There are some things in the universe that you simply can’t escape. Death. Taxes. Black holes. If you time it right, you can even experience all three at once.
Black holes are made out to be uncompromising monsters, roaming the galaxies, voraciously consuming anything in their path. And their name is rightly deserved: once you fall in, once you cross the terminator line of the event horizon, you don’t come out. Not even light can escape their clutches.
But in movies, the scary monster has a weakness, and if black holes are the galactic monsters, then surely they have a vulnerability. Right?
Black holes are strange regions where gravity is strong enough to bend light, warp space and distort time.
In the 1970s, theoretical physicist Stephen Hawking made a remarkable discovery buried under the complex mathematical intersection of gravity and quantum mechanics: Black holes glow, ever so slightly, and, given enough time, they eventually dissolve.
Wow! Fantastic news! The monster can be slain! But how? How does this so-called Hawking Radiation work?
Well, general relativity is a super-complicated mathematical theory. Quantum mechanics is just as complicated. It’s a little unsatisfying to respond to “How?” with “A bunch of math,” so here’s the standard explanation: the vacuum of space is filled with virtual particles, little effervescent pairs of particles that pop into and out of existence, stealing some energy from the vacuum to exist for the briefest of moments, only to collide with each other and return to nothingness.
Every once in a while, a pair of these particles pops into existence near an event horizon, with one partner falling in and the other free to escape. Unable to collide and evaporate, the escapee goes on its merry way as a normal non-virtual particle.
Voila: The black hole appears to glow, and in doing so — in doing the work to separate a virtual particle pair and promote one of them into normal status — the black hole gives up some of its own mass. Subtly, slowly, over the eons, black holes dissolve. Not so black anymore, huh?
Here’s the thing: I don’t find that answer especially satisfying, either. For one, it has absolutely nothing to do with Hawking’s original 1974 paper, and for another, it’s just a bunch of jargon words that fill up a couple of paragraphs but don’t really go a long way to explaining this behavior. It’s not necessarily wrong, just…incomplete.
First things first: “Virtual particles” are neither virtual nor particles. In quantum field theory — our modern conception of the way particles and forces work — every kind of particle is associated with a field that permeates all of space-time. These fields aren’t just simple bookkeeping devices. They are active and alive. In fact, they’re more important than particles themselves. You can think of particles as simply excitations — or “vibrations” or “pinched-off bits,” depending on your mood — of the underlying field.
Sometimes the fields start wiggling, and those wiggles travel from one place to another. That’s what we call a “particle.” When the electron field wiggles, we get an electron. When the electromagnetic field wiggles, we get a photon. You get the idea.
Sometimes, however, those wiggles don’t really go anywhere. They fizzle out before they get to do something interesting. Space-time is full of the constantly fizzling fields.
What does this have to do with black holes? Well, when one forms, some of the fizzling quantum fields can get trapped — some permanently, appearing unfortunately within the newfound event horizon. Fields that fizzled near the event horizon end up surviving and escaping. But due to the intense gravitational time dilation near the black hole, thy appear to come out much, much later in the future.
In their complex interaction and partial entrapment with the newly forming black hole, the temporary fizzling fields get “promoted” to become normal everyday ripples — in other words, particles.
So, Hawking Radiation isn’t so much about particles opposing into existence near a present-day black hole, but the result of a complex interaction at the birth of a black hole that persists until today.
One way or the other, as far as we can tell, black holes do dissolve. I emphasize the “as far as we can tell” bit because, like I said at the beginning, generality is all sorts of hard, and quantum field theory is a beast. Put the two together and there’s bound to be some mathematical misunderstanding.
But with that caveat, we can still look at the numbers, and those numbers tell us we don’t have to worry about black holes dying anytime soon. A black hole with the mass of the sun will last a wizened 10^67 years. Considering that the current age of our universe is a paltry 13.8 times 10^9 years, that’s a good amount of time. But if you happened to turn the Eiffel Tower into a black hole, it would evaporate in only about a day. I don’t know why you would, but there you go.
A giant blob of gas and dust far off in the universe mysteriously glows bright green, and astronomers have finally figured out why. Two huge galaxies were observed in the blob’s core, and they’re surrounded by a swarm of smaller galaxies in what appears to be the birth of a massive cluster of galaxies.
Astronomers spotted the blob’s central galaxies using the Atacama Large Millimeter/submillimeter Array (ALMA) and the Very Large Telescope at the European Southern Observatory in Chile. The glowing space blob was first discovered in 2000, and the source of its light has been a mystery ever since.
One study published in 2011 suggested that polarized light emitted by the blob could have come from hidden galaxies. The new observations with ALMA and VLT allowed researchers to pinpoint two big galaxies as the sources of this light.
Further observations by the Hubble Space Telescope and the Keck Observatory in Hawaii revealed the swarm of small, faint galaxies surrounding the bigger two in the heart of the blob. Here, galaxies are forming stars at 100 times the rate of the Milky Way.
A giant green “space blob” – called the Lyman-alpha blob LAB-1 – is seen in this composite of two different images taken by the Very Large Telescope in Chile. The LAB-1 space blob is 300,000 light-years across, making it one of the largest known single objects in the universe.
Credit: ESO/M. Hayes
“For a long time, the origin of the extended Lyman-alpha light has been controversial,” Jim Geach, the study’s lead author, said in a statement. “But with the combination of new observations and cutting-edge simulations, we think we have solved a 15-year-old mystery.”
So-called “Lyman-alpha blobs” are some of the biggest things in space. This particular space blob, named SSA22-Lyman-alpha Blob 1 (LAB-1), is the largest of its kind. It measures about 300,000 light-years across, or three times the size of the Milky Way galaxy.
LAB-1 is located 11.5 billion light-years from Earth, so the light we observe from it is almost as old as the universe (13.8 billion years). This means that looking at LAB-1 provides a window into the early history of the universe.
Lyman-alpha blobs consist mainly of hydrogen gas and emit a particular wavelength of ultraviolet light called Lyman-alpha radiation. The light looks green to viewers on Earth, because its wavelength is stretched by the expanding universe during its long trip here.
This is a snapshot from a computer simulation of the evolution of a Lyman-alpha Blob similar to LAB-1. Gas within the dark matter halo is color- coded so that cold gas (mainly hydrogen) appears red and hot gas appears white. At the center of this system are two star-forming galaxies surrounded by hot gas and many smaller satellite galaxies that appear as small red clumps.
Once they had observed the sources of light from within the blob, the researchers created simulations of galaxy formation using NASA’s Pleiades supercomputer. They wanted to show that ultraviolet light — a byproduct of star formation — scatters off hydrogen gas to create a bright, glowing mega-blob like LAB-1.
“Think of a streetlight on a foggy night — you see the diffuse glow because light is scattering off the tiny water droplets,” Geach said in the same statement. “A similar thing is happening here, except the streetlight is an intensely star-forming galaxy and the fog is a huge cloud of intergalactic gas. The galaxies are illuminating their surroundings.”
The simulations also track gas and dark matter in the blob as it evolves into a galaxy. “Lyman-alpha Blob-1 is the site of formation of a massive elliptical galaxy that will one day be the heart of a giant cluster,” Geach added
Monster black holes can be millions of times more massive than the sun. If a star happens to wander too close, the black hole’s extreme gravitational forces can tear the star into shreds, in an event called “stellar tidal disruption.”
This kind of stellar destruction may also spit out a bright flare of energy in the form of ultraviolet and X-ray light. The two new studies examine how surrounding dust absorbs and re-emits the light from those flares, like a cosmic echo, according to a statement from NASA’s Jet Propulsion Laboratory (JPL).
“This is the first time we have clearly seen the infrared-light echoes from multiple tidal disruption events,” Sjoert van Velzen, a postdoctoral fellow at Johns Hopkins University and lead author of one study, said in the statement.
