scholarly journals Blue extreme disk-runaway stars with Gaia EDR3

2021 ◽  
Vol 646 ◽  
pp. L4
Author(s):  
Andreas Irrgang ◽  
Markus Dimpel ◽  
Ulrich Heber ◽  
Roberto Raddi
Keyword(s):  
Milky Way ◽  
Galactic Center ◽  
Galactic Disk ◽  
Space Mission ◽  
Early Type ◽  
Proper Motions ◽  
Supermassive Black Hole ◽  
Early Type Stars ◽  
Runaway Stars ◽  
Potential Origin

Since the discovery of hypervelocity stars in 2005, it has been widely believed that only the disruption of a binary system by a supermassive black hole at the Galactic center (GC), that is, the so-called Hills mechanism, is capable of accelerating stars to beyond the Galactic escape velocity. In the meantime, however, driven by the Gaia space mission, there is mounting evidence that many of the most extreme high-velocity early-type stars at high Galactic latitudes do originate in the Galactic disk and not in the GC. Moreover, the ejection velocities of these extreme disk-runaway stars exceed the predicted limits of the classical scenarios for the production of runaway stars. Based on proper motions from the Gaia early data release 3 and on recent and new spectrophotometric distances, we studied the kinematics of 30 such extreme disk-runaway stars, allowing us to deduce their spatial origins in and their ejection velocities from the Galactic disk with unprecedented precision. Only three stars in the sample have past trajectories that are consistent with an origin in the GC, most notably S5-HVS 1, which is the most extreme object in the sample by far. All other program stars are shown to be disk runaways with ejection velocities that sharply contrast at least with classical ejection scenarios. They include HVS 5 and HVS 6, which are both gravitationally unbound to the Milky Way. While most stars originate from within a galactocentric radius of 15 kpc, which corresponds to the observed extent of the spiral arms, a group of five stars stems from radii of about 21−29 kpc. This indicates a possible link to outer Galactic rings and a potential origin from infalling satellite galaxies.

scholarly journals PG 1610+062: a runaway B star challenging classical ejection mechanisms

2019 ◽  
Vol 628 ◽  
pp. L5 ◽  
Author(s):  
A. Irrgang ◽  
S. Geier ◽  
U. Heber ◽  
T. Kupfer ◽  
F. Fürst
Keyword(s):  
Main Sequence ◽  
Milky Way ◽  
Galactic Center ◽  
Rotational Velocity ◽  
Proper Motions ◽  
B Stars ◽  
Supermassive Black Hole ◽  
Ejection Mechanism ◽  
Runaway Stars ◽  
Spiral Arm

Hypervelocity stars are rare objects, