Our standing amid the stars

By this point, we have all seen so many pretty Hubble pictures that we are in danger of pretty-Hubble-picture burnout. We have seen exploding stars galore. We have seen majestic pillars of gas that are spawning new solar systems. We have seen galaxies colliding, galaxies getting ripped apart, galaxies becoming mired in their own ennui. We have seen Mars and Jupiter and Saturn in such stark close-ups that we can detect the cosmetic surgery scars.

It feels as if we have seen it all. Literally. The whole cosmos, soup to nuts. Here is a real headline on a November news release from Stanford: "High-precision measurements confirm cosmologists' standard view of the universe." All figured out; everyone go home now.

So, you can just imagine the challenge that Nasa's Hubble Space Telescope scientists faced earlier this year. In May, astronauts aboard the space shuttle Atlantis flew to the Hubble and removed an old camera and replaced it with a better one. They fixed two other instruments. Crew members installed new gyroscopes and batteries. After five spacewalks and much derring-do, Hubble was, in effect, a brand-new space telescope.

But what to look at next? The Hubble people had to pick targets to demonstrate the revamped telescope's abilities. They would call these images the Early Release Observations, or ERO (at Nasa, everything has an abbreviation). They wanted to produce pictures with lots of "Wow Factor".

The rollout came in early September at Nasa headquarters in Washington. Big shots showed up, such as the new Nasa administrator, Charles Bolden, and Senator Barbara Mikulski of Maryland, the "Godmother of the Hubble", and all seven astronauts from the Atlantis mission. Nasa beamed the news conference around the planet. After much hoo-ha and throat-clearing, the moment came. The ERO. The journalists pounded out their stories, which all said pretty much the same thing: "Wow."

You see the danger here: Wow can turn into Whatever. The whole enterprise can start to feel a little superficial. It is too easy to get blissed out on the eye candy. We can become a little too star-struck.

So here is our challenge: We will go back and look once again at these new pictures but this time we will probe deeper, think harder and search for any messages in the light that careens into Hubble's mirror. We will do a deep reading of the cosmic text. And we will ask the hard question: What is space telling us?

Let us start with the Butterfly Nebula, technically known as Planetary Nebula NGC 6302. The Butterfly Nebula is the product of a star in its death throes. The star is about 3,800 light-years away, in the constellation Scorpius. Those wings are actually hot streams of particles being ejected by the star into interstellar space. As the star starts to run out of hydrogen and helium fuel, its core contracts, and, simultaneously, the intense radiation of the star blows the outer layers into space. It is not an explosion but more of a spewing.

Our knowledge about star mechanics comes largely from models, equations and number-crunching. But this Hubble image of the butterfly lets the models spring to life. The butterfly tells us the truth: The universe is wild.

The Butterfly Nebula is a freeze frame of the seeding of the universe with the material for future stars, planets and life. The universe, to be chemically interesting, and to give rise to life, has to have stars. And stars have to die. Carl Sagan was right: We are star stuff.

Next up, the stellar jet in the Carina Nebula. One star is firing jets of material in opposite directions. If Earth were directly in the path of a relatively nearby stellar jet, it would be lights out for all of us. Ditto if we were close to a supernova or to two super-dense neutron stars colliding and emitting a burst of gamma rays.

"We are in a very lucky, quiescent place in the universe," says Matt Mountain, the director of the Space Telescope Science Institute in Baltimore.

A light-year is about 10 trillion kilometres. The cloud we are looking at in the Carina Nebula is about three light-years from top to bottom. Earth has a diameter of about 13,000 kilometres so if Earth were in this picture, it would be imperceptibly tiny.

Now we come to the globular star cluster Omega Centauri. And gosh, that is a lot of stars. This single image shows a region containing about 100,000 stars, out of roughly 10 million in the globular cluster.

The stars are different colours because they have different masses or are at different stages of their lives, which affect their temperature and brilliance. In a sense, this image of the Omega Centauri cluster is a chart of star life.

Until the late 1800s, scientists doubted that Earth had been around for billions of years because they could not see how the Sun could be on fire for such a long time. But it is not on fire. A star is a fusion reactor. Life on Earth can evolve for a long time because stars are fairly efficient at transforming matter into sunshine.

