Expanding the Y Dwarf Census with Spitzer

Expanding the Y Dwarf Census with Spitzer Follow-up of the Coldest CatWISE Solar Neighborhood Discoveries

We present Spitzer 3.6μm and 4.5μm follow-up of 170 candidate extremely cool brown dwarfs newly discovered via the combination of WISE and NEOWISE imaging at 3−5μm. CatWISE, a joint analysis of archival WISE and NEOWISE data, has improved upon the motion measurements of AllWISE by leveraging a >10× time baseline enhancement, from 0.5 years (AllWISE) to 6.5 years (CatWISE). As a result, CatWISE motion selection has yielded a large sample of previously unrecognized brown dwarf candidates, many of which have archival detections exclusively in the WISE 4.6μm (W2) channel, suggesting that they could be both exceptionally cold and nearby. Where these objects go undetected in WISE W1 (3.4μm), Spitzer can provide critically informative detections at 3.6μm. Of our motion-confirmed discoveries, seventeen have a best-fit Spitzer [3.6]−[4.5] color most consistent with spectral type Y. CWISEP J144606.62−231717.8 (μ≈1.3″/yr) is likely the reddest, and therefore potentially coldest, member of our sample with a very uncertain [3.6]−[4.5] color of 3.71 ± 0.44 magnitudes. We also highlight our highest proper motion discovery, WISEA J153429.75−104303.3, with μ≈2.7″/yr. Given that the prior list of confirmed and presumed Y dwarfs consists of just 27 objects, the Spitzer follow-up presented in this work has substantially expanded the sample of identified Y dwarfs. Our new discoveries thus represent significant progress toward understanding the bottom of the substellar mass function, investigating the diversity of the Y dwarf population, and selecting optimal brown dwarf targets for JWST spectroscopy.

http://arxiv.org/abs/1911.12372

Buckyballs in space form by SiC grain erosion

 Formation of C60 from silicon carbide grains in evolved stars

Scientists have long been puzzled by the existence of so-called "buckyballs"—complex carbon molecules with a soccer-ball-like structure—throughout interstellar space. Now, a team of researchers from the University of Arizona has proposed a mechanism for their formation in a study published in the Astrophysical Journal Letters. Carbon 60, or C₆₀ for short, whose official name is Buckminsterfullerene, comes in spherical molecules consisting of 60 carbon atoms organized in five-membered and six-membered rings. The name "buckyball" derives from their resemblance to the architectural work of Richard Buckminster Fuller, who designed many dome structures that look similar to C₆₀. Their formation was thought to only be possible in lab settings until their detection in space challenged this assumption.

https://phys.org/news/2019-11-mysteries-interstellar-buckyballs.html

A catalogue of photometrically selected brown dwarfs

Brown dwarf census with the Dark Energy Survey year 3 data and the thin disk scale height of early L types

In this paper we present a catalogue of 11,745 brown dwarfs with spectral types ranging from L0 to T9, photometrically classified using data from the Dark Energy Survey (DES) year 3 release matched to the Vista Hemisphere Survey (VHS) DR3 and Wide-field Infrared Survey Explorer (WISE) data, covering approx 2,400 deg2 up to i_AB=22. The classification method follows the same photo-type method previously applied to SDSS-UKIDSS-WISE data. The most significant difference comes from the use of DES data instead of SDSS, which allow us to classify almost an order of magnitude more brown dwarfs than any previous search and reaching distances beyond 400 parsecs for the earliest types. Next, we also present and validate the GalmodBD simulation, which produces brown dwarf number counts as a function of structural parameters with realistic photometric properties of a given survey. We use this simulation to estimate the completeness and purity of our photometric LT catalogue down to i_AB=22, as well as to compare to the observed number of LT types. We put constraints on the thin disk scale height for the early L population to be around 450 parsecs, in agreement with previous findings. For completeness, we also publish in a separate table a catalogue of 20,863 M dwarfs that passed our colour cut with spectral types greater than M6. Both the LT and the late M catalogues are found at this https URL

