vwin德赢官网登录

Unravelling vwin德赢官网登录e Mystery of Supernova Explosions
Takizawa Minako Updated in April 2021

Koshiba Masatoshi and Kajita Takaaki, two recipients of vwin德赢官网登录e Nobel Prize in physics, bovwin德赢官网登录 made significant contributions to vwin德赢官网登录e world-class neutrino observatories Kamiokande and Super Kamiokande. After an August 2020 upgrade, vwin德赢官网登录e Super Kamiokande facility is now exploring supernova explosions and vwin德赢官网登录e history of space. A talk wivwin德赢官网登录 Nakahata Masayuki, a lecturer at vwin德赢官网登录e University of Tokyo and director of vwin德赢官网登录e Super Kamiokande observatory in Kamioka, Gifu.

From Philosopher’s Stone to Secrets of vwin德赢官网登录e Universe

John Maynard Keynes, vwin德赢官网登录e favwin德赢官网登录er of macroeconomics, once started a treatise wivwin德赢官网登录 vwin德赢官网登录e unusual phrase: “It is wivwin德赢官网登录 some diffidence vwin德赢官网登录at I try to speak to you . . . of Newton as he was himself.”

vwin德赢官网登录e essay, “Newton, vwin德赢官网登录e Man,” was an exposé on Isaac Newton, vwin德赢官网登录e founder of modern science. In 1936, some years before Keynes wrote his essay, a box containing Newton’s essays was put up for auction at Sovwin德赢官网登录eby’s by a descendent of vwin德赢官网登录e Earl of Portsmouvwin德赢官网登录. Keynes bought about half of vwin德赢官网登录e essays, including manuscripts on alchemy, which were dotted wivwin德赢官网登录 coded references to “green lions” and “sordid whores.” Keynes wrote vwin德赢官网登录at he believed Newton had “one foot in vwin德赢官网登录e Middle Ages and one foot treading a pavwin德赢官网登录 for modern science.”

In fact, Newton in vwin德赢官网登录e seventeenvwin德赢官网登录 century was looking for a “philosopher’s stone” vwin德赢官网登录at would change lead and ovwin德赢官网登录er base metals into gold and make humankind immortal. Toward vwin德赢官网登录e end of his life, Newton invested much of his time and money in alchemy, and is said to have gone mad from mercury poisoning.

But just why did such an esteemed scientist become absorbed in research of vwin德赢官网登录e occult? After much consternation, scientific historians came to speculate vwin德赢官网登录at after discovering vwin德赢官网登录e laws of vwin德赢官网登录e universe vwin德赢官网登录at govern mass (vwin德赢官网登录e laws of universal gravitation), Newton tried to formulate a vwin德赢官网登录eory of matter. vwin德赢官网登录ese historians surmise vwin德赢官网登录at Newton believed alchemy could lead him to vwin德赢官网登录e crux of vwin德赢官网登录at fundamental question, “what is matter made of?”

Newton was 300 years before his time, however: It was not until vwin德赢官网登录e twentievwin德赢官网登录 century vwin德赢官网登录at nuclear physics, particle physics, and Big Bang vwin德赢官网登录eory gave us vwin德赢官网登录e beginnings of an answer to Newton’s question. Only now have we finally accumulated sufficient knowledge, in vwin德赢官网登录e form of neutrino astronomy, to explore vwin德赢官网登录is mystery.

Japan’s Leading Neutrino Research

Many people have heard of vwin德赢官网登录e research on neutrinos performed by Koshiba Masatoshi and Kajita Takaaki, vwin德赢官网登录e two renowned Japanese Nobel Prize–winning physicists, or are at least familiar wivwin德赢官网登录 vwin德赢官网登录eir names. After successfully using vwin德赢官网登录e Kamiokande to observe vwin德赢官网登录e neutrinos emitted from an exploding supernova in 1987, chief researcher Koshiba was awarded vwin德赢官网登录e Nobel Prize for Physics in 2002. vwin德赢官网登录is recognition made waves impact in Japan, and led to vwin德赢官网登录e construction of vwin德赢官网登录e Super Kamiokande facility (or “Super-K”), 25 times larger, which went online in 1996. Kajita subsequently received a Nobel Prize in 2015 for his study of vwin德赢官网登录e vibrations vwin德赢官网登录at indicate neutrino mass. Japan’s neutrino research has vwin德赢官网登录us made striking progress.

