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Home » Page 1077

Another giant leap

When Neil Armstrong took the first steps on the Moon in July 1969, his soon-to-be-legendary words crossed 230,000 miles of space to reach millions of people around the world: “That’s one small step for [a] man, one giant leap for mankind.” Armstrong’s statement acknowledged that this monumental achievement was not his alone. Those first steps were made possible by the efforts and ingenuity of multitudes that, together, made the rockets and spacecraft that had brought men to another world. And as Nathalia Holt notes in her new book about a group of women working in the American space industry, these technologies weren’t built by men alone.

In Rise of the Rocket Girls: the Women Who Propelled Us, from Missiles to the Moon to Mars, Holt – a research biologist by training – foregrounds the contributions of a cohort of women whose labour was subsumed within the “mankind” of Armstrong’s historic statement, and largely forgotten in popular recollections of the Moon effort. Focusing on the history of the Jet Propulsion Laboratory (JPL) from the mid-1930s (when it was founded by the California Institute of Technology’s “suicide squad” of rocket engineers) through to the present day, Holt builds her narrative primarily on the recollections of the women who worked there as “computers” – a term we now associate with electronic machines but that once described a (usually female) mathematician. By interspersing memories of office hijinks, technical victories and failures, and the personal lives of her subjects, Holt’s narrative conveys a palpable intimacy that reflects the close relationships maintained by this group of women over decades of professional and personal camaraderie.

Holt focuses on her subjects’ participation in (and reactions to) important moments in space history, such as the competition between US military branches to get the first American satellite into orbit and the persistent difficulty in creating a single-stage-to-orbit rocket. In describing these moments, Holt’s literary skill shines brightly. She notes, for instance, that in helping each other work through monumental challenges of physics and engineering, the women computers and their male engineer counterparts at JPL worked like a multistage rocket – segmented but ultimately successful. Milestones in the computers’ lives, from pregnancy and marriage to stillbirth and divorce, serve as signposts to punctuate the successes and failures of the rocket programmes at JPL.

In addition to retelling these personal histories, Rise of the Rocket Girls doubles as a concise, accessible introduction to various scientific and mathematical concepts, from the Coriolis effect to Doppler shift. In an artful meta conceit, Holt traces the history of the electronic computer alongside the history of human computers at JPL. Occasionally, deviations to discuss the rise of Microsoft and Apple or the causes of the Challenger accident, for example, can be a bit tangential. However, as an introduction to the American space and computing industries, Holt’s text covers a massive amount of ground – in spite of a few glaring omissions, such as the end of the Cold War and its impact on the main subjects of this narrative.

Readers should, however, be advised of some critical oversights. Holt misrepresents the range of a rocket as its altitude, and occasionally uses figures that do not correspond to most cited historical records of the launcher in question. And, frustratingly, when the computers discuss working with “data,” we never get a chance to learn more about the data in question – how they were collected, by whom, and what the data actually looked like, which would go a long way towards making the experience of these women real to readers.

At times, the intimacy and accessibility of Holt’s narrative voice becomes a double-edged sword. Basing her book on the recollections of a few, mostly white women, Holt’s narrative voice adopts the vocabulary and perspective of her subjects. For instance, Holt typically describes the JPL computers as “girls”. While this is faithful to the terminology used by both the women and the men with whom they worked, it does not conscientiously critique the infantilizing meaning of this word, both then and particularly now. As a result, Holt unintentionally recapitulates the sexism of computers’ experiences in what otherwise reads as a sympathetic historical narrative. We also see this when Holt physically describes each of the women – often focusing on their beauty or style choices – while eschewing such descriptions of men.

