News Article | August 19, 2016
The distant planet GJ 1132b intrigued astronomers when it was discovered last year. Located just 39 light-years from Earth, it might have an atmosphere despite being baked to a temperature of around 450 degrees Fahrenheit. But would that atmosphere be thick and soupy or thin and wispy? New research suggests the latter is much more likely. Harvard astronomer Laura Schaefer (Harvard-Smithsonian Center for Astrophysics, or CfA) and her colleagues examined the question of what would happen to GJ 1132b over time if it began with a steamy, water-rich atmosphere. Orbiting so close to its star, at a distance of just 1.4 million miles, the planet is flooded with ultraviolet or UV light. UV light breaks apart water molecules into hydrogen and oxygen, both of which then can be lost into space. However, since hydrogen is lighter it escapes more readily, while oxygen lingers behind. "On cooler planets, oxygen could be a sign of alien life and habitability. But on a hot planet like GJ 1132b, it's a sign of the exact opposite - a planet that's being baked and sterilized," said Schaefer. Since water vapor is a greenhouse gas, the planet would have a strong greenhouse effect, amplifying the star's already intense heat. As a result, its surface could stay molten for millions of years. A "magma ocean" would interact with the atmosphere, absorbing some of the oxygen, but how much? Only about one-tenth, according to the model created by Schaefer and her colleagues. Most of the remaining 90 percent of leftover oxygen streams off into space, however some might linger. "This planet might be the first time we detect oxygen on a rocky planet outside the solar system," said co-author Robin Wordsworth (Harvard Paulson School of Engineering and Applied Sciences). If any oxygen does still cling to GJ 1132b, next-generation telescopes like the Giant Magellan Telescope and James Webb Space Telescope may be able to detect and analyze it. The magma ocean-atmosphere model could help scientists solve the puzzle of how Venus evolved over time. Venus probably began with Earthlike amounts of water, which would have been broken apart by sunlight. Yet it shows few signs of lingering oxygen. The missing oxygen problem continues to baffle astronomers. Schaefer predicts that their model also will provide insights into other, similar exoplanets. For example, the system TRAPPIST-1 contains three planets that may lie in the habitable zone. Since they are cooler than GJ 1132b, they have a better chance of retaining an atmosphere.
News Article | January 7, 2016
After decades of studies and research, scientists have estimated the age of the observable universe to be roughly 13.8 billion years old. The connection between distance and the speed of light -- explained by Albert Einstein's theory of relativity -- has allowed scientists to look at different regions of the vast outer space which lie 13.8 billion light-years away. The age and distance of the universe -- are these small hints to the possible existence of alien life? Scientists have yet to form a firm conclusion, but in late November last year, some experts were able to detect five mysterious radio bursts which may have all come from outside the Milky Way galaxy. These radio signals were discovered after an "alien megastructure" was reported to be orbiting around a distant star known as KIC 8462852. "It almost doesn't matter where you point your telescope, because there are planets everywhere. If there's somebody out there, there are going to be so many of them out there that I do think there's a chance," explained astronomer Seth Shostak of the Search for Extraterrestrial Intelligence (SETI) Institute in California. Now, a new study presented at the annual meeting of the American Astronomical Society in Florida suggests that an old, densely-packed and isolated group of stars located within the Milky Way may possibly sustain extraterrestrial life. These stars, collectively called globular clusters, may be a cradle of advanced civilizations, experts said. The Possibility Of Alien Life In Globular Star Clusters Scientists from the Harvard-Smithsonian Center for Astrophysics (CfA) and the Tata Institute of Fundamental Research in Mumbai believe that globular star clusters may be the first place in our galaxy to contain intelligent life beyond Earth. What exactly are globular star clusters? These are densely-packed and tight groups that contain thousands or millions of stars. These balls of star clusters may be about 100 