arXiv subjects

Noam Soker

Publications and source records attributed to Noam Soker.

At least 235 records · Page 13Linked to original sources

arXiv2017

What planetary nebulae can tell us about jets in core collapse supernovae

We compare the morphology of the core collapse supernova remnant (CCSNR) W49B with the morphology of many planetary nebulae (PNe), and deduce the orientation of the jets that shaped this CCSNR and estimate their energy. We find morphological features that are shared by some PNe and by the CCSNR W49B. In PNe these features, such as a barrel-shaped main body, are thought to be shaped by jets. We use these morphological similarities to deduce that the jets that shaped SNR W49B were launched along the symmetry axis of the `barrel', and to speculate that this CCSNR has two opposite lobes (or ears), that are too faint to be observed. We crudely estimate that the jets that shaped the CCSNR into a barrel shape had a kinetic energy that amounts to about one quarter to one third of the energy of the entire CCSNR. The morphological similarities strengthen the suggestion that jets play a central role in the explosion of massive stars.

astro-ph.SR↗

arXiv2017

Type II intermediate-luminosity optical transients (ILOTs)

We propose that in a small fraction of intermediate luminosity optical transients (ILOTs) powered by a strongly interacting binary system, the ejected mass in the equatorial plane can block the central source from our line of sight. We can therefore observe only radiation that is reprocessed by polar outflow, much as in type~II active galactic nuclei (AGN). An ejection of $M_{\rm ej,e}=10^{-4} ~\rm{M_\odot} ~ (1 ~\rm{M_\odot})$ at 30 degrees from the equatorial plane and at a velocity of $v_{\rm e} = 100 ~\rm{km~s^{-1}}$ will block the central source in the NIR for about 5 years (500 years). During that period of time the object might disappear in the visible band, and be detected only in the IR band due to polar dust. We raise the possibility that the recently observed disappearance of a red giant in the visible, designated N6946-BH1, is a type~II ILOT rather than a failed supernova. For this case we estimate that the ejected mass in the polar direction was $M_{\rm ej,p}\approx 10^{-3} ~\rm{M_\odot}$. Our scenario predicts that this event should reinstate its visible emission in several decades.

astro-ph.SR↗

arXiv2017

A jet-driven dynamo (JEDD) from jets-inflated bubbles in cooling flows

I suggest that the main process that amplifies magnetic fields in cooling flows in clusters and group of galaxies is a jet-driven dynamo (JEDD). The main processes that are behind the JEDD is the turbulence that is formed by the many vortices formed in the inflation processes of bubbles, and the large scale shear formed by the propagating jet. It is sufficient that a strong turbulence exits in the vicinity of the jets and bubbles, just where the shear is large. The typical amplification time of magnetic fields by the JEDD near the jets and bubbles is approximately hundred million years. The amplification time in the entire cooling flow region is somewhat longer. The vortices that create the turbulence are those that also transfer energy from the jets to the intra-cluster medium, by mixing shocked jet gas with the intra-cluster medium gas, and by exciting sound waves. The JEDD model adds magnetic fields to the cyclical behavior of energy and mass in the jet-feedback mechanism (JFM) in cooling flows.

astro-ph.CO↗

arXiv2016

Hitomi observations of Perseus support heating by mixing

We compare the velocity dispersion of the intracluster medium (ICM) of the Perseus cluster of galaxies as observed by the Hitomi X-ray telescope to our three-dimensional hydrodynamical simulations of jet-inflated bubbles in cluster cooling flows, and conclude that the observations support the mixing-heating mechanism of the ICM. In the mixing-heating mechanism the ICM is heated by mixing of hot bubble gas with the ICM. This mixing is caused by vortices that are formed during the inflation process of the bubble. Sound waves and turbulence are also excited by the vortices, but they contribute less than 20 per cents to the heating of the ICM. Shocks that are excited by the jets contribute even less.

astro-ph.GA↗

arXiv2016

Simulating the Onset of Grazing Envelope Evolution of Binary Stars

We present the first three-dimensional gas-dynamical simulations of the grazing envelope evolution (GEE) of stars, with the goal of exploring the basic flow properties and the role of jets at the onset of the GEE. In the simulated runs, a secondary main-sequence star grazes the envelope of the primary asymptotic giant branch (AGB) star. The orbit is circular at the radius of the AGB primary star on its equator. We inject two opposite jets perpendicular to the equatorial plane from the location of the secondary star, and follow the evolution for several orbital periods. We explore the flow pattern by which the jets eject the outskirts of the AGB envelope. After one orbit the jets start to interact with gas ejected in previous orbits and inflate hot low-density bubbles.