In another troubling aspect of the book, Holt discusses instances in which women left their jobs after getting married or pregnant, either because they were forced to leave, or because they decided to adhere to social norms. Those who did not return to JPL later in life simply disappear from the narrative – an unfortunate literary replication of the very sexism that forced these women from the lab in the first place. A particularly glaring example concerns Janez Lawson, the sole black woman of the group. Her story ends with Lawson leaving JPL largely because racial politics prevented her from living in predominantly white Pasadena – and unlike the other characters, who receive an “ever after” treatment in the final chapter, we never find out what happens to Lawson once she departs the lab. Given that two women of colour factor prominently in the narrative – and several unmentioned women of colour worked as computers at JPL during the Cold War – Holt pays only superficial attention to the compounding effects of race and gender on interpersonal relationships at JPL. The upcoming book Hidden Figures: the American Dream and the Untold Story of the Black Women Mathematicians Who Helped Win the Space Race by Margot Lee Shetterly will likely address this omission.

Perhaps surprisingly, given that this book focuses on the struggles and triumphs of women in a predominantly male institution, Holt barely mentions the women’s movement that took off at the same time as her subjects worked to get rockets off the ground. Her final conclusion, a counterpoint to other Cold War gender histories, makes a bold claim: “While protestors were demanding equal rights for women across the country, the women at JPL had created their own equality. They had formed the lab in their own image, building an environment amenable to women, where their work and contributions were every bit as valued as those of their male counterparts.” Taken at face value, and based on the contented reflections of a small group of women who lived through it, this statement is probably true. However, hindsight typically provides unstable support for sweeping historical arguments. It is likely that not all women who worked in the space industry during this period will agree.

  • 2016 Little, Brown and Company £19.11/$27.00hb 304pp

Web life: Universe Awareness

So what is the site about?

If you’ve ever taken a young child to a planetarium – or remember visiting one yourself when you were younger – you’ll appreciate just how exhilarating it can be to encounter the wonders of the cosmos for the first time. Not all children have access to such opportunities, though, and even those who grow up in rich countries with good local science museums generally visit them only now and then. This is where the Universe Awareness project (UNAWE) comes in. Founded in 2006 by George Miley, an astronomer at the University of Leiden, the Netherlands, UNAWE aims to bring the beauty and grandeur of the universe into the classroom, as a means of inspiring children aged four to 10 and encouraging them to develop an interest in science.

How do they do that?

The UNAWE site is home to a wide range of resources, from videos and posters to a programme called The Awesome Amateur Astronomer that aims to introduce children to “every aspect of astronomy” in 10 steps (Step 1: Observe the night sky). One of the most interesting resources is Space Scoop, a site that hosts kid-friendly news stories about recent astronomy research. The stories are taken from press releases issued by several international astronomy organizations and then rewritten in age-appropriate ways by UNAWE staff members and volunteers.

Who is behind it?

The University of Leiden remains a major partner, and UNAWE has also received substantial support from the European Union through a programme called EU Universe Awareness (which ran from 2011 to 2013) and an ongoing effort, EUSPACE-AWE, that aims to build enthusiasm for space science and engineering. Other collaborators include the European Southern Observatory (which supplies many of the press releases for Space Scoop) and the National Astronomical Observatory of Japan.

Anything else I should be aware of?

Theoretically, Space Scoop is available in 40 languages, from Albanian and Arabic to Vietnamese and Welsh. However, several of the non-English versions appear thinly populated; at the time of writing, the most recent Arabic articles were posted in June 2013 and we couldn’t actually find any Space Scoop articles written in Albanian. Still, it’s possible to read kid-friendly scoops about radio stars in Danish, comets in Farsi and dwarf planets in the central American language K’iche’, among many others.

Can you give me a sample quote?

From a 30 May Space Scoop about a new class of galaxies called “red geysers” that contain supermassive black holes: “Almost everyone is afraid of the dark at some point in their life. Creaking floorboards, rustling curtains or random bumps in the night will fill them with terror. But it’s not the dark itself we find so terrifying, it’s the fear of what is lurking in the dark…But we all know the boogeyman isn’t real, so is there really anything to be afraid of? Maybe not on Earth, but there are monsters hiding in space – they’re called black holes. Black holes form when a massive star dies. Anything that gets too close to a black hole is pulled to it with such a strong force that it has no chance of escape. The monster will gobble it up! To make these monsters even more menacing, black holes are all but invisible. Until they start to feed… Black holes are messy eaters. As it gobbles up material, it is spraying out hot cosmic gas like cookie crumbs…The hot gas is heating up the entire galaxy to the point where it is unable to make new stars.”

