domingo, 24 de febrero de 2013

Zeroing in on the Mystery of Dark Matter --"We are on the Verge of Detecting a New Particle of Nature"

The galaxies and other structures we see in the universe are made predominantly of undected dark matter. "We are so excited because we believe we are on the threshold of a major discovery," said Michael Turner, director of the Kavli Institute for Cosmological Physics at the University of Chicago, at a conference of the American Association for the Advancement of Science (AAAS). The existence of Dark matter presents a serious threat to the so-called Standard Model of physics mainly because it does not explain gravity.
"On the cosmology side we now understand that this mysterious dark matter holds together our galaxy and the rest of the Universe," said Turner. "And the tantalizing thing on the cosmology side is that we have an airtight case that the dark matter is made of something new... there is no particle in the Standard Model that can account for dark matter."
"The real question is why dark matter has six times the energy that is in ordinary matter," said Lisa Randall of Harvard University. "It could be 10 trillions times bigger... This is an intriguing sign that there is maybe some other interaction we can detect."
The ultimate dark-matter sleuth is the new Alpha Magnetic Spectrometer, also designated AMS-02, a particle physics experiment module aboard the International Space Station (ISS), which captures gamma rays coming from collisions of dark matter particles.
AMS functions by sampling these high-energy particles from deep space. The sensitivity of the AMS is more than 100 to 1,000 times more sensitive than previous instruments. The first results will be published in two to three weeks, according to Samuel Ting, a Nobel laureate and professor at the Massachusetts Institute of Technology (MIT) who is the mastermind of the two-billion-dollar project. Its experiments will help researchers study the formation of the universe and search for evidence of dark matter and antimatter.
The device is equipped with over 300,000 data channels that require compression with an on-board supercomputer before the information can be transmitted to Earth. “The space station [AMS device] can detect particles of practically unlimited energy,” Ting says, which means that it can also hunt for proposed galaxies made of the elusive dark matter.
Ting oversees  a 500 member global team of scientist to work on this 1.5 billion dollar project, made possible because US President Barack Obama who proposed to extend the space station for a minimum of 5 years beyond 2015, with an additional budget of 3 billion dollars per year.
In an interview with BBC News Ting stated: “This really is the very first very, very precise particle physics detector. You enter into a totally new domain. It's very hard to predict what you'll find."
Space-based spectrometers are not something new, but this instrument is particularly important because it represents the first one of its type to take a superconducting magnet to low-Earth orbit. The international physics community hopes that, through measurements collected with the AMS, they will be able to answer at least a small portion of yet-unanswered, Universe-related questions that deal with the origins and the future of the cosmos.
Its observations will probably build up on those obtained by the Italian satellite PAMELA, a high-energy particle observer launched in 2006. This observatory has already gathered some interesting leads on pinpointing the first clear pieces of evidence on dark matter, and the AMS will have the ability to either permanently confirm or deny these findings, and the dark matter/dark energy theory as a whole.* 
Dark matter makes up about 23 percent of the mass-energy content of the universe, even though we don’t know what it is or have yet to directly see it (which is why it’s called “dark”)

The image above is one of the most detailed maps of dark matter in our universe ever created. The location of the dark matter (tinted blue) was inferred through observations of magnified and distorted distant galaxies seen in this picture. 
"Figuring out what is dark matter has become a problem that astrophysicists, cosmologists and particle physicists all want to solve, because dark matter is central to our understanding of the universe," says Michael S. Turner – Rauner Distinguished Service Professor and Director of the Kavli Institute for Cosmological Physics at the University of Chicago. 

"We now have a compelling hypothesis, namely that dark matter is comprised of WIMPs (Weakly Interacting Massive Particle), particles that don’t radiate light and interact rarely with ordinary matter. After decades of trying to figure out how to test the idea that dark matter is made up of WIMPs, we have three ways to test this hypothesis. Best of all, all three methods are closing in on being able to either confirm or falsify the WIMP. So the stars have truly aligned."

A theoretical cosmologist trained in both particle physics and astrophysics, Michael Turner coined the term “dark energy” and helped establish the interdisciplinary field that combines cosmology and elementary particle physics. 

"Ten years ago," Turner says, "I don't think you would've found astronomers, cosmologists, and particle physicists all agreeing that dark matter was really important. And now, they do. And all of them believe we can solve the problem soon. It's wonderful listening to particle physicists explain the evidence for dark matter, and vice versa –astronomers explaining WIMPs as dark matter. "

"As cosmologists," said Rocky Kolb, who studies the application of elementary-particle physics to the very early Universe, and is the co-author with Michael Turner of The Early Universe, the standard textbook on particle physics and cosmology, "one of our jobs is to understand what the universe is made of. To a good approximation, the galaxies and other structures we see in the universe are made predominantly of dark matter. We have concluded this from a tremendous body of evidence, and now we need to discover what exactly is dark matter. The excitement now is that we are closing in on an answer, and only once in the history of humans will someone discover it. "

"Nothing in cosmology makes sense without dark matter, says Turner. "We needed it to form galaxies, stars and other structures in the Universe. And so it's absolutely central to cosmology. We also know that none of the particles known to exist can be the dark matter particle. So it has to be a new particle of nature. Remarkably, our most conservative hypothesis right now is that the dark matter is a new form of matter – out there to be discovered and to teach us about particle physics."

"Dark matter is absolutely central to cosmology, said Turner, "and the evidence for it comes from many different measurements: the amount of deuterium produced in the big bang, the cosmic microwave background, the formation of structure in the Universe, galaxy rotation curves, gravitational lensing, and on and on."

"There is five times more dark matter than ordinary matter, and its existence allows us to understand the history of the universe beginning from a formless particle soup until where we are today," said Turner. "If you said, 'You no longer have dark matter,' our current cosmological model would collapse. We would be back to square one."

"Dark matter particles, or WIMPs," said Turner, "don’t interact with ordinary matter often. It's taken 25 years to improve the sensitivity of our detectors by a factor of a million, and now they have a good shot at detecting the dark matter particles. Because of the technological developments, we think we are on the cusp of a direct detection. Likewise for indirect detection. We now have instruments like the Fermi satellite (the Fermi Gamma-ray Space Telescope) and the IceCube detector (the IceCube Neutrino Observatory at the South Pole) that can detect the ordinary particles (positrons, gamma rays or neutrinos) that are produced when dark matter particles annihilate, indirectly allowing dark matter to be detected. IceCube is big enough to detect neutrinos that are produced by dark matter annihilations in the sun."

Answering the observation that the dark matter particle might not be detectable, Turner said that for 20 to 30 years, this idea that dark matter is part of a unified theory has been our Holy Grail and has led to the WIMP hypothesis and the belief that the dark matter particle is detectable. "But there’s a new generation of physicists that is saying, 'Well, there's an alternative view. Dark matter is actually just the tip of an iceberg of another world that is unrelated to our world. And I cannot even tell you about that world. There are no rules for that other world, at least that we know of yet.' 

Sadly, this point of view could be correct and might mean the solution to the dark matter problem is still very far away, that discovering what dark matter actually is could be 100 years away.

Image Credit: NASA/JPL-Caltech/ESA/Institute of Astrophysics of Andalusia, University of Basque Country/JHU

Source:  The Daily Galaxy via and AFP 2013

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