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National Aeronautics and Space Administration

Age of the : Size of the Universe: 10 - 25 Billion Years Cosmic Times 25 Billion Light Years 1965 MURMUR OF A BANG Big Hiss Missed Galaxies Still Misbehaving Recent attempts to weigh galaxies still come San Diego. Other researchers are finding similar By Others up a bit short. Two spiral galaxies under study, mismatches in galaxies everywhere, and no one One of the biggest surprises from the recent NGC 3521 and NGC 972, have weighed in at has yet offered a comfortable explanation. discovery of the ’s faded thunder is 80 billion and 12 billion suns, respectively. The About the only consolation galactic weight how many times others have missed it. puzzle is why the amount of starlight from these watchers may have is that their missing mat- Just last year, Russians Andrei Doroshkevic galaxies doesn’t add up to such huge amounts of ter problem is far less extreme than that of and Igor Novikov published a study that calcu- matter. Caltech astronomer Fritz Zwicky. In 1933, he lated correctly that, if the Big Bang happened, The starlight measurements of the two gal- pioneered similar measurements, though on a the remnant heat would now be between 1 and axies are based on careful accounting of the grander scale. Assuming that all the mass in a 10 degrees Kelvin. They even proposed search- galaxies’ total luminosity, or magnitude, as re- galaxy contributes to its brightness, he calculat- ing for the signal in sky temperature measure- corded on photographic plates. It also takes into ed the amount of luminous matter in the entire ments made by Edward Ohm in 1961. account the way the galaxies’ stars are arranged Coma cluster of galaxies, and then measured the Ironically, Ohm had gathered that data using from their centers to the edges. speeds of the galaxies as they orbited the cluster. the same Holmdel used by Arno The mass measurement is based on the same Zwicky came up with a mass-to-light ratio of Penzias and Robert Wilson this year at Bell idea that long ago allowed astronomers to cal- about 500, implying that 99 percent of the mat- Laboratories to identify the 3.5 degrees Kel- culate the mass of the Sun: if a relatively small- ter in the cluster is hidden. At the moment, most vin background radiation of the Big Bang. But mass object orbits a very large-mass object at a astronomers dismiss such extreme numbers as Ohm found a 3.3 degrees Kelvin noise that he known speed, the larger object’s mass can be de- astronomical flukes. assumed was coming from the antenna itself. termined mathematically. The same ap- The Bell Laboratories team has been able to say plies to stars orbiting a galaxy’s center of grav- with far more confidence that the faint excess ity. static truly came from space, because they had Since the motions of the extremely distant to weed out the antenna’s own noise to arrive at stars are not detectable through any telescope, their conclusions. researchers sampled slivers of galactic starlight There were two other near misses as well. from different parts of the galaxies and split the Ten years ago Émile Le Roux reported a back- light into spectra – their rainbows of color. These ground radiation of 3 degrees Kelvin, plus or spectra contain patterns of lines, representing minus 2 degrees, while studying the sky in the different energies, that shift in proportion to the speeds of the stars.

hoto courtesy of 33-centimeter radio wavelength at Paris’ Nan- P çay Radio Observatory. In 1957, Russian Tigran To make comparisons easier, astronomers McDonald Observatory image of NGC3521. Inset

Robert Wilson (left) and Arno Penzias stand in front of their horn reflector antenna in Holmdel, New Jersey. They Shmaonov nearly made the discovery, reporting blend luminosity and mass measurements into a shows detail in the central region (at the same scale). discovered a radiation signal that matches that expected by theorists who proposed that the universe began with a that he measured a background temperature of single number called a mass-to-light ratio. Our hot explosion called the “big bang”. This discovery was made by accident as they tried to track down the source 4 degrees Kelvin, give or take 3 degrees, while Sun, for example, has a mass-to-light ratio of of unwanted noise in their receiver. looking at the 3.2-centimeter wavelength of mi- one “solar mass” divided by one solar luminosi- crowaves. ty, which equals 1. A ratio greater than 1 implies : Astronomers have identified a faint cosmic colleagues. This, they conclude, was the time The missing piece in both Le Roux’s and more mass than luminosity – which means that radio rumble as the distant roar of the universe’s when the universe began with a Big Bang from Shmaonov’s work was the connection of what some mass is not accounted for. Express Trains birth. The discovery not only provides the first a very hot, dense ball of primordial matter and they had seen, to theoretical predictions from the In the case of NGC 3521, measurements from observational evidence that the universe started energy. Big Bang made as early as 1948. It was a mat- the University of Texas’ powerful 82-inch tele- with a “big bang,” but it also has implications Stunning and significant as the discovery is, to ter of having the right data, without a theory to scope at McDonald Observatory give it a mass- To Netherworlds