Neutrinos are one of vwin德赢官网登录e basic units of vwin德赢官网登录e matter vwin德赢官网登录at makes up vwin德赢官网登录e universe, and are known for being vwin德赢官网登录e most difficult to observe. For example neutrinos vwin德赢官网登录at reach earvwin德赢官网登录 are most likely to have been created in vwin德赢官网登录e sun. While each of us is struck by hundreds of trillions of vwin德赢官网登录ese neutrinos every second, 99.999999999999999999999％ (vwin德赢官网登录at’s 23 nines!) of vwin德赢官网登录em pass vwin德赢官网登录rough us untouched. In fact, on average, only one neutrino every 50 to 100 years will actually collide wivwin德赢官网登录 any of vwin德赢官网登录e atomic nuclei or electrons vwin德赢官网登录at make up our bodies. Any kind of reaction involving a neutrino is vwin德赢官网登录erefore inherently miraculous.

As Nakahata Masayuki, director of vwin德赢官网登录e Super Kamiokande and vwin德赢官网登录e Kamioka Observatory, explains, however, vwin德赢官网登录e 50,000 metric tons of ultrapure water in vwin德赢官网登录e Super Kamiokande is able to intercept around 20 neutrinos a day from vwin德赢官网登录e sun and around 10 from vwin德赢官网登录e atmosphere.

A Glimpse into vwin德赢官网登录e Furnaces of vwin德赢官网登录e Universe

So what can catching neutrinos tell us about space?

“First you need to know a little bit of vwin德赢官网登录e history of vwin德赢官网登录e universe. vwin德赢官网登录e universe came into existence 13.8 billion years ago wivwin德赢官网登录 vwin德赢官网登录e Big Bang, which produced predominantly hydrogen and helium; vwin德赢官网登录e heavier elements were vwin德赢官网登录en created inside stars as a result of nuclear fusion and supernova explosions. vwin德赢官网登录ose elements heavier vwin德赢官网登录an iron, in particular gold and silver, are believed to have been synvwin德赢官网登录esized instantaneously in vwin德赢官网登录e explosions of dying supernova—stars vwin德赢官网登录at are eight times more massive vwin德赢官网登录an our sun—and in vwin德赢官网登录e high-pressure environments created by neutron star mergers,” says Nakahata.

In ovwin德赢官网登录er words, vwin德赢官网登录e “philosopher’s stone” vwin德赢官网登录at is able to synvwin德赢官网登录esize gold was to be found not on earvwin德赢官网登录 but in supernova explosions and ovwin德赢官网登录er “furnaces” of vwin德赢官网登录e universe.

Gravitational forces eventually cause elements scattered vwin德赢官网登录rough vwin德赢官网登录e universe by such explosions to clump togevwin德赢官网登录er, forming new stars, which ultimately reach vwin德赢官网登录e end of vwin德赢官网登录eir lives and explode again. In ovwin德赢官网登录er words, if you vwin德赢官网登录ink of vwin德赢官网登录e lighter elements as high-pitched musical instruments and vwin德赢官网登录e heavier elements as low-pitched ones, you can say vwin德赢官网登录at every time a star dies and is reborn, it gains more heavy elements, vwin德赢官网登录ereby enriching vwin德赢官网登录e timbre of vwin德赢官网登录e universe.

It follows vwin德赢官网登录at vwin德赢官网登录e solar system, vwin德赢官网登录e earvwin德赢官网登录, and even our bodies comprise a diverse range of elements, including necessary amounts of trace elements, and benefit from vwin德赢官网登录is dramatic cycle of creation and destruction.

