Astrofysik
Astrofysik er den gren af den astronomiske videnskab, som omhandler universets fysik.
Astrofysik er en meget bred videnskabsgren, som omfatter himmellegemers karakteristika (egenskaber), så som mekanik, statistisk mekanik, termodynamik, relativitetsteori, atomfysik, partikelfysik, kvantemekanik, væskedynamik (Fluid Dynamics), plasmafysik, optisk fysik, temperatur, tryk, luminositet (lysstyrke), størrelser, masse, massefylde, energikilder, kemisk sammensætning, samt en del andre emner. En af de mest kendte astrofysiske fomularer er E=mc². Denne beskriver sammenhægngen mellem energi og masse. Dette matematiske gennembrud blev fundet af kongen af astrofysik, Albert Einstein.
Astrofysik udgør de(n) væsentligste del(e) af moderne astronomisk forskning.
Astronomiske massefylder
Her er en tabel over astronomiske massefylder:
| "Eksotiske" stoffer | massefylde (× 1.000 kg/m³ eller g/cm³) |
|---|---|
| Hypotetisk maximons middelmassefylde | 3,6 · 1093 |
| Sort huls middelmassefylde (1 kilogram, anvender Schwarzschild-radius) | 7,3 · 1076 |
| Kvarkstjernes middelmassefylde | 6,53 · 1015 (?) |
| Neutronstjernes middelmassefylde | 9,1 · 1013 — 2 · 1015 typisk 7 · 1014 |
| Atomkerne | (2,2–3,6) · 1014 |
| Sort huls middelmassefylde (10 solmasser, anvender Schwarzschild-radius) | 1,8 · 1014 |
| Hvid dværgs middelmassefylde | 105–109, typisk 107 |
| Brun dværgs middelmassefylde | typisk 106 |
| Jordens middelmassefylde | 5,515–5,519 |
| Solens middelmassefylde | 1,4 |
| Sort huls middelmassefylde (1 milliard solmasser, anvender Schwarzschild-radius) | 0,018 (mindre massefylde end vand!) |
Kilder/referencer
- Rebuttal of North and Nieto. Martin Selbrede. Hypotetisk maximons middelmassefylde. (engelsk)
- The Physics Factbook: Density (Specific Gravity) (engelsk)
Se også
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From the source site, courtesy of NASA/JPL-Caltech: Generations of stars can be seen in this new infrared portrait from NASA's Spitzer Space Telescope. In this wispy star-forming region, called W5, the oldest stars can be seen as blue dots in the centers of the two hollow cavities (other blue dots are background and foreground stars not associated with the region). Younger stars line the rims of the cavities, and some can be seen as pink dots at the tips of the elephant-trunk-like pillars. The white knotty areas are where the youngest stars are forming. Red shows heated dust that pervades the region's cavities, while green highlights dense clouds.
W5 spans an area of sky equivalent to four full moons and is about 6,500 light-years away in the constellation Cassiopeia. The Spitzer picture was taken over a period of 24 hours.
Like other massive star-forming regions, such as Orion and Carina, W5 contains large cavities that were carved out by radiation and winds from the region's most massive stars. According to the theory of triggered star-formation, the carving out of these cavities pushes gas together, causing it to ignite into successive generations of new stars.
This image contains some of the best evidence yet for the triggered star-formation theory. Scientists analyzing the photo have been able to show that the ages of the stars become progressively and systematically younger with distance from the center of the cavities.