http://arxiv.org/abs/1903.10806

Detection of the nearest Jupiter analog in radial velocity and astrometry data

The presence of Jupiter is crucial to the architecture of the Solar System and models underline this to be a generic feature of planetary systems. We find the detection of the difference between the position and motion recorded by the contemporary astrometric satellite Gaia and its precursor Hipparcos can be used to discover Jupiter-like planets. We illustrate how observations of the nearby star ε Indi A giving astrometric and radial velocity data can be used to independently find the orbit of its suspected companion. The radial velocity and astrometric data provide complementary detections which allow for a much stronger solution than either technique would provide individually. We quantify ε Indi A b as the closest Jupiter-like exoplanet with a mass of 3 MJup on a slightly eccentric orbit with an orbital period of 45 yr. While other long-period exoplanets have been discovered, ε Indi A b provides a well constrained mass and along with the well-studied brown dwarf binary in orbit around ε Indi A means that the system provides a benchmark case for our understanding of the formation of gas giant planets and brown dwarfs. 

http://arxiv.org/abs/1910.06804

Four newborn planets transiting the young solar analog V1298 Tau

Four newborn planets transiting the young solar analog V1298 Tau

Exoplanets orbiting pre-main sequence stars are laboratories for studying planet evolution processes, including atmospheric loss, orbital migration, and radiative cooling. V1298 Tau, a young solar analog with an age of 23±4 Myr, is one such laboratory. The star is already known to host a Jupiter-sized planet on a 24 day orbit. Here, we report the discovery of three additional planets --- all between the size of Neptune and Saturn --- based on our analysis of K2 Campaign 4 photometry. Planets c and d have sizes of 5.6 and 6.4R⊕, respectively and with orbital periods of 8.25 and 12.40 days reside 0.25% outside of the nominal 3:2 mean-motion resonance. Planet e is 8.7 R⊕ in size but only transited once in the K2 time series and thus has a period longer than 36 days, but likely shorter than 223 days. The V1298 Tau system may be a precursor to the compact multiplanet systems found to be common by the Kepler mission. However, the large planet sizes stand in sharp contrast to the vast majority of Kepler multis which have planets smaller than 3R⊕. Simple dynamical arguments suggest total masses of < 28M⊕ and < 120M⊕ for the c-d and d-b planet pairs, respectively. The implied low masses suggest that the planets may still be radiatively cooling and contracting, and perhaps losing atmosphere. The V1298 Tau system offers rich prospects for further follow-up including atmospheric characterization by transmission or eclipse spectroscopy, dynamical characterization through transit-timing variations, and measurements of planet masses and obliquities by radial velocities.

http://arxiv.org/abs/1910.04563

An unusually large gaseous transit in a debris disc

An unusually large gaseous transit in a debris disc

We present the detection of an unusually large transient gas absorption in several ionized species in the debris disc star HD 37306 using high-resolution optical spectra. We have been analysing a large sample of debris discs searching for circumstellar gas absorptions aiming to determine the frequency of gas in debris discs. HD 37306 stood out showing remarkably broad absorptions superimposed onto several photospheric Ca II, Fe II and Ti II lines. The observed absorptions, unlike typical exocometary transits, lasted for at least eight days. Here we analyse simultaneous spectroscopic and photometric data of the event and evaluate different scenarios that might explain the observed features. We conclude that the most likely scenario might be an exocometary break-up releasing a significant amount of gas close to the star, producing an occulting "ring"/"torus" shape. 

http://arxiv.org/abs/1910.04747

Detection of phosphorus-bearing molecules towards a Solar-type protostar

Detection of phosphorus-bearing molecules towards a Solar-type protostar

Phosphorus is a key ingredient in terrestrial biochemistry, but is rarely observed in the molecular ISM and therefore little is known about how it is inherited during the star and planet formation sequence. We present observations of the phosphorus-bearing molecules PO and PN towards the Class I low-mass protostar B1-a using the IRAM 30m telescope, representing the second detection of phosphorus carriers in a Solar-type star forming region. The P/H abundance contained in PO and PN is ~10^−10-10^−9 depending on the assumed source size, accounting for just 0.05-0.5% of the solar phosphorus abundance and implying significant sequestration of phosphorus in refractory material. Based on a comparison of the PO and PN line profiles with the shock tracers SiO, SO2, and CH3OH, the phosphorus molecule emission seems to originate from shocked gas and is likely associated with a protostellar outflow. We find a PO/PN column density ratio of ~1-3, which is consistent with the values measured in the shocked outflow of the low-mass protostar L1157, the massive star-forming regions W51 and W3(OH), and the galactic center GMC G+0.693-0.03. This narrow range of PO/PN ratios across sources with a range of environmental conditions is surprising, and likely encodes information on how phosphorus carriers are stored in grain mantles.

