Category: Space related



DARK MATTER

To weigh the universe, scientists use two kinds of cosmic scales: one to measure all the regular matter out there, and another to deduce how much invisible dark matter remains hidden underneath. These calculations have been taken further than ever before by a new study that tallied both types of mass in smaller and more distant groups of galaxies than any previous projects. The project found that these faraway galactic clusters have roughly the same proportion of dark matter to regular matter as the closer galaxy groups do. The findings could help astronomers understand more about dark matter, as well as its even stranger sibling – dark energy.

Invisible universe

Dark matter is a form of stuff that does not interact with light, so cannot be seen, but makes its presence felt by exerting a gravitational pull on normal matter.

Astronomers measure how much dark matter lies in galaxies by a fluke of physics called gravitational lensing. This phenomenon, predicted by Einstein’s theory of general relativity, causes light to curve as it flies through space-time that has been dented by the gravity of large bodies of mass.

For example, groups of massive galaxies will gravitationally warp the space-time around them, forcing light to bend as it passes through, and causing them to look distorted when their light reaches our telescopes. Scientists can tell how much total mass there is by how much of this distortion occurs.

Next, researchers calculate how much normal matter is in a cluster of galaxies by looking at its X-ray light, since the light must be coming from only the regular stars and gas that make up the cluster.

Comparing these two calculations — the total matter to just the regular matter — gives a ratio astronomers call the mass-luminosity relation. So far, the mass-luminosity relation has been measured well for nearby, large galaxy clusters, but there has not been good enough X-ray data to probe farther or smaller, dimmer clusters of galaxies.

“We can map out the big cities, but no one’s been able to map out the villages yet,” said Alexie Leauthaud of the Lawrence Berkeley National Laboratory in Berkeley, Calif., leader of the new study.

New ranges

Astronomers used observations from the European Space Agency’s XMM-Newton satellite and from NASA’s Chandra satellite, as well as data from the Hubble Space Telescope’s Cosmic Evolution Survey (COSMOS). These ultra-high resolution photos allowed the scientists to extend the mass-luminosity relation further than ever before.

With such dim objects, the gravitational lensing wasn’t immediately apparent. So researchers used a statistical analysis to measure the orientation and shape of the galaxies to find small distortions due to so-called weak lensing.

They found that the same general ratio of dark matter to normal matter prevailed in these distant, small clusters as for nearby, larger clusters.

“We didn’t know what to expect going down to lower masses or [farther distances], and we find this nice simple relationship,” Leauthaud told SPACE.com. “Now the aim is to find out why we find this nice, simple relationship.”

Dark energy enigma

The finding may help shed light on an even more bizarre aspect of the universe – dark energy. Dark energy is the name given to whatever mysterious force is causing the universe to accelerate as it expands.

“We want to try to understand the properties of dark energy,” Leauthaud said. “One way to measure properties of dark energy is to measure the number of structures that have formed for a given amount of dark matter.”

Dark energy basically works against gravity in a tug-of-war. While gravity constantly pulls mass inward, encouraging things to clump together and condense into smaller space, dark energy does the opposite. This force somehow pulls everything apart, causing everything in the universe to move away from everything else at ever-increasing speeds.

When mass clumps together enough to form galaxies, it means that gravity has won on those scales, helping things to stick together despite the pull of dark energy. So the more astronomers can measure when and how structures formed in the universe, the better they can understand just how far dark energy’s pull reaches.

What is dark matter and dark energy?

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NASA definitions…

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New galaxy cluster

 

The most massive conglomeration of galaxies ever spotted in the early universe has been found, astronomers say.

This behemoth galaxy cluster contains about 800 trillion suns packed inside hundreds of galaxies. And it’s not even finished growing.

The newfound cluster, called SPT-CL J0546-5345, is about 7 billion light-years from Earth, meaning that its light has taken that long to reach us. Thus, astronomers are seeing this clump as it was 7 billion years ago.

By now, it likely will have quadrupled in size, researchers said. The universe is about 13.7 billion years old.

“This galaxy cluster wins the heavyweight title,” astronomer Mark Brodwin of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., said in a statement. “It’s among the most massive clusters ever found at this distance.”

While there are some heavier clusters in the near universe, if we could see this cluster as it is today, it would likely rank among the most massive clusters of all, the researchers said.

Brodwin and colleagues reported the discovery in a recent edition of the Astrophysical Journal.

Dark energy

The discovery could help scientists piece together the early history of our universe, as well as how strange stuff called dark energy played a role.

Seven billion years ago, our solar system – which is about 4.5 billion years old – was not yet born. This cluster must have formed relatively soon after the Big Bang to have amassed such a girth so early, scientists said.

“This cluster is full of ‘old’ galaxies, meaning that it had to come together very early in the universe’s history — within the first 2 billion years,” Brodwin said.

These days, new galaxy clusters cannot form because of the universe’s accelerating rate of expansion – each galaxy is flying apart from all others at ever-increasing speeds. This is thought to be caused by a mysterious force scientists have named dark energy.

Scientists think dark energy is behind the universe’s mysteriously accelerating expansion, but they can’t establish for sure that this force exists.

Weighing massive clusters like SPT-CL J0546-5345 could help astrophysicists  pin down the nature of this odd quantity.

South Pole vision

The galaxy cluster was spotted by a new, huge 33-foot (10-meter) telescope at the South Pole, where the observatory benefits from an exceptionally clear, dry and stable atmosphere that enables extremely crisp high-resolution photos.

The so-called South Pole Telescope, funded by the National Science Foundation and run by scientists at more than a dozen international institutions, is finishing up its first survey of a huge swath of the sky in relatively long-wavelength, low-frequency submillimeter light.

Once the survey is complete, the researchers hope to find many more previously unknown giant galaxy clusters.

“After many years of effort, these early successes are very exciting,” Brodwin said. “The full SPT survey, to be completed next year, will rewrite the book on the most massive clusters in the early universe.”