Hyper-velocity and tidal stars from binaries disrupted by a massive Galactic black hole

Hills, J. G.

doi:10.1038/331687a0

Cited by 647 publications

(802 citation statements)

References 8 publications

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“…As mentioned in the introduction, the first HVSs to be detected were massive hot stars that originated from the Galactic center (Hills 1988). Recent studies (e.g., Palladino et al 2014) have shown that low-mass F or G stars can also travel with extremely high velocities, often exceeding the local Galactic escape velocity.…”

Section: High-velocity Starsmentioning

confidence: 99%

“…Previously, most of the high-to-hyper-velocity stars were thought to be young (relatively massive) hot stars originating from the Galactic center (e.g., Hills 1988;Brown 2015, and references therein). However, the recent SEGUE study by Palladino et al (2014) used a combination of radial velocities and proper motions to show that lowmass F and G stars could be traveling with high enough speed to allow them to escape the Galaxy, and that these stars did not originate in the Galactic center (see also Kollmeier et al 2010;Nidever et al 2012).…”

Section: Introductionmentioning

confidence: 99%

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Chemical abundances in a high-velocity RR Lyrae star near the bulge

Hansen¹,

Rich

Koch

et al. 2016

A&A

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Low-mass variable high-velocity stars are interesting study cases for many aspects of Galactic structure and evolution. Until recently, the only known high-or hyper-velocity stars were young stars thought to originate from the Galactic center. Wide-area surveys such as APOGEE and BRAVA have found several low-mass stars in the bulge with Galactic rest-frame velocities higher than 350 km s −1 . In this study we present the first abundance analysis of a low-mass RR Lyrae star that is located close to the Galactic bulge, with a space motion of ∼-400 km s −1 . Using medium-resolution spectra, we derived abundances (including upper limits) of 11 elements. These allowed us to chemically tag the star and discuss its origin, although our derived abundances and metallicity, at [Fe/H] = −0.9 dex, do not point toward one unambiguous answer. Based on the chemical tagging, we cannot exclude that it originated in the bulge. However, its retrograde orbit and the derived abundances combined suggest that the star was accelerated from the outskirts of the inner (or even outer) halo during many-body interactions. Other possible origins include the bulge itself, or the star might have been stripped from a stellar cluster or the Sagittarius dwarf galaxy when it merged with the Milky Way.

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Section: High-velocity Starsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Chemical abundances in a high-velocity RR Lyrae star near the bulge

Hansen¹,

Rich

Koch

et al. 2016

A&A

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“…As these events were more frequent when the galaxy was still young, these stars are also predominantly old. A third small population of the outer halo are the so-called hypervelocity stars (HVSs) which are ejected via a three-body interaction involving the supermassive black hole (SMBH) in the Galactic center (Hills 1988). Such stars have no age constraints and should be metal-rich since they originate in the innermost region of the galaxy.…”

Section: Introductionmentioning

confidence: 99%

Kinematics in galactic tidal tails

Piffl¹,

Williams²,

Steinmetz³

2011

A&A

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Context. Recent observations of stars with unusually high radial velocities in the Galactic stellar halo have raised new interest in so-called hypervelocity stars. Traditionally, it is assumed that the velocities of these stars could only come from an interaction with the supermassive black hole in the Galactic center. It was suggested that stars stripped off a disrupted satellite galaxy could reach similar velocities and leave the Galaxy. Aims. In this work we study the kinematics of tidal debris stars in detail to investigate the implications of the new scenario and the probability that the observed sample of hypervelocity stars could partly develop out of such a galaxy collision. Methods. We used a suite of N-body simulations following the encounter of a satellite galaxy with its Milky Way-type host galaxy to gather statistics on the properties of stripped-off stars. We study especially the orbital energy distribution of this population. Results. We quantify the typical pattern in angular and phase space formed by the debris stars. We further develop a simple stripping model to predict the kinematics of stripped-off stars. We show that the distribution of orbital energies in the tidal debris takes a typical form that can be described quite accurately by a simple function. Based on this we develop a method predicting the energy distribution that allows us to evaluate the significance and the implications of highvelocity stars in satellite tidal debris. Conclusions. Generally the tidal collisions of satellite galaxy produce stars that escape into intragalactic space even if the satellite itself is on a bound orbit. The main parameters determining the maximum energy kick a tidal debris star can get is the initial mass of the satellite and only to a lower extent its orbit. Main contributors to an unbound stellar population created in this way are massive satellites (M sat > 10 9 M ). We thus expect intragalactic stars to have a metallicity higher than the surviving satellite population of the Milky Way. However, the probability that the observed HVS population is significantly contaminated by tidal debris stars appears low in light of our results.

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“…The high eccentricity of the G2/DSO trajectory suggests that it might be possible to connect this object with hypothetical events of the three-body interaction (Hills 1988) involving the SMBH as the origin of stars on bound orbits near SMBH (Gould & Quillen 2003, see Fig. 14).…”

Section: Binary Embedded Within Common Envelopementioning

confidence: 99%

Dust-enshrouded star near supermassive black hole: predictions for high-eccentricity passages near low-luminosity galactic nuclei

Karas

Eckart

2014

A&A

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Context. Supermassive black holes reside in cores of galaxies, where they are often surrounded by a nuclear cluster and a clumpy torus of gas and dust. Mutual interactions can set some stars on a plunging trajectory towards the black hole. Aims. We model the pericentre passage of a dust-enshrouded star during which the dusty envelope becomes stretched by tidal forces and is affected by the interaction with the surrounding medium. In particular, we explore under which conditions these encounters can lead to periods of enhanced accretion activity. Methods. We discuss different scenarios for such a dusty source. To this end, we employed a modification of the Swift integration package. Elements of the cloud were modelled as numerical particles that represent the dust component that interacts with the optically thin gaseous environment. Results. We determine the fraction of the total mass of the dust component that is diverted from the original path during the passages through the pericentre at 10 3 Schwarzschild radii and find that the main part of the dust ( 90% of its mass) is significantly affected upon the first crossing. The fraction of mass captured at the second passage generally decreases to very low values. Conclusions. As an example, we show predictions for the dusty source evolution assuming the current orbital parameters of the G2 cloud (also known as Dusty S-Cluster Object, DSO) in our Galactic centre. Encounter of a core-less cloud with a supermassive black hole is, most likely, a non-repeating event: the cloud is destroyed. However, in the case of a dust-enshrouded star, part of the envelope survives the pericentre passage. We discuss an offset of 0.3 arcsec between the centre of mass of the diverted part and the star along the eccentric orbit. Finally, we examine an interesting possibility of a binary star embedded within a common wind envelope that becomes dispersed at the pericentre passage.

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Hyper-velocity and tidal stars from binaries disrupted by a massive Galactic black hole

Cited by 647 publications

References 8 publications

Chemical abundances in a high-velocity RR Lyrae star near the bulge

Chemical abundances in a high-velocity RR Lyrae star near the bulge

Kinematics in galactic tidal tails

Dust-enshrouded star near supermassive black hole: predictions for high-eccentricity passages near low-luminosity galactic nuclei

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