http://arxiv.org/abs/1910.04539

The HH 212 interstellar laboratory: astrochemistry as a tool to reveal protostellar disks on Solar System scales

The HH 212 interstellar laboratory: astrochemistry as a tool to reveal protostellar disks on Solar System scales

The investigation of star forming regions have enormously benefited from the recent advent of the ALMA interferometer. More specifically, the unprecedented combination of high-sensitivity and high-angular resolution provided by ALMA allows one to shed light on the jet/disk systems associated with a Sun-like mass protostar. Also astrochemistry enjoyed the possibility to analyze complex spectra obtained using large bandwidths: several interstellar Complex Organic Molecules (iCOMs; C-bearing species with at least 6 atoms) have been imaged around protostars. This in turn boosted the study of the astrochemistry at work during the earliest phases of star formation paving the way to the chemical complexity in planetary systems where Life could emerge. There is mounting evidence that the observations of iCOMs can be used as unique tool to shed light, on Solar System scales (< 50 au), on the molecular content of protostellar disk. The increase of iCOMs abundances occur only under very selective physical conditions, such as those associated low-velocity shocks found where the infalling envelope is impacting the rotating accretion disk. The imaging of these regions with simpler molecules such as CO or CS is indeed paradoxically hampered by their high abundances and consequently high line opacities which do not allow the observers to disentangle all the emitting components at these small scales. In this respect, we review the state-of-the art of the ALMA analysis about the standard Sun-like star forming region in Orion named HH 212. We show (i) how all the physical components involved in the formation of a Sun-like star can be revealed only by observing different molecular tracers, and (ii) how the observation of iCOMs emission, observed to infer the chemical composition of star forming regions, can be used also as unique tracer to image protostellar disks on Solar System scales.

http://arxiv.org/abs/1910.04442

Graphene oxide nanoparticles in the ISM

Graphene Oxide Nanoparticles in the Interstellar Medium

Dust particles play a major role in the formation, evolution and chemistry of interstellar clouds, stars and planetary systems. Commonly identified forms include amorphous and crystalline carbon-rich particles and silicates. Also present in many astrophysical environments are polycyclic aromatic hydrocarbons (PAHs), detected through their infrared emission, and which are essentially small flakes of graphene. Astronomical observations over the past four decades have revealed a widespread unassigned Extended Red Emission (ERE) feature which is attributed to luminescence of dust grains. Numerous potential carriers for ERE have been proposed but none has gained general acceptance. In this Letter it is shown that there is a strong similarity between laboratory optical emission spectra of graphene oxide and ERE, leading to this proposal that emission from graphene oxide nanoparticles is the origin of ERE and that these are a significant component of interstellar dust. The proposal is supported by infrared emission features detected by the Infrared Space Observatory (ISO) and the Spitzer Space Telescope.

http://arxiv.org/abs/1908.07787

A direct correspondence between a planet and a dust gap

Kinematic detection of a planet carving a gap in a protoplanetary disc
We still do not understand how planets form, or why extra-solar planetary systems are so different from our own solar system. But the last few years have dramatically changed our view of the discs of gas and dust around young stars. Observations with the Atacama Large Millimeter/submillimeter Array (ALMA) and extreme adaptive-optics systems have revealed that most --- if not all --- discs contain substructure, including rings and gaps, spirals, azimuthal dust concentrations, and shadows cast by misaligned inner discs. These features have been interpreted as signatures of newborn protoplanets, but the exact origin is unknown. Here we report the kinematic detection of a few Jupiter-mass planet located in a gas and dust gap at 130 au in the disc surrounding the young star HD 97048. An embedded planet can explain both the disturbed Keplerian flow of the gas, detected in CO lines, and the gap detected in the dust disc at the same radius. While gaps appear to be a common feature in protoplanetary discs, we present a direct correspondence between a planet and a dust gap, indicating that at least some gaps are the result of planet-disc interactions.

