In less time than it takes you to get ready for work, some X-ray emitting space objects become hundreds of times brighter than usual, then dim back down. But what those objects are, astronomers haven鈥檛 yet figured out.

In 2003 and 2007, scientists detected two near a galaxy called NGC 4697. No one had found anything like them before or since 鈥� until astronomer at the University of Alabama in Tuscaloosa announced today that his team has caught two more such flares.

Irwin鈥檚 team originally planned to search through data from the to find star-sized black holes in groups of old stars around other galaxies. These black holes can up their X-ray emissions by a factor of five to 10 in around an hour as material swirls around the point of no return and gives off energy.

鈥淏ut we found these extreme objects that varied by factors of 100 to 200,鈥� says Irwin. 鈥淪o it was a bit of an accident that we found the flares, as we were not originally looking for something so spectacular.鈥�

In earlier X-ray observations of 70 galaxies, they found two such sources, around galaxies NGC 4636 and NGC 5128. The mystery objects both flared up in seconds and dimmed back to baseline X-ray brightness in about an hour. One erupted five times while telescopes happened to be watching, which means it probably acts up about every 1.8 days.

Excitable emitters

These new observations are very similar to the original flare spotted in 2003 and 2007, meaning their sources are probably similar objects.

鈥淭here鈥檚 a lot of consistency there, and that鈥檚 well-documented,鈥� says at the Harvard-Smithsonian Center for Astrophysics. 鈥淭hat opens up the mystery for everyone, which is, 鈥榃hat are they?鈥� 鈥�

Irwin and colleagues present a few ideas. Maybe they鈥檙e intermediate-mass black holes 鈥� which are rare and not well understood 鈥� devouring a meal. Or they could be neutron stars rapidly stealing material from a nearby companion.

鈥淚 think that people over the next weeks and months will come up with even more suggestions,鈥� DiStefano says, and then do the necessary work to distinguish between the possibilities.

Whatever these excitable emitters are, the Milky Way doesn鈥檛 have anything like them, so we will just have to get to know the neighbours.

The most powerful explosions in the universe may be shot out of a cannon. A long-term look at the brightest gamma-ray burst in the past 30 years suggests that the standard model of how these blasts work is flawed.

A new theory of how they work, dubbed the cannonball model, is challenging the traditional explanation, known as the fireball model.

Gamma-ray bursts, which were first discovered in the 1970s, appear to come from random spots in the sky about once per day. They can release more energy in a few seconds than the sun will in its expected 10-billion-year lifespan.

All this power could wreak havoc on Earth: gamma-ray bursts have been linked to mass extinctions, and may have catalysed genetic mutations that help life to diversify. But to understand how these flashes have shaped the cosmos, scientists need to understand exactly how they work.

These explosions are thought to happen when massive stars collapse into black holes, and when ultra-dense stars crash into each other and become one object. They then fade in a period known as the afterglow, during which they emit other kinds of radiation, such as X-rays. But the details of how they generate this radiation remain fuzzy.

Fires or cannons?

The standard explanation, called the fireball model, involves the doomed stars ejecting a violent jet of cone-shaped plasma shells. These travel at different speeds and overtake each other like racehorses, colliding violently and emitting gamma rays as they do.

The shells then barrel into the diffuse space between stars, creating two shock waves that move in opposite directions. Those shock waves radiate the afterglow.

But an underdog model, known as the cannonball, has the radiation originating from a sphere rather than a cone. In this model, fast-moving balls of plasma, called plasmoids, shoot from a star as it dies. When the electrons of these plasmoids encounter radiation from the star鈥檚 death throes, they boost it up to gamma-ray energies, creating the burst.

The plasmoids then merge and sweep up charged particles, which they accelerate with their magnetic field. That acceleration powers the afterglow radiation, similar to how particle accelerators work on Earth.

Burst models

Now, of the Israel Institute of Technology in Haifa 鈥� one of the authors of the cannonball model 鈥� and his colleagues have applied both models to an exceptional gamma-ray burst called GRB 130427A, which went off in April 2013 and lasted an unprecedented 20 hours.

The team analysed two and a half years of observations from the Chandra and XMM-Newton X-ray telescopes that showed how the burst鈥檚 afterglow faded over time. Both models give specific predictions about how the afterglow should look, and Dar and his colleagues claim their cannonball model works better.

In particular, this burst does not show a 鈥渏et break鈥� 鈥� a period of rapid fading of X-rays that the fireball model predicts. The scientists also examined 28 other bright bursts, and say their model works with these too.

But the cannonball model creates new problems, such as uncertainties over how the plasmoids form. And of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, raises another reason for scepticism: most research on this model comes from its creators, and it may seem to work better simply because it has been studied less.

