Warped Galaxies Reveal Signs of Universe's Hidden Dark Matter (SPACE.com)

Warped visions of distant galaxy clusters are offering a reflection of the invisible matter inside them that astronomers are using to map the unseen side of the universe.

Using the Hubble Space Telescope, astronomers have observed the first of a number of galaxy clusters that they hope to use to build a cosmic census of hidden dark matter. Dark matter, thought to make up 98 percent of all matter in the universe, cannot be seen, only felt through its gravitational pull.

To find out where dark matter lies, and how much of it there is, scientists look for an effect called gravitational lensing. This bending of light is caused when mass — including dark matter — warps space-time, causing light to travel a crooked path through it. The end effect is a curvy, funhouse-mirror type view of distant cosmic objects.

The observed lensing is always stronger than it should be based on the visible matter alone. By compensating for this effect, researchers can deduce what component is caused by the presence of dark matter. [Spectacular Hubble Photos]

Scientists are planning to observe a total of 25 galaxy clusters under a project called CLASH (Cluster Lensing and Supernova survey with Hubble).

One of the first objects observed for the new census is the galaxy cluster MACS J1206.2-0847. This conglomeration of galaxies is one of the most massive structures in the universe, and its gigantic gravitational pull causes stunning gravitational lensing.

In addition to curving of light, gravitational lensing often produces double images of the same galaxy. In the new observation of cluster MACS J1206.2-0847, astronomers counted 47 multiple images of 12 newly identified galaxies.

By conducting the survey, astronomers are attempting not just to weigh these distant behemoths, but to learn more about when and how they formed. Theory suggests that the first galaxy clusters came together between 9 billion and 12 billion years ago.

Some previous research suggests that dark matter is packed more densely inside galaxy clusters than previously thought. If the new study can confirm that, it may mean that the universe's galaxy clusters formed earlier than most scientists assume.

You can follow SPACE.com senior writer Clara Moskowitz on Twitter @ClaraMoskowitz. Follow SPACE.com for the latest in space science and exploration news on Twitter @Spacedotcom and on Facebook.

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Moons Around Asteroid Reveal a Giant Rubble Pile (SPACE.com)

Nola Taylor Redd, SPACE.com Contributor
Space.com Nola Taylor Redd, Space.com Contributor
space.com – 1 hr 20 mins ago

Like the ancient Egyptian queen it was named for, the asteroid Kleopatra has birthed twins — a pair of moons that have helped scientists learn that the huge space rock is a rubble pile rather than a chunk of solid rock.

These two moons, named Alexhelios and Cleoselene after the twin children of the queen, were discovered in 2008. Now, astronomers studying their orbits have deduced that their parent asteroid is a jumble of loosely held rocks.

"That's the point of looking for triple and binary asteroids," study co-author Franck Marchis of the University of California, Berkeley told SPACE.com. "They're the only ones that allow us to measure the mass of the system." [See asteroid Kleopatra and its rocky moons]

Studying the asteroid system

Since the researchers knew Kleopatra's orbit, they were able to use data from various telescopes — including several operated by amateur astronomers — to observe Kleopatra as she passed between Earth and various bright stars.

They also used measurements from as far back as 1980 to examine other, similar passes. For each transit, they timed how long the star "winked" out of view from various positions on the planet. [Photos: Asteroids in Deep Space]

Because each location views the asteroid differently, combining these observations allowed the team to calculate the space rock's size and shape, as well as to view the moons and measure their orbit.

Having determined the orbits of Kleopatra's satellites, the team, lead by primary author Pascal Descamps of the Institut de Mecanique Celeste et de Calculs des Ephemerides (IMCCE) of the Observatoire de Paris, then was able to calculate the mass of the system as a whole.

With mass and size in hand, figuring out the asteroid's density was a breeze. The researchers concluded that the asteroid was not a solid rock.

"Our observations of the orbits of the two satellites of 216 Kleopatra imply that this large metallic asteroid is a rubble pile, which is a surprise," Marchis said in a statement.

The team reported its results in the February issue of the journal Icarus.

Big asteroid surprise

There are a number of smaller asteroids throughout the solar system that are loose, gravitationally bound piles of rock rather than solid objects.

But to find one in such a large system is surprising. At about 135 miles (217 km) in length, Kleopatra is among the largest of these rubble pile asteroids discovered over the past few years, topped only by 174-mile (280 km) 87 Sylvia.

"You expect something (this size) to be less porous," Marchis told SPACE.com.

In fact, given the density of its likely primary iron components, Kleopatra is between 30 and 50 percent empty space.

The rubble pile structure of the asteroid provides clues to its formation, as well as that of its satellites, researchers said. The collision of two larger, rocky asteroids likely resulted in the destruction of one, and the resulting rubble was held together by gravity.

As the pile continued to spin, it slowly shed mass, including its two moons. The outermost moon, Alexhelios, likely spiraled out around 100 million years ago, while the inner moon, Cleoselene, began its journey within the last 10 million years.

Kleopatra was discovered in 1880. Astronomers used stellar transits to determine it was elongated, but it wasn't until 2000 that it was revealed to be shaped more like a dog bone than a cigar. Descamps' team wanted to study whether the bulges at the end were connected to the body of the asteroid or were separate pieces entirely.

The team continues to study other binary or triple asteroid systems, but the tools that allow them to do so are limited.

"The only telescope in the world that can detect these (types of systems) is the Keck, because it has the largest aperture and the best AO (adaptive optic) system," Marchis said.  

However, thousands of astronomers vie for the use of the largest optical and infrared telescope. Marchis expressed his hope that more telescopes like the 33-foot (10-meter) giants in Hawaii will be built, allowing more research to be done.

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