Candidate Hypervelocity Red Clump Stars in the Galactic Bulge Found Using the VVV and Gaia Surveys*

Luna, A.; Minniti, D.; Alonso-García, J.

doi:10.3847/2041-8213/ab5c27

Cited by 13 publications

(27 citation statements)

References 58 publications

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“…Some other mechanisms of generating HVSs have been proposed, including the interactions between a star and the binary black hole at the center (Yu & Tremaine 2003), the interactions between binary stars and binary black holes , the interactions between the MW and a dwarf galaxy (Abadi et al 2009), and star formation in the outflows driven by an active galactic nucleus (Wang & Loeb 2018;Silk et al 2012). Since the serendipitous discovery of the first HVS (Brown et al 2005), ∼90 high-velocity stars have been identified as candidate HVSs (see, e.g., Hirsch et al 2005;Edelmann et al 2005;Brown et al 2006Brown et al , 2009Brown et al , 2012Brown et al , 2014Brown et al , 2018Tillich et al 2011;Li et al 2012Li et al , 2015Li et al , 2021Pereira et al 2013;Zheng et al 2014;Huang et al 2017;Marchetti et al 2017;Neugent et al 2018;Massey et al 2018;Hattori et al 2018a;Erkal et al 2019;Du et al 2019;Luna et al 2019;Koposov et al 2020).…”

Section: Introductionmentioning

confidence: 99%

Probing modified Newtonian dynamics with hypervelocity stars

Chakrabarty

Ostorero

Gallo

et al. 2022

A&A

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We show that measuring the velocity components of hypervelocity stars (HVSs) can discriminate between modified Newtonian dynamics (MOND) and Newtonian gravity. Hypervelocity stars are ejected from the Galactic center on radial trajectories with a null tangential velocity component in the reference frame of the Galaxy. They acquire tangential components due to the nonspherical components of the Galactic gravitational potential. Axisymmetric potentials only affect the latitudinal components, vθ, and non-null azimuthal components, vϕ, originate from non-axisymmetric matter distributions. For HVSs with sufficiently high ejection speed, the azimuthal velocity components are proportionate to the deviation of the gravitational potential from axial symmetry. The ejection velocity threshold is ∼750 km s−1 for 4 M⊙ stars and increases with decreasing HVS mass. We determine the upper limit of vϕ as a function of the galactocentric distance for these high-speed HVSs if MOND, in its quasi-linear formulation QUMOND, is the correct theory of gravity and either the triaxial Galactic bulge or a nonspherical hot gaseous halo is the primary source of the azimuthal component, vϕ. In Newtonian gravity, the HVSs within 60 kpc of the Galactic center may easily have vϕ values higher than the QUMOND upper limit if the dark matter halo is triaxial or if the dark matter halo and the baryonic components are axisymmetric but their two axes of symmetry are misaligned. Therefore, even a limited sample of high-speed HVSs could in principle allow us to distinguish between the QUMOND scenario and the dark matter model. This test is currently limited by (i) the lack of a proper procedure to assess whether a star originates from the Galactic center and thus is indeed an HVS in the model one wishes to constrain; and (ii) the large uncertainties on the galactocentric azimuthal velocity components, which should be reduced by at least a factor of ∼10 to make this test conclusive. A proper procedure to assess the HVS nature of the observed stars and astrometric measurements with microarcsecond precision would make this test feasible.

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Section: Introductionmentioning

confidence: 99%

Probing modified Newtonian dynamics with hypervelocity stars

Chakrabarty

Ostorero

Gallo

et al. 2022

A&A

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“…Recently, our knowledge on the kinematics of Milky Way stars both fast and slow has been revolutionized by the European Space Agency's ongoing Gaia mission (Gaia Collaboration et al 2016bCollaboration et al , 2018Collaboration et al , 2021a. With unprecedented astrometric measurements of ∼2 billion Galactic sources and radial velocity measurements for a subset of ∼millions of cool, bright stars, Gaia has demystified the origins of some HVS candidates (Irrgang et al 2018;Brown et al 2018;Erkal et al 2019;Kreuzer et al 2020) recategorized others as spurious detections and/or bound stars (Boubert et al 2018(Boubert et al , 2019Marchetti 2021), and discovered new (candidate) stars with extreme velocities (Bromley et al 2018;Shen et al 2018;Hattori et al 2018;Du et al 2019;Luna et al 2019;Marchetti et al 2019;Li et al 2021;Marchetti 2021). While these unbound star candidates are each fascinating in their own right, it is conspicuous that promising genuine HVS candidates, i.e.…”

Section: Introductionmentioning

confidence: 99%

Constraints on the Galactic Centre environment from Gaia hypervelocity stars II: The evolved population

