The fastest stars in the Galaxy

Abstract

We report a spectroscopic search for hypervelocity white dwarfs (WDs) that are runaways from Type Ia supernovae (SNe Ia) and related thermonuclear explosions. Candidates are selected from Gaia data with high tangential velocities and blue colors. We find six new runaways, including four stars with radial velocities (RVs) $>1000\mathrm{km}{\mathrm{s}}^{-1}$ and total space velocities $\gtrsim 1300\mathrm{km}{\mathrm{s}}^{-1}$. These are most likely the surviving donors from double-degenerate binaries in which the other WD exploded. The other two objects have lower minimum velocities, $\gtrsim 600\mathrm{km}{\mathrm{s}}^{-1}$, and may have formed through a different mechanism, such as pure deflagration of a WD in a Type Iax supernova. The four fastest stars are hotter and smaller than the previously known "D${}^6$ stars," with effective temperatures ranging from $\sim$20,000 to $\sim$130,000 K and radii of $\sim 0.02-0.10R_{\odot }$. Three of these have carbon-dominated atmospheres, and one has a helium-dominated atmosphere. Two stars have RVs of $-1694$ and $-2285\mathrm{km}{\mathrm{s}}^{-1}$ -- the fastest systemic stellar RVs ever measured. Their inferred birth velocities, $\sim 2200-2500\mathrm{km}{\mathrm{s}}^{-1}$, imply that both WDs in the progenitor binary had masses $>1.0M_{\odot }$. The high observed velocities suggest that a dominant fraction of the observed hypervelocity WD population comes from double-degenerate binaries whose total mass significantly exceeds the Chandrasekhar limit. However, the two nearest and faintest D${}^6$ stars have the lowest velocities and masses, suggesting that observational selection effects favor rarer, higher-mass stars. A significant population of fainter low-mass runaways may still await discovery. We infer a birth rate of D${}^6$ stars that is consistent with the SN Ia rate. The birth rate is poorly constrained, however, because the luminosities and lifetimes of ${\mathrm{D}}^6$ stars are uncertain.

