About a decade later, physicist Raymond Davis set up the first neutrino observatory in a gold mine, nearly a mile beneath the Black Hills of South Dakota. An underground location assured the measurements would be free from disruptive cosmic rays. In continuous operation for a few decades, Davis’s detector kept watch on the torrent of neutrinos flung into the solar system as the Sun burned its nuclear fuel. It provided the first hint that the neutrino had a smidgen of mass after all. More advanced underground observatories constructed in the 1990s provided the ultimate proof, a confirmation that won the lead researchers for the experiments—Takaaki Kajita at the Super-Kamiokande detector in Japan and Arthur McDonald at the Sudbury Neutrino Observatory in Canada—the Nobel Prize in Physics in 2015.
Neutrino detectors and observatories can now be found or are under construction around the globe: not only in Antarctica, Japan, and Canada, but also in France, Russia, Italy, and India. And they are beginning to extend their searches beyond the neutrinos emanating from the Sun to the more powerful particles trekking through the cosmos. While weighing less than a billionth of the mass of a proton, each captured neutrino will help scientists understand the universe’s history, structure, and future fate.
CHAPTER TWENTY-TWO
Eavesdropping on the Universe
The Galileo of radio astronomy
EVEN at fifty-five miles per hour, the desolate terrain seems to pass by in slow motion. Only an occasional stand of piñon pines on the side of a hill or, farther off, the stark profile of an erosion-sculpted mountain breaks the monotony.
But suddenly, after driving over a rise on Route 60, a few dozen miles west of Socorro, New Mexico, the weary traveler comes upon a spectacular sight: in the distance are twenty-seven dishlike antennas, lined up for miles over the flat, desert Plains of San Agustin. Airline pilots who fly over the ancient, mile-high lakebed have long called this gigantic Y-shaped installation “the mushroom patch.” But ever since this facility was first dedicated in 1980, astronomers have simply referred to it as the VLA, for Very Large Array, one of radio astronomy’s premier eyes on the universe.
Its majestic white dishes move in unison, like a mechanical version of the Rockettes, New York City’s legendary dance company, to gather the radio waves sent out by myriad celestial objects. On one day, the antennas might trace the wispy outlines of a gaseous nebula to see how its molecules tumble and collide, leading astronomers to the birthplace of new stars. The next day, the dishes could point toward a supernova and snap a “radio picture” of the debris racing away from the monstrous explosion.
The array’s particular strength is acting like a giant zoom lens. For a few months at a time, the antennas are crowded close, each arm of the Y no more than half a mile long. This setup provides a sort of wide-angle view of the heavens, perhaps to trace the gas clouds in a nearby galaxy. But to get a closer look, the antennas are periodically transported along railroad tracks out to greater distances, up to thirteen miles (twenty-one kilometers) along each arm. In the most extended arrangement, as the Earth sweeps the antennas around, the individual dishes collectively simulate the capability of a single antenna spanning some twenty-two miles (thirty-five kilometers), roughly the size of Dallas, Texas.
The Karl G. Jansky Very Large Array.
(Courtesy of NRAO/AUI)
Over the array’s nearly four decades of service, thousands of scientists from around the world have used the VLA to study the cosmos. Sometimes their focus is near—within our own solar neighborhood—and at other times out to the farthest reaches of space-time. On one occasion, visitors from Hollywood even took their turn: in the 1997 movie Contact, a fictional astronomer played by actress Jodie Foster used the iconic scopes to find radio proof for the existence of intelligent extraterrestrials.
But by the 1990s the National Radio Astronomy Observatory (NRAO), which operates the New Mexico array, recognized that the facility was getting long in the tooth, hindered by its 1970s-vintage electronics. So, in partnership with Canada and Mexico, the NRAO spent a decade upgrading the array’s technology—from installing state-of-the-art receivers and fiber-optic transmission lines, to obtaining an innovative supercomputer to swiftly correlate its data. Ever since its completion in 2012, the new array has been detecting signals more than ten times fainter than the original system and is covering a radio-frequency range three times as wide, making it “by far the most sensitive such radio telescope in the world,” says former NRAO director Fred K. Y. Lo. Need to take a cellphone call from Jupiter, some half a billion miles away? The new array can do it.
Given this transforming reincarnation, the NRAO decided it was also time to update the VLA’s humdrum name, and so solicited suggestions via the internet from both the public and the scientific community. Candidate names flooded in from 17,023 people in more than sixty-five countries. Sifting through some 16,000 unique names, NRAO officials at last chose a new moniker that was eminently suitable. At a rededication ceremony that took place on March 31, 2012, the New Mexico facility was formally renamed the Karl G. Jansky Very Large Array.
Although hardly a household name, Karl Jansky is a pioneering giant to radio astronomers. He’s the Galileo of radio astronomy. In the 1930s, Jansky set up a unique radio receiver amid central New Jersey’s potato fields, and with it became the first to wrench astronomy away from its dependence on the optical spectrum, beyond the narrow hand of electromagnetic radiation visible to the human eye. His first, provisional step ultimately led to a new and golden age of astronomy that thrives to this day. But, as is often the case in astronomical history, Jansky began his investigations for a totally different reason.
In 1928, fresh out of college with a degree in physics and newly hired by Bell Telephone Laboratories, the twenty-two-year-old was assigned to investigate long-radio-wave static that was disrupting transatlantic radio-telephone communications. To track down the sources, he eventually built a steerable antenna—a spindly network of brass pipes hung over a wooden frame that rolled around on Model-T Ford wheels. It was known around the lab as “Jansky’s merry-go-round.”
Setting up his antenna near Bell’s Holmdel station, Jansky soon learned that thunderstorms were a major cause of the disruptive clicks and pops during a radio phone call. But there was a steady yet weaker hiss that he also kept receiving. After a year of detective work, Jansky at last established in 1932 that the disruptive 20-megahertz static (a frequency between the United States AM and FM bands) didn’t originate in the Earth’s atmosphere, or on the Sun, or from anywhere within our solar system. To his surprise, he saw that it was coming from the direction of the Sagittarius constellation, where the center of our home galaxy, the Milky Way, is located. Jansky affectionately dubbed the signal his “star noise.” For Jansky it hinted at processes going on in the galactic core, some 26,000 light-years distant, that were not revealed by visible light rays emanating from that region. For unlike visible light, radio waves are able to cut through the intervening celestial gas and dust, in the manner of a radar signal passing through a fog.
Karl Jansky with his “merry-go-round,” the historic radio antenna that initiated the field of radio astronomy.
(Reused with permission of Nokia Corporation)
Jansky’s unexpected discovery made front-page headlines in the New York Times on May 5, 1933, with readers being reassured that the galactic radio waves were not the “result of some form of intelligence striving for intra-galactic communication.” Ten days later NBC’s public affairs–oriented Blue Network broadcast the signal across the United States for the radio audience to hear. One reporter said it “sounded like steam escaping from a radiator.”
By 1935, Jansky speculated that the cosmic static was coming either from the huge number of stars in that region or from “some sort of thermal agitation of charged particles,” which was closer to the truth. Years later, astronomers confirmed that the noise was being emitted by violent streams of electrons spiraling about in the magnetic fields of our galaxy. Just as an e
lectric current, oscillating back and forth within an earthbound broadcast antenna, releases waves of radio energy into the air, these energetic particles broadcast radio waves out into the cosmos. And Jansky was the first to detect them. He was Earth’s first eavesdropper on the universe.
Despite the worldwide publicity, however, few astronomers then appreciated Jansky’s new “ear” on the universe. Most were more comfortable with lenses and mirrors than with radio receivers. It was not until after World War II, spurred by the military development of radar technology, that the infant field at last took off. During the subsequent decades, radio telescopes were mapping the locations of colossal clouds of gas over the breadth of the Milky Way, discovering the existence of neutron stars from their metronomic radio “beeping,” and helping astronomers unmask quasars as the violent cores of newborn galaxies in the distant cosmos. The instruments’ greatest coup? Capturing the fossil whisper of creation, the remnant radiation from the Big Bang, now cooled down to a uniform wash of microwaves that blankets the universe.
Jansky, alas, saw none of this happen. Long burdened with a chronic kidney ailment, he died in 1950 at the early age of forty-four. In his last experiments, he was trying out a newfangled gadget called a transistor to improve a radio amplifier.
Yet his legacy lives on with the new and improved Jansky Array in New Mexico, whose resolution and sensitivity are billions of times greater than those of the original merry-go-round. Even when the array is inevitably replaced or supplanted in the far future, Karl Jansky’s name will still reverberate within the halls of radio astronomy. In 1973, the International Astronomical Union gave his name to a scientific unit. The jansky is a measure of the strength of an astronomical radio source.
CHAPTER TWENTY-THREE
The Once and Future Quasar
Discovering the universe’s more violent side
I smiled when I heard the news. In 2017 an international team of astronomers had just announced the discovery of the most distant quasar, the luminous core of a newly forming galaxy situated a whopping 13 billion light-years away. That means the light from this quasar started on its journey less than a billion years after the Big Bang. The universe was just a toddler at the time.
I was amused because this headline has regularly been appearing in the news for more than half a century—and continues to this day. There’s no news like old news. The most-distant-quasar record has gotten replaced as often as a newborn’s diapers. It all started when Caltech astronomer Maarten Schmidt recognized the first quasar on February 5, 1963. And in doing so, he revealed an entirely new side to the universe’s personality, one that both surprised and amazed astronomers. That’s because they had all grown up thinking of the universe as fairly serene.
Hints that the early cosmos was edgier than once imagined had started arriving in the late 1950s. At that time the noted British radio astronomer Martin Ryle reported that he counted more far-off cosmic radio sources than expected; the intense radio signals suggested that distant (and therefore, from our viewpoint, young) galaxies were more active than the older galaxies in our present-day universe. Spurred on by such discoveries in radio astronomy and not wanting to miss the boat, the United States built its own state-of-the-art radio observatories. One of them was a complex situated in California’s Owens Valley and run by Caltech. Soon this observatory began studying radio sources with better resolution. So much so that in 1960 it was able to narrow down the location of a particularly strong source, labeled 3C 48 for being the forty-eighth object in the Third Cambridge Catalogue of radio sources.
Given these better coordinates, astronomer Allan Sandage then swiftly used the grand 200-inch (5-meter) Hale telescope atop southern California’s Palomar Mountain to see what visible celestial object might be situated at that spot. Expecting to see a galaxy, he instead found a blue pinpoint of light, a real surprise. At first, everyone just assumed it was a star in our own galaxy, making it the first known “radio star.” But there was a catch: “I took a spectrum the next night,” said Sandage, “and it was the weirdest spectrum I’d ever seen.”
Over the next two years, a handful of similar objects were discovered, adding to the mystery. On first look they appeared to be simply faint blue stars within the Milky Way, just like 3C 48. But again, the light waves emanating from these so-called radio stars displayed spectral features unlike those of any star ever observed. It was like riding down a familiar turnpike and finding all the road signs written in gibberish. Optical astronomers couldn’t even find evidence that hydrogen, the main component of all stars, was present in these objects. Yet, everyone kept assuming they were stars because, well, they looked like stars through an optical telescope. Not until February 1963 was the identity of these peculiar radio beacons finally unmasked.
Maarten Schmidt in the
1960s, when he recognized
the true nature of the first
quasar.
