The origin of dust in galaxies is still a mystery (1, 2, 3, 4). The majority of the refractory elements are produced in supernova explosions but it is unclear how and where dust grains condense and grow, and how they avoid destruction in the harsh environments of star-forming 3 Figure 3 shows the resulting confidence interval for the two parameters a max and α around the best fit values of a min = 0.001 µm, a max = 4.2 µm and α = 3.6. It is evident that only size distributions extending to grain radii that are significantly larger than that of MW interstellar medium (21, 22) dust ( 0.25 µm) can reproduce the supernova extinction curve (Figure 2). The 2 σ lower limit on the maximum grain size is a max > 0.7 µm. We cannot perform a similar analysis of the late epoch because the intrinsic line profile at this epoch is unknown and likely highly affected by extinction (13). However, we note that the blueshift velocities change only marginally with wavelength (Extended Data Figure 6), suggestive of large grains also at this epoch. Figure 4 illustrates the continuous build-up of dust as a function of time. The increasing attenuation of the lines is accompanied by increasing emission in the near-infrared (NIR) spectra, from a slight excess over a supernova blackbody fit at early times to total dominance at the late epoch. We fitted the spectra with black bodies which for the NIR excess yield a constant blackbody radius of (1.0 ± 0.2) × 10 16 cm at the early epochs, and a temperature that declines from ∼ 2,300 K to ∼ 1,600 K from day 26 onwards. At the late epoch, we obtain a black-body radius of (5.7 ± 0.2) × 10 16 cm and a temperature of ∼ 1,100 K. The high temperatures detected at the early epochs suggest that the NIR excess is due to thermal emission from carbonaceous dust, rather than silicate dust, which has a lower condensation temperature of ∼ 1, 500 K (1). The high temperatures rule out suggestions that the NIR emission is due to pre-existing dust or a dust echo (11) (Figure 1), the accelerated dust formation occurring at later times ( Figure 4) and at larger radius is possibly facilitated by the bulk ejecta material, which travels on average at a velocity of ∼ 7, 500 km s −1 at early epochs (Extended Data Figure 4).Our detection of large grains soon after the supernova explosion suggests a remarkably rapid and efficient mechanism for dust nucleation and growth. The underlying physics is poorly understood but may involve a two-stage process governed by early dust formation in a cool, dense shell, 5 followed by accelerated dust formation involving ejecta material. For Type IIP supernovae, the growth of dust grains can be sustained up to 5 years past explosion (25). The dense CSM around Type IIn supernovae may provide conditions to facilitate dust growth beyond that. The process appears generic, in that other Type IIn supernovae like SN 1995N, SN 1998S, SN 2005ip, and SN 2006jd exhibited similar observed NIR properties (8, 10, 26, 27) and growing dust masses, consistent with the trend revealed here for SN 2010...

The 2012 explosion of SN 2009ip raises questions about our understanding of the late stages of massive star evolution. Here we present a comprehensive study of SN 2009ip during its remarkable re-brightening(s). Highcadence photometric and spectroscopic observations from the GeV to the radio band obtained from a variety of ground-based and space facilities (including the VLA, Swift, Fermi, HST and XMM) constrain SN 2009ip to be a low energy (E ∼ 10 50 erg for an ejecta mass ∼ 0.5 M ) and likely asymmetric explosion in a complex medium shaped by multiple eruptions of the restless progenitor star. Most of the energy is radiated as a result of the shock breaking out through a dense shell of material located at ∼ 5 × 10 14 cm with M ∼ 0.1 M , ejected by the precursor outburst ∼ 40 days before the major explosion. We interpret the NIR excess of emission as signature of dust vaporization of material located further out (R > 4 × 10 15 cm), the origin of which has to be connected with documented mass loss episodes in the previous years. Our modeling predicts bright neutrino emission associated with the shock break-out if the cosmic ray energy is comparable to the radiated energy. We connect this phenomenology with the explosive ejection of the outer layers of the massive progenitor star, that later interacted with material deposited in the surroundings by previous eruptions. Future observations will reveal if the luminous blue variable (LBV) progenitor star survived. Irrespective of whether the explosion was terminal, SN 2009ip brought to light the existence of new channels for sustained episodic mass-loss, the physical origin of which has yet to be identified.

