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Astroquizzical : solving the cosmic puzzles of our planets, stars and galaxies
\"Looking up at the night sky, we see not only stars twinkling in their constellations and planets caught mid-orbit but our cosmic family tree. We are here on Earth because billions of years ago the Big Bang created the atoms that, over unimaginable periods of time, formed the stars and galaxies. Generations of stars that burned, exploded, or collided long before our planet was formed created the carbon of our bodies and the iron in our blood. In Astroquizzical, astrophysicist Jillian Scudder takes readers on a curiosity-driven journey through outer space, traveling back in time from Earth to the stars and galaxies to the cosmic explosions of the Big Bang. Scudder proceeds--astroquizzically--question by question, answering and explaining such queries as \"What color is the universe?,\" \"Do all planets spin the same way?,\" and \"How many galaxies are there?\" Along the way, she proposes a series of thought experiments, including \"What would happen if we split the sun in half?\" and \"What happens to time dilation at the speed of light?\" She covers meteors, the aurora, and the Moon (Earth's cosmic companion); Jupiter's stripes and Pluto's mountains; red dwarfs, brown dwarfs, and white dwarfs; the deaths of stars and the abundance of galaxies; and much more. Striking color images illustrate astrophysical marvels.\" -- Back Cover
Book
Ultrahigh-energy photons up to 1.4 petaelectronvolts from 12 γ-ray Galactic sources
The extension of the cosmic-ray spectrum beyond 1 petaelectronvolt (PeV; 10
15
electronvolts) indicates the existence of the so-called PeVatrons—cosmic-ray factories that accelerate particles to PeV energies. We need to locate and identify such objects to find the origin of Galactic cosmic rays
1
. The principal signature of both electron and proton PeVatrons is ultrahigh-energy (exceeding 100 TeV) γ radiation. Evidence of the presence of a proton PeVatron has been found in the Galactic Centre, according to the detection of a hard-spectrum radiation extending to 0.04 PeV (ref.
2
). Although γ-rays with energies slightly higher than 0.1 PeV have been reported from a few objects in the Galactic plane
3
–
6
, unbiased identification and in-depth exploration of PeVatrons requires detection of γ-rays with energies well above 0.1 PeV. Here we report the detection of more than 530 photons at energies above 100 teraelectronvolts and up to 1.4 PeV from 12 ultrahigh-energy γ-ray sources with a statistical significance greater than seven standard deviations. Despite having several potential counterparts in their proximity, including pulsar wind nebulae, supernova remnants and star-forming regions, the PeVatrons responsible for the ultrahigh-energy γ-rays have not yet been firmly localized and identified (except for the Crab Nebula), leaving open the origin of these extreme accelerators.
Observations of γ-rays with energies up to 1.4 PeV find that 12 sources in the Galaxy are PeVatrons, one of which is the Crab Nebula.
Journal Article
A star explodes : the story of Supernova 1054
\"About 7,500 years ago, a star exploded in our galaxy, burning bright as billions of suns. It took thousands of years for the light of this explosion to reach Earth, but in the year 1054, people of the Chinese court recorded a new star in the night sky that shone brighter than all the other stars. A guest star, they called it, and they marvelled as its light shone even through the bright of day.\"-- Front jacket flap.
BOOK
An extreme magneto-ionic environment associated with the fast radio burst source FRB 121102
Fast radio bursts are millisecond-duration, extragalactic radio flashes of unknown physical origin1,2,3. The only known repeating fast radio burst source4,5,6—FRB 121102—has been localized to a star-forming region in a dwarf galaxy7,8,9 at redshift 0.193 and is spatially coincident with a compact, persistent radio source7,10. The origin of the bursts, the nature of the persistent source and the properties of the local environment are still unclear. Here we report observations of FRB 121102 that show almost 100 per cent linearly polarized emission at a very high and variable Faraday rotation measure in the source frame (varying from +1.46 × 105 radians per square metre to +1.33 × 105 radians per square metre at epochs separated by seven months) and narrow (below 30 microseconds) temporal structure. The large and variable rotation measure demonstrates that FRB 121102 is in an extreme and dynamic magneto-ionic environment, and the short durations of the bursts suggest a neutron star origin. Such large rotation measures have hitherto been observed11,12 only in the vicinities of massive black holes (larger than about 10,000 solar masses). Indeed, the properties of the persistent radio source are compatible with those of a low-luminosity, accreting massive black hole10. The bursts may therefore come from a neutron star in such an environment or could be explained by other models, such as a highly magnetized wind nebula13 or supernova remnant14 surrounding a young neutron star.
Journal Article
Preferential occurrence of fast radio bursts in massive star-forming galaxies
Fast radio bursts (FRBs) are millisecond-duration events detected from beyond the Milky Way. FRB emission characteristics favour highly magnetized neutron stars, or magnetars, as the sources
1
, as evidenced by FRB-like bursts from a galactic magnetar
2
,
3
, and the star-forming nature of FRB host galaxies
4
,
5
. However, the processes that produce FRB sources remain unknown
6
. Although galactic magnetars are often linked to core-collapse supernovae (CCSNe)
7
, it is uncertain what determines which supernovae result in magnetars. The galactic environments of FRB sources can be used to investigate their progenitors. Here, we present the stellar population properties of 30 FRB host galaxies discovered by the Deep Synoptic Array (DSA-110). Our analysis shows a marked deficit of low-mass FRB hosts compared with the occurrence of star formation in the Universe, implying that FRBs are a biased tracer of star formation, preferentially selecting massive star-forming galaxies. This bias may be driven by galaxy metallicity, which is positively correlated with stellar mass
8
. Metal-rich environments may favour the formation of magnetar progenitors through stellar mergers
9
,
10
, as higher-metallicity stars are less compact and more likely to fill their Roche lobes, leading to unstable mass transfer. Although massive stars do not have convective interiors to generate strong magnetic fields by dynamo
11
, merger remnants are thought to have the requisite internal magnetic-field strengths to result in magnetars
11
,
12
. The preferential occurrence of FRBs in massive star-forming galaxies suggests that a core-collapse supernova of merger remnants preferentially forms magnetars.
Analysis of the stellar population properties of 30 host galaxies of fast radio bursts (FRBs) suggests an abundance of FRBs in massive star-forming galaxies, and implies that the formation of FRB sources—magnetars—is linked to core-collapse supernovae of stellar merger remnants.
Journal Article
Pulsar emission amplified and resolved by plasma lensing in an eclipsing binary
Radio pulsars scintillate because their emission travels through the ionized interstellar medium along multiple paths, which interfere with each other. It has long been realized that, independent of their nature, the regions responsible for the scintillation could be used as ‘interstellar lenses’ to localize pulsar emission regions
1
,
2
. Most such lenses, however, resolve emission components only marginally, limiting results to statistical inferences and detections of small positional shifts
3
–
5
. As lenses situated close to their source offer better resolution, it should be easier to resolve emission regions of pulsars located in high-density environments such as supernova remnants
6
or binaries in which the pulsar’s companion has an ionized outflow. Here we report observations of extreme plasma lensing in the ‘black widow’ pulsar, B1957+20, near the phase in its 9.2-hour orbit at which its emission is eclipsed by its companion’s outflow
7
–
9
. During the lensing events, the observed radio flux is enhanced by factors of up to 70–80 at specific frequencies. The strongest events clearly resolve the emission regions: they affect the narrow main pulse and parts of the wider interpulse differently. We show that the events arise naturally from density fluctuations in the outer regions of the outflow, and we infer a resolution of our lenses that is comparable to the pulsar’s radius, about 10 kilometres. Furthermore, the distinct frequency structures imparted by the lensing are reminiscent of what is observed for the repeating fast radio burst FRB 121102, providing observational support for the idea that this source is observed through, and thus at times strongly magnified by, plasma lenses
10
.
Radiation from the ‘black widow’ pulsar B1957+20 is amplified when a companion brown dwarf passes in front of the source, suggesting that plasma flowing from the companion acts as a lens.
Journal Article
The diffuse γ-ray background is dominated by star-forming galaxies
The Fermi Gamma-ray Space Telescope has revealed a diffuse γ-ray background at energies from 0.1 gigaelectronvolt to 1 teraelectronvolt, which can be separated into emission from our Galaxy and an isotropic, extragalactic component
1
. Previous efforts to understand the latter have been hampered by the lack of physical models capable of predicting the γ-ray emission produced by the many candidate sources, primarily active galactic nuclei
2
–
5
and star-forming galaxies
6
–
10
, leaving their contributions poorly constrained. Here we present a calculation of the contribution of star-forming galaxies to the γ-ray background that does not rely on empirical scalings and is instead based on a physical model for the γ-ray emission produced when cosmic rays accelerated in supernova remnants interact with the interstellar medium
11
. After validating the model against local observations, we apply it to the observed cosmological star-forming galaxy population and recover an excellent match to both the total intensity and the spectral slope of the γ-ray background, demonstrating that star-forming galaxies alone can explain the full diffuse, isotropic γ-ray background.
The diffuse, isotropic background of gamma rays comes mainly from star-forming galaxies, according to a physical model of gamma-ray emission.
Journal Article
Vela pulsar wind nebula X-rays are polarized to near the synchrotron limit
Pulsar wind nebulae are formed when outflows of relativistic electrons and positrons hit the surrounding supernova remnant or interstellar medium at a shock front. The Vela pulsar wind nebula is powered by a young pulsar (B0833-45, aged 11,000 years)
1
and located inside an extended structure called Vela X, which is itself inside the supernova remnant
2
. Previous X-ray observations revealed two prominent arcs that are bisected by a jet and counter jet
3
,
4
. Radio maps have shown high linear polarization of 60% in the outer regions of the nebula
5
. Here we report an X-ray observation of the inner part of the nebula, where polarization can exceed 60% at the leading edge—approaching the theoretical limit of what can be produced by synchrotron emission. We infer that, in contrast with the case of the supernova remnant, the electrons in the pulsar wind nebula are accelerated with little or no turbulence in a highly uniform magnetic field.
Polarization can exceed 60% at the leading edge of the inner part of the Vela pulsar wind nebula; in contrast with the case of the supernova remnant, the electrons in the pulsar wind nebula are accelerated with little or no turbulence in a highly uniform magnetic field.
Journal Article
Very-high-energy particle acceleration powered by the jets of the microquasar SS 433
SS 433 is a binary system containing a supergiant star that is overflowing its Roche lobe with matter accreting onto a compact object (either a black hole or neutron star)
1
–
3
. Two jets of ionized matter with a bulk velocity of approximately 0.26
c
(where
c
is the speed of light in vacuum) extend from the binary, perpendicular to the line of sight, and terminate inside W50, a supernova remnant that is being distorted by the jets
2
,
4
–
8
. SS 433 differs from other microquasars (small-scale versions of quasars that are present within our own Galaxy) in that the accretion is believed to be super-Eddington
9
–
11
, and the luminosity of the system is about 10
40
ergs per second
2
,
9
,
12
,
13
. The lobes of W50 in which the jets terminate, about 40 parsecs from the central source, are expected to accelerate charged particles, and indeed radio and X-ray emission consistent with electron synchrotron emission in a magnetic field have been observed
14
–
16
. At higher energies (greater than 100 gigaelectronvolts), the particle fluxes of
γ
-rays from X-ray hotspots around SS 433 have been reported as flux upper limits
6
,
17
–
20
. In this energy regime, it has been unclear whether the emission is dominated by electrons that are interacting with photons from the cosmic microwave background through inverse-Compton scattering or by protons that are interacting with the ambient gas. Here we report teraelectronvolt γ-ray observations of the SS 433/W50 system that spatially resolve the lobes. The teraelectronvolt emission is localized to structures in the lobes, far from the centre of the system where the jets are formed. We have measured photon energies of at least 25 teraelectronvolts, and these are certainly not Doppler-boosted, because of the viewing geometry. We conclude that the emission—from radio to teraelectronvolt energies—is consistent with a single population of electrons with energies extending to at least hundreds of teraelectronvolts in a magnetic field of about 16 microgauss.
Observations of teraelectronvolt γ-rays accelerated by the jets of the miniature quasar SS 433 are reported.
Journal Article
On the Determination of the Evolutionary Status of Supernova Remnants from Radio Observation Data
This paper aims to give a brief review of a new concept for the preliminary determination of the evolutionary status of supernova remnants (SNRs). Data obtained by radio observations in continuum are used. There are three different methods underlying the new concept: The first one is based on the location of the observationally obtained radio surface brightness and the corresponding diameter of an SNR in theoretically derived Σ– D tracks, the second one is based on the forms of radio spectra, and the third one is based on the magnetic field strengths that are estimated through the equipartition (eqp) calculation. Using a combination of these methods, developed over the last two decades by the Belgrade SNR Research Group, we can estimate the evolutionary status of SNRs. This concept helps radio observers to determine preliminarily the stage of the evolution of an SNR observed in the radio domain. Additionally, this concept was applied to several SNRs, observed by the Australia Telescope Compact Array, and the corresponding results are reviewed here. Moreover, some of the results are revised in this review to reflect the recently published updated Σ– D and eqp analyses.
Journal Article