Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Type Ia supernovae (SN Ia) are powerful stellar explosions that provide important distance indicators in cosmology. Recently, we proposed a new SN Ia mechanism that involves a nuclear fission chain reaction in an isolated white dwarf (WD). The first solids that form as a WD starts to freeze are actinide rich and potentially support a fission chain reaction. In this Letter, we explore thermonuclear ignition from fission heating. We perform thermal diffusion simulations and find at high densities, above about 7 × 10<jats:sup>8</jats:sup> g cm<jats:sup>−3</jats:sup>, that fission heating can ignite carbon burning. This could produce an SN Ia or another kind of astrophysical transient.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The population of binary black hole mergers identified through gravitational waves has uncovered unexpected features in the intrinsic properties of black holes in the universe. One particularly surprising and exciting result is the possible existence of black holes in the pair-instability mass gap, ∼50–120 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Dense stellar environments can populate this region of mass space through hierarchical mergers, with the retention efficiency of black hole merger products strongly dependent on the escape velocity of the host environment. We use simple toy models to represent hierarchical merger scenarios in various dynamical environments. We find that hierarchical mergers in environments with high escape velocities (≳300 km s<jats:sup>−1</jats:sup>) are efficiently retained. If such environments dominate the binary black hole merger rate, this would lead to an abundance of high-mass mergers that is potentially incompatible with the empirical mass spectrum from the current catalog of binary black hole mergers. Models that efficiently generate hierarchical mergers, and contribute significantly to the observed population, must therefore be tuned to avoid a “cluster catastrophe” of overproducing binary black hole mergers within and above the pair-instability mass gap.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have conducted a NanoSIMS-based search for presolar material in samples recently returned from C-type asteroid Ryugu as part of JAXA's Hayabusa2 mission. We report the detection of all major presolar grain types with O- and C-anomalous isotopic compositions typically identified in carbonaceous chondrite meteorites: 1 silicate, 1 oxide, 1 O-anomalous supernova grain of ambiguous phase, 38 SiC, and 16 carbonaceous grains. At least two of the carbonaceous grains are presolar graphites, whereas several grains with moderate C isotopic anomalies are probably organics. The presolar silicate was located in a clast with a less altered lithology than the typical extensively aqueously altered Ryugu matrix. The matrix-normalized presolar grain abundances in Ryugu are <jats:inline-formula> <jats:tex-math> <?CDATA ${4.8}_{-2.6}^{+4.7}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>4.8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2.6</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>4.7</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac83bdieqn1.gif" xlink:type="simple" /> </jats:inline-formula> ppm for O-anomalous grains, <jats:inline-formula> <jats:tex-math> <?CDATA ${25}_{-5}^{+6}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>25</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>5</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>6</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac83bdieqn2.gif" xlink:type="simple" /> </jats:inline-formula> ppm for SiC grains, and <jats:inline-formula> <jats:tex-math> <?CDATA ${11}_{-3}^{+5}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>11</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>5</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac83bdieqn3.gif" xlink:type="simple" /> </jats:inline-formula> ppm for carbonaceous grains. Ryugu is isotopically and petrologically similar to carbonaceous Ivuna-type (CI) chondrites. To compare the in situ presolar grain abundances of Ryugu with CI chondrites, we also mapped Ivuna and Orgueil samples and found a total of 15 SiC grains and 6 carbonaceous grains. No O-anomalous grains were detected. The matrix-normalized presolar grain abundances in the CI chondrites are similar to those in Ryugu: <jats:inline-formula> <jats:tex-math> <?CDATA ${23}_{-6}^{+7}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>23</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>6</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>7</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac83bdieqn4.gif" xlink:type="simple" /> </jats:inline-formula> ppm SiC and <jats:inline-formula> <jats:tex-math> <?CDATA ${9.0}_{-3.6}^{+5.4}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>9.