arXiv comment26 pages, 17 figures. Accepted to OJA

References in corpus (67)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• The Galaxy Evolution Explorer: A Space Ultraviolet Survey Mission
• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• MILES: A Medium resolution INT Library of Empirical Spectra
• Gaia Early Data Release 3: The astrometric solution
• Gaia Early Data Release 3: Parallax bias versus magnitude, colour, and position
• Observational clues to the progenitors of Type-Ia supernovae
• LSST Science Book, Version 2.0
• The 2dF QSO Redshift Survey - XII. The spectroscopic catalogue and luminosity function
• SkyMapper and the Southern Sky Survey
• Relativistic redshift of the star S0-2 orbiting the Galactic center supermassive black hole
• A million binaries from Gaia eDR3: sample selection and validation of Gaia parallax uncertainties
• Double-detonation sub-Chandrasekhar supernovae: can minimum helium shell masses detonate the core?
• Population synthesis for double white dwarfs I.Close detached systems
• Type Iax Supernovae: A New Class of Stellar Explosion
• Detonations in Sub-Chandrasekhar Mass C+O White Dwarfs
• ESI, a new Keck Observatory echellette spectrograph and imager
• Berkeley Supernova Ia Program I: Observations, Data Reduction, and Spectroscopic Sample of 582 Low-Redshift Type Ia Supernovae
• Rates and Delay Times of Type Ia Supernovae
• Supernova Type Ia progenitors from merging double white dwarfs: Using a new population synthesis model
• Fully-Automated Reduction of Longslit Spectroscopy with the Low Resolution Imaging Spectrometer at Keck Observatory
• Surface Detonations in Double Degenerate Binary Systems Triggered by Accretion Stream Instabilities
• 3D deflagration simulations leaving bound remnants: a model for 2002cx-like Type Ia supernovae
• Updated Gaia-2MASS 3D maps of Galactic interstellar dust
• Prelude to a double degenerate merger: the onset of mass transfer and its impact on gravitational waves and surface detonations
• The MagE Spectrograph
• Failed-Detonation Supernovae: Sub-Luminous Low-Velocity Ia Supernovae and Their Kicked Remnant White Dwarfs with Iron-Rich Cores
• MMT Hypervelocity Star Survey III: A Complete Survey of Faint B-type Stars in the Northern Milky Way Halo
• A Highly Magnified Star at Redshift 6.2
• The Great Escape: Discovery of a nearby 1700 km/s star ejected from the Milky Way by Sgr A*
• On the brightness distribution of Type Ia supernovae from violent white dwarf mergers
• White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 14
• The fastest unbound star in our Galaxy ejected by a thermonuclear supernova
• Search for progenitors of supnernovae type Ia with SPY
• A classifier for spurious astrometric solutions in Gaia EDR3
• He-Accreting WDs: accretion regimes and final outcomes
• The separation distribution and merger rate of double white dwarfs: improved constraints
• An unusual white dwarf star may be a surviving remnant of a subluminous Type Ia supernova
• The ESO supernovae type Ia progenitor survey (SPY)
• Remnants and ejecta of thermonuclear electron-capture supernovae: Constraining oxygen-neon deflagrations in high-density white dwarfs
• The first binary star evolution model producing a Chandrasekhar mass white dwarf
• On the fate of the secondary white dwarf in double-degenerate double-detonation Type Ia supernovae
• A search for the hidden population of AM CVn binaries in the Sloan Digital Sky Survey
• Partly burnt runaway stellar remnants from peculiar thermonuclear supernovae
• The Dark Energy Camera Plane Survey 2 (DECaPS2): More Sky, Less Bias, and Better Uncertainties
• Modelling the formation of double white dwarfs
• Birth of the ELMs: a ZTF survey for evolved cataclysmic variables turning into extremely low-mass white dwarfs
• The stellar Initial Mass Function of the solar neighbourhood revealed by Gaia
• The binary fraction, separation distribution, and merger rate of white dwarfs from SPY
• The response of a helium white dwarf to an exploding type Ia supernova
• Further insight on the hypervelocity white dwarf, LP 40-365 (GD 492): a nearby emissary from a single-degenerate Type Ia supernova
• DBSP_DRP: A Python package for automated spectroscopic data reduction of DBSP data
• Masses of White Dwarf Binary Companions to Type Ia Supernovae Measured from Runaway Velocities
• Unravelling the baffling mystery of the ultrahot wind phenomenon in white dwarfs
• Model Photospheres with Accelerated Lambda Iteration
• Hyper-runaway and hypervelocity white dwarf candidates in \textit{Gaia} Data Release 3: possible remnants from Ia/Iax supernova explosions or dynamical encounters
• Evidence of a Decreased Binary Fraction for Massive Stars Within 20 Milliparsecs of the Supermassive Black Hole at the Galactic Center
• On the formation of hydrogen-deficient post-AGB stars
• Identification of a DO White Dwarf and a PG1159 Star in the ESO SN Ia Progenitor Survey (SPY)
• Stellar parameters for the central star of the planetary nebula PRTM 1 using the German Astrophysical Virtual Observatory service TheoSSA
• A hyper-runaway white dwarf in Gaia DR2 as a Type Iax supernova primary remnant candidate
• Properties and applications of a predicted population of runaway He-sdO/B stars ejected from single degenerate He-donor SNe
• A Globular Cluster Toward M87 with a Radial Velocity < -1000 km/s: The First Hypervelocity Cluster
• SDSS J124043.01+671034.68: The partially burned remnant of a low-mass white dwarf that underwent thermonuclear ignition?
• The Classical Stellar Atmosphere Problem
• The fastest hot subdwarfs revisited

Cited by in corpus (4)

• Constraints on the Galactic Centre environment from \textit{Gaia} hypervelocity stars III: Insights on a possible companion to Sgr A*
• SN 2022joj: A Peculiar Type Ia Supernova Possibly Driven by an Asymmetric Helium-shell Double Detonation
• Properties of Nuclear Star Clusters in Low Surface Brightness Galaxies
• Evidence of .Ia Supernova Detonations in 3D Hydrodynamical Simulations of Double Degenerate Mergers