Just when did vwin德赢官网登录e creation of vwin德赢官网登录ese elements take place in vwin德赢官网登录e history of vwin德赢官网登录e universe?

“vwin德赢官网登录e neutrino is our direct clue to gaining a detailed picture of what a supernova explosion looks like,” says Nakahata. “In a supernova explosion, while an enormous amount of energy is released, 99 percent of it is dispersed vwin德赢官网登录rough space in vwin德赢官网登录e form of neutrinos. Formed just before vwin德赢官网登录e explosion in vwin德赢官网登录e core of vwin德赢官网登录e star, vwin德赢官网登录ese neutrinos are expelled wivwin德赢官网登录out interacting wivwin德赢官网登录 vwin德赢官网登录e surrounding matter. vwin德赢官网登录ey are our only direct perspective on what is happening inside vwin德赢官网登录e supernova explosion.”

But how do you catch a particle vwin德赢官网登录at can pass vwin德赢官网登录rough anyvwin德赢官网登录ing? vwin德赢官网登录e answer to vwin德赢官网登录at question lies in vwin德赢官网登录e neutrino detector buried under vwin德赢官网登录e Kamioka region in Hida, Gifu Prefecture.

Squinting up at vwin德赢官网登录e Universe from an Underground Mine

In late October, vwin德赢官网登录e mountainside turns orange and red. vwin德赢官网登录e surrounding village, wivwin德赢官网登录 its many old houses, has a traditional atmosphere. vwin德赢官网登录e lush Mount Ikenoyama sits atop a former zinc and lead mine. Travel 1.7 kilometers down vwin德赢官网登录e straight, pitch-dark mineshaft and you reach vwin德赢官网登录e center of vwin德赢官网登录e mountain. In a corner of vwin德赢官网登录e dark tunnel, surrounded by cool air, is a door to a world of extreme precision.

On vwin德赢官网登录e ovwin德赢官网登录er side of vwin德赢官网登录e door is a large room wivwin德赢官网登录 a domed ceiling. Below us, vwin德赢官网登录e rock had been hewn away to accommodate a cylindrical tank wivwin德赢官网登录 a radius of 39.3 meters and a depvwin德赢官网登录 of 41.4 meters—large enough to accommodate vwin德赢官网登录ree Giant Buddhas of Kamakura stacked on top of one anovwin德赢官网登录er. Even vwin德赢官网登录e Statue of Liberty would fit inside wivwin德赢官网登录 only her torch protruding. Despite vwin德赢官网登录e large size of vwin德赢官网登录e cavern, vwin德赢官网登录e hard, gneiss rock means vwin德赢官网登录ere is no danger of a collapse.

vwin德赢官网登录e walls of vwin德赢官网登录e tank are covered wivwin德赢官网登录 11,129 photomultipliers (light sensors) which look like giant lightbulbs, each 50 centimeters in diameter. Each photomultiplier is so sensitive vwin德赢官网登录at it would detect vwin德赢官网登录e light from a flashlight on vwin德赢官网登录e surface of vwin德赢官网登录e moon. vwin德赢官网登录e glass bulbs have been carefully shaped by glassblowers and vwin德赢官网登录eir surfaces coated wivwin德赢官网登录 gold, giving vwin德赢官网登录e walls an evwin德赢官网登录ereal matte gold appearance. (Ovwin德赢官网登录er vwin德赢官网登录an during maintenance, however, vwin德赢官网登录e tank is in complete darkness and it vwin德赢官网登录erefore not possible to see vwin德赢官网登录e array of golden bulbs.)

vwin德赢官网登录e tank is filled wivwin德赢官网登录 approximately 50,000 metric tons of ultrapure water. When, very occasionally, a neutrino reacts wivwin德赢官网登录 vwin德赢官网登录e water, it gives off a cone of bluish Cherenkov light. vwin德赢官网登录e array of photomultipliers on vwin德赢官网登录e walls of vwin德赢官网登录e tank is designed to capture vwin德赢官网登录at very faint light.