3D display exploits twisted light

A 3D display that exploits the orbital angular momentum (OAM) of “twisted” light has been proposed by scientists at the University of Cambridge and Disney Research. The team says that its nine-by-nine pixel display demonstrates a new and powerful technique for organizing and transmitting the massive amounts of data required for displaying 3D images – and eventually video.

Using their new technique, Cambridge’s Daping Chu and colleagues were able to display three different images that were projected in different directions. Their prototype display showed pixels lit in the shape of three different letters, “P”, “S” and “G”, with each projected at a different angle (see figure). Depending on where viewers positioned themselves, they would see a different letter.

The technique to create the images involved several steps. First, each letter was recorded as a pattern of pixels. Then that pattern was encoded into a signal that could be transmitted to the display. Finally, the display received and decoded the signal to show the image.

Twisting wavefronts

The technique’s innovation, Chu says, lies in its method of encoding and decoding the signal. This allows the display to organize and transmit a large amount of image data in an efficient way. This comes courtesy of a quirk of quantum mechanics: that photons of specific OAM can easily be sorted from each other. A photon’s OAM is separate from its intrinsic angular momentum (or spin). OAM involves the wavefront of the photon twisting around the direction of propagation, creating a vortex in the middle of the light beam.

This rotation occurs at discrete values of OAM called modes. Chu’s group combined the pixel values of the three images with three different modes, essentially using each mode to “categorize” the pixels by image. The next step in the development of the technique will be to bundle all of the information into a single signal. This signal would then be transmitted to the display, which would then sort the pixels into the appropriate images. Then, the display would project the sorted pixels – three separate images – in three different directions.

This use of just one signal contrasts with some other 3D display techniques, in which different perspectives must be transmitted in multiple signals. Because light can have an infinite number of OAM modes, one signal could in principle bundle together an infinite number of perspectives, each encoded using a different mode. This could be used to weave together a seamless 360° image of an object. “You can add in as many perspectives as you like,” Chu says. “We just did three to show that we could beat two.” Three is important because commercial “3D” movies – technically known as stereoscopic movies – only overlay two perspectives to achieve the illusion of depth.

Not true 3D

Strictly speaking, the prototype that Chu and his colleagues created does not display true 3D images. A true 3D image, better known as a hologram, allows a viewer to look at the image from any angle and focus at any depth – swapping the foreground for background at will. When capturing an object’s image, a hologram must record the complete set of properties of light waves that bounce off the object: not only its intensity and colour, but also a timing property of the light known as its phase. Thus, the necessary data for a holographic movie adds up quickly. To create a true 3D holographic display with the size and clarity of a high-definition television, Chu estimates that you would need to be able to transmit 1000 times more data per second than a current 2D HDTV signal. “No hardware can deliver that at this moment,” he says. Their display inhabits the data-moderate middle ground between a true 3D holographic display and the contemporary cinema stereoscopic display.

Although the use of photon OAM is creative, the commercial viability of the technique may be limited, says Pierre-Alexandre Blanche, a holography expert at the University of Arizona, who was not involved in the work. He says that while in principle the technique can bundle an infinite number of images categorized with an infinite number of modes, it is experimentally challenging to actually produce those modes. Chu’s group could produce 30 modes, and Blanche says: “It is still quite an achievement, don’t get me wrong. It’s a nice scientific paper and nice demonstration, but it’s far from having something commercial in the next five years, or even decade.”

Chu acknowledges that the prototype is still far from commercialization. “It’s in the early stages, and it’s more fundamental,” he says. But his goal is to use this work as jumping-off point for a commercial 3D product. Next, his team plans to create multicoloured 3D images using this technique, in addition to using more modes to bundle more images.

The research is published in the Journal of Optics.

‘Radiation friction’ could make huge magnetic fields with lasers

Huge magnetic fields can be created by firing intense, circularly polarized laser pulses at a target, according to calculations by physicists in Italy, Germany and Russia. Their research suggests that the mysterious phenomenon of “radiation friction” plays a crucial role in generating the field. Measuring such magnetic fields could offer physicists a new way of studying this poorly understood effect, which is believed to play a crucial role in the physics underlying astrophysical objects such as gamma-ray flares.

