Some of the brightest objects in the known universe may abruptly go dark at the whims of the black holes that power them, new research shows.
A recent study reveals a dramatic example of this newly discovered type of object, called a “changing-look quasar,” which seems to have winked out in as little as a decade when its black hole no longer had gas to suck in.
“This is an intrinsic change in the gas that’s falling on the supermassive black hole,” Jessie Runnoe, a postdoctoral student at Pennsylvania State University and lead author of the new work, said at a news conference Jan. 8. Runnoe presented the results of the changing-look quasar at the American Astronomical Society meeting in “At least temporarily, the supermassive black hole has run out of fuel,” Runnoe said.
At the center of most galaxies lies a supermassive black hole weighing thousands to a billion times as much as the sun. As black holes swallow up nearby gas and dust, they can emit light and radio waves that shine brightly across the universe — a feature called a quasar.
However, if the material the black hole is sucking in runs out, the quasar’s powerful light appears to shut down quickly, the new research suggests. Astronomers are used to looking at objects that change over millions or billions of years, so the researchers were surprised to spot an object that changed over a decade or less.
“This is a brand-new phenomen[on],” John Ruan, a graduate student in astronomy at the University of Washington in Seattle, said at the same conference. Ruan is co-author of the new paper, and also led an archival search for more changing-look quasars in the Sloan Digital Sky Survey.
“We’ve never actually seen a quasar just turn off before,” he said.
In early 2015, after the discovery of the first changing-look quasar, Runnoe and her colleagues decided to visually search for the objects by eye rather than by computer in the Time Domain Spectroscopic Survey (TDSS), which incorporates data from Sloan and other sky surveys to identify objects that vary in brightness over time. And they uncovered a particularly striking example.
A strange object known as J1011+5422 lies approximately 3.4 billion light-years from Earth, and when it was first spotted by Sloan in 2003, it looked like a regular quasar. But when TDSS followed up in 2015, just 12 years later, the light from the bright quasar had faded away. Only the light from its parent galaxy shone through.
“The difference is pretty dramatic,” Runnoe said. “This is the most dramatic one we’ve found.”
Previous evidence suggested that quasars shut off over tens or hundreds of thousands of years, Ruan said.
“To observe a quasar shutting off in just a few years is very surprising,” he added.
The results were detailed Nov. 18 in the journal Monthly Notices of the Royal Astronomical Society.
Several phenomena could be responsible for the sudden cutoff in light streaming from the quasar, and Runnoe and her colleagues sought to determine which was responsible for J1011′s dramatic shutdown.
The most obvious cause would be a massive cloud of gas and dust moving between the quasar and the Earth. But after combing through more than a decade’s worth of observations made by Sloan, the astronomers concluded that the quasar slowly shut down over a period of at least 7 years, finally disappearing by 2015. In contrast, it should have taken a giant molecular cloud several decades to obscure the quasar. Furthermore, the team saw no signs of the cloud’s chemistry in the dimming light from the quasar — something they would have expected to see, especially as quasars are already used to study the chemistry of such clouds.
The researchers also considered that the original object was not a quasar at all but instead only an extremely bright flare caused by a star wandering too close to the black hole and being torn apart. However, such disruptions typically occur over months rather than years, making it an extremely unlikely scenario.
If aliens are out there, they may all be dead.
It might be relatively easy for life to evolve on hospitable planets throughout the universe, but very hard for it to get any kind of a foothold, a new study suggests.
This could be the answer, the study’s authors say, to the famous Fermi Paradox, which in its simplest form asks, “Where is everybody?”
Chopra and co-author Charley Lineweaver, also of ANU, posit that environmental conditions on young planets are unstable, and there is thus likely only a small window of time for life to get going, even on initially hospitable worlds.
In the first 500 million years or so of a wet, rocky planet’s life, for example, it will be too hot and heavily bombarded to support life. Life could emerge over the next 500 million years, as the planet cools and the impact rates settle down a bit.
During that time, however, the planet will probably be losing its liquid water, perhaps as the result of a runaway greenhouse effect (as occurred on Venus), or perhaps because it got too cold. There’s a good chance that the planet will end up shifting from habitable to uninhabitable, as Venus and Mars apparently did, by roughly 1 billion to 1.5 billion years after its formation — unless life gets going fast enough to stabilize things, Chopra and Lineweaver say.
“Between the early heat pulses, freezing, volatile content variation, and runaway positive feedbacks, maintaining life on an initially wet rocky planet in the habitable zone may be like trying to ride a wild bull. Most life falls off,” they write in the study, which was published in the journal Astrobiology. “Life may be rare in the universe, not because it is difficult to get started, but because habitable environments are difficult to maintain during the first billion years.”
The researchers term this idea the “Gaian bottleneck” hypothesis. They contrast it with the “emergence bottleneck” concept, which postulates that it’s tough for life to get started at all.
It’s unclear, of course, which of these hypotheses better represents reality, or if either of them represents reality well at all. But there are possible (albeit difficult and time-consuming) ways to test such ideas out, the researchers said.
“One intriguing prediction of the Gaian bottleneck model is that the vast majority of fossils in the universe will be from extinct microbial life, not from multicellular species such as dinosaurs or humanoids that take billions of years to evolve,” Lineweaver said in the same statement.
Clusters of stars can harvest enough gas from their galaxies to give birth to a new generation of stars of their own, new research shows.
This finding could help shed light on how the building blocks of galaxies evolve, scientists added.
