Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS

Program Information

Transcript
"Mysteries of Deep Space"
Program 2: "Exploding Stars and Black Holes"

Narrator
Star light, star bright. Which star will die tonight?

Alex Filippenko
Supernova should be coming up right about now.....there it is!! It is!! Itís a supernova....look at all the undulations..... Weíve got another one.

Narrator
In the death of a star, astronomers probe the clash of cosmic forces...

Mario Livio
Gravity wins the final battle and the thing collapses to form a black hole.

Narrator
...the strange limits of our universe.

Paul Davies
It wouldnít be just the obliteration of all matter and energy, but of space and time as well.

Narrator
The universe reveals its deepest secrets, in a blinding flash...


Series Title: "Mysteries Of Deep Space"
Program Title: "To the Edge of the Universe"


Narrator
To some there is no vision more reassuring: the cycles of the sun and the moon, the heavens ceaselessly turning. The night sky is unchanging and eternal -- Or so it seems.

But modern astronomy has given us a much different vision: a universe that roils and vents its rage...

In fierce radiation jets that erupt from newborn stars.

In netherworlds where matter billions of times the mass of our sun collapses to a single point.

In the most violent explosions since the Big Bang...

The supernova.

Stan Woosley
Supernovae are the grandest explosions in the present universe. They put out, in a period of 10 seconds, as much energy as all of the stars and galaxies and quasars in the rest of the observable universe put together. And the energy is not just a great fireworks display; it also gives rise to a shock wave that propagates through the star and the conditions in that shock wave give rise to a lot of the elements of which planets and you and I are created.

Narrator
In the cataclysmic energy of a supernova, astronomers are studying the nature of the universe... its past and its ultimate future.

Throughout history, our vision of space has been shaped by a handful of rare exploding stars visible to the naked eye.

In the year 1054, stargazers in North America spotted a supernova near a crescent moon. The same event was also recorded in China, Korea and the Middle East.

In Europe, supernova sightings helped dispel the prevailing belief that the heavens are static and unchanging.

The astronomer Tycho Brahe saw one in the year 1572. He wrote: "I was led into such perplexity by the unbelievability of the thing that I began to doubt the faith of my own eyes."

Johannes Kepler recorded the next one in 1604, in the constellation Serpens. Galileo used it to make his case for a whole new approach to astronomy, based on the idea that change is a fundamental part of the cosmos.

Today, when or where the next supernova will appear, no one knows. But as they say, seek and ye shall find.

Song
ëThis is my story, this is my song....
Praising my saviour all the day long.í

Bob Evans
The Lord bless you and keep you... The Lord make his face to shine on you and be gracious to you.The lord lift up his countenance and give you his peace...

Narrator
By day, Reverend Bob Evans preaches the Gospel to the devoted faithful in churches near the town of Coonabarabran, Australia.

Bob Evans
...now and forever more, Amen.

Narrator
But he has another flock he knows just as intimately.

By night, heís a backyard astronomer of world renown. Since 1980, he has sighted no fewer than thirty supernovae -- more than any other amateur on earth.

On the side of his telescope, heís chalked up the locations and dates of his discoveries.

The secret to Evansí success is his familiarity with the night sky. He has thousands of galaxies committed to memory, and can spot the sudden brightening of stars within them.

Bob Evans
In this particular case, the new star appeared in the middle of the dark dust lane. Back in 1985, a supernova appeared in this galaxy and this other photograph shows us the supernova here in the ring of the galaxy. I found it with a ten-inch telescope from a spot beside the road near the town of Bathust, a long way from home.

Narrator
Once every branch of science depended on the ranks of amateurs. Today, thatís true only for astronomy.

Evansí discoveries are a windfall for professionals. Spotting a supernova as soon as its light reaches earth gives them a chance to study it from its outset.

Tonight, Evans is joining the ranks of the pros with an observing run at the Siding Springs Observatory near his home.

Bob Evans
Thereís a... quite a bright star just west of the galaxy, another one southwest, then qute a faint star northwest..and several bright stars around it.......

Narrator
Here, Evans can see deeper into space. But in truth, he prefers his backyard.

There, his speed and flawless memory command the thousand-odd galaxies that make up the local region of our universe.

And itís there that he has his best chance at spotting the big one: an exploding star so close and so bright it becomes legend.

Only one like that has appeared in the nearly four hundred years since Galileoís time. Observers in the Southern Hemisphere saw it in a dwarf galaxy just beyond our Milky Way.

For many astronomers this was the event of a lifetime.

Robert Kirshner
Supernova 1987A in the large Magellanic Cloud, has been a big adventure for me. Ah, I remember on the day in February in 1987 when, ah, I got a phone call and somebody said, "Have you heard about the supernova?" It was clear that something big had happened.

Narrator
Now, more than a decade later, they are still tracking the progress of ë87A. Ultraviolet rays bursting from the supernova have caused clouds of gas, expelled long before the explosion, to glow like giant florescent rings.

Bob Kirshner
And now we're getting a chance to see the whole star in its neighborhood by using the space telescope to observe the expanding debris and the stuff that was in the neighborhood that was really lost from the star before the explosion. So we get a whole chance to check out the theory of stellar evolution and theory for the mechanics of supernovae by looking at a good case. And 1987A is surely the best case that we've had.

Narrator
In the brilliant drama of a starís death, we glimpse the violence that ruled its life.

Mario Livio
Stars spend their entire life fighting gravity. If there would be no other force, gravity would pull all parts of the star and make it collapse to a point. What the star manages to do is to ignite nuclear reactions at the center of the star which cause a very high temperature and high pressure. And this pressure gives an outwards force which holds the star against gravity. So only as long as the star has this nuclear energy available, it can really hold against gravity.

Narrator
Stars the size of our sun can keep the inward pull of gravity in check and burn for billions of years.

Not so for a large star. It burns hot and fast, and steadily packs its core with denser and denser elements.

Stan Woosley
And as it evolves, it burns lighter elements into heavier ones -- hydrogen into helium, helium into carbon, carbon into magnesium, and so on -- and eventually reaching the heaviest element that nuclear fusion can produce, iron, in its core. And so when you have a mass of iron about one-and-a-half times the mass of the sun, it no longer has a source of nuclear energy to hold itself up.

Narrator
Before it actually blows up, a star is first seized with convulsions. It throws its outer layers into the surrounding galaxy.

Eta Carinae is a star nearly a hundred times the mass of our sun, and a supernova waiting to happen. It has expelled two fiery lobes of gas that stretch nine trillion miles from end to end.

At any moment, Eta Carinae could fall victim to the gravity intensifying within.

This computer simulation shows the cataclysm that can unfold within a large starís core. Energy released in the collapse heats the star from the inside out to billions of degrees. Within hours, a pressure wave rushes outward, and the star erupts...

Our models of supernova explosions are steadily improving. Now astronomers have begun to enlist them in the study of even larger forces at work in the universe.

For the last week astronomers around the world have been combing the distant universe for exploding stars.

Tonight, with a dozen sightings in hand, a team has come to Hawaiiís Mauna Kea volcano. Their destination is the Keck Observatory, and one of the largest and most advanced telescopes in the world.

Alex Filippenko
...I mean, thatís a little bit inefficient, going back and forth.

Saul Perlmutter
I mean if all we have is half a night, we can come back and repeat them...

Narrator
Leading the study, Saul Perlmutter and Alex Filippenko are here to answer a profound question: how and when will the universe one day come to an end?

Alex Filippenko
So that indeed is the star....if you could bring it a tad above the slit......

Narrator
A singular explosion, the Big Bang, set the cosmos in motion some fifteen billion years ago. Ever since, the universe has been locked in a duel -- between the momentum of expansion and the inward pull of its own gravity.

