Are black holes truly black? A new laboratory experiment points toward “no.”
Using a simulated black hole made from soundwaves, scientists have observed a phenomenon known as Hawking radiation: a faint energy emission that, in theory, is created right at the edge of a black hole’s event horizon, or the point beyond which even light cannot escape.
If Hawking radiation comes from astrophysical black holes (not just those created in a lab), it would mean these objects are not entirely dark. It could also help scientists solve a paradox posed by black holes, and perhaps shed light on one of the most significant problems facing modern physics.
Black holes are strange regions where gravity is strong enough to bend light, warp space and distort time
Jeff Steinhauer, an experimental physicist at the Technion — Israel Institute of Technology in Israel, and lead author on the new study, told Space.com.
According to Steinhauer, earlier calculations by cosmologist Stephen Hawking (who came up with the theory that bears his name) combined the theories of quantum physics and gravity. The current experiment tests those calculations, providing the first strong evidence that they are correct, Steinhauer said.
“A black hole is a testing ground for the laws of physics,” Steinhauer said.
Swimming against the current
There’s a tricky concept in physics that says that pairs of particles constantly blink into existence throughout space. One is a particle of normal matter and the other is its exact opposite, or antiparticle, so the two annihilate one another, and there’s no change to the universe’s energy balance sheet. These are called virtual particles. When this happens near the edge, or event horizon, of a black hole, the particles can avoid complete destruction; one can fall inside while the other escapes.
But observing such interactions in nature has remained difficult, the Hawking radiation around a black hole (if it exists) is so faint that it can’t be seen from Earth around known black holes (most of which are very far away). In addition to the distance, the Hawking radiation is likely overwhelmed by radiation from other sources, Steinhauer said.
“It makes it seemingly almost impossible to see this very slight radiation coming from the black hole,” he said.
The same problem applies in a laboratory, where any heat can create background radiation that overwhelms the lab-produced Hawking radiation. To eliminate that problem, Steinhauer’s experiment ran at less than a billionth of a degree above absolute zero.
In the analogue black hole, a line of cold rubidium atoms stream from a laser to create a form of matter known as a Bose-Einstein condensate. The cold gas flows faster than the speed of sound in one direction, so that a sound wave trying to go against the flow can’t manage to move forward. In this respect, the slower moving sound wave is like a particle trying to escape from a black hole.
“It’s like trying to swim against the river,” Steinhauer said. “If the river is going faster than you can swim, you go backwards, even though you feel like you’re going forward.”
The upstream attempt is analogous to light in a black hole trying to escape, he said. Sound waves trying to move forward instead fall backward. If two virtual particles were created near the edge of the event horizon, one particle could be consumed by the black hole (the fast-moving stream), while the other escapes, avoiding destruction. The escaping particles are called Hawking radiation.
A method of creating a black hole using sound waves was proposed in 1981, and since then scientists have struggled to simulate Hawking radiation in the lab. Two years ago, Steinhauer performed an experiment that measured Hawking radiation after something was deliberately crashed into the event horizon of the analogue black hole. This new experiment took more of a wait-and-see stance, waiting for the particle-antiparticle pair to appear without external stimulation, more like what happens in the depths of space.
Just as Hawking theorized, the simulated black hole spit out the predicted particles, a sign of Hawking radiation.
“What I saw suggests that a real black hole might emit something,” Steinhauer said.
The new finding also has larger implications for the field of physics, he said. One of the biggest mysteries in physics is why Einstein’s theory of gravity (which describes large-scale interactions in the universe) doesn’t seem to be compatible with quantum mechanics (which describes very small-scale interactions).
“Combining gravity with quantum physics is one of the main goals of physics today,” Steinhauer said. “Hawking made the first steps toward that.”
The simulated black hole tested Hawking’s equations.
“His calculations predicted there should be light from a black hole,” Steinhauer said. “It turns out his calculations were correct.”
One intriguing result of the artificial black hole involved insight into the information paradox. According to Einstein’s theory of general relativity, everything that crosses the event horizon of a black hole is consumed, including information. As the escaping particle steals energy from a black hole, the massive object can shrink over time, eventually evaporating into nothing. Of course, this assumes it has stopped consuming nearby material and thus isn’t putting on new weight. Theoretically, a black hole can shrink into nothing, taking with it the information carried by or about the particles it consumed.
“Information has vanished,” he said. “It’s like it goes into the black hole and disappears.”
Since quantum mechanics suggests that information can’t be lost, that raises a paradox.
According to Hawking’s calculations, the surviving particles contain no useful information about how the black hole formed and what it consumed, suggesting that information vanished with the black hole itself.
Steinhauer’s black hole revealed that the higher energy particle pairs remained entangled, even after one was swallowed by the event horizon. Entangled particles are able to share information instantaneously, even when they are separated by great distances, a phenomenon sometimes described as “spooky action at a distance.”
“Some of the solutions to this [paradox] probably rely on entanglement,” Steinhauer said.
Scientists not associated with the research who were interviewed by Nature News and Physics World both said that while the experiment appears to have measured Hawking radiation, it does not necessarily prove that Hawking radiation exists around black holes in space.
This research suggests that Ceres might still be warmed by radioactive material in its interior, scientists say.
With a diameter of about 585 miles (940 kilometers), Ceres is by far the biggest member of the asteroid belt located between Mars and Jupiter. Previous remote analysis of Ceres using ground- and space-based telescopes suggested that it was not as dense as other large asteroids such as Vesta. This suggested that Ceres was not made up solely of rock, but composed partly of both icy and rocky material.
However, scientists weren’t sure how the innards of Ceres were structured. Whereas Earth developed an onion-like structure fully differentiated into distinct layers — an outer crust, a central core and a mantle layer between the two — prior research suggested that Ceres might only be partially differentiated into more vague zones, or perhaps not differentiated at all. Shedding light on the structure of Ceres might, in turn, yield insight into how it and other asteroids and dwarf planets evolved over time.
One property of Ceres that might reveal more about its structure is how easy or difficult it is for the dwarf planet to spin. This property, technically known as the moment of inertia, is related to how mass is distributed within a celestial body: The lower the moment of inertia, the more dense material is concentrated in a body’s center.
To determine the moment of inertia of Ceres, scientists needed to analyze the dwarf planet’s gravity field. Anything that has mass has a gravity field that attracts objects toward it, and the strength of this field depends on a body’s mass. Because the mass of bodies such as Earth and Ceres is not spread out evenly, this means their gravity fields are stronger in some places on their surfaces and weaker in others.
The researchers examined gravity-field data that NASA’s Dawn spacecraft gathered from its close encounter with Ceres. Their work suggests that Ceres is only partially differentiated, with a core made of rock overlaid by a shell composed of a mix of icy, salty and rocky material that is about 43.5 to 120 miles (70 to 190 km) thick.
“The partial differentiation suggests that Ceres was hot at one point, but it did not fully separate the water and other volatiles from its rocky components,” study lead author Ryan Park, a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, told Space.com.
The scientists also detected signs that Ceres’ interior might still be warm. This was a bit of a surprise, because previous research suggested that a body as small as Ceres should have cooled off a long time ago. This new finding indicates that Ceres might have a warm interior because of heat from radioactive material, Park said.
Two separate studies suggest that galactic radiation would quickly degrade biological material on the surface of Mars and Jupiter’s ocean-harboring moon Europa, two of the prime targets in the search for past or present extraterrestrial life.
Objects in the solar system are bathed in radiation from the sun and large planets such as Jupiter. But the largest doses come from galactic cosmic rays (GCRs), which stream in from faraway sources such as exploding stars.
Earth’s thick atmosphere protects life here from the damaging effects of GCRs. But life on other worlds would not be so lucky; modern Mars has a thin atmosphere, for example, and Europa has virtually no atmosphere at all. Both worlds therefore are bombarded by high levels of radiation, which could spell doom for any fossils that may have once existed on the worlds’ surfaces.