Size matters. If a star has more than about eight times the mass of Sun, at some point, gravity will overwhelm the dying force of its fusion reaction and the core will collapse to a point of unfathomable density. When that happens, a shock wave forms, and all the outer layers of the star are exploded into space at about 16,000 kilometres per second. That is your supernova.

When the red supergiant star Betelgeuse blows — and it will someday, erupting on Orion's shoulder, 640 light-years from Earth — it will be so bright we will be able to see it in the daytime. All that will be left will be a tiny neutron star. A teaspoon of a neutron star would weigh about a billion tonnes. Very, very large stars, bigger than Betelgeuse, collapse into something even denser than a neutron star: a black hole. The matter is so dense that nothing, not even light, can escape its gravity.

It is hard to look at the Omega Centauri image without thinking: We are not alone. How could we be? The universe is so flamboyantly abundant and huge and awesome. J. William Schopf, a legendary UCLA professor who studies the origin of life, says: "I find it really, really difficult to imagine that the universe is not teeming with life. I don't know about intelligent life but I think there must be a bunch of that out there, too. Our star is a normal, main-sequence star, so there is nothing special about it. We live on a rocky planet that has a lot of liquid water but the Earth is 98 per cent just like Venus, except Venus is closer to the Sun. And I think such planets must be very common. There is nothing special about us, as far as I can tell."

This is a common sentiment among scientists. But there is a counterargument: There are a lot more ways to be dead than to be alive in this universe. W hen you look at all those stars in this globular cluster, you are looking at a patch of sky where life may never have taken hold. The stars are so close together that they would create a gravitational maelstrom that would prevent planet formation. Moreover, exploding stars would sterilise everything nearby.

"When you have gone to a globular cluster, you've gone to a not terribly good neighbourhood," says Mario Livio, an astrophysicist with the Space Telescope Science Institute.

Earths are not exactly a dime a dozen. Our own solar system appears to be chock-a-block with dead worlds. Mars may have had life once but if there is any left, it is hanging by its alien fingernails.

Schopf's recitation of the Copernican Principle — the realisation that the universe doesn't revolve around Earth, that we are not in a special position — can be extended even further: Not only is the universe not about us, the universe isn't necessarily about the thing we love most, which is life.

The final picture is called Stephan's Quintet. At first glance, it looks like four galaxies. But then you see that the central object is two merging galaxies. The four orange-yellow galaxies will probably merge into a single galaxy; the blue-white galaxy is much closer to us and just happens to be in the line of sight of the other four.

But wait: There aren't just five galaxies here. There are hundreds of them. Only the round objects with X-shaped spikes are stars. Most of the other dots, streaks and smudges are distant galaxies.

This is, in a sense, a four-dimensional scene. With this two-dimensional image, we are looking at three-dimensional structures but we are also looking back in time — the fourth dimension. Each layer of the image represents a different epoch of cosmic history. We see the faintest galaxies as they were billions of years ago. "To me, it's like a geologist's core sample," astronomer Eric Chaisson of Tufts University says of the image. So what does it all mean?

That we are small, is one obvious message. This has been humbling, this investigation of space. The Copernican Principle keeps hammering flat our presumptions of specialness. But wait: Perhaps we are just getting started. We will star-trek across the cosmos! We will seed the universe with human intelligence and meet fascinating alien races. The problem with this scenario is that Nasa has put the Buck Rogers stuff on hold for the moment. Costs too much. So it doesn't look as if we're going to be visiting Stephan's Quintet anytime soon.

Where does that leave us with regard to outer space? It leaves us with a job: to gaze. It is our duty to look at the universe.

Let Eric Chaisson explain it: "If we weren't here, the galaxies would twirl, the stars would shine, and the universe would go on being its magnificent self. It is almost like we are animated conduits for the universe's self-reflection. If life did not occur in the universe, then the universe in all its awesomeness and magnificent beauty would not be appreciated. The universe would not come to know itself."

So, keep looking at those pretty Hubble pictures. Or, better yet, go outside on a clear night. Get away from the city. Look up and stare into the firmament.

And then say: "Wow."

- To see Hubble images online, go to www.hubblesite.org.