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3.6</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>5.4</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac83bdieqn5.gif" xlink:type="simple" /> </jats:inline-formula> ppm carbonaceous grains. Thus, our results provide further evidence in support of the Ryugu–CI connection. They also reveal intriguing hints of small-scale heterogeneities in the Ryugu samples, such as locally distinct degrees of alteration that allowed the preservation of delicate presolar material.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We calculate the electron–positron pair production rate at the base of the jet of Cyg X-1 by collisions of photons from its hot accretion flow using the measurement of its average soft gamma-ray spectra by the Compton Gamma Ray Observatory and INTEGRAL satellites. We have found that this rate approximately equals the flow rate of the leptons emitting the observed synchrotron radio-to-IR spectrum of the jet, calculated using an extended jet model following that of Blandford &amp; Königl. This coincidence shows the jet composition is likely to be pair dominated. The same coincidences were found before in the microquasar MAXI J1820+070 and in the radio galaxy 3C 120, which shows that the considered mechanism can be universal for at least some classes of relativistic jets. Furthermore, we recalculate the jet power of Cyg X-1. The presence of pairs can strongly reduce the power in the bulk motion of ions, which then limits the parameter space at which the jet can power the ∼5 pc nebular structure present in its vicinity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a comparison between the average atomic gas mass, 〈<jats:italic>M</jats:italic> <jats:sub>Atom</jats:sub>〉 (including hydrogen and helium), the average molecular gas mass, 〈<jats:italic>M</jats:italic> <jats:sub>Mol</jats:sub>〉, and the average stellar mass, 〈<jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub>〉, of a sample of star-forming galaxies at <jats:italic>z</jats:italic> ≈ 0.75–1.45 to probe the baryonic composition of galaxies in and during the epoch of peak star formation activity in the universe. The 〈<jats:italic>M</jats:italic> <jats:sub>Atom</jats:sub>〉 values of star-forming galaxies in two stellar-mass-matched samples at <jats:italic>z</jats:italic> = 0.74–1.25 and <jats:italic>z</jats:italic> = 1.25–1.45 were derived by stacking their H<jats:sc>i</jats:sc> 21 cm signals in the GMRT-CAT<jats:italic>z</jats:italic>1 survey. We find that the baryonic composition of star-forming galaxies at <jats:italic>z</jats:italic> ≳ 1 is dramatically different from that at <jats:italic>z</jats:italic> ≈ 0. For star-forming galaxies with 〈<jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub>〉 ≈ 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, the contribution of stars to the total baryonic mass, <jats:italic>M</jats:italic> <jats:sub>Baryon</jats:sub>, is ≈61% at <jats:italic>z</jats:italic> ≈ 0, but only ≈16% at <jats:italic>z</jats:italic> ≈ 1.3, while molecular gas constitutes ≈6% of the baryonic mass at <jats:italic>z</jats:italic> ≈ 0, and ≈14% at <jats:italic>z</jats:italic> ≈ 1.3. Remarkably, we find that atomic gas makes up ≈70% of <jats:italic>M</jats:italic> <jats:sub>Baryon</jats:sub> in star-forming galaxies at <jats:italic>z</jats:italic> ≈ 1.3. We find that the ratio 〈<jats:italic>M</jats:italic> <jats:sub>Atom</jats:sub>〉/〈<jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub>〉 is higher at both <jats:italic>z</jats:italic> ≈ 1.3 and at <jats:italic>z</jats:italic> ≈ 1.0 than in the local universe, with 〈<jats:italic>M</jats:italic> <jats:sub>Atom</jats:sub>〉/〈<jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub>〉 ≈ 1.4 at <jats:italic>z</jats:italic> ≈ 1.0 and ≈ 4.4 at <jats:italic>z</jats:italic> ≈ 1.3, compared to its value of ≈0.5 today. Further, we find that the ratio 〈<jats:italic>M</jats:italic> <jats:sub>Atom</jats:sub>〉/〈<jats:italic>M</jats:italic> <jats:sub>Mol</jats:sub>〉 in star-forming galaxies with 〈<jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub>〉 ≈ 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> is ≈2.3 at <jats:italic>z</jats:italic> ≈ 1.0 and ≈5.0 at <jats:italic>z</jats:italic> ≈ 1.3. Overall, we find that atomic gas is the dominant component of the baryonic mass of star-forming galaxies at <jats:italic>z</jats:italic> ≈ 1.3, during the epoch of peak star formation activity in the universe.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on the discovery by the Zwicky Transient Facility of an asteroid orbiting entirely within the orbit of Venus, the first known example of this orbital class. The asteroid's perihelion is closer to the Sun than the aphelion of Mercury, and its diameter is estimated at about 1.8 km assuming an albedo of 0.2. The object was first observed on 2020 January 4 in four exposures obtained 7 minutes apart during an evening twilight survey. Its IAU-recognized designation is 594913 ‘Ayló’chaxnim.