6 C o l u m b i a U n i v e r s i t y RECORD September 6, 2002

New Findings on Cosmic Gamma-Ray Glow Shed Light on the Structure of the Universe(Continued from Page 1)

confirm an earlier predictionthat galaxy clusters containingup to several thousand MilkyWay-size galaxies each are stillaccumulating material from thesurrounding space, and, in theprocess, are boosting particleenergies high enough to pro-duce a faint gamma ray glow.

The Compton Gamma RayObservatory (GRO), whichended its mission in a fiery (butcontrolled) plunge into thePacific in June of 2000, collect-ed energetic gamma rays reach-ing Earth from space, formingthe database. Each little packetof this radiation contained morethan 10 billion times the energypresent in the light our eyes cansee. Much of this radiationemerged from the densest,hottest, and most violentregions of the cosmos--the sur-faces of neutron stars and thevicinities of supermassive blackholes. But Scharf and Mukher-jee have now concluded that asignificant portion of thegamma rays originated in thecold, dark regions of intergalac-tic space. Their discoveryappears to confirm a predictionby Avi Loeb of Harvard and EliWaxman of the Weizmann Insti-tute in Rehovot, Israel thatintergalactic matter, drawntogether by its mutual gravita-tional attraction, can producecopious quantities of gammaray emission.

We know, for instance, fromobservations of the uniform glow

of microwaves suffusing spacethat the universe was born with aremarkably smooth distributionof matter. By the time it was halfa million years old, the biggestbumps on the smooth sea of cos-mic material were no larger thanan ant compared to the height ofthe Empire State Building. Four-teen billion years later, however,we live in a galaxy that is, onaverage, more than a milliontimes denser than the universe asa whole. Today's universe issprinkled with such dense galax-ies surrounded by vast voids,and the problem of explaininghow we got from such a smoothto such a lumpy distribution ofmatter is a central problem ofmodern cosmology.

A rather successful modelconstructed over the last twodecades for this evolution froma smooth to a lumpy distribu-tion posits that the tiny, ant-likelumps slowly accumulatedmore and more of their sur-rounding material simply as aresult of gravitational attraction.Bigger and bigger lumpsformed, embedded in filamentsof gas connecting and flowingtoward them, forming a perva-sive cosmic web. As such gasfalls together, however, it reach-es speeds of several thousandmiles per second and, workingwith the weak magnetic fieldsof intergalactic space, thisprocess can accelerate electronsto extremely high energies.Loeb and Waxman calculatedthe rate at which such electronswould collide with the

microwaves left overfrom the Big Bangand boost them togamma ray energies.From this, they con-cluded that if thelargely invisible webof cosmic matter wasaccumulating asexpected, the majori-ty of the sky'sgamma-ray glowcould arise from thisprocess.

Scharf and Mukher-jee's new researchcompared a catalog ofthe several thousandgalaxy clusters in thelocal universe withthe Compton GROdatabase. Usingsophisticated statisti-cal techniques, theyshowed that the skysurrounding the mostmassive clusters wass y s t e m a t i c a l l ybrighter than otherregions. The enhance-ment observed wasvery similar to thatpredicted by the mod-els.

"This result notonly resolves thequestion of where all thesegamma rays are coming from,"Scharf said, "but provides anew probe of the gravity-drivenpicture of structure formation inthe Universe."

Mukherjee added: "This dis-covery also gives us one of thefirst estimates on how magne-

tized intergalactic space mustbe, something that will need tobe included in future models forhow galaxies and clustersform."

The authors predict that futureobservatories will see glowinggamma-ray haloes 30 millionlight years across surroundinggalaxy clusters. The GLAST

mission, due for launch in 2006,will now add to its target listmany of the nearest largeagglomerations of matter inorder to watch the formation ofstructure in the universe throughits gamma-ray eyes. For more,visit http:// www.columbia.edu/cu/news/02/08/gamma_rays.html.

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housing conditions remainedunchanged. Furthermore,reports of satisfaction withthe city and police protectionimproved.