Dar counters that scientists should look long-term at lots of gamma-ray bursts and let the two models go head to head. 鈥淕amma-ray-burst theory should be judged by confronting its key falsifiable predictions with observations rather than by consensus and prejudices,鈥� he says.

Journal reference:听

If habitable planets can form inside globular clusters, they would make nice homes for advanced civilisations that talk to each other and travel between the stars.

Globular clusters are dense clumps of stars, with about a million suns packed into a sphere some 100 light years across. They formed early in the Milky Way鈥檚 history, around 10 billion years ago. Previously, astronomers had dismissed the possibility that they could host inhabited planets, because their old stars lack planet-building heavy elements and the close proximity of the neighbours could destabilise the orbits of any planets that did form.

But according to a new computer model, such clusters possess a 鈥渟weet spot鈥� where small stars can hang on to planets in their habitable zones, where temperatures are right for liquid water and perhaps life. These stars are so close together that hypothetical civilisations wouldn鈥檛 have to go as far to travel between the stars as humans would have to.

Tightly packed

鈥淚n this region, planetary systems in habitable zones of stars can survive,鈥� says of the Harvard-Smithsonian Center for Astrophysics, who presented the work at a meeting of the in Kissimmee, Florida today. 鈥淎nd yet it鈥檚 dense enough that it may facilitate interstellar travel.鈥�

We currently know of just one planet inside a globular cluster, in the cluster known as M4. But that could partly be because planets are hard to find amid the bright glow of the closely packed stars, Di Stefano says.

Her team also points out that planets exist around stars that have just a tenth the amount of heavy elements as the sun does, and while the puffy giants like Jupiter tend to form around metal-rich stars, Earth-sized planets don鈥檛 show the same preference.

Their simulations indicate that in the sweet-spot, habitable-zone planets could remain in stable, liveable orbits around their home stars, resisting the gravitational tugs from other nearby stars.

The stars now left in globular clusters are low-mass, meaning they live slow and die old. That longevity could give life a chance to get a foothold and then evolve over long periods of time, potentially developing advanced technology.

Trip to the stars

Any tech-savvy residents could embark into space to set up outposts in nearby systems, or try to communicate with others (if they exist) on short timescales.

In the crowded space, a message sent from aliens around one star to its closest stellar neighbour would arrive in just two weeks. If they wanted to take a one-way trip to the nearest star at 1听percent of the speed of light, that journey would take just 4.2 years.

Di Stefano called this an opportunity to look for broadcasts or other technological signals from intelligent civilisations.

, the former head of SETI research at the SETI Institute in Mountain View, California, considers that a possibility. 鈥淭here are only a small number of globular clusters, they are closer than galaxies, and they fit in the field of view of the ,鈥� she says, referring to the Institute鈥檚 dedicated alien-hunting telescopes in Hat Creek, California. 鈥淚t wouldn鈥檛 be a huge project to look at all that are visible from Hat Creek and see what鈥檚 there.鈥�

Image credit: ESA/Hubble and NASA

It鈥檚 the ultimate alternative energy source. Some of the mysterious radio signals flashing far outside our galaxy may be powered by cosmic batteries. Black holes and neutron stars may hook up into a kind of circuit just before they collide, producing ultra-short, ultra-bright blasts of radio waves.

Astronomers first detected a fast radio burst (FRB) in 2007 鈥� a big flash that released more energy in a few milliseconds than the sun does in a month. Since then, we have found 10 more. Their origins remained a mystery, with theories ranging from star flares to messages from ET.

Now a study suggests that some of the bursts come from black holes in orbit with neutron stars, the dense cores of collapsed stars. When these duos spiral towards each other, their close approach creates a sort of battery, which creates the power that sends these strange bursts into space.

Light bulb moment

In this scenario, the black hole passes within its companion neutron star鈥檚 magnetic field, and the two link up form a circuit. The motion from both objects鈥� orbits and spins generates an electric current, which flows along the magnetic field lines that stretch between them.

鈥淚f you hold a disconnected light bulb and wave a magnet around, you can turn on the light,鈥� says of Columbia University in New York. 鈥淲aving magnetic fields create electricity. The black hole battery works similarly.鈥�

The neutron star鈥檚 鈥渨aving鈥� magnetic field generates electricity, and plasma carries electric current along the field lines. As the charged plasma particles travel along the field lines, the area lights up in radio waves.

As the black hole and neutron star spiral closer, the battery鈥檚 power grows. In the few milliseconds just before the merger, the 鈥渂ulb鈥� suddenly lights up super-bright. From far away, the radio waves from that final countdown appear as a sudden burst.