Mars is the most Earth-like world in the solar system. Scientists think Mars once harbored a large ocean of liquid water that the planet lost, along with its atmosphere, billions of years ago.
While scientists consider it unlikely that life exists at the Martian surface today, many researchers hope to find evidence that Martian life existed in the past. That evidence would come in the form of fossilized microorganisms or biological molecules such as amino acids, the building blocks of proteins.
But finding that evidence would require such molecules to persist on Mars or Europa. To check if this is likely, Alexander Pavlov, a planetary scientist at NASA’s Goddard Space Flight Center in Maryland, and his colleagues set out to test how amino acids withstand doses of radiation similar to those experienced at the Martian surface.
Previous studies that dosed only amino acids found they could survive for up to 1 billion years under Martian conditions. However, Pavlov’s team mixed the amino acids with rocky material similar to that found on Mars, generating conditions a rover is more likely to sample. The researchers found that the amino acids were degraded by radiation in as few as 50 million years.
“More than 80 percent of the amino acids are destroyed for dosages of 1 megagray, which is equivalent to 20 million years,” Pavlov said in March, during a presentation at the 47th Lunar and Planetary Science Conference in The Woodlands, Texas. “If we’re going for ancient biomarkers, that’s a very big problem.”
The scientists then combined the surface sample with water to simulate historically wet regions on Mars; these are the places considered most favorable to life. Water accelerated the degradation of the biomarkers, destroying some in as few as 500,000 years and all within 10 million years.
The odds of finding signs of life in hydrated minerals near the Martian surface therefore aren’t great, the researchers said.
Cold temperatures slow the degradation process down, but not enough for long-term preservation, the scientists said. Material lasted no more than 100 million years when exposed to Mars-like GRC levels.
These findings could be bad news for missions that plan to search for signs of ancient life on the Martian surface, the researchers said.
“We are extremely unlikely to find primitive amino acid molecules in the top 1 meter [3.3 feet] [of the crust], due to cosmic rays,” Pavlov said. “It would be critical to provide missions with 2-meter [6.6 m] drilling capabilities, or chose landing sights with freshly exposed rocks.”
Such rocks would have been kicked up from beneath the surface by asteroid or comet impacts within the last 10 million years, he said.
In 2020, the European Space Agency and Russia plan to launch a life-hunting Mars rover that can drill up to 2 meters down. The mission will be the second phase of the ExoMars mission; the first phase, which consists of an orbiter and a landing demonstrator, launched in March.
Jupiter’s moon Europa is considered one of the best places to search for life beyond Earth. A global ocean sloshes beneath the moon’s icy shell, fed by thermal vents that could possibly generate the energy needed for life to evolve.
NASA aims to launch a flyby mission to Europa in the 2020s, and the agency is considering adding a lander to the mission profile as well
Europa’s ice shell is thought to be miles thick on average, so a lander wouldn’t be able to drill through the ice (except perhaps in a few select spots). But signs of Europan life, if it exists, may rise up from the ocean onto the surface.
Indeed, Europa has reddish surface features that have been identified as salts, which likely came from beneath. Scientists have also tentatively identified, but not confirmed, plumes like those found on Saturn’s moon Enceladus, which could shoot water-rich material — and, possibly, signs of life — from the ocean to the surface.
Like Pavlov, Luis Teodoro, a planetary scientist at NASA’s Ames Research Center in California, was concerned with GCR radiation, and how dosages could affect the hunt for life. But Teodoro focused on Europa, not Mars.
Simulating the conditions at Europa, Teodoro found that the moon’s GCR dosages were comparable to those on the Red Planet.
“Radiation is going to play a major role at Europa in the top few meters — actually, dare I say, dozen meters — of Europa’s surface,” Teodoro said at the same conference.
He said his simulations suggest that hardy “extremophile” microbes found in some of Earth’s harshest environments would survive no more than 150,000 years in the top 3.3 feet (1 m) of Europa’s icy crust. Organic biomarkers buried within 3.3 feet of the surface would last only 1 to 2 million years, he said.
