Artist concept of AMS-2 mounted on the ISS.

The Alpha Magnetic Spectrometer 2 (AMS-2), like other space-borne observatory satellites, will make its observations outside of Earth's atmosphere, attached to the International Space Station—but unlike "conventional" satellite observatories such as the Hubble Space Telescope, Kepler, and the Solar Dynamics Observatory, AMS-2 will not observe electromagnetic radiation (light), but rather cosmic rays.

Cosmic rays are energetic, electrically charged subatomic particles whizzing through space, originating from various places such as the Sun, distant stars and supernovae, and other high-energy sources from the most distant reaches of the known Universe. Most cosmic rays are simply high-speed protons (hydrogen nuclei) and alpha particles (helium nuclei). Less than 1% of cosmic rays are heavier atomic nuclei, and electrons. All of these particles are things familiar to us on Earth, the main differences being their exotic origins and their extremely high speeds—often approaching the speed of light.

A tiny fraction of cosmic rays are exotic particles indeed: antimatter, in the form of positrons (the positively charged antimatter counterpart of electrons) and anti-protons.

What is AMS-2 looking for? In a nutshell, it's looking for what we cannot see…. Only about 5% of the Universe is composed of "ordinary" matter—the stuff we are made of, and which we can see with telescopes out in the universe by virtue of the light it emits: stars, galaxies, nebulae, giant molecular clouds, and more.

An estimated 95% of the Universe's bulk is made up of "dark" stuff—dark matter (about 20%) and dark energy. Some of this dark matter may be accounted for by massive objects that we can't see, such as black holes, but the primary constituent probably consists of exotic particles that defy direct detection. A number of particles that fit this bill have been theorized, like neutrinos, and more recently neutralinos. In theory, interactions between neutralinos should produce charged particles in the form of cosmic rays that AMS-2 should be able to detect. If it does, then we'll have observational evidence for the existence of this exotic particle, which would shed some light onto some of the Universe's dark mystery….

AMS-2 will also look for antimatter. The Big Bang theory (the theory, not the TV show) of the formation of the Universe suggests that there should be equal parts matter and its counterpart antimatter, but so far we've mostly seen only the former. While there are positrons and anti-protons flying about that can be accounted for by processes involving nuclear interactions, if AMS-2 can detect a more complex anti-particle, like an anti-helium nucleus (an atom composed of two anti-protons, two anti-neutrons, and two positrons), then we'll have an example of antimatter that formed by more complex processes than a random nuclear collision or decay.

AMS-2's "lens" is not made of glass, but of magnetic fields. Conventional telescopes bend and focus light with glass lenses or curved mirrors, but AMS-2 will observe electrically charged cosmic rays, which can be collected and sorted with magnetic force. AMS-2 will count cosmic rays, determine what types of particles they are, and how much energy they possess (how fast they are moving).

From Earth's surface observing cosmic rays is nearly impossible, at best. The particles interact with the nuclei of atoms in our atmosphere, forming a different subatomic particle and a burst of "secondary" cosmic radiation—which can be detected by ground-based instruments, but only as "second hand" news. In fact, it is cosmic ray interactions with ordinary carbon (carbon 12) in Earth's atmosphere that transform them into the radioisotope carbon 14, which scientists take advantage of to determine how long a sample of formerly living material has been dead (as in carbon dating).

So, stay tuned for news on what scientists discover as they peer into the very dark darkness of a currently unknown realm of existence. Should be exciting….

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The first evidence for dark matter came from Fritz Zwicky’s observation of the Coma Galaxy Cluster. Image Credit: NASA, JPL-Caltech, SDSS, Leigh Jenkins, Ann Hornschemeier (Goddard Space Flight Center), et al.

Dark matter (think of matter as a fancy word for stuff) is one of the most exciting but also potentially frustrating phenomena in cosmology today. It plays no detectable role on Earth in deciding how far we can throw a baseball, or determining the characteristics of the complicated materials we use to build computers. In fact the only reason we know that it exists at all is by looking through telescopes at objects so distant that it would take hundreds of millions of years to get to them even traveling at the speed of light. And yet we believe there is almost six times as much dark matter in the universe as the regular matter that we can see and feel and touch. Recent results of the Cryogenic Dark Matter Search (CDMS) may have brought us a step closer to understanding this elusive material.

Dark matter’s discovery belongs to Fritz Zwicky. Known for a bullying personality and a fondness for doing one-armed pushups in the Caltech dining hall, Zwicky also measured the Coma Galaxy Cluster in 1933, and noticed that galaxies seemed to be moving far more quickly than gravitational theory would predict. Either the theory of gravity had to be wrong, or some other hidden form of matter–dark matter–must be playing a role here. (Careful! This is not to be confused with antimatter, which stars in Dan Brown’s Angels and Demons, or with dark energy, an even more bizarre cosmological idea.)

Subsequent measurements have corroborated Zwicky’s conclusions, and today we can say with a fair degree of confidence that dark matter must exist. Still, we don’t have any idea why this is so or what dark matter might actually be.

Enter CDMS, a whopper of an experiment buried deep within the Soudan mine of northern Minnesota and consisting of a collaboration of no fewer than 18 experimental research groups scattered across the world. Some of the most promising theories predict that dark matter consists of a deluge of particles constantly washing through the distant galaxies we see, but also through our own Milky Way Galaxy and in particular through the Earth. Such particles, coined sometime in the 1980s as Weakly Interacting Massive Particles (or WIMPs), should be detectable on extraordinarily rare occasions if you can put your detector in a pristine enough location.