Cosmic fingerprint

Unlike other FRBs, these would have a distinct fingerprint 鈥� a preview of dimmer radio waves followed by two peaks in brightness 鈥� that will allow scientists to distinguish them from other bursts in the future.

Battery-powered bursts can鈥檛 be the only kind out there, though, because not enough of these binary systems exist. 鈥淏ut I do think it tells us that there are many, many possible scenarios for FRBs,鈥� says of West Virginia University in Morgantown, who was part of the first FRB discovery.

Battery-powered FRBs could also help prove Einstein right. His theory of general relativity predicts that when these two massive objects merge, the powerful collision sends shock waves through space-time. No one has ever seen these so-called gravitational waves. But new instruments like should be able to spot the ones emanating from a collision between a neutron star and a black hole. If astronomers can pick up the pair鈥檚 final FRB broadcast, it should help confirm the existence of gravitational waves and unravel their origins.

鈥淚t鈥檚 probably safe to say that as many as 5000 FRBs could be discovered over the next five years,鈥� says of the California Institute of Technology in Pasadena. With any luck, some of those will be battery-powered, and come nicely packaged with confirmation of general relativity.

Journal article: The Astrophysical Journal Letters, DOI: arXiv:1511.02870

Image credit: Dana Berry/NASA

鈥淚n most social undertakings, there is a group that actually joins forces and works,鈥� says at the the Faculty of Information Studies in Novo Mesto, Slovenia. 鈥淎nd there is a group of free-riders that typically benefits from work being done, without contributing much.鈥�

Levnajic and his colleagues simulated this scenario. Digital people in a virtual population each had a randomly assigned tendency to collaborate on a problem or 鈥渇reeload鈥� 鈥� working alone and not sharing their findings. The team ran simulations to see whether there was an optimum crowdsource size for problem-solving.

It turned out there was 鈥� and surprisingly, the most effective crowd was not the largest possible. In fact, the simulated society was at its problem-solving best when just half the population worked together.

Smaller crowds contained too few willing collaborators with contrasting but complementary perspectives to effectively solve a problem. But if the researchers ran simulations with larger crowds, the freeloaders it contained naturally 鈥渄efected鈥� to working alone 鈥� knowing that they could benefit from any solutions the crowd reached, while also potentially reaping huge benefits if they could solve the problem without sharing the result ().

But does that happen in reality?

鈥淐rowdsourcing is interesting precisely because humans are not simple,鈥� says of the University of Harvard.

Consequently, Levnajic鈥檚 team will soon study the behaviour of real-world crowds.

This article appeared in print under the headline 鈥淐rowdsourcing works best if some don鈥檛 help鈥�

Alien worlds could be more alien than we thought (Image: ESO)

Is Earth the odd planet out? Many of our galaxy鈥檚 habitable planets probably have a chemical composition that is quite different from Earth鈥檚.

Vardan Adibekyan of the听Institute of Astrophysics and Space Sciences, Portugal, and colleagues looked at stars with a similar mass and radius to the sun that are known to have planets in their habitable zones, where water stays liquid. They found that these stars tended to have less iron and other metals than stars that host only inhospitable worlds.

Planets are built from the same basic material as their stars. 鈥淢ost of the properties of planets of different types strongly depend on their host stars鈥� chemistry,鈥� says Adibekyan. This suggests that planets in the habitable zone are typically lower in certain metals than Earth is.

In fact, metal-rich stars like our sun tend to have large rocky planets wrapped in huge gaseous envelopes.

This difference in composition between Earth and most other habitable-zone worlds could be explained if habitable-zone planets were more likely to form in our galaxy鈥檚 distant past. Heavy elements like iron form when stars explode and scatter them around interstellar spaces. When the galaxy was young, fewer stars died this way, so the new stars they spawned contained less of these elements.

If habitable-zone planets are more likely to be born orbiting these metal-poor stars, fewer are being created now. But stars have long lives, so the habitable planets that formed long ago should still be around. 鈥淭he total number of planets in the habitable zone should increase with time,鈥� Adibekyan says.

鈥淚t鈥檚 an intriguing idea,鈥� says Sarah Ballard of MIT, who was not part of the research. But the small number of habitable planets we鈥檝e found so far makes her cautious about over interpreting the results.

Journal reference:

Does it duplicate or destroy? Quantum mechanics says neither (Image: Visuals Unlimited, Inc./Victor Habbick/Getty)

It鈥檚 another shot in the black hole wars. The edge of a black hole might be a brick wall, says Nobel laureate , against which information about in-falling stuff bounces back like a tennis ball.