“If we want to put a landeron the surface of Europa to check if life is there, we most likely are going to see something destroyed — mangled materials, mainly organics — from this huge dosage of radiation,” he said.
There is hope, however, that fresh surface ice deposits could still contain biomarkers that scientists could successfully identify as life. So it’s important to determine if Europa does indeed spout plumes that bring fresh material to the surface, Teodoro said.
Europa also is exposed to another source of radiation that Earth and Mars avoid: the radiation from Jupiter. Teodoro said he plans to include the effects of Jupiter’s doses in future models.
For now, however, his research seems to suggest that hunting for existing life or fossils on the icy moon may remain a challenge. But Teodoro said he hasn’t given up completely on the cool world.
“Maybe this is all telling us life is not at the surface,” he said, expressing his hope that evidence of alien organisms instead lies beneath the ice.
The gas cloud, a nebula called LHA 120-N55, is about 163,000 light-years away from Earth and is situated in the Large Magellanic Cloud, a nearby dwarf galaxy that’s one of the Milky Way’s satellites. The image was taken by the VLT’s FOcal Reducer and low dispersion Spectrograph (FORS2), and its location in space is pinpointed in a new video.
The gaseous N55 is inside of a superbubble, a vast structure which occurs when winds from new stars and shockwaves from supernova explosions, caused by dying stars, blow away the gas and dust those stars used to possess. The process carves bubble-shaped holes in the gas.
Emission nebula LHA 120-N55 shines in this image from the European Southern Observatory’s Very Large Telescope.
ESO “The material that became N55, however, managed to survive as a small remnant pocket of gas and dust,” ESO officials said in a statement. “It is now a standalone nebula inside the superbubble and a grouping of brilliant blue and white stars — known as LH 72 — also managed to form hundreds of millions of years after the events that originally blew up the superbubble.”
Those brilliant stars are quite young — too young to have created the superbubble — but they are responsible for the bright colors in the image. Their radiation is stripping away electrons inside the hydrogen atoms of N55, which makes the gas glow; that vibrant glow is seen as an indication of new stars.
This region will see a lot of upheaval in a few million years, ESO officials added, when some of these young stars begin to go supernova. “In effect, a bubble will be blown within a superbubble, and the cycle of starry ends and beginnings will carry on in this close neighbour of our home galaxy,” they said.
Astronomers using NASA’s Hubble Space Telescope have discovered a moon orbiting Makemake, which is the second-brightest object in the distant Kuiper Belt beyond Neptune. (Pluto is the brightest of these bodies.)
The newfound satellite — the first ever spotted around Makemake — is 1,300 times fainter than the dwarf planet and is thought to be about 100 miles (160 kilometers) in diameter, researchers said. The moon was spotted 13,000 miles (20,900 km) from the surface of Makemake, which itself is 870 miles (1,400 km) wide. [See images of the dwarf planet Makemake]
“Makemake is in the class of rare Pluto-like objects, so finding a companion is important,” Alex Parker of the Southwest Research Institute (SwRI) in Boulder, Colorado, who led the image analysis for the Hubble observations, said in a statement today (April 26).
“The discovery of this moon has given us an opportunity to study Makemake in far greater detail than we ever would have been able to without the companion,” Parker added.
For example, further observations of the moon — which has been provisionally named S/2015 (136472) 1, and nicknamed MK 2 — should allow astronomers to calculate the density of Makemake, which should tell them if the dwarf planet and Pluto are made of similar stuff.
Additional Hubble observations should also reveal the shape of MK 2’s orbit around Makemake. If the orbit is tightly circular, the moon was probably created by a long-ago giant impact, just like the five satellites in the Pluto system were, researchers said. A looping, elliptical orbit, on the other hand, would suggest that MK 2 was once a free-flying Kuiper Belt object that Makemake captured.
The Hubble discovery images suggest that MK 2 is as dark as charcoal, which seems surprising given that Makemake is so bright. One possible explanation is that the moon’s gravity is too weak to hold onto reflective ices, which sublimate off MK 2’s surface into space, researchers said.
Makemake orbits the sun at an average distance of 45.7 astronomical units (AU) and completes one lap around the star every 309 Earth years. (One AU is the Earth-sun distance — about 93 million miles, or 150 million km.) The dwarf planet is even farther away than Pluto, which lies 39.5 AU from the sun on average and orbits once every 248 Earth years.
Makemake is one of five objects officially recognized as a dwarf planet by the International Astronomical Union (IAU). The others are the Kuiper Belt denizens Pluto, Eris and Haumea, and Ceres, which lies in the main asteroid belt between Mars and Jupiter.
Ceres is the only one of these five that doesn’t have at least one moon.
The IAU defines a dwarf planet as an object that orbits the sun and is massive enough to have been forced into a spherical shape by its own gravity but has not “cleared its neighborhood” of other orbiting material. (Pluto falls short on this last count, according to IAU officials, which is why the former ninth planet was reclassified as a dwarf planet in 2006.)
MK 2 was spotted in observations made by Hubble’s Wide Field Camera 3 in April 2015, after several previous Makemake observation campaigns had failed to turn up any satellites.
“Our preliminary estimates show that the moon’s orbit seems to be edge-on, and that means that often when you look at the system you are going to miss the moon because it gets lost in the bright glare of Makemake,” Parker said.
Supermassive black holes are the most extreme objects in the known universe, with masses millions or even billions of times the mass of our sun. Now astronomers have been able to study one of these behemoths inside a strange, distant quasar and they’ve made an astonishing discovery — it’s spinning one-third the speed of light.
Studying a supermassive black hole some 3.5 billion light-years away is no easy feat, but this isn’t a regular object: it’s a quasar that shows quasi-periodic brightening events every 12 years or so — a fact that has helped astronomers reveal its extreme nature.
Quasars are extremely bright accretion disks in galactic cores driven by copious quantities of matter falling into the central supermassive black hole. The vast majority of galaxies are thought to contain supermassive black holes, though modern galaxies have calmed down and quasars no longer shine. But it’s a different story for galaxies that are billions of light-years away.
The object at the center of the strange quasar called OJ287 “weighs in” at 18 billion solar masses and is one of the biggest supermassive (or ultramassive?) black holes in the known universe. Interestingly, it is also one of the most well-studied quasars as it is located very close to the apparent path of the sun’s motion across the sky as seen from Earth — a region where historic searches for asteroids and comets are regularly carried out. Therefore, astronomers have over 100 years of serendipitous brightness data for OJ287, allowing them to predict when the next flaring event would be.
On closer inspection of the flaring events that occurred in recent decades, astronomers realized that rather than a single brightening event occurring every 12 years, the brightening is actually a double peak, providing a clue as to what might be causing it. ANALYSIS: Black Holes Slug it Out in Quasar Deathmatch Mauri Valtonen of University of Turku, Finland, and his international team used several optical telescopes around the world in conjunction with NASA’s SWIFT X-ray space telescope to realize that these 12-year double-brightening events are triggered by a smaller black hole in orbit around OJ287.
Valtonen is the lead author of the study published in the Astrophysical Journal. The massive black hole possesses a very hot accretion disk, a key component of a quasar.
The material accumulates in the disk and gets pulled into the black hole, feeding it. Along the way, the disk material is heated and emits powerful electromagnetic radiation. OJ287’s smaller black hole partner, which itself is still 100 solar masses (still a huge black hole!) has a highly elongated orbit, swinging close to the more massive black hole every 12 years.
During closest approach, the smaller black hole “splashes” into OJ287’s accretion disk once during the incoming swing and once more as it swings around the black hole’s far side, creating 2 distinct flaring events, as this diagram demonstrates: An illustration of the binary black hole system in OJ287. The predictions of the model are verified by observations.
This periodic close encounter stirs up the supermassive black hole’s accretion disk material, rapidly heating it twice in rapid succession. This is what causes OJ287’s strange brightenings every 12 years. With this binary black hole model in mind, the researchers were able to predict when the latest event was due to occur.
