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The Week in Space and Physics: The Nobel Prize
On fast flashes of light and the Nobel Prize, failed stars that look like planets, New Horizons and commercial space stations.
More people have been into space than have won a Nobel Prize in physics. It is, without a doubt, the most prestigious award in the field, given for the discovery that confers the greatest benefit on humankind. This year the judges awarded it to three European physicists who pioneered new methods for making ultra-short pulses of light.
To understand why this was deserving of the award, it helps to first think of a camera. This, of course, is a device that can capture light, converting it into a permanent image on chemical film or in digital memory. For stationary objects this is easily done, requiring little more than the ability to point and click. Yet for fast-moving objects - a racing cyclist say, or a hummingbird’s wings - the task becomes more complex.
If the image is exposed for too long, the target will be blurred; its finer details lost in a smear of light. To avoid that, a photographer must play with time and light - finding, essentially, a way to gather enough light in a short enough time to avoid blur. One option is to simply shorten the exposure; but for the cases when that doesn’t work, a photographer can instead fire a short, intense flash of light.
A hummingbird, for example, flaps its wings dozens of times per second. To the naked eye this movement is invisible, but a photographer can capture a sharp image of a hummingbird by creating a short burst of light. That, if timed correctly, illuminates the wings so briefly that they appear frozen in space, producing a sharp image in the camera’s eye.
When it comes to the things physicists are interested in - electrons and molecules - the flashes involved become incredibly short. Molecules move on the scale of femtoseconds - each equal to one quadrillionth of a second. Electrons are even faster, oscillating so rapidly that you have only attoseconds - of which one thousand are in every femtosecond - to image them.
Molecule imaging is done with sophisticated lasers. These can make flashes of light a few femtoseconds in length, allowing physicists to capture the motion of dancing molecules. Attosecond flashes, however, are much harder. Since light waves themselves vibrate on the order of once per femtosecond, lasers cannot flash on and off more quickly.
In the 1980s, Anne L’Huillier, the first of the three prize winners, discovered a way to get around this limit, thus opening the door to attosecond flashes. Firing a laser through argon gas, she found, would create higher frequency flashes of light, right down to the attosecond scale. This was interesting, but not yet useful. The flashes came too fast to allow for imaging, and anyway it was hard to measure how long they really were.
In the early 2000s, the two other winners - Pierre Agostini and Ferenc Krausz - refined L’Huillier’s work into a usable tool. Crucially Agostini confirmed that the flashes really were attoseconds in length. Then, to make them actually useful, Krausz succeeded in isolating an individual pulse of light.
The prize, as a whole, was awarded for the development of these techniques. Together they now allow researchers to view the world on a timescale that was once thought out of reach. The pioneers of atomic theory - Einstein among them - could hardly have imagined we would one day actually view the world they uncovered.
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Giant Planets… or Failed Stars?
Students of astronomy sometimes ask if Jupiter is a failed star. It isn’t - Jupiter never had anywhere near the mass needed to ignite nuclear fusion in its core. More deeply, though, the question misunderstands a difference in the way stars and planets form.
Planets tend to build from the bottom up, growing by accumulating rock and ice. Even worlds as large as Jupiter can, over millions of years, form in this way. Nothing stops them from growing even larger - though reason says that gigantic planets must be rare, and certainly never big enough to become stars.
Instead, stars burst into being when clouds of gas collapse under gravitational pressure; a process that is more top down than bottom up. Researchers have found, however, that this process can indeed result in failed stars. Warm objects, known as brown dwarfs, are born when a cloud collapses but lacks the mass to sustain fusion.
Brown dwarfs, at least the ones we’ve seen, are still big objects. The smallest - at least according to theory - should be at least three times as heavy as Jupiter. In practice, however, we rarely see objects smaller in mass than ten Jupiters, since they glow too faintly for our telescopes to see. That left a gap in our observations, obscuring the transition between the biggest planets and the smallest failed stars.
The arrival of the James Webb has changed that. In a recent survey of the Orion Nebula, the telescope picked out hundreds of objects lying in this gap; each measuring between half and thirteen times the mass of Jupiter. All were moving independently, that is, without an accompanying star, though dozens of them were spotted travelling in pairs.
Astronomers had expected to find a clear cut off point between large planets and small brown dwarves (more properly known as “planetary mass objects”). Yet the observations didn’t show this. Instead the images show dozens of objects that seem to be either very large planets or very small brown dwarves. Which they are, and how they achieved their unexpected sizes, remains unclear.
Possibly, the scientists behind the survey say, these are big planets that were kicked out of their solar systems. But this seems unlikely, especially since many of them seem to come in pairs. Instead they may have formed like stars out of collapsing gas clouds. Yet if this is indeed the case, it is still puzzling. It should not be possible, theory says, to end up with such small objects in this way.
Whatever the explanation is, the discovery once again shows how the James Webb is forcing astronomers to rethink their theories. It underlines, too, how little of the cosmos we have been able to see; and how much we have therefore been missing.
Keeping an Eye on the Kuiper Belt
After visiting Pluto in 2015, NASA’s New Horizons probe has spent the last eight years flying through the Kuiper Belt. In 2019, following a slight change in trajectory, New Horizons passed by Arrokoth, the most distant object ever visited by humanity.
Since New Horizons still has fuel and power, scientists reckon the probe could fly by another object, should any suitable targets turn up. Researchers are, anyway, keen for New Horizons to keep exploring the Kuiper Belt, as no other spacecraft is likely to visit for at least two decades.
Yet a review by NASA earlier this year put that potential in doubt. The science benefits of continuing the Kuiper Belt mission were limited, they said. Reassigning the probe to study how the Sun affects the outer solar system would be a better use of resources. This, however, would rule out the chance of a future fly-by of another Kuiper Belt object.
The report sparked an immediate outcry among planetary scientists. They argued that reassigning New Horizons would mean losing valuable and hard to get data. NASA now seems to have listened to those pleas, agreeing to extend the probe’s planetary science work until the end of the decade.
Still, NASA does intend to redirect some of New Horizons’ focus towards solar physics. And though the decision keeps the possibility of another fly-by alive, it is unclear how likely it is for one to happen: so far, at least, no suitable objects have been found along the spacecraft’s trajectory.
Overall, however, the outcome seems to be a decent compromise. The probe will shift its priorities, focusing more on the Sun than the Kuiper Belt. At the same time, NASA will keep the potential for more exploration alive, should the chance arise.
Shaking Up Commercial Space Stations
At the end of 2021, NASA awarded funds to three companies to begin the development of a set of private space stations. These, NASA hopes, will mean American astronauts still have somewhere to go when the current space station shuts down in the early 2030s.
Last week, however, one of those three companies officially abandoned their plans. Northrop Grumman, which currently builds a resupply vessel for the ISS, had planned to build a station with room for eight astronauts. Yet in an announcement at the International Astronautical Congress, they said they would instead form a partnership with another company, Nanoracks.
Nanoracks was one of the original three companies funded by NASA, meaning the agency will now only fund designs for two space stations. The other - a station named Orbital Reef - is supported by Blue Origin. Reports, however, suggest partners in the project are thinking about backing out, potentially leaving it in limbo.