for how it might end. some astronomers it wasn’t a surprise. Theorists make sense of them. Penzias and Wilson would to-light ratio of 4 or greater. NGC 972 is a bit Astronomers have discovered a racing The faint radio hiss comes in the form of including , Ralph Alpher and have fared no better had not their neighbors at less worrisome, with a ratio of 1.2. These results towards the edge of the known universe at the were reported in recent issues of Astrophysical 7.3-centimeter microwaves, which lie on the had argued in the late 1940s for Princeton helped them recognize the noise as unprecedented speed of 450 million miles per Journal by teams of researchers led by Marga- electromagnetic spectrum between radio waves a Big Bang and that its remnant heat ought to the long-sought remnant radiation. hour – two-thirds of the speed of light! This and ret Burbidge of the University of California at and infrared light. The microwaves come from be still detectable. In 1949, Alpher and Herman other new-found quasars have more than speed every direction in space, without regard to time reworked some of Gamow’s earlier calculations going for them, however. The fact that these of day or season. The background radiation and actually predicted that the remaining strange objects are visible to us from these signal matches that expected by some theorists radiation would now have a temperature of “a far distances means they must be fantastically who proposed that the universe began with a hot few degrees Kelvin.” The new observations SUPERNOVAE LEAVE BEHIND bright. explosion of hydrogen about seven billion years of this background radiation support their For years, radio astronomers have seen ago and has been cooling ever since. prediction. COSMIC X-RAY GENERATORS quasi-stellar objects, or quasars, adding them The discovery of what’s being called “cosmic Where Alpher and Herman went wrong, to a growing list of unexplained “loud” radio Two years after discovering that the universe black body radiation,” where the wavelength however, is in thinking that the dying thunder of hum was coming from every direction in the sources all over the sky. In 1960, astronomers is awash in X-rays, astronomers are starting to sky, with a particularly intense X-ray source of radiation emitted is directly related to the the Big Bang would be drowned out by today’s managed to match a quasar with an object seen pinpoint discrete sources with greater accuracy from the direction of the constellation Scorpius. temperature, was made more or less by accident starlight, cosmic ray particles, and the other by optical telescopes. But it was only two years – and none of which resemble your doctor’s X- They named the new spot Scorpius X-1. Unlike by Arno Penzias and Robert Wilson of Bell noisy emissions of an active universe. Instead, it ago that astronomers Jesse Greenstein and ray machine. the Crab nebula, however, Sco X-1 remains a Telephone Laboratories. The two were trying appears that the remnants of the Big Bang have Maarten Schmidt managed to determine the One source is the Crab nebula, the remnant of celestial mystery, as it still has not been tracked to track down the source of unwanted radio cooled in a way that channels energy into specific a supernova that exploded nearly 900 years ago. to any known heavenly object. speed of one. noise in the 20-foot horn reflector antenna at bandwidths. This is what Dicke and his team Another, designated Ophiuchus XR-1, lies tan- X-ray astronomers hope someday to make That was when Greenstein and Schmidt split

the Crawford Hill Laboratory in Holmdel, N.J. suspected and one reason they were planning to talizingly close to the site of another past super- their work a little easier by placing instruments the visible light from quasar 3C 273 into its

The “Holmdel horn” antenna was built to test look in the microwave realm. It’s also how they nova, SN 1604. In fact, the distribution of X-ray in a stable, longer-term orbit that allows more spectrum of colors. What they found was jaw

telecommunications with the Echo satellite. knew Penzias’ and Wilson’s excess microwave sources in the galaxy mimics that of the known observation time. Until then, the data from those dropping. The telltale pattern of spectral lines,