http://arxiv.org/abs/1907.02538

Confirmation of C60+ in the interstellar medium

Confirming interstellar C+60 using the Hubble Space Telescope

Recent advances in laboratory spectroscopy lead to the claim of ionized Buckminsterfullerene (C60+) as the carrier of two diffuse interstellar bands (DIBs) in the near-infrared. However, irrefutable identification of interstellar C60+ requires a match between the wavelengths and the expected strengths of all absorption features detectable in the laboratory and in space. Here we present Hubble Space Telescope (HST) spectra of the region covering the C60+ 9348, 9365, 9428 and 9577 {\AA} absorption bands toward seven heavily-reddened stars. We focus in particular on searching for the weaker laboratory C60+ bands, the very presence of which has been a matter for recent debate. Using the novel STIS-scanning technique to obtain ultra-high signal-to-noise spectra without contamination from telluric absorption that afflicted previous ground-based observations, we obtained reliable detections of the (weak) 9365, 9428 {\AA} and (strong) 9577 {\AA} C60+ bands. The band wavelengths and strength ratios are sufficiently similar to those determined in the latest laboratory experiments that we consider this the first robust identification of the 9428 {\AA} band, and a conclusive confirmation of interstellar C60+.

http://arxiv.org/abs/1904.08821

Astrophysical detection of the helium hydride ion

Primordial molecule detected in space for the first time

Within 100,000 years of the Big Bang, the very first molecule emerged, an improbable marriage of helium and hydrogen known as a helium hydride ion, or HeH⁺. "It was the beginning of chemistry," said David Neufeld, a professor at John's Hopkins University and co-author of a study published Wednesday detailing how—after a multi-decade search—scientists finally detected the elusive molecule in space. Theoretical models had long since convinced astrophysicists that HeH⁺ came first, followed—in a precise order—by a parade of other increasingly complex and heavy molecules.
HeH⁺ had also been studied in the laboratory, as early as 1925.

https://phys.org/news/2019-04-elusive-molecule-universe-space.html

Brown dwarfs formed in a protoplanetary disk?

Are brown dwarfs failed stars or super-planets? 

Brown dwarfs fill the "gap" between stars and the much smaller planets—two very different types of astronomical objects. But how they originate has yet to be fully explained. Astronomers from Heidelberg University may now be able to answer that question. They discovered that the star ν Ophiuchi in the Milky Way is being orbited by two brown dwarfs, which in all probability formed along with the star from a gas and dust disk, just as planets do.

https://phys.org/news/2019-04-brown-dwarfs-stars-super-planets.html

Discovery of a nearby stellar stream in Gaia DR2

Extended stellar systems in the solar neighborhood - II. Discovery of a nearby 120° stellar stream in Gaia DR2

We report the discovery of a large, dynamically cold, coeval stellar stream that is currently traversing the immediate solar neighborhood at a distance of only 100 pc. The structure was identified in a wavelet decomposition of the 3D velocity space of all stars within 300 pc to the Sun. Its members form a highly elongated structure with a length of at least 400 pc, while its vertical extent measures only about 50 pc. Stars in the stream are not isotropically distributed but instead form two parallel lanes with individual local overdensities, that may correspond to a remnant core of a tidally disrupted cluster or OB association. Its members follow a very well-defined main sequence in the observational Hertzsprung-Russell diagram and also show a remarkably low 3D velocity dispersion of only 1.3 km/s. These findings strongly suggest a common origin as a single coeval stellar population.

http://arxiv.org/abs/1901.06387

JCMT/SCUBA-2 Continuum Observations of Pre-protostellar Evolution

SCOPE: SCUBA-2 Continuum Observations of Pre-protostellar Evolution - Survey Description and Compact Source Catalogue

We present the first release of the data and compact-source catalogue for the JCMT Large Program SCUBA-2 Continuum Observations of Pre-protostellar Evolution (SCOPE). SCOPE consists of 850-um continuum observations of 1235 Planck Galactic Cold Clumps (PGCCs) made with the Submillimetre Common-User Bolometer Array 2 on the James Clerk Maxwell Telescope. These data are at an angular resolution of 14.4 arcsec, significantly improving upon the 353-GHz resolution of Planck at 5 arcmin, and allowing for a catalogue of 3528 compact sources in 558 PGCCs.

