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Posts Tagged ‘universe’

Take Hydra, a cluster of galaxies about three billion light years away. Astronomers have measured the distance from the Earth to Hydra by looking at the light coming from the cluster. Through a prism, Hydra’s hydrogen looks like four strips of red, blue-green, blue-violet and violet. But during the time it takes Hydra’s light to reach us, the bands of color have shifted down toward the red end—the low-energy end—of the spectrum. On their journey across the universe, the wavelengths of light have stretched. The farther the light travels, the more stretched it gets. The farther the bands shift toward the red end, the farther the light has traveled. The size of the shift is called the redshift, and it helps scientists figure out the movement of stars in space. Hydra isn’t the only distant cluster of galaxies that displays a redshift, though. Everything is shifting, because the universe is expanding. It’s just easier to see Hydra’s redshift because the farther a galaxy is from our own, the faster it is moving away.

There is no limit to how fast the universe can expand, says physicist Charles Bennett of Johns Hopkins University. Einstein’s theory that nothing can travel faster than the speed of light in a vacuum still holds true, because space itself is stretching, and space is nothing. Galaxies aren’t moving through space and away from each other but with space—like raisins in a rising loaf of bread. Some galaxies are already so far away from us, and moving away so quickly, that their light will never reach Earth. “It’s like running a 5K race, but the track expands while you’re running,” Bennett says. “If it expands faster than you can run, you’ll never get where you’re going."

Have a science question you've always wondered about? Send an email to fyi@popsci.com

The project mapped more than 43,000 galaxies picked from the Two-Micron All-SkySurvey (2MASS), which scanned the entire sky in three near-infrared wavelengths. But 2MASS alone offered an incomplete picture. To achieve the third dimension, astronomers needed to know not only how galaxies relate spatially on a flat map, but how far away they are from Earth and each other. So the 2MASS Redshift Survey began measuring the galaxies’ redshifts, one by one, using two telescopes in Arizona and Chile.

Redshifting is the way in which a galaxy’s light is stretched into longer wavelengths by the expansion of the universe. The farther a galaxy is from Earth, the greater its redshift. By analyzing those measurements, the 2MRS was able to achieve that important third dimension, and to produce the map you see above.

But 2MRS isn’t just notable for mapping faraway galaxies. It also made great strides closer to home. Regions nearer the Milky Way tend to be difficult to observe, as they are obscured by the dust and gas in our own galaxy. The near-infrared wavelengths employed by 2MASS are better at penetrating this dust, giving us a better look at our own galactic neighborhood.

A higher res version of the pic is available here.

[Harvard-Smithsonian Center for Astrophysics]

The WiggleZ project used NASA’s Galaxy Evolution Explorer space telescope and a massive Australian observatory to peer back 7 billion years in time, equivalent to the cosmic time span that has been dominated by dark energy. It's the first time a single study has looked at such a lengthy period of cosmic history.

Dark energy was first proposed in the 1990s as astronomers discovered supernovae were moving away from us at accelerating speeds. This did not fit with prevailing theories of gravity, so scientists determined a new force called dark energy was to blame. The new survey independently verifies those earlier cosmological expansion observations, according to researchers at NASA and the Swinburne University of Technology in Melbourne, Australia.

The universe is about 13.7 billion years old, according to the best estimates, and for a little more than half that life it was dominated by the influence of gravity. All the baryonic matter, meaning matter with atoms and their constituent parts, was close enough together for gravity to have an influence. It helped form galaxies and galaxy clusters, for instance. But roughly 8 billion years after the Big Bang first flung everything apart, as the universe grew more and more diffuse, gravity’s power apparently succumbed to the increasing influence of dark energy. Galaxy cluster formation slowed down. Things started to fall apart.

To measure this, the researchers used a 3-D map created by NASA’s Galaxy Evolution Explorer, which identified bright, young galaxies in the distant universe. Then the team used the Anglo-Australian Telescope to gather detailed light information about each galaxy. They examined the patterns of distance between pairs of galaxies, which tend to wind up about 490 million light years apart. (This has to do with sound waves left over from the very early universe that resulted in areas of higher or lower pressure.) As the universe has expanded because of dark energy, this pattern has shifted.

The team also measured the rate at which galaxy clusters have been growing, and were able to show that something is counteracting gravity, slowing down the clusters’ formation.

