Andromeda Galaxy Research Articles

Reproducibility of the First Image of a Black Hole in the Galaxy M87 From the Event Horizon Telescope Collaboration

This paper presents an interdisciplinary effort to develop and share sustainable knowledge necessary to analyze, understand, and use published scientific results to advance reproducibility in multi-messenger astrophysics. Specifically, we target the breakthrough work associated with generating the first image of a black hole called M87. The Event Horizon Telescope Collaboration computed the image. Based on the artifacts made available by EHT, we deliver documentation, code, and a computational environment to reproduce the first image of a black hole. Our deliverables support discovery in multi-messenger astrophysics by providing all the necessary tools for generalizing methods and findings from the EHT use case. Challenges encountered during the reproducibility of EHT results are reported. Our effort results in an open-source, containerized software package that enables the public to reproduce the first image of a black hole in the galaxy M87.

The Rate and Spatial Distribution of Novae in M31 as Determined by a 20 Year Survey

A long-term (1995–2016) survey for novae in the nearby Andromeda galaxy (M31) was conducted as part of the Research-Based Science Education initiative. During the course of the survey 180 nights of observation were completed at Kitt Peak, Arizona. A total of 262 novae were either discovered or confirmed, 40 of which have not been previously reported. Of these, 203 novae form a spatially complete sample detected by the KPNO/WIYN 0.9 m telescope within a field centered on the nucleus of M31. An additional 50 novae are part of a spatially complete sample detected by the KPNO 4 m telescope within a larger field. Consistent with previous studies, it is found that the spatial distribution of novae in both surveys follows the bulge light of M31 somewhat more closely than the overall background light of the galaxy. After correcting for the limiting magnitude and the spatial and temporal coverage of the surveys, a final nova rate in M31 is found to be yr−1, which is considerably lower than recent estimates. When normalized to the K-band luminosity of M31, this value yields a luminosity-specific nova rate, ν K = 3.3 ± 0.4 yr. By scaling the M31 nova rate using the relative infrared luminosities of M31 and our Galaxy, a nova rate of yr−1 is found for the Milky Way.

Jets, Disks and Winds from Spinning Black Holes: Nature or Nurture?

A brief summary is given of an alternative interpretation of the Event Horizon Telescope observations of the massive black hole in the nucleus of the nearby galaxy M87. It is proposed that the flow is primarily powered by the black hole rotation, not the release of gravitational energy by the infalling gas. Consequently, the observed millimetre emission is produced by an “ergomagnetosphere” that connects the black hole horizon to an “ejection disk” from which most of the gas supplied at a remote “magnetopause” is lost through a magnetocentrifugal wind. It is argued that the boundary conditions at high latitude on the magnetopause play a crucial role in the collimation of the relativistic jets. The application of these ideas to other types of source is briefly discussed.

Testing black hole equatorial reflection symmetry using Sgr A* shadow images

The recently released images of the supermassive black holes in the M87 galaxy and the galaxy of our own make probing black hole spacetimes and testing general relativity (GR) possible. The violation of equatorial reflection symmetry of black hole spacetimes is clearly a smoking gun of physics beyond GR. In this paper, we place constraints on the violation of black hole reflection symmetry using the bounds on the ring size of the $\mathrm{Sgr}\text{ }{\mathrm{A}}^{*}$ black hole images, which are consistent with the critical curve radius predicted in GR within $\ensuremath{\sim}10%$. Adopting a theory-agnostic framework, we consider a Kerr-like metric in which the violation of reflection symmetry is parametrized by a single parameter, without altering the multipoles of the black hole. The critical curves are always vertically symmetric due to the existence of hidden symmetry associated with the Killing tensor, even though the spacetime is reflection asymmetric. We find that the size of critical curves is sensitive to the amount of reflection symmetry being violated, and place the first constraints on the parameter space of the model using the $\mathrm{Sgr}\text{ }{\mathrm{A}}^{*}$ images.