(AIP Emilio Segrè Visual Archives,
John Irwin Slide Collection)
On the fifth day of that month, the thirty-three-year-old Schmidt, who had arrived a few years earlier at Caltech from the Netherlands, was sitting at his desk attempting to write an article for the British journal Nature on the radio star known as 3C 273. He had just obtained an optical spectrum of this strange object, using the Hale telescope. With the spectrum spread before him, Schmidt came to recognize a familiar pattern of spectral lines that had eluded him for weeks. The pattern resembled the light waves typically emitted by simple hydrogen—but they were in the wrong place. That’s why hydrogen had appeared to be missing! The hydrogen lines were there, but shifted waaaay over, toward the red end of the spectrum. That meant this starlike object was moving away from us at a tremendous speed. Just as the pitch of an ambulance siren gets lower as it races away, a light wave is stretched when its source recedes from us, and, because a light wave at the red end of the spectrum is longer, we say it gets “redder.” This “redshift” lets astronomers gauge not only how fast a celestial object is moving but also its distance, because—as Edwin Hubble found in 1929—there’s a systematic link between a galaxy’s speed and its distance in our expanding universe. The faster the velocity, the more distant the galaxy.
In this way, Schmidt swiftly grasped what that redshift meant. 3C 273 was not an unusual star situated within the Milky Way, but rather a bizarre object located about two billion light-years away (one of the farthest cosmic distances ever recorded at that time). 3C 273 was rushing away from us at some 30,000 miles (48,000 kilometers) per second, carried outward with the swift expansion of the universe. Schmidt knew that only an incredibly bright source could be visible from such a distance; he figured 3C 273 was radiating the power of trillions of stars and suspected it was the brilliant and very disturbed nucleus of a distant galaxy. This galaxy appeared starlike only because it was so far away.
With that revelation, all fell into place. The spectra of other mystifying radio stars were quickly deciphered. These blue, extragalactic specks were soon christened quasi-stellar radio sources (QSRS). Before long, they were simply called quasars. For his role in vastly extending the boundaries of the visible universe, Schmidt made the cover of Time magazine.
An image of 3C 273, the first identified quasar,
taken by the Hubble Space Telescope.
(ESA/Hubble & NASA)
3C 273 is now considered relatively close to us, as quasars go. Its distance is small potatoes compared with those of later finds. Today’s record holders are more than six times as far away. And the fact that earthbound observers are able to photograph such quasars across the vastness of the universe means that these objects are the most powerful denizens of the heavens.
What could possibly be the source of a quasar’s monstrous energy? That’s the first thing everyone asked when 3C 273’s secret was revealed. “The insult was not that they radiate so much energy,” said Schmidt, “but that this energy was coming from a region probably no more than a light-week across.” Astro
nomers came to know this by seeing the quasars dim and brighten over a matter of weeks or days. In the case of 3C 273, they checked old photographic plates of the 13th-magnitude object, going back some seventy years. In one picture it was faint, a month later it was brighter. Such relatively swift and sizable fluctuations meant that the quasar’s power source was small, perhaps less than the diameter of our solar system. (Any small luminosity change in a vastly larger object would get lost in the noise.) Yet from such a cosmically tiny region spewed the energy of billions of suns. Tapping into such a cosmic dynamo for just one second would power the world for a billion billion years.
Since Schmidt’s discovery, quasars have been closely examined by an array of telescopes—radio, infrared, optical, and X-ray. And all point to one answer to a quasar’s identity: it’s a supermassive black hole residing in the center of a young, gas-filled galaxy. The vast energies are likely released as matter spirals in toward the black hole, and also by the spinning hole itself acting as a powerful dynamo, causing huge beams of energy to shoot out of the black hole’s north and south poles.
The center of our home galaxy, the Milky Way, was probably a quasar in the distant past. The black hole lurking there, estimated to contain the mass of around four million suns, is now fairly quiet, having grabbed all the nearby “food” it can get. Its engine is on idle, but this behemoth might wake up one day, perhaps as we slowly collide with our close neighbor, the Andromeda galaxy, about four billion years from now.
To the Big Bang and Beyond
Dispatches from Planet 3 Page 12