The last brightening happened on Nov. 18, 2015, only a few days before Valtonen’s prediction, confirming his team’s binary black hole model. But through these observations, the supermassive black hole’s spin could also be calculated and it’s fast. The team’s observations show that it is spinning at a third of the speed of light. Interestingly, from the historical data of OJ287, the team was also able to calculate how much energy is being lost from the system via gravitational waves. Of course, gravitational waves are currently a very hot topic, having been directly detected for the first time by the US-based Laser Interferometer Gravitational-wave Observatory (LIGO) and announced last month.
That LIGO detection was the signature produced by 2 orbiting and merging black holes, a discovery that not only confirmed one of Einstein’s final predictions of general relativity, but also directly confirmed the existence of 2 black holes merging as one. ANALYSIS: We Just Heard the Spacetime ‘Chirp’ of Black Hole Rebirth Though the gravitational waves of the OJ287 black hole binary are too weak to be detected by the current generation of gravitational wave detectors (as the source is far too distant), the Nov. 18 brightening
This periodic close encounter stirs up the supermassive black hole’s accretion disk material, rapidly heating it twice in rapid succession. This is what causes OJ287’s strange brightenings every 12 years. With this binary black hole model in mind, the researchers were able to predict when the latest event was due to occur.
The last brightening happened on Nov. 18, 2015, only a few days before Valtonen’s prediction, confirming his team’s binary black hole model. But through these observations, the supermassive black hole’s spin could also be calculated and it’s fast. The team’s observations show that it is spinning at a third of the speed of light. Interestingly, from the historical data of OJ287, the team was also able to calculate how much energy is being lost from the system via gravitational waves. Of course, gravitational waves are currently a very hot topic, having been directly detected for the first time by the US-based Laser Interferometer Gravitational-wave Observatory (LIGO) and announced last month. That LIGO detection was the signature produced by 2 orbiting and merging black holes, a discovery that not only confirmed one of Einstein’s final predictions of general relativity, but also directly confirmed the existence of 2 black holes merging as one.
We Just Heard the Spacetime ‘Chirp’ of Black Hole Rebirth Though the gravitational waves of the OJ287 black hole binary are too weak to be detected by the current generation of gravitational wave detectors (as the source is far too distant), the Nov. 18 brightening of the quasar serves as a fitting celebration for Einstein’s theory that he presented almost exactly 100 years before on Nov. 25, 1915.
Infant stars may release bursts of light when they collide with and devour dense clumps of matter that otherwise might have gone on to form planets, new research suggests. The new finding has larger implications for understanding how stars grow and evolve early in their lives — specifically, that stars may grow through chaotic series of violent events, instead of steadily getting larger, as previously thought, the authors of the new work noted.
Stars coalesce from vast clouds of gas and dust, and planets emerge from whirling disks of leftover matter that surround newborn stars. Young stars that are still feeding on their parent clouds are known as protostars, while the disks of material that give rise to planets are known as protoplanetary disks.
Previous research often envisioned protostars growing in a simple manner, steadily accumulating or accreting fuel from surrounding clouds. However, protostars are often far dimmer than expected, given their estimated average rates of accretion. With the new finding, scientists now have evidence that protostars may evolve in an extremely chaotic way, sporadically accreting dense clumps of gas from their surrounding protoplanetary disks.
For the new work, astronomers focused on protostars known as FU Orionis objects. These young stars, also known as FUors, are known to experience dramatic spikes in brightness, the researchers said. Previous work suggested that FUors brightened because their accretion rates suddenly increased by a factor of 1,000 or more, and staying that way for decades or longer. To learn more about these outbursts, scientists used the Subaru Telescope, located at the Mauna Kea Observatories in Hawaii, to analyze four of the 11 confirmed FUors, located between 1,500 and 3,500 light-years from the Milky Way.