The Photon Ring in M87*

We report measurements of the gravitationally lensed secondary image—the first in an infinite series of so-called “photon rings”—around the supermassive black hole M87* via simultaneous modeling and imaging of the 2017 Event Horizon Telescope (EHT) observations. The inferred ring size remains constant across the seven days of the 2017 EHT observing campaign and is consistent with theoretical expectations, providing clear evidence that such measurements probe spacetime and a striking confirmation of the models underlying the first set of EHT results. The residual diffuse emission evolves on timescales comparable to one week. We are able to detect with high significance a southwestern extension consistent with that expected from the base of a jet that is rapidly rotating in the clockwise direction. This result adds further support to the identification of the jet in M87* with a black hole spin-driven outflow, launched via the Blandford–Znajek process. We present three revised estimates for the mass of M87* based on identifying the modeled thin ring component with the bright ringlike features seen in simulated images, one of which is only weakly sensitive to the astrophysics of the emission region. All three estimates agree with each other and previously reported values. Our strongest mass constraint combines information from both the ring and the diffuse emission region, which together imply a mass-to-distance ratio of and a corresponding black hole mass of (7.13 ± 0.39) × 109 M ⊙, where the error on the latter is now dominated by the systematic uncertainty arising from the uncertain distance to M87*.

Star Cluster Formation and Evolution in M101: An Investigation with the Legacy Extragalactic UV Survey

We present Hubble Space Telescope WFC3/UVIS (F275W, F336W) and ACS/WFC optical (F435W, F555W, and F814W) observations of the nearby grand-design spiral galaxy M101 as part of the Legacy Extragalactic UV Survey (LEGUS). Compact sources detected in at least four bands were classified by both human experts and the convolutional neural network StarcNet. Human experts classified the 2351 brightest sources, retrieving N c = 965 star clusters. StarcNet, trained on LEGUS data not including M101, classified all 4725 sources detected in four bands, retrieving N c = 2270 star clusters. The combined catalog represents the most complete census to date of compact star clusters in M101. We find that for the 2351 sources with both a visual- and machine-learning classification StarcNet is able to reproduce the human classifications at high levels of accuracy (∼80%–90%), which is equivalent to the level of agreement between human classifiers in LEGUS. The derived cluster age distribution implies a disruption rate of over 107 < τ < 108.5 yr for cluster masses ≥103.55 M ⊙ for the central region of M101 and for cluster masses ≥103.38 M ⊙ in the northwest region of the galaxy. The trends we recover are weaker than those of other nearby spirals (e.g., M51) and starbursts, consistent with the M101 environment having a lower-density interstellar medium, and providing evidence in favor of environmentally dependent cluster disruption in the central, southeast, and northwest regions of M101.

Study of the Very High Energy Emission of M87 through its Broadband Spectral Energy Distribution

The radio galaxy M87 is the central dominant galaxy of the Virgo Cluster. Very high-energy (VHE, ≳0.1 TeV) emission from M87 has been detected by imaging air Cherenkov telescopes. Recently, marginal evidence for VHE long-term emission has also been observed by the High Altitude Water Cherenkov Observatory, a gamma-ray and cosmic-ray detector array located in Puebla, Mexico. The mechanism that produces VHE emission in M87 remains unclear. This emission originates in its prominent jet, which has been spatially resolved from radio to X-rays. In this paper, we construct a spectral energy distribution from radio to gamma rays that is representative of the nonflaring activity of the source, and in order to explain the observed emission, we fit it with a lepto-hadronic emission model. We found that this model is able to explain nonflaring VHE emission of M87 as well as an orphan flare reported in 2005.