http://arxiv.org/abs/1902.10180

Methylamine and other N-bearing species in NGC 6334I MM1-3

Methylamine and other simple N-bearing species in the hot cores NGC 6334I MM1-3

In the search for the building blocks of life, nitrogen-bearing molecules are of particular interest since nitrogen-containing bonds are essential for the linking of amino acids and ultimately the formation of larger biological structures. The elusive molecule methylamine (CH3NH2) is thought to be a key pre-biotic species but has so far only been securely detected in the giant molecular cloud Sgr B2. We identify CH3NH2 and other simple nitrogen-bearing species towards three hot cores in NGC 6334I. Column density ratios are derived in order to investigate the relevance of the individual species as precursors of biotic molecules. 

http://arxiv.org/abs/1902.07060

Prebiotic relevance of interstellar ices

Interstellar ices: a possible scenario for symmetry breaking of extraterrestrial chiral organic molecules of prebiotic interest

In the laboratory, the photo-and thermochemical evolution of ices, made of simple molecules of astrophysical relevance, always leads to the formation of semi-refractory water-soluble organic residues. Targeted searches for specific molecules do reveal the notable presence of two families of important molecular ''bricks of life'': amino acids, key molecules in metabolism, and sugars, including ribose, the backbone of RNA molecules which support the genetic information in all living entities.

http://arxiv.org/abs/1902.04575

New brown dwarf candidates from Gaia DR2

New ultra-cool and brown dwarf candidates in Gaia DR2

Context. The second Gaia data release (Gaia DR2) contains high precision positions, parallaxes and proper motions for 1.3 billion sources. The resulting Hertzsprung-Russell diagram reveals fine structures all over the mass range. Aims. This paper aims to investigate the content of Gaia DR2 at the low-mass end and to characterize ultra-cool and brown dwarfs.

https://arxiv.org/abs/1809.08244

Carbon and oxygen in metal-poor halo stars

Carbon and oxygen are key tracers of the Galactic chemical evolution; in particular, a reported upturn in [C/O] towards decreasing [O/H] in metal-poor halo stars could be a signature of nucleosynthesis by massive Population III stars. We reanalyse carbon, oxygen, and iron abundances in thirty-nine metal-poor turn-off stars.

https://arxiv.org/abs/1901.03592

Discovery of Galactic dwarf satellite Antila 2

The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2

We report the discovery of a Milky-Way satellite in the constellation of Antlia. The Antlia 2 dwarf galaxy is located behind the Galactic disc at a latitude of $b\sim 11^{\circ}$ and spans 1.26 degrees, which corresponds to $\sim2.9$ kpc at its distance of 130 kpc.

https://arxiv.org/abs/1811.04082

G11.92-0.61 MM1b: a star forming like a planet

A young star caught forming like a planet

Astronomers have captured one of the most detailed views of a young star taken to date, and revealed an unexpected companion in orbit around it. The main object, referred to as MM 1a, is a young massive star surrounded by a rotating disc of gas and dust that was the focus of the scientists' original investigation.
https://phys.org/news/2019-01-star-flips-planet-forming-disk-pole.html

Circumbinary disk perpendicular to orbital plane

Double star system flips planet-forming disk into pole position

New research led by an astronomer at the University of Warwick has found the first confirmed example of a double star system that has flipped its surrounding disc to a position that leaps over the orbital plane of those stars...

https://phys.org/news/2019-01-star-flips-planet-forming-disk-pole.html

Cloud fragmentation and star formation

As clouds fall apart, a new star is born

Using the ALMA observatory in Chile, a group of astronomers led by MPIA's Henrik Beuther has made the most detailed observation yet of the way that a giant gas cloud fragments into dense cores, which then act as the birthplaces ...

https://phys.org/news/2019-01-clouds-fall-star-born.html

Planet 9 or an icy disc? Complementary hypotheses

Shepherding in a Self-Gravitating Disk of Trans-Neptunian Objects

A relatively massive and moderately eccentric disk of trans-Neptunian objects (TNOs) can effectively counteract apse precession induced by the outer planets, and in the process shepherd highly eccentric members of its population into nearly-stationary configurations which are anti-aligned with the disk itself.

