For a new generation, the Milky Way beckons

For a new generation, the Milky Way beckons

UGC 12158, an example of a barred spiral galaxy • ESA/Hubble

Originally published 1 March 1993

Gath­er round, chil­dren, and lis­ten to my tale of com­ing of age in the Milky Way.

When I was your age, we thought our­selves cit­i­zens of the Solar Sys­tem. The siz­zling sur­face of Venus, the ice­caps and canals of the Red Plan­et, Sat­urn’s air-wrapped moon Titan: these were the out­er­most hori­zons of our imaginations.

What­ev­er exist­ed beyond Plu­to — those thou­sand bil­lion stars in the whirling disk of our Milky Way Galaxy — were too remote, too vast, to com­pre­hend. The Milky Way was the thresh­old of infinity.

But — ah! — with­in the precincts of the Solar Sys­tem we found room enough for adven­ture. We vis­it­ed the crys­tal palaces of Jupiter’s moons. We met and mat­ed with beau­ti­ful, green-skinned aliens from Plan­et X. We fought off refrac­to­ry Vesu­vians intent upon the col­o­niza­tion of Earth.

And, at last, we sent space­craft called Mariner, Viking, Voy­ager, and Mag­el­lan on jour­neys of dis­cov­ery to every plan­et (save one) that cir­cles the sun.

It’s old hat now. The Solar Sys­tem is ter­ra cog­ni­to. The rings of Uranus are as famil­iar to us as our own back­yards. Mer­cury’s sun-baked face is a bore. But that is as it should be. We are old now. It is time for a new gen­er­a­tion to look into space.

Your gen­er­a­tion.

Astronomers are blaz­ing the way beyond the yawn­ing gulf that sep­a­rates the Solar Sys­tem from our neigh­bor­ing worlds. With fab­u­lous new tele­scopes, they are map­ping the thou­sand bil­lion stars. You, my chil­dren, will be cit­i­zens of the Milky Way.

Com­put­ers, too, are tele­scopes of sorts. They allow astronomers to cal­cu­late the dynam­ics of gas and stars in far­away regions of the Galaxy; the results of the cal­cu­la­tions can be com­pared with obser­va­tions, allow­ing astronomers to turn sta­t­ic obser­va­tions into history.

Imag­ine, chil­dren, a jour­ney to the cen­ter of the Milky Way, a place hid­den for­ev­er from our visu­al inspec­tion by the dust and gas that fill the space between the stars. Radio waves and X‑rays pen­e­trate the mists, revealing…

We used to believe that the Milky Way was a nor­mal spi­ral galaxy, with star­ry arms pin­wheel­ing out from the very cen­ter. But no! It is a barred spi­ral. Two spoke-like arms extend straight out from the cen­ter of the Galaxy on oppo­site sides, then bend to wrap their way to our neigh­bor­hood some 30,000 light-years from the center.

The rotat­ing bars pump gas towards the cen­ter of the Galaxy — this can be cal­cu­lat­ed with com­put­ers and observed with tele­scopes. Mon­strous clouds of gas fall inwards along a sequence of wild­ly danc­ing orbits, col­lid­ing, shak­ing off ener­gy, shin­ing with a fierce invis­i­ble light.

Now we approach the cen­tral bulge or nucle­us of the Milky Way, a region as small com­pared to the Galaxy as a grape­fruit seed at the cen­ter of a din­ner plate. Here the pres­sure of the gas builds, as if in a pres­sure cook­er, until it explodes — schoosh! schoosh! — in bursts of out­rush­ing wind.

One might think that with so much gas at such high pres­sure, stars would spring prodi­gious­ly into exis­tence, for it is out of the inter­stel­lar gas that stars are born. But the rate of star for­ma­tion in the nucle­us is mod­est. The vio­lence, the stir­ring, the intense mag­net­ic fields, inhib­it grav­i­ty from gath­er­ing togeth­er the stuff of new stars.

As we draw clos­er to the cen­ter — to the pin­point at the cen­ter of the din­ner plate — things become strange indeed, not qui­es­cent, as one might expect at the eye of a storm, but more vio­lent. Strong mag­net­ic fields squirt jets of gas out of the galaxy, and super­no­va explo­sions trig­ger mas­sive disruptions.

At the core of the Galaxy, stars flash into exis­tence, blaze with a quick inten­si­ty, and explode. Stars col­lide, or tear at each oth­er with grav­i­ta­tion­al claws. The den­si­ty of stars is a mil­lion times greater than in the arms of the Galaxy. If there are inhab­i­tants of plan­ets here — which seems unlike­ly giv­en the ter­ri­ble vio­lence of the neigh­bor­hood — their night sky shines with a fierce brilliance.

At the very axis of the Milky Way prob­a­bly lies a black hole with the mass of a mil­lion suns — the mon­ster in the pool, the dark heart of the Galaxy. Episod­i­cal­ly, fits of gas stream into the black hole, gush­ing ener­gy out­ward before dis­ap­pear­ing for­ev­er into oblivion.

Every dark pool should have its mon­ster. Every dark pool should be haloed with light. The Milky Way is qui­es­cence and vio­lence, radi­ance and dark­ness, life and death — a whirlpool of cre­ation and destruction.

Astronomers have sketched the thou­sand bil­lion stars. The Milky Way is no longer the thresh­old of infin­i­ty; we have plumbed its depths, searched its hid­den cran­nies, and glimpsed worlds more won­der­ful and bizarre than any­thing we have known in our Solar Sys­tem. It is home.

Go to sleep now, chil­dren. As the first true cit­i­zens of the Milky Way you’ll need your rest. Your cen­tu­ry is about to begin.


This bed­time sto­ry draws upon “The Cen­tre of the Milky Way” by Leo Blitz, James Bin­ney, K. Y. Lo, John Bal­ly and Paul T. P. Ho in the Feb­ru­ary 4, 1993 issue of Nature. -Ed.

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