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Home , George Smoot

National Aeronautics and Space Administration

Age of the : Size of the Universe: 12-20 Billion Years Cosmic Times 30 Billion Light Years 1993 Baby Universe’s First Picture Hunt Heats Up The mystery of dark matter just deepened with a new report of about 20 trillion -worth of the invisible, unexplained stuff hiding out in a small cluster of . The vast store of dark matter was found us- ing the ROSAT X-ray . ROSAT detected a gigantic cloud of very hot gas in a very un- expected place: the seemingly empty space be- tween two galaxies. This cloud is a surprise be- cause its great heat – detected from its radiation of X-rays – should have made the gas quickly dissipate. The existence of the hot gas cloud can only be explained by the existence of a gravitational force to hold it in place. Only dark matter could do the job without being seen, explains Richard

Photo credit: NASA Mushotzky of NASA’S Goddard Space Flight COBE’s map of the sky, showing minute fluctuations in the cosmic microwave background. Astronomers estimate Center. that this map shows the background radiation 300,000 years after the . (NASA image) What’s more, the hot gas requires an amazing 30 times more dark matter than visible matter in the cluster to achieve this, says Mushotzky. The What did the newborn universe look like? Scientists have now confirmed the existence normal matter ROSAT observed is just a small In 1965, scientists peered into the distance with of these very slight – but now clearly measurable fraction of what’s really there.