astro-ph.SR↗

arXiv2016

Pre-explosion dynamo in the cores of massive stars

We propose a speculative scenario where dynamo amplification of magnetic fields in the core convective shells of massive stars, tens of years to hours before they explode, leads to envelope expansion and enhanced mass loss rate, resulting in pre-explosion outbursts (PEOs). The convective luminosity in the burning shells of carbon, neon, oxygen, and then silicon, are very high. Based on the behavior of active main sequence stars we speculate that the convective shells can trigger magnetic activity with a power of about 0.001 times the convective luminosity. Magnetic flux tubes might buoy outward, and deposit their energy in the outer parts of the envelope. This in turn might lead to the expansion of the envelope and to an enhanced mass loss rate. If a close binary companion is present, mass transfer might take place and lead to an energetic outburst. The magnetic activity requires minimum core rotation and that the stochastic magnetic activity be on its high phase. Only in rare cases these conditions are met, accounting for that only the minority of core collapse supernovae (CCSNe) experience PEO. Such a pre-explosion magnetic activity might have implications for the explosion mechanism itself.

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arXiv2016

The jet feedback mechanism (jfm) in stars, galaxies and clusters

I review the influence jets and the bubbles they inflate might have on their ambient gas as they operate through a negative jet feedback mechanism (JFM). I discuss astrophysical systems where jets are observed to influence the ambient gas, in many cases by inflating large, hot, and low-density bubbles, and systems where the operation of the JFM is still a theoretical suggestion. The first group includes cooling flows in galaxies and clusters of galaxies, star-forming galaxies, young stellar objects, and bipolar planetary nebulae. The second group includes core collapse supernovae, the common envelope evolution, the grazing envelope evolution, and intermediate luminosity optical transients. The suggestion that the JFM operates in these four types of systems is based on the assumption that jets are much more common than what is inferred from objects where they are directly observed. Common to all eight types of systems reviewed here is the presence of a compact object inside an extended ambient gas. The ambient gas serves as a potential reservoir of mass to be accreted on to the compact object. If the compact object launches jets as it accretes mass, the jets might reduce the accretion rate as they deposit energy to the ambient gas, or even remove the entire ambient gas, hence closing a negative feedback cycle.

astro-ph.HE↗

arXiv2016

Explaining Two Recent Intermediate Luminosity Optical Transients (ILOTs) by a Binary Interaction and Jets

We propose that two recent intermediate luminosity optical transients (ILOTs), M31LRN 2015 and SN 2015bh (SNHunt 275; PTF 13efv) can be accounted for with a stellar binary model involving mass transfer that leads to the launching of jets. We inspect observations of the ILOT M31LRN 2015 and conclude that it cannot be explained by the onset of a common envelope evolution (CEE). Instead we conjecture that a $M \simeq 1 - 3 ~\rm{M_\odot}$ main sequence star accreted $\simeq 0.04 ~\rm{M_\odot}$ from the giant star, possibly during a periastron passage. The main sequence star accreted mass through an accretion disc, that launches jets. The radiation from the disk and the collision of the jets with the ambient gas can account for the luminosity of the event. Along similar lines, we suggest that the 2013 eruption of SN 2015bh (SNHunt~275) can also be explained by the High-Accretion-Powered ILOT (HAPI) model. In this case a massive secondary star $M_2 \gtrsim 10 ~\rm{M_\odot}$ accreted $\approx 0.05 ~\rm{M_\odot}$ from a much more massive and more evolved star during a periastron passage. If the much more energetic 2015 outburst of SN 2015bh (SNHunt 275) was not a supernova explosion, it might have been a full almost head-on merger event, or else can be accounted for by a the HAPI-jets model in a very highly eccentric orbit.

astro-ph.SR↗

arXiv2016

The influence of mergers and ram-pressure stripping on black hole-bulge correlations

We analyse the scatter in the correlation between super-massive black hole (SMBH) mass and bulge stellar mass of the host galaxy, and infer that it cannot be accounted for by mergers alone. The merger-only scenario, where small galaxies merge to establish a proportionality relation between the SMBH and bulge masses, leads to a scatter around the linear proportionality line that increases with the square root of the SMBH (or bulge) mass. By examining a sample of 103 galaxies we find that the intrinsic scatter increases more rapidly than expected from the merger-only scenario. The correlation between SMBH masses and their host galaxy properties is therefore more likely to be determined by a negative feedback mechanism that is driven by an active galactic nucleus. We find a hint that some galaxies with missing stellar mass reside close to the centre of clusters and speculate that ram-pressure stripping of gas off the young galaxy as it moves near the cluster centre, might explain the missing stellar mass at later times.

