310 I I ' I I I I "I' Ly <'U 410Tr~~5tO~Li-'-LU61~ '~7iO' 810 2-9-8076/Gravity waves/~pril WS/Head I ' i The tantalizing quest for 2 gravity waves 3 4' When scientists finally detect s a form of energy they have never ~J-"I " seen but know exists, ~ll " e,,, bJ' \.-=:''2..-> '~~9~ a new era in astronomy By Arthur Fisher , , i2 • ~ I 15! 16 17' 18 J 20 1 ElITE UJ 1111 III II III III II UliJ+lill : IillJ~-,--;L-i-Wj~_'_LUjljLLI-LWjJJLj_LU1LUllj-L--'-;:;l-L-- 10 2 10 310,4 10' 5 1 0 "610 70 28 I 2-9-8076/Gravity Waves/April PS ! Overline for box: 21 ~~Jrn](~XOOOfXJ(~n~~~l!OOd:roiti::nn)q{ I 31 Two indirect proofs for gravity waves I ! 4,, 5 Overline I u Battling the limits of modern technology 8 Quote for p. 88 ;',1 ~iDC~KXl>lli~ "In about fifteen years, we , ? '"I will want big, space-based 13 1 laser systems, using, say a J,4 frame. I! lO-kilometer R~H~R 1"1 16 1 17' I 181 J 2°1 E L,' TE I~---.l-LJ.'" I' "J"""" 1~~,-,----+---LJ_-.l ~t .. --,-1 --t-.l--,,-~I ' I . - 1 0 21(.' 3 I 298076/gravity waves/af/apr/caps-l I 11 L!iWto credi t--uper photo with man=:> 1f)2 Alan J. Knapp 3 G cre::.t--lower photo :0::::> 4 Cliff Olson 1. 1 ~ 151 I 16 1 lJ 18 i t 19 20 -- 2--+ .-~"+--'~--' ~- 3 '.' . /;I j 21ii9S076/ cravi ty waves/af/anr/cans-12J.._. "" ,\.../ t~), 3. Cryogenic bar detector (above) I < " gets check by Prof. David Douglass; S at Uni versi ty of Rochester. c Alurnim.111 cylinder, inside vYin- 7 dowed shield, has been rolled 8 out of red cryostat, which cools 9 system to a fe-VI degrees above 10 absolute zero. If a gravity 1" wave passes through the bar, ,. its length will change by a 1C minute 8'l10unt, a change that 1~ will be detected by supercon- 15, duoting devices at each end of 16' the bar. 17, Early testbed, left, for ~ 18' a lUN-noise laser interferometer 19! detector was built by Robert L. 201 Forward ~ Gaylord E. Moss and .l _ 0 0'0 I 'U o _ 298076/gravity waves/af/apr/caps~J Larry Miller at Hughes Research 2 Labs. First such antenna, built 3 in 1972, had an effective length V 1 4 of eight meters. There are noV! 5 plans to build laser detectors 6 more than a kilometer long. 7 8 9 10 11 12 13 14 15 i 16 i 17 18 19 20 1 -oj ~~-81.~; "U 3 '0 410 5 0 610 70 293076/gravity waves/af/apr/cap$-4 (!) 2 3 First bar-type gravity wave detector I ~---'"'-..-"'--~-.--~-- -- I 4 ! (above), developed by Joseph we~er at V"e 1 I 5 University of Jifl8.ryland, appears lat EinEitein 6 I I exhi bi t at Smithsonian Insti tut~on. Robert I I 7 For!lard's proposed free-space l~ser aniJenna -1 ..,. ~, 1 I , I s to detect gravity waveS from th~ Crab Nebula I ~'. h . rt' t' d' t' ht " t " lS s.:.. own In a lS s ren l lOD, I·,iY'lg.:..~ • !VeD ral. i :[ 10 satellite of three has laser an:; beam , s~litter. I 11 Two outer' spacecraft have reflec~ors. Gravity Ii I I ."'" '.'