Globular clusters are densely packed, spherical collections of up to millions of stars orbiting the outskirts of galaxies. These clusters are up to 13 billion years old, making them among the oldest structures in the universe
“Star clusters are building blocks of galaxies — almost all stars formed in star clusters,” said study lead author Chengyuan Li, an astronomer at Peking University in Beijing.
Stars in globular clusters are thought to all form at the same time in a single burst from a common cloud of gas. After that point, star formation ends in those clusters.
“In a star cluster, the first stellar generation usually contains very massive stars, and those very massive stars will contribute very high-energy photons — that is, X-ray photons — into their environment,” Li told Space.com. “A cluster is initially gas-rich, but after that first batch of massive stars pours their energetic photons out, most of the gas will get accelerated and escape from the cluster. About 3 million to 10 million years later, the star cluster will be gas-free, hence quenching the star-forming process.”
However, about a decade ago, astronomers discovered signs that old globular clusters, ones more than 10 billion years old, often possess younger stars. Now, Li and his colleagues said they have strong evidence that the reason globular clusters may have younger stars is that they experienced more than one star-forming event, or “starburst.”
The researchers analyzed data from the Hubble Space Telescope regarding three globular clusters located in two dwarf galaxies orbiting the Milky Way. Two of the clusters, NGC 1783 and NGC 1696, are located about 160,000 light-years away from Earth in the Large Magellanic Cloud, and the third, NGC 411, is located about 190,000 light-years away in the Small Magellanic Cloud. NGC 1783 is about 180,000 times the mass of the sun, while NGC 1696 is about 50,000 solar masses and NGC 411 is about 32,000 solar masses.
The astronomers found that these globular clusters, which are each about 1.5 billion years old, are home to groups of stars a few hundred million years younger than other stars in the clusters. These younger stars make up about 0.2 to 2 percent the masses of those clusters.
Specifically, NGC 1783 is mostly about 1.4 billion years old, but some groups of its stars are 450 million and 890 million years old; NGC 1696 is mostly about 1.5 billion years old, but some of its stars are 500 million years old. And in 1.4-billion-year-old NGC 411, some stars are 320 million years old.
One potential explanation for these apparent differences in ages is that these stars only look relatively young, but are in fact “blue stragglers.” Such stars look younger due to an infusion of extra fuel they get after they either siphon gas from their neighbors or swallow other stars whole. However, the colors and locations of these younger stars are not what one would expect of blue stragglers from previous work, the researchers said.
Instead, Li and his colleagues calculated that as the orbits of these globular clusters took them through the gaseous disks of their galaxies, the clusters could have collected or accreted enough stray gas and dust to trigger new waves of star formation.
“Traditionally, scientists did not expect that a young star cluster can form additional stars after its initial formation,” Li said. “Our finding indicates that the evolution of a star cluster is much more complicated than what we thought — there must be frequent interactions between star clusters and their environment.”
Future research will aim to extend the findings to other globular clusters in the Magellanic Clouds and the Milky Way, the researchers said.
A huge alien world orbits 600 billion miles (1 trillion kilometers) from its host star, making its solar system the largest one known, a new study reports.
Astronomers have found the parent star for a gas-giant exoplanet named 2MASS J2126, which was previously thought to be a “rogue” world flying freely through space. The planet and its star are separated by about 7,000 astronomical units (AU), meaning the alien world completes one orbit every 900,000 years or so, researchers said. (One AU is the average distance from Earth to the sun — about 93 million miles, or 150 million km).
For comparison, Neptune lies about 30 AU from the sun, Pluto averages about 40 AU from Earth’s star and scientists think the newly hypothesized “Planet Nine” never gets more than 600 to 1,200 AU away from the sun.
“The planet is not quite as lonely as we first thought, but it’s certainly in a very long-distance relationship,” study lead author Niall Deacon, of the University of Hertfordshire in England, said in a statement.
The previous record for most widely separated planet and star was 2,500 AU, researchers said.
Deacon and his colleagues analyzed databases of rogue planets, young stars and brown dwarfs — strange objects bigger than planets, but too small to ignite the internal fusion reactions that power stars — to see if they could link any of them together.
The team found that 2MASS J2126, which was discovered eight years ago, and a red dwarf star called TYC 9486-927-1 are moving through space together about 104 light-years from Earth, strongly implying that they’re part of the same system.
The researchers were able to deduce a rough age for TYC 9486-927-1 and 2MASS J2126, based on the lithium signature in the star’s spectrum: between 10 million and 45 million years old. (Lithium is destroyed relatively early in a star’s life, so the more lithium a star has, the younger it is.)
2MASS J2126 has therefore completed a maximum of 50 orbits around the star so far.
Knowledge of the planet’s age allowed the researchers to calculate a mass for the planet: about 12 to 15 times that of Jupiter. Previous studies had estimated 2MASS J2126′s temperature to be about 2,730 degrees Fahrenheit (1,500 degrees Celsius). The planet appears to be broadly similar in these characteristics to the alien world Beta Pictoris b — but 2MASS J2126 orbits more than 700 times farther from its star than Beta Pictoris b does, team members said.
The odds that life could exist on 2MASS J2126 are very low, researchers said. But a hypothetical observer on the gas giant would see its sun as merely a bright star in the sky, and might not even realize that the planet and star were connected, they added. (It takes light from TYC 9486-927-1 a month to get to the planet; sunlight takes about 8 minutes to get to Earth.)
The exotic planetary system probably did not form from a large spinning disk of dust and gas, the way that Earth’s solar system did, study team members said. But exactly how it did take shape remains a mystery.
“How such a wide planetary system forms and survives remains an open question,” co-author Simon Murphy, of the Australian National University in Canberra, said in the same statement.