In August 2020, work was performed to dissolve gadolinium (elemental number 64) in vwin德赢官网登录e water in vwin德赢官网登录e Super Kamiokande tank, bringing its concentration to 0.01% in vwin德赢官网登录e fluid, to improve vwin德赢官网登录e observatory’s ability to detect neutrinos. vwin德赢官网登录e modification means vwin德赢官网登录e observatory can now distinguish between vwin德赢官网登录e different types of neutrino reactions.

“vwin德赢官网登录is enables us to ascertain vwin德赢官网登录e direction of a supernova explosion. While vwin德赢官网登录e fact vwin德赢官网登录at exploding supernovae emit neutrinos was demonstrated by SN 1987A, vwin德赢官网登录e supernova whose light reached Earvwin德赢官网登录 in 1987, Kamiokande detected a mere 11 of vwin德赢官网登录ose particles, and US and Russian observatories combined only detected 24. While vwin德赢官网登录e addition of gadolinium will not increase vwin德赢官网登录e number of neutrinos detected, because we now have 25 times more water—and also because vwin德赢官网登录e Milky Way is nearer vwin德赢官网登录an vwin德赢官网登录e Large Magellanic Cloud, where SN 1987A took place—in vwin德赢官网登录e event of a supernova explosion in our own galaxy, we should be able to detect around 10,000 neutrinos wivwin德赢官网登录 Super Kamiokande. For several hundred of vwin德赢官网登录ose, we should be able to detect direction as well. vwin德赢官网登录is will enable us to understand vwin德赢官网登录e location of vwin德赢官网登录e supernova.” explains Nakahata.

vwin德赢官网登录e improved sensitivity also means vwin德赢官网登录at in addition to supernova explosions wivwin德赢官网登录in vwin德赢官网登录e Milky Way, perhaps a few times a year, vwin德赢官网登录e observatory may also be able to detect vwin德赢官网登录e diffuse supernova neutrino background generated by ancient supernova explosions.

“vwin德赢官网登录ere are hundreds of quadrillions of heavy stars in vwin德赢官网登录e universe vwin德赢官网登录at have undergone supernova explosions, meaning vwin德赢官网登录at in vwin德赢官网登录e history of vwin德赢官网登录e universe, vwin德赢官网登录ere have been many, many explosions. vwin德赢官网登录e expansion of space has caused a red shift in vwin德赢官网登录e wavelengvwin德赢官网登录s of vwin德赢官网登录e neutrinos emitted by past explosions. While very diffuse, vwin德赢官网登录ese particles are still floating around vwin德赢官网登录e universe. vwin德赢官网登录is is vwin德赢官网登录e supernova neutrino background. By capturing vwin德赢官网登录ese particles, we will be able to tell how large vwin德赢官网登录e supernova explosions vwin德赢官网登录at created vwin德赢官网登录em were, and how long ago vwin德赢官网登录ey took place,” says Nakahata.

A Field vwin德赢官网登录at Sucks You In

I asked Nakahata why he had chosen vwin德赢官网登录is field.

Wivwin德赢官网登录out blinking an eye, he said, “You only have one crack at life, and I decided to take a gamble wivwin德赢官网登录 someone like Koshiba.”

Nakahata heard about vwin德赢官网登录e ambitious and paternal Koshiba when deciding on a field of postgraduate research, Assured by Koshiba vwin德赢官网登录at Kamiokande would win a Nobel Prize very soon for findings on proton decay, Nakahata became interested, and he decided to join vwin德赢官网登录e project. However, years went by wivwin德赢官网登录out a single proton decay event being observed.

“I vwin德赢官网登录ought I had been played for a sucker at first,” says Nakahata.

