December 21, 2021 4:36:21 pm
Written by Dennis Overbye
There are only a few times in the history of a species when it gains the know-how, the audacity and the tools to greatly advance the interrogation of its origins. Humanity is at such a moment, astronomers say.
According to the tale that they have been telling themselves (and the rest of us) for the past few decades, the first stars flickered on when the universe was about 100 million years old.
They burned hard and died fast in spectacular supernova explosions, dispelling the gloomy fog of gas left over from the primordial fireworks known as the Big Bang 13.8 billion years ago. From those sparks came all that we care about in the universe — the long, ongoing chain of cosmic evolution that has produced everything from galaxies and planets to microbes and us.
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But is that story right?
The tools to address that question and more are at hand. Sitting in a spaceport in French Guiana, wrapped like a butterfly in a chrysalis of technology, ambition, metal and wires, is the biggest, most powerful and, at $10 billion, most expensive telescope ever to be launched into space: the James Webb Space Telescope. Its job is to to look boldly back in time at the first stars and galaxies.
“We’re looking for the first things to come out of the Big Bang,” said John Mather of the Goddard Space Flight Center in Green Belt, Maryland, the chief scientist for the telescope. Or, as he likes to ask: “How did we get here from the Big Bang?”
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If all goes well — always a dubious prospect in the space business — the telescope will be loaded onto an Ariane 5 rocket and, Friday morning, blast off on a million-mile journey to a spot beyond the moon where gravitational forces commingle to create a stable orbit around the sun.
Over the next 29 days on its way up, the chrysalis will unfold into a telescope in a series of movements more complicated than anything ever attempted in space, with 344 “single points of failure,” in NASA lingo, and far from the help of any astronaut or robot should things become snarled.
“Six months of high anxiety,” engineers and astronomers call it.
First, antennas will pop out and aim at Earth, enabling communication. Then the scaffolding for a sunscreen the size of a tennis court will open, followed by the sunscreen itself, made of five thin sheets of a plastic called Kapton.
Finally, 18 gold-plated beryllium hexagons will snap into place to form a segmented mirror 6.5 meters, or 21 feet, across. By then, the telescope will have reached its destination, a point called L2, floating on its sun shield and aimed at eternity.
Astronomers will then spend six months tweaking, testing and calibrating their new eye on the cosmos.
Looking back at the fog
The James Webb Space Telescope, named after the NASA administrator who led the agency through the Apollo years, is a collaboration between NASA, the Canadian Space Agency and the European Space Agency. Its official mission is to explore a realm of cosmic history that was inaccessible to Hubble and every telescope before it.
“We are all here because of these stars and galaxies,” said Alan Dressler of the Carnegie Observatories in Pasadena, California.
That mission requires the Webb to be tuned to a different kind of light than our eyes or the Hubble can see. Because of the expansion of the cosmos, those earliest stars and galaxies are rushing away from Earth so fast that their light is shifted to longer, redder wavelengths, much as the siren from an ambulance shifts to a lower register as it speeds by.
What began as blue light from an infant galaxy 13 billion years ago has been stretched to invisible infrared wavelengths — heat radiation — by the time it reaches us today.
To detect those faint emanations, the telescope must be very cold — less than 45 degrees Celsius above absolute zero — so that its own heat does not wash out the heat being detected. Hence the sun shield, which will shade the telescope in permanent, frigid darkness.
Even before the Hubble Space Telescope was launched, in 1990, astronomers were arguing about what should come next. Dressler was the head of a committee proposing a Next Generation Space Telescope powerful enough to see the first stars and galaxies in the universe. It would need to be at least 4 meters in diameter (Hubble’s mirror was only 2.4 meters across) and highly sensitive to infrared radiation, and it would cost $1 billion.
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NASA was game, but Dan Goldin, the agency’s administrator, worried that a 4-meter telescope would not be keen-eyed enough to detect those first stars. In 1996, he marched into a meeting of the American Astronomical Society and scolded Dressler and his committee for being too cautious. The new telescope, he said, would be 8 meters wide, a drastic leap in power, cost and development time.
