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Two giant, linearly polarized radio lobes have been found emanating from the Galactic Centre, and are thought to originate in a biconical, star-formation-driven outflow from the Galaxy’s central 200 parsecs that transports a huge amount of magnetic energy, about 10 55 ergs, into the Galactic halo Magnetic outflows at the Galactic Centre A radio polarization survey of the southern sky with the Parkes Radio Telescope has revealed two huge, polarized radio lobes extending far out into the Galactic halo from the Galactic Centre region. The lobes are largely coincident with the 'Fermi bubbles', recently discovered regions of γ-ray emission reaching far above and below the Galactic Centre. The radio lobes are permeated by strong magnetic fields, and appear to originate as a biconical outflow driven by star formation rather than by a black hole. The nucleus of the Milky Way is known to harbour regions of intense star formation activity as well as a supermassive black hole 1 . Recent observations have revealed regions of γ-ray emission reaching far above and below the Galactic Centre (relative to the Galactic plane), the so-called ‘Fermi bubbles’ 2 . It is uncertain whether these were generated by nuclear star formation or by quasar-like outbursts of the central black hole 3 , 4 , 5 , 6 and no information on the structures’ magnetic field has been reported. Here we report observations of two giant, linearly polarized radio lobes, containing three ridge-like substructures, emanating from the Galactic Centre. The lobes each extend about 60 degrees in the Galactic bulge, closely corresponding to the Fermi bubbles, and are permeated by strong magnetic fields of up to 15 microgauss. We conclude that the radio lobes originate in a biconical, star-formation-driven (rather than black-hole-driven) outflow from the Galaxy’s central 200 parsecs that transports a huge amount of magnetic energy, about 10 55 ergs, into the Galactic halo. The ridges wind around this outflow and, we suggest, constitute a ‘phonographic’ record of nuclear star formation activity over at least ten million years.

We review the observations of supernova remnants (SNRs) and pulsar-wind nebulae (PWNe) that give information on the strength and orientation of magnetic fields. Radio polarimetry gives the degree of order of magnetic fields, and the orientation of the ordered component. Many young shell supernova remnants show evidence for synchrotron X-ray emission. The spatial analysis of this emission suggests that magnetic fields are amplified by one to two orders of magnitude in strong shocks. Detection of several remnants in TeV gamma rays implies a lower limit on the magnetic-field strength (or a measurement, if the emission process is inverse-Compton upscattering of cosmic microwave background photons). Upper limits to GeV emission similarly provide lower limits on magnetic-field strengths. In the historical shell remnants, lower limits on B range from 25 to 1000 μG. Two remnants show variability of synchrotron X-ray emission with a timescale of years. If this timescale is the electron-acceleration or radiative loss timescale, magnetic fields of order 1 mG are also implied. In pulsar-wind nebulae, equipartition arguments and dynamical modeling can be used to infer magnetic-field strengths anywhere from ∼5 μG to 1 mG. Polarized fractions are considerably higher than in SNRs, ranging to 50 or 60% in some cases; magnetic-field geometries often suggest a toroidal structure around the pulsar, but this is not universal. Viewing-angle effects undoubtedly play a role. MHD models of radio emission in shell SNRs show that different orientations of upstream magnetic field, and different assumptions about electron acceleration, predict different radio morphology. In the remnant of SN 1006, such comparisons imply a magnetic-field orientation connecting the bright limbs, with a substantial density gradient across the remnant.

Turbulence in the Milky Way Turbulence is a well-studied phenomenon in disciplines ranging from meteorology to cardiology, but astrophysical turbulence — acting over physical scales spanning 10 15 orders of magnitude — stretches current theories to their limits. Until now, insight into interstellar turbulence has been limited by our inability to image the small-scale structure associated with turbulent motions. This paper presents the first direct images of turbulence in interstellar gas. Using radio-continuum images of a patch of the Galactic plane, observed with the Australia Telescope Compact Array, Gaensler et al . report that the gradient of the Stokes vector ( Q,U ) provides an image of magnetized turbulence in diffuse ionized gas, seen as a complex filamentary web of discontinuities in gas density and magnetic field. The turbulence in the warm ionized medium has a relatively low sonic Mach number of approximately Mach 2. The interstellar medium of the Milky Way is multiphase 1 , magnetized 2 and turbulent 3 . Turbulence in the interstellar medium produces a global cascade of random gas motions, spanning scales ranging from 100 parsecs to 1,000 kilometres (ref. 4 ). Fundamental parameters of interstellar turbulence such as the sonic Mach number (the speed of sound) have been difficult to determine, because observations have lacked the sensitivity and resolution to image the small-scale structure associated with turbulent motion 5 , 6 , 7 . Observations of linear polarization and Faraday rotation in radio emission from the Milky Way have identified unusual polarized structures that often have no counterparts in the total radiation intensity or at other wavelengths 8 , 9 , 10 , 11 , 12 , and whose physical significance has been unclear 13 , 14 , 15 . Here we report that the gradient of the Stokes vector ( Q , U ), where Q and U are parameters describing the polarization state of radiation, provides an image of magnetized turbulence in diffuse, ionized gas, manifested as a complex filamentary web of discontinuities in gas density and magnetic field. Through comparison with simulations, we demonstrate that turbulence in the warm, ionized medium has a relatively low sonic Mach number, M s  ≲ 2. The development of statistical tools for the analysis of polarization gradients will allow accurate determinations of the Mach number, Reynolds number and magnetic field strength in interstellar turbulence over a wide range of conditions.

We have measured the Faraday rotation toward a large sample of polarized radio sources behind the Large Magellanic Cloud (LMC) to determine the structure of this galaxy's magnetic field. The magnetic field of the LMC consists of a coherent axisymmetric spiral of field strength [approximately]1 microgauss. Strong fluctuations in the magnetic field are also seen on small (<0.5 parsec) and large ([approximately]100 parsecs) scales. The large bursts of recent star formation and supernova activity in the LMC argue against standard dynamo theory, adding to the growing evidence for rapid field amplification in galaxies.

Flares back in fashion On 27 December last year, SGR1806–20, a soft γ-ray repeater in Sagittarius, released a giant flare that has been called the brightest explosion ever recorded. SGRs are X-ray stars that sporadically emit low-energy γ-ray bursts. They are thought to be magnetars: neutron stars with observable emissions powered by magnetic dissipation. Five papers in this issue report initial and follow-up observations of this event. The data are remarkable: for instance in a fifth of a second, the flare released as much energy as the Sun radiates in a quarter of a million years. Such power can be explained by catastrophic global crust failure and magnetic reconnection on a magnetar. Releasing a hundred times the energy of the only two previous SGR giant flares, this may have been a once-in-a-lifetime event for astronomers, and for the star itself. Two classes of rotating neutron stars—soft γ-ray repeaters (SGRs) and anomalous X-ray pulsars—are magnetars 1 , whose X-ray emission is powered by a very strong magnetic field ( B ≈ 10 15  G). SGRs occasionally become ‘active’, producing many short X-ray bursts. Extremely rarely, an SGR emits a giant flare with a total energy about a thousand times higher than in a typical burst 2 , 3 , 4 . Here we report that SGR 1806–20 emitted a giant flare on 27 December 2004. The total (isotropic) flare energy is 2 × 10 46  erg, which is about a hundred times higher than the other two previously observed giant flares. The energy release probably occurred during a catastrophic reconfiguration of the neutron star's magnetic field. If the event had occurred at a larger distance, but within 40 megaparsecs, it would have resembled a short, hard γ-ray burst, suggesting that flares from extragalactic SGRs may form a subclass of such bursts.

Magnetic fields play a pivotal role in the physics of interstellar medium in galaxies 1 , but there are few observational constraints on how they evolve across cosmic time 2 – 7 . Spatially resolved synchrotron polarization maps at radio wavelengths reveal well-ordered large-scale magnetic fields in nearby galaxies 1 , 8 , 9 that are believed to grow from a seed field via a dynamo effect 10 , 11 . To directly test and characterize this theory requires magnetic field strength and geometry measurements in cosmologically distant galaxies, which are challenging to obtain due to the limited sensitivity and angular resolution of current radio telescopes. Here, we report the cleanest measurements yet of magnetic fields in a galaxy beyond the local volume, free of the systematics traditional techniques would encounter. By exploiting the scenario where the polarized radio emission from a background source is gravitationally lensed by a foreground galaxy at z  = 0.439 using broadband radio polarization data, we detected coherent μG magnetic fields in the lensing disk galaxy as seen 4.6 Gyr ago, with similar strength and geometry to local volume galaxies. This is the highest redshift galaxy whose observed coherent magnetic field property is compatible with a mean-field dynamo origin. The detection and characterization of a large-scale ordered magnetic field through a gravitational lens in a galaxy beyond the local volume allows us to elucidate how such magnetic fields come about, supporting a mean-field dynamo origin.

Flares back in fashion On 27 December last year, SGR1806–20, a soft γ-ray repeater in Sagittarius, released a giant flare that has been called the brightest explosion ever recorded. SGRs are X-ray stars that sporadically emit low-energy γ-ray bursts. They are thought to be magnetars: neutron stars with observable emissions powered by magnetic dissipation. Five papers in this issue report initial and follow-up observations of this event. The data are remarkable: for instance in a fifth of a second, the flare released as much energy as the Sun radiates in a quarter of a million years. Such power can be explained by catastrophic global crust failure and magnetic reconnection on a magnetar. Releasing a hundred times the energy of the only two previous SGR giant flares, this may have been a once-in-a-lifetime event for astronomers, and for the star itself. Soft γ-ray repeaters (SGRs) are ‘magnetars’, a small class of slowly spinning neutron stars with extreme surface magnetic fields, B ≈ 10 15 gauss (refs 1 , 2 –3 ). On 27 December 2004, a giant flare 4 was detected from the magnetar SGR 1806 - 20 (ref. 2 ), only the third such event recorded 5 , 6 . This burst of energy was detected by a variety of instruments 7 , 8 and even caused an ionospheric disturbance in the Earth's upper atmosphere that was recorded around the globe 9 . Here we report the detection of a fading radio afterglow produced by this outburst, with a luminosity 500 times larger than the only other detection of a similar source 10 . From day 6 to day 19 after the flare from SGR 1806 - 20, a resolved, linearly polarized, radio nebula was seen, expanding at approximately a quarter of the speed of light. To create this nebula, at least 4 × 10 43  ergs of energy must have been emitted by the giant flare in the form of magnetic fields and relativistic particles.

Fast radio bursts (FRBs) are highly dispersed millisecond-duration radio flashes probably arriving from far outside the Milky Way1,2. This phenomenon was discovered at radio frequencies near 1.4 gigahertz and so far has been observed in one case3 at as high as 8 gigahertz, but not at below 700 megahertz in spite of substantial searches at low frequencies4,5,6,7. Here we report detections of 13 FRBs at radio frequencies as low as 400 megahertz, on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) using the CHIME/FRB instrument8. They were detected during a telescope pre-commissioning phase, when the sensitivity and field of view were not yet at design specifications. Emission in multiple events is seen down to 400 megahertz, the lowest radio frequency to which the telescope is sensitive. The FRBs show various temporal scattering behaviours, with the majority detectably scattered, and some apparently unscattered to within measurement uncertainty even at our lowest frequencies. Of the 13 reported here, one event has the lowest dispersion measure yet reported, implying that it is among the closest yet known, and another has shown multiple repeat bursts, as described in a companion paper9. The overall scattering properties of our sample suggest that FRBs as a class are preferentially located in environments that scatter radio waves more strongly than in the diffuse interstellar medium in the Milky Way.

We have detected an x-ray nebula around the binary millisecond pulsar B1957+20. A narrow tail, corresponding to the shocked pulsar wind, is seen interior to the known Hα bow shock and proves the long-held assumption that the rotational energy of millisecond pulsars is dissipated through relativistic winds. Unresolved x-ray emission likely represents the shock where the winds of the pulsar and its companion collide. This emission indicates that the efficiency with which relativistic particles are accelerated in the postshock flow is similar to that for young pulsars, despite the shock proximity and much weaker surface magnetic field of this millisecond pulsar.

Supermassive black holes and supernova explosions at the centres of active galaxies power cycles of outflowing and inflowing gas that affect galactic evolution and the overall structure of the Universe 1 , 2 . While simulations and observations show that this must be the case, the range of physical scales (over ten orders of magnitude) and paucity of available tracers make both the simulation and observation of these effects difficult 3 , 4 . By serendipity, there lies an active galaxy, Centaurus A (NGC 5128) 5 , 6 , at such a close proximity as to allow its observation over this entire range of scales and across the entire electromagnetic spectrum. In the radio band, however, details on scales of 10–100 kpc from the supermassive black hole have so far been obscured by instrumental limitations 7 , 8 . Here we report low-frequency radio observations that overcome these limitations and show evidence for a broad, bipolar outflow with velocity of 1,100 km s −1 and mass-outflow rate of 2.9  M ⊙  yr −1 on these scales. We combine our data with the plethora of multiscale, multi-wavelength, historical observations of Centaurus A to probe a unified view of feeding and feedback, which we show to be consistent with the chaotic cold accretion self-regulation scenario 9 , 10 . Previously unresolved radio features of nearby Centaurus A reveal transition regions for both the feeding of this active galaxy and the feedback mechanism for recycling energy back into the surrounding medium.