The new images of the flaring newborn stars “were surprising and fascinating, and nothing like anything previously observed around young stars,” representativesofthe National Institutes of Natural Sciences (NINS) in Japan said in a statement. (NINS is one of the managing institutions of the National Astronomical Observatory of Japan, where some of the paper’s authors are based.) The researchers discovered “tails” projecting from the protoplanetary material around the young stars, as well as spikes of gas and dust.
The researchers created computer simulations that suggested that the proto-planetary disks of newly formed stars could be gravitationally unstable and can fragment, creating dense clumps of gas that can collide with the stars, helping them grow and creating those bright bursts of light. “We suggest a previously unrecognized evolutionary stage in the formation of stars and protoplanetary disks,” study lead author Hauyu Baobab Liu, an astronomer at the Academia Sinica Institute of Astronomy and Astrophysics in Taipei, Taiwan, told Space.com.
These observations may reveal that clumps of gas and dust fall into the stars (helping them grow) in a more chaotic fashion than once thought. Credit: Science Advances, H. B. Liu This unstable phase of a protostar’s life might last several hundred thousand years, the scientists added. “Although more simulations are required to match the simulations to the observed images, these images show that this is a promising explanation for the nature of FU Ori[onis]outbursts,” NINS representatives said in the statement. The scientists detailed their findings online Feb. 5 in the journal Science Advances.
A powerful greenhouse effect can destroy a planet’s chances of hosting life, a new study suggests.
Until proven otherwise, scientists on Earth assume water is necessary for life to arise on other planets. In the search for life outside the solar system, scientists focus on a “habitable zone” around other stars. Inside such a habitable zone, Earth-like planets are neither too hot nor too cold for liquid water to exist on the surface.
A planet that orbits too close to its sun may become parched because of the solar heat. But now, scientists think an extreme greenhouse effect can also push a planet into dry conditions — similar to what happened on Venus.
The new research shows that warming due to carbon dioxide is as powerful as solar heat due to orbit when it comes to drying out a planet. The modeling study was published today (Feb. 9) in the journal Nature Communications.
“This is interesting because it tells you that you need to know more than just the position of a planet to know whether it might be habitable or not,” said Max Popp, lead author of the study and a postdoctoral researcher at the Max Planck Institute for Meteorology in Hamburg, Germany.
In the case of hot, hellish Venus, water that evaporated from the planet’s surface built up high in the planet’s atmosphere and eventually escaped into space. This is called a “moist greenhouse.” Today, the atmosphere of Venus is almost entirely carbon dioxide. (Earth is able to keep its water because this planet’s upper atmosphere is quite dry.)
To better understand the conditions that trigger such extreme greenhouse effects, Popp and his colleagues created a 3D model of an Earth-like planet that was entirely covered by water. This simulated water-world meant the scientists could ignore the complicated effects of continents and seasons.
The researchers discovered that once carbon dioxide levels in the model reached 1,520 parts per million, the planet’s climate was unstable. The surface temperatures rapidly jumped to about 135 degrees Fahrenheit (57 degrees Celsius), creating a warm, moist greenhouse regime, the study reported. (The measurement means there are 1,520 molecules of carbon dioxide for every 1 million air molecules.)
“A planet like Earth will eventually change to a very warm climate, and it will occur relatively abruptly,” Popp told Live Science.
The researchers think changes in large-scale cloud patterns drive the warm, moist greenhouse effect, Popp said. The location and thickness of cloud cover can change how much solar heat is trapped on a planet.
Although the findings suggest that greenhouse gases can be as lethal for a planet as orbiting too close to a sun, this process would occur at carbon dioxide levels significantly higher than those experienced on Earth today, the researchers said.
Popp said it’s likely impossible for human activity to induce a similar moist greenhouse effect on Earth. To do so, human activity would have to raise the concentration of CO2 in the atmosphere considerably, even more than if all the available fossil fuel reserves were burned, the researchers said.
“This is an idealized study designed to give a comparison between solar [heating] and carbon dioxide,” Popp said. As such, Popp said a similar scenario wouldn’t happen on Earth anytime soon.
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.
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.
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.