Some scientists have suggested that a big undiscovered body lying on the far outer reaches of the solar system could be responsible for many of the mass extinction events throughout Earth’s history, by shaking up the distant comet repository known as the Oort Cloud and sending some its denizens screaming toward our planet.
But Planet Nine — a newly proposed but not yet confirmed world perhaps 10 times more massive than Earth that’s thought to orbit far beyond Pluto — probably could not have triggered such “death from the skies” events, researchers said.
“I suspect it has something like zero effect on us,” said Mike Brown of the California Institute of Technology (Caltech) in Pasadena.
Brown and lead author Konstantin Batygin, also of Caltech, suggested the existence of Planet Nine in a paper that was published last week. They infer the planet’s presence based on indirect evidence: Computer models suggest that a distant, unseen world has shaped the strange orbits of a number of small objects in the Kuiper Belt, the ring of icy bodies beyond Neptune.
Planet Nine likely has an elliptical orbit, coming within 200 to 300 astronomical units (AU) of the sun at its closest approach and getting as far away as 600 to 1,200 AU, Brown said. (One AU is the distance from Earth to the sun — about 93 million miles, or 150 million kilometers).
Neptune orbits about 30 AU from the sun, and Pluto never gets farther than 49 AU from our star. So Planet Nine, if it exists, is very distant indeed — but not distant enough, Brown said, to stir up any of the trillions of comets in the Oort Cloud, which begins perhaps 5,000 AU from the sun.
The existence of such a “perturber” has been hypothesized as a way to explain the mysterious periodicity of big extinction events on Earth, which have recurred roughly every 27 million years over the last quarter-billion years or so.
“Really big planets really far away could do that,” Brown told Space.com. “Planet Nine is smaller than all these things that people have called ‘Planet X’ — that’s always been sort of Jupiter-sized, or even brown dwarf-sized, or something. This is a good bit smaller, and a good bit closer; it’s not in the realm of the comets.”
The putative Planet Nine also completes one orbit every 10,000 years or so, he added.
“That sounds like a long time, but it’s a pretty short orbit,” Brown said. “If it were doing this thing every time it went around the sun, it would’ve been doing a lot of it, and I don’t think there’s anything going on like that.”
Astronomer Scott Sheppard of the Carnegie Institution for Science in Washington, D.C., who is not part of the Batygin/Brown team, voiced similar sentiments. (Sheppard is conducting a hunt for undiscovered objects in the outer solar system; he co-discovered 2012 VP113 — one of the “trans-Neptunian objects,” or TNOs, whose orbital characteristics hint at the existence of Planet Nine.)
If Planet Nine exists, it could conceivably dislodge some TNOs (not Oort Cloud comets) and send them toward the inner solar system, Sheppard said.
“But most likely, the unknown massive object has been out there a very long time and thus cleared most objects near it long ago,” Sheppard told Space.com via email.
“I do think it could throw a few small objects into the inner solar system every so often, but I don’t think it would significantly increase the odds for a mass extinction event,” he added.
Densely packed groups of stars may make excellent cradles for complex space-traveling life to evolve. Despite studies that claim these environments, known as globular clusters, may be too harsh for life, a new study argues for a more optimistic view based on the evolving understanding of where planets lie outside the solar system.
“A globular cluster might be the first place in which intelligent life is identified in our galaxy,” lead study author Rosanne Di Stefano, of the Harvard-Smithsonian Center for Astrophysics, said in a statement. Di Stefano presented the new research today (Jan. 6) here at the 227th meeting of the American Astronomical Society.Globular clusters are massive groupings of millions of stars in a region only 100 light-years across. The clusters date back to the early life of the Milky Way — nearly 10 billion years ago. (For comparison, the universe is approximately 13.7 billion years old.) Although these clusters’ age raises some questions, it also provides ample time for civilizations that emerged to evolve and become complex
The advanced age of globular clusters means their stars are older, as well. The heavy elements found in younger stars, which are made up of previous generations, aren’t found within the hearts of globular cluster stars. This material, which would have been missing from the disks of dust and gas that built the star, is also required to build planets, so some scientists argue that worlds also would be missing from globular clusters.
But Di Stefano and her colleague Alak Ray, of Tata Institute of Fundamental Research in India, pointed out that stars have been found around noncluster stars that lack significant amounts of these elements. Although massive gas worlds tend to orbit stars with heavier elements, smaller rocky worlds that resemble Earth can be found around stars with varying amounts of the material.
“It’s premature to say there are no planets in globular clusters,” Ray said.
The dense population of the clusters also raises concerns about their habitability. The sun’s nearest stellar neighbor lies about four light-years (24 trillion miles, or 39 trillion kilometers) away. In a globular cluster, neighboring stars could be as much as 20 times closer. If a nearby star came too close, the effects of its gravity could fling a planet from its orbit.
In this case, the older age of the stars is an advantage. Di Stefano and Ray noted that bright stars like the sun would have been born, lived and died, leaving behind only faint, long-lived dwarf stars. These dimmer stars would require planets to orbit closer to their sun in order to maintain liquid water on their surface — a key requirement for the evolution of life as we know it. Their close orbits could help shield them from interactions with passing stars, according to a statement from the Harvard-Smithsonian Center for Astrophysics (CfA).
The presence of an old star could also indicate an older planet. On Earth, life is thought to have evolved after about 3.5 billion years. According to the CfA statement, a 10-billion-year-old planet would give life time to not only bloom, but evolve into intelligent and technologically advanced beings. Life on these ancient worlds would have had ample time to become a spacefaring species.
