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Matter vs antimatter

Nebulae in space

The Big Bang model suggests equal quantities of matter and antimatter should have formed, but the antimatter is nowhere to be seen out in space. A new experiment gives clues as to why matter has come to dominate.

  • Big Bang model suggests equal amounts of matter and antimatter
  • But only matter is seen widespread throughout the universe
  • New experiment gives clues as to why matter is dominant

A large collaboration of physicists working at the Fermilab Tevatron particle collider in the USA has found evidence for a possible explanation for the prevalence of matter over antimatter in the universe.

They found that smashing protons together in their experiment produced short-lived particles called “B mesons” that almost immediately broke down into debris that included slightly more matter than antimatter.

When particles of matter and antimatter collide, they annihilate each other and release energy. If there is slightly more matter to begin with, then all the antimatter will be annihilated, leaving a small excess of matter.

This sort of matter/antimatter asymmetry accounts for the fact that just about all the material in the universe is made of the normal matter we’re familiar with.

The Fermilab Tevatron

The Fermilab Tevatron (circular feature in background) is used to smash atomic particles together at high speed.

The Big Bang model suggests that equal amounts of matter and antimatter should have been formed, but the antimatter seems to have disappeared—everything in the universe seems to be made of normal matter. Why?

Physicists have long known about processes described by current physics theory that would produce tiny excesses of matter, but the amounts the theories predict are far smaller than necessary to create the universe we observe.

The Tevatron experiments suggest that we are on the verge of accounting for the quantities of matter that exist today.

But the truly exciting implication is that the experiment implies that there is new physics, beyond the widely accepted Standard Model, that must be at work.

If that’s the case, major scientific developments lie ahead.

The results emerge from a complicated and challenging analysis, and have yet to be confirmed by other experiments.

If the matter/antimatter imbalance holds up under the scrutiny of researchers at the Large Hadron Collider in Europe and competing research groups at Fermilab, it will likely stand as one of the most significant milestones in high-energy physics, according to Roy Briere of Carnegie Mellon University in Pittsburgh.

The results have been published in the journals Physical Review Letters and Physical Review D.

Adapted from information issued by APS / NASA / ESA / Orsola De Marco (Macquarie University).

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Cosmic baby photo

The all-sky microwave image of the universe made by the Planck space telescope.

The all-sky microwave image of the universe made by the Planck space telescope.

  • Map of the entire sky at microwave wavelengths
  • Shows the afterglow of the Big Bang
  • Will lead to better understanding of cosmic evolution

Scientists operating Europe’s space telescope, Planck, have released the mission’s first image of the whole sky.

“This is the moment that Planck was conceived for,” says European Space Agency (ESA) Director of Science and Robotic Exploration, David Southwood.

Planck picks up microwave wavelengths. What it sees are microwaves coming from near and far in the universe.

In particular, it is studying the microwave “glow” left over from the Big Bang 13.7 billion years ago—the cosmic microwave background radiation (CMBR). When we look at the CMBR, we’re seeing the oldest view we’ve ever had of the universe.

The CMBR has cooled right down from its fireball days, and is now at a temperature of about –270 degrees Celsius (only 2.7 degrees above absolute zero).

The new image is a map of the microwaves picked up from all different directions in space.

The oval shape of the map is similar to an oval-projection map of Earth, where cartographers take a round object (the Earth) and spread it out onto a flat shape. With Planck, it is a microwave map of the sky that is spread onto a flat surface.

Artist's impression of Planck

An artist's impression of the Planck telescope in its near-Earth location in space.

Why is the universe clumpy?

Stretching across the middle of the map is a mess of microwaves that come from sources within our Milky Way galaxy.

Of more interest is the mottled, reddish areas above and below. This is where Planck can see past the Milky Way to the distant universe beyond. The mottling comes from tiny temperature differences from one point to another in the CMBR.

In 1992, a forerunner of Planck, the Cosmic Microwave Background Explorer (COBE) spacecraft made the first detailed map of the CMBR. It showed the mottling effect.

The mottling effect is thought to reflect the way the universe has become “clumpy”—a combination of huge voids of empty space, and vast clusters and superclusters of galaxies.

