Higher-Z Supernova Cosmology Project
An absolutely Byron-esque article from the NY Times concerning our expanding universe.
BALTIMORE — It was a quiet cloudy Saturday afternoon, and Dr. Adam Riess was more than a day into his search for a star.
Not just any star, but the galumphing galaxy-scorching explosion of a star giving way to age and gravity. These exploding stars, supernovae, can be seen across the universe. In them Dr. Riess can read the fate and nature of the universe.
Somewhere in the data on his computer screen, he hoped, was evidence of a star that had died before the Earth and Sun were born. He and his team had until Tuesday to find it.
But things were not going well. "You know how nature likes to guard her secrets," he said, his voice trailing off.
He was dressed in a flannel shirt, baggy jeans and sneakers. On the wall over his computer hung a set of Dallas Cowboy bobble-head dolls. But his computer screen opened onto galaxies on the other side of the universe, stately kingdoms of stars, recorded by the Advanced Camera for Surveys on the Hubble Space Telescope and radioed to the Space Telescope Institute here.
Through Hubble's electronic gaze, these galaxies appeared as bits of indistinct fluff. But five years ago, as a member of one of two teams racing to divine the future of the universe, Dr. Riess used this type of data in a calculation that rocked astronomy. The expansion of the universe was speeding up under the influence of a mysterious antigravity, a "dark energy" embedded in space itself.
Since then, dark energy has prompted an outpouring of papers and speculations. The urgency of the supernova observations has been underscored by studies of radiation left over from the Big Bang, which suggest that dark energy constitutes some three-quarters of the weight of the universe. What is it? Where does it come from? Is it forever?
"It's so strange," Dr. Riess said. "We have to be sure it's real."
To find out, Dr. Riess and his colleagues have embarked on a search for the oldest supernovae they can find, stars whose light was traveling through the universe before dark energy made a mark on it. Clicking and pointing and running cursors over the flecks of light that Hubble sends to their computers, the researchers are looking for the one pixel out of a billion that is their exploding star.
That is the stargazing that appeals to Dr. Riess, who shares few of the classical astronomical virtues. He cannot identify the constellations. ("I can only find the Big Dipper," he admits.) He does not like to stay up late. "I always regret it in the morning."
Dr. Riess, the youngest of three children of an engineer and a psychologist, was born in Washington and raised in Warren, N.J. He studied physics at M.I.T. before taking up astronomy in graduate school at Harvard, where he studied with Dr. Robert P. Kirshner, an authority on supernovae.
Eventually, Dr. Riess became an expert in what he calls "back end analysis" of telescope data, particularly of exploding stars, work he continued as a postdoctoral student at Berkeley. Those analytic skills would be invaluable in the race to determine the fate of the universe.
For cosmology, the exploding stars of choice are known as Type Ia. They originate on dense burned-out cinders about the size of Earth that are known to astronomers as white dwarfs. Eventually, the Sun will end as a white dwarf, ever fading and cooling.
But if a white dwarf has a companion star, it can have a violent, brief resurrection as a Type Ia supernova. In that case, the intense gravity of the white dwarf can steal material from its neighbor. When its mass exceeds a critical limit, about 1.4 times the mass of the Sun, the star destroys itself in a fury as bright as four billion suns.
Because all Type Ia explosions start from the same point, astronomers have long hoped that their brightness is uniform enough to serve as "standard candles." In other words, knowing how bright they actually are and how bright they appear to be through a telescope, scientists may be able to calculate how far away they are.
In the late 1980's a group of astronomers and physicists led by Dr. Saul Perlmutter, a physicist at the Lawrence Berkeley National Laboratory, began an ambitious effort to comb the cosmos for distant supernovae. Dr. Perlmutter was hoping to compare their distances to their speeds, to learn how fast the universe had been expanding since its creation in the Big Bang and how much it was slowing today, and thus whether everything would end one day in "big crunch."
In 1996, another band of astronomers, including Dr. Riess and Dr. Kirshner, formed their own team to pursue the supernovae. The group, led by Dr. Brian Schmidt of the Mount Stromlo and Siding Spring Observatories in Australia, called itself the High-Z Supernova Search.
"We were the supernova pundits," said Dr. Riess. His contribution was to show how to correct for the fact that the Type Ia's were not quite as uniform as General Electric light bulbs after all. In 1992, Dr. Mark Phillips at the Cerro Tololo Interamerican Observatory in Chile, showed that brighter explosions faded more slowly than dimmer ones. By following the supernova's history, or "light curve," astronomers could sharpen their estimates of its intrinsic brilliance and, thus, its distance.
Dr. Riess found a way to sharpen the estimates using the stars' colors. Brighter bursts were bluer than dimmer ones.
But by the end of 1997, the two teams were baffled. Their data did not show that the expansion of the universe was slowing, as astronomical orthodoxy had long held. In fact it appeared to be speeding up, seemingly under the influence of some kind of cosmic repulsion. Einstein had theorized such a force in 1917 but later renounced it.
At first, Dr. Riess feared that he had made a mistake. But then he heard that Dr. Perlmutter's team was getting similar weird results. "I thought, `Whoa, what are the odds that we would both make the same mistake?' " Dr. Riess recalled.
Neither team was eager to report such a strange result. In January 1998, Dr. Riess flew back East and married his M.I.T. sweetheart, Nancy Schondorf, who works in industrial design in Baltimore. Two days later, on the eve of his honeymoon, he crunched the data again and concluded that the effect was real. Einstein's fudge factor was back.
"Approach these results not with your heart or head but with your eyes," read an e-mail message that he sent to his teammates, encouraging them to trust the data that they had so painstakingly analyzed. "We are observers after all!"
On the morning that Science magazine published an article about the discovery, Dr. Riess arrived at his office in Berkeley to a ringing telephone, a call from CNN, the first of many. "I was on the phone for days," he recalled.
"The universe is behaving like a driver who slows down approaching a red stoplight and then hits the accelerator when the light turns green," he told the BBC.
Dr. Perlmutter's group soon chimed in with its identical result. The fact that two competing groups had agreed meant that astronomers had to take the news seriously.
The Exploration: A Gold Rush In the Sky
The discovery of dark energy set off a kind of gold rush in the sky, as the two groups and other astronomers sought to confirm their strange results.
"More supernovae have been discovered in the last four years than in the previous 40 years," Dr. Riess said. "That's incredible."
Meanwhile, theorists have been busy. "This is the major challenge to fundamental physics," said Dr. David Gross, the director of the Kavli Institute for Theoretical Physics in Santa Barbara, Calif.
The leading explanation so far, Dr. Riess said, is Einstein and his old fudge factor, the cosmological constant. According to modern quantum theory, the emptiness of space foams with evanescent particles, and their energy should act as an antigravity.
Because the repulsion originates in space itself, as the universe expands and makes more space, the "push" from the cosmological constant rises steeply as the universe grows bigger, shooting the galaxies outward faster and faster, until they are going so fast that most of them cannot be seen anymore.
The universe will appear cold and dark.
Other theorists pin their hopes on "quintessence," other energy fields predicted by speculative theories of physics, or even interactions with a parallel universe.
In principle, astronomers could tell which model was right by tracing the history of the universe over the last few billion years, through supernovae and other means.
Dr. Perlmutter has proposed building a satellite observatory, the Supernova Acceleration Probe, or SNAP, to do that work, a notion that NASA recently endorsed in a "road map" for studies of the universe.
Dr. Schmidt's team has begun a project called Essence. Using a telescope in Chile, they hope to find 200 supernovae. At least half a dozen other projects are under way to examine the history of dark energy, using supernovae and
The Search: Around the Curve of Cosmic Time
The evidence that the universe is accelerating, as Dr. Riess explains, is still tantalizingly thin, just a few dozen tiny blotches on the electronic detectors that have replaced photographic film in telescopes.
But dust or chemical changes over the course of cosmic time may also have dimmed the electronic images of these supernovae. A way to find out, Dr. Riess explained, is to look back to the era before dark energy began to do its work, roughly seven billion years ago, when the universe was half its present age.
If the universe is truly accelerating, a supernova from then should appear relatively brighter than expected.
In 2001, Dr. Riess and his collaborators found such a supernova at a distance of 11 billion light-years, meaning that it was a messenger from 11 billion years ago, far beyond the purported turnaround. The Hubble telescope had inadvertently recorded it two years earlier, and it proved to be twice as bright as expected, a crucial, but not clinching, vote for dark energy.
"This is of such importance, one object is not enough," Dr. Riess declared.
As a result, he and his colleagues are out to find more supernovae out in the cosmic abyss, a quest that he calls the Higher-Z Supernova Cosmology Project.
"Z is the astronomical symbol for redshift, a measure of how much the light of receding galaxies has been lengthened in wavelength, or reddened, the way a police siren sounds lower when it is going away. The higher the redshift, the farther away a galaxy is.
For the mission, the project has arranged to piggyback on a worldwide survey of cosmic origins.
Every 45 days in the fall and winter, the Hubble telescope is observing the same two little patches of sky, one in the south and another in the north.
Each patch is a fraction of a full moon wide. But within this pencil beam into eternity are tens of thousands of galaxies, trillions upon trillions of stars.
In 45 days, a lot can happen to a few trillion stars. Stars swirl about one another like couples on a tango floor, blinking in and out of view. Asteroids streak by. Black holes burp, inflaming the centers of galaxies or quasars. Most important, at least a few stars will explode, turning a distant galaxy into a funeral pyre.
The resulting picture, actually a mosaic of 16 images, or "tiles," from this cycle of observations had started emerging from the science institute's computers the day before, on Friday morning.
Dr. Riess's teams went to work, examining each tile as it came in, looking for gold. They had until Tuesday, when the next observing commands were to be sent up to the Hubble, to find their star and "pull the trigger" to point the space telescope at it.
Now, on Saturday afternoon, sitting at his computer, Dr. Riess clattered his fingers over the keyboard. The screen in front of him turned a pebbly gray, scattered with small black blotches. It looked like sand and showed the difference between one of those tiles now and the same piece of sky 45 days earlier — "before" electronically subtracted from "after."