The new studies use data from NASA’s Wide-field Infrared Survey Explorer (WISE). The NASA study led by van Velzen used these “echoes” to identify three black holes in the act of devouring stars. The second study, led by Ning Jiang, a postdoctoral researcher at the University of Science and Technology of China, identified a potential fourth light echo.
Flares emitted from stellar tidal disruptions are extremely energetic and “destroy any dust” that is within the immediate neighborhood, according to NASA. However, a patchy, spherical web of dust that resides a few trillion miles (half a light-year) from the black hole can survive the flare and absorb light released from the star being gobbled up
“The black hole has destroyed everything between itself and this dust shell,” van Velzen said in the statement. “It’s as though the black hole has cleaned its room by throwing flames.”
The absorbed light heats the more distant dust, which in turn gives off infrared radiation that the WISE instrument can measure. These emissions can be detected for up to a year after the flare is at its brightest, the statement said. Scientists are able to characterize and locate the dust by measuring the delay between the original light flare and the subsequent echoes, according to the NASA study, which will be published in the Astrophysical Journal.
“Our study confirms that the dust is there, and that we can use it to determine how much energy was generated in the destruction of the star,” Varoujan Gorjian, an astronomer at JPL and co-author of the paper led by van Velzen, said in the statement.
Many supermassive black holes in the centers of galaxies possess a thick ring of material known as a torus. Appearing like a supersized doughnut, astronomers have long thought that these features were created by churned-up material from the galactic core itself, falling into the black hole’s gravitational well.
However, according to powerful new observations by the the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, this conventional model is, apparently, far too simple.
While studying the environment surrounding the supermassive black hole in the core of the barred spiral galaxy NGC 1068 47 million light-years away, ALMA was able to track clouds of material being flung outwards by the black hole, creating its own torus rather than material falling in.
WATCH VIDEO: The Race To See The Black Hole At Our Galaxy’s Core
“Think of a black hole as an engine,” said astronomer Jack Gallimore, of Bucknell University in Lewisburg, Pennsylvania, in a statement. “It’s fueled by material falling in on it from a flattened disk of dust and gas. But like any engine, a black hole can also emit exhaust.”
Black holes consuming matter possess accretion disks, which are basically flat and hot features that swirl around the black hole’s event horizon. The innermost section of the accretion disk is so hot that it generates X-ray and ultraviolet radiation, but further out, the disk is cooler and emits infrared and millimeter wavelength radiation. ALMA is very sensitive to the latter, allowing the observatory to track the motion of the gases in the outermost portion of NGC 1068’s accretion disk.
The torus of material harboring the supermassive black hole is highlighted in the pullout box. This region, which is approximately 40 light-years across, is the result of material flung out of the black hole’s accretion disk.
While following cool clouds of carbon monoxide gas inside this cooler accretion disk region, Gallimore’s team saw the clouds lift off the disk. As they become ionized by the superheated portion of the accretion disk, the clouds started to interact with the black hole’s powerful magnetic field. The gas was then flung away from the accretion disk at high speed, far faster than the rotational speed of the disk itself.
“These clouds are traveling so fast that they reach ‘escape velocity’ and are jettisoned in a cone-like spray from both sides of the disk,” said Gallimore. “With ALMA, we can for the first time see that it is the gas that is thrown out that hides the black hole, not the gas falling in.”
The vast majority of galaxies are known to contain supermassive black holes in their cores. They have a symbiotic relationship and the activity of black holes are known to have a powerful influence over the galaxies as a whole, even impacting the rate of star formation. Now, with observatories like ALMA, we’re beginning to see the intricacies of this relationship and their impact on the hearts of galaxies.
A star’s mysterious evolution recently came to light using the Hubble Space Telescope, which spotted the star cooling after a rapid temperature increase in the past. Th find is all the more extraordinary given that this sort of process usually exceeds a human lifetime, according to astronomers.
The researchers explained the process behind the rebirth of the star (called SAO 244567) in this new animation.
“SAO 244567 is one of the rare examples of a star that allows us to witness stellar evolution in real time,” Nicole Reindl, a postdoctoral researcher from the University of Leicester in the U.K. who led the study, said in a statement. “Over only 20 years the star has doubled its temperature, and it was possible to watch the star ionizing its previously ejected envelope [of dust and gas], which is now known as the Stingray Nebula.”
Astronomers have seen many changes in the star, which is 7,000 light-years from Earth, in the past 45 years. Between 1971 and 2002, they saw the surface temperature of the star increase by almost 72,000 degrees Fahrenheit (40,000 degrees Celsius). But the new observations with Hubble’s cosmic origins spectrograph reveal that the star is cooling and expanding.
In 2014, Reindl’s team proposed that SAO 244567 — whose low mass makes it hard to explain the rapid temperature fluctuations — may have just undergone a “helium-shell flash event,” which happens when helium briefly ignites outside the heart, or core, of the star. Once the heating flash completes, SAO 244567 should regress in its evolution and cool. The new observations suggest this 2014 theory was correct, Reindl said in the same statement.
“The release of nuclear energy by the flash forces the already very compact star to expand back to giant dimensions — the born-again scenario,” Reindl said.
She added that the team will need to refine their calculations to better explain SAO 244567’s behavior, which can’t be accounted for in current models of star evolution.
Hundreds of black holes could be lurking inside a cluster of stars that orbits the Milky Way galaxy, a new study shows.
NGC 6101 is a globular cluster (a dense, spherical collection of ancient stars) orbiting the center of the Milky Way. Using computer models, scientists recently showed that some strange characteristics of NGC 6101 could be explained by the presence of hundreds of black holes — something scientists have never observed in a globular cluster.
Black holes can form when massive stars die in a fiery explosion called a supernova. This type of blast is thought to kick the black hole away from its birth site, according to Mark Gieles, a professor of astrophysics at the University of Surrey in England and one of the authors of the new study. But the existence of so many black holes within the globular cluster would suggest that these “kicks” are not as powerful as scientists previously thought, Gieles said in a video detailing the new work.
Finding black holes is difficult, because astronomers can’t see them the same way they can see stars and other objects in the universe. That’s because black holes are so dense that not even light can escape the pull of their gravity.
While black holes may be difficult to spot, computer simulations can help predict where they might be hiding. Gieles and colleagues at the University of Surrey were inspired to create simulations of NGC 6101 after another group published their observations of the cluster last year.
The cluster’s structure didn’t make sense at first. Usually, in globular clusters, heavy stars move to the center, while lightweight stars tend to migrate to the periphery — a process known as “mass segregation.” But NGC 6101 has very few stars near its center. “We found that this is not at all what you would expect for a normal stellar system,” Gieles said in the video about the study.
“It reminded us of previous work where we looked at the influence black holes can have on globular clusters, and we had the idea, ‘Maybe we could explain it by simply putting some black holes into the cluster,'” Miklos Peuten, a Ph.D student in astrophysics at the University of Surrey and lead author of the research paper, said in the same video.
To make sense of the missing mass segregation, the team recreated the entire 13-billion-year evolution of the cluster. Without black holes, the simulation didn’t match their real observations of the system. But once they threw black holes into the mix, their simulations matched their observations perfectly. Black holes could be the missing piece of the NGC 6101 puzzle.
“The next step would be to look at other globular clusters which also have strange profiles” and see if black holes can explain those as well, Peuten said in the video, adding that this “would help us to understand how black holes are created and how black holes evolve.”
The star, located almost 11,000 light-years from Earth, has a mass 30 times that of the sun, and it’s still growing. Astronomers found that this star is still in the process of collecting material from its parent cloud of gas and dust, which means it is only a baby in cosmic terms and is expected to be even more massive by the time it grows up, according to a statement from the University of Cambridge, where the research was conducted. A young star such as this is also known as a protostar.
Due to their incredibly large size, protostars such as this are difficult to locate in Earth’s galaxy (the Milky Way) and are hard to study because they live fast and die young and are generally very far away.
