tugas geofisika : suhu curie

Curie point in ferromagnetic materials
The Curie point of a ferromagnetic material is the temperature above which it loses its characteristic ferromagnetic ability (768°C or 1414 °F for iron). At temperatures below the Curie point the magnetic moments are partially aligned within magnetic domains in ferromagnetic materials. As the temperature is increased towards the Curie point, the alignment (magnetization) within each domain decreases. Above the Curie point, the material is purely paramagnetic and there are no magnetized domains of aligned moments.


At temperatures above the Curie point, an applied magnetic field has a paramagnetic effect on the magnetization, but the combination of paramagnetism with ferromagnetism leads to the magnetization following a hysteresis curve with the applied field strength. The destruction of magnetization at the Curie temperature is a second-order phase transition and a critical point where the magnetic susceptibility is theoretically infinite.
One application of this effect is in magneto-optical storage media, where it is used for erasing and writing of new data. Famous examples include the Sony Minidisc format, as well as the defunct CD-MO format.
Other uses include temperature control in soldering irons such as those made by Metcal and the Weller WTCPT and, in general, where a temperature-controlled magnetization is desirable.


[edit] Curie temperature in piezoelectric materials
In analogy to ferromagnetic materials, the Curie temperature is also used in piezoelectric materials to describe the temperature above which the material loses its spontaneous polarization and piezoelectric characteristics. In lead zirconate titanate (PZT), the material is tetragonal below Tc and the unit cell contains a displaced central cation and hence a net dipole moment. Above Tc, the material is cubic and the central cation is no longer displaced from the centre of the unit cell. Hence, there is no net dipole moment and no spontaneous polarization.
Curie-Weiss law k = C / (T − Weiss constant)

pusat galaksi bimasakti adalah blackhole

Pusat Galaksi adalah titik rotasi dari galaksi Bima Sakti. Letaknya adalah sekitar 7,6 kilopersecs (25.000 tahun cahaya) dari Bumi diarah rasi Sagitarius, Ophiuchus dan Scorpius dimana Galaksi Bima Sakti terlihat lebih cemerlang. Pada pusat ini ditemukan Lubang Hitam supermasif.

Lokasi dan Bukti

Karena debu antar bintang yang menutupi jarak pandang, pusat galaksi tidak bisa dipelajari lewat spektrum warna, sinar ultra ungu, maupun sinar X. Informasi yang bisa didapat tentang pusat galaksi hanya melalui observasi pada sinar gama, Sinar-X keras (hard X-ray), infra merah, sub-milimeter dan gelombang radio. Koordinat pusat galaksi pertama kalinya ditemukan oleh Harlow Shapley pada tahun 1918 didalam tulisannya mengenai distribusi 'globular cluster'. Di dalam persamaan sistem ekuator angka ini adalah: RA 17h45m40.04s, Dec -29° 00' 28.1" (J2000 epoch).

Super massive black hole
Main article: Sagittarius A*

The complex astronomical radio source Sagittarius A appears to be located almost exactly at the Galactic Center, and contains an intense compact radio source, Sagittarius A*, which coincides with a supermassive black hole at the center of our Galaxy. Accretion of gas onto the black hole, probably involving a disk around it, would release energy to power the radio source, itself much larger than the black hole. The latter is too small to see with present instruments.

A study in 2008 which linked radio telescopes in Hawaii, Arizona and California (Very Long Baseline Interferometry) measured the diameter of Sagittarius A* to be 0.3 AU (44 million kilometers).[3][4]

Scientists at the Max Planck Institute for Extraterrestrial Physics in Germany using Chilean telescopes have confirmed the existence of a super massive black hole at the galactic center. This black hole is of the order 4 million solar masses.[5]