Constraining Mass of M31 Combing Kinematics of Stars, Planetary Nebulae and Globular clusters

We construct a multiple-population discrete axisymmetric Jeans model for the Andromeda (M31) galaxy, considering three populations of kinematic tracers: 48 supergiants and 721 planetary nebulae (PNe) in the bulge and disk regions, 554 globular clusters extending to ∼30 kpc, and halo stars extending to ∼150 kpc of the galaxy. The three populations of tracers are organized in the same gravitational potential, while each population is allowed to have its own spatial distribution, rotation, and internal velocity anisotropy. The gravitational potential is a combination of stellar mass and a generalized NFW dark matter halo. We created two sets of models, one with a cusped dark matter halo and one with a cored dark matter halo. Both the cusped and cored model fit kinematics of all the three populations well, but the cored model is not preferred due to a too high concentration compared to that predicted from cosmological simulations. With a cusped dark matter halo, we obtained total stellar mass of 1.0 ± 0.1 × 1011 M ⊙, dark matter halo virial mass of M 200 = 7.0 ± 0.9 × 1011 M ⊙, virial radius of r 200 = 184 ± 4 kpc, and concentration of c = 20 ± 4. The mass of M31 we obtained is at the lower side of the allowed ranges in the literature and consistent with the previous results obtained from the H i rotation curve and PNe kinematics. Velocity dispersion profile of the outer stellar halo is important in constraining the total mass while it is still largely uncertain. Further proper motion of bright sources from Gaia or the Chinese Space Station Telescope might help on improving the data and lead to stronger constraints on the total mass of M31.

Contribution from TeV halos to the isotropic gamma-ray background

Recent observations have shown that pulsars are surrounded by extended regions which emit TeV-scale gamma rays through the inverse Compton scattering of very high energy electrons and positrons. Such TeV halos are responsible for a large fraction of the Milky Way's TeV-scale gamma-ray emission. In this paper, we calculate the gamma-ray spectrum from the population of TeV halos located within the Andromeda Galaxy, predicting a signal that is expected to be detectable by the Cherenkov Telescope Array. We also calculate the contribution from TeV halos to the isotropic gamma-ray background, finding that these sources should contribute significantly to this flux at the highest measured energies, constituting up to $\ensuremath{\sim}20%$ of the signal observed above $\ensuremath{\sim}0.1\text{ }\text{ }\mathrm{TeV}$. We also comment on the implications of our results for the origin of the diffuse neutrino flux detected by IceCube.

Dust Emission as a Function of Stellar Population Age in the Nearby Galaxy M33

Dust emission at 8 μm has been extensively calibrated as an indicator of current star formation rate for galaxies and ∼kpc-size regions within galaxies. Yet, the exact link between the 8 μm emission and the young stellar populations in galaxies is still under question, as dust grains can be stochastically heated also by older field stars. In order to investigate this link, we have combined midinfrared images from the Spitzer Space Telescope with a published star cluster candidates catalog for the Local Group galaxy M33. M33 is sufficiently close that the Spitzer's 8 μm images resolve individual regions of star formation. Star clusters represent almost-single-age stellar populations, which are significantly easier to model than more complex mixtures of stars. We find a decrease in the 8 μm luminosity per unit stellar mass as a function of age of the star clusters, with a large scatter that is consistent with varying fractions of stellar light absorbed by dust. The decrease and scatter both confirm findings based on more distant galaxies and are well described by simple models for the dust emission of a young stellar population. We conclude that the dust emission at 8 μm depends sensitively on the age of the stellar population, out to at least the oldest age analyzed here: ∼400 Myr. This dependence complicates the use of the 8 μm emission as a star formation rate indicator, at least for small galactic regions and individual star-forming regions. By leveraging the Spitzer legacy, this investigation paves the way for future explorations with the James Webb Space Telescope.

A Dynamical Model of the M101/NGC 5474 Encounter

We present the first dynamical simulation that recreates the major properties of the archetypal nearby spiral galaxy M101. Our model describes a grazing but relatively close (∼14 kpc) passage of the companion galaxy NGC 5474 through M101's outer disk approximately 200 Myr ago. The passage is retrograde for both disks, yielding a relatively strong gravitational response while suppressing the formation of long tidal tails. The simulation reproduces M101's overall lopsidedness, as well as the extended NE Plume and the sharp western edge of the galaxy’s disk. The post-starburst populations observed in M101's NE Plume are likely a result of star formation triggered at the point of contact where the galaxies collided. Over time, this material will mix azimuthally, leaving behind diffuse, kinematically coherent stellar streams in M101's outer disk. At late times after the encounter, the density profile of M101's disk shows a broken “upbending” profile similar to those seen in spiral galaxies in denser environments, further demonstrating the connection between interactions and long-term structural changes in galaxy disks.