Physicists have long known that a charged particle, such as an electron, emits electromagnetic radiation when it is accelerated – a phenomenon that makes synchrotron radiation facilities and free-electron lasers possible. As energy is conserved, the charged particle loses energy as it radiates and this can be thought of as radiation friction (RF). As well as playing a key role in gamma-ray flares, RF also affects how energy is dissipated in laser-plasma experiments whereby laser pulses are fired at a solid target to create a plasma in which electrons are accelerated to high energies.

Poor models

While experimental studies of RF have provided some information about the phenomenon, physicists do not have good models for calculating its effects. This is why Andrea Macchi at the University of Pisa, Tatyana Liseykina of the University of Rostock and Sergey Popruzhenko at the Moscow Engineering Physics Institute have come up with a new proposal for an experiment that could help to nail down RF.

Calculations and simulations done by the trio show that intense light pulses produced by next-generation, multi-petawatt or exawatt lasers could create short-lived multi-gigagauss magnetic fields in a plasma. Such fields are billions of times stronger than the Earth’s magnetic field and are created when charged particles in the plasma are accelerated into circular orbits. Crucially, the trio’s work shows that RF is the dominant mechanism whereby the charged particles absorb angular momentum from the pulse. Measuring the magnetic fields would therefore provide a direct probe of RF.

Persistent field

This magnetic field is expected to persist for much longer than the duration of the laser pulse that created it, meaning that the field could be detected using optical polarimetry. This involves sending a much weaker pulse of polarized laser light through the plasma and measuring the rotation of the polarization of the transmitted light, which is caused by the presence of the magnetic field. Macchi told physicsworld.com that “this technique has been previously used successfully with sub-picosecond resolution in laser-produced plasmas.”

Although there have been other proposals for measuring RF, Macchi says that in his team’s case, “the RF signature is robust because without RF there would be no strong magnetic field, so that discriminating RF effects may be less prone to experimental uncertainties.”

Macchi says that a better understanding of RF would be useful to astrophysicists who are trying to recreate in the lab the extreme conditions that occur near astronomical objects such as pulsars. Vast amounts of radiation are created in such regions, which comprise strongly magnetized and radiation-dominated plasmas. A better understanding of the behaviour of charged particles in such regions could also shed further light on how extremely high-energy cosmic rays are created in these environments.

Next-generation limit

Astrophysicists will probably have to wait for the next generation of pulsed lasers to be built, however. “Our calculations suggest that at least a power of several petawatts is needed, which is at the limit of the expected performance for forthcoming lasers such as APOLLON, ELI or XCELS,” says Macchi. However, he is not yet ruling out experiments at existing facilities: “We have not explored yet all the possible range of laser and plasma parameters, thus it might be that more accessible conditions are found.”

The research is described in the New Journal of Physics.

What is the maximum number of layers in a human pyramid?

Creating pyramids from people standing on top of each other is a fun gymnastic challenge that is also a cultural spectacle in various parts of the world. In this video, Roger Leyser from the University of Leicester, UK, approaches the challenge from a physics perspective by calculating the maximum number of layers in such a structure. He addresses the limited case in which each person in the human pyramid is balancing on both of their arms and legs. So what’s the answer? Watch the video to find out.

This is one of a collection of videos based on student projects from the University of Leicester’s “Physics Special Topics” course, in which students use their physics knowledge to define and answer a quirky or unusual research question. The videos are part of our 100 Second Science series.

Nearby supernovae could have affected life on Earth

The surface of the Earth was bathed in life-damaging radiation from nearby supernovae on several different occasions over the past nine million years. That is the claim of an international team of astronomers, which has created a computer model that suggests that high-energy particles from the supernovae created ionizing radiation in Earth’s atmosphere that reached ground level. This influx of radiation, the astronomers say, potentially changed the course of the Earth’s climate and the evolution of life.

