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TOP > Report & Column > The Forefront of Space Science > 2008 > Real Identity of “Dark Particle AcceleratorETo Be Explored by “SUZAKUE/span>

The Forefront of Space Science

Real Identity of “Dark Particle AcceleratorETo Be Explored by “SUZAKUE><br>
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Cosmic ray - mysterious fundamental element of the universe -

In outer space, charged particles called “cosmic raysEaccelerated to ultra-high energy are fling about. The highest energy of even a single particle of proton or electron reaches up to a level of 1020 electron volts or 1 calorie. It might cause a big trouble if such a particle would collide with us. Such high-energy cosmic rays, however, are very rare. Usually, energy of most cosmic rays is about 109 electron volts. They exist in the universe as many as one ray passes through an area of finger tip per second.

As mentioned above, cosmic ray is one of the harshest fundamental elements of the universe. Nevertheless, even today, nearly 100 years after Hess discovered cosmic ray in 1912, a fundamental question “by what celestial bodies are cosmic rays accelerated?Estill remains as a mystery. One of reasons to impede our approach is interstellar magnet field, which exists commonly in the universe. In interstellar magnetic field, charged particles perform gyro motion or rotation around the magnetic field. Since magnetic fields are usually very small, radius of cosmic ray’s gyro motion is very large. However, as distance to extrasolar bodies is very far, several to several thousands light years, when such particles arrive at earth, we cannot identify from where they come.

Meanwhile, if cosmic ray particles release photons, as light go straight, we can “seeEsource of acceleration. When accelerated electrons perform gyro motion in magnetic field, they radiate light called synchrotron X-rays. In addition, when electrons interact with photons in cosmic background radiation or protons collide with molecular clouds, high-energy TeV gamma rays (TeV: tera electron volts, tera means 1012) of 1 billion times of X-ray or 1 trillion times of visible light are emitted. By identifying these lights, we can locate source of cosmic rays. In 1995, a Japanese X-ray astronomical satellite ASCA discovered synchrotron X-ray in the shock wave of the supernova remnant (aftermath of huge explosion occurred at star’s death) named SN 1006, which exploded in 1006. Thus, the satellite pinpointed the site of acceleration of electron constitute of cosmic ray. However, number of bodies identified in the past as ones to accelerate cosmic rays is far less than that for explaining all cosmic rays. We needed to explore further.

Mysterious body “dark particle acceleratorE/span>

In the meantime, very mysterious bodies were discovered in 2005. HESS team (of course, named after Hess who discovered cosmic ray) for TeV gamma ray telescopes, mainly composed of German researchers, explored our Galactic system and discovered a number of new celestial bodies. These bodies are present along the Galactic plane. Most of the bodies are diffuse. Judging from these facts, it is apparent that the new bodies belong to our Galactic system. In addition, since high-energy light is emitted, there is no doubt that the new bodies are accelerators of cosmic rays. Strangely enough, however, with observations by visible light, radiowave, infrared, and X-ray which are frequently observed our Galaxy, we cannot locate the bodies. As they are mysterious accelerators with unknown real nature, they were named ”dark particle acceleratorEjust like name in SF novels. This discovery caused a great sensation. We were excited partly because they might be sources of cosmic ray acceleration to have been awaited for one hundred years. But, the biggest reason to attract us is the fact that “there exist numbers of bodies in the universe that humankind has never known even in the 21st century.Ebr>
What is “dark particle acceleratorEall about? Various researchers are proposing various assumptions. For examples, “they are remnants of supernova that exploded a long time ago, they are pulsar nebula, they are remnants of gamma ray burst, they are molecular clouds that collide with the Galactic plane, they are sites of dark matter pair annihilation, etc.EA variety of theories have been raised with no limitations. I guess that theoretical researchers also get carried away for the discovery of new celestial bodies.

Figure 1
Figure 1. HESS J1745-303 which was confirmed to be a dark particle accelerator by SUZAKU. Color image is by SUZAKU while contour lines are by HESS. The body radiating TeV gamma ray does not shine in X-ray at all.

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