“An average star like our sun is formed over a few million years, whereas massive stars are formed orders of magnitude faster — around 100,000 years,” John Ilee, lead author of the study from Cambridge’s Institute of Astronomy, said in the statement. “These massive stars also burn through their fuel much more quickly, so they have shorter overall life spans, making them harder to catch when they are infants.”
But the astronomers behind the new work were able to do just that: catch the star during a key stage of its birth. Their findings revealed that massive stellar bodies like this form from rotating discs of gas and dust, also known as the stars’ parent clouds. This process is very similar to the way that much smaller stars like Earth’s sun form, astronomers said in the statement.
Using the Submillimeter Array (SMA) in Hawaii and the Karl G. Jansky Very Large Array (VLA) in New Mexico, the astronomers found that the new protostar lives in an infrared dark cloud, which is an ideal region for star formation because it is very cold and dense.
With thick surrounding clouds of gas and dust, these areas are generally difficult to observe using telescopes. However, the astronomers were able to peer through the clouds and measure the radiation emitted from the dust around the star and its chemical signatures. Their findings revealed the presence of a “Keplerian” disc that’s rotating more quickly at its center.
“This type of rotation is also seen in the solar system — the inner planets rotate around the sun more quickly than the outer planets,” Ilee explained. “It’s exciting to find such a disc around a massive young star, because it suggests that massive stars form in a similar way to lower-mass stars, like our sun.”
The new findings were published Aug. 9 in the Monthly Notices of the Royal Astronomical Society.
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.
There may be an alien planet lurking within Earth’s own solar system.
If the hypothetical Planet Nine does indeed exist, the sun probably ripped the world away from another star long ago, a new study suggests.
“It is almost ironic that while astronomers often find exoplanets hundreds of light-years away in other solar systems, there’s probably one hiding in our own backyard,” study lead author Alexander Mustill, an astronomer at Lund University in Sweden, said in a statement. [The Evidence for Planet Nine in Pictures]
Earlier this year, astronomers Konstantin Batygin and Mike Brown, both of the California Institute of Technology in Pasadena, announced the possible existence of Planet Nine, a world perhaps 10 times as massive as Earth that’s thought to lie in the outer solar system, far beyond Pluto’s orbit.
Nobody has seen Planet Nine; Batygin and Brown inferred its existence from the odd orbits of a half-dozen small bodies in the frigid zone beyond Neptune known as the Kuiper Belt.
Some scientists around the world are looking for Planet Nine through a variety of telescopes, while others are trying to figure out where it came from (if the planet does indeed exist).
Some researchers think Planet Nine probably formed within the solar system. The world coalesced closer to the sun than it currently lies and was booted to the far outer reaches by some kind of gravitational interaction, the idea goes.
But the new study, which reports the results of computer modeling work, supports a more exotic origin story: Planet Nine was likely stolen from another star about 4.5 billion years ago, when the sun and many other members of its stellar birth cluster were in close proximity to each other, Mustill and his colleagues said.
“When the sun later departed from the stellar cluster in which it was born, Planet Nine was stuck in an orbit around the sun,” Mustill said.
More work will be required to firm up this hypothesis, the researchers stressed; after all, the existence of Planet Nine is still an open question. (A long-ago capture would likely have left an “imprint” on some small objects beyond Neptune, so further study of these bodies could shed light on Planet Nine’s formation, the researchers wrote.)
But if Mustill and his colleagues are right, Planet Nine could be an even more interesting place than scientists had imagined.
“This is the only exoplanet that we, realistically, would be able to reach using a space probe,” Mustill said.
The new study was published online last month in the journal Monthly Notices of the Royal Astronomical Society. You can read an abstract for free here: http://mnrasl.oxfordjournals.org/content/460/1/L109
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.
It’s unclear whether Planet Nine exists, but astronomers are already digging into the mystery of the hypothetical world’s birth.