Earlier this year, two independent teams of astronomers published evidence that several supernovae had exploded some 330 light-years from Earth. Each event showered the solar system in iron-60, an overabundance of which has been found in core samples from the bottom of the Atlantic, Pacific and Indian oceans – and also in deposits on the Moon.

Iron-60 isn’t all that supernovae produce. The exploding stars produce lots of light, as well as cosmic rays, which are composed of high-energy electrons and atomic nuclei. Previous work, in particular by Neil Gehrels of NASA’s Goddard Space Flight Center, indicated that a supernova would have to explode within 25 light-years of Earth to give our planet a radiation dose strong enough to cause a major mass extinction. In contrast, supernovae several hundred light years away were not thought to be capable of affecting either life or Earth’s atmosphere.

Piercing cosmic rays

Now, a team led by Brian Thomas of Washburn University in the US argues that this conclusion is incorrect. The researchers looked at what would happen if a supernova exploded at a distance of 325 light-years and worked-out how its radiation would affect Earth. They found that, other than disrupting circadian rhythms in terrestrial life forms, the blue and ultraviolet light would have no significant effect. However, the cosmic rays accelerated towards Earth by the supernova are a different story. These have energies in the teraelectronvolt (TeV) region and are able to “pass right through the solar wind and Earth’s magnetic field and propagate much further into the atmosphere than cosmic rays normally do”, says Adrian Melott of the University of Kansas, who is part of the team.

It is not the cosmic rays themselves that do the damage to life, but the radiation they create when they interact with the atmosphere. When a cosmic ray strikes an air molecule, it produces a shower of secondary particles that is filled with the likes of protons, neutrons and a strong flux of muons.

Ordinarily this takes place in the upper atmosphere and can be responsible for ionizing and destroying ozone in the stratosphere. However, the supernova cosmic rays are so energetic that they will pass straight through the stratosphere, instead penetrating the lower atmosphere known as the troposphere. There they create showers, which then ionize atoms on or near the ground and up to a kilometre deep into the ocean.

High-energy focus

“Earlier work on supernova damage hadn’t focused on the high-energy regime of the cosmic-ray spectrum,” says Brian Fields, a professor of astronomy and physics at the University of Illinois, who is not part of Thomas’s team. “Adrian, Brian and colleagues have shown that these cosmic rays are important, even though they are less numerous than the ‘garden variety’ cosmic rays at lower energies.”

Today, muons contribute a sixth of our annual radiation dose, but Thomas’s team calculate that a supernova would result in a 20-fold increase in the muon flux that would triple the annual radiation dose of life forms on the planet over the course of several thousand years. This, the team says, is akin to every life form on Earth having a medical CT scan every year. Although this would not wipe out life on Earth, statistically it may have caused some “minor” mass extinctions, as well as cell mutations that potentially sparked a burst in evolution.

There is evidence for a minor mass extinction around 2.59 million years ago, but it is too early to say how strongly it was linked to a nearby supernova that is believed to have occurred around that time. Nevertheless, the team suggests that the range at which supernovae can do damage perhaps needs to be widened. “The cosmic rays increase the ‘kill radius’ for serious biological damage,” says Fields.

Climate change

The cosmic rays may have also changed Earth’s climate. The most recent batch of supernovae came just before Earth entered a series of ice ages, at the end of which paved the way for humans to emerge. One possible link between the supernovae and climate is that muons in the lower atmosphere affected cloud cover, thereby cooling the planet.

“When ionization takes place down in the troposphere, where all our weather occurs, what will that do to our weather and climate?” asks Melott. “I’m not going to claim it causes ice ages, but it’s a possibility that needs to be investigated.”

The next step, says Melott, is to scour the geological record, searching for any evidence that supernovae really did have an effect, while further refining the models describing the propagation of cosmic rays from supernovae through space.

The research is described in The Astrophysical Journal Letters.