https://arxiv.org/abs/1804.06859

Protostars in massive "starless" cores

Massive and low-mass protostars in massive "starless" cores

The infrared dark clouds (IRDCs) G11.11$-$0.12 and G28.34$+$0.06 are two of the best-studied IRDCs in our Galaxy. These two clouds host clumps at different stages of evolution, including a massive dense clump in both clouds that is dark even at 70 and 100$μ$m.

https://arxiv.org/abs/1901.07582

Binarity of massive young stellar objects

A pilot survey of the binarity of Massive Young Stellar Objects with $K$ band adaptive optics

We present the first search for binary companions of Massive Young Stellar Objects (MYSOs) using AO-assisted $K$ band observations, with NaCo at the VLT. We have surveyed 32 MYSOs from the RMS catalogue, probing the widest companions, with a physical separation range of 400 - 46,000 au, within the predictions of models and observations for multiplicity of MYSOs.

https://arxiv.org/abs/1901.04716

An O-type protostar forming in an accretion disk

An Asymmetric Keplerian Disk Surrounding the O-type Protostar IRAS16547$-$4247

During the last decades, a great interest has emerged to know 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.

https://arxiv.org/abs/1901.04896

The most massive binary star known

Weighing Melnick 34: the most massive binary system known

Here we confirm Melnick 34, an X-ray bright star in the 30 Doradus region of the Large Magellanic Cloud, as an SB2 binary comprising WN5h+WN5h components. We present orbital solutions using 26 epochs of VLT/UVES spectra and 22 epochs of archival Gemini/GMOS spectra.

https://arxiv.org/abs/1901.04769

Wide co-moving binary and multiple stars

A catalog of wide binary and multiple systems of bright stars from Gaia-DR2 and the Virtual Observatory

Binary and multiple stars have long provided an effective empirical method of testing stellar formation and evolution theories. In particular, the existence of wide binary systems (separations $>$20,000 au) is particularly challenging to binary formation models as their physical separations are beyond the typical size of a collapsing cloud core ($\sim$5,000$-$10,000 au).

https://arxiv.org/abs/1901.03730

Dissolving star cluster Ruprecht 147

Ruprecht 147: a paradigm of dissolving star cluster

We employed recent Gaia/DR2 data to investigate the dynamical status of the nearby (300 pc), old (2.5 Gyr) open cluster Ruprecht~147. We found prominent leading and trailing tails of stars along the cluster orbit, which demonstrates that Ruprecht~147 is losing stars at fast pace.

https://arxiv.org/abs/1901.04253

Stars surrounded by iron dust

Discovery of stars surrounded by iron dust in the LMC

We consider a small sample of oxygen-rich, asymptotic giant branch stars in the Large Magellanic Cloud, observed by the Spitzer Space Telescope, exhibiting a peculiar spectral energy distribution, which can be hardly explained by the common assumption that dust around AGB stars is primarily composed of silicate grains.

https://arxiv.org/abs/1901.03621

First detection of interstellar glycolonitrile

First detection of the pre-biotic molecule glycolonitrile (HOCH2CN) in the interstellar medium

Theories of a pre-RNA world suggest that glycolonitrile (HOCH$_2$CN) is a key species in the process of ribonucleotide assembly, which is considered as a molecular precursor of nucleic acids. In this Letter, we report the first detection of this pre-biotic molecule in the interstellar medium (ISM) by using ALMA data obtained at frequencies between 86.5$\,$GHz and 266.5$\,$GHz toward the Solar-type protostar IRAS16293-2422 B.

https://arxiv.org/abs/1901.02576

Evidence for crystallisation in white dwarfs

Astronomers discover first direct evidence of white dwarf stars solidifying into crystals

The first direct evidence of white dwarf stars solidifying into crystals has been discovered by astronomers at the University of Warwick, and our skies are filled with them. Observations have revealed that dead remnants of stars like our Sun, called white dwarfs, have a core of solid oxygen and carbon due to a phase transition during their lifecycle similar to water turning into ice but at much higher temperatures.

https://phys.org/news/2019-01-astronomers-evidence-white-dwarf-stars.html

Helium flash origin of heavy isotopes

Stellar corpse reveals clues to missing stardust

Everything around you - your desk, your laptop, your coffee cup - in fact, even you - is made of stardust, the stuff forged in the fiery furnaces of stars that died before our sun was born. Probing the space surrounding ...

https://phys.org/news/2018-12-stellar-corpse-reveals-clues-stardust.html