“Once planets form, they can survive for long periods of time — even longer than the age of the universe,” said Di Stefano.
While nearby stars may cause planets to be less stable, they can be a boon for interstellar travel. With nearby stars in galactic clusters as much as 20 times closer than the sun’s nearest neighbors, the opportunities for potential exploration, settlement and communication could be enhanced, the new study suggests.
“We call it the ‘globular cluster opportunity,’” Di Stefano said. “Sending a broadcast between the stars wouldn’t take any longer than a letter from the U.S. to Europe in the 18th century.”
Communication directed from one star in a globular cluster to the next could help scientists to spot advanced civilizations, CfA’s statement added. Targeting globular clusters with SETI search methods could reveal radio or laser broadcasts sent from one stellar system to the next.
Messages wouldn’t be the only things that could pass between the stars — spaceships could travel more easily from one system to the next, Di Stefano noted.
“The [NASA] Voyager probes are 100 billion miles [160 billion km] from Earth, or one-tenth as far as it would take to reach the closest star if we lived in a globular cluster,” Di Stefano said.
Launched in 1977, Voyager 1 and 2 were sent to the outer solar system. After passing the gas giants, the two probes continued on to the edge of the solar system and into interstellar space.
“That means sending an interstellar probe is something a civilization at our technological level could do in a globular cluster,” Di Stefano said.
A new technique could allow scientists to photograph potentially life-supporting planets in nearby multistar systems, its developers say.
The most straightforward way to learn about alien planets is to look at them directly with a telescope, rather than relying on indirect methods such as noticing their effects on the stars they circle.
Direct imaging of exoplanets requires a way to blot out the overwhelming glare of a star. This task is challenging enough when a one-star system is the target, and it’s even tougher with multistar systems. This latter fact is a problem, because binary stars are common throughout the Milky Way galaxy. Indeed, the nearest stellar system to Earth, Alpha Centauri, consists of two stars, known as Alpha Centauri A and B. (A third star, called Proxima Centauri, also lies nearby; it is considered by some astronomers to be part of this system as well.)
Most systems featuring sunlike stars “are actually multi[-star systems],” Ruslan Belikov, an astronomer at NASA’s Ames Research Center in California, said during a session at the 227th meeting of the American Astronomical Society here Wednesday (Jan. 7). “A telescope that is only imaging single-star systems will generally miss these.”
“Alpha Centauri, which is the closest star to us, would be by far the best target [for direct imaging] … if it wasn’t binary,” he added. Because of Alpha Centauri’s proximity to Earth (about 4.3 light-years), researchers could use a relatively small space telescope to get a close look.
But Belikov and his colleagues have come up with a possible solution for this problem.
Scientists hoping to directly image an exoplanet use special tools on or in front of a telescope to block out a star’s light, and they can also use optical techniques through a telescope’s mirrors or processing after the image is collected to cancel out extra noise and interference.
Belikov’s group figured out how to deform mirrors enough to blot out the disruptive effects of two stars at once, beyond the usual limit of how much interference a mirror can correct for. This and other modifications could theoretically allow astronomers to image planets in binary systems such as Alpha Centauri, Belikov said.
Going beyond the deformable mirror’s usual limit relies on a faint grating pattern introduced on many mirrors as a byproduct of the manufacturing process — something that can lead to tiny distortions often seen as a bug of such mirrors rather than a feature.
“We as scientists delight in disproving conventional wisdom in such things, but in this case it’s especially so,” Belikov said. “The reason we can do this impossible thing is because of something that is generally considered to be a deficiency.”
The newly proposed set of techniques can be applied to telescopes without complex hardware modifications, Belikov said. Finding a way to look at multiple-star systems like Alpha Centauri using a similar process could lead to glimpses of interesting alien planets — in Alpha Centauri’s case, with a much smaller telescope than previously thought possible. But Belikov’s AAS talk had another takeaway message as well.
“The most important conclusion of all is to have zero respect for authority telling you that something is impossible,” he said. “Unless it’s a law of physics.”
Get ready for your close-up, black holes: The Event Horizon Telescope (EHT), which will take some of the best images of black holes ever captured by humans, is ramping up its worldwide network of telescopes.
By 2018, the EHT will be an observatory that harnesses the power of nine telescopes around the world, including ones in Chile, Arizona, Hawaii, Antarctica and Greenland. These instruments will work together to get higher-resolution images than any of these scopes can achieve alone. The target of their observations will be black holes — scientists hope to see the material moving around these dark monsters, as well as the shadow of the black hole itself.
“One thing that could excite the public almost as much as a Pluto flyby would be a picture of a black hole, up close and personal,” Feryal Ӧzel, a professor of astronomy and astrophysics at the University of Arizona, said during a talk here at the 227th meeting of the American Astronomical Society, where a few thousand astronomers and astrophysicists have gathered to discuss the latest news in the field. (Ӧzel’s comment was made in reference to the massive public interest in the images captured by NASA’s New Horizons probe, which flew by the dwarf planet last July.) [The Strangest Black Holes in the Universe]
Other telescopes have studied black holes in the past, but the goal of the EHT is to take images that surpass the resolution of any previous black-hole snapshots. With that information, scientists would be able to see the area around a black hole — a place where the pull of gravity is so extreme that very strange things happen.
For example, the black hole at the center of the galaxy known as Messier 87 has a massive, narrow jet of material, roughly 5,000 light-years long, spewing away from it. In contrast, the black hole at the center of the Milky Way — Sagittarius A* — has very little matter around it and no jets. In galaxies known as active galactic nuclei (AGNs), black holes accelerate huge clouds of material around them, and radiate more light than the entire Milky Way galaxy. What leads to such a drastic difference between these objects? With EHT, Ӧzel said, scientists may finally be able to answer that question.
