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Wednesday, June 17, 2009

Soal Latihan Astrofisika

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Soal Latihan Astrofisika - 15 Juni 2009


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Monday, June 15, 2009

First Extra-Galactic Planet Spotted in Andromeda

A star in the Andromeda galaxy has a "companion" with six times the mass of Jupiter.

There's no end to the ingenuity of these astronomers.

We've now spotted some 300 extra-solar planets, with rate of discovery increasing at an extraordinary rate. Astronomers have only seen one of these planets directly; the rest have all been inferred because of the effect that they have on their parent stars: changing their brightness or making them wobble. Of course, you have to be able to see the stars to do this kind of work, so astronomers can only see extra-solar planets in our local region of the Milky Way.

Until now. Gabriele Ingrosso at the National Institute of Nuclear Physics, in Italy, and pals say that there is a way to spot planets in other galaxies. The trick is to exploit a phenomenon called microlensing in which the gravity of one star focuses the light from a more distant one toward Earth.

The advantage of microlensing is that it works best for more distant objects, so it's ideal for planet hunting in other galaxies. In theory, it should be possible to see Earth-size objects in this way. The disadvantage is that microlensing is a relatively rapid, one-off event that lasts a few days at most. That makes observations difficult to verify.

It's hard to see individual stars like this, let alone planets. Astronomers have so far spotted only about a dozen stars in Andromeda in this way, and plans are afoot to search for lots more.

But get this: the light from one of these Andromedan stars showed a distinct variability that the discoverers attribute to an orbiting companion.

And today, a new analysis from Ingrosso and co shows that this companion has a mass about six times that of Jupiter. That's heading into brown-dwarf territory, but it's also well within planetary territory too.

Which means that we may well have seen our first extra-galactic planet.

Source : Tecnology Review

Original reference : Pixel-lensing as a way to detect extrasolar planets in M31.

Soal-soal Latihan

Berikut ini ditampilkan beberapa soal "kelas berat". Silakan dicoba dan didiskusikan dengan teman atau guru di sekolah Anda.
  1. Having observed the sunrise every day in the same location, the astronomer noticed that the azimuth of the sunrise point changes in the range of 90° during the year. Please find the latitude of the observation place. The refraction and solar disk size can be neglected.
  2. Two stars have the same physical parameters. They are observed close to each other in the sky, but their distances are different. Both stars and the observer are situated inside the uniform cloud of interstellar dust. The photometric measurements of these stars in B band gave the results 11m and 17m, in V band the results were 10m and 15m. What is the ratio of distances to these stars? Assume that the extinction property of interstellar dust is proportional to the wavelength in the degree of (–1.3).
  3. The magnitude of total umbral lunar eclipse is equal to 1.865. Please find the duration of totality. The expansion of the umbra caused by atmosphere can be disregarded
  4. The radius of the Galaxy is equal to 15 kpc, the thickness of its disk being many times less. The mass of the galaxy is equal to 1011 solar masses and it is distributed uniformly in the volume of the galaxy. Two stars are rotating around the center of the galaxy in the same direction by the circular orbits with radii equal to 5 kpc and 10 kpc. Please find the synodic period of the first star while observing from the vicinity of the second star.
  5. The white dwarf with radius 6000 km, surface temperature 10000 K and mass equal to solar one moves through the interstellar cluster of comet cores, each one has radius 1 km and density 1 g/cm3. How many comets must fall on the white dwarf every day to increase its luminosity in two times?
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