Evans,

Marchetti,

Rossi

2022

Preprint

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A dynamical encounter between a stellar binary and Sgr A* in the Galactic Centre (GC) can tidally separate the binary and eject one member with a velocity beyond the escape speed of the Milky Way. These hypervelocity stars (HVSs) can offer insight into the stellar population in the inner parsecs of the Milky Way. In a previous work, our simulations showed that the lack of main sequence HVS candidates in current data releases from the Gaia space mission with precise astrometry and measured radial velocities places a robust upper limit on the ejection rate of HVSs from the GC of 3 × 10 −2 yr −1 . We improve this constraint in this work by additionally considering the absence of post main sequence HVSs in Gaia Early Data Release 3 as well the existence of the HVS candidate S5-HVS1. This evidence offers degenerate joint constraints on the HVS ejection rate and the stellar initial mass function (IMF) in the GC. For a top-heavy GC IMF as suggested by recent works, our modelling motivates an HVS ejection rate of η = 0.7 +1.5 −0.5 × 10 −4 yr −1 . This preferred ejection rate can be as large as 10 −2 yr −1 for a very top-light IMF and as low as 10 −4.5 yr −1 if the IMF is extremely top-heavy. Constraints will improve further with future Gaia data releases, regardless of how many HVS candidates are found therewithin.

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“…On the observational side, it was W. R. Brown who serendipitously discovered the first HVS candidate: a B-type star escaping the MW with a galactocentric velocity of ∼700 km s −1 (Brown et al 2005). Many HVS candidates were later found in both targeted and un-targeted surveys (e.g., Hirsch et al 2005;Edelmann et al 2005;Brown et al 2006aBrown et al ,b, 2007aBrown et al ,b, 2009Brown et al , 2012Brown et al , 2014Tillich et al 2011;Li et al 2012Li et al , 2015Li et al , 2021Pereira et al 2013;Zheng et al 2014;Huang et al 2017;Neugent et al 2018;Du et al 2019;Luna et al 2019;Koposov et al 2020). Some of these observed stars have speeds lower than the Galactic escape velocity: they are referred to as "bound HVSs".…”

Section: Introductionmentioning

confidence: 99%

Probing the shape of the Milky Way dark matter halo with hypervelocity stars: A new method

Gallo

Ostorero

Chakrabarty

et al. 2022

A&A

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We propose a new method for determining the shape of the gravitational potential of the dark matter (DM) halo of the Milky Way (MW) with the galactocentric tangential velocities of a sample of hypervelocity stars (HVSs). We compute the trajectories of different samples of HVSs in a MW where the baryon distribution is axisymmetric and the DM potential either is spherical or is spheroidal or triaxial with radial-dependent axis ratios. We create ideal observed samples of HVSs with known latitudinal components of the tangential velocity, vϑ, and azimuthal component of the tangential velocity, vφ. We determine the shape of the DM potential with the distribution of |vϑ| when the Galactic potential is axisymmetric, or with the distribution of |vϑ| and of a function, $ \bar{v}_{\varphi} $, of vφ when the Galactic potential is non-axisymmetric. We recover the correct shape of the DM potential by comparing the distribution of |vϑ| and $ \bar{v}_{\varphi} $ of the ideal observed sample against the corresponding distributions of mock samples of HVSs that traveled in DM halos of different shapes. We use ideal observed samples of ∼800 HVSs, which are the largest samples of 4 M⊙ HVSs ejected with the Hills mechanism at a rate ∼10−4 yr−1, currently outgoing, and located at more than 10 kpc from the Galactic Center. In our ideal case of galactocentric velocities with null uncertainties and no observational limitations, the method recovers the correct shape of the DM potential with a success rate S ≳ 89% when the Galactic potential is axisymmetric, and S > 96% in the explored non-axisymmetric cases. The unsuccessful cases yield axis ratios of the DM potential that are off by ±0.1. The success rate decreases with decreasing size of the HVS sample: for example, for a spherical DM halo, S drops from ∼98% to ∼38% when the sample size decreases from ∼800 to ∼40 HVSs. Accurate estimates of the success rate of our method applied to real data require more realistic samples of mock observed HVSs. Nevertheless, our analysis suggests that a robust determination of the shape of the DM potential requires the measure of the galactocentric velocity of a few hundred HVSs of robustly confirmed galactocentric origin.

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Candidate Hypervelocity Red Clump Stars in the Galactic Bulge Found Using the VVV and Gaia Surveys*

Cited by 13 publications

References 58 publications

Probing modified Newtonian dynamics with hypervelocity stars

Probing modified Newtonian dynamics with hypervelocity stars

Constraints on the Galactic Centre environment from Gaia hypervelocity stars II: The evolved population

Probing the shape of the Milky Way dark matter halo with hypervelocity stars: A new method

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