.'a-\7e \vould change distance betwern satelli tes. I I 1 13 " Massi ve cIJ7 0genic alUJ11i.nlul1 detec~or nOYi ! bar -----.. ...... - ~---'~~'-"".... -.---.,.. ""-t --- ......... ",. -""+-- I I[ 1< operating at Stanford University: (right~ above) , I 15 was built by team headed by Will~am Fairbafr:. i 16 Photo shows large cryostat wi th ~nd rempved, 17 gi ving view of five-ton bar wi th}n, wi tf. , , ! 18 instr'umentation ~~d suspension. lDetail~ and I ' J dimensi ons are given by drawings 1 opposite I ! ~\ pl.ge.) Use of liquid nitrogen anI! liqui • • , , F I I I , , , , i , , I'" " ElITE UJ i I II iii II II I IIJ I IllJJ--llJiL;~J~LJ~ "--L~~+-'-'LJl~~-4JlJ-,; ~Ll~-1~' _' J c~-Ll-i,_-'-',,_-' 10 210 3!0! 4'0 5'0 6!0 7'0' E:, , 298076/gravity waves/af/caps!apr-5 I I helium cools detector to about ltwo deijrees I ' 2 above absolute zero. I "~ ,,--n_::;V Bin Bw~ I I 4 ~ber)David K. LYD1h I 5 ~Stanf6td/~ Univ~rsity 6 cv 7 State-of-the-art bar detector at Stanford Univers~ty is isolated 8 from all external noise by special mech~~cal filters. 9 cv 11 @ Dipole electromagnetic waves and quadrupole gravity waves I When electromagnetic wave (light, etc.) strikes charged J ~ 131 particle, it oscillates in a simple, back-and-forth dipole 141 mode, perpendicular to the direction of the wave. 15 16 v 17 When gravity wave strikes mass, one dimension will ~ I 18 contract, other will expand, im pl~~e Iperpendicular to direction i 19 of wave. These quadrupole moti9ns revJ1rse on next half-cycle of wave. I 20 I --riV Lie PICA TTTH TTl I 111Trtr~T~;~' ,'- " EliTE tLJ-1~J"""'1"",1'" _L1_J~-,-L1---+lJ--"l~ __ L -,~ i 1" l' 0 20 2980761gravi ty waveslaf I capslapr-6 tV hre.e.. 2 II kinds ~, of gravity wave detectors 3 ------Doppler ranging uses radio signal between 4 spacecraft and Earth. When gravity wave passes, distance between two changes, introducing detecta~ Doppler frequency shift. f CD '-_~_____Bar detector changes length V.0;-11'ftJ gravity , wave passes. Ultrasensitive transducers alor€ or at ends of bar translate minute motion to voltages tha t must be amplified. i d 'G) E), I t.a~er i!!!-erfe;:..o~ bOlLT1ces light bea'!', many 1 I 161 i times between mirrors mmmted Tn masses. ! 171 Gravi ty wave changes dista.'1ce ~etween ,mirrors, 1 18' I 1 producing interference patternlon scrden. 19 i 20 • < ...... ~Drawina ~~O~~~ ,,- -~ O'U I 'U blU 2-9-8076/Gravity waves/Apri:':~/~";o~­ The first evidence 0 any rind forx the existence I 21 of gravity waves comes npt fro sensing them directly I I 3 but from XRIK observing their effect on the behavior of /~. \ 4 / a bizarre astronomical object called a binary pulsar. I 5 I ~7\)f A pulsar, believed to bel a raplidlYR spinning neutron ~~! /' 6 I <:0' / star, emits strong radiol signa;ls in periodic beeps. But ,//- 7 , I i pulsar PSR 1913+16, discovereq by a team of University S 9 of Massachusetts astronolers in 