astro-ph.GA↗

arXiv2016

Angular momentum fluctuations in the convective helium shell of massive stars

We find significant fluctuations of angular momentum within the convective helium shell of a pre-collapse massive star - a core-collapse supernova progenitor - which may facilitate the formation of accretion disks and jets that can explode the star. The convective flow in our model of an evolved M_ZAMS=15Msun star, computed with the sub-sonic hydrodynamic solver MAESTRO, contains entire shells with net angular momentum in different directions. This phenomenon may have important implications for the late evolutionary stages of massive stars, and for the dynamics of core-collapse.

astro-ph.SR↗

arXiv2016

Explaining the most energetic supernovae with an inefficient jet-feedback mechanism

We suggest that the energetic radiation from core-collapse super-energetic supernovae (SESNe) is due to a long lasting accretion process onto the newly born neutron star (NS), resulting from an inefficient operation of the jet-feedback mechanism. The jets that are launched by the accreting NS or black hole (BH) maintain their axis due to a rapidly rotating pre-collapse core, and do not manage to eject core material from near the equatorial plane. The jets are able to eject material from the core along the polar directions, and reduce the gravity near the equatorial plane. The equatorial gas expands, and part of it falls back over a timescale of minutes to days to prolong the jets-launching episode. According to the model for SESNe proposed in the present paper, the principal parameter that distinguishes between the different cases of CCSN explosions, such as between normal CCSNe and SESNe, is the efficiency of the jet-feedback mechanism. This efficiency in turn depends on the pre-collapse core mass, envelope mass, core convection, and most of all on the angular momentum profile in the core. One prediction of the inefficient jet-feedback mechanism for SESNe is the formation of a slow equatorial outflow in the explosion. Typical velocity and mass of this outflow are estimated to be approximately 1000 km/s and greater than about 1 solar mass, respectively, though quantitative values will have to be checked in future hydrodynamic simulations.

astro-ph.HE↗

arXiv2016

Bipolar rings from jet-inflated bubbles around evolved binary stars

We show that a fast wind that expands into a bipolar nebula composed of two opposite jet-inflated bubbles can form a pair of bipolar rings around giant stars. Our model assumes three mass loss episodes: a spherical slow and dense shell, two opposite jets, and a spherical fast wind. We use the FLASH hydrodynamical code in three-dimensions to simulate the flow, and obtain the structure of the nebula. We assume that the jets are launched from an accretion disk around a stellar companion to the giant star. The accretion disk is assumed to be formed when the primary giant star and the secondary star suffer a strong interaction accompanied by a rapid mass transfer process from the primary to the secondary star, mainly a main sequence star. Later in the evolution the primary star is assumed to shrink and blow a fast tenuous wind that interacts with the dense gas on the surface of the bipolar structure. We assume that the dense mass loss episode before the jets are launched is spherically symmetric. Our results might be applicable to some planetary nebulae, and further emphasize the large variety of morphological features that can be formed by jets. But we could not reproduce some of the properties of the outer rings of SN1987A. It seems that some objects, like SN1987A, require a pre-jets mass loss episode with a mass concentration at mid-latitudes.

astro-ph.SR↗

arXiv2016

Orbital Parameters for the $250 M_\odot$ Eta Carinae Binary System

We show that recent observations of He I and N II lines of $η$ Carinae may provide support for an orbital orientation where the secondary star is closest to us at periastron passages. This conclusion is valid both for the commonly assumed masses of the two stars, and for the higher stellar masses model where the very massive evolved primary star mass is $M_1=170 M_\odot$ and its hot secondary star mass is $M_2 = 80 M_\odot$. The later model better explains the change in the orbital period assuming that the ninetieth century Great Eruption was powered by accretion onto the secondary star. Adopting the commonly used high eccentricity $e \simeq 0.9$ and inclination $i=41^\circ$, we obtain a good fit to newly released Doppler shift observations of He I emission and absorption lines assuming they are emitted and absorbed in the acceleration zone of the secondary stellar wind. Our model in which the secondary star is in the foreground at periastron is opposite to the view presented recently in the literature.