Cosmologists want to know: will space go on expanding forever? Or will gravity someday bring it crashing together in a "Big Crunch?"

To answer this question, the team will use exploding stars as cosmic speedometers... To measure how fast gravity is slowing the expansion of the universe.

Alex Filippenko
We need to know not only the expansion rate of the universe now, but also the past history of the expansion rate. We think that the universe was expanding faster in the past than it is now, and thatís because all of the galaxies in the universe are pulling on all the other galaxies.

Narrator
To get the data they need, it will take superb viewing conditions. Theyíre in for a disappointment. A major storm is blowing across the Pacific.

Now Filippenko has a tough call: to try to launch the study as planned... or cut his losses and merely verify some of the sightings.

Alex Filippenko
The weather is critical because we're looking at objects which are, for the type of data we're trying to get, theyíre at the tough end of even what this telescope can do. When the clouds come over, that means that our data are certainly compromised...

One of the purposes of the Keck observations was to not only see what kind of a supernova it is, but to see details in the spectra which no other telescope can do on Earth.

Alex Filippenko
Okay, it looks like weíre getting ready to open. So letís just go ahead and do it.

Narrator
The team has just three nights at Keck, and each one is precious.

As darkness engulfs Mauna Kea, the distant universe is poised to surrender its light to Keckís gaze.

Alex Filippenko
Great, maybe half the night can be salvaged.

Narrator
Hopes are high.

Alex Filippenko
Okay, I'm gonnaí start an exposure. This will be number 69 on the low res disk.

Terry
So your first object is HD 19445.

Alex Filippenko
Okay, so we're at the hairy edge, but we might be able to get some good data. Certainly seeing a star this faint coming in so brightly means I donít think we have a thick layer of clouds out there.

Narrator
Filippenko is looking for a certain type of supernova, one that for most of its life resembled the sun.

Our star was born some five billion years ago -- and will begin to die in another four. Its fate is in stark evidence throughout our galaxy.

The sun will swell and become a red giant. Its planets, including earth, will be swallowed and incinerated.

A billion years later, it will begin to convulse, and expel its outer layers.

Those layers may form a ring of expanding gas, like the famed Helix Nebula. A powerful wind still blowing from the star sculpts the inside of this great halo.

In the center is the starís exposed heart. Known as a white dwarf, it is the size of Earth -- one millionth what it once was.

If, by chance, another star is in orbit around a white dwarf, something extraordinary can happen.

The intense gravity of the white dwarf draws gas from its companion. At last, its mass reaches a critical limit.

Astronomers can determine how bright this type of supernova should be. The dimmer one appears to us, the farther away it is.

Alex Filippenko
These are the most powerful explosions we know of in the universe aside from the creation of the universe itself, the Big Bang. Besides being exciting, the power of the explosions makes these objects visible at very great distances, which is what makes it possible for Saul and myself to look for these things and use them to study cosmologically interesting parameters, like the expansion rate of the universe and the curvature of the universe. These are among the most luminous objects we know of.

Narrator
For all the Filippenkoís grand ambitions, his time is running short. Skies are turning overcast.

Alex Filippenko
Youch. Well thereís something there. Thereís one trace. Oh, man. I think thereís a cloud passing through our field right now. Yeah, things are not very good right now. Theyíre getting worse.

Narrator
As much as any telescope, patience is the astronomerís tool. They can only hope the weather clears.

In any given galaxy, supernovae are rare events -- About one every century. And yet their impact is profound.

Alex Filippenko
I study exploding stars partly because I find the concept that atoms in my body were cooked up inside stars, and especially inside exploding stars, I find that concept to be completely mind-blowing. And I'd like to understand the process by which this occurs in the universe. Really weíre studying our own origins at a very fundamental level.

Narrator
Exploding stars are the wellspring of life. Evidence abounds in our own galaxy.

They seed their environments with carbon, oxygen, iron and other elements necessary for life. Destruction is by no means the supernovaís only legacy.

Stan Woosley
Aside from just being dramatic explosions and making the heavy elements, supernovae influence their surroundings. The gas and dust that exists between stars, the so-called "interstellar medium," is shoved around by the supernovae. It blows bubbles in them. It can compress clouds that might be ready to form and perhaps trigger star formation.

Narrator
A star hatchery percolates along the edge of the Pinwheel Galaxy, fifty million light years from earth. This massive cloud of gas is lush with regeneration.

In places like this, the energy let loose by supernovae stirs the celestial mix. Shock waves from the explosions cause gas to condense, then ignite.

Stars are born, sometimes hundreds at a time.

An infant star scars its environment with the violence of its birth. As matter collapses inward, jets of radiation burst forth like machine gun rounds.

In the fold of our home galaxy, the Eagle Nebula is one of the richest of the great star nurseries.

Intense stellar winds have sculpted a majestic castle of gas. Inside these giant columns, stars are being born.

Yet for the dying stars that set this process in motion, the consequences are grim.

Supernovae leave in their wake a range of bizarre objects. Among them, a tiny dense ball of neutrons.

Mario Livio
You form an object that we call a neutron star, which is something that has the mass of our sun, but a radius of only about six miles or so. That is a very compact object. Every centimeter cubed of that mass has a mass of a hundred-million tons.

Narrator
Because of its intense gravity, a neutron star is a perfect sphere, with a surface like polished metal.

Bob Kirshner
It has the mass of the star, but it only has the size of a city. And the structure of that matter is that it's like ordinary matter, where there are electrons and so on orbiting around, ah, ah, nuclei, but with all the electrons sort of squashed into the nuclei and the particles up close together. So something that we think of as incredibly dense, like lead, is really mostly empty space. And if you squish all the empty space out of it and get the nuclei right up next to each other, thatís something that has the density of a neutron star.

Narrator
The existence of neutron stars was first proposed in the 1930s. It wasnít until the í60s that hard evidence was finally detected.

Within the remnants of some supernovae, astronomers detected a presence that pulsed with radio signals.

Paul Davies
When these were discovered by a graduate student in England in the 1960s, the supervisor thought that they should not announce the discovery for a few months, partly in order to check the -- that it was a genuine astronomic object. But also because of the possibility that this might be an alien signal. And in fact, the code name for the object in the early days was LGM, to stand for Little Green Men.

Narrator
Aliens it was not. Strange it was.

The Crab Nebula is the shell of the same supernova that caught the attention of so many cultures in the year 1054. Deep within, astronomers found a pulsar, a neutron star that spins rapidly, emitting radio waves.

Now scientists are using the Hubble Space Telescope to zero in on the pulsar -- The star on the left. It is spewing waves of radiation that have etched circular patterns in the surrounding gas.

Yet, some dying stars meet a fate that is stranger still. Nature, it seems, has contrived a monster.

Early in this century, Albert Einstein speculated about a star with such intense gravity that absolutely nothing, not even light, escaped its grasp. He at once dismissed this prospect as impossible.

Paul Davies
The notion that you could squeeze something without limits, you know, right down to a zero size, was considered basically absurd and offensive. And so there was a sort of temperamental reaction against this idea of total gravitational collapse right through until the 1950s.

Narrator
What once seemed beyond reason now defines the frontiers of science. Astronomers believe that when a large star explodes, enough matter can collapse into its core that it literally exits the known universe.

Mario Livio
If the mass of that core is large, is larger than about three times the mass of our sun, nothing at the end can stop the final collapse. Gravity wins the final battle and the thing collapses to form a black hole.

Narrator
Black holes: welcome to the distant edge of space.

Evil Dead II man
For Godís sake! How do you stop it!

Narrator
For this trip, itís one way only.

