Planck Reveals Dusty Problem for BICEP2s Gravitational Waves
The likelihood that a South Pole-based telescope detected elusive gravitational waves earlier this year has just taken another nosedive. Continue reading →
The likelihood that a South Pole-based telescope detected elusive gravitational waves earlier this year has just taken another nosedive.
According to a new and highly-anticipated galactic dust map released by the European Planck space telescope today, the region of sky studied by the BICEP2 telescope appears to contain significant quantities of interstellar dust; dust that may be obscuring the primordial light in which BICEP2 apparently detected the signal of gravitational waves. And this is bad news; the possible detection of gravitational waves may have been a false alarm all along.
In a nutshell, last March, astrophysicists led by John Kovac of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., announced the potentially historic discovery that their experiment had, for the first time, detected the signal of gravitational waves etched into the ancient ‘glow' of the Big Bang - a ubiquitous radiation seen at the outermost reaches of the observable Universe known as the cosmic microwave background, or simply CMB.
The discovery of gravitational waves would be historic in itself, but the ramifications of seeing gravitational waves in the CMB would be far-ranging. These gravitational waves would have their origins just after the Big Bang during a rapid period of expansion known as "inflation." This would therefore provide captivating evidence for one of the leading theories of cosmic birth. Also, as the gravitational waves would have been generated when the universe was very tiny, it would raise questions about a quantum gravity origin and provide evidence for the existence of the hypothetical graviton.
In short, the discovery of ancient gravitational waves could tie up some of the most fundamental questions of the quantum and cosmological nature of our Universe.
BICEP2 is a very sensitive telescope built with the intent to spot a specific type of polarization theorized to be caused by the presence of gravitational waves in the CMB known as "B-mode polarization." In the March announcement, the excited BICEP2 team were so sure of their findings that they announced the discovery before their results were published in a peer-reviewed journal. Almost immediately, the astronomy community criticized the BICEP2 announcement, suggesting that insufficient consideration for interstellar dust may be interfering with the CMB polarization signal.
Our galaxy is known to be filled with interstellar dust, so any astronomical observations beyond our galaxy have to peer through that dust. Therefore, corrections for the polarizing effects by the dust needs to be made. Planck, which was launched to the Earth-sun L2 point (in the Earth's shadow) in 2009, has been gradually surveying the whole sky in an effort to map the dust so its effects can be better understood.
Although the BICEP2 team contested that they did take the dusty interference into account before the March announcement, the dust data they used as a reference was incomplete and, as it turns out, woefully underestimated the quantity of dust along BICEP2′s line of sight.
In the long-awaited Planck dust maps described today in a paper published by the arXiv preprint service, it appears that although the region of sky studied by BICEP2 is by no means the most dusty part, it is still obscured by a significant quantity of dust - certainly enough to interfere with any CMB signal.
"The level of dust in the BICEP2 region is clearly significant, and also higher than pre-Planck estimates," Jamie Bock, of NASA's Jet Propulsion Laboratory and BICEP2 team member, told Nature News. According to critics, this new map casts the original BICEP2 results into serious doubt - the majority of the CMB polarization was therefore likely caused by the intervening galactic dust and not gravitational waves. Though there may still indeed be a gravitational wave signal in the BICEP2 results, its effect would be minuscule when compared with this dusty interference.
It is worth noting, however, that the Planck results are not a direct comparison to the BICEP2 data, so this new dust map cannot conclusively say the BICEP2 ‘discovery' was false. Planck observes in radio frequencies of 353 GHz, whereas the BICEP2 signal was detected at 150 GHz.
So what's next? The BICEP2 gravitational wave announcement may have been premature, but it is still the most precise measurement of a possible gravitational wave signal in the CMB. Since July, both science teams have been collaborating on a joint paper that will take the Planck dust data into consideration. Also, we now have a map which highlights regions of low interstellar dust density, providing an un-obscured view of the CMB, so future gravitational wave searches can be more directed.
Hopefully, we're still on the trail to detecting gravitational waves, but as today's announcement has proven, our dust-ridden Milky Way is proving to be a huge challenge to one of the biggest astrophysical questions being asked by modern science.