a radio telescope, and discovered a microwave – energy differences. Smoot and his team created If that sort of dark matter ratio holds true Photo credit: NASA background that was rather plain and featureless. an all-sky map of these microwave variations, throughout the cosmos, dark matter could deter- Hot X-ray emitting gas (shown in purple) was discovered by the ROSAT satellite to be present in this group of gal- Today’s technology has drawn a more detailed illustrating for the first time these , mine the fate of the universe. Its could axies. The presence of the gas provides evidence for the existence of dark matter. (NASA image) picture of this cosmic microwave background, or “lumps”, in the oldest light in the universe. be enough to someday reverse the direction of should be. The simplest explanation is that mat- Weakly Interacting Massive Particles (WIMPs) telling us there’s a lot more to the story…and The COBE data shows the afterglow from the matter and energy flung out by the Big Bang ter is a lot more evenly spread through the gal- could be shooting harmlessly through us right providing further evidence of the Big Bang. very early universe, only 300,000 years after and pull the universe back together into a “Big axy than it appears. In other words, dark matter now, a million per second, and we wouldn’t “If you’re religious, it’s like looking at God,” the Big Bang. The current is Crunch,” say some researchers. is tugging at these stars and keeping them in the know it. said George Smoot, an astrophysicist at the estimated at 12 to 20 billion years. An earlier case for the existence of dark mat- . Another possibility is that the there are a lot University of California, Berkeley and leader of COBE excited scientists three years ago ter was that made by astronomer in Despite the new ROSAT discovery and its of dark, cold dead stars out there that can’t be the research team that unveiled the discovery. He with data that exactly matched what they had 1970. She studied the rotation rate of stars in the enormous implications, scientists haven’t been detected with our current technology. These was addressing a room packed with scientists at expected from a Big Bang universe. COBE Andromeda galaxy and found that it just didn’t very successful in figuring out what exactly MAssive Compact Halo Objects (MACHOs) a meeting of the American Physical Society. measured the spectrum of light from the CMB make sense. The stars in the disc further from dark matter is. Some think it might be a type of would probably be concentrated in the halo of According to , the universe and found that it was, as predicted, in the form the galactic center were not rotating more slow- subatomic particle that has mass but only inter- stars found immediately above and below the expanded from an unthinkably small and dense of a perfect blackbody curve. These data were ly than those closer in, as models predicted they acts with normal matter through gravity. These galactic disk. ball of energy, distributing hot radiation – and collected by COBE on an instrument designed by space itself – outward in all directions. As the John Mather of NASA’s Goddard Space Flight universe expanded and cooled, this hot ball Center, who also headed the COBE project. of energy produced freshly minted particles, With the addition of the latest findings, the eight- Pulsar Gravitational first in the form of quarks and electrons, then decade-old Big Bang theory, with the addition of Fool-Proofing Galactic ‘Candles’ protons and neutrons, which combined to make , is now firmly the lead model for how Waves Win the nuclei of hydrogen and helium. Over time, the universe began. Other models either cannot This year’s Nobel Prize in was The “standard candle” used for measuring can counteract the inward crush of gravity of the gravity gathered the denser clumps of gas into account for COBE’s results or must undertake awarded for the amazing discovery of the first the distance to other galaxies just got a much- star on itself. The white dwarf collapses and ex- the familiar galaxies, stars, and planets of the some difficult and unsavory contortions to do evidence, albeit indirect, for the existence of needed tune-up. plodes as a Type Ia supernova. modern universe. All the while, the radiation so. gravitational waves. For years, the bright supernovae created by Since all Type Ia’s are created by the explo- that was emitted in all directions by that early The lumps in the map do not correlate with In 1974, Princeton University astronomers the deaths of white dwarf stars in binary sys- sion of a white dwarf star as it exceeds a critical hot gas gradually shifted into the microwave anything particular in the night sky today, but they Russell A. Hulse and Joseph H. Taylor located tems, known as Type Ia supernovae, have been mass, astronomers believed they should all have PSR 1913+16, which is a special type of super- energy range as the universe expanded. We are of distinct importance, say the researchers. If a standard candle. Wherever they occurred, they the same intrinsic brightness. and be useful as a dense neutron star called a pulsar. This pulsar see this radiation today as a cosmic microwave the CMB was perfectly uniform, according to were believed to have roughly the same intrinsic measuring stick to distant galaxies. In addition, emits a radio pulse every 59 milliseconds as it background (CMB). theory, we could not exist! So while the greatest brightness. So scientists used them to calculate Type Ia’s may be visible at distances greater than rotates on its axis. It is locked in a dizzying Data from the 1960s did not show deviations variations in the CMB are only at a level of one the distance to the galaxies in which they occur. the Cepheid variable stars, identified as standard eight-hour orbit with another star, which is likely in the CMB energy across the entire sky; part in 100,000, they are sufficient to ultimately But recent research has revealed a way to great- candles in 1912 by Henrietta Leavitt. to be another neutron star. however, in 1967, astrophysicists Martin Rees lead to the current structures in the universe. ly improve the accuracy of these calculations. But it turns out that not all Type Ia’s are equal Four years later, after some careful timing and Dennis Sciama predicted such deviations. Princeton astrophysicist David Spergel In the 1940s, astronomers realized superno- either. A large sampling of supernovae has re- measurements of the pulsar, they found that the The