“The crowd went wild,” Dressler recalled recently. “But many of us knew from that day on that this was big trouble. Webb became the perfect storm: The more expensive it got, the more critical it was that it not fail, and that made it even more expensive.”
Doubled in size, the telescope could no longer fit aboard any existing rocket. That meant the telescope’s mirror would have to be foldable and would have to assemble itself in space. NASA eventually settled on a mirror 6.5 meters wide — almost three times the size of Hubble’s and with seven times the light-gathering power. But all the challenges of developing and building it remained.
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If the foldable mirror operates as planned, the mission could augur a new way to launch giant telescopes too big to fit on rockets. Only last month, a National Academy of Sciences panel recommended that NASA develop a giant space telescope 8 meters or more across to look for habitable planets. But if Webb’s origami fails, NASA and the astronomical community will have to take a long walk back to the drawing board.
“NASA committed too early to a particular design,” Dressler said. “I think this discouraged creative solutions that might have delayed the start of construction but made the telescope better and more affordable and, in the end, faster to launch.”
The setbacks mounted. At one point, the telescope was projected to cost about $5 billion and be ready in 2011; in the end, it took almost $10 billion and 25 years.
Cost overruns and mistakes threatened to suck money from other projects in NASA’s science budget. The journal Nature called it “the telescope that ate astronomy.” Ten years ago, Congress considered canceling it outright.
Naming the telescope was its own challenge. In 2002, Sean O’Keefe, the NASA administrator at the time, announced that the instrument would be named for Webb, who had been a champion of space science and the agency’s leader during the crucial days of the Apollo program. Some astronomers were disappointed that it did not honor a scientist, like the Hubble Telescope or the Einstein X-ray Observatory do. Some of them were critical of Webb, questioning his role in a purge of gay men and lesbians from the State Department during the Truman administration.
Others in the astronomy community joked that the telescope’s initials stood for the “Just Wait Space Telescope.” The delays were par for the course, Mather said: “We had to invent 10 new technologies to build this telescope, and that’s always harder than people think it will be.”
Designing the foldable mirror and the sunscreen was particularly difficult. In early 2018, the sunscreen was torn during a rehearsal of the unfolding process, and the project was set back again.
Finally, last October, the telescope arrived by ship in French Guiana, where it would be launched aboard an Ariane 5 rocket. But the telescope’s troubles were not over. As technicians prepared to attach it to the spacecraft, a clamp let loose unexpectedly and the whole instrument quivered.
The launch date was pushed back four days, from Dec. 18 to Dec. 22, while NASA confirmed that the telescope had not been damaged. A few days later, a broken data cable set the adventure back another couple of days.
An auspicious past
Almost 14 billion years ago, when the universe was less than 1-trillionth of a second old, quantum fluctuations in the density of matter and energy gave rise to lumps that would become the first stars.
These stars were different from those we now see in the night sky, scientists believe, because they were composed of only hydrogen and helium created in the thermonuclear furnace of the Big Bang. Such stars might have quickly grown to be hundreds of times more massive than the sun and then just as quickly exploded as supernovas. They do not exist in the present-day universe, it seems.
For all their brilliance, these early stars might still be too faint to be seen individually with the Webb, Mather said. But, he added, “they come in herds,” clumps that might be the seeds for the earliest protogalaxies, and they explode: “We can see them when they explode.”
Those supernova explosions are surmised to have began the process, continuing today, of seeding the galaxy with heavier and more diverse elements like oxygen and iron, the things necessary for planets and life.
A top item on the agenda will be to hunt for those first galaxies, Marcia Rieke of the University of Arizona said. Rieke has spent the last 20 years leading the development of a special camera, the Near Infrared Red Camera, or NIRcam, one of four instruments that take the light gathered by the telescope mirror and convert it into a meaningful image or a spectrum.
So far, the earliest and most distant known galaxy, discovered by the Hubble, dates to a time 400 million years after the Big Bang. The Webb telescope will be able to see back farther, to a mere 100 million years after the Big Bang.