This information was combined with data about how quickly the galaxy pairs are moving away from us, and together that verifies the earlier supernova findings: Yes, they are moving away, and yes, it is happening faster and faster.

Dark energy accounts for about 73 percent of the mass-energy of the universe. Dark matter, which is only slightly better understood, makes up about 23 percent of the universe. The remaining 4 percent is baryonic matter — galaxies, stars, the solar system, and you.

Dark energy will continue to speed up this cosmic expansion, and someday, everything will be so far apart that we won’t be able to see other galaxies or even other stars in the Milky Way. Let's hope we find ETs before then.

[ScienceDaily]

Neutrinos are subatomic particles created by radioactive decay or nuclear reactions. Like other types of extrasolar radiation, they emerge from energetic cosmic events and constantly bombard Earth. Neutrinos are unique among cosmic particles, however, in that they carry no electric charge. The magnetic fields of stars and planets bend the paths of charged particles, making it impossible for scientists to identify their origin. But neutrinos fly in a straight line: Catch one, and you can trace it back to whatever produced it, which makes them one of the easiest means of probing the far reaches of the universe.

Detecting a neutrino, however, is a bit like trying to catch a flea with a fishing net—the particles are so small that trillions of them travel through Earth every second without even hitting an atom. So the researchers at IceCube employ a clever technique to spot indirect evidence of neutrinos.

Every day, several dozen neutrinos passing through IceCube will hit a hydrogen or oxygen atom in the ice and eject another particle, called a muon, that emits a blue light. In Antarctica’s nearly pure ice, the photo sensors can spot such a flash a football field away, and with dozens of sensors registering each muon, scientists can triangulate the neutrino’s exact path through the ice and extrapolate it to its source.

IceCube’s size allows it to measure ultra-high-energy neutrinos, particles that pack as much energy as one of Roger Federer’s serves, says Spencer Klein, a physicist at Lawrence Berkeley National Laboratory who will monitor IceCube’s output. The sources of these neutrinos, he says, are mysterious. The main suspects are super-massive black holes that spit intense jets of particles, or collisions involving a neutron star and a black hole. “Or maybe something unknown,” Klein says. “It’s hard to explain how you get such energetic particles, but it’s clear that they exist.”

The unknown something, he says, could be dark matter, the invisible mass that makes up 90 percent of the universe. The existence of dark matter was proposed in 1933, but scientists still know very little about what it is or how it acts. One theory is that it consists of weakly interacting particles. If enough of these particles congregate, they might annihilate one another and produce a burst of neutrinos, which IceCube could detect to help reveal some characteristics of dark matter. If the neutrinos originate from the Earth or sun, it would confirm that dark-matter particles exist and that they are attracted by gravity. And if the sun emits relatively more neutrinos than Earth, that’s an indication that dark-matter particles interact more strongly with hydrogen, which provides insight into the matter’s quantum behavior.

Once IceCube’s final seven strands of sensors are in place, it will detect 100 neutrinos a day, 14 times as many as the two-year-old French neutrino detector Antares. IceCube will not only help scientists identify the source of cosmic rays, dark matter and other objects that influence the universe’s evolution, it will produce unexpected discoveries, says Francis Halzen, the principal investigator on Ice Cube. From Galileo’s refracting spyglass to the Hubble Space Telescope, he notes, every time scientists turn a higher-fidelity tool to the cosmos, they find something new. “If IceCube observes separated pairs of particles, they might be supersymmetric, a new and very different type of matter,” Klein says. “That would be extremely exciting.”

WMAP, a joint project of NASA and Princeton University, launched in 2001 with the goal of studying the cosmic microwave background, basically the atoms remaining that began releasing radiation closest to the Big Bang. This data has allowed cosmologists an unprecedented amount of insight into the earliest workings of the universe, enabling them to answer with reasonable certainty such questions as "how old is the universe?"

In fact, WMAP is actually listed in the Guinness Book of World Records for its success in pinpointing the age of the universe more precisely than any other tool in history: 13.75 billion years old, give or take 0.11 billion.

The first WMAP research, released in 2003, managed to prove the quantities of different types of matter in the universe. Says Wired: "By comparing computer models of what hypothetical universes with different compositions should look like to WMAP’s view of the actual universe, the team of cosmologists proved that 73 percent of the universe is made of dark energy, 22.4 percent is dark matter and just 4.6 percent is the regular, visible matter that makes up stars, planets and people."