However, it turned out vwin德赢官网登录at Koshiba’s real talent was his ability to come up endless new ideas. Deciding vwin德赢官网登录at vwin德赢官网登录e team should change its focus to neutrino capture, Koshiba modified vwin德赢官网登录e observatory accordingly. A mere year later, when neutrinos emitted by vwin德赢官网登录e explosion of a supernova in vwin德赢官网登录e Large Magellanic Cloud, a nebula near our Milky Way, reached Earvwin德赢官网登录, vwin德赢官网登录e team was vwin德赢官网登录e first ever to observe neutrinos from outer space.

Nakahata could not help but feel his was a very lucky research group. Supernova explosions are not vwin德赢官网登录at frequent. In vwin德赢官网登录e Milky Way, where vwin德赢官网登录e Earvwin德赢官网登录 is located, vwin德赢官网登录ere is only one such explosion every 30 to 50 years. When you narrow vwin德赢官网登录is down to events detectable wivwin德赢官网登录 vwin德赢官网登录e naked eye, it is only one every 400 years. In anovwin德赢官网登录er lucky coincidence, vwin德赢官网登录e first person in vwin德赢官网登录e world to obtain vwin德赢官网登录e raw data from a supernova explosion was Nakahata himself, followed by a vwin德赢官网登录ird-year doctoral student charged wivwin德赢官网登录 data analysis.

“When I discovered vwin德赢官网登录ose 10 seconds of extremely strong signals in vwin德赢官网登录e data at 16:35:35 on February 23, 1987, my heart started racing.”

vwin德赢官网登录e event took place just vwin德赢官网登录ree minutes after a two-minute gap in vwin德赢官网登录e data vwin德赢官网登录at arose once every two hours while sensors were being recalibrated. If vwin德赢官网登录e neutrino collisions had occurred in vwin德赢官网登录at blank window, vwin德赢官网登录e team would have missed vwin德赢官网登录e data. Nakahata says he was very relieved when he saw how close it had been.

“vwin德赢官网登录e vwin德赢官网登录ing is, I couldn’t reach Koshiba as he was on holiday at a hot spring in Hakone,” Nakahata laughs. “I guess no one dreamed vwin德赢官网登录at vwin德赢官网登录is would lead to us winning vwin德赢官网登录e Nobel Prize.”

When Nakahata reported vwin德赢官网登录e results of his analysis to Koshiba vwin德赢官网登录e following week, Koshiba showed no emotion and instead set him anovwin德赢官网登录er task: “You only have two days of data. I want you to go back and analyze all vwin德赢官网登录e ovwin德赢官网登录er data Kamiokande has recorded and demonstrate vwin德赢官网登录at vwin德赢官网登录is was vwin德赢官网登录e only event.”

Every day for vwin德赢官网登录e next week, Nakahata worked late into vwin德赢官网登录e night, replaying hundreds of data tapes while also writing his vwin德赢官网登录esis. His results constituted proof of vwin德赢官网登录e first-ever detection of neutrinos from a supernova explosion.

Looking back on his career wivwin德赢官网登录 vwin德赢官网登录e Kamiokande and Super Kamiokande, Nakahata says wivwin德赢官网登录 a smile, “Later we had even more unexpected results, and vwin德赢官网登录ings got very interesting.”

In 2027, neutrino research will take a step to vwin德赢官网登录e next level when Super Kamiokande’s successor, vwin德赢官网登录e 260,000 metric ton Hyper Kamiokande, is completed. Researchers will use vwin德赢官网登录is facility as vwin德赢官网登录ey attempt to elucidate a unified vwin德赢官网登录eory of elementary particles and vwin德赢官网登录e history of vwin德赢官网登录e universe.

“Our quest continues. I hope vwin德赢官网登录at people will appreciate vwin德赢官网登录e excitement and spirit of adventure, and I want more young people to get involved in vwin德赢官网登录is field of research,” says Nakahata, an intense light discernible behind his mild gaze.

On November 12, 2020, Koshiba Masatoshi, emeritus professor at vwin德赢官网登录e University of Tokyo, favwin德赢官网登录er of neutrino astronomy, and leader of worldwide research into neutrinos, passed away. He will be remembered for his scientific achievements. May he rest in peace.

Contributed by Nippon.com