The large amounts of dust detected in sub-millimeter galaxies and quasars at high redshift pose a challenge to galaxy formation models and theories of cosmic dust formation. At z > 6 only stars of relatively high mass (> 3 Msun) are sufficiently short-lived to be potential stellar sources of dust. This review is devoted to identifying and quantifying the most important stellar channels of rapid dust formation. We ascertain the dust production efficiency of stars in the mass range 3-40 Msun using both observed and theoretical dust yields of evolved massive stars and supernovae (SNe) and provide analytical expressions for the dust production efficiencies in various scenarios. We also address the strong sensitivity of the total dust productivity to the initial mass function. From simple considerations, we find that, in the early Universe, high-mass (> 3 Msun) asymptotic giant branch stars can only be dominant dust producers if SNe generate <~ 3 x 10^-3 Msun of dust whereas SNe prevail if they are more efficient. We address the challenges in inferring dust masses and star-formation rates from observations of high-redshift galaxies. We conclude that significant SN dust production at high redshift is likely required to reproduce current dust mass estimates, possibly coupled with rapid dust grain growth in the interstellar medium.Comment: 72 pages, 9 figures, 5 tables; to be published in The Astronomy and Astrophysics Revie

The binary neutron star merger GW170817 was the first multi-messenger event observed in both gravitational and electromagnetic waves. 1,2 The electromagnetic signal began ∼ 2 seconds post-merger with a weak, short burst of gamma-rays, 3 which was followed over the next hours and days by the ultraviolet, optical and near-infrared emission from a radioactivelypowered kilonova. [4][5][6][7][8][9][10][11] Later, non-thermal rising X-ray and radio emission was observed. 12,13 The low luminosity of the gamma-rays and the rising non-thermal flux from the source at late times could indicate that we are outside the opening angle of the beamed relativistic jet. Alternatively, the emission could be arising from a cocoon of material formed from the interaction between a jet and the merger ejecta. [13][14][15] Here we present late-time optical detections and deep near-infrared limits on the emission from GW170817 at 110 days post-merger. Our new observations are at odds with expectations of late-time emission from kilonova models, being too bright and blue. 16,17 Instead, the emission arises from the interaction between the relativistic ejecta of GW170817 and the interstellar medium. We show that this emission matches the expectations of a Gaussian structured relativistic jet, which would have launched a high luminosity short GRB to an aligned observer. However, other jet structure or cocoon models can also match current data -the future evolution of the afterglow will directly distinguish the origin of the emission.For the Hubble Space Telescope (HST), the end of Sun constraint for GW170817 was on 6 December 2017 (∼ 110 rest-frame days post-merger), and we immediately obtained deep observations in the optical and infrared (see Table 1 and Methods for details of the observations and reduction). The new images were astrometrically aligned to our earlier epoch HST data in order to accurately locate the merger site and perform photometry (see Methods). Images of the merger site in each of our filters are shown in Figure 1. We detect emission at the location of the merger in the optical F606W and F814W filters (central wavelengths, λ cen ∼ 589, 802 nm, respectively). For the near-IR filters F140W and F160W (λ cen ∼ 1392, 1527 nm, respectively) we could not establish significant detections and so can place only upper limits on the transient flux at these wavelengths. Optical and near-infrared light curves for the counterpart to GW170817, including our recent observations, are shown in Figure 2.A detection in the optical or near-IR at such late times is not expected from the family of kilonova models currently in use. Indeed, most detailed studies stop at ∼ 30 days where predicted luminosities correspond to 30 mag, 16, 18 undetectable for even HST. Alternative models of kilonova emission with a slower decay of the light curves 17 would nevertheless predict redder emission than we observe. Initially blue, with M r,AB − M H,AB 0.4 mag at 1.5 days 19 , GW170817 evolved to become very red, with M F606W,AB − M F160W,AB = 2.8 mag at 11 d...