Mario Livio
Well, it's -- it maybe sounds like science fiction... But you know that there are tides, for example, on Earth caused by the moon. Where the seaís closest to the moon, it is being drawn farther out, so you get a tide, for example. Now the same thing would happen if you have an object falling into a black hole, say. The only thing is that because the gravitational force there is so large, the tide will be enormous so that things will eventually start to be torn to pieces. In fact, that tidal force increases to infinity by the time you fall into the black hole. So at first, you know, larger objects will be torn, but then smaller -- eventually even on the atomic scale, atoms will be torn apart and then nuclei of atoms will be torn apart even on that small scale. So all matter will in fact lose the identity as we know it, and by the time you really fall into the black hole, in effect we donít even have the right physics to describe everything that will happen.

Narrator
From our vantage on earth, we define our universe by familiar criteria. But black holes defy discovery. What after all can we detect of objects that emit no light?

Bob Kirshner
The fact is we donít have enough cases where we really know what's going on to be able to study it in detail. We'd like to know, for example, if the black holes are a little different from the theory and at the moment weíre just at the stage of finding out whether there are good candidates for black holes, things that we think canít be neutron stars, canít be white dwarfs, canít be anything else. The usual argument for a black hole is somebody shrugging and saying, "Well, what else can it be?"

Narrator
In 1991, astronauts placed one of the milestones of modern science into orbit. The Compton Gamma Ray Observatory monitors high energy radiation that pummels our upper atmosphere.

In 1994, it picked up a sudden eruption in the Constellation Scorpius.

Astronomers around the world zeroed in on the source. A network of radio telescopes stretching from the Caribbean to Hawaii recorded a rare specter.

This is the object that came into view. Matter rushing into it is sending out jets of intense radiation.

This week marks the culmination of a year-long effort to study the object. Teams in eight countries are simultaneously training their most advanced technology on it, to discover its true nature.

From a telescope in the Andes Mountains, in the heart of Chile, the astronomer Charles Bailyn was the first to pinpoint its location. Now heís venturing back to the observatory at Cerro Tololo -- to prove once and for all itís a black hole.

Charles Bailyn
Itís the strange objects that always tell you the most about, ah -- about the universe and about science. So, if you want to increase your knowledge of how gravity works, for example, you don't look at things falling on the Earth, which we understand. You look at the really, really strong gravitational fields that happen near black holes. Ah, and those are the things where our current theories might possibly break down.

Charles Bailyn
Okay, Luis, letís make this slew.

Narrator
No one has ever proven conclusively the existence of a black hole. If ever there was an opportunity, this may be it.

Charles Bailyn
Okay, so, are we guiding?

Voice
Yes!

Charles Bailyn
Good, umm...

Narrator
Looming within the dense star fields of our Milky Way, 10,000 light years away, this is the brightest and most spectacular object of its kind. Whatís more, itís not alone.

A normal star circles the object in a dance of death. Gas from the star flows into the object through a disk, while jets of radiation shoot from its poles.

So powerful is the objectís gravity, that the companion starís shape is being distorted and squashed, causing its appearance to dim, then brighten as it makes its orbit.

Charles Bailyn
As it goes around, ah, the black hole, we're gonna start seeing the edge-on, rather than side-on, so you can see less of it. So it's gradually going to get fainter because in the time we're watching it tonight it's going to go, uh, from almost side-on to almost end-on.

Charles Bailyn
But that one definitely has promise donít you think...

Narrator
Though Bailyn and his team canít view the object directly, they can study its companion.

Mario Livio
If you remember in Alice in Wonderland there is a Cheshire Cat. The cheshire cat disappears from view and only leaves its smile behind to be seen. Black holes have this property. They disappear from the eye, but they leave their smile behind. They leave their gravitational force behind and it is by that that we then see them and are able to infer their properties.

Charles Bailyn
Ahh, and then, where is the bright star, is this it?...

Narr>


Transfer interrupted!