neutron stars and QCD-axion minihalos around primordial black holes
2021
Probing the QCD axion dark matter (DM) hypothesis is extremely challenging as the axion interacts very weakly with Standard Model particles. We propose a new avenue to test the QCD axion DM via transient radio signatures coming from encounters between neutron stars (NSs) and axion minihalos around primordial black holes (PBHs). We consider a general QCD axion scenario in which the PQ symmetry breaking occurs before (or during) inflation coexisting with a small fraction of DM in the form of PBHs. The PBHs will unavoidably acquire around them axion minihalos with the typical length scale of parsecs. The axion density in the minihalos may be much higher than the local DM density, and the prese…
Gauge theory phase diagrams from holography
2014
Discovery of an Exceptionally Strong β -Decay Transition of $^{20}$F and Implications for the Fate of Intermediate-Mass Stars
2019
A significant fraction of stars between 7-11 solar masses are thought to become supernovae, but the explosion mechanism is unclear. The answer depends critically on the rate of electron capture on $^{20}$Ne in the degenerate oxygen-neon stellar core. However, due to the unknown strength of the transition between the ground states of $^{20}$Ne and $^{20}$F, it has not previously been possible to fully constrain the rate. By measuring the transition, we have established that its strength is exceptionally large and enhances the capture rate by several orders of magnitude. This has a decisive impact on the evolution of the core, increasing the likelihood that the star is (partially) disrupted b…