聮t Hooft was responding to Stephen Hawking鈥檚 25 August announcement of a new solution to the information paradox 鈥� a problem that has plagued scientists for 40 years.

The paradox is this: if any object, be it an iPhone or an elephant, ventures into a black hole, it stays there. From the outside, we will never be able to learn about any of its characteristics, information about it disappears behind the black curtain.

But in 1974, Hawking discovered that quantum weirdness at their edges causes black holes to leak radiation in the form of photons. This radiation, dubbed Hawking radiation, makes black holes slowly lose mass and evaporate.

Eventually, they pop completely out of existence, snuffing out all the details that lived inside. But quantum mechanics says information can neither be created nor destroyed, so the information has to go somewhere. Where?

Doomed pachyderm

鈥淭he answer is that matter going into the hole has an effect on outgoing Hawking particles,鈥� says 聮t Hooft. 鈥淗awking did not believe that at first, but gradually he is revising that opinion.鈥�

Hawking鈥檚 new claim is that if, say, an elephant passes over the edge of a black hole, the information about its elephant-ness stays on the edge as a holographic imprint. When the Hawking radiation seeps out, it carries that imprint with it. But questions remained: how does the in-falling matter make a mark? And how does that mark tattoo itself onto the outgoing radiation?

鈥淗awking鈥檚 paper generated a lot of discussion,鈥� says 聮t Hooft. This made him revisit an idea he had first proposed in 1987. 鈥淚 realised I can do a better calculation,鈥� he says.

聮t Hooft鈥檚 idea says gravity answers both questions. If an elephant starts to slip over the edge, the animal鈥檚 gravitational field changes. When outgoing Hawking radiation passes through that gravitational field, its path is altered, and can convey information about the doomed pachyderm.

Information about it, like its mass, then bounces back into space, although the animal itself is not so lucky.

Information duplication

鈥淓ven though we describe modes of infalling matter that 鈥榖ounce back against the horizon鈥�, these bounces only refer to the information our particles are carrying, while the particles will continue their way falling inwards,鈥� 聮t Hooft writes in the paper.

聮t Hooft鈥檚 and Hawking鈥檚 ideas have a similar problem, though: information overload. Their solutions might actually make a second copy of the information, creating information instead of destroying it.

If the poor elephant goes into the black hole, all of its characteristics go with it. But that information also hangs out on the horizon in Hawking鈥檚 case, or bounces back out in 聮t Hooft鈥檚.

鈥淨uantum mechanics forbids such duplication,鈥� says Steven Giddings of the University of California, Santa Barbara. It鈥檚 also unclear how a gravity-only information transfer meshes with quantum mechanics. 鈥淭he devil is in those details,鈥� says Giddings.

The battle over black holes is far from over. We will have to wait for more, in a state of information underload, to see what really happens on the edge of a black hole.

Journal reference: Arxiv,

(Image: Detlev Van Ravenswaay/Science Photo Library)

BILLIONS of years ago, Neptune made one giant leap. This jump left behind a close-knit group of icy objects called the Kuiper belt kernel, 6.5 billion kilometres from the sun, according to a new study.

The Kuiper belt is a collection of icy planetesimals that sits beyond Neptune. Astronomers estimate that it has trillions of members, including dwarf planets like Pluto 鈥� remnants of the solar system鈥檚 formation more than 4 billion years ago that have hardly changed since.

Most of the Kuiper belt鈥檚 population is scattered far above and below the neat plane in which the planets lie. Members of the kernel, however, stick tightly to that plane and to each other. No one knew why, until of the Southwest Research Institute in Boulder, Colorado, made a simulation of them.

His simulation rewinds the solar system鈥檚 history, showing the kernel鈥檚 formative years (). The kernel started life in Neptune鈥檚 gravitational clutches, but further from the sun. The planet slowly wandered outwards, and pushed these icy objects with it.

But, when it was 4.2 billion kilometres from our star, Neptune shifted its orbit suddenly, probably because of a close encounter with another planet. The kernel couldn鈥檛 keep up: the objects escaped Neptune and remained together, exactly where they were at the time.

Learning more about the Kuiper belt鈥檚 composition and how it is distributed can help us understand the solar system鈥檚 babyhood and how it matured. NASA鈥檚 New Horizons mission, which flew past Pluto last month and beamed us the first-ever close-up pictures of the dwarf planet, will help pin down these details.

鈥淭he Kuiper belt is a perfect clue to understanding how the solar system evolved since its formation,鈥� says Nesvorny.

This article appeared in print under the headline 鈥淣eptune鈥檚 jump left a weird ring of icy bodies鈥�

This cosmic clock can鈥檛 keep time (Image: ESA/INTEGRAL/IBIS-ISGRI/S. Grebenev et al.)