The historic detection of gravitational waves from a binary neutron star merger (GW170817) and its electromagnetic counterpart led to the first accurate (sub-arcsecond) localization of a gravitational-wave event. The transient was found to be ∼10″ from the nucleus of the S0 galaxy NGC 4993. We report here the luminosity distance to this galaxy using two independent methods. (1) Based on our MUSE/VLT measurement of the heliocentric redshift (z helio =0.009783±0.000023), we infer the systemic recession velocity of the NGC 4993 group of galaxies in the cosmic microwave background (CMB) frame to be v CMB = 3231±53kms −1. Using constrained cosmological simulations we estimate the line-of-sight peculiar velocity to be v pec =307±230kms −1 , resulting in a cosmic velocity of v cosmic =2924±236 kms −1 (z cosmic =0.00980±0.00079) and a distance of D z =40.4±3.4 Mpc assuming a local Hubble constant of H 0 =73.24±1.74 kms −1 Mpc −1. (2) Using Hubble Space Telescope measurements of the effective radius (15 5±1 5) and contained intensity and MUSE/VLT measurements of the velocity dispersion, we place NGC 4993 on the Fundamental Plane (FP) of E and S0 galaxies. Comparing to a frame of 10 clusters containing 226 galaxies, this yields a distance estimate of D FP =44.0±7.5 Mpc. The combined redshift and FP distance is D NGC 4993 =41.0±3.1 Mpc. This "electromagnetic" distance estimate is consistent with the independent measurement of the distance to GW170817 as obtained from the gravitational-wave signal (D 43.8 GW 6.9 2.9 =-+ Mpc) and confirms that GW170817 occurred in NGC 4993.

Aims. We investigate whether stellar dust sources i.e. asymptotic giant branch (AGB) stars and supernovae (SNe) can account for dust detected in 5 < z < 6.5 quasars (QSOs). Methods. We calculate the required dust yields per AGB star and per SN using the dust masses of QSOs inferred from their millimeter emission and stellar masses approximated as the difference between the dynamical and the H 2 gas masses of these objects. Results. We find that AGB stars are not efficient enough to form dust in the majority of the z > 5 QSOs, whereas SNe may be able to account for dust in some QSOs. However, they require very high dust yields even for a top-heavy initial mass function.Conclusions. This suggests additional non-stellar dust formation mechanism e.g. significant dust grain growth in the interstellar medium of at least three out of nine z > 5 QSOs. SNe (but not AGB stars) may deliver enough heavy elements to fuel this growth.

Very massive stars in the final phases of their lives often show unpredictable outbursts that can mimic supernovae, so-called, "SN impostors", but the distinction is not always straightforward. Here we present observations of a luminous blue variable (LBV) in NGC 2770 in outburst over more than 20 yr that experienced a possible terminal explosion as type IIn SN in 2015, named SN 2015bh. This possible SN (or "main event") had a precursor peaking ∼40 days before maximum. The total energy release of the main event is ∼1.8 × 10 49 erg, consistent with a <0.5 M shell plunging into a dense CSM. The emission lines show a single narrow P Cygni profile during the LBV phase and a double P Cygni profile post maximum suggesting an association of the second component with the possible SN. Since 1994 the star has been redder than an LBV in an S-Dor-like outburst. SN 2015bh lies within a spiral arm of NGC 2770 next to several small star-forming regions with a metallicity of ∼0.5 solar and a stellar population age of 7-10 Myr. SN 2015bh shares many similarities with SN 2009ip and may form a new class of objects that exhibit outbursts a few decades prior to a "hyper eruption" or final core-collapse. If the star survives this event it is undoubtedly altered, and we suggest that these "zombie stars" may evolve from an LBV to a Wolf-Rayet star over the timescale of only a few years. The final fate of these stars can only be determined with observations a decade or more after the SN-like event.

SN 2008D was discovered while following up an unusually bright X-ray transient (XT) in the nearby spiral galaxy NGC 2770. We present early optical spectra (obtained 1.75 days after the XT) which allowed the first identification of the object as a supernova (SN) at redshift z = 0.007. These spectra were acquired during the initial declining phase of the light curve, likely produced in the stellar envelope cooling after shock breakout, and rarely observed. They exhibit a rather flat spectral energy distribution with broad undulations, and a strong, W-shaped feature with minima at 3980 and 4190Å (rest frame). We also present extensive spectroscopy and photometry of the SN during the subsequent photospheric phase. Unlike SNe associated with gamma-ray bursts, SN 2008D displayed prominent He features and is therefore of Type Ib. Subject headings: supernovae: individual (SN 2008D) OBSERVATIONS OF SN 2008DOn 2008 January 9.56 UT, while observing the supernova (SN) 2007uy in the nearby spiral galaxy NGC 2770 (z = 0.007), the X-Ray Telescope onboard Swift detected a bright X-ray transient (XT), with a peak luminosity of 6 × 10 43 erg s −1 and a duration of about 10 minutes