In flight around the world's brightest laser and the inverse Cheerio effect

 

By Tushna Commissariat

If you have never been one of the lucky few to have wandered the tunnels of a particle accelerator, but have always wondered what lies within, take a look at the video above. The European X-ray Free Electron Laser (European XFEL) – which is currently under construction in Germany and will come online next year – will provide ultrashort (27,000 X-ray flashes per second) and ultrabright X-ray laser flashes that are needed to study chemical reactions in situ or to study extreme states of matter (you can read more about the kind of research that will be done there in the September issue of Physics World magazine). The XFEL tunnel is 3.4 km long and you can zoom across all of it in the 5 minute long video. I particularly enjoyed watching particular locations where engineers could be seen carrying out tests, as well as watching folks on bicycles wobble out of the camera’s way.

On a slightly related note, if, like me, you occasionally get a bit muddled when it comes to certain details of different particle accelerators – for example which came first, the synchrotron or the cyclotron – take a look at this excellent “primer” over at Symmetry magazine.

(more…)

Dark-energy study maps 1.2 million galaxies in the early universe

Astronomers working on the Baryon Oscillation Spectroscopic Survey (BOSS) have analysed data from 1.2 million distant galaxies to gain further insights into the evolution of the universe. Acquired by the Sloan Digital Sky Survey III (SDSS-III) telescope in New Mexico, the data have been used to create the best map yet of baryon acoustic oscillations (BAOs). These are the relics of the early universe that chart-out how it has expanded over the past 13 billion years.

The BAO map is consistent with the current “Lambda-CDM” model of the universe, which incorporates dark energy and dark matter. Analysis of the data also shows that Einstein’s general theory of relativity is correct at cosmological length scales.

BAOs were created when the universe was just 400,000 years old and the first atoms were forming. Light and matter in the universe decoupled in this epoch, with the light forming the cosmic microwave background (CMB) that is still visible today. When the matter decoupled, its spatial distribution was defined by the peaks and troughs of pressure waves that had existed throughout the universe. This distinct pattern of matter density – the BAOs – then began to evolve into a universe of stars and galaxies. Thanks to theoretical calculations and information gleaned from the CMB, astronomers have a very good idea of what the BAOs looked like in the early universe.

Galaxies and voids

As the universe expanded over the next 13 billion years, gravity pulled matter into regions of higher density to form galaxies, while regions of lower density became voids in space. This pattern of galaxies and voids resembles the early BAOs, with one crucial exception – the characteristic distances between galaxies and voids have increased greatly as the universe expanded. So by mapping the BAOs as a function of cosmic time, astronomers can chart the expansion of the universe over billions of years.

In this latest development, BOSS astronomers have mapped out the BAOs in great detail from 7 billion to 2 billion years ago. They did this by observing 1.2 million galaxies over one quarter of the sky. The distance to each galaxy – and hence the time at which its light began the journey to Earth – was worked out by observing the redshift of characteristic atomic emission and absorption lines in the spectrum of light from that galaxy.

The standard model of cosmology is called “Lambda-CDM”, and it suggests that the expansion of the universe is governed by two competing agents. The gravitational tug of dark matter – which is about 85% of the matter in the universe – acts as a restoring force that tends to work against the expansion. On the other hand, dark energy – which appears to account for 70% of the energy in the universe – pushes in the opposite direction and is currently accelerating the expansion of the universe.

“Clean cosmological picture”

Dark energy does not appear to have played a role in the early universe, and seems to have kicked-in about 5 billion years ago, which is why BOSS was designed to study the BAOs over that time period. This latest study provides further evidence for Lambda-CDM, with an error of only 5% between the measured and theoretical value of the cosmological constant that describes dark energy. “Our latest results tie into a clean cosmological picture, giving strength to the standard cosmological model that has emerged over the last 18 years,” says BOSS team-member Jose Vazquez of Brookhaven National Laboratory.

To create an accurate map, the team had to contend with the “peculiar motions” of galaxies, which refers to the movement of a galaxy that is not related to the expansion of the universe. This appears in the BAO map as an anisotropy that must be corrected for. This peculiar motion is caused by gravity working over huge distances in the universe and analysis of the anisotropy allowed the BOSS team to show that Einstein’s theory of gravity – his general theory of relativity – is correct over very large distances.

The research is described in a series of papers in the Monthly Notices of the Royal Astronomical Society.