“These reported improve-ments in indicators of well-being suggest that New YorkCity families have been veryresilient despite a downturnin the U.S. economy and theemotional scars of Septem-ber 11,” said Social WorkProfessor Julien Teitler, whoco-authored the surveyreport. “The improvement inperceptions of the city as aplace to live also confirmreports that the spirit of NewYorkers remains strong.”

However, other findingsfrom the survey show nega-tive effects in several areasafter September 11. Twelvepercent of interviewed adultsreported that either they or afamily member lost workbecause of the World TradeCenter attacks. In addition,14 percent reported newhealth problems. Thirty-onepercent of New York Cityadults reported sleepingpoorly, 32 percent reportedhaving problems concentrat-ing at work and 38 percentsaid they preferred to stay athome and not go to work orother places as a result of theattacks on the World TradeCenter.

Other findings of theadults surveyed revealed a

This computer simulation image reveals filaments of invisible dark matter, uponwhich ordinary matter gathers. Over millions to billions of years, visible web-likestructure appears. Galaxies slowly form along the filaments, like pearls on astring. Galaxy clusters arise where filaments intersect. Gamma rays emitted fromgalaxy clusters serve as probes to the early structure formation in the Universe.

negative impact of the attackson the city’s children. Forty-two percent of adults withchildren (791 of the total sam-ple) reported that they had cutdown on their children’s free-dom to travel around the city.

Eight percent of adults withchildren reported their childhad a new health problemattributable to September 11,with 44 percent of these par-ents seeking help for theirchild. In addition, 17 percentreported that after September11 their child often wanted tostay at home and not go toschool or other places withouta parent. Seventeen percentsaid that their child has oftenfelt afraid of being in crowdedplaces. Twenty-seven percentreported that their child wor-ried that the parent might goaway and never come back.

Reports of ill effects of Sep-tember 11 were especiallyprevalent among foreign-bornadults in New York City, com-prising of 40 percent of theadults surveyed. Immigrantswere almost twice as likely asU.S.-born adults to report lossof their job or the job of a fam-ily member; they were 17 per-cent more likely to reportproblems concentrating atwork, and were twice as likelyto report that their child wasafraid of crowded places.

Despite the improved per-ceptions of New York City, thesurvey’s researchers said thefindings of the survey indicatecertain sectors of New York

City residents may requirespecial assistance in order torebound from the September11 tragedy—needs that maybe addressed with health andsocial service interventions.

The New York Social Indi-cators Survey (SIS) is con-ducted at Columbia Universi-ty’s School of Social Workby professors Irwin Garfinkeland Julien Teitler. The SIS isdesigned to assess the wellbeing of New York City resi-dents. The survey interviews1,500 adult New Yorkers inall five boroughs by phoneevery two years.

The survey collects infor-mation about human, finan-cial, and social assets; eco-nomic and social living con-ditions; and perceptions ofthe city and its services. Thesurvey also measures thesources and extent of exter-nal support from govern-ment, family and friends,community and religiousprograms, and employers.SIS is conducted in four lan-guages.

The 2002 data for the sur-vey, officially titled the NewYork Social IndicatorsSurvey, were collected fromMarch through June.

Additional informationabout the Social IndicatorsSurvey can be found at theSocial Indicators SurveyCenter website: www. siscen-ter.org. A full report on the2002 SIS will be releasedlater in the fall of 2002.

NYC Residents More Content Despite Lingering Concerns

Bollinger Addresses Staff OutdoorsFor his first public campus appearance since he assumed the pres-

idency in June, Lee C. Bollinger chose Columbia’s largest office partythis summer, a bar-be-que thrown for the 1,700 staff that help run theUniversity. The event is hosted annually by Emily Lloyd, executivevice president for administration, who oversees the departmentsresponsible for employment, security, building and grounds mainte-nance, student services and IT support.

“People who work for large institutions often do not receive creditfor all they do,” Bollinger said after an official introduction to thegathering by Lloyd. “But just by walking around campus the past fewweeks I am already extremely impressed by what you do. It shows,from the beautiful landscaping, to the care taken in maintaining thetrees, the presence of security officers and great food service.”

RECORD PHOTO BY EILEEN BARROSO