subtlety of the variations- just 30 millionths observed at the meeting, “It’s the most important vae came in two flavors: some (later called Type vealed that the pattern of brightening and fad- two stars are spinning closer to each other by of a degree - made them extremely hard to detect discovery in in the past 20 years.” I) did not show any evidence of containing hy- ing over days – known as a light curve – var- about three millimeters per orbit. That could until NASA’s Cosmic Background Explorer drogen, while others (denoted Type II) did. The ies a great deal. Astronomer Mark Phillips at only happen if something was pulling energy satellite (COBE) was launched in 1989. lack of hydrogen means that the star has used the Cerro Tololo Interamerican Observatory out of the system. But what was it? up the basic fuel that drives nuclear reactions in Chile found that the infrared light curves of Einstein’s theory of general relativity in stars. Type II’s were found to result from the some brighter Type Ia’s fade more slowly over provides the answer. It predicts that two massive death of a single, massive star. In the 1980s, the first 15 days than do those of dimmer ones. objects tearing around in a strong gravitational however, it became clear that some Type I’s By sorting the dim, fast-fading supernovae field radiate gravitational waves out into space. Inflation in the Universe This extracts energy from their orbits, and causes also come from the death of a massive star. The from the bright, slow-fading ones, Phillips ar- The Big Bang theory has a problem, say sci- force and the electro-weak force. If so, it would them to drop in closer to each other. The 8-hour remaining Type I’s, now called Type Ia, were rived at a luminosity-decline relation. It allows -35 entists. It can’t go from a tiny ball of energy to have occurred 10 sec after the Big Bang when orbit should be 75 microseconds shorter every found instead to result from the collapse of a calculation of a correction factor for supernovae the universe we see today without some help: an the universe was 1027 kelvins. year. white dwarf star in a binary star system. that are dimmer than the standard Type Ia su- adjustment called inflation. After inflation, the expansion of the universe After 18 years of refinement, Taylor has In a binary system, a white dwarf can gain pernova. Astronomers can adjust the distance Astronomers observe that the overall tem- continued, but at a slower rate. As space ex- honed down the timing of PSR 1913+16’s mass from its companion star. With sufficient accordingly, and increase the accuracy of the perature of the cosmic microwave background panded, the universe cooled and matter formed. orbital periods to within 0.3 percent of general mass gained from the companion, the white distance measurements. dwarf reaches a critical mass at which nothing (CMB) is nearly smooth and uniform. The tem- Within the first second after the Big Bang, relativity predictions - strong confirmation of the perature can become uniform only if distant re- quarks, neutrinos, and electrons appeared, then existence of the gravitational waves predicted gions can interact and exchange energy. The protons and neutrons. by Einstein. fastest interactions occur at the speed of light. Inflation makes another remarkable predic- The pulsars won’t be colliding any time However, at the time the CMB radiation was tion: how stars and galaxies formed in the uni- soon. Although each neutron star is 7 miles in diameter and 1.4 times the mass of the , they emitted, two regions that are far apart on the sky verse. Since our cosmic neighborhood would are still about a million miles apart. At their today would have been separated by more than have been microscopic in size prior to inflation, Pancake or Oatmeal Universe – present rate, it will take 300 million years for the light travel distance in the young universe. quantum fluctuations in the density of matter in the stars to merge. So why is the CMB so nearly uni- this region would be stretched by inflation to What’s for Breakfast? form? astronomical proportions. After inflation, these Inflation theory explains this by stating that fluctuations would be faint in contrast, but over shortly after the Big Bang, the universe un- time, the slightly over-dense regions would at- Over its lifetime, the universe started out ter and energy. Objects from planets and stars derwent a very rapid expansion in a very short tract neighboring matter through the action of smooth, but has grown lumpy. to galaxies and galaxy clusters are easily de- amount of time. This expansion grew the size of gravity. This would initiate the gradual process The COBE results present what’s been tectable. Nonetheless, overall the universe is the universe by a factor of 1026 in about 10-33 sec- of galaxy formation. Thus inflation simultane- called an isotropic, or smooth, early universe much smoother than was predicted by the origi- onds. Thus, regions once in contact with each ously explains why the CMB is so nearly, but not – with measured variations in the cosmic mi- nal Big Bang. This problem has been solved by other are now in far flung regions of the uni- exactly, uniform and ultimately how we came to crowave background radiation of only 1 part inflation.

verse. The overall uniformity of the background be! in 100,000! You might say that, at that time, While the early universe was extremely

temperature expanded with inflation. Particle Scientists are now more satisfied that with the universe was like the surface of a pancake: smooth compared to today, those minuscule Courtesy Princeton Plasma Physics Laboratory used by permission Jr., Taylor © Joseph Hooton smooth at a glance, with differences in texture lumps in it were vital. Through the action of think that inflation might be a natural the addition of inflation, the Big Bang describes Russell A. Hulse and Joseph H. Taylor, both of Princ- seen only under closer inspection. gravity, they led to the much bigger lumps we by-product of the transition in which the grand the universe we live in. eton University, shared the 1993 The universe today is more like a bowl of see today, the ones that make our very existence for their discovery of evidence of gravitational waves, unified force separated into the strong nuclear confirming the prediction by Einstein in 1916. oatmeal, with real “lumps” and clumps of mat- possible.

www..gov For Lessons & Teacher Guide, see http://cosmictimes.gsfc.nasa.gov/ NW-2009-5-075-GSFC (5 of 6)