Irvine

Rare View of Ancient Galaxy Crash Revealed.

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Astronomers caught a glimpse of two star-forming galaxies as they collided 11 billion light-years away. The smashup could eventually produce one giant elliptical galaxy, researchers say

Astronomers have caught two big ancient galaxies in the act of colliding, shedding new light on the role such megamergers played in galactic evolution during the universe’s youth.

The colossal smashup will eventually produce one giant elliptical galaxy, researchers said, suggesting that most such behemoths formed rapidly in this manner long ago, rather than growing slowly over time by gobbling up a series of relatively small galaxies.

“I think at least 90 percent of elliptical galaxies at this mass were formed through this channel,” study lead author Hai Fu, of the University of California, Irvine, told SPACE.com. [Photos of Great Galactic Crashes]

Two galaxies becoming one

The merger is occurring 11 billion light-years away, meaning that astronomers are seeing the two colliding galaxies as they were about 3 billion years after the Big Bangthat created the universe. During this epoch, “red and dead” elliptical galaxies full of old stars were common.

Fu and his colleagues initially thought the two merging galaxies were a singleton, dubbed HXMM01, when they saw it with the European Space Agency’s infraredHerschel space telescope.

But follow-up observations with a variety of other instruments, both on the ground and in space, revealed that HXMM01 is actually two galaxies on a collision course, separated by about 62,000 light-years at the moment.

The gas-rich two-galaxy system contains the stellar equivalent of about 400 billion suns and is churning out new stars at a fantastic clip — about 2,000 per year, researchers said. For comparison, just two to three new stars are born every year in our own Milky Way.

At this rate, the newly forming elliptical galaxy will exhaust its gas reservoirs and cease birthing stars in just 200 million years, going red and dead in what researchers describe as a surprisingly short period of time.

“The common thought was that massive galaxies form by accreting smaller galaxies and the growth, though rapid, would last more than 200 million years,” co-author Asantha Cooray, also of UC-Irvine, told SPACE.com via email.

“And the formation was expected to not be as efficient as we have observed,” Cooray added. “The 40 percent efficiency of star formation, the efficiency at which gas is converted to stars in one rotation of the system, was unexpected.”

Fu and his colleagues report their results online today (May 22) in the journal Nature.

Star-formation mystery

The HXMM01 system’s startling efficiency explains how elliptical galaxies can go red and dead so fast, Fu and Cooray said. Ellipticals’ quick transformation had been a mystery, with some astronomers suggesting that their star-forming raw materials had been ejected by superpowerful phenomena such as quasars.

But this efficiency raises intriguing new questions, which Fu and his colleagues hope to tackle by further studying these ancient galaxies and their merging progenitors.

They want to “truly understand what is going on in those galaxies — why the star-formation efficiency is 10 times higher than normal star-forming galaxies,” Fu said. “That part is a total mystery right now.”

Source: http://www.scientificamerican.com

 

Physicists Twist Water into Knots .

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A 3-D-printed vortex-maker may improve understanding of braided fluids in nature, such as in the sun’s outer atmosphere, superconductive materials, liquid crystals and quantum fields

More than a century after the idea was first floated, physicists have finally figured out how to tie water in knots in the laboratory. The gnarly feat, described today in Nature Physics, paves the way for scientists to experimentally study twists and turns in a range of phenomena — ionized gases like that of the Sun’s outer atmosphere, superconductive materials, liquid crystals and quantum fields that describe elementary particles.

Lord Kelvin proposed that atoms were knotted “vortex rings” — which are essentially like tornado bent into closed loops and knotted around themselves, as Daniel Lathrop and Barbara Brawn-Cinani write in an accompanying commentary. In Kelvin’s vision, the fluid was the theoretical ‘aether’ then thought to pervade all of space. Each type of atom would be represented by a different knot.

Kelvin’s interpretation of the periodic table never went anywhere, but his ideas led to the blossoming of the mathematical theory of knots, part of the field of topology. Meanwhile, scientists also have come to realize that knots have a key role in a host of physical processes.

Creating a knot in a fluid bears little resemblance to tying a knot in a shoelace, say Dustin Kleckner and William Irvine, physicists at the University of Chicago in Illinois. The entire three-dimensional (3D) volume of a fluid within a confined region, such as a vortex, must be twisted. Kleckner and Irvine have now created a knotted vortex using a miniature version of an airplane wing built with a 3D printer.

During an airplane’s flight, a wing induces a rotational or vortex-like motion of air currents that gives lift to an airplane. When a wing at rest suddenly accelerates, it creates two vortices of air circulating in opposite directions. The researchers submerged their tiny wings in a tank of water and gave it a sudden acceleration to create a knotted structure (videos below and at top).

Capturing images of the knot was another technical tour-de-force. Fluid dynamicists often use colored dye to trace the motion of fluids, but Kleckner and Irvine injected tiny gas bubbles into the water that were drawn to the center of the knotted vortex by buoyancy forces. A high-speed laser scanner capable of producing CT-scan views of the fluid at 76,000 frames per second enabled the researchers to reconstruct the 3D arrangement of the bubbles, thus revealing the knots.

“The authors have managed a remarkable achievement to be able to images these vortex knots,” says Mark Dennis, an optical physicist at the University of Bristol, UK, who has made knotted vortices from light beams. The new study, he adds, transforms abstract notions about physical processes involving knots into testable ideas in the laboratory.

“Knotted vortices are an ideal model system for allowing us to study the precise way in which knots untie themselves in a real physical field,” says Irvine.

Knotted vortices show up in several branches of physics. Particle physicists, for example, have proposed that ‘glueballs’, hypothetical agglomerations of gluons — the elementary particles that bind quarks to form protons and neutrons — are tightly knotted quantum fields.

And in January, scientists reported evidence of ‘unbraiding’ or relaxation of knotted magnetic fields that may help to transfer heat to the Sun’s corona, or outer atmosphere, explaining why the plasma in this region is much hotter than the Sun’s surface.

Source: Scientific American.