The Week in Space and Physics #3
Every few milliseconds a radio signal flashes somewhere in the midst of the Vela constellation. It has been doing so for thousands of years, as far as we know; acting almost like a lighthouse, deep in space. Yet this is no artificial structure, no alien message from across the galaxy. Instead this pulsing signal is a marker: the tombstone of a long dead star.
This signal, known as the Vela pulsar, probably formed twelve thousand years ago in the fiery heat of a supernova. As the core of that dying star collapsed, it began to spin rapidly and – as it became denser and denser –started to produce a powerful magnetic field.
The result, after the dust of the supernova settled, was a highly magnetic neutron star. The magnetic field acts, in a way, as a gradual drag on its spin, ripping electrons from the surface of the star. As those electrons swirl through the field they accelerate, creating two beams of radio waves shooting away from the surface.
Those beams rotate with the star, sweeping across the heavens. Whenever one of those beams pass over the Earth we see a sudden flash of radio energy, a repeating signal with extraordinary stability. Indeed, pulsars flash so regularly and predictably that some have considered using them as clocks or for navigation in deep space.
Gradually, however, this process slows the star’s rotation. Eventually - after a few million years - the spin slows enough that electrons are no longer accelerated, and the beams fade away. That, ultimately, puts on a limit on how slowly pulsars can flash. Indeed, all known pulsars flash rapidly, at most once every few seconds.
So when astronomers last week reported a signal flashing once every eighteen minutes, it came as somewhat of a surprise. The object appears rather like a pulsar, producing a regular burst of radio energy. Since it must be spinning slowly - at least by the standards of pulsars - there is, though, no obvious way it can produce so much energy.
One possible explanation is a magnetar: a neutron star with an intense and twisted magnetic field. Astronomers have spotted magnetars pulsing in the past, but always on short timescales. This object could be the first “long period” magnetar, an object that exists in theory but has never before been seen in reality.
The intense magnetism of those stars should create bizarre physics, from squashed atoms to distorting space itself. That could indeed create things that look impossible: from slow flashing pulsars to sudden and extreme bursts of energy.
An Inter-Galactic Supernova?
Something strange lingers in the vast voids between galaxies. Back in 2019, astronomers Anna Kapinska and Emil Lenc found two ghostly radio signals coming from deep space. Each was circular in shape and glowing faintly in radio frequencies.
The astronomers soon found more examples of them and – lacking any clear explanation of their origin – named them ORCs, or Odd Radio Circles. Their properties proved tough to pin down; with researchers unable to say how far away they were, or how big they were or even what, exactly, was producing their faint radio glow.
One such radio circle, it turned out, lies somewhere between our galaxy and two small neighbours. That made it close enough - around one hundred thousand light years distant - to examine in detail.
Having done so, the astronomers think the object is actually the remains of a supernova – but with an interesting twist. The dying star was likely expelled from our galaxy, or perhaps one of our neighbours, millions of years ago. It then spent its final years drifting in the cold void of intergalactic space.
When it exploded – perhaps only a few thousand years ago – it did so far from any other star or gas clouds. This serene environment allowed the supernova to form an almost perfectly circular shell of expanding debris. Such bubbles are often seen inside galaxies – the Earth may even lie within one – but none has ever been seen outside a galaxy before.
The discovery, ironically, means the object probably isn’t an ORC after all. Astronomers had previously considered the idea that they represented intergalactic supernova but dismissed it. Far too many ORCs have been found, they reasoned, and there is no still clear evidence whether ORCs sit inside galaxies or form in the spaces between them.
Still, though the mystery of the ORCs will linger on, the discovery of an intergalactic supernova is an interesting one. Further measurements will, of course, be needed to confirm that it really is one, but astronomers calculate that a dozen or so other remnants should be visible from Earth.
The Hunt for X(3872)
For years physicists have been hunting down a mysterious particle known only as X(3872). Hints of it first surfaced in Japan in 2003, but traces of it have since been spotted in laboratories across the planet. Never, though, has the particle stuck around long enough for physicists to get a good enough look at it.
That’s a shame, because there’s a very good chance X(3872) is something exotic, a type of particle rarely seen before. One option is a tetraquark – a particle made of one more quark than the more familiar protons and neutrons. But it could also be a “mesonic molecule”, a hypothetical class of particle that may have existed in the heat of the Big Bang.
Though physicists still haven’t worked out which of those possibilities is true, they have just managed to uncover hundreds more detections of the particle. A team at the Large Hadron Collider in Switzerland used machine learning to analyse the vast amounts of data pumped out by the accelerator. Hidden in that data, they found, were over a hundred detections of X(3872).
That proves, for the first time, that collisions of the type used in the LHC can indeed produce the mysterious particle. The collider is currently closed for maintenance and upgrades – but once it reopens, physicists will be sure to start hunting X(3872) in earnest.
SpaceX to Touch The Moon?
An old SpaceX rocket, launched seven years ago, seems to be on a direct collision course with the Moon. That, at least, is the prediction of Bill Gray, an astronomer and programmer who attempted to track and forecast the trajectory of the old rocket.
The rocket in question is a Falcon 9 launched back in 2015. As the satellite it was carrying needed to be sent far from Earth, SpaceX were unable to retrieve the rocket after launch. Ever since it has been in a chaotic orbit high above our planet. With the help of amateur astronomers, Gray was able to accurately measure this orbit – and thus discovered that it is on track to hit the Moon in early March.
That – despite sensational headlines – is not much of a problem. Indeed, NASA has deliberately crashed rocket bodies into the Moon before. The clouds of dust thrown up by such an impact can be tracked and measured from orbiting satellites, giving astronomers insight into the materials found on the lunar surface.
Whether that will be possible in this case remains to be seen. The expected impact date is still too far in the future to be certain about where – or even if – the collision will take place.