light-years across each other on average, and are as old as the Milky Way galaxy itself. Our galaxy is home to about 150 globular star clusters, where most of them orbit the galactic outskirts. On average, these star clusters may be 10 to 12 billion years old, just a couple billion years younger than the observable universe. But Houston, We Have A Problem The stars within globular clusters have fewer of the essential elements considered as "building blocks" of planets, such as silicon (Si) and iron (Fe), because these elements must be formed in earlier generations of stars. This lack in heavy elements has led other scientists to argue that globular star clusters are less likely to contain planets. In fact, only one planet has been found within globular clusters: the oldest known exoplanet called PSR B1620-26 b or Methuselah. Still, astronomers Rosanne DiStefano and Alak Ray said these views are "too pessimistic." "It's premature to say there are no planets in globular clusters," said Ray. The duo explained that a lot of exoplanets have been discovered around host stars that are only one-tenth as rich with metals as our Sun. While planets that are Jupiter-sized are found more around stars that contained higher levels of Fe and Si, planets that are Earth-sized show no such bias. Another main problem: because globular clusters are too close-knit, this specific environment could threaten the possible formation and existence of planets within it. Scientists said a neighboring star could wander too close to a planetary system, consequently disrupting the gravitational forces and resulting to the unfortunate hurling of worlds into interstellar space. What Could Be the Right Clue? DiStefano and Ray explained that the habitable zone or the "Goldilocks" zone of a star varies greatly. The Goldilocks zone is the right distance at which planets would be not too warm or not too cold to have liquid water. Brighter stars have more distant Goldilocks zones, and have shorter life spans. Because globular clusters are old, these extremely bright stars have died out. In contrast, planets that orbit around dimmer stars huddle closer to each other. These dimmer stars are faint and closer, but they also live long enough to become red dwarfs. Potentially habitable planets that these faint stars host would orbit nearby and be relatively safe from stellar interactions. "Once planets form, they can survive for long periods of time, even longer than the current age of the universe," said DiStefano. What If Planets Within Globular Clusters Evolve? If livable planets could form within globular star clusters and survive for billions of years, extraterrestrial life in said planets would have enough time to become complex and even develop intelligence. The alien civilization would truly be different from our own. In our solar system, the nearest star is about four light-years (24 trillion miles) away. In a globular cluster, the nearest star may be 20 times closer or only one trillion miles apart. Interstellar exploration and communication, as well as space travel, would definitely be easier. DiStefano and Ray call this potential theory the "Globular Cluster Opportunity." "Sending a broadcast between the stars wouldn't take any longer than a letter from the U.S. to Europe in the 18th century," said DiStefano. Space missions would definitely take less time. NASA's Voyager probes are 100 billion miles away from our planet. In terms of globular cluster distance, this is one-tenth as far as it would take to reach the nearest star. A civilization at Earth's current technological level could easily send interstellar probes within the realm of a globular star cluster. DiStefano said the nearest globular cluster to our planet is thousand light-years away. This is why it is difficult for us to find planets, particularly in a space environment with a crowded core. However, it is possible to detect globular cluster planets on galactic outskirts. Through gravitational lensing, scientists might even spot free-floating planets or planets whose gravity magnifies light from a star. Lastly, scientists say that using SETI search methods to target globular clusters is an intriguing idea. SETI uses arrays of radio telescopes called Allen Telescope Array (ATA) to look for laser or radio broadcasts. Astronomer Frank Drake used the Arecibo radio telescope to broadcast the first deliberate message from our planet to outer space, a message directed to globular cluster Messier 13 (M13) or the Hercules Globular Cluster.
News Article | January 6, 2016
Densely packed stellar balls, known as globular clusters, could be the best places to search for alien life, according to research presented today at the 227th annual meeting of the American Astronomical Society. Globular clusters pack nearly one million stars into an area only 100 light-years across, and are nearly as old as the Milky Way itself. Approximately 150 of these ancient stellar relics lurk on the outskirts of our galaxy. “Globular clusters could be the first place in which intelligent life is found in our galaxy. This research shows they could be great places to look for other intelligent civilizations,” Rosanne DiStefano, an astronomer at the Harvard-Smithsonian Center for Astrophysics (CfA), said during the meeting. Globular clusters are estimated to have formed over 10 billion years ago, and as a result the stars within the cluster contain fewer of the ingredients needed to form planets. However if habitable planets do form within the cluster, they will likely be around for a lot longer than planets that form around massive stars, giving life more time to evolve. Habitable zones—the area around a star that can support liquid water—vary greatly depending on the size of the star. The ones surrounding more massive stars will be further away, while these zones around smaller, dimmer stars will be much closer. This is good news in the crowded, stellar neighborhood of a globular cluster. It means any potential habitable planets would huddle close to their host star and be safe from the gravitational tug of other stars. The majority of stars residing within these clusters are called “red dwarfs.” These types of stars are usually smaller than our Sun, and so they have longer lives and can support planets for billions of years, providing any potential life forms ample time to evolve beyond microbes into intelligent beings. “Once a planet has formed, it can survive for long periods of time, even billions of years,” DiStefano explained. But don’t get too excited yet, so far only one planet has been detected in a globular cluster. Most astronomers think these stellar populations are too crowded for planets to form, and are concerned about the lack of planet-forming ingredients like silicon and iron. DiStefano and her colleagues remain optimistic and think we shouldn’t rule out clusters completely. DiStefano explained that exoplanets have been detected around metal-poor stars, and while massive Jupiter-sized planets seems to prefer metal-rich stars, smaller Earth-sized planets seem to have no preference and can form around a variety of stars. Good news for alien hunters. Life on a planet within one of these clusters would be vastly different than what we experience here on Earth. The closest star to our Solar System is four light-years or 24 trillion miles away. However, within a cluster stellar neighbors are only about one trillion miles away, helping facilitate interstellar communication and exploration. DiStefano refers to this as “the globular cluster opportunity” and believes the close proximity would help support any potential life, making interstellar outposts easier to establish. Travel time within the cluster would take less time, and if there was a civilization at our technological level, sending probes between outposts would definitely be possible, according to DiStefano. So, how do we make contact? The first step is identifying more planets within clusters. Since clusters are densely packed and contain dim stars, detecting planets within the crowded cores of clusters are very difficult to identify, and DiStefano believes that it could be easier to detect planets on the outskirts. Another, more intriguing method might be to partner up with SETI to look for signs of radio communications from the cluster, something DiStefano would like to get more involved with. DiStefano is confident many more planets within these clusters will be discovered; it’s just a matter of time. “In my mind there is no doubt,” she said. “More planets within these clusters are waiting to be found.”
The blue-white dot at the center of this image is supernova 2012cg, seen by the 1.2-meter telescope at Fred Lawrence Whipple Observatory. At 50 million light-years away, this supernova is so distant that its host galaxy, the edge-on spiral NGC 4424, appears here as only an extended smear of purple light. Credit: Peter Challis/Harvard-Smithsonian CfA A team of astronomers including Harvard's Robert Kirshner and Peter Challis has detected a flash of light from the companion to an exploding star. This is the first time astronomers have witnessed the impact of an exploding star on its neighbor. It provides the best evidence on the type of binary star system that leads to Type Ia supernovae. This study reveals the circumstances for the violent death of some white dwarf stars and provides deeper understanding for their use as tools to trace the history of the expansion of the universe. These types of stellar explosions enabled the discovery of dark energy, the universe's accelerating expansion that is one of the top problems in science today. The subject of how Type Ia supernovae arise has long been a topic of debate among astronomers. "We think that Type Ia supernovae come from exploding white dwarfs with a binary companion," said Howie Marion of The University of Texas at Austin (UT Austin), the study's lead author. "The theory goes back 50 years or so, but there hasn't been any concrete evidence for a companion star before now." Astronomers have battled over competing ideas, debating whether the companion was a normal star or another white dwarf. "This is the first time a normal Type Ia has been associated with a binary companion star," said team member and professor of astronomy J. Craig Wheeler (UT Austin). "This is a big deal." The binary star progenitor theory for Type Ia supernovae starts with a burnt-out star called a white dwarf. Mass must be added to that white dwarf to trigger its explosion - mass that the dwarf pulls off of a companion star. When the influx of mass reaches the point that the dwarf is hot enough and dense enough to ignite the carbon and oxygen in its interior, a thermonuclear reaction starts that causes the dwarf to explode as a Type Ia supernova. For a long time, the leading theory was that the companion was an old red giant star that swelled up and lost matter to the dwarf, but recent observations have virtually ruled out that notion. No red giant is seen. The new work presents evidence that the star providing the mass is still burning hydrogen at its center, that is, that this companion star is still in the prime of life. According to team member Robert P. Kirshner of the Harvard-Smithsonian Center for Astrophysics, "If a white dwarf explodes next to an ordinary star, you ought to see a pulse of blue light that results from heating that companion. That's what theorists predicted and that's what we saw. "Supernova 2012cg is the smoking—actually glowing—gun: some Type Ia supernovae come from white dwarfs doing a do-si-do with ordinary stars." Located 50 million light-years away in the constellation Virgo, Supernova 2012cg was discovered on May 17, 2012 by the Lick Observatory Supernova Search. Marion's team began studying it the next day with the telescopes of the Harvard-Smithsonian Center for Astrophysics. "It's important to get very early observations," Marion said, "because the interaction with the companion occurs very soon after the explosion." The team continued to observe the supernova's brightening for several weeks using many different telescopes, including the 1.2-meter telescope at Fred Lawrence Whipple Observatory and its KeplerCam instrument, the Swift gamma-ray space telescope, the Hobby-Eberly Telescope at McDonald Observatory, and about half a dozen others. "This is a global enterprise," Wheeler said. Team members hail from about a dozen U.S. universities, as well as institutions in Chile, Hungary, Denmark, and Japan. What the team found was evidence in the characteristics of the light from the supernova that indicated it could be caused by a binary companion. Specifically, they found an excess of blue light coming from the explosion. This excess matches with the widely accepted models created by U.C. Berkeley astronomer Dan Kasen for what astronomers expect to see when a star explodes in a binary system. "The supernova is blowing up next to a companion star, and the explosion impacts the companion star," Wheeler explained. "The side of that companion star that's hit gets hot and bright. The excess blue light is coming from the side of the companion star that gets heated up." Combined with the models, the observations indicate that the binary companion star has a minimum mass of six suns. "This is an interpretation that is consistent with the data," said team member Jeffrey Silverman, stressing that it is not concrete proof of the exact size of the companion, like would come from a photograph of the binary star system. Silverman is a postdoctoral researcher at UT Austin. Only a few other Type Ia supernovae have been observed as early as this one, Marion said, but they have not shown an excess of blue light. More examples are needed. "We need to study a hundred events like this and then we'll be able to know what the statistics are," Wheeler said. The work is published today in The Astrophysical Journal. More information: "SN 2012cg: Evidence for Interaction Between a Normal Type Ia Supernova and a Non-Degenerate Binary Companion," G. H. Marion et al., 2016, Astrophysical Journal, Preprint: arxiv.org/abs/1507.07261
The Regolith X-Ray Imaging Spectrometer, or REXIS, was developed by researchers and students at the Harvard-Smithsonian Center for Astrophysics (CfA) and the Massachusetts Institute of Technology (MIT), both in Cambridge, Mass. It is only the second student experiment to fly on a NASA interplanetary mission. "With Harvard undergraduates, we designed a wide-field X-ray imaging instrument that was built by students at MIT," says Harvard astronomer and Deputy Instrument Scientist Josh Grindlay. Richard Binzel at MIT is Instrument Scientist for REXIS. "A principal goal for REXIS was educating students," says instrument scientist and Harvard astronomer Jaesub Hong. The mission, called the Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx), will be launched with an Atlas V from Cape Canaveral, Florida. After its two-year journey to Bennu, the spacecraft will spend nearly two years making observations and measurements before collecting a surface sample and returning it to Earth. REXIS will help the mission team select the sample site by characterizing the asteroid"s surface. Bennu emits X-rays through a process known as fluorescence, in which X-rays from the Sun make atoms on the asteroid"s surface glow at specific energies, depending on which chemical elements are present. "REXIS can image enhanced patches of glowing elements like magnesium, silicon, or iron that are typical in chondrite-type asteroids," says instrument scientist Branden Allen. The asteroid Bennu is about 1,600 feet across, about twice the height of Boston's John Hancock Tower. REXIS will be able to resolve details about 18 feet across. Like many asteroids, Bennu represents a relic from the solar system's formation. It formed as bits of primitive material stuck together over time. As a result, it can tell scientists about the history of our solar system. Asteroids like Bennu may have delivered water, carbon, and other substances crucial to life to the early Earth. REXIS is a $5 million project that involved nearly 50 undergraduate students from MIT and Harvard. Explore further: OSIRIS-REx team prepares for next step in NASA's asteroid sample return mission