CMYK

THE HINDU IN SCHOOL I MONDAY I DECEMBER 22 I 2014

3SCIENCE & TECHWord of the dayStave off (Verb): to prevent something from happening Used in a sentence: Yoga can stave off bone-related diseasesSuggested by: G.Amit Your turn! Pick a word from today’s TheHindu in School meaning of which you do not know and send it to usat school@thehindu.co.in (Subject: Word of the day)

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We are all made of the samebuilding blocks: particlessuch as protons, neutronsand electrons. All the mat-ter we can see is made ofthese particles. But what ifthey were only a small por-tion of all the matter in theUniverse? What if therewere other forms of matter?As strange as it may seem,the current model describ-ing the Universe assumesthe existence of an unseentype of matter.

Cosmic whirling dancesGravity is the invisible

bound that makes applesfall towards the ground andsatellites like the Moon or-bit around the Earth insteadof flying away. The Moon isindeed always falling to-wards us, but its velocitymakes it drift sideways andcircle instead of fallingstraight down. It will alwayscontinue to circle and its ve-

locity is set by the mass ofthe Earth and by the dis-tance between the two ce-lestial bodies. If the Earthwas more massive, theMoon would spin fasteraround us!

On bigger scales, galaxiesare also held by gravity. Gal-axies often look like magnif-icent whirlpools, in whichbillions of stars and hugeamounts of gas orbit arounda central black hole. As forthe Moon, the speed atwhich these stars rotateshould be set by the mass ofthe galaxy and by the dis-tance from its center. Themore massive a galaxy is,the faster its stars rotate.

Some mass is missing!But stars actually orbit

faster than they should, as ifgalaxies were much moremassive than observationssuggest. Could there besome matter we can't see? Isour theory of gravitationwrong? The easiest answeris to assume that there issome additional invisiblematter in all galaxies: darkmatter. This assumption isnot necessarily strange, asour perception of the Uni-verse is always limited: forexample, our eyes can't see

ultraviolet or infrared light,although we know it exists.

The current model de-scribing the Universe used

by most astrophysicists as-sumes the existence of adark matter that is funda-mentally different from all

other types of matter. Itwouldn't be made of pro-tons, neutrons and elec-trons as we are. Indeed, the

amount ofordinarymatter wasset once andfor all at thebeginning ofour Universe,and it can'taccountfor thelargeamountof dark matter that is need-ed to explain the velocitiesof stars in galaxies. Thereshould be more than five

times moredark matterthan ordinarymatter!

In search fordark matter

Uncoveringdarkmatteris oneof the

big challenges of physics to-day. But as dark mattershouldn't emit or absorbany light, nor interact much

with ordinary matter, itshould be totally invisibleand almost impossible todetect directly. Hundreds ofdark matter particles maybe just crossing your bodyright now, without you not-icing anything! We can justobserve its gravitational in-fluence on the visible mat-ter at large scales, or hope todetect compatible new par-ticles in colliders such as theones at CERN, in Switzer-land. Much is expected fromparticle colliders in the nextfew years.

It might also be possibleto explain the velocities ofstars in galaxies withoutdark matter. That would re-quire to change our modelsdrastically! Notably, wewould have to change ourconception of gravitation it-self. Dark matter is still oneof the great mysteries of theUniverse, but the next fewyears might be crucial forour understanding of it.Stay tuned!

(Jonathan Freundlich is aPhD student at the ParisObservatory, in France,working on star formationand galaxy evolution. Theauthor can be reached at jo-nathan.freun-dlich@obspm.fr)

The dark side of the Universe

STILL IN THE DARK The Whirlpool Galaxy is a typical spiral galaxy with starsand gas rotating around its center. CREDITS: NASA/HUBBLE

Did you know?● The Swiss astronomer Fritz Zwicky first

used the term “dark matter” in the 1930sto explain the velocities inside a clusterof galaxies and the apparent missingmass, but the idea became much morepopular in the 1970s with U.S. astronomerVera Rubin and her observations of thevelocities of stars in galaxies.

● The Israeli physicist Mordehai Milgromproposed a serious alternative theory todark matter in 1983, which modifiesNewton's law of gravitation.

● Collisions of highly energetic particles cansometimes produce new types ofparticles. The Large Hadron Collider(LHC) at CERN is the largest and mostpowerful particle collider in the world.

ASTROPHYSICAL SERIES

Jonathan Freundlich

Dark matter:the knownand theunknown

We are staying with conesthis time around as well.But from inverted conesthat are used to hold and eatice creams, we are movingon to those that are used inthe festive period of Christ-mas and New Year: theChristmas tree. An integralpart of the festivities, hav-ing a Christmas tree anddecorating it is now done bymany people, irrespectiveof the religion they follow.

The lighting used, as youmight have noticed, is key tothe decorations. Tradition-ally, wax candles were usedsince the 17th century todecorate the tree. The prob-lem, however, is obvious.The danger of dried woodcatching fire was imminent,which meant that people of-ten had to huddle aroundtheir trees when the candleswere lit, with emergencybuckets of sand and waterto douse the fire if it came tothat.