On December 17^th, CDMS disclosed the final results of their most recent experiment, and they have reported two events that seem likely to have been caused by WIMPS. Statistically, they find that these events have only a 23 percent chance of being a coincidence. If they are real events, this will certainly be a landmark moment in the history of physics.

However, the search for dark matter has been marred by controversy before. Another large experiment called DAMA in Italy has insisted for years that they have irrefutable evidence for dark matter particles at their own detector. Unfortunately, many other experiments are in direct conflict with DAMAs claims, and consequently nobody seems to take that group seriously. Consequently, CDMS researchers are being careful not to overstate their case.

In the end the hunt goes on, perhaps rightly so. After all, there is a 23 percent chance of dark matter being something else entirely, and if the odds of winning the lottery were 23 percent I would be running off to buy a ticket right now.

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The Sloan Telescope used to conduct BOSS

One of those is BOSS, the Baryon Oscillation Spectroscopic Survey, is a new project to create a 3-D map of over 2 million galaxies and quasars representing the best data ever obtained on the large-scale structure of the universe. Baryon oscillations began as pressure waves through the hot plasma of the early universe. Those waves left an imprint on the matter that makes up the universe, including the dark matter. The survey will essentially act as a ruler, in order to measure how the universe has been expanding.

Next Monday, you’ll be able to meet David Schlegel, the principal investigator of BOSS. He’ll be part of a panel of Lawrence Berkeley Laboratory scientists discussing their search for dark energy. As a primer, check out QUEST’s story on Dark Energy from last year. The piece features astrophysicist Saul Perlmutter, who will also be speaking at the event.

See QUEST's Video on Dark Energy below:

QUEST on KQED Public Media.

Dark Secrets: What Science Tells Us About the Hidden Universe

Where: Berkeley Repertory Theater, 2025 Addison Street, Berkeley

When: Monday, October 26th 7-830 PM

Cost: FREE

Details: No mystery is bigger than dark energy — the elusive force that makes up three-quarters of the Universe and is causing it to expand at an accelerating rate. KTVU Channel 2 health and science editor John Fowler will moderate a panel of Lawrence Berkeley National Laboratory scientists who use phenomena such as exploding stars and gravitational lenses to explore the dark cosmos.

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Sitting in a small, non-descript room in the basement of the Lawrence Berkeley National Lab in Berkeley, physics graduate student Hannah Swift and physicist Saul Perlmutter are searching for supernovae, stars destroyed in huge explosions millions or billions of years ago. (They're looking for ones that exploded billions of years ago). Through a computer hooked up to Hawaii's Keck 2 telescope -– one of the largest in the world –- they are able to follow along as UC Berkeley post-doc Rahman Amanullah, a team member who had traveled to Hawaii a few days earlier, supervises the night's observation.

Their goal is to use a device called a spectrograph to get a spectra of five to eight supernovae. This spectrum is a "photograph" of the light emitted by the supernova and it allows scientists to determine whether they are the type Ia supernovae that are useful for their research. By figuring out how far away these type Ia supernovae are (or "were," since by the time their light reaches us, they have long since vanished) and observing how much the light traveling towards the Earth has shifted towards red wavelengths, they can determine how long ago the star exploded. With this information, they're building a history of the expansion of the universe. The weather in Hawaii is good, and the researchers are forecasting a good "seeing."

It's encouraging and moving to see how young these researchers are. Swift is a twenty-something from Kansas. She's so young that she has always understood the universe to be accelerating, that is, expanding faster and faster. She has never thought that the universe is decelerating, which is what the scientific community believed before 1998, when Perlmutter's team at Lawrence Berkeley National Lab and another team simultaneously reported their findings that the universe is accelerating. When this announcement was made, Swift was in the 8th grade. Perlmutter himself is only in his 40s. When he started his post-doc, he and his colleagues had to beg for time on the big telescopes. That wasn't that long ago: our understanding of the universe has shifted very fast.

A few days later, Swift invites us back to the lab to show us some of the data the researchers gathered during the observation. They obtained spectra for five supernovae – a good night's work. Swift is now in the process of figuring out which of the supernovae are type Ia's. To do this, she's comparing their spectrograms to the spectra of a standard type Ia. Light is a very useful tool because different elements emit light of different wavelengths. Swift shows me the spectrogram for a standard type Ia. It has telltale peaks and valleys that reveal what exploding type Ia supernovae eject when they explode – silicon and cobalt, among other elements.

I wonder what big changes in the way we understand our universe will be commonplace when my one-year-old niece is in her 20s. What new discoveries will we use as points of reference in the coming decades? (Assuming we're hip enough to use astronomical discoveries as points of reference!) Will scientists know by then the nature of dark energy, the now-mysterious "something" that is making the universe accelerate, pushing its fabric apart? Will I be able to preface a comment to my niece with, "When you were little, before we knew what dark energy is…"? And will she be able to reply, "Aunt Gabi, you're so ooold!" I suspect she'll do the latter no matter what.

Watch the "Dark Energy" TV Story online, as well as find additional links and resources. Also don't miss our online photo set.

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