The Astrophysical Distance Scale. V. A 2% Distance to the Local Group Spiral M33 via the JAGB Method, Tip of the Red Giant Branch, and Leavitt Law

The J-region asymptotic giant branch (JAGB) method is a new standard candle that is based on the stable intrinsic J-band magnitude of color-selected carbon stars, and has a precision comparable to other primary distance indicators such as Cepheids and the TRGB. We further test the accuracy of the JAGB method in the Local Group galaxy M33. M33's moderate inclination, low metallicity, and nearby proximity make it an ideal laboratory for tests of systematics in local distance indicators. Using high-precision optical BVI and near-infrared JHK photometry, we explore the application of three independent distance indicators: the JAGB method, the Cepheid Leavitt law, and the TRGB. We find: μ 0(TRGB I ) = 24.72 ± 0.02 (stat) ± 0.07 (sys) mag, μ 0(TRGBNIR) = 24.72 ± 0.04 (stat) ± 0.10 (sys) mag, μ 0(JAGB) = 24.67 ± 0.03 (stat) ± 0.04 (sys) mag, and μ 0(Cepheid) = 24.71 ± 0.04 (stat) ± 0.01 (sys) mag. For the first time, we also directly compare a JAGB distance using ground-based and space-based photometry. We measure μ 0(JAGBF110W) = 24.71 ± 0.06 (stat) ± 0.05 (sys) mag using the (F814W−F110W) color combination to effectively isolate the JAGB stars. In this paper, we measure a distance to M33 accurate to 2% and provide further evidence that the JAGB method is a powerful extragalactic distance indicator that can effectively probe a local measurement of the Hubble constant using spaced-based observations. We expect to measure the Hubble constant via the JAGB method in the near future, using observations from the James Webb Space Telescope.

Ergomagnetosphere, ejection disc, magnetopause in M87 – I. Global flow of mass, angular momentum, energy, and current

ABSTRACT We interpret the 1.3 mm VLBI observations made by the Event Horizon Telescope of the black hole in M87. It is proposed that, instead of being a torus of accreting gas, the observed annular ring is a rotating, magnetically dominated ergomagnetosphere that can transmit electromagnetic angular momentum and energy outward to the disc through a combination of large scale magnetic torque and small scale instabilities. It is further proposed that energy may be extracted by magnetic flux threading the ergosphere through the efficient emission of long wavelength electromagnetic disturbances on to negative energy orbits, after the invariant B2 − E2 approaches zero on small scales. In this way, the spinning black hole and its ergosphere not only power the jets but also the ejection disc so as to drive away most of the gas supplied near the Bondi radius. This outflow takes the form of an MHD wind, extending over many decades of radius, with a unidirectional magnetic field, that is collimated by the infalling gas across a magnetopause. This wind, in turn, collimates the relativistic jets and the emission observed from the jet sheath may be associated with a return current. A model for the global flow of mass, angular momentum, energy, and current, on scales from the horizon to the Bondi radius, is outlined and discussed.

Two Massive Close Binaries with Twin Components in the Nearby Galaxy M31

Massive contact binaries contain two early-type stars that have filled their respective critical Roche lobes and share a common envelope. Their formation and evolution are still unknown. Searching for massive binaries in special evolutionary stages is required to solve this problem. Many massive binaries in the Andromeda galaxy (M31) have been found out and they provide an ideal laboratory to explore the formation of massive contact binaries and to test evolutionary models in massive binaries. By analyzing the light curves of two massive binaries containing twin components, M31V J00452011+4145037 (hereafter J004520) and M31V J00450522+4138462 (hereafter J004505), observed by Vilardell et al., we found that J004520 is a semidetached binary with a mass ratio of 0.924 and a lobe-filling secondary, while J004505 is a deep-contact binary with a mass ratio of 0.974 and a fill-out factor of 88%. Both of them evolved from originally detached binaries via case A mass transfer and are at a critical evolutionary state with the shortest possible period and the highest possible mass ratio (q = 1). The evolution of J004520 has passed the critical state and cannot evolve into a contact binary, while J004505 is just close to the key state. The asymmetric light curve of J004505 is explained by the presence of a hot spot on the less-massive component caused by mass transfer from the more-massive one; the same conclusion can be obtained from the O − C curve. These results support the conclusion that massive contact binaries are formed from mass transfer between the two components and only some systems can evolve into the contact stage.

Technologies and Principles Indicated in The Black Hole Image

On April 10, 2019, Event Horizon Telescope (EHT) released the first image of a black hole in the M87 galaxy [3]. This picture became popular on the Internet all over the world and a great number of people started to discuss it. However, many of them could not understand the scientific meaning of this picture and the laborious process to capture this image. Therefore, this paper is going to explain the works and results of EHT to non-physicists. This paper is separated into two parts, including the technologies and principles that are indicated in the black hole image. Technologies include very long baseline interferometry (VLBI), which is used to increase the details of the image and the general-relativistic magnetohydrodynamics (GRMHD) simulation used to simulate different black hole models. The principles contain Kerr’s model, which is the main model used in EHT’s research and Doppler effect. This research also discussed that the image of the black hole is similar to the Kerr’s model. However, some alternatives of the the Kerr model are different from the actual data.

A Spectroscopic Study of Blue Supergiant Stars in Local Group Spiral Galaxies: Andromeda and Triangulum

Low-resolution LAMOST and Keck spectra of blue supergiant stars distributed over the disks of the Local Group spiral galaxies M31 and M33 are analyzed to determine stellar effective temperatures, gravities, metallicities, and reddening. Logarithmic metallicities at the center of the galaxies (in solar units) of 0.30 ± 0.09 and 0.11 ± 0.04 and metallicity gradients of −0.37 ± 0.13 dex/R 25 and −0.36 ± 0.16 dex/R 25 are measured for M31 and M33, respectively. For M33 the 2D distribution of metallicity indicates a deviation from azimuthal symmetry with an off-center peak. The flux-weighted gravity−luminosity relationship (FGLR) of blue supergiant stars is used to determine a distance modulus of 24.51 ± 0.13 mag for M31 and 24.93 ± 0.07 mag for M33. For M31 the FGLR distance agrees well with other methods. For M33 the FGLR-based distance is larger than the distances from Cepheids studies, but it is in good agreement with work on eclipsing binaries, planetary nebulae, long-period variables, and the tip of the red giant branch.

Testing Horndeski Gravity from EHT Observational Results for Rotating Black Holes

The Event Horizon Telescope (EHT) collaboration recently unveiled the first image of the supermassive black hole M87*, which exhibited a ring of angular diameter θ d = 42 ± 3 μas, a circularity deviation of ΔC ≤ 0.1, and also inferred a black hole mass of M = (6.5 ± 0.7) × 109 M ⊙. This provides a new window onto tests of theories of gravity in the strong-field regime, including probes of violations of the no-hair theorem. It is widely believed that the Kerr metric describes astrophysical black holes, as encapsulated in the critical but untested no-hair theorem. Modeling Horndeski gravity black holes—with an additional hair parameter h besides the mass M and spin a of the Kerr black hole—as the supermassive black hole M87*, we observe that to be a viable astrophysical black hole candidate, the EHT result constrains the (a, h) parameter space. However, a systematic bias analysis indicates that rotating Horndeski black hole shadows may or may not capture Kerr black hole shadows, depending on the parameter values; the latter is the case over a substantial part of the constrained parameter space, allowing Horndeski gravity and general relativity to be distinguishable in the said space, and opening up the possibility of potential modifications to the Kerr metric.