When the Holmdel horn was aimed at zenith, noise was a significant discovery. supernova remnants, suggesting that supernovae five floating minutes in space is much prized for which signify the presence of specific elements, Penzias and Wilson found that it picked up the The discovery of this cosmic black body may leave behind X-ray generators. The exact study. were shifted dramatically to the red side of 7.3-centimeter microwave signal consistent radiation has driven more nails into the coffin cause of the X-ray radiation is still a mystery, the spectrum, the optical equivalent of a train with a temperature of 6.7 degrees Kelvin. of the “steady-state” universe theory, favored but if Ophiuchus XR-1 does, indeed, originate whistle’s tone dropping as the train moves away. That is to say, it corresponded to 6.7 degrees by many astronomers not long ago. Steady- from a supernova remnant, then a comparison In the case of 3C 273, the corresponded above the theoretical value of absolute zero, at state theory holds that the eternal expansion of of these two sources may peel back some of the to an astonishing speed of 16 percent of the which there is no thermal energy at all. After the universe is spurred on by the spontaneous mystique. speed of light – more than 100 million miles per subtracting natural microwave energy emissions creation of particles in empty space. Such a The feat of narrowing down these sources hour. The same technique was used by Schmidt from Earth’s atmosphere and energy losses in theory does not predict the cosmic black body should not be underestimated. Scientists had to and Caltech’s Allan Sandage to clock the latest the antenna itself, Penzias and Wilson were left radiation, making it incompatible with the new develop improvements to astronomical X-ray record holder, dubbed quasar BSO-1. with an unexplained temperature of about 3.5 data. instruments for rockets and then obtain enough No one has yet explained what a quasar degrees Kelvin, give or take one degree, coming The Big Bang implies a range of possible observing time on them for sufficient measure- is, but Sandage reported, “We do know that from empty space. fates for the universe. It will either expand and ments. Rockets are needed because X-rays can- [quasars] provide us with the long-sought keys

Luckily, just down the road some Princeton cool forever as an “open universe,” according to not penetrate Earth’s atmosphere. The atmo- to determine the size and .” sphere protects life from dangerous X-rays in scientists had the solution. Astronomer Robert Dicke and his team, or it is a “closed universe.” Scientists are confident that at least one theory space, but it also makes advancing the fledgling Dicke and his team were in the process of In a closed universe the gravity of all the can be ruled out. Quasars are not coded messages field of X-ray rather difficult and ex- building a for the express matter in the universe will pull it back together from a super-civilization, as has been suggested pensive. purpose of finding the whisper of the Big Bang. into another hot ball, breaking down matter and by Russian astronomer Nikolai Kardashev. It is The identification of these X-ray sources is When they heard about Penzias’ and Wilson’s energy into their basic building blocks. Then the culmination of about three years of rocket highly improbable that any civilization could mystery microwave hiss, they knew it was it will explode again into another, totally new flights searching for sources other than the Sun, broadcast messages with the power of 10,000 their prey. After conferring, the Bell Lab and universe. Dicke refers to this version of a closed which is weak in X-rays. The first rocket launch billion suns.

Princeton teams announced the discovery in universe as an “oscillating universe.” This option in 1962 used its precious five minutes in space to Any message from quasars may be from

a pair of letters published in the July issue of resembles the steady-state model in at least one observe the Moon in X-rays. Riccardo Giacconi the universe itself. Astronomers at the 200- Astrophysical Journal. respect: it has no ultimate beginning or end. inch Mount Palomar telescope hope that, by

and his team at American Science and Engineer- Photo credit: NASA

“The presence of thermal radiation remaining Sadly, however, it offers no way of detecting ing, Inc. expected to discover minerals fluoresc- measuring the distance to more quasars, they An Aerobee rocket launches from Wallops Island, from the fireball is to be expected if we can trace what came before the last bang and no escape ing in X-rays as a result of being hit by heavy Virginia. This rocket is similar to those used in recent can catch sight of some that started shining when the expansion of the universe back to a time from being crushed together into another hot atomic particles from the Sun. discoveries of cosmic X-ray sources such as Scorpius the universe was just seven percent of its current when the temperature was of the order of ten ball before the next. What they found instead was unexpected and X-1 and, more recently, the Crab nebula and Ophiuchus age. Some of that light, perhaps 15 billion years billion degrees Kelvin,” wrote Dicke and his far more amazing. A seemingly uniform X-ray XR-1. old, is only now reaching Earth.

www..gov For Lessons & Teacher Guide, see http://cosmictimes.gsfc.nasa.gov/ NW-2009-5-074-GSFC (4 of 6)