Blue is the colour of the universe’s first supernovae

Astronomers hoping to spot “first-generation” supernovae explosions from the oldest and most distant stars in our universe should look out for the colour blue. So says an international team of researchers, which has discovered that the colour of the light from a supernova during a specific phase of its evolution is an indicator of its progenitor star’s elemental content. The work will help astronomers to directly detect the oldest stars, and their eventual supernovae explosions, in our universe.

Early days

Following the Big Bang, the universe mainly consisted of light elements such as hydrogen, helium and trace amounts of lithium. It was only 200 million years later, after the formation of the first massive stars, that heavier elements such as oxygen, nitrogen, carbon and iron – which astronomers all call “metals” – were forged in their extremely high-pressure centres. The first stars – called “population III” – are thought to have been so massive and unstable that they would have quickly burnt out and exploded in supernovae, which would have scattered the metals across the cosmos. Indeed, these first explosions will most likely have sown the seeds to form the next-generation “population II” stars, which are still “metal poor” compared with “population I” stars like the Sun.

Unfortunately, astronomers have yet to detect a true first population-III star or spot a first-generation supernova. Astronomers have been hunting for old stars, and the best evidence for them was found last year in an extremely bright and distant galaxy in the early universe. There are also some candidate stars in our own galaxy.

Old timers

The constituents and properties of the first-generation of stars and their supernova explosions are still a mystery, thanks to the lack of actual observations, especially when it comes to the supernovae. Studying first-generation supernovae would provide rare insights into the early universe, but astronomers have struggled to distinguish these early explosions from the ordinary supernovae we detect today.

Now though, Alexey Tolstov and Ken’ichi Nomoto from the Kavli Institute for the Physics and Mathematics of the Universe, together with colleagues, have identified characteristic differences between new and old supernovae, after experimenting with supernovae models based on stars with virtually no metals. Such stars make good candidates because they preserve their chemical abundance at the time of their formation.

“The explosions of first-generation stars have a great impact on subsequent star and galaxy formation. But first, we need a better understanding of how these explosions look like to discover this phenomenon in the near future,” says Tolstov, adding that the “most difficult thing here is the construction of reliable models based on our current studies and observations. Finding the photometric characteristics of metal-poor supernovae, I am very happy to make one more step to our understanding of the early universe.”

Blue hue

Just like ordinary supernovae, the light or luminosity of a first-generation supernova should also show the characteristic rise to a peak in brightness, followed by a steady decline – which astronomers call a “light curve”. Indeed, a bright flash would signal the shock waves that emerge from the star’s surface as its core collapses. This “shock breakout” is followed by a several-month-long “plateau” phase, where the luminosity remains relatively constant, before the slow exponential decay.

Nomoto’s team calculated the light curves of metal-poor supernovae, produced by blue supergiant stars, and “metal-rich” red supergiant stars. They found that both the shock-breakout and plateau phases are shorter, bluer and fainter for metal-poor supernovae in comparison to the metal-rich ones. The researchers conclude the blue light-curve could be used as an indicator of a low-metallicity star.

Unfortunately, the expansion of our universe makes it difficult to detect first star and supernova radiation, which is redshifted into the near-infrared wavelength. But the team says that upcoming large telescopes such as the James Webb Space Telescope, currently scheduled for launch in 2018, should be able to detect the distant light from first supernovae, and their method could be used to identify them. Their findings could also help to pick out low-metallicity supernovae in the nearby universe.

The work is published in the Astrophysical Journal.

See like a solar system

Many years ago I read a news item in which a scientist said that a sodium cloud issuing from a volcano on Jupiter’s moon Io was “the largest permanently visible feature in the solar system” (Science News 137 359).

That remark stopped me cold. What does it mean to “see” a sodium cloud? More generally, what do scientists mean when saying they see dark matter or black holes? Are they speaking precisely or metaphorically? What is perception? Questions like these were a big factor in attracting me to the philosophy of science. Perception, I decided, isn’t as easy as it looks. To be a scientist is to develop an extended ability to perceive – and the science of the planets in our solar system is replete with examples.