Milky Way and M31 rotation curves: ΛCDM versus MOND

We analyze the existing rotation-curve data of the Milky Way and M31 galaxies that extends to very large distances and low accelerations. We find a systematic downward trend in the weak acceleration (large distances) segment of the radial acceleration. A similar downward trend has been noticed in the $\Lambda$CDM EAGLE simulation, while the deviation from the generic MOND prediction would need to be ascribed to an external field effect, or possibly a post facto selected acceleration function $\mu(x)$.

The science case and challenges of space-borne sub-millimeter interferometry

Ultra-high angular resolution in astronomy has always been an important vehicle for making fundamental discoveries. Recent results in direct imaging of the vicinity of the supermassive black hole in the nucleus of the radio galaxy M87 by the millimeter VLBI system Event Horizon Telescope and various pioneering results of the Space VLBI mission RadioAstron provided new momentum in high angular resolution astrophysics. In both mentioned cases, the angular resolution reached the values of about 10–20 microarcseconds (0.05–0.1 nanoradian). Further developments towards at least an order of magnitude “sharper” values, at the level of 1 microarcsecond are dictated by the needs of advanced astrophysical studies. The paper emphasis that these higher values can only be achieved by placing millimeter and submillimeter wavelength interferometric systems in space. A concept of such the system, called Terahertz Exploration and Zooming-in for Astrophysics, has been proposed in the framework of the ESA Call for White Papers for the Voyage 2050 long term plan in 2019. In the current paper we present new science objectives for such the concept based on recent results in studies of active galactic nuclei and supermassive black holes. We also discuss several approaches for addressing technological challenges of creating a millimeter/sub-millimeter wavelength interferometric system in space. In particular, we consider a novel configuration of a space-borne millimeter/sub-millimeter antenna which might resolve several bottlenecks in creating large precise mechanical structures. The paper also presents an overview of prospective space-qualified technologies of low-noise analogue front-end instrumentation for millimeter/sub-millimeter telescopes. Data handling and processing instrumentation is another key technological component of a sub-millimeter Space VLBI system. Requirements and possible implementation options for this instrumentation are described as an extrapolation of the current state-of-the-art Earth-based VLBI data transport and processing instrumentation. The paper also briefly discusses approaches to the interferometric baseline state vector determination and synchronisation and heterodyning system. The technology-oriented sections of the paper do not aim at presenting a complete set of technological solutions for sub-millimeter (terahertz) space-borne interferometers. Rather, in combination with the original ESA Voyage 2050 White Paper, it sharpens the case for the next generation microarcsecond-level imaging instruments and provides starting points for further in-depth technology trade-off studies.

Dark matter effect on the weak deflection angle by black holes at the center of Milky Way and M87 galaxies

In this paper, we investigated the effect of dark matter on the weak deflection angle by black holes at the galactic center. We consider three known dark matter density profiles such as the Cold Dark Matter, Scalar Field Dark Matter, and the Universal Rotation Curve from the Burkert profile. To achieve this goal, we used how the positional angles are measured by the Ishihara et al. method based on the Gauss–Bonnet theorem on the optical metric. With the help of the non-asymptotic form of the Gauss-Bonnet theorem, the longitudinal angle difference is also calculated. First, we find the emergence of apparent divergent terms on the said profiles, which indicates that the spacetime describing the black hole-dark matter combination is non-asymptotic. We showed that these apparent divergent terms vanish when the distance of the source and receiver are astronomically distant from the black hole. Using the current observational data in the Milky Way and M87 galaxies, we find interesting behaviors of how the weak deflection angle varies with the impact parameter, which gives us some hint on how dark matter interacts with the null particles for each dark matter density profile. We conclude that since these deviations are evident near the dark matter core radius, the weak deflection angle offers a better alternative for dark matter detection than using the deviation from the black hole shadow. With the dark matter profiles explored in this study, we find that the variation of the values for weak deflection angle strongly depends on the dark matter mass on a particular profile.