Edison’s lampsAnd then, Thomas Edi-

son perfected his incandes-cent lamps. When he strungtogether a number of theseincandescent bulbs andused it on his Menlo Parklaboratory compound in1880, he was not only ad-vertising his work, but alsolaying a precursor to themodern Christmas lights.

The man who is creditedas the first to use theselights for a Christmas tree isEdward H. Johnson. John-son, who was responsiblefor initially hiring Edison,worked hard with Edison’sIllumination Company andeventually became a com-pany vice president.

Staying in a section ofNew York City that wasamong the first to be wiredfor electricity, Johnsonused 80 small red, blue andwhite electrical lampsstrung together with a sin-gle power cord to light the

Christmas tree in his home.A reporter named Croffut,who happened to visitJohnson, wrote a glowingreport in the Detroit Postand Tribune that was filledwith superlatives highlight-ing exactly what he hadseen. From December 22,1882, the Christmas treewas literally seen in a newlight.

With people still remain-ing sceptical about the us-age of electricity indoors,the idea surely didn’t catchfire immediately. Even afterAmerican President GroverCleveland had employedmulti-coloured electriclights for the family’s WhiteHouse tree, it remained afad for the rich, owing to itshigh prices, even whenrented.

Sets shopThe credit for popularis-

ing Christmas lights gener-ally goes to Albert Sadacca.Legend has it that as a teen-ager Sadacca was influencedby reading an account of abad fire caused by a candle-lit tree bursting into flames.

Hailing from a family thatsold ornamental novelties,he set up a business to sellcoloured Christmas lights.

With the public’s trust inelectricity improving, andmass production of lampsreducing the rates, Sadac-ca’s timing was perfect,which meant that sales im-proved drastically. By 1925,Sadacca’s company pro-posed that a number ofcompanies selling Christ-mas lights come together,forming a consortiumcalled the NOMA ElectricCorporation. Even thoughNOMA no longer exists, itwas the world leader inChristmas-light industryfor over four decades.

Christmas lights these

days either employ incan-descent lamps or LEDlights, which is growing inpopularity. While most ofthe initial models came inseries connection, whereinthe failure of one lampmeant that the entire light-ing failed, models thesedays are available both inseries and parallel connec-tions.

Lights on, celebrate!

NOW A FAD Christmas lights these days either employ incandescent lamps orLED lights. PHOTO: AFP

A.S.Ganesh

Question: What is the full form of NOMA? Sendyour answers to ganesh.a.s@thehindu.co.in withyour name, class, school and location. [Subject:eye] Last week’s answer: Four different claims tothe ice cream cone were mentioned in lastweek’s article. Prashanth Bunage fromKarnataka Public School, Bidar was among thefirst to get it correct. Congratulations!

AN EYE FOR AN I

Shedding light on Christmasdecoration lights

NEW YORK: When astronautsat the International SpaceStation (ISS) asked peopleon Earth to send them aspanner, it took just a clickof the mouse to "email" thehardware to them,literally. 

The ISS commanderBarry Wilmore needed awrench. The California-

based company Made InSpace that designed the 3Dprinter aboard the ISS de-cided to create instructionsfor them on Earth andemailed it to them. 

Previously, if an astro-naut needed a specific toolit would have to be flown upon the next mission to theISS which could take

months, media reportssaid.  This was the first timehardware was developedusing the 3D printer al-ready with the ISS astro-nauts using instructionssent in the email. 

Earlier, the 3D printer atthe ISS created the firstprinted object in space - apart of the printer itself -

paving the way for futurelong-term spaceexpeditions. 

NASA controllers fromEarth sent the command tothe printer to make the firstprinted part: a faceplate ofthe casing.  This demon-strated that the printer canmake replacement partsfor itself.  IANS

When NASA 'emailed' a spanner to ISS 

WASHINGTON: A new study byresearchers from the Uni-versity of Missouri and theVirginia Tech suggests that

the bacteria involved in thedecay of ancient organismsalso play a key role in thepreservation of fossil. 

The team studied a fossil-ised animal from the Ediac-aran Period calledConotubus that lived over540 million years ago. 

Earlier theories on fossilformation focused on pas-sive processes, where nor-mal decay is stopped bysealing off the sedimentswhere the animal is buried. 

Decay helps feed theprocess

"Our team is instead de-tailing a scenario where theactual decay helped 'feed'the process turning the or-ganisms into fossils - in thiscase, the decay of the orga-nisms played an active rolein creating fossils," ex-plained James Schiffbauer,assistant professor of geo-logical sciences at the Uni-versity of Missouri and lead

author.  "Most of the ani-mals that had once lived onthe earth - with estimateseclipsing 10 billion specieswere never preserved in thefossil record. But we nowhave a spectacular view of atinier fraction of soft-bod-ied animals," pointed outShuhai Xiao, professor ofgeobiology at Virginia Tech. 

The decay of the orga-nisms played an active rolein creating fossils, showedthe study. IANS

New clues about fossil formation found