Thursday, October 3, 2019
X-ray transient Essay Example for Free
X-ray transient Essay The good news is that there are more binaries which reveal the possibility of a black hole, that which is much stronger than in Cygnus X-1 (Lochner, 2006, p. 2). In the year 1975, an X-ray transient known as A0620-00 was discovered. In the mid-80s, it was found that the mass of this object was more than 3. 5 solar masses. This fact alone eradicates the possibility of a neuron star, since neuron stars usually possess solar masses of 1. 5. In fact, the discovery of A0620-00 may have put into question the feasibility of other theories. Nonetheless, the best finding regarding black holes is V404 Cygni. This star was found to have an estimated 10 solar masses. Several journals have also written about the existence of black holes. In the 1995 edition of Annual Reviews of Astronomy and Astrophysics,there was a review conducted by Kormendy and Richstone, which implied the eight galaxies were thought to have Ã¢â¬Å"massive dark objects in their centers (Bunn, 1995, p. 1). Ã¢â¬ These cores were found to have masses which range from 1 million to several billion times that of the sun. Their massiveness was determined by noting how Ã¢â¬Å"the speed with which stars and gas orbit around the center of the galaxy: the faster the orbital speeds, the stronger the gravitational force required to hold the stars and gas in their orbits (Bunn, 1995, p. 1). Ã¢â¬ In fact, this is how astronomy usually measures masses. There are two reasons why these massive galactic centers were deemed as black holes. To begin with, the centers are Ã¢â¬Å"too dense and dark (Bunn, 1995, p. 1)Ã¢â¬ to even be considered as a group of stars, or just merely stars. Ã¢â¬Å"Second, the only promising theory to explain the enigmatic objects known as quasars and active galaxies postulates that such galaxies have supermassive black holes at their cores (Bunn, 1995, p. 1). Ã¢â¬ Even though these reasons point out that the galactic centers are really black holes, there is no sufficient evidence to prove it. Nonetheless, there is a continuous discovery for proofs that systems do include black holes. According to Bunn (1995), Ã¢â¬Å"a nearby active galaxy was found to have a water maser system (a very powerful source of microwave radiation) near its nucleus. Using the technique of very-long-baseline interferometry, a group of researchers was able to map the velocity distribution of the gas with very fine resolution (p. 1). Ã¢â¬ They also determined that the velocity was Ã¢â¬Å"less than half a light-year of the center of the galaxy (Bunn, 1995, p. 1). Ã¢â¬ It is from this fact that they deemed the object as a black hole, simply because only a black hole can have that much mass concentrated in such a small volume (Bunn, 1995, p. 1). All these results are included in January 12, 1995 issue of Nature, vol. 373. , as was reported by Miyoshi et al (Bunn, 1995, p.1). Is there a possibility that the Sun can be a black hole? No. According to Bunn (1995), Ã¢â¬Å"only stars that weigh considerably more than the Sun end their lives as black holes (p. 1). Ã¢â¬ For about five billion years, the Sun will remain in its present state. After that, the Sun will undergo a phase wherein it will be a red giant star. The Sun will then end its life as a white dwarf star. If there are black holes, are there white ones? According to Bunn (1995), Ã¢â¬Å"the equations of general relativity have an interesting mathematical property: they are symmetric in time. That means that you can take any solution to the equations and imagine that time flows backwards rather than forwards, and youll get another valid solution to the equations. If you apply this rule to the solution that describes black holes, you get an object known as a white hole (p. 1). Ã¢â¬ If a black hole then pulls objects in, a white hole would then push things out. The former sucks in, the latter spits out. However, there is no proof that white holes exist, and there are no studies to point out if their existence is a possibility. There has also been speculations about the existence of what is called worm holes. What is a worm hole? It is Ã¢â¬Å"a theoretical opening in space-time that one could use to travel to far away places very quickly (Lochner, 2006, p. 2). Ã¢â¬ It is characterized by Ã¢â¬Å"two copies of the black hole geometry connected by a throat the throat, or passageway, is called an Einstein-Rosen bridge (Lochner, 2006, p. 2). Ã¢â¬ As is indicated in the definition, it is merely theoretical. There is no scientific basis nor experimental evidence for such existence. However, it is indeed amazing to think that such existence is possible. Do black holes disappear or evaporate? Even astronomers are not sure as to how black holes end their existence. Bunn (1995) notes that Ã¢â¬Å"Back in the 1970s, Stephen Hawking came up with theoretical arguments showing that black holes are not really entirely black: due to quantum-mechanical effects, they emit radiation. The energy that produces the radiation comes from the mass of the black hole. Consequently, the black hole gradually shrinks. It turns out that the rate of radiation increases as the mass decreases, so the black hole continues to radiate more and more intensely and to shrink more and more rapidly until it presumably vanishes entirely (p. 1)Ã¢â¬ This is a mere theory. There have been no proof or scientific conclusions as to how black holes really diminish. Black holes are just one of the many things included in the vast universe we are a part of. Thanks to science and the technological advancements at present, we can have greater awareness and knowledge of what is within our universe but beyond our reach. References Bunn, T. (1995). Black Hole FAQ List. Retrieved December 13, 2007, from http://cosmology. berkeley. edu/Education/BHfaq. html. Lochner, J. (2007). Black Holes. Retrieved December 13, 2007, from http://imagine. gsfc. nasa. gov/docs/science/know_l2/black_holes. html.