WMAP's studies are immensely popular--the three studies (2003, 2008, January 2010) released by the WMAP team are also the three most highly-cited studies of the past ten years in all of physics and astronomy. The nine-year gathering of data is over, largely due to the weakening of the satellite's batteries, but there's still lots to analyze. Another study will come in about two years, and there doesn't seem to be any doubt that it too will bring fascinating revelations. The team is currently working on figuring out what happened in the first trillionth of a trillionth of a second of the universe's life.

So thanks and goodbye, WMAP. I hope you enjoy your retirement, orbiting the sun.

[NASA and Wired]

Watch "violent relaxation" in action

Scientists at the Argonne National Laboratory, the Flash Center at the University of Chicago and the Harvard-Smithsonian Center for Astrophysics used supercomputers to model the colossal forces involved in galaxy collisions just like the one above. Astrophysicists would like to know more about dark matter’s role in galaxy evolution, and sophisticated computer models are helpful. They’re also awesome to watch.

The above image of the Bullet Cluster is actually a combination of data sets from the Chandra X-Ray Observatory, the Hubble Space Telescope and the Magellan telescope in Chile. The pink light represents the temperature and density of normal matter; the visible stars represent the galaxies; and the blue light represents contour levels from dark matter, detected from the way it bends light behind the clusters.

As the cluster collides, the dark matter cores slip past each other without interacting, so in the image, it looks like they’re moving ahead of the normal matter.

Most of the universe is made up of dark matter, which gets its name simply because no one knows what it is. Scientists do know that it doesn’t interact with normal matter, except gravitationally. So how do you model something like that? Very carefully, it turns out.

The computer code simulates the interaction of both normal matter, also called baryonic matter, and dark matter. But modeling both types of matter required very different computations.

As the galaxies swirl together, baryonic matter mixes and generates turbulence. This process is pretty well understood, so programmers used hydrodynamic code to model the regular-matter collisions.

But dark matter only interacts gravitationally, so programmers couldn’t generalize. They modeled each particle individually, in a process called an N-body code.

As the galaxies’ dark matter cores reach equilibrium and start to orbit each other, their gravitational influence mixes up the normal matter some more. Ultimately, the mixing of hot gas is completely driven by the violent motion of the dark matter. The simulation is yet another demonstration of the powerful role dark matter plays in the universe.

Check it out below.

[Discovery News]

The paper, recently submitted to Physical Review Letters and posted to the physics arXiv, suggests the fine structure constant is not actually constant at all. This could mean that if we were in a different place or time period, atoms would not stay together and nothing — neither planets nor people — could exist.

A team led by John Webb at the University of New South Wales, Australia, has been studying whether the fine structure constant, otherwise known as alpha, changes over time. Alpha is a special number that essentially describes the strength of the electromagnetic force. The famous physicist Richard Feynman called its value "one of the greatest damn mysteries of physics." If it is not 1/137.036, things fall apart.

If alpha was different in the past, the universe might have looked different, too, which could be determined by looking at distant interstellar gases and how they absorb light. Observations by Webb and others at the Keck Observatory in Hawaii suggest that this is exactly the case — over time, alpha has changed ever so slightly.

Competing studies did not find the same result, however, so this is still a controversial idea. But it’s a fair bet Webb’s follow-up is even more tendentious: He says alpha also changes over space. According to his theory, we’re smack in the Goldilocks zone, where alpha is exactly the right value to make matter possible.

This paper happened because Webb and his team wanted to reexamine their Keck findings, which suggested alpha was a tiny bit smaller about 9 billion years in the past. They went to the Very Large Observatory in Chile to check it out, and were shocked by what they saw: the further they looked, the bigger alpha got. The discrepancy is even stranger given the two telescopes’ positions: they are in two different hemispheres, so they look in two different directions.

So, to recap: in one direction, alpha was once smaller; in exactly the opposite direction, it was once bigger. This implies that alpha continuously varies throughout space. As Technology Review’s physics blog puts it, that's a mind-blowing result. If it’s true and can be verified, it could mean the universe is much larger than what we can see, and that the laws of physics vary within it.

It would not be possible for our type of life to exist in a place where alpha were any different. So here’s to here and now.

[The Economist]