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Profile Details
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Hire Dr. Alexey Bobrick
Sweden
USD 80 /hr

Expert in Theoretical Physics; Astrophysics; Machine Learning; Statistics; Finance; Teaching; Leadership/Organization

Profile Summary
Subject Matter Expertise
Services
Scientific writing Journal article, News article, Educational content
Data science & analysis Simple data analysis, Complex data analysis, Statistical analysis, Algorithm design, Data visualization
Academic research Internet research, Evidence-based answers, Secondary data compilation, Literature search
Work Experience

Lund University

- Present

PhD in Theoretical Astrophysics

Lund University

October 2010 - Present

Education

Licenciate in Theoretical Astrophysics

Lund University

October 2010 - May 2016

MSc in Theoretical Physics (General Relativity)

Belarusian State University

September 2009 - June 2010

BSc in Theoretical Physics

Belarusian State University

September 2005 - June 2009

Certifications
  • Certification details not provided.
Publications
JOURNAL ARTICLE
Alexey Bobrick, Gianni Martire (2021). Introducing physical warp drives . Classical and Quantum Gravity.
Late-time Observations of Calcium-rich Transient SN 2019ehk Reveal a Pure Radioactive Decay Power Source @article{87f5c74a21db4204ab92a2731fa117c7, title = "Late-time Observations of Calcium-rich Transient SN 2019ehk Reveal a Pure Radioactive Decay Power Source", abstract = "We present multiband Hubble Space Telescope imaging of the calcium-rich supernova (SN) SN 2019ehk at 276-389 days after explosion. These observations represent the latest B-band to near-IR photometric measurements of a calcium-rich transient to date and allow for the first opportunity to analyze the late-time bolometric evolution of an object in this observational SN class. We find that the late-time bolometric light curve of SN 2019ehk can be described predominantly through the radioactive decay of 56Co for which we derive a mass of M(56Co) = (2.8 ± 0.1) × 10-2 M o. Furthermore, the rate of decline in bolometric luminosity requires the leakage of γ-rays on timescale t γ = 53.9 ± 1.30 days, but we find no statistical evidence for incomplete positron trapping in the SN ejecta. While our observations cannot constrain the exact masses of other radioactive isotopes synthesized in SN 2019ehk, we estimate a mass ratio limit of M(57Co)/M(56Co) ≤ 0.030. This limit is consistent with the explosive nucleosynthesis produced in the merger of low-mass white dwarfs, which is one of the favored progenitor scenarios in early-time studies of SN 2019ehk. ", author = "Jacobson-Gal{\'a}n, {Wynn V.} and Raffaella Margutti and Kilpatrick, {Charles D.} and John Raymond and Edo Berger and Blanchard, {Peter K.} and Alexey Bobrick and Foley, {Ryan J.} and Sebastian Gomez and Griffin Hosseinzadeh and Danny Milisavljevic and Hagai Perets and Giacomo Terreran and Yossef Zenati", year = "2021", doi = "10.3847/2041-8213/abdebc", language = "English", volume = "908", journal = "Astrophysical Journal Letters", issn = "2041-8213", publisher = "IOP Publishing", number = "2", } . Astrophysical Journal Letters.
J. Vos, A. Bobrick, M. Vučković(2020). Observed binary populations reflect the Galactic history . Astronomy & Astrophysics. {EDP} Sciences
Alexey Bobrick, Wynn V. Jacobson-Galán, Raffaella Margutti, Charles D. Kilpatrick, Daichi Hiramatsu, Hagai Perets, David Khatami, Ryan J. Foley, John Raymond, Sung-Chul Yoon, et al. (2020). SN 2019ehk: A Double-peaked Ca-rich Transient with Luminous X-Ray Emission and Shock-ionized Spectral Features . The Astrophysical Journal.
Alexey Bobrick, Wynn Jacobson-Galan, Raffaella Margutti, Charles Kilpatrick, Daichi Hiramitsu, Hagai Perets, David Khatami, Ryan Foley, John Raymond, Sung-Chul Yoon, et al.(2020). SN 2019ehk: A Double-Peaked Ca-rich Transient with Luminous X-ray Emission and Shock-Ionized Spectral Features . Astrophysical Journal. 898. (2). American Astronomical Society
Faint Rapid Red Transients from Neutron Star - CO White Dwarf Mergers @article{01b977155e4c4997a36dcb4311d3609d, title = "Faint Rapid Red Transients from Neutron Star - CO White Dwarf Mergers", abstract = "Mergers of neutron stars (NS) and white dwarfs (WD) may give rise to observable explosive transientevents. We use 3D hydrodynamical (SPH) simulations, as well as 2D hydrodynamical-thermonuclearsimulations (using the FLASH AMR code) to model the disruption of CO-WDs by NSs, whichproduce faint transient events. We post-process the simulations using a large nuclear network andmake use of the SuperNu radiation-transfer code to predict the observational signatures and detailedproperties of these transients. We calculate the light-curves (LC) and spectra for five models of NS -CO-WD mergers. The small yields of56Ni (few×10−3M) result in faint, rapidly-evolving reddenedtransients (RRTs) with B (R) - peak magnitudes of at most∼−12 (−13) to∼−13 (−15), muchshorter and fainter than both regular and faint/peculiar type-Ia SNe. These transients are likely to beaccompanied by several months-long, 1–2 mag dimmer red/IR afterglows. We show that the spectraof RRTs share some similarities with rapidly-evolving transients such as SN2010x, although RRTsare significantly fainter, especially in the I/R bands, and show far stronger Si lines. We estimate thatthe upcoming Large Synoptic Survey Telescope could detect RRTs at a rate of up to∼10−70 yr−1,through observations in the R/I bands. The qualitative agreement between the SPH and FLASHapproaches supports the earlier hydrodynamical studies of these systems.", author = "Yossef Zenati and Alexey Bobrick and Hagai Perets", year = "2020", month = apr, doi = "10.1093/mnras/staa507", language = "English", volume = "493", pages = "3956--3965", journal = "Monthly Notices of the Royal Astronomical Society", issn = "1365-2966", publisher = "Oxford University Press", number = "3", } . Monthly Notices of the Royal Astronomical Society.
Observed binary populations reflect the Galactic history. Explaining the orbital period-mass ratio relation in wide hot subdwarf binaries. @article{9fae528bef474833b73d8b3631bfb766, title = "Observed binary populations reflect the Galactic history. Explaining the orbital period-mass ratio relation in wide hot subdwarf binaries.", abstract = "Context. Wide hot subdwarf B (sdB) binaries with main-sequence companions are outcomes of stable mass transfer from evolved red giants. The orbits of these binaries show a strong correlation between their orbital periods and mass ratios. The origins of this correlation have, so far, been lacking a conclusive explanation. Aims. We aim to find a binary evolution model which can explain the observed correlation. Methods. Radii of evolved red giants, and hence the resulting orbital periods, strongly depend on their metallicity. We performed a small but statistically significant binary population synthesis study with the binary stellar evolution code MESA. We used a standard model for binary mass loss and a standard metallicity history of the Galaxy. The resulting sdB systems were selected based on the same criteria as was used in observations and then compared with the observed population. Results. We have achieved an excellent match to the observed period-mass ratio correlation without explicitly fine-tuning any parameters. Furthermore, our models produce a very good match to the observed period-metallicity correlation. We predict several new correlations, which link the observed sdB binaries to their progenitors, and a correlation between the orbital period, metallicity, and core mass for subdwarfs and young low-mass helium white dwarfs. We also predict that sdB binaries have distinct orbital properties depending on whether they formed in the Galactic bulge, thin or thick disc, or the halo. Conclusions. We demonstrate, for the first time, how the metallicity history of the Milky Way is imprinted in the properties of the observed post-mass transfer binaries. We show that Galactic chemical evolution is an important factor in binary population studies of interacting systems containing at least one evolved low-mass (Minit <  1.6 M⊙) component. Finally, we provide an observationally supported model of mass transfer from low-mass red giants onto main-sequence stars.", author = "Joris Vos and Alexey Bobrick and Maja Vuckovic", year = "2020", doi = "10.1051/0004-6361/201937195", language = "English", journal = "Astronomy & Astrophysics", issn = "1432-0746", publisher = "EDP Sciences", } . Astronomy and Astrophysics.
Formation Constraints Indicate a Black Hole Accretor in 47 Tuc X9 @article{d97a085c55b44c8883f35ae6edea0236, title = "Formation Constraints Indicate a Black Hole Accretor in 47 Tuc X9", abstract = "The luminous X-ray binary 47 Tuc X9 shows radio and X-ray emission consistent with a stellar-mass black hole (BH) accreting from a carbon-oxygen white dwarf. Its location, in the core of the massive globular cluster 47 Tuc, hints at a dynamical origin. We assess the stability of mass transfer from a carbon-oxygen white dwarf onto compact objects of various masses, and conclude that for mass transfer to proceed stably, the accretor must, in fact, be a BH. Such systems can form dynamically by the collision of a stellar-mass BH with a giant star. Tidal dissipation of energy in the giant's envelope leads to a bound binary with a pericenter separation less than the radius of the giant. An episode of common-envelope evolution follows, which ejects the giant's envelope. We find that the most likely target is a horizontal-branch star, and that a realistic quantity of subsequent dynamical hardening is required for the resulting binary to merge via gravitational wave emission. Observing one binary like 47 Tuc X9 in the Milky Way globular cluster system is consistent with the expected formation rate. The observed 6.8-day periodicity in the X-ray emission may be driven by eccentricity induced in the ultra-compact X-ray binary's orbit by a perturbing companion.", keywords = "binaries: close, globular clusters: individual (47 Tuc), stars: black holes, X-rays: binaries", author = "Church, {Ross P.} and Jay Strader and Davies, {Melvyn B.} and Alexey Bobrick", year = "2017", month = dec, day = "10", doi = "10.3847/2041-8213/aa9aeb", language = "English", volume = "851", journal = "Astrophysical Journal Letters", issn = "2041-8213", publisher = "IOP Publishing", number = "1", } . Astrophysical Journal Letters.
Alexey Bobrick, Ross P. Church, Jay Strader, Melvyn B. Davies(2017). Formation Constraints Indicate a Black Hole Accretor in 47 Tuc X9 . The Astrophysical Journal. 851. (1). p. L4. American Astronomical Society
Mass transfer in white dwarf-neutron star binaries @article{9f4d026e425e41e78dfa8f8b2abfccff, title = "Mass transfer in white dwarf-neutron star binaries", abstract = "We perform hydrodynamic simulations of mass transfer in binaries that contain a white dwarf and a neutron star (WD-NS binaries), and measure the specific angular momentum of material lost from the binary in disc winds. By incorporating our results within a long-term evolution model, we measure the long-term stability of mass transfer in these binaries. We find that only binaries containing helium white dwarfs (WDs) with masses less than a critical mass of M-WD, (crit) = 0.2 M-circle dot undergo stable mass transfer and evolve into ultracompact X-ray binaries. Systems with higher mass WDs experience unstable mass transfer, which leads to tidal disruption of the WD. Our low critical mass compared to the standard jet-only model of mass-loss arises from the efficient removal of angular momentum in the mechanical disc winds, which develop at highly super-Eddington mass-transfer rates. We find that the eccentricities expected for WD-NS binaries when they come into contact do not affect the loss of angular momentum, and can only affect the long-term evolution if they change on shorter time-scales than the mass-transfer rate. Our results are broadly consistent with the observed numbers of both ultracompact X-ray binaries and radio pulsars with WD companions. The observed calcium-rich gap transients are consistent with the merger rate of unstable systems with higher mass WDs.", keywords = "hydrodynamics, methods: numerical, binaries: close, stars: neutron, white dwarfs", author = "Alexey Bobrick and Davies, {Melvyn B.} and Church, {Ross P.}", year = "2017", month = jun, day = "1", doi = "10.1093/mnras/stx312", language = "English", volume = "467", pages = "3556--3575", journal = "Monthly Notices of the Royal Astronomical Society", issn = "1365-2966", publisher = "Oxford University Press", number = "3", } . Monthly Notices of the Royal Astronomical Society.
DISSERTATION THESIS
Interacting Giants and Compact Stars @phdthesis{be5d96b7bc9b46ef9b64cacebb56cc2a, title = "Interacting Giants and Compact Stars", abstract = "This thesis is based on four papers dealing with various aspects of interactions in binary stars. Interactions between stars occur at nearly all stages of their evolution and can take many forms. For example, stars may lose material to a binary companion, merge, interact with groups of other stars in star clusters and explode in binary systems, among other interactions.The first paper in this thesis, Bobrick et al. (2017) (Paper I), models how white dwarfs interact with neutron stars as they spiral into contact due to gravitational wave emission. Through the use of hydrodynamic simulations with the Oil-on-Water code, we investigated the process of mass transfer in such binaries. We found that early phases of interactions in these systems lead to significant loss of angular momentum, driving systems to merge more often than previously expected. The third paper in the thesis, Bobrick et al. (2021a) (Paper III), describes the subsequent evolution of the white dwarf-neutron star binaries containing a massive white dwarf after they merge. In this case, the white dwarf gets shredded into a disc, reaching high temperatures leading to nuclear reactions. These nuclear reactions in the disc produce nickel-56 that gets ejected with the rest of the material from the vicinity of the neutron star. As the ejected material expands, the radioactive nickel-56 heats the material, causing it to glow and become observable as a supernova-like transient event. We used hydrodynamic simulations based on the Water code and a nuclear processing code Torch to study nucleosynthesis in the disc, and a supernova spectral synthesis code SuperNu to model how these events may be observed. Unlike papers I and III, which dealt with compact objects, papers II and IV focussed on interactions involving giant stars. In the second paper, Vos et al. (2020) (Paper II), we modelled how mass transfer between red giants and main-sequence stars can give rise to subdwarf B stars. These subdwarf B stars are remnant cores of the red giants that ignited helium while losing mass. By performing a population study based on detailed stellar structure code MESA, we found that the orbits of such subdwarf B binaries bear imprints of the chemical history of our Galaxy. The fact that the Milky Way had changed its metal content over time allowed us to explain the orbital periods of the known subdwarf B binaries. In our fourth study, Bobrick et al. (2021b) (Paper IV), we investigated the formation history of Betelgeuse, which is a red supergiant visible to the naked eye. It has been recently realised that Betelgeuse is likely an outcome of a merger between two stars that were ejected from their birth environment. To test this scenario, we used the FewBody code together with a Monte Carlo-based model of dynamical interactions in the Milky Way star clusters and synthesised a population of stars which may lead to the formation of Betelgeuse. We have confirmed that a stellar merger is indeed a likely mechanism behind the formation of Betelgeuse.", keywords = "(stars) Binaries: General, (stars): neutron, (stars): subdwarfs, (stars): supergiants, hydrodynamics, nuclear reactions, nucleosynthesis, abundances, (stars) Binaries: General, (stars): neutron, (stars): subdwarfs, (stars): supergiants, hydrodynamics, nuclear reactions, nucleosynthesis, abundances, Fysicumarkivet A:2021:Bobrick", author = "Alexey Bobrick", note = "Defence details Date: 2021-06-17 Time: 13:00 Place: Lundmarksalen, Astronomihuset. Join via zoom: https://lu-se.zoom.us/j/65506982507 External reviewer(s) Name: Tauris, Thomas Title: Professor Affiliation: Aarhus University, Denmark ---", year = "2021", month = jun, day = "17", language = "English", isbn = "978-91-7895-901-3", publisher = "Lund University (Media-Tryck)", school = "Lund Observatory", } .