Shogo Masaki of the Department of Physics at Nagoya University and Masataka Fukugita and Naoki Yoshida of the University of Tokyo’s Institute of Physics and Mathematics of the Universe (IMPU) collaborated in an experiment to create a computer simulation that would hopefully figure out the location of dark matter. In late January, their experiment was successful.

The term intergalactic refers to the physical space between galaxies where matter is hardly distributed. Scientists previously thought that intergalactic space comprised of nothing, being only empty, and that galaxies, in contrast, have the highest concentration of matter. Masaki, Fukugita, and Yoshida, however, have discovered that these intergalactic zones are packed with clumps of dark matter.

In addition, they also learned that galaxies do not have clear, defined edges; instead, they “have long outskirts of dark matter that extend to their nearby galaxies” according to IMPU’s press release. These “outskirts” contain much of the matter – and dark matter – in the universe.

The existence of dark matter was proposed by Swiss astronomer Fritz Zwicky in the 1930s. Since then, there have been numerous experiments around the globe involving dark matter. Dark matter’s nature is still enigmatic: it is an invisible, dense substance, and it cannot even be detected by instruments. Scientists do know that dark matter takes up about 23% of the Universe, with dark energy taking up 72% and the rest (planets and stars, for example) only 4%.

Furthermore, contrary to popular belief, dark matter is not random – it is uniform and organized. Masaki and his colleagues gathered recent observational data of 24 million galaxies from the Sloan Digital Sky Survey (SDSS) and created a large simulation of matter distribution. With their knowledge of the large density of dark matter, they used gravitational lensing to find the substance’s location.

Because dark matter is so dense, it causes space and light from stars, galaxies, and other light-emitting objects to bend, making these celestial objects appear bigger and brighter. With gravitational lensing, Masaki and his colleagues measured how the galaxies’ light was bent, allowing them to locate dark matter.

Dark matter remains as elusive as ever: although we have found exactly where dark matter is, we still do not know what it is, but scientists are closer than ever to understanding the mysterious substance’s nature. Masaki, Fukugita, and Yoshida have published a paper describing details of their experiment in The Astrophysical Journal. A PDF of the preprint version is found here.

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Japanese scientists have finally solved a decades-old mystery about Japan’s most famous dog.   The death of Hachiko has finally been determined.

The legendary dog, an Akita, was adopted by a professor at the University of Tokyo in 1924.  Hachiko used to wait at a train station for his master every day.  In 1925, the professor died suddenly and never returned to the train station.  Every day for the next nine years, Hachiko would wait at the station for his lost owner.  He was given away after the professor’s death but would routinely escape—going back to his old home he shared with his owner.  Hachiko eventually figured out that his owner no longer lived at the home, so the dog would wait at the train station.

The story of Hachiko moved Tokyo residents to build a statue immortalizing the faithful companion.   Hollywood made a movie about the dog in 2009 with Richard Gere, a remake of a Japanese film that was released in 1987.  The dog was such a model of loyalty that his organs were preserved when he died in 1935.

Japanese scientists were able to use these preserved organs to settle the mystery of Hachiko’s death.  They discovered that he died of cancer and worms and not because he swallowed a chicken skewer.  Legend in Japan has maintained that Hachiko died after consuming a skewer of grilled chicken – Japanese barbecue called yakitori – that ruptured his stomach.  University of Tokyo veterinarians, by examining Hachiko’s innards, found that the dog had terminal cancer and also a filaria infection – worms.  Four yakitori sticks remained in Hachiko’s stomach, but they did not damage his stomach or cause death, said Kazuyuki Uchida, one of veterinarians.  “Hachiko certainly had yakitori given by a street vendor at Shibuya,” he said. “But the sticks were unrelated to his death, and the rumor is groundless.”

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