“Is it the magnetic field structure that is different? Is it the spin that is different? Or is it something else about the accretion flow that is different?” Ӧzel said. “This will open a brand-new window into studying accretion physics.”
And then there’s Einstein. His theory of general relativity has been tested using observations in Earth’s solar system — for example, the way light bends around the sun — and beyond. But there are few cosmic environments as extreme as the one around a black hole, where the gravity can be millions of times stronger than it is around a star. As a result, the EHT will reveal the effects of gravity (which are described by the theory of relativity) “on scales that have never been probed before,” said Ӧzel, who is a scientist on the EHT project team and is leading some of the theoretical work that will be combined with the observations. “Get to the edge of a black hole, and the general relativity tests you can perform are qualitatively and quantitatively different,” Ӧzel said.
Understandably, Ӧzel and other black-hole scientists are eager to start getting data from EHT. One of the major requirements of imaging black holes in such high resolution is to have a very large telescope. In fact, Ӧzel said that achieving the resolution of EHT effectively requires a telescope the size of the Earth.
“Of course nobody would fund an Earth-sized telescope,” Ӧzel said. But the “next-best thing” is to combine observations from multiple telescopes on the surface of the Earth that are separated by very large distances, Ӧzel said. With this technique, scientists can observe an object in significantly higher resolution than the telescopes could achieve alone — effectively giving scientists an “Earth-size” telescope.
The first data from the EHT project were collected in the mid-2000s, by three telescopes — one each in Hawaii, Arizona and California. The group collaborated to look at the black hole at the center of the Milky Way galaxy, called Sagittarius A*. In 2014, the collaboration added the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to its array, and doubled its resolution, according to the EHT website.
Six telescopes in the EHT array are already taking data, and a total of nine are expected to be contributing to the project by 2018, according to Shep Doeleman, principal investigator for EHT.
Early in 2015, the collaboration added the South Pole Telescope to its array, which connected the other telescopes such that the EHT effectively spanned the entire Earth. In 2017, the EHT will be able to make observations with ALMA that will boost its sensitivity by a factor of 10, Doeleman told Space.com in an email. In 2018, an additional telescope will join the group from Greenland.
“One of the innovative aspects of the EHT is that we use existing telescopes at the highest altitudes (where they are above most of the atmosphere) and outfit them with specialized instrumentation that enables us to link them together,” Doeleman said. “So we don’t build new dishes, and we leverage over a [billion dollars] of existing telescopes.”
However, there are still obstacles, he noted. “Last year, one of the facilities participating in the EHT had to close due to lack of funding,” Doeleman said. “We can still do all the EHT [work] planned because new sites are coming online, but we remain ‘en guard’ for threats against EHT sites.”
The search for signs of life beyond the solar system is kicking into a higher gear.
Scientists are working to compile a catalog of gases that could potentially be evidence of life, so researchers will know what to look for when scanning the atmospheres of rocky, Earth-like alien planets.
“Every way we have possible, people [are] trying to find exo-Earths,” planetary scientist Sara Seager, of the Massachusetts Institute of Technology, said last month at the American Astronomical Society’s Extreme Solar Systems III conference in Hawaii.
“We have a shot at finding signs of life in the next decade or so,” she added. “The question is, what will we look for?”
Astronomers have discovered nearly 2,000 exoplanets to date. Scientists are beginning to probe the upper atmospheresof some of those worlds using instruments such as NASA’s Hubble Space Telescope. As technology improves, researchers should be able to see deeper into these alien atmospheres, and with better precision.
The search for alien “biosignatures” typically centers on the kinds of gases produced by Earth organisms, because Earth life is the one example that scientists have to work with. As a result, Seager called oxygen “our favorite biosignature gas.” A close second is methane, she added.
But there are thousands of other molecules produced by life on Earth that are not directly related to keeping an organism alive.
With the exception of the noble gases — helium, neon, argon, xenon, krypton and radon — life produces every gas available in Earth’s atmosphere, she added. Living organisms may not always be the dominant method of production, but they play a role.
Seager and her team compiled a list of 14,000 different molecules that could conceivably be biosignatures on alien worlds. This enormous database should aid scientists as they search the atmospheres of planets around other stars.
Scientists have studied the atmospheres of more than three dozen worlds beyond the solar system, to some degree. The number is so small because most of the exoplanets that have been discovered to date lie hundreds or thousands of light-years away — generally, too distant to probe in any detail with current instruments. (More than half of all confirmed exoplanets were spotted by NASA’s Kepler space telescope, whose search field lay relatively far away.) But the situation should change soon. NASA’s Transiting Exoplanet Survey Satellite(TESS), which is scheduled to launch in 2017, will hunt for planets around more than half a million nearby stars. While it will not be able to detect Earth-like planets around sunlike stars, TESS should be able to identify Earth-size planets circling dimmer red dwarfs, in regions where they could host liquid water on their surfaces, mission team members said.
NASA’s $8.8 billion James Webb Space Telescope (JWST), which should launch in 2018, will be able to perform atmospheric studies of the rocky worlds found by TESS. Indeed, TESS should discover dozens of “super-Earths” — planets slightly bigger than Earth — whose atmospheres JWST can probe, NASA officials have said. So, if life is common and widespread throughout the Milky Way galaxy, the TESS-JWST pair should give researchers a decent shot at detecting it.
