Thursday, 5 January 2017

Signals From Space - Keep Calm and Carry On!

Source of mysterious deep space radio wave discovered for the first time | Science | The Guardian

Scientists have identified the source of a pulse of radio signals first detected in 2016 of a type only known about since 2007.

The so-called fast radio bursts (FRBs) most probably came from a dwarf galaxy some 3 billion light years from Earth, so the pulse only began its journey when Earth was just a few million years old, maybe when life was just getting going.

But it's nothing for alien conspiracists to get excited over; nor is it anything for creationists to start to panic over. It almost certainly isn't a signal from some other intelligence in a distant galaxy. However, exactly what it is is still a bit of a mystery.

The reason we can fairly safely rule out an intelligent civilisation is because of the sheer energy which would have been needed to send out the pulse. It would have needed the energy output of our sum over 10,000 years to be blasted into space in a few milliseconds. Such a concentration of energy would have been greater than any imaginable civilisation on a planet of any size could produce. We can be fairly certain therefore that whatever generated this pulse of energy was something natural. Something of the order of a neutron star or something collapsing into a black hole.

Fast radio bursts1, 2 are astronomical radio flashes of unknown physical nature with durations of milliseconds. Their dispersive arrival times suggest an extragalactic origin and imply radio luminosities that are orders of magnitude larger than those of all known short-duration radio transients3. So far all fast radio bursts have been detected with large single-dish telescopes with arcminute localizations, and attempts to identify their counterparts (source or host galaxy) have relied on the contemporaneous variability of field sources4 or the presence of peculiar field stars5 or galaxies4. These attempts have not resulted in an unambiguous association6, 7 with a host or multi-wavelength counterpart. Here we report the subarcsecond localization of the fast radio burst FRB 121102, the only known repeating burst source8, 9, 10, 11, using high-time-resolution radio interferometric observations that directly image the bursts. Our precise localization reveals that FRB 121102 originates within 100 milliarcseconds of a faint 180-microJansky persistent radio source with a continuum spectrum that is consistent with non-thermal emission, and a faint (twenty-fifth magnitude) optical counterpart. The flux density of the persistent radio source varies by around ten per cent on day timescales, and very long baseline radio interferometry yields an angular size of less than 1.7 milliarcseconds. Our observations are inconsistent with the fast radio burst having a Galactic origin or its source being located within a prominent star-forming galaxy. Instead, the source appears to be co-located with a low-luminosity active galactic nucleus or a previously unknown type of extragalactic source. Localization and identification of a host or counterpart has been essential to understanding the origins and physics of other kinds of transient events, including gamma-ray bursts12, 13 and tidal disruption events14. However, if other fast radio bursts have similarly faint radio and optical counterparts, our findings imply that direct subarcsecond localizations may be the only way to provide reliable associations.

So far, of the eighteen FRBs detected since 2007, this is the only one to have occurred several times. The fact that this one has recurred several time shed some light on the nature of their source. For example, one theory for FRBs was that they resulted from some cataclysmic even such as an exploding supernova or a neutron star collapsing into a black hole. However, there are one-off events. Recurrence rules out these possible sources.

One of the candidates is a so-called magnetstar - a neutron star surrounded by the matter ejected as the parent star exploded at the end of its normal life. Neutron stars are a special sort of super-dense star resulting from the collapse of a star when the final stage of fusion of helium into heavier elements ends and the star explodes out the heavier elements so formed and the remaining core collapses. At this stage in the life of a star one of three things can happen:
  1. The core can collapse to become a white dwarf.
  2. If large enough, it can collapse further under its own gravity to become a black hole.
  3. It can collapse to a point at which gravity is enough for the atomic structure to breakdown and to force all the protons and electrons together to become neutrons with none of the space between the nucleus and the orbital electrons normally seen in atoms.

These latter are the super-dense neutron stars which, due to conservation of angular momentum as they collapse are rotating at extremely high speeds - often with a rotation period measured in fractions of a second. 

So, although it would be wonderful to say we have detected signs of intelligent, technologically advanced life in another galaxy, we haven't. It would have been good to watch the reactions of religions as they struggled to come to terms with the realisation that any claims they make for the uniqueness of Earth have just been destroyed, as have any claims they make for humans being the entire purpose of the Universe.

What we have done though is discover yet another example of order emerging naturally from the background chaos in the Universe, and this is something creationists especially have huge difficulty with as the 'impossibility' of order arising naturally from chaos is a central creationist dogma. It was long ago refuted by the mathematics of chaos theory of course, but concrete examples are harder for them to cope with than theories and hard sums.

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