"This is where it all becomes science slash art," Dr. Riess said as he slid his cursor over interesting features, calling up close-ups recorded at different times and through filters that isolate selected wavelengths of light. By comparing the intensities of different wavelengths, the astronomers can determine the prospective supernova's color and, thus, its type. For example, the Type Ia explosions look red, he said.
"It's kind of weird," Dr. Peter Garnavich, an astronomer from the University of Notre Dame, noted at one point. "You look across billions of light-years and hope the photons get here by Tuesday."
So far, Dr. Riess's art had yet to fail him. The weekend search was his team's third. In each of the earlier searches, the team had found a supernova about nine billion light-years out, worth "pulling the trigger" and commanding the Hubble's attention.
This time around, they have chosen to name their supernovae after characters in Tolkien's "Lord of the Rings." But as Saturday afternoon wore on, the only supernova that had been found was too nearby for their purposes. Moreover, the telescope was refocused between the last two episodes of observing, changing the apparent sizes of galaxies and making it look as if they had changed in the interval, even if they had not.
One supernova candidate turned out to be an improbable sequence of four cosmic ray hits on the same pixel, "like a bad hand of poker," Dr. Riess muttered.
Picking through the specks and fluff like an unsatisfied diner, Dr. Riess conceded that he was growing a little frustrated, adding that it was too early to be discouraged.
To show what a real supernova looked like, he called up images of Aphrodite, which they had found earlier in the fall. It blinked on and off in the before and after frames like a Christmas tree light. "When it's good, it's good," he said.
Dark Questions: Dr. Einstein, Call Home
At 11 a.m. the next day, Dr. Garnavich bounded up the stairs to Dr. Riess's office, breathing hard. "Did you see the one in 34?" he asked, referring to the patch of sky that he had been scrutinizing.
"Holy behemoth," Dr. Riess said as he quickly called the image up on his computer screen. The bright dot in a spiral galaxy was clearly a supernova. But then enthusiasm waned.
"It's way too bright," Dr. Riess said.
That meant it was too nearby for their purposes. From its size and color, they estimated that the spiral galaxy was about four billion light-years away, almost modern in cosmic terms.
They agreed that it was a good candidate for the Essence team.
Within minutes, they came upon another burst, next to a scruff of spiral structure. "Hey, this looks pretty good," Dr. Riess said.
But again it was too close, a mere six billion light-years away.
"We're going after more distant prey," Dr. Riess said.
Over lunch, thanks to a trek to the local deli to bring back sandwiches, conversation turned from the mechanics of supernova hunting to its meaning.
Saying he did not care whether it was dark energy or some other effect that had dimmed the supernova, he said:
"I would like what we find to be real, not spurious. The only thing I would really find disappointing is if at the end someone came along and said, `You guys really screwed up your measurements.'
"I don't want it to be like cold fusion. I want it to be part of science that has to be weaved into the studies of supernovae."
He recalled reading as a student about cold fusion, the sensational claim that thermonuclear reactions could be performed at room temperature in a test tube and thinking, "Free energy for everybody." But when researchers could not duplicate the work, it became "a bizarre thing that had no place in science."
"I would hate that we become synonymous with cold fusion," Dr. Riess said, adding that dark energy was unlikely to go away at this point. But, he said, he worries that astronomy has too many "dark" things. Besides dark energy, there is dark matter — clouds of invisible particles, perhaps left over from the Big Bang, that apparently swaddle the visible galaxies. Like dark energy, dark matter has never been detected directly. Its existence has been inferred from its gravitational effects on the sliver of cosmos that astronomers can see. But that assumes that they know what gravity is.
"Maybe what we discovered is our ignorance about gravity," Dr. Riess said, about the 1998 discovery. "We need some young Einstein to come along and say, `You dummies.' "
It was unhealthy, he said, that observations had gotten so far ahead of theory. It is usually theorists who tell physicists and astronomers what experiments and measurements are important to do.
"The mind is more powerful than any telescope," Dr. Riess declared.
By late Sunday, the supernova possibilities were dwindling. A tiny television set in the corner of Dr. Riess's office was tuned to the Baltimore Ravens-Cleveland Browns game as he went about cleaning up loose ends and waiting for his teams to finish searching.
If Peter doesn't turn something up in an hour, I'm toast," Dr. Riess said. "Maybe I'm already toasted. If this had been the first search, I'd have been upset. This run has had funny luck stamped all over it."
By the end of the weekend, they had logged four supernovae — called Denethor, Bilbo, Frodo and Smeagol, after the gollum in "The Lord of the Rings" — that were good enough to give to the Essence team. But none were good enough to "pull the trigger" on Hubble.
"It's a lot like fishing," Dr. Riess said. "You have to enjoy the process, because some days you're just not going to catch any.
"We'll find them next time."
Only two observations really:
Is the article right about the Sun becoming (eventually) a white dwarf?
You can't bloody escape Jackson and his mythical cohorts can you?
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