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on a search for continuous gravitational waves (GWs) from NS 1987A, the neutron star born in SN 1987A. The search covered a frequency band of 75–275 Hz, included a wide range of spin-down parameters for the first time, and coherently integrated 12.8 days of LIGO data below 125 Hz and 8.7 days of LIGO data above 125 Hz from the second Advanced LIGO–Virgo observing run. We found no astrophysical signal. We set upper limits on GW emission as tight as an intrinsic strain of 2 × 10<jats:sup>−25</jats:sup> at 90% confidence. The large spin-down parameter space makes this search the first astrophysically consistent one for continuous GWs from NS 1987A. Our upper limits are the first consistent ones to beat an analog of the spin-down limit based on the age of the neutron star and hence are the first GW observations to put new constraints on NS 1987A.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We examine a rare and interesting observation of magnetic reconnection embedded in a large-scale region of strong turbulence in which magnetic field annihilation is energizing ions and electrons. The magnetic reconnection event is in Earth’s magnetotail and is associated with enhanced energetic particle fluxes indicating local particle acceleration. Despite substantial electric and magnetic field fluctuations throughout the surrounding, large-scale region, the ongoing magnetic reconnection has many similar properties to laminar, 2D magnetic reconnection including Hall electric fields, Hall magnetic fields, a thin electron current sheet, and ion and electron jets. Notably, the electron jet emerging from the electron diffusion region (EDR) appears to transport sufficient off-diagonal momentum to infer that off-diagonal electron stress can support the reconnection electric field in the EDR even in a turbulent environment. Although the electron jet appears to be briefly (∼1 s) deflected or possibly interrupted by an electromagnetic disturbance, the reconnection appears to otherwise continue for a long period (∼30 minutes) as evidenced by a persistent ion jet. This particular finding implies that the fundamental electron-scale processes inside of the EDR in turbulent magnetic reconnection are not necessarily distinct from those in laminar magnetic reconnection. These observations provide direct confirmation that magnetic reconnection can not only be responsible for but also can continue in regions of large-scale turbulence. Because the electric and magnetic fields of strong turbulence are linked to particle acceleration, it follows that particle acceleration also can continue as a consequence of turbulent magnetic reconnection.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Close encounters of stars to the Sun could affect life on Earth through gravitational perturbations of comets in the Oort cloud or exposure to ionizing radiation. By integrating orbits through the Galactic potential, I identify which of 33 million stars in Gaia DR3 with complete phase space information come close to the Sun. 61 stars formally approach within 1 pc, although there is high confidence in only 42 (two thirds) of these, the rest being spurious measurements or (in) binary systems. Most of the stars will encounter within the past or future 6 Myr; earlier/later encounters are less common due to the magnitude limit of the Gaia radial velocities (RVs). Several close encountering stars are identified for the first time, and the encounter times, distances, and velocities of previously known close encounters are determined more precisely on account of the significantly improved precision of Gaia DR3 over earlier releases. The K7 dwarf Gl 710 remains the closest known encounter, with an estimated (median) encounter distance of 0.0636 pc (90% confidence interval 0.0595–0.0678 pc) to take place in 1.3 Myr. The new second closest encounter took place 2.8 Myr ago: this was the G3 dwarf HD 7977, now 76 pc away, which approached within less than 0.05 pc of the Sun with a probability of one third. The apparent close encounter of the white dwarf <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="object" xlink:href="UPM J0812-3529" xlink:type="simple">UPM J0812-3529</jats:named-content> is probably spurious due to an incorrect RV in Gaia DR3.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present Atacama Large Millimeter/submillimeter Array observations at ≈100 GHz with 0.″05 (3 pc) resolution of the kiloparsec-scale jet seen in the nearby Seyfert galaxy NGC 1068, and we report the presence of parsec-scale blobs at the head of the jet. The combination of the detected radio flux (≈0.8 mJy), spectral index (≈0.5), and blob size (≈10 pc) suggests a strong magnetic field of <jats:italic>B</jats:italic> ≈ 240 <jats:italic>μ</jats:italic>G. Such a strong magnetic field most likely implies magnetic field amplification by streaming cosmic rays. The estimated cosmic-ray power of the jet may exceed the limit set by the star formation activity in this galaxy. This result suggests that even modest-power jets can increase the galactic cosmic-ray content while propagating through the galactic bulge.</jats:p>