In January, Konstantin Batygin and Mike Brown of the California Institute of Technology in Pasadena announced that they had inferred the existence of Planet Nine based on the strange orbits of a half dozen small bodies in the Kuiper Belt beyond Neptune.
Planet Nine, Batygin and Brown suggested, is perhaps 10 times more massive than Earth and orbits the sun at an average distance of about 700 astronomical units (AU). (One AU is the Earth-sun distance — 93 million miles, or 150 million kilometers.) [The Evidence for Planet Nine in Pictures]
Some astronomers are now scanning the sky in an attempt to find the putative planet, while others are tackling another mystery: How did Planet Nine come to be?
There are a number of possible origin stories, researchers say. For example, Planet Nine may be a former exoplanet that was captured by our solar system’s gravity.
This scenario appears to be far-fetched, however. Gongjie Li and Fred Adams, both of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, performed computer simulations to estimate the odds that Planet Nine was plucked from a passing star system or nabbed as a formerly free-floating “rogue planet.” In both cases, the odds are less than 2 percent, the researchers report in a new study
So it’s likely that Planet Nine is native to our solar system. But did it form in its present location, or begin life much closer to the sun and then get booted into the outer solar system by a gravitational interaction of some kind?
Both scenarios are possible, Scott Kenyon, of the CfA, and Benjamin Bromley, of the University of Utah, report in two new studies of their own, which are also based on computer modeling work.
Given the right initial conditions, Planet Nine could have coalesced near where it’s now thought to lie within 1 billion to 2 billion years of the solar system’s birth, Kenyon and Bromley found. But their simulations also give credence to the idea that interactions with Jupiter and Saturn kicked Planet Nine out from a formerly tighter orbit.
“Think of it like pushing a kid on a swing: If you give them a shove at the right time, over and over, they’ll go higher and higher,” Kenyon said in a statement, adding that this scenario is “the simplest solution.”
The gravitational boot, if it occurred, didn’t have to come from a fellow planet. In their paper, Li and Adams also considered the possibility that Planet Nine was tugged outward by one of the sun’s stellar neighbors. But their simulations pegged the probability of this scenario at 10 percent at best, suggesting that, in most cases, a passing star would have kicked Planet Nine out of our solar system completely.
So the fog of mystery surrounding Planet Nine remains thick. But that fog could clear someday, provided that this mysterious world actually exists — and astronomers are able to get a decent look at it.
“The nice thing about these scenarios is that they’re observationally testable,” Kenyon said. “A scattered gas giant will look like a cold Neptune, while a planet that formed in place will resemble a giant Pluto with no gas.”
The study by Li and Adams has been accepted for publication in The Astrophysical Journal Letters. Kenyon and Bromley have submitted their two papers to The Astrophysical Journal.
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.
Stephen Hawking, Yuri Milner and Mark Zuckerberg helm the board for a new initiative, Breakthrough Starshot, whose technology could be used to someday reach Earth’s neighboring star Alpha Centauri after just a 20-year journey. Besides being an easy target — it’s among the closest stars to the sun — astronomers have been eying our stellar neighbors for potential Earth-like planets.
“This is Alpha Centauri, our neighboring star,” Milner said in a news conference yesterday (April 12). “But in space, neighboring does not mean very near. Alpha Centauri is over 4 light-years away […] that’s 25 trillion miles. And the problem is, space travel as we know it is slow. If [humanity’s fastest-moving spacecraft] Voyager had left our planet when humans first left Africa, travelling at 11 miles a second, it would be arriving at Alpha Centauri just about now
Milner said that his proposed Starshot technology could get a tiny spacecraft to the system, traveling at 20 percent the speed of light, in around 20 years. But barring that, it would be a long trip indeed.
The stars of Alpha Centauri lie 4.3 light-years from us, which is around 270,000 times the distance from the Earth to the sun. Milner said that to travel that distance within a generation, a chemical rocket like the ones we use today would need fuel equivalent to the weight of all the stars in the Milky Way. A fusion rocket could reach the system in 50 years, but the technology is still far from viable. His proposed Starshot technology could make it there in 20.