Like Kepler, TESS and JWST will use the “transit method,” detecting and studying alien worlds when they pass in front of their host stars from the telescopes’ perspective. But a different technique, known as direct imaging, is not so dependent on such favorable cosmic alignments.
As its name suggests, direct imaging refers to snapping actual photographs of exoplanets. This is tough to do, especially for relatively small, distant or close-orbiting alien worlds, but technological advances promise to extend the technique to more and more planets as time marches on.
For example, an instrument known as a coronagraph can be attached to a telescope, to block out the overwhelming glare from the parent star. Just as placing your hand over the sun allows you to see an airplane flying by, a coronagraph can help scientists directly image a wealth of planets and learn more about them. Seager said NASA is considering adding a coronograph to its proposed WFIRST-AFTA mission, which could study exoplanet atmospheres, along with other tasks.
Another possibility is a starshade, or external occulter, a massive, petal-shaped object that sits in space a set distance from the telescope, blocking starlight like a coronagraph does. In principle, any telescope (including JWST) can use a starshade, because this kind of light-blocker doesn’t have to be built into the instrument.
Studying exoplanet atmospheres via the transit method is generally limited to larger bodies such as super-Earths around dim stars. But direct imaging, including observations performed with starshades, holds a great deal of potential for spotting and studying Earth-size worlds circling sunlike stars, Seager said.
“The starshade must happen,” said Seager, who is chair of NASA’s Exoplanet Occulter Science and Technology Definition Team.
Now, scientists think they may have an answer to this long-standing puzzle: The constant pummeling that formed Earth may have altered its composition.
Earth formed by accretion — the gradual accumulation of bits of matter due to their mutual gravitational pull. Heat from the radioactivity of accreting meteorites and from the impacts of rocks constantly bombarding the newborn Earth caused the planet to melt enough for heavy materials to sink downward. This resulted in an iron-rich core, above which lay a rocky mantle and crust
The most primitive meteorites, known as chondrites, are the primordial material from which the planets were formed. Among these, previous research found that enstatite chondrites have a mix of isotopes that is remarkably similar to that of Earth, which suggests they might be the raw material from which Earth originated. (Isotopes are versions of an element that have different numbers of neutrons.)
Strangely, Earth appears to be low in silicon, potassium and sodium, and enriched in magnesium, calcium and aluminum, compared with enstatite chondrites. Now, for the first time, scientists think they may have an explanation for this mystery.
“The most exciting aspect of these results is that it is the first time that anyone comes close to answering the question, ‘Why does Earth have the same isotopic composition as enstatite chondrites but a different chemical composition?’”study lead author Asmaa Boujibar, a planetary scientist at NASA’s Johnson Space Center in Houston, told Space.com.
In experiments, the researchers melted enstatite chondrites at various pressures. This procedure mimicked how accreting rock might have behaved during Earth’s formation.
The experiments suggested that the heat of the newborn Earth left the rocks constituting its crust enriched in silicon and relatively low in magnesium. The research team’s computer models then suggested that the many cosmic impacts that pulverized the young Earth stripped a great deal of this crust off the planet, leaving Earth relatively depleted of silicon and rich in magnesium.
The heat from these impacts also would have made potassium, sodium; calcium and aluminum escape as gases from Earth. However, much of the calcium and aluminum would have condensed and returned back to Earth. That could help explain why the proportions of these elements on Earth are different from their proportions in enstatite chondrites, the researchers said.
The nature of the impacts that might have caused this heat-based loss of matter from Earth remain uncertain, Boujibar said, adding that the impacts might have involved giant rocks, very fast rocks or very hot rocks.
Uncovering the nature of these impacts would shed light on how Earth formed, she added. For instance, very fast rocks might be the result of Jupiter moving closer and then farther away from, the sun and gravitationally slinging around rocks at high speeds, while very hot rocks were seen in the solar system soon after it formed.
Boujibar and her colleaguesdetailed their findings online Sept. 23 in the journal Nature Communications.
Scientists are referring to the resurrected cloud as a “radio phoenix,” named after the mythical bird that is reborn from its ashes, because the high-energy electrons within it are once again radiating mostly at radio frequencies, according to a statement from NASA. The cloud is found in Abell 1033, a galaxy cluster of more than 350 galaxies about 1.6 million light-years from Earth.
The above video shows new images of Abell 1033 created using light collected by NASA’s Chandra X-ray Observatory, radio emissions collected by the Very Large Array, and optical light from the Sloan Digital Sky Survey. Combining data from these telescopes, as well as the Westerbork Synthesis Radio Telescope in the Netherlands, astronomers were able to figure out what brought the radio phoenix back to life.
Astronomers working on the project believe the supermassive black hole that sits near Abell 1033′s center erupted long ago, releasing a stream of high-energy electrons (subatomic particles that make up atoms) that formed a cloud hundreds of thousands of light-years wide and radiating radio emissions. As the electrons gradually lost energy over millions of years, the cloud’s emissions began to fade, the NASA statement said.
Galaxy clusters can consist of hundreds or even thousands of individual galaxies, as well as dark matter, and huge reservoirs of hot gas, the NASA statement said. As the electron cloud in Abell 1033 grew dimmer, another cluster of galaxies slammed into the original cluster, sending shock waves through the system.
These shock waves, similar to sonic booms produced by supersonic jets, passed through the dormant cloud of particles, compressed the cloud and re-energized the electrons, essentially waking them up. The now wide-awake electrons once again radiated radio frequencies — the phoenix had risen from the ashes.
The image of Abel 1033 shows X-rays from Chandra in pink and radio data from the VLA in green. Background imagery comes from observations from the SDSS and a map of the density of galaxies, made from the analysis of optical data, is seen in blue.
Astronomers believe this image shows the radio phoenix soon after it was resurrected, because these types of radio sources fade “very quickly” (on a cosmic scale) when located close to the center of a galaxy cluster, the NASA statement said. Because of the intense density, pressure and magnetic fields near the center of Abell 1033, scientists expect the radio phoenix to radiate for tens of millions of years.
Researchers have a new way to rank the life-hosting potential of alien worlds.
The “habitability index” metric could help guide the operations of future observatories, such as NASA’s James Webb Space Telescope (JWST), that will scan exoplanet atmospheres for signs of life, scientists said.
“Basically, we’ve devised a way to take all the observational data that are available and develop a prioritization scheme so that as we move into a time when there are hundreds of targets available, we might be able to say, ‘OK, that’s the one we want to start with,” study lead author Rory Barnes, of the University of Washington, said in a statement.
Traditionally, assessing habitability has been a yes-or-no affair, with researchers attempting to determine whether or not an alien world resides in the “habitable zone” of its host star. This region of space, also known as the “Goldilocks zone,” is that just-right range of distances that can allow the existence of liquid water on a planet’s surface.
But the new index is more involved, integrating information about an exoplanet’s composition (e.g., rocky or not rocky), reflectivity and orbital path to come up with the probability that it can indeed support liquid surface water.
The original concept “was a great first step, but it doesn’t make any distinctions within the habitable zone,” Barnes said. “Now it’s as if Goldilocks has hundreds of bowls of porridge to choose from.”
Calculations performed in the new study, which has been accepted for publication in the Astrophysical Journal, suggest that the best candidates for alien life are exoplanets that receive about 60 to 90 percent as much energy from their host stars as Earth gets from the sun, researchers said.
Astronomers have discovered nearly 2,000 exoplanets to date, and many more await confirmation by follow-up observations and analysis. More than half of these finds have come courtesy of NASA’s Kepler space telescope, which notices the tiny brightness dips caused when planets cross the face of, or transit, their host stars from the instrument’s perspective.
JWST, which is scheduled to launch in late 2018, will also make use of such transits. Among many other tasks, the $8.8 billion observatory will study starlight that passes through exoplanet atmospheres for signs of oxygen, methane and other gases that could have been produced by living organisms.
The new habitability index should help scientists optimize JWST’s life-hunting work, study team members said.
“This innovative step allows us to move beyond the two-dimensional habitable zone concept to generate a flexible framework for prioritization that can include multiple observable characteristics and factors that affect planetary habitability,” co-author Victoria Meadows, also of the University of Washington, said in the same statement. “The power of the habitability index will grow as we learn more about exoplanets from both observations and theory.”
If you could hear the stuff that swirls around black holes, superdense white dwarfs and young stars, what would it sound like? Probably like the empty spaces on the radio dial, researchers say.
Simone Scaringi, a postdoctoral researcher at the Max Planck Institute in Germany, studies “accretion disks” around massive objects. An accretion disk is acollection of matter that gathers in a disc shape around a rotating object. Scaringi and his team looked at flickering in the light emissions of galactic nuclei, black holes, young stellar objects and white dwarfs, which are the collapsed remnants of massive stars. You can hear what accretion disks around black holes sound like here.
Using observations from NASA’s Kepler space telescope, ground-based instruments and the European Space Agency’s XMM-Newton satellite, the scientists found it’s possible to turn the flickering into sound.
“It’s something I always wanted to try and do,” Scaringi told Space.com. “This project gave me a good excuse to give it a try. For me, it’s the obvious way to explain this research. … I can show it’s a different type of noise.”
The flickering comes from the energy released by material in accretion disks that falls in toward the central object. Scaringi treated the flashes’ frequency as that of a sound wave; for example, a frequency of 10 flashes a second was converted to a wave consisting of 10 cycles per second, or 10 Hertz. There was one “cheat”: Scaringi had to scale the frequencies to the range of human hearing, as most of them would be far too low for humans to hear.
The result is a white-noise-like sound, which helps illustrate the team’s main finding: The physics of accretion disks scale up and down and remain mostly the same, no matter how massive the object at the center of the disk is.
To many people, this finding might be intuitive; after all, stirring creamer into a cup of coffee produces a shape not unlike that of a spiral galaxy. And scientists and philosophers have remarked on the similarity between the shapes of spiral galaxies and accretion discs around stars.
Intuitions, however, are often wrong. Many scientists were unsure whether the same physical laws applied at widely differing scales. One issue, Scaringi said, is relativity. Black holes, for example, have the mass of multiple suns — millions or billions of suns in the case of the supermassive black holes at the centers of galaxies. The difference in gravitational forces between the area near the black hole’s “point of no return,” called the event horizon, and the regions farther away is large, whereas for young stars it is comparatively small.
Scaringi’s team has shown that the behavior of accretion disks will scale up; one can apply the same basic laws to a large black hole, or a galaxy, or a young solar system. But the mechanism is still unknown.
“As far as the detailed modeling is concerned, we’re still not there,” Scaringi said. “We seem to observe that it turns out that they all seem to scale, but the detailed physics as to why the scaling relation holds is not clear yet.”
The study appears in the Oct. 9 issue of the journal Science Advances.
A huge telescope array will allow scientists to conduct the most sensitive and exhaustive search for signs of alien civilizations to date when it comes online, the project’s backers say.
