At the heart of most, if not all, giant galaxies lies a supermassive black hole. When dust and gas falls into the central black hole, it heats up and emits intense radiation. Quasars, some of the brightest objects in the cosmos, are powered by these phenomena. In these artist’s impressions of a quasar, the rotating ring of matter, and powerful jets of particles thrown out at close to the speed of light can be seen.
Credit: ESA/Hubble (M. Kornmesser)
Odd pair of aging stars sculpt spectacular shape of planetary nebula
The new study confirms a long-debated theory about what shapes these objects.
Astronomers using the European Southern Observatory’s (ESO) Very Large Telescope (VLT) have discovered a pair of stars orbiting each other at the center of one of the most remarkable examples of a planetary nebula. The new result confirms a long-debated theory about what controls the spectacular and symmetric appearance of the material flung out into space.
Planetary nebulae are glowing shells of gas around white dwarfs — Sun-like stars in the final stages of their lives. Fleming 1 is a beautiful example that has strikingly symmetric jets that weave into knotty curved patterns. It is located in the southern constellation Centaurus the Centaur and was discovered just over a century ago by Williamina Fleming, a former maid who was hired by Harvard College Observatory after showing an aptitude for astronomy.
Astronomers have long debated how these symmetric jets could be created, but no consensus has been reached. Now, a research team led by Henri Boffin from ESO has combined new VLT observations of Fleming 1 with existing computer modeling to explain in detail for the first time how these bizarre shapes came about.
The team used ESO’s VLT to study the light coming from the central star. They found that Fleming 1 is likely to have not one but two white dwarfs at its center, circling each other every 1.2 days. Although binary stars have been found at the hearts of planetary nebulae before, systems with two white dwarfs orbiting each other are very rare.
“The origin of the beautiful and intricate shapes of Fleming 1 and similar objects has been controversial for many decades,” said Henri Boffin. “Astronomers have suggested a binary star before, but it was always thought that in this case the pair would be well separated, with an orbital period of tens of years or longer. Thanks to our models and observations, which let us examine this unusual system in great detail and peer right into the heart of the nebula, we found the pair to be several thousand times closer.” When a star with a mass up to eight times that of the Sun approaches the end of its life, it blows off its outer shells and begins to lose mass. This allows the hot inner core of the star to radiate strongly, causing this outward-moving cocoon of gas to glow brightly as a planetary nebula.
While stars are spherical, many of these planetary nebulae are strikingly complex, with knots, filaments, and intense jets of material forming intricate patterns. Some of the most spectacular nebulae, including Fleming 1, present point-symmetric structures. For this planetary nebula, it means that the material appears to shoot from both poles of the central region in S-shaped flows. This new study shows that these patterns for Fleming 1 are the result of the close interaction between a pair of stars — the surprising swansong of a stellar couple.
“This is the most comprehensive case yet of a binary central star for which simulations have correctly predicted how it shaped the surrounding nebula — and in a truly spectacular fashion,” said Brent Miszalsk from the South African Astronomical Observatory and the South African Large Telescope.
The pair of stars in the middle of this nebula is vital to explain its observed structure. As the stars aged, they expanded, and for part of this time, one acted as a stellar vampire, sucking material from its companion. This material then flowed in toward the vampire, encircling it with a disk known as an accretion disk. As the two stars orbited one another, they both interacted with this disk and caused it to behave like a wobbling spinning top — a type of motion called precession. This movement affects the behavior of any material that has been pushed outward from the poles of the system, such as outflowing jets. This study now confirms that precessing accretion disks within binary systems cause the stunningly symmetric patterns around planetary nebulae like Fleming 1.
The deep images from the VLT also have led to the discovery of a knotted ring of material within the inner nebula. Such a ring of material is also known to exist in other families of binary systems and appears to be a telltale signature of the presence of a stellar couple.
“Our results bring further confirmation of the role played by interaction between pairs of stars to shape, and perhaps even form, planetary nebulae,” said Boffin.
Maui’s dolphin and calf (Cephalorhynchus hectori maui)- New Zealand native and also the worlds rarest dolphin. Watercolour, 2014. E.Scheltema.
One of our most mysterious and intriguing states of consciousness is the dream. We lose consciousness when we enter the deep waters of sleep, only to regain it as we emerge into a series of uncanny private realities. These air pockets of inner experience have been difficult for psychologists to study scientifically and, as a result, researchers have mostly resorted to measuring brain activity as the sleeper lies passive. But interest has recently returned to a technique that allows real-time communication from within the dream world.
