Acceleration and manipulation of electron bunches underlie most electron and X-ray devices used for ultrafast imaging and spectroscopy. New terahertz-driven concepts offer orders-of-magnitude ...improvements in field strengths, field gradients, laser synchronization and compactness relative to conventional radio-frequency devices, enabling shorter electron bunches and higher resolution with less infrastructure while maintaining high charge capacities (pC), repetition rates (kHz) and stability. We present a segmented terahertz electron accelerator and manipulator (STEAM) capable of performing multiple high-field operations on the 6D-phase-space of ultrashort electron bunches. With this single device, powered by few-micro-Joule, single-cycle, 0.3 THz pulses, we demonstrate record THz-acceleration of >30 keV, streaking with <10 fs resolution, focusing with >2 kT/m strength, compression to ~100 fs as well as real-time switching between these modes of operation. The STEAM device demonstrates the feasibility of THz-based electron accelerators, manipulators and diagnostic tools enabling science beyond current resolution frontiers with transformative impact.
Abstract
We observed the W51 high-mass star-forming complex with the Atacama Large Millimeter/submillimeter Array’s longest-baseline configurations, achieving an angular resolution of ∼20 mas, ...corresponding to a linear resolution of ∼100 au at
D
W51
= 5.4 kpc. The observed region contains three high-mass protostars in which the dust continuum emission at 1.3 mm is optically thick up to a radius ≲1000 au and has brightness temperatures ≳200 K. The high luminosity (≳10
4
L
⊙
) in the absence of free–free emission suggests the presence of massive stars (
M
≳ 20
M
⊙
) at the earliest stages of their formation. Our continuum images reveal remarkably complex and filamentary structures arising from compact cores. Molecular emission shows no clear signs of rotation or infall on scales from 150 to 2000 au; we do not detect disks. The central sources drive young (
t
dyn
∼ 100 yr), fast (
v
∼ 100 km s
−1
), powerful (
M
⊙
yr
−1
), collimated outflows. These outflows provide indirect evidence of accretion disks on scales
r
≲ 100–500 au (depending on the object). The active outflows are connected to fossil flows that have different orientations on larger spatial scales, implying that the orientations of these small disks change over time. These results together support a variant of an accretion model for high-mass star formation in which massive protostars do not form a large, stable Keplerian disk during their early stages but instead accrete material from multiple massive flows with different angular momentum vectors. This scenario therefore contrasts with the simplified classic paradigm of a stable disk+jet system, which is the standard model for low-mass star formation, and provides experimental confirmation of a multidirectional and unsteady accretion model for massive star formation.
Most massive stars form in dense clusters where gravitational interactions with other stars may be common. The two nearest forming massive stars, the BN object and Source I, located behind the Orion ...Nebula, were ejected with velocities of ∼29 and ∼13 km s−1 about 500 years ago by such interactions. This event generated an explosion in the gas. New ALMA observations show in unprecedented detail, a roughly spherically symmetric distribution of over a hundred 12CO J = 2−1 streamers with velocities extending from VLSR = −150 to +145 km s−1. The streamer radial velocities increase (or decrease) linearly with projected distance from the explosion center, forming a "Hubble Flow" confined to within 50″ of the explosion center. They point toward the high proper-motion, shock-excited H2 and Fe ii "fingertips" and lower-velocity CO in the H2 wakes comprising Orion's "fingers." In some directions, the H2 "fingers" extend more than a factor of two farther from the ejection center than the CO streamers. Such deviations from spherical symmetry may be caused by ejecta running into dense gas or the dynamics of the N-body interaction that ejected the stars and produced the explosion. This ∼1048 erg event may have been powered by the release of gravitational potential energy associated with the formation of a compact binary or a protostellar merger. Orion may be the prototype for a new class of stellar explosiozn responsible for luminous infrared transients in nearby galaxies.
Abstract
Using James Webb Space Telescope near-infrared data of the inner Orion Nebula, Pearson & McCaughrean detected 40 Jupiter-mass binary objects (JuMBOs). These systems are not associated with ...stars and their components have masses of giant Jupiter-like planets and separations in the plane of the sky of order ∼100 au. The existence of these wide free-floating planetary-mass binaries was unexpected in our current theories of star and planet formation. Here we report the radio continuum (6.1 and 10.0 GHz) Karl G. Jansky Very Large Array detection of a counterpart to JuMBO 24. The radio emission appears to be steady at a level of ∼50
μ
Jy over timescales of days and years. We set an upper limit of ≃15 km s
−1
to the velocity of the radio source in the plane of the sky. As in the near-infrared, the radio emission seems to be coming from both components of the binary.
For the past few decades, there has been great interest in determining if even the most massive stars in our galaxy (namely the spectral O-type stars) are formed in a similar manner as the low- and ...intermediate-mass stars, that is, through the presence of accreting disks and powerful outflows. Here, using sensitive observations of the Atacama Large Millimeter/Submillimeter Array, we report a resolved Keplerian disk (with 15 synthesized beams across its major axis) surrounding the deeply embedded O-type protostar IRAS 16547−4247. The disk shows some asymmetries that could arise because the disk is unstable and fragmenting or because of different excitation conditions within the disk. The enclosed mass estimated from the disk Keplerian radial velocities is 25 3 M . The molecular disk is at the base of an ionized thermal radio jet and is approximately perpendicular to the jet axis orientation. We additionally find the existence of a binary system of compact dusty objects at the center of the accreting disk, which indicates the possible formation of an O-type star and a companion of lower mass. This is not surprising due to the high binary fraction reported in massive stars. Subtracting the contribution of the dusty disk plus the envelope and the companion, we estimated a mass of 20 M for the central star.
Natural selection shapes cancer genomes. Previous studies used signatures of positive selection to identify genes driving malignant transformation. However, the contribution of negative selection ...against somatic mutations that affect essential tumor functions or specific domains remains a controversial topic.
Here, we analyze 7546 individual exomes from 26 tumor types from TCGA data to explore the portion of the cancer exome under negative selection. Although we find most of the genes neutrally evolving in a pan-cancer framework, we identify essential cancer genes and immune-exposed protein regions under significant negative selection. Moreover, our simulations suggest that the amount of negative selection is underestimated. We therefore choose an empirical approach to identify genes, functions, and protein regions under negative selection. We find that expression and mutation status of negatively selected genes is indicative of patient survival. Processes that are most strongly conserved are those that play fundamental cellular roles such as protein synthesis, glucose metabolism, and molecular transport. Intriguingly, we observe strong signals of selection in the immunopeptidome and proteins controlling peptide exposition, highlighting the importance of immune surveillance evasion. Additionally, tumor type-specific immune activity correlates with the strength of negative selection on human epitopes.
In summary, our results show that negative selection is a hallmark of cell essentiality and immune response in cancer. The functional domains identified could be exploited therapeutically, ultimately allowing for the development of novel cancer treatments.
Abstract
We present a high-angular resolution (∼1″) and wide-field (
2
.′
9
×
1
.′
9
) image of the 1.3 mm continuum, CO(
J
= 2–1) and SiO(
J
= 5–4) line emissions toward an embedded protocluster, ...FIR 3, FIR 4, and FIR 5, in the Orion Molecular Cloud 2 obtained from the Atacama Large Millimeter/submillimeter Array. We identify 51 continuum sources, 36 of which are newly identified in this study. Their dust masses, projected sizes, and H
2
gas number densities are estimated to be 3.8 × 10
−5
–1.1 × 10
−2
M
⊙
, 290–2000 au, and 6.4 × 10
6
–3.3 × 10
8
cm
−3
, respectively. The results of a Jeans analysis show that ∼80% of the protostellar sources and ∼15% of the prestellar sources are gravitationally bound. We identify 12 molecular outflows traced in the CO(
J
= 2–1) emission, six of which are newly detected. We spatially resolve shocked gas structures traced by the SiO(
J
= 5–4) emission in this region for the first time. We identify shocked gas originating from outflows and other shocked regions. These results provide direct evidence of an interaction between dust condensation, FIR 4, and an energetic outflow driven by HOPS-370 located within FIR 3. A comparison of the outflow dynamical timescales, fragmentation timescales, and protostellar ages shows that the previously proposed triggered star formation scenario in FIR 4 is not strongly supported. We also discuss the spatial distribution of filaments identified in our continuum image by comparing it with a previously identified hub-fiber system in the N
2
H
+
line.
We present sensitive and high angular-resolution (∼0 2-0 3) (sub)millimeter (230 and 345 GHz) continuum and CO(2−1)/CO(3−2) line archive observations of the disk star system in UX Tauri carried out ...with the Atacama Large Millimeter/Submillimeter Array. These observations reveal the gas and dusty disk surrounding the young star UX Tauri A with a large signal-to-noise ratio (>400 in the continuum and >50 in the line), and for the first time we detect the molecular gas emission associated with the disk of UX Tauri C (with a size for the disk of <56 au). No (sub)millimeter continuum emission is detected at the 5 level (0.2 mJy at 0.85 mm) associated with UX Tauri C. For the component UX Tauri C, we estimate a dust disk mass of ≤0.05 M⊕. Additionally, we report a strong tidal disk interaction between both disks, UX Tauri A/C, separated 360 au in projected distance. The CO line observations reveal marked spiral arms in the disk of UX Tauri A and an extended redshifted stream of gas associated with the UX Tauri C disk. No spiral arms are observed in the dust continuum emission of UX Tauri A. Assuming a Keplerian rotation we estimate the enclosed masses (disk+star) from their radial velocities in 1.4 0.6 M for UX Tauri A, and 70 30/sin i Jupiter masses for UX Tauri C (the latter coincides with the mass upper limit value for a brown dwarf). The observational evidence presented here lead us to propose that UX Tauri C has a close approach of a possible wide, evolving, and eccentric orbit around the disk of UX Tauri A, causing the formation of spiral arms and a stream of molecular gas falling toward UX Tauri C.
Abstract
Theoretical and numerical works indicate that a strong magnetic field should suppress fragmentation in dense cores. However, this has never been tested observationally in a relatively large ...sample of fragmenting massive dense cores. Here, we use the polarization data obtained in the Submillimeter Array Legacy Survey of Zhang et al. to build a sample of 18 massive dense cores where both fragmentation and magnetic field properties are studied in a uniform way. We measured the fragmentation level,
N
mm
, within the field of view common to all regions of ∼0.15 pc, with a mass sensitivity of ∼0.5
M
☉
, and a spatial resolution of ∼1000 au. In order to obtain the magnetic field strength using the Davis–Chandrasekhar–Fermi method, we estimated the dispersion of the polarization position angles, the velocity dispersion of the H
13
CO
+
(4–3) gas, and the density of each core, all averaged within 0.15 pc. A strong correlation is found between
N
mm
and the average density of the parental core, although with significant scatter. When large-scale systematic motions are separated from the velocity dispersion and only the small-scale (turbulent) contribution is taken into account, a tentative correlation is found between
N
mm
and the mass-to-flux ratio, as suggested by numerical and theoretical works.
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