In that foggy realm, Rieke expects to find dozens more infant galaxies, she said. Astronomers believe these were the building blocks for the clusters of galaxies visible today, agglomerations of trillions of stars.
Along the way, these galaxies somehow acquire supermassive black holes at their centers, with masses millions or billions larger than the sun. But how and when does this happen, and which comes first: the galaxy or its black hole?
Priyamvada Natarajan, an astrophysicist at Yale, and her colleagues are among those hoping to use the Webb to find an answer to the origins of these black holes.
Did they come from the collapses of those first stars? Or were the black holes already there, legacies of the Big Bang?
“A lot is on the line, intellectually in terms of our understanding of black-hole growth, and practically in terms of careers for the younger members of our team and that of others working on this important open question,” Natarajan said. “Assuming, of course, that all goes well, and JWST takes data as expected.”
Worlds beyond the sun
In the years that the Webb telescope has been in development, the hunt for and study of exoplanets — worlds that orbit other stars — has become the fastest-growing area of astronomy. Scientists now know that there are as many planets in the galaxy as there are stars.
“Everything we have learned about exoplanets has been a surprise,” Mather said.
Seeking such a surprise, he said, the telescope will look at Alpha Centauri, a star only 4 1/2 light-years from Earth: “We don’t expect planets there, but who knows?”
As it turns out, infrared emissions are also ideal for studying exoplanets. As an exoplanet passes in front of its star, its atmosphere is backlit, enabling scientists on Earth to study the spectroscopic signatures of elements and molecules. Ozone is one such molecule of interest, as is water, said Sara Seager, a planetary expert at the Massachusetts Institute of Technology.
The astronomers with viewing time on the Webb telescope have made a list of about 65 exoplanets to observe; all are relatively nearby, circling small stars known as red dwarfs. None is a true analog to our planet, an Earth 2.0 orbiting a sunlike star, Mather said. Finding one of those will require a bigger, next-generation space telescope. But they could be habitable nonetheless.
As a result, some of the most anticipated early observations with the Webb will be of the planets in the Trappist-1 system, just 40 light-years away. There, seven planets circle a dim red-dwarf star. Three are Earth-size rocks orbiting in the habitable zone, where water could exist on the surface.
Seager is part of a team that has first dibs on observing one of the most promising of these exoplanets, Trappist-1e. The researchers will begin by trying to determine whether the world has an atmosphere.
“Nothing is scheduled yet,” she said, and recounted the many steps needed before the telescope is operational.
“I liken it to waking someone up from a coma. You don’t ask them to run a marathon right away. It’s step-by-step testing.”
Mather, when asked what he was looking forward to studying, mentioned primordial galaxies, dark energy and black holes.
“What I really hope for is something we don’t expect,” he said.
Measuring the universe, again
Wendy Freedman could be excused for thinking she is living through a déjà vu moment.
Thirty years ago, before the Hubble Space Telescope was launched, eminent astronomers were arguing bitterly about how fast the universe was expanding. At issue was the correct value of the Hubble constant, which has been called the most important number in the universe. It measures the cosmic expansion rate, but astronomical measurements disagreed by a factor of two on its value. This meant astronomers could not reliably compute the age or fate of the cosmos or the distance to other galaxies.
The Hubble Telescope was to resolve this impasse, and Freedman, now at the University of Chicago, wound up running a “key project” that settled on an answer. But recent measurements have revealed a new disagreement about the cosmic expansion rate. And Freedman finds herself again in the middle, using a new space telescope to remeasure the Hubble constant.
“Today we have a chance to learn something about the early universe,” she said in an email. “As we have gotten increasingly higher accuracy, the issue has changed — we can now ask if there are cracks in our current standard cosmological model. Is there some new missing fundamental physics?”
“So yes, it is exciting,” she said. “Once again, a new fantastic space telescope that will allow us to resolve a controversy!”
And that, doubtless, will create new ones. As Klaus Pontoppidan, an astronomer with the Space Telescope Science Institute, said at a recent news conference: “The telescope was built to answer questions we didn’t know we had.”
This article originally appeared in The New York Times.
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