Ra­dio waves help ‘see’ cos­mos

Penticton Herald - - OPINION - KEN TAP­PING

As you come onto our ob­ser­va­tory site, you get a good view of the as­sort­ment of an­ten­nas that act as the sig­nal col­lec­tors for our ra­dio tele­scopes.

In front of you, in the dis­tance, near the lab­o­ra­tory and work­shop build­ings, is the 26-me­tre dish an­tenna. On the right lie the four huge troughs of the an­ten­nas for the CHIME (Cana­dian Hy­dro­gen In­ten­sity Map­ping Ex­per­i­ment) and on your left the rail­way track and seven nineme­tre an­ten­nas mak­ing up our Syn­the­sis Ra­dio Tele­scope.

Th­ese an­ten­nas, spread over a 600-me­tre east-west line, form a ra­dio cam­era, mak­ing im­ages of the sky as we would see it if we could see ra­dio waves. Record­ing an im­age takes about 10 days, with the an­ten­nas be­ing moved to dif­fer­ent po­si­tions each day. The re­sult is a ra­dio im­age with about the same level of de­tail at ra­dio wave­lengths as we get with the un­aided hu­man eye, us­ing vis­i­ble light.

So, why do we bother with ra­dio tele­scopes? We do it for the same rea­son as we do as­tron­omy at in­frared and other wave­lengths. Dif­fer­ent wave­length ranges give us com­pletely dif­fer­ent views of the uni­verse and what is go­ing on in it.

Elec­tro­mag­netic waves, which in­clude gamma rays, X-rays, ul­tra­vi­o­let, in­frared and ra­dio waves, are dis­tin­guished only by their wave­length. Gamma rays have the short­est wave­lengths and ra­dio waves the longest. All th­ese waves come in lit­tle pack­ets called quanta, which can­not be bro­ken into smaller bits.

The amount of en­ergy needed to make one quan­tum of elec­tro­mag­netic waves de­pends on its wave­length. If the re­quired en­ergy to make quanta with a par­tic­u­lar wave­length is not avail­able, those quanta will not be pro­duced. Ra­dio quanta have the low­est en­ergy of all, and can be pro­duced in re­gions with in­suf­fi­cient en­ergy to pro­duce any­thing else.

A good ex­am­ple is the cold, dark ma­te­rial form­ing the dark lanes and blobs in the Milky Way. We can only see this ma­te­rial op­ti­cally be­cause it is sit­ting in front of stars and glow­ing clouds of gas. In fact there is a lot of that dark, cold stuff out there, and ra­dio tele­scopes can de­tect and im­age it.

We have found that this ma­te­rial makes up most of the stuff in our and most other galax­ies. It is the raw ma­te­rial for mak­ing new stars and plan­ets, and its grav­ity has a large say in what goes on, so we are very in­ter­ested in map­ping and study­ing it and how it be­haves.

At other ra­dio wave­lengths, the gas and dust clouds are trans­par­ent and we can see what is hap­pen­ing be­yond. There are lots of dis­tant, high-en­ergy ob­jects that give off ra­dio waves as well as light and other waves, which we can only see with ra­dio tele­scopes be­cause our op­ti­cal view is blocked by clouds of gas and dust.

Prob­a­bly the big­gest as­set to ra­dio as­tron­omy is the ra­dio emis­sion pro­duced by cold cos­mic hy­dro­gen gas.

Hy­dro­gen atoms are the sim­plest in na­ture; they con­sist of a sin­gle pro­ton with a soli­tary or­bit­ing elec­tron.

Oc­ca­sion­ally, due to starlight or other causes, the elec­tron flips over, and when it flips back, it gives off a quan­tum of ra­dio emis­sion, with a wave­length of 21 cen­time­tres.

Since there are a lot of hy­dro­gen atoms out there, this emis­sion can be de­tected by ra­dio tele­scopes and the clouds of hy­dro­gen gas imaged.

This is one of the main pur­poses of our Syn­the­sis Ra­dio Tele­scope. Over the last ten years or so, the hy­dro­gen clouds in our part of the gal­axy were mapped as part of the Cana­dian Ga­lac­tic Plane Sur­vey.

The project also in­cluded map­ping the hot clouds of gas near new-born stars and count­ing the ra­dio galax­ies and quasars ly­ing far be­yond our gal­axy.

Over the last cou­ple of decades we have found that many of the mol­e­cules form­ing and re­act­ing in those cold, dark, gas and dust clouds have de­tectable ra­dio sig­na­tures, and many of them play roles in the chem­istry of life. Venus lies low in the dawn glow. Af­ter dark Mars is low in the south and Saturn low in the south­west. The Moon will reach First Quar­ter on the 15th. Ken Tap­ping is an as­tronomer with the Na­tional Re­search Coun­cil's Do­min­ion Ra­dio Astro­phys­i­cal Ob­ser­va­tory, Pen­tic­ton.

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