astro-ph.SR↗

arXiv2016

Binary interactions with high accretion rates onto main sequence stars

Energetic outflows from main sequence stars accreting mass at very high rates might account for the powering of some eruptive objects, such as merging main sequence stars, major eruptions of luminous blue variables, e.g., the Great Eruption of Eta Carinae, and other intermediate luminosity optical transients (ILOTs; Red Novae; Red Transients). These powerful outflows could potentially also supply the extra energy required in the common envelope process and in the grazing envelope evolution of binary systems. We propose that a massive outflow/jets mediated by magnetic fields might remove energy and angular momentum from the accretion disk to allow such high accretion rate flows. By examining the possible activity of the magnetic fields of accretion disks we conclude that indeed main sequence stars might accrete mass at very high rates, up to ~0.01 Mo/yr for solar type stars, and up to ~1 Mo/yr for very massive stars. We speculate that magnetic fields amplified in such extreme conditions might lead to the formation of massive bipolar outflows that can remove most of the disk's energy and angular momentum. It is this energy and angular momentum removal that allows the very high mass accretion rate on to main sequence stars.

astro-ph.SR↗

arXiv2016

Jittering-jets explosion triggered by the standing accretion shock instability

We show that the standing accretion shock instability (SASI) that has been used to ease the shock revival in core collapse supernovae (CCSNe) neutrino-driven explosion models, might play a much more decisive role in supplying the stochastic angular momentum required to trigger an explosion with jittering jets. We find that if the kinetic energy associated with the transverse (non radial) motion of the SASI is larger than about ten percent of the energy associated with the energy of the accreted gas, then the stochastic angular momentum can reach about five percent of the Keplerian specific angular momentum around the newly born neutron star. Such an accretion flow leaves an open conical region along the poles with an average opening angle of about 5 degrees. The outflow from the open polar regions powers an explosion according to the jittering-jets model.

astro-ph.HE↗

arXiv2016

Using Intermediate-Luminosity Optical Transients (ILOTs) to reveal extended extra-solar Kuiper belt objects

We suggest that in the rare case of an Intermediate-Luminosity Optical Transient (ILOTs) event, evaporation of extra-solar Kuiper belt objects (ExtraKBOs) at distances of d ~ 500 - 10000AU from the ILOT can be detected. If the ILOT lasts for 1 month to a few years, enough dust might be ejected from the ExtraKBOs for the IR emission to be detected. Because of the large distance of the ExtraKBOs, tens of years will pass before the ILOT wind disperses the dust. We suggest that after an ILOT outburst there is a period of months to several years during which IR excess emission might hint at the existence of a Kuiper belt analog (ExtraK-Belt).

astro-ph.SR↗

arXiv2016

Jets launched at magnetar birth cannot be ignored

I question models for powering super energetic supernovae (SESNe) with a magnetar central engine that do not include jets that are expected to be launched by the magnetar progenitor. I show that under reasonable assumptions the outflow that is expected during the formation of a magnetar can carry an amount of energy that does not fall much below, and even surpasses, the energy that is stored in the newly born spinning neutron star (NS). The rapidly spinning NS and the strong magnetic fields attributed to magnetars require that the accreted mass onto the newly born NS possesses high specific angular momentum and strong magnetic fields. These ingredients are expected, as in many other astrophysical objects, to form collimated outflows/jets. I argue that the bipolar outflow in the pre-magnetar phase transfers a substantial amount of energy to the supernova (SN) ejecta, and it cannot be ignored in models that attribute SESNe to magnetars. I conclude that jets launched by accretion disks and accretion belts are more likely to power SESNe than magnetars are. This conclusion is compatible with the notion that jets might power all core collapse SNe (CCSNe).

astro-ph.HE↗

arXiv2016

Launching jets from accretion belts

We propose that sub-Keplerian accretion belts around stars might launch jets. The sub-Keplerian inflow does not form a rotationally supported accretion disk, but it rather reaches the accreting object from a wide solid angle. The basic ingredients of the flow are a turbulent region where the accretion belt interacts with the accreting object via a shear layer, and two avoidance regions on the poles where the accretion rate is very low. A dynamo that is developed in the shear layer amplifies magnetic fields to high values. It is likely that the amplified magnetic fields form polar outflows from the avoidance regions. Our speculative belt-launched jets model has implications to a rich variety of astrophysical objects, from the removal of common envelopes to the explosion of core collapse supernovae by jittering jets.

astro-ph.SR↗