Astronomers want to know why matter in the universe tended to clump into the clusters and superclusters, leaving the huge voids behind. It’s thought that the Big Bang explosion was “non-uniform”, ie. stuff spread out unevenly.

The mottling effect in the CMBR is thought to reflect that unevenness.

The initial discovery of the CMBR with ground-based antennae in 1964 led to its discoverers winning the Nobel Prize for Physics. This was followed by up another Nobel Prize for Physics in 2006 for two of the leaders of the COBE mission.

A scientific Eldorado

Planck is only a quarter of the way through its four-year mission. In that time, it will make four complete scans of the cosmos, building a very detailed map of the CMBR.

“We’re not giving the answer. We are opening the door to an Eldorado where scientists can seek the nuggets that will lead to deeper understanding of how our Universe came to be and how it works now,” says Southwood.

“The image itself and its remarkable quality is a tribute to the engineers who built and have operated Planck. Now the scientific harvest must begin.”

Story by Jonathan Nally, Editor,

Images courtesy ESA / LFI & HFI Consortia / C. Carreau

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Galaxy distance record smashed

A cluster of galaxies 9.6 billion light-years away

Astronomers have spotted galaxies 9.6 billion light-years away (circled). The arrows indicate galaxies that are likely located at the same distance, clustered around the centre of the image. The contours indicate X-ray emission coming from the cluster. This false colour image covers an area of the sky about 1/10th the size of the Moon.

A team of astronomers from Germany and Japan has discovered the most distant cluster of galaxies known so far — 9.6 billion light-years away.

The X-ray and infrared observations showed that the cluster hosts predominantly old, massive galaxies, demonstrating that the galaxies must have formed earlier than 9.6 billion years ago, ie. when the universe was still very young.

These and similar observations therefore provide new information not only about early galaxy evolution but also about history of the universe as a whole.

Clusters of galaxies are the largest “building blocks” in the universe. Our galaxy, the Milky Way, is part of the Virgo cluster, comprising some 1,000 to 2,000 galaxies.

By observing galaxies and clusters that are very distant from Earth, astronomers can look back in time, as the galaxies’ light was emitted a long time ago and took millions or billions of light-years to reach the astronomers’ telescopes.

Invisible to the naked eye

Astronomers had to use infrared wavelengths, invisible to the naked eye, because the expansion of the universe — which forces distant galaxies to have large velocities — shifts their light from visible to infrared wavelengths.

The Multi-Object Infrared Camera and Spectrometer (MOIRCS) at the Subaru Telescope detects near-infrared wavelengths, at which the galaxies are most luminous.

“The MOIRCS instrument has an extremely powerful capability of measuring distances to galaxies. This is what made our challenging observation possible,” says Masayuki Tanaka from the University of Tokyo.

The Subaru Observatory

The Japanese Subaru Observatory, located in Hawaii.

“Although we confirmed only several massive galaxies at that distance, there is convincing evidence that the cluster is a real, gravitationally bound cluster.”

That the individual galaxies are indeed held together by gravity is confirmed by observations in a very different wavelength band. The gas between the galaxies in clusters is heated to extreme temperatures and emits light at much shorter wavelengths. The team therefore used the XMM-Newton space observatory to look for this radiation in X-rays.

“Despite the difficulties in collecting X-ray photons … we detected a clear signature of hot gas in the cluster,” explains Alexis Finoguenov from the Max Planck Institute for Extraterrestrial Physics.

Record smashed by 400 million light-years

The combination of these different observations led to the pioneering discovery of the galaxy cluster at a distance of 9.6 billion light-years — some 400 million light-years further into the past than the previously most distant cluster known.

An analysis of the data collected about the individual galaxies shows that the cluster contains already an abundance of evolved, massive galaxies that formed some two billion years earlier.

As the processes for galaxy aging are slow, the presence of these galaxies means the cluster must have come about through the merger of massive galaxy groups, each nourishing its dominant galaxy.

The team is continuing the search for more distant clusters.

Adapted from information issued by MPE /NAOJ / Subaru.