Source: Nature News
Planck's full-sky galactic dust map of the northern galactic hemisphere (left) and southern galactic hemisphere (right). The map shows galactic dust density where blue regions indicates low density and red indicates high density. The patch of sky observed by the BICEP2 telescope is indicated in the rectangle (southern galactic hemisphere).
10. Saturn Moon Titan Explored
On Jan. 14, 2005, the European Space Agency's Huygens probe dropped through Titan's atmosphere after a seven-year trek attached to NASA's Cassini spacecraft. Huygens wasn't designed to live for very long after atmospheric reentry, but it unveiled a mysterious outer solar system world to us for the first time. Before this mission, very little was known about Saturn's largest moon, and scientists were unsure whether Huygens would land on a rocky surface or in an ocean. Titan's thick atmosphere -- composed of primarily nitrogen and clouds of methane and ethane, about 50 percent thicker than our atmosphere -- signaled to scientists that Titan was similar to a young Earth. Observations from the Huygens probe and Cassini spacecraft tell us that Titan and Earth share many features, such as sand dunes and lakes. But these features are heavily laced with organic molcules that could support life, leading researchers to speculate about Titan's potential to nurture microbes.
9. Moon Water Confirmed
India's Chandrayaan-1 satellite confirmed the presence of water on the moon in September 2009, building on flyby observations by other probes on their way elsewhere. Although the lunar surface is still drier than Earth's driest desert, evidence of water is there, hinting at a solar wind interaction with the moon's surface that produces water and hydroxyl molecules. It may not be an oasis up there, but future moon colonists could extract and purify the traces of water from the surface to use for drinking, food cultivation, oxygen and fuel. Or, our colonists could take a trek to the moon's poles to mine water from the deepest craters On Oct. 9, 2009, NASA dropped a spent rocket into a crater to produce a 100-foot-wide hole. They found water there too. That rocket produced a massive plume of dust that was analyzed by the Lunar Reconnaissance Orbiter (LRO) and ground-based observatories. At least 25 gallons of water ice was detected in the plume.
8. Organic Chemistry Collected from Comet's Tail
In 2004, the NASA Stardust mission chased after Comet Wild 2 to find out if the icy mass contained the building blocks for life, since meteorites found on Earth contained organic chemistry that originated from space. Sure enough, in August 2009, NASA announced that they had found samples of glycine -- an amino acid -- in Stardust's collection plates. It didn't stop there, there's increasing evidence that exoplanets orbiting distant stars contain organic chemistry in their atmospheres. In 2008, organic chemicals were detected in the disk surrounding a star called HR 4796A, 220 light-years from Earth. And most recently, NASA's Hubble and Spitzer space telescopes detected carbon dioxide, methane and water vapor in the atmosphere of an exoplanet called HD 209458b. These discoveries, sparked by Stardust, have transformed our understanding about how life may have formed on Earth. They also give us a strong hint that life may not be unique to Earth; the universe appears to be manufacturing organic chemistry everywhere.
7. A Supermassive Black Hole on Our Doorstep
There's a monster living in the center of our galaxy, 26,000 light-years from Earth. By 2008, astronomers tracking the behavior of stars orbiting an invisible point confirmed that the monster is a supermassive black hole called Sagittarius A*. A lone star called "S2," with a very fast orbit, has been tracked since 1995 around this invisible point. In 2002, Rainer Schödel and his team at the Max Planck Institute for Extraterrestrial Physics announced that the only explanation for S2's fast orbit was that it was circling a very compact, massive object -- a supermassive black hole -- that was stopping the star from flinging out of its orbit into space. In 2008, after S2 completed one 16-year orbit, it was confirmed that the star was orbiting a black hole with a gargantuan mass of approximately 4.3 million suns. The confirmation of a supermassive black hole in the center of the Milky Way boosted the theory that most galaxies contain a supermassive black hole at their cores.
6. Big Bang "Echo" Mapped for the First Time
In June 2001, NASA set out to find the ancient "echo" of the Big Bang by mapping the cosmic microwave background (CMB) radiation that buzzes like static throughout the cosmos, using the Wilkinson Microwave Anisotropy Probe (WMAP) . When the universe was born, vast amounts of energy were unleashed, which eventually condensed into the stuff that makes up the mass of what we see today. The radiation that was created by the Big Bang still exists, but as faint microwaves. By mapping slight variations in the CMB radiation, the probe has been able to precisely measure the age of the universe (13.73 billion years old) and work out that a huge 96 percent of the mass of the universe is made up of stuff we cannot see. Only 4 percent of the cosmic mass is held in the stars and galaxies we observe; the rest is held in "dark energy" and "dark matter."
