The Week in Space and Physics: The Vela Pulsar
The Week in Space and Physics: The Vela Pulsar
On the Vela Pulsar, solar storms, the Euclid telescope and the odds of coming up heads
It was surely a spectacular sight. Twelve millennia ago, when a star exploded in the southern constellation of Vela, its light must have shone as brightly as the Moon. Though no written records exist from that time - civilization, indeed, had barely gotten started - the remnants of the supernova linger to this day, lying almost a thousand light years from Earth.
Marking the site is a pulsar; an object that flashes on and off eleven times every second. It formed as the core of the dying star was crushed under incredible pressure. So high was the intensity that its electrons and protons combined, forming a sphere of pure neutrons. The resulting material is among the densest known, so that a single teaspoon of it weighs billions of tonnes.
The physics of such dense objects is not easy to study. We do know, however, that the Vela pulsar is spinning rapidly and is highly magnetic. Much of that came from the dying star - as it collapsed its angular momentum was conserved, leaving the neutron star spinning several times per second. Its magnetic fields were also trapped and magnified, creating the intense field that today surrounds the pulsar.
When magnets spin rapidly they create electric currents. In pulsars those currents are directed along the poles of the magnetic field, sending two jets of charged particles - electrons and protons, mostly - shooting off into space. As the pulsar spins, then, those jets repeatedly sweep across space, rather like the beam of a lighthouse sweeping through the night sky. From Earth, we see this as a steady flash turning on and off with startling regularity.
In a recent discovery, HESS, a telescope in Namibia designed to look for high energy photons, found dozens of energetic particles streaming out of the Vela pulsar. To the researchers’ surprise, these were far more energetic than any seen coming from a pulsar before - some, indeed, carried twenty times the energy of the previous record.
It’s not quite clear how the pulsar can be emitting such energetic particles. Some interaction in the pulsar’s magnetic and electric fields must be accelerating them - but our current theories struggle to explain how they can be accelerated quite so much. More observations of Vela and other pulsars will certainly be needed.
Since pulsars are such extreme objects, they can serve as tests of the limits of modern physics. Vela, which is one of the closest and youngest known pulsars, makes an excellent target for such research. In this case, the discovery of such energetic radiation probably doesn’t mean we need to rewrite the laws of physics. It may, however, mean we need to rethink our models of how pulsars work.
Ancient Trees Reveal a Massive Solar Storm
According to a group of French researchers, a massive solar storm hit the Earth fourteen thousand years ago. The evidence they uncovered suggests the storm was larger than any other so far known - far larger, indeed, than any storm we have observed in the past two centuries of active measurement.
When such solar storms hit our planet, they subtly alter the composition of the atmosphere. In particular, they tend to raise the levels of a radioactive atom known as carbon-14. Over time, as those atoms find their way into trees and plants, they end up leaving their mark on tree rings.
This means ancient trees can offer a record of past solar activity. In this case, researchers examined wood from tree stumps preserved in a river bed in the French Alps. Some of that wood, they found, is close to fourteen and a half thousand years old.
Measurements then showed a carbon-14 spike occurred some 14,300 years ago, suggesting that a major storm hit the Earth back then. Comparison with polar ice records - which also preserve fingerprints of the past atmosphere - added further evidence to support the idea.
If this was a storm, then it was a big one; at least ten times more powerful than the largest seen in the past two centuries. That event - in 1859 - damaged the telegraph systems then running across America. Should something similar happen today it would threaten electrical grids; possibly leaving entire continents without power for weeks. A storm ten times larger - as now seems possible - would be catastrophic.
But it is not yet certain these big spikes are really solar storms. A handful of other spikes are known in the tree ring record, some of which occurred in the first millennium AD. Historical records of the events are sparse, which - since they should have sparked astonishing aurora - is slightly odd. Some scientists, indeed, think these spikes could be linked to slower, less damaging, events that stretched over weeks or months.
One possibility is a sequence of large, but not gigantic, solar storms hitting in succession. Or, perhaps, they were made by shock waves emanating from a nearby supernova or even a gamma ray burst. Whatever the cause, they at least seem to be rare events, happening no more than once or twice per millennium.
Commissioning Euclid
Europe’s new space telescope, Euclid, has now spent three months in space. As with other missions, much of that time has been spent on commissioning and calibrating the telescope in preparation for its scientific work. Unfortunately, things have not gone quite as planned.
The first problem arose soon after launch. Engineers saw stray light entering the spacecraft’s delicate optics, threatening its ability to take the sensitive images needed for its mission. Fortunately an easy solution was found: after rotating the telescope by a few degrees, engineers saw the extra light had gone.
Then, however, a worse problem cropped up. The system Euclid used to orientate itself correctly was not working properly - and, in some cases, was operating so badly that stars were appearing as smeared lines of light.
To point itself correctly, Euclid is relying on a system called the “Fine Guidance Sensor”. This detects the positions of known stars around the spacecraft and then uses them to hold the telescope steady. Yet in some cases cosmic rays were confusing its sensor, causing it to lose track of the stars and begin moving around.
The solution, according to Euclid project manager Giuseppe Racca, was a software update. This will make the spacecraft operate with more stability, but it will also slow it down slightly, thus extending its three year mission by a few months. This should not be too much of a problem, ESA says, and - with the software patch tested - they are now moving on with the rest of the commissioning.
A few more weeks will be needed to complete that. Euclid should, unless other problems crop up, then begin scientific work in November. Despite the early problems, scientists seem impressed with the images produced so far by Euclid. Few of these, sadly, have been publicly released. For that we’ll probably have to wait a few more weeks.
Heads or Tails?
How fair is a coin toss? Perfectly, you might hope, especially since coin tosses have been used to decide the outcome of everything from football matches to elections. Yet studies have found that all coin tosses actually show a slight bias towards one side, thanks, it would seem, to the laws of physics that govern their motion.
In the biggest study of its kind, a group of (no doubt slightly bored) researchers recently devoted themselves to tossing coins and recording the outcomes. After conducting more than three hundred thousand tosses, they found that coins were slightly more likely to land facing the same side they started with. A coin that starts out facing heads, in other words, has a 51% chance of landing facing heads as well.
This, they say, is probably down to a slight wobble created by the motion of tossing. As the coin moves through the air, this wobble means the coin spends more time with the initial side facing up - and, therefore, makes it fractionally more likely to land like that too.