Not all the universe鈥檚 clocks tick reliably. After decades of stability, a fast-rotating baby pulsar called B0540-69 recently slammed on its brakes. It鈥檚 the brightest and youngest one we鈥檝e ever seen shift its identity this way, and its unpredictable behaviour will help astronomers figure out why pulsars shine in the first place, what makes them stable and what shakes them up.

Pulsars are the dense neutron stars left after supernovas. They blast beams of radiation from their magnetic poles, which sweep past Earth like the rays from a lighthouse as they rotate.

Many pulsars spin and gradually wind down at such reliable rates that scientists consider them 鈥渃osmic clocks鈥�, using them to test theories like general relativity and search for gravitational waves.

Astronomers calculate a pulsar鈥檚 age based on how its spin compares to its braking. In their young years, pulsars rotate much faster and also slow down faster than their mature counterparts, before they lose energy and enter maturity. B0540-69 clocks in at just 1700 years old.

But some pulsars鈥� timekeeping is out of joint. flip-flop between two states. In the 鈥渙ff鈥� state, they hardly emit radio waves, and they slow down gradually. But when 鈥渙n鈥�, they beam bright and brake harder. Previously, astronomers had only seen the spin switch occur in older, dimmer pulsars that flip back and forth regularly. That made B0540-69鈥檚 sudden slow-down a surprise.

Not so stable spinner

For 27 years after its discovery in 1984, B0540-69 slowed at the same steady rate. But astronomers announced this week that in December 2011, according to observations from the the Swift and RXTE X-ray telescopes, it suddenly started slowing down 36 per cent faster. Frank Marshall of NASA鈥檚 Goddard Space Flight Center in Greenbelt, Maryland, had watched the pulsar鈥檚 X-rays for more than 12 years and thought of it as a stable spinner. Then he saw it change radically in a matter of weeks.

The pulsar鈥檚 magnetic field might be to blame for its misbehaviour. When they are on, intermittent pulsars鈥� magnetic fields fill with plasma 鈥� a sea of charged particles, such as electrons and protons 鈥� and this generates radio waves. When pulsars switch off, that means the magnetic field lines have changed and let plasma leak out. Further observations of B0540-69 can help confirm that explanation, or point to another one.

Categorising B0540-69 as 鈥渋ntermittent鈥� will require further observations of its radio waves. But understanding how this bright young thing fits into the puzzle will help astronomers answer fundamental questions about pulsars, like what鈥檚 inside them and why they shine at all.

鈥淪ometimes it is the strangest behaving sources that teach us the most,鈥� says of McGill University in Canada. The naughty ones teach us how the nice ones tick.

Journal reference: Astrophysical Journal Letters, accepted for publication, arXiv.org/abs/1506.05765

Black hole on the rocks, anyone? (Image: Buena Vista Images/Getty)

If there were a bar at the centre of the Milky Way, it wouldn鈥檛 be short of ice. There鈥檚 plenty of the stuff, made of water as well frozen hydrocarbons, right next to the galaxy鈥檚 central supermassive black hole.

Astronomers had seen evidence for ice in interstellar space: both water and hydrocarbon molecules absorb light at specific wavelengths, leaving telltale signatures in infrared observations. But they thought the ice must be located relatively close to Earth 鈥� between our planet and the middle of the galaxy rather than right in the galactic centre, which would be too hot and radiation-filled for ice to survive.

New observations using the European Southern Observatory鈥檚 Very Large Telescope in Chile show that ice can 鈥� and does 鈥� survive there. Jihane Moultaka of the Research Institute in Astrophysics and Planetology in Toulouse, France, and her team made a map of where the ice appeared, and then used a novel technique to subtract the signatures from nearby, leaving only the ones from the middle of the galaxy.

Then they compared those locations to those of dust lanes. Where the dust clusters were thickest, the ice signatures showed up abundantly.

Dust shield

The team believe the ice survives by sticking to densely clustered dust grains, which shield them from the heat and radiation that could otherwise bake them. 鈥淰ery low temperatures are seemingly present in the very close environment of the supermassive black hole,鈥� says Moultaka. The ice they spotted there was at temperatures between -263听掳C and -193听掳C.

The tenacity of the ice bodes well for star birth near black holes at the centres of galaxies. Stars need cold, dusty gas to form, the existence of which isn鈥檛 a given in the galactic core. 鈥淭he presence of young stars in the centre of our galaxy is hardly understandable given the harsh environment of the supermassive black hole,鈥� says Moultaka. But with ice chilling in the galactic core, it seems reasonable.

Journal reference: