Fermi Observations of Dwarf Galaxies Provide New Insights on Dark Matter

There's more to the cosmos than meets the eye. About 80 percent of the matter in the universe is invisible to telescopes, yet its gravitational influence is manifest in the orbital speeds of stars around galaxies and in the motions of clusters of galaxies. Yet, despite decades of effort, no one knows what this "dark matter" really is. Many scientists think it's likely that the mystery will be solved with the discovery of new kinds of subatomic particles, types necessarily different from those composing atoms of the ordinary matter all around us. The search to detect and identify these particles is underway in experiments both around the globe and above it.

Scientists working with data from NASA's Fermi Gamma-ray Space Telescope have looked for signals from some of these hypothetical particles by zeroing in on 10 small, faint galaxies that orbit our own. Although no signals have been detected, a novel analysis technique applied to two years of data from the observatory's Large Area Telescope (LAT) has essentially eliminated these particle candidates for the first time.

"In effect, the Fermi LAT analysis compresses the theoretical box where these particles can hide," said Jennifer Siegal-Gaskins, a physicist at the California Institute of Technology in Pasadena, Calif., and a member of the Fermi LAT Collaboration. Earlier today, she discussed the latest results of space based dark matter searches in an invited talk at a meeting of the American Physical Society (APS) in Atlanta, Ga.

WIMPs, or Weakly Interacting Massive Particles, represent a favored class of dark matter candidates. Some WIMPs may mutually annihilate when pairs of them interact, a process expected to produce gamma rays the most energetic form of light that the LAT is designed to detect.

NASA's Hubble Finds Most Distant Galaxy Candidate Ever Seen in Universe

Astronomers have pushed NASA's Hubble Space Telescope to its limits by finding what is likely to be the most distant object ever seen in the universe. The object's light traveled 13.2 billion years to reach Hubble, roughly 150 million years longer than the previous record holder. The age of the universe is approximately 13.7 billion years.

The tiny, dim object is a compact galaxy of blue stars that existed 480 million years after the big bang. More than 100 such mini-galaxies would be needed to make up our Milky Way. The new research offers surprising evidence that the rate of star birth in the early universe grew dramatically, increasing by about a factor of 10 from 480 million years to 650 million years after the big bang.

"NASA continues to reach for new heights, and this latest Hubble discovery will deepen our understanding of the universe and benefit generations to come,” said NASA Administrator Charles Bolden, who was the pilot of the space shuttle mission that carried Hubble to orbit. “We could only dream when we launched Hubble more than 20 years ago that it would have the ability to make these types of groundbreaking discoveries and rewrite textbooks.”

Astronomers don't know exactly when the first stars appeared in the universe, but every step farther from Earth takes them deeper into the early formative years when stars and galaxies began to emerge in the aftermath of the big bang.

"These observations provide us with our best insights yet into the earlier primeval objects that have yet to be found," said Rychard Bouwens of the University of Leiden in the Netherlands. Bouwens and Illingworth report the discovery in the Jan. 27 issue of the British science journal Nature.

This observation was made with the Wide Field Camera 3 starting just a few months after it was installed in the observatory in May 2009, during the last NASA space shuttle servicing mission to Hubble. After more than a year of detailed observations and analysis, the object was positively identified in the camera's Hubble Ultra Deep Field-Infrared data taken in the late summers of 2009 and 2010.


The object appears as a faint dot of starlight in the Hubble exposures. It is too young and too small to have the familiar spiral shape that is characteristic of galaxies in the local universe. Although its individual stars can't be resolved by Hubble, the evidence suggests this is a compact galaxy of hot stars formed more than 100-to-200 million years earlier from gas trapped in a pocket of dark matter.

"We're peering into an era where big changes are afoot," said Garth Illingworth of the University of California at Santa Cruz. "The rapid rate at which the star birth is changing tells us if we go a little further back in time we're going to see even more dramatic changes, closer to when the first galaxies were just starting to form."

The proto-galaxy is only visible at the farthest infrared wavelengths observable by Hubble. Observations of earlier times, when the first stars and galaxies were forming, will require Hubble’s successor, the James Webb Space Telescope (JWST).

The hypothesized hierarchical growth of galaxies -- from stellar clumps to majestic spirals and ellipticals -- didn't become evident until the Hubble deep field exposures. The first 500 million years of the universe's existence, from a z of 1000 to 10, is the missing chapter in the hierarchical growth of galaxies. It's not clear how the universe assembled structure out of a darkening, cooling fireball of the big bang. As with a developing embryo, astronomers know there must have been an early period of rapid changes that would set the initial conditions to make the universe of galaxies what it is today.

"After 20 years of opening our eyes to the universe around us, Hubble continues to awe and surprise astronomers," said Jon Morse, NASA's Astrophysics Division director at the agency's headquarters in Washington. "It now offers a tantalizing look at the very edge of the known universe -- a frontier NASA strives to explore."

Hubble is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the telescope. The Space Telescope Science Institute (STScI) conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington.

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So you Think you can Solve a Cosmology Puzzle?

Cosmologists have come up with a new way to solve their problems. They are inviting scientists, including those from totally unrelated fields, to participate in a grand competition. The idea is to spur outside interest in one of cosmology's trickiest problems -- measuring the invisible dark matter and dark energy that permeate our universe.

The results will help in the development of new space missions, designed to answer fundamental questions about the history and fate of our universe.

"We're hoping to get more computer scientists interested in our work," said cosmologist Jason Rhodes of NASA's Jet Propulsion Laboratory in Pasadena, Calif., who is helping to organize the challenge, which begins on Dec. 3, 2010. "Some of the mathematical problems in our field are the same as those in machine-learning applications -- for example facial-recognition software."

JPL and several European Universities, including The University of Edinburgh and University College London in the United Kingdom, are helping to support the event, which is funded by a European Union group called Pattern Analysis, Statistical Modelling and Computation Learning. The principal investigator is Thomas Kitching of the University of Edinburgh.

This year, the competition, which has operated since 2008, is called GREAT 2010, after GRavitational lEnsing Accuracy Testing. The challenge is to solve a series of puzzles involving distorted images of galaxies. Occasionally in nature, a galaxy is situated behind a clump of matter that is causing the light from the galaxy to bend. The result is a magnified and skewed image of the galaxy. In the most extreme cases, the warping results in multiple images and even a perfect ring, called an Einstein Ring after Albert Einstein, who predicted the effect. But most of the time, the results are more subtle and a galaxy image is distorted just a tiny bit -- not even enough to be perceived by eye. This is called weak gravitational lensing, or just weak lensing for short.

Weak lensing is a powerful tool for unlocking the fabric of our universe. Only four percent of our universe consists of the stuff that makes up people, stars and anything with atoms. Twenty-four percent is dark matter -- a mysterious substance that we can't see but which tugs on the regular matter we can see. Most of our universe, 72 percent, consists of dark energy, which is even more baffling than dark matter. Dark energy is gravity's nemesis -- where gravity pulls, dark energy pushes. By studying lensed, or distorted, galaxies, scientists can create better maps of dark matter -- and by studying how dark matter changes over time, they can better understand dark energy.

Weak lensing is a promising method for tackling these questions. The 2010 U.S. National Research Council Decadal Survey on astronomy and astrophysics has ranked mission proposals using this method as high priorities.

The GREAT 2010 challenge is designed to improve weak-lensing know-how. Participants will start with fuzzy pictures of galaxies that have been distorted ever so slightly by invisible dark matter parked in front of them. The effect is so small that you can't see it with your eyes. The problem is even trickier because the telescopes are also distorting the galaxy images to an even greater degree than the dark matter. It takes complex techniques -- mathematical models and image-analysis algorithms -- to tease apart these various influences and ultimately discover how dark matter is warping a galaxy's shape.

"This is an image-analysis challenge. You don't need to be an astronomer or cosmologist to help measure the weak-lensing effect," said Kitching. "This challenge is meant to encourage a multidisciplinary approach to the problem."

Participants will have nine months to solve a series of thousands of puzzles. The winners will be announced at a closing ceremony and workshop held at JPL. Prize-winners can expect some kind of cool gadget -- as well as the satisfaction of having brought the world one step closer to understanding what makes our universe tick.

Detailed Dark Matter Map Yields Clues to Galaxy Cluster Growth

Astronomers using NASA's Hubble Space Telescope took advantage of a giant cosmic magnifying glass to create one of the sharpest and most detailed maps of dark matter in the universe. Dark matter is an invisible and unknown substance that makes up the bulk of the universe's mass.

The new dark matter observations may yield new insights into the role of dark energy in the universe's early formative years. The result suggests that galaxy clusters may have formed earlier than expected, before the push of dark energy inhibited their growth. A mysterious property of space, dark energy fights against the gravitational pull of dark matter. Dark energy pushes galaxies apart from one another by stretching the space between them, thereby suppressing the formation of giant structures called galaxy clusters. One way astronomers can probe this primeval tug-of-war is through mapping the distribution of dark matter in clusters.

A team led by Dan Coe at NASA's Jet Propulsion Laboratory in Pasadena, Calif., used Hubble's Advanced Camera for Surveys to chart the invisible matter in the massive galaxy cluster Abell 1689, located 2.2 billion light-years away. The cluster's gravity, the majority of which comes from dark matter, acts like a cosmic magnifying glass, bending and amplifying the light from distant galaxies behind it. This effect, called gravitational lensing, produces multiple, warped, and greatly magnified images of those galaxies, like the view in a funhouse mirror. By studying the distorted images, astronomers estimated the amount of dark matter within the cluster. If the cluster's gravity only came from the visible galaxies, the lensing distortions would be much weaker.

Based on their higher-resolution mass map, Coe and his collaborators confirm previous results showing that the core of Abell 1689 is much denser in dark matter than expected for a cluster of its size, based on computer simulations of structure growth. Abell 1689 joins a handful of other well-studied clusters found to have similarly dense cores. The finding is surprising, because the push of dark energy early in the universe's history would have stunted the growth of all galaxy clusters.

"Galaxy clusters, therefore, would had to have started forming billions of years earlier in order to build up to the numbers we see today," Coe explains. "At earlier times, the universe was smaller and more densely packed with dark matter. Abell 1689 appears to have been well fed at birth by the dense matter surrounding it in the early universe. The cluster has carried this bulk with it through its adult life to appear as we observe it today."