Star birth, star death

The night sky reminds us that we inhabit but a small por­tion of space and time, a tiny frag­ment of our vast galaxy, a brief moment in a uni­verse vast beyond human comprehension.

These days, humans live a cen­tury or so if they are lucky. Stars last 100 mil­lion cen­turies. A recent walk in the Zaleski State For­est reminded me that we humans can still see the long life of a star from begin­ning to ending.

This time of the year, the acorns fall like rain. It’s hard not to get bonked on the head at least once. My bonk pro­duced a rev­e­la­tion. I saw the acorns fall. I saw the tiny seedlings with their huge leaves. I saw the mighty, mature oak. And I saw its rot­ting rem­nants on the ground.

The uni­verse is the ulti­mate for­est. Look around, and you will see stars at every stage of their development.

They are born in huge clouds of hydro­gen gas and dust called emis­sion neb­u­lae. One of the best of them can be seen in the sum­mer sky as the sea­son wanes.

Look almost straight over­head in the early evening for the con­stel­la­tion Cygnus. It looks like a large cross lying on its side. Just down and to the left of the north-most star (the top star in the cross) is a large, faint patch of light. It is just vis­i­ble in binoc­u­lars on a crystal-clear night from dark, rural skies.

You are look­ing at the North Amer­i­can Neb­ula, so named because of its strik­ing resem­blance to our con­ti­nent. In a tele­scope, use the low­est power avail­able. The part by the “Gulf of Mex­ico” is eas­i­est to see.

Enmeshed in the North Amer­i­can Neb­ula are hot, new baby stars that will last per­haps 10 bil­lion years.

At the west­ern end of the same con­stel­la­tion, the sit­u­a­tion is reversed. Down and to the right from the west-most star in the cross is a faint star. That star is embed­ded in a faint arc of light that is just vis­i­ble with large binoc­u­lars away from city lights.

Nearby to the north is another faint arc. The two wisps of light, called the Veil Neb­ula, seem to form a bro­ken circle.

In a large ama­teur tele­scope, they have the sub­tle look of smoke ris­ing from a dying ember. Their detailed fil­a­ments, undu­la­tions, and cataracts of light are played out against the vel­vet black­ness of space behind and inter­twined within them.

I spent over a thou­sand bucks build­ing my tele­scope. When I saw the Veil for the first time, I knew it was worth it. That, my friends, is a thousand-dollar view.

Dur­ing their lives, stars com­bine hydro­gen into helium in a stu­pen­dous hydrogen-bomb explo­sion that lasts 10 bil­lion years.

But this seething ther­monu­clear reac­tion is noth­ing com­pared to what hap­pens to some stars when they reach the end of their life cycles. Hav­ing used up their sup­ply of hydro­gen, they self destruct, send­ing their sub­stance back out into space, per­haps to form the build­ing blocks of new stars.

As stars like our sun use up the hydro­gen in their hot cen­ters, they expand to gigan­tic sizes and turn red. The nor­mal evo­lu­tion of a large star is from the rel­a­tively sta­ble yel­low star like our sun to a bloated red giant, over 500 times the diam­e­ter of our sun.

Often these red giants col­lapse into very dense balls, called white dwarfs, which are only a few thou­sand miles in diam­e­ter. Imag­ine most of the sub­stance of our sun, which is over 850,000 miles in diam­e­ter, con­densed into a sphere only half the diam­e­ter of Earth, about 4,000 miles across.

A small por­tion of the star’s sub­stance is blown into space, form­ing a rapidly expand­ing shell of gas made up mostly of hydrogen.

Some stars end their lives in a much more vio­lent expan­sion. They explode with bril­liance hun­dreds of mil­lions of times greater than their orig­i­nal bright­ness. Such explo­sions, or super­novas, are com­monly observed in other galax­ies. They briefly shine brighter than the their galaxy, which is made up of bil­lions of stars.

The Veil Neb­ula is the rem­nant of such a cataclysm.

Forged in the inferno of such an explo­sion are the heav­ier ele­ments found on rocky plan­ets like our Earth. Met­als like cop­per and iron can be formed in no other way than in the belly of a super­nova. The gold you wear around your neck and in the ring around your fin­ger is the beau­ti­ful arti­fact of the spec­tac­u­lar death of a star bil­lions of years ago.

The cloud of dust and gas sur­round­ing the Veil was expelled at about 1,000 miles per sec­ond. The super­nova that caused it hap­pened a long time ago, per­haps 40,000 years.

The expan­sion of these arcs of light has decreased to only 45 miles per sec­ond, slowed by the other dust and gas that inhabit the inter­stel­lar medium in the area. In a few tens of thou­sands of years, they will no longer be vis­i­ble. They will have blended into the gas and dust between the stars.

Per­haps their hydro­gen will form new stars. Per­haps their met­als will make up the sub­stance of new plan­ets, their gold to adorn the forms of new races.

Human life is short, a can­dle in the wind com­pared to the blaz­ing con­fla­gra­tion we call a star. But with the invest­ment of a few hun­dred dol­lars and a sleep­less night or two, we can in the short expanse of our brief can­dles the full range of stel­lar evolution.

Tom Burns is the direc­tor of Ohio Wes­leyan University’s Perkins Obser­va­tory. He can be reached at tlburns@owu.edu.

Posted by Tom Burns on Sep 3 2012. You can follow any responses to this entry through the RSS Feed. Comments can be made below.