The Square Kilometer Array (SKA), currently planned to begin construction in 2018, could enable the search for intelligent alien life to piggy-back on other scientific observations, scouring the galaxy with unprecedented precision.
“A unique aspect for the search of life in the universe is the question of whether advanced lifeevolves intelligence,” Andrew Siemion said at the Astrobiology Science Conference in Chicago in June. [13 Ways to Hunt Intelligent Alien Life]
Siemion, who holds joint appointments with the University of California, Berkeley, the Netherlands Institute for Radio Astronomy and Radbound University in the Netherlands, hunts for signs of alien technology in the universe.
“The only way to answer that in the foreseeable future is to look directly for evidence” of intelligence, Siemion said. “For that, you need a large telescope.”
The Square Kilometer Array is an enormous radio telescope that will be built in South Africa and Australia. Funded by a consortium of different countries, the SKA will combine thousands of small antennaeacross the globe instead of a single large dish, allowing unprecedented sensitivity in radio astronomy.
Using such a costly instrument for a single scientific study, especially one as speculative as the search for extraterrestrial intelligence (SETI), is unheard of in astronomy. But SETI scientists figured out a way to obtain significant telescope time nearly 30 years ago, when they began to piggy-back on other users’ observations at the enormous Arecibo Observatory in Puerto Rico, duplicating their observations with very little loss of sensitivity. Today, SETI researchers are able to obtain thousands of hours of observations annually, which they diligently scrutinize for radio signals from beyond Earth.
According to Siemion, data from the SKA could be similarly piggy-backed. But while Arecibo utilizes a single large dish, the SKA will be much larger than the biggest radio telescope operating today, allowing scientists to search for fainter signals.
Construction on the SKA should begin in 2018. The first phase, planned for completion by 2020, would allow for about 10 percent of the collecting area of the full instrument at low and mid-range frequencies.
According to a paper Siemion authored last fall, a five-year campaign by the first phase of the SKA could allow scientists to survey more than 10,000 stars. When completed, the SKA could detect signals as faint as those emitted by aircraft radars on Earth from every star within almost 200 light-years.
Earth began leaving its mark in the galaxy when humanity started transmitting signals by radio. These signals radiate outward from the planet, and could theoretically be detected by other civilizations. Given the enormous size of the spectrum that radio waves cover, scientists have suggested a number of preferred frequencies to hunt for extraterrestrial communication. [The Serious Search for Intelligent Life: 4 Key Questions (Video)]
As technology has improved on Earth, however, humanity has begun to reduce the radio-wave leakage into space. This could suggest that the window for observing accidentally broadcast signals is brief — perhaps only a century or so. While scientists still hope to detect such signals, they also aim to find deliberately transmitted radio waves, which have been designed to travel through space.
The SKA concentrates on a frequency region known as the “terrestrial microwave window,” the spectral region of low natural noise between the galactic background and the emission and absorption of water and oxygen in Earth’s atmosphere. These frequencies can travel through the space between stars and through the water-laden atmosphere of Earth or any other planet with ease, leading scientists to suspect that distant civilizations might use them to communicate
SETI scientists aren’t just searching for signals broadcast at random. They also hope to eavesdrop on interplanetary communications.
If alien technology spreads to multiple planets within a single system, it is feasible to expect these various outposts to communicate with one another. If those planets lie along Earth’s line of sight, and observations are made when the planets are communicating with each other, it is possible that the SKA could pick up those broadcasts, researchers said.
In addition to the recent spate of planets unearthed by NASA’s Keplermission, the European Space Agency’s Gaia spacecrat and future missions such as NASA’s Transiting Exoplanet Survey Satellite(TESS) could produce a catalog of properly aligned planetary systems to watch. Life-hunting researchers have already begun eavesdropping on some of Kepler’s discoveries, for example.
“We’re going to have all kinds of data to figure out how to build these databases in coming years,” Siemion said.
Although the terrestrial microwave window will be the primary focus of the SETI search with the SKA, Siemion cautions that it is not the only potential signal for communication.
“We don’t know exactly what E.T. is going to do,” he said.
Stephen Hawking may have just solved one of the most vexing mysteries in physics — the “information paradox.”
Einstein’s theory of general relativity predicts that the physical information about material gobbled up by a black hole is destroyed, but the laws of quantum mechanics stipulate that information is eternal. Therein lies the paradox.
Hawking — working with Malcolm Perry, of the University of Cambridge in England, and Harvard University’s Andrew Stromberg — has come up with a possible solution: The quantum-mechanical information about infalling particles doesn’t actually make it inside the black hole.
“I propose that the information is stored not in the interior of the black hole, as one might expect, but on its boundary, the event horizon,” Stephen Hawking said during a talk today (Aug. 25) at the Hawking Radiation conference, which is being held at the KTH Royal Institute of Technology in Stockholm, Sweden.
The information is stored at the boundary as two-dimensional holograms known as “super translations,” he explained. But you wouldn’t want super translations, which were first introduced as a concept in 1962, to back up your hard drive.
“The information about ingoing particles is returned, but in a chaotic and useless form,” Hawking said. “For all practical purposes, the information is lost.”
Hawking also discussed black holes — whose gravitational pull is so intense that nothing, not even light, can escape once it passes the event horizon — during a lecture last night (Aug. 24) in Stockholm.
It’s possible that black holes could actually be portals to other universes, he said.
“The hole would need to be large, and if it was rotating, it might have a passage to another universe. But you couldn’t come back to our universe,” Hawking said at the lecture, according to a KTH Royal Institute of Technology statement. “So, although I’m keen on spaceflight, I’m not going to try that.”