The rabbit hole between these worlds of consciousness turns out to be the lucid dream, where people become aware that they are dreaming and can influence what happens within their self-generated world. Studies suggest that the majority of people have had a lucid dream at some point in their life but that the experience is not common. As a result, there is now a minor industry in technologies and training techniques that claim to increase your chance of having a lucid dream although a recent scientific review estimated that the effect of any particular strategy is moderate at best. Some people, however, can reliably induce lucid dreams and it’s these people who are allowing us to conduct experiments inside dreams.
When trying to study an experience or behaviour, cognitive scientists usually combine subjective reports, what people describe about their experience, with behavioural experiments, to see what effect a particular state has on how people reason, act or remember. But both are difficult in dreamers, because they can’t tell you much until they wake up and active participation in experiments is difficult when you are separated from the world by a blanket of sleep-induced paralysis.
This paralysis is caused by neurons in the brainstem that block signals from the action-generating areas in the brain to the spinal nerves and muscles. The shutdown happens when Rapid Eye Movement or REM sleep starts, meaning that dreaming of even the most energetic actions results in no more than a slight twitch. One of the few actions that are not paralysed, however, is eye movement. This is where REM sleep gets its name from and this window of free action provides the lucid dreamer a way of signalling to the outside world.
Using a procedure first verified by sleep researcher Stephen LaBerge, the sleeper can signal to researchers when they have begun their lucid dream by using pre-arranged eye movements. The person moves their eyes in the agreed way in the dream, which occur as genuine eye movements, which are recorded and verified by electrodes that are placed around the eye sockets.
This simple but ingenious technique has allowed a series of experiments on the properties of the dream world and how they are reflected in brain function. These neuroscientific studies have been important for overcoming an initial objection to the concept of lucid dreaming: that lucid dreamers were awake but just relaxed, or perhaps even fraudulent, claiming to be experiencing a dream world when they were not. Studies led by neuropsychologists Ursula Voss and Martin Dresler have shown that the brain activity during lucid dreaming bears the core features of REM sleep but is distinct from both non-lucid dreaming and the awake state, suggesting that it is not just a case of wishful thinking on the part of either the participants or the researchers.
Some of the most interesting studies involve in-dream experiments, where participants are asked to complete pre-arranged actions in their lucid dreams while using eye movements to signal the beginning and end of their behavioural sequences. A recent study by neuroscientist Daniel Erlacher and his colleagues at the University of Bern compared how long it took to complete different tasks while lucid dreaming and while awake. These included counting, walking a specified number of steps, and a simple gymnastics-like routine. They found that the “mental action” of counting happened at the same speed regardless of whether volunteers were dreaming or awake, but the “physical actions” took longer in dreams than in real life. The research team suggested that this might be due to not having the normal sensory feedback from the body to help the brain work out the most efficient way of coordinating itself.
There is also an amateur community of lucid dream enthusiasts keen to explore this unique form of virtual reality. This stretches from the fringes of the New Age movement who want to use lucid dreams to access other planes of existence (best of luck with that), to a more technologically oriented community of dream hackers who sample scientific research to try to find reliable methods for triggering lucidity. The connection with established studies can be a little haphazard and methods veer between the verified and the barely tested. In some online discussion boards, there have been reports of people using medications intended for Alzheimer’s sufferers, which have the side-effect of causing vivid dreams, based on little more than hearsay and data reported in a patent application.
Some researchers have highlighted the potential of lucid dreaming to advance the science of consciousness but it’s a difficult area to study. The currents of consciousness run unpredictably through the tides of sleep and the science of dreaming is still very much in the age of exploration. It’s also a conceptual problem that some feel unequipped to tackle. After all, what can we make of consciousness when it creates a new world and our experience of it?
By Shaw, George, 1751-1813
Nodder, Frederick Polydore,
Publication info London :Printed for Nodder & co,1789.
Will you sleep for seven thousand years - until the world is different? What if it is exactly the same when, finally, you choose to wake up?
Radiograph of the hands shows arachnodactyly resulting from Marfan syndrome.
It’s neat how human beings have learned enough about ourselves to the point that - by and large - if something goes wrong we can just open up our guts and fix it. Pretty neat. Good job.