1974 with the world's I 10 i largest radio telescope ~t Arecibo, P.R., is unique. I sequence, 11 I Its beeps decelerate an~ acce~erate in a regular ~axxKXR I 12 lasting about eight hou~s. From this, the astronomers, I, 'I 13 led by Joseph Taylor, deduced ,that the pulsar was rapidly \f.fr"~,; 14 I y I orbiting around another Iver rndssive object--another neu­ ~ I Ii 15 tron star £i)~;a;-,"".lI"'''''''ll:nUillt.....OaWb~l''61ii<i€il-JI~(-fl~I~I - - !ftrrTdd- . .j;~fl.a:,t;tc-;!m~:ti:dteeC-:it1L:.a::I1trrl:t:i:·~~':ee,. 16 __ ._. ____. I! E"t " .r.; ,~ '.' /.~ ~Vh''''' I .' "' ~. \I I j -{ J.'...--,----..",---:;--;--rc- (-!he only sucg . ev~r fourid. J" . ,.." l.--:-:-~ . J ~""~7;7'nr~~~~~~ 171 v·, .\. ,.-e: t> ., c'\ "i c. 17 tv. H' I ' Einstein's theory o~ 65erll Relativity predicts that 181 ---.. --- . I) I .js I f.", f~ I 0 r b ,,·r, ( i d· I ~r- 19 ",,0 "",,he bo"," ""I'ratil~~-"'1 ,hould pro~ 1 20 duce a considerable quantty of gravity waves, and that I I I ELITE 4~HU+ [ i [ [ I [ [ [ [ IIlJ I IllJlJlJ II L: I i I II I I UUjlillIUlljilltlm-Ll~u I i I~EJ r, 1 1 0 2 0 -310. -4lo 5 0 610 7 '0 ----sJe 2-9-8076/Gravity waves/tpril SiR? ". - the energy radiated should ~e SIOrlY extracted from the 2 orbit of the system, gradua~ly de~reasing its period as 3 the superdense stars spirallcloser to one another. Ein- 4 [. I I stein's equations predict aldecretse of one-ten-thousandth I I ~ ':)00: 10,1: 7 .;.-" 5[ \)" Q \ \ '-' l ...) \')'''1 i -' , ( " --~- l I of a second per year for~g s,steffl.-1\nd after four years 6 of observations, Taylor's t~am announced, in late 1978, 7 . I s that ultraprec~,e measuremeIjlts of the radio signals gave 'I .I....-! t·",-4' . i OV',~?'J"""''t, ' [ 9 a value l!!:f almost exac. y-w&..t had been calculaEsa. The ~ [ , I I I 10 closeness of the match not pn1y provides strong--even i 11 i though indirect--proof of the existence 'of gravity waves, 12 I , but also further bolsters E~nstein's theories of gravity I I I I 13 [ I against some compe ting theoties. l"ntiS could be tIre death 14 kttell for maRY sf the ot:~-t:heeti~-or--gravitati-on,JL~­ said Stanford' 5 GHffo:E'a Hi,4.i: ;-m1--~uthoritT-on- -the-subject. As Taylor said of what te ca1~ed "an accidental dis- I';: I [ I ' covery originally," the astkonomeks had an ideal situa- 16 I i e i ! 17 ion/or tlis ting relativity ~heory~-a moving clock (the I I I I 18 l pulsar) with a very prescis~ rate of ticking and a high -. Sc'" 300 [\",[o",.i.,.; ~c~ $<'<-1" 10 velocity" "It's a1smost as ~f we had designed the sy~tim I 2'>J ourselves and putR it out there sbecifica11y to do this measurement." I ' l' 0 2i O ~---31o- ----4T6 T-'----516 ----,- ~f;lo--~--~-710~- ~ ~81G 2-9-8076/Gravity waveS/Fis~er/APjil PS/4-t r;", Another indirect ind]catio that gravity waves do I J indeed i exist came more rdcentl~, and more dramatically.