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Seven wonders of the Milky Way
Blast off to the oldest star in our galaxy, zoom around planetary nebulae dubbed \"the butterflies of space,\" circle past humongous, ringed exoplanets, and close in on newly discovered orbs that just might support alien life. David Aguilar, former Director of Science Information at the Harvard Smithsonian Center for Astrophysics, and creator of Cosmic Catastrophes and Seven Wonders of the Solar System, takes us on a unique space journey through the Milky Way.
Book
Rotation Curve of the Milky Way and the Dark Matter Density
We review the current status of the study of rotation curve (RC) of the Milky Way, and present a unified RC from the Galactic Center to the galacto-centric distance of about 100 kpc. The RC is used to directly calculate the distribution of the surface mass density (SMD). We then propose a method to derive the distribution of dark matter (DM) density in the in the Milky Way using the SMD distribution. The best-fit dark halo profile yielded a local DM density of ρ ⊙ = 0.36 ± 0.02 GeV cm − 3 . We also review the estimations of the local DM density in the last decade, and show that the value is converging to a value at ρ ⊙ = 0.39 ± 0.09 GeV cm − 3 .
Journal Article
A Reservoir of Ionized Gas in the Galactic Halo to Sustain Star Formation in the Milky Way
Without a source of new gas, our Galaxy would exhaust its supply of gas through the formation of stars. Ionized gas clouds observed at high velocity may be a reservoir of such gas, but their distances are key for placing them in the galactic halo and unraveling their role. We have used the Hubble Space Telescope to blindly search for ionized high-velocity clouds (iHVCs) in the foreground of galactic stars. We show that iHVCs with 90 < lVLSRl £ 170 kilometers per second (where VLSR is the velocity in the local standard of rest frame) are within one galactic radius of the Sun and have enough mass to maintain star formation, whereas iHVCs with lVLSRl > 170 kilometers per second are at larger distances. These may be the next wave of infalling material.
Journal Article
Exoplanets
Introduces exoplanets, examining the planets outside of our solar system, discussing what makes them habitable, and exploring the efforts to discover new life.
Book
Two stellar-mass black holes in the globular cluster M22
Two flat-spectrum radio sources in the Milky Way globular cluster M22 are thought to be accreting stellar-mass black holes; the identification of two black holes in one cluster shows that the ejection of black holes from clusters is not as efficient as predicted by most models.
One cluster, but two black holes
The current consensus is that a typical globular star cluster can accommodate just one stellar-mass black hole. Many more will be created, but all but one will be ejected following dynamical interactions. New observations of the Milky Way globular cluster M22, however, reveal the presence of two radio sources in one cluster, with properties typical of accreting black holes each more than ten times the mass of the Sun. This suggests that the ejection of black holes is not as efficient as predicted by most models. And it may not stop there: the authors speculate that there could be a population of tens of black holes in M22, either as single black holes or in binaries where there is no mass transfer taking place.
Hundreds of stellar-mass black holes probably form in a typical globular star cluster, with all but one predicted to be ejected through dynamical interactions
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. Some observational support for this idea is provided by the lack of X-ray-emitting binary stars comprising one black hole and one other star (‘black-hole/X-ray binaries’) in Milky Way globular clusters, even though many neutron-star/X-ray binaries are known
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. Although a few black holes have been seen in globular clusters around other galaxies
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,
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, the masses of these cannot be determined, and some may be intermediate-mass black holes that form through exotic mechanisms
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. Here we report the presence of two flat-spectrum radio sources in the Milky Way globular cluster M22, and we argue that these objects are black holes of stellar mass (each ∼10–20 times more massive than the Sun) that are accreting matter. We find a high ratio of radio-to-X-ray flux for these black holes, consistent with the larger predicted masses of black holes in globular clusters compared to those outside
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. The identification of two black holes in one cluster shows that ejection of black holes is not as efficient as predicted by most models
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, and we argue that M22 may contain a total population of ∼5–100 black holes. The large core radius of M22 could arise from heating produced by the black holes
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.
Journal Article
Finding our place in the universe : how we discovered Laniakea-- the Milky Way's home
\"The book tells the story of how Courtois and her cosmography colleagues discovered and mapped the Laniakea galactic supercluster, the first and most accurate description to date of our home galaxy's location in the universe. Courtois reveals the joys and challenges of international astronomy research and collaborations, humanizing the scientists along the way and making the science accessible. She also makes an effort to shed light on the life and work of herself and other women astronomers. It's a story that would appeal to a wide audience.\"-- Provided by publisher.
Book
A Gaia Early DR3 Mock Stellar Catalog: Galactic Prior and Selection Function
We present a mock stellar catalog, matching in volume, depth and data model the content of the planned Gaia early data release 3 (Gaia EDR3). We have generated our catalog (GeDR3mock) using galaxia, a tool to sample stars from an underlying Milky Way (MW) model or from N-body data. We used an updated Besançon Galactic model together with the latest PARSEC stellar evolutionary tracks, now also including white dwarfs. We added the Magellanic clouds and realistic open clusters with internal rotation. We empirically modeled uncertainties based on Gaia DR2 (GDR2) and scaled them according to the longer baseline in Gaia EDR3. The apparent magnitudes were reddened according to a new selection of 3D extinction maps. To help with the Gaia selection function we provide all-sky magnitude limit maps in G and BP for a few relevant GDR2 subsets together with the routines to produce these maps for user-defined subsets. We supplement the catalog with photometry and extinctions in non-Gaia bands. The catalog is available in the Virtual Observatory (http://dc.g-vo.org/tableinfo/gedr3mock.main) and can be queried just like the actual Gaia EDR3 will be. We highlight a few capabilities of the Astronomy Data Query Language with educative catalog queries. We use the data extracted from those queries to compare GeDR3mock to GDR2, which emphasises the importance of adding observational noise to the mock data. Since the underlying truth, e.g., stellar parameters, is know in GeDR3mock, it can be used to construct priors as well as mock data tests for parameter estimation. All code, models and data used to produce GeDR3mock are linked and contained in galaxia_wrap (https://github.com/jan-rybizki/Galaxia_wrap), a python package, representing a fast galactic forward model, able to project MW models and N-body data into realistic Gaia observables.
Journal Article
The Sagittarius impact as an architect of spirality and outer rings in the Milky Way
Reshaping the Galaxy
Since its discovery more than a decade ago, the Sagittarius dwarf galaxy (Sgr), a satellite galaxy of our own Milky Way, has been recognized as a local analogue to the numerous mergers thought to be common in galaxies throughout the Universe. Traditionally, Sgr has been treated as a negligible perturber to the Galactic disk. New simulations of the response of the Milky Way to the infall of the Sgr reveal that, on the contrary, Sgr has played an important part in shaping the disk morphology. Past impacts have triggered the formation of spiral structure and influenced bar evolution.
Like many galaxies of its size, the Milky Way is a disk with prominent spiral arms rooted in a central bar
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, although our knowledge of its structure and origin is incomplete. Traditional attempts to understand our Galaxy’s morphology assume that it has been unperturbed by major external forces. Here we report simulations of the response of the Milky Way to the infall of the Sagittarius
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dwarf galaxy (Sgr), which results in the formation of spiral arms, influences the central bar and produces a flared outer disk. Two ring-like wrappings emerge towards the Galactic anti-Centre in our model that are reminiscent of the low-latitude arcs observed in the same area of the Milky Way. Previous models have focused on Sgr itself
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to reproduce the dwarf’s orbital history and place associated constraints on the shape of the Milky Way gravitational potential, treating the Sgr impact event as a trivial influence on the Galactic disk. Our results show that the Milky Way’s morphology is not purely secular in origin and that low-mass minor mergers predicted to be common throughout the Universe
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probably have a similarly important role in shaping galactic structure.
Journal Article