This chart shows most of the stars visible with the unaided eye on a clear night. The star Alpha Centauri is one of the brightest stars in the southern sky (marked with a red circle). It lies just 4.3 light-years from the Earth and one component in a triple star system. Image released Oct. 17. 2012.
Astronomers have discovered an Earth-size planet orbiting one of the nearest stars in our galaxy. Learn more about Alpha Centauri in our full infographic.
From Earth, Alpha Centauri appears as a single point of light: It’s one of the brightest stars in the southern sky. Through a telescope, one can make out the system’s two stars Alpha Centauri A and its smaller, dimmer companion Alpha Centauri B. Each has a mass that is about the same as the Earth’s sun, and they orbit one another at about the same distance that Uranus orbits the sun.
A third star, Proxima Centauri, is slightly closer to Earth — it’s actually the nearest star outside the Earth’s solar system. That star is much smaller and dimmer: it’s just 0.12 times the mass of the sun, or 1.5 times the size of Jupiter, and it shines faintly at a cautious distance from the other two. In fact, some astronomers question whether it’s part of the system at all, or just passing through.
Astronomers first realized the bright star Alpha Centauri was a tightly orbiting pair in 1689, and Proxima Centauri was first spotted in 1915.
In 2012, researchers used an instrument called the High Accuracy Radial velocity Planet Searcher to detect a planet around Alpha Centauri B. The instrument, which is part of the European Space Agency’s La Silla Observatory in Chile, measured tiny wobbles in the star that suggested that a planet was orbiting it — likely just a bit bigger than Earth, orbiting its star every 3.24 days.
Since then, researchers have tried to verify the planet’s existence using transits — a slight dimming in the star as the planet passes by — but haven’t found additional, conclusive evidence. And a re-examination of the original study suggested that the planet might be an artifact of the data processing, according to a report by the deep-space exploration site Centauri Dreams.
Regardless, because of their nearness, the Alpha Centauri twins and Proxima Centauri offer a promising location to look for planets at a distance — especially using direct imaging — if researchers can filter out the complexities of the double star. And they also seem to be a good place to visit. The distance may be vast, but it could be relatively easy for Starshot’s nanocraft or other interstellar travelers to blast through and beam back information to Earth about the system with a bit more than a four-year delay. While planets orbiting those stars would see a starscape that is quite different from Earth’s, the stars’ similarity to the sun would make their habitable zones an intriguing place to look for Earth analogues.
“Astronomers estimate that there is a reasonable chance of an Earth-like planet existing in the ‘habitable zones’ of Alpha Centauri’s three-star system,” Breakthrough Starshot representatives said in a statement. “A number of scientific instruments, ground-based and space-based, are being developed and enhanced, which will soon identify and characterize planets around nearby stars.”
And then it could be time to go take a look.
The hunt is on to find “Planet Nine” — a large undiscovered world, perhaps 10 times as massive as Earth and four times its size — that scientists think could be lurking in the outer solar system. After Konstantin Batygin and Mike Brown, two planetary scientists from the California Institute of Technology, presented evidence for its existence this January, other teams have searched for further proof by analyzing archived images and proposing new observations to find it with the world’s largest telescopes. Just this month, evidence from the Cassini spacecraft orbiting Saturn helped close in on the missing planet.
Many experts suspect that within as little as a year someone will spot the unseen world, which would be a monumental discovery that changes the way we view our solar system and our place in the cosmos. “Evidence is mounting that something unusual is out there — there’s a story that’s hard to explain with just the standard picture,” says David Gerdes, a cosmologist at the University of Michigan who never expected to find himself working on Planet Nine.