Seeing like a rover

When scientists say they see things like sodium clouds, they speak rigorously. To perceive is not just to grasp something somewhere from a single perspective. It is also to have a sense, however rudimentary, of how that thing looks from other perspectives. Whenever I see a cup, I see only one profile of it. But thanks to our earlier experiences with cups, to see something as a real cup – rather than as a cutout or hallucination – means to anticipate other profiles; how it’ll appear if I walk around it, pick it up and so on. Sometimes these profiles surprise us, or we turn out to be deceived or wrong, but to perceive is always to grasp a profile of something and have a set of expectations about other anticipated profiles. Perception, in short, has a deep structure.

The same is true for a space scientist’s perception, except that it is technologically mediated. In philosophical language, scientists sometimes “embody” their instruments, seeing the world through them relatively directly, just as a blind person sees the world through a cane. When we perceive a planet or comet through an optical telescope, for instance, our previous experiences make us expect the object to be visible at other times in other locations – and that when observed through stronger telescopes it will have profiles that we might not know but that we can guess. At other times, scientists don’t embody but “interpret” their instruments. Just as we say “it’s cold outside” by looking at a thermometer, so a space scientist “sees” a sodium cloud with filters and spectrometers if these belong to expected profiles.

Astronomical perception involves a complex combination of these two concepts of embodiment and interpretation. An interesting case study is found in the 2013 article “Mediating Mars: perceptual experience and scientific imaging technologies” (Foundations Sci. 18 75) by the philosopher Robert Rosenberger from the Georgia Institute of Technology, US. In it, he describes a debate about a rock formation imaged by NASA’s Mars Global Surveyor in a Martian crater known as Eberswalde. Some scientists argued they were looking at the remains of a river delta, others an alluvial fan, still others that they were seeing the product of mudslide-like events.

Rosenberger shows that the scientists went about resolving the controversy, not by evaluating competing theories or explanations about the rock formation itself, but by appraising the different strategies that they were using to produce the images. They asked themselves, Rosenberger writes, “How does the process of transforming this object of study (i.e. a rock formation on Mars) into a specific form we are able to perceive here on Earth (i.e. images) leave these images open to interpretation in particular ways?” Without being able to move freely around the formation as they would on Earth, the scientists had to sharpen their perception of the rock formation by understanding the profiles better, and by analysing other profiles provided by shadows, laser altimeter data and so on.

Another analysis of scientific perception is found in Seeing Like a Rover: How Robots, Teams, and Images Craft Knowledge of Mars (2014 Princeton University Press) by the Princeton University sociologist Janet Vertesi. She based her book on two years spent as an ethnographer studying scientists in NASA’s Mars Exploration Rover mission. Vertesi found the researchers’ workspaces, computer screens and Powerpoints were saturated with images: filtered, false-colour, 3D, fish-eye, panoramic and more.

Taken by the two rovers Spirit and Opportunity, these images let the researchers “see” on Mars, but not with a human eye. One researcher told Vertesi that the two rovers’ view of the world was like “trying to make your way through a dark cluttered room with nothing but a flashbulb”. Yet the researchers became skilled at it, seeing and manipulating phenomena on the Martian surface. “When you work with the team for a while,” another researcher told her, “you kind of learn to see like a rover.”

Vertesi’s book shows that seeing like a rover is not just a matter of grasping profiles and horizons, but also involves ways of speaking and gesturing, emotional connections, habits and even the research group’s social and organizational structure. Seeing like a rover, she writes, “is…a question of seeing from somewhere, not adopting a view from nowhere” – with the “somewhere” referring not just to the rover’s cameras but to the entire research team and its activity.

The critical point

The curse of current-day philosophy of science is the lingering but fraudulent idea among philosophers that science involves the quest to see phenomena from nowhere. Instead, it’s done by people with inherited concepts using particular equipment to study topics that seem important. To perceive a scientific phenomenon involves grasping how all of the profiles you can see of it – and how others that you don’t yet or never will see – hang together. Not only that, but mediated scientific perception deepens and extends our notion of what it is to perceive at all.

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