5. Hubble Gets to Grips with Dark Energy
In 2002, the Hubble Space Telescope was upgraded with a new instrument, the Advanced Camera for Surveys, that revealed the presence of a mysterious force called "dark energy." The camera was set up to help researchers understand why Type Ia supernovae were dimmer than expected. Hubble's observations of these supernovae discovered that they weren't dimmer because the stars were different (they should all explode with the same brightness). The only explanation was that the universe's expansion was unexpectedly and inexplicably speeding up. This accelerated expansion was making the light dim over vast cosmic distances. Hubble's discovery led to a better understanding of what dark energy is -- an invisible force that opposes gravity, causing the universe's expansion to speed up. WATCH VIDEO about Hubble's most recent upgrade.
4. Eris Discovered; Pluto Demoted
In January 2005, Mike Brown and his team at Palomar Observatory, Calif. discovered 136199 Eris, a minor body that is 27 percent bigger than Pluto. Eris had trumped Pluto and become the 9th largest body known to orbit the sun. In 2006, the International Astronomical Union (IAU) decided that the likelihood of finding more small rocky bodies in the outer solar system was so high that the definition "a planet" needed to be reconsidered. The end result: Pluto was reclassified as a dwarf planet and it acquired a "minor planet designator" in front of its name: "134340 Pluto." WATCH VIDEO about Pluto's demotion to a minor planet. Mike Brown's 2005 discovery of Eris was the trigger that changed the face of our solar system, defining the planets and adding Pluto to a growing family of dwarf planets.
3. Dark Matter Detected
In the summer of 2006, astronomers made an announcement that helped humans understand the cosmos a little better: They had direct evidence confirming the existence of dark matter -- even though they still can't say what exactly the stuff is. The unprecedented evidence came from the careful weighing of gas and stars flung about in the head-on smash-up between two great clusters of galaxies in the Bullet Cluster. Until then, the existence of dark matter was inferred by the fact that galaxies have only one-fifth of the visible matter needed to create the gravity that keeps them intact. So the rest must be invisible to telescopes: That unseen matter is "dark." The observations of the Bullet Cluster, officially known as galaxy cluster 1E0657-56, did not explain what dark matter is. They did, however, give researchers hints that dark matter particles act a certain way, which they can build on. -- Larry O'Hanlon
2. Mars Surface Gives up Signs of Water
In 2008, NASA's Mars Phoenix lander touched down on the Red Planet to confirm the presence of water and seek out signs of organic compounds. Eight years before, the Mars Global Surveyor spotted what appeared to be gullies carved into the landscape by flowing water. More recently, the Mars Expedition Rovers have uncovered minerals that also indicated the presence of ancient water. But proof of modern-day water was illusive. Then Phoenix, planted on the ground near the North Pole, did some digging for samples to analyze. During one dig, the onboard cameras spotted a white powder in the freshly dug soil. In comparison images taken over the coming days, the powder slowly vanished. After intense analysis, the white powder was confirmed as water ice. This discovery not only confirmed the presence of water on the Red Planet, it reenergized the hope that some kind of microbial life might be using this water supply to survive.
1. Alien Planets Spotted Directly
The first alien planets -- called exoplanets -- were being detected in the early 1990s, but not directly. In 2000, astronomers detected a handful by looking for a star's "wobble," or a star's slight dimming as the exoplanet passed in front of it. Today we know of 400 exoplanets. In 2008, astronomers using the Hubble Space Telescope and the infrared Keck and Gemini observatories in Hawaii announced that they had "seen" exoplanets orbiting distant stars. The two observatories had taken images of these alien worlds. The Keck observation was the infrared detection of three exoplanets orbiting a star called HR8799, 150 light-years from Earth. Hubble spotted one massive exoplanet orbiting the star Fomalhaut, 25 light-years from Earth. These finds pose a profound question: How long will it be until we spot an Earth-like world with an extraterrestrial civilization looking back at us?