He is just one of many scientists who leapt at the chance to prove — or disprove — the team’s careful calculations. Batygin and Brown made the case for Planet Nine’s existence based on its gravitational effect on several Kuiper Belt objects — icy bodies that circle the sun beyond Neptune’s orbit. Theoretically, though, its gravity should also tug slightly on the planets, moons and even any orbiting spacecraft. With this in mind, Agnès Fienga at the Côte d’Azur Observatory in France and her colleagues checked whether a theoretical model (one that they have been perfecting for over a decade) with the new addition of Planet Nine could better explain slight perturbations seen in Cassini’s orbit. Without it, the eight planets in the solar system, 200 asteroids and five of the most massive Kuiper Belt objects cannot perfectly account for it. The missing puzzle piece might just be a ninth planet. So Fienga and her colleagues compared the updated model, which placed Planet Nine at various points in its hypothetical orbit, with the data. They found a sweet spot—with Planet Nine 600 astronomical units (about 90 billion kilometers) away toward the constellation Cetus — that can explain Cassini’s orbit quite well.
Although Fienga is not yet convinced that she has found the culprit for the probe’s odd movements, most outside experts are blown away. “It’s a brilliant analysis,” says Greg Laughlin, an astronomer at Lick Observatory, who was not involved in the study. “It’s completely amazing that they were able to do that so quickly.” Gerdes agrees: “That’s a beautiful paper.” The good news does not end there. If Planet Nine is located toward the constellation Cetus, then it could be picked up by the Dark Energy Survey, a Southern Hemisphere observation project designed to probe the acceleration of the universe. “It turns out fortuitously that the favored region from Cassini is smack dab in the middle of our survey footprint,” says Gerdes, who is working on the cosmology survey. “We could not have designed our survey any better.”
Although the survey was not planned to search for solar system objects, Gerdes has discovered some (including one of the icy objects that led Batygin and Brown to conclude Planet Nine exists in the first place). Laughlin thinks this survey has the best immediate chance of success. He is also excited by the fact that Planet Nine could be so close. Although 600 AUs—roughly 15 times the average distance to Pluto—does sound far, Planet Nine could theoretically hide as far away as 1,200 AUs. “That makes it twice as easy to get to, twice as soon,” Laughlin says. “And not just twice as bright but 16 times as bright.”
And the Dark Energy Survey is not the only chance to catch the faint world. It should be possible to look for the millimeter-wavelength light the planet radiates from its own internal heat. Such a search was proposed by Nicolas Cowan, an exoplanet astronomer at McGill University in Montreal, who thinks that Planet Nine might show up in surveys of the cosmic microwave background (CMB), the pervasive afterglow of the big bang. “CMB experiments have historically used solar system giant planets to calibrate their instruments, so we know that current and planned CMB experiments are sensitive enough to measure the flux from Planet Nine if it is as bright as we think it is,” Cowan says. Already, cosmologists have started to comb through data from existing experiments, and astronomers with many different specialties have also joined in on the search. “I love that we can take this four-meter telescope and find a rock 100 kilometers in diameter that is a billion kilometers past Neptune with the same instrument that we are using to do extragalactic stuff and understand the acceleration of the universe,” Gerdes says. In the meantime Batygin and Brown are proposing a dedicated survey of their own.
In a recent study they searched through various sky maps to determine where Planet Nine cannot be. “We dumpster-dived into the existing observational data to search for Planet Nine, and because we didn’t find it we were able to rule out parts of the orbit,” Batygin says. The zone where the planet makes its farthest swing from the sun as well as the small slice of sky where Fienga thinks the planet could be now, for example, have not been canvassed by previous observations. To search the unmapped zones, Batygin and Brown have asked for roughly 20 observing nights on the Subaru Telescope on Mauna Kea in Hawaii. “It’s a pretty big request compared to what other people generally get on the telescope,” Brown says. “We’ll see if they bite.” If they do, Brown is convinced he will have his planet within a year. “I really want to see what it looks like,” says Batygin, who adds that his aspiration drives him to search for the unseen world. But Laughlin takes it a step further: “I think [the discovery] would provide amazing inspiration for the next stage of planetary exploration,” he says. We now have another opportunity to see one of the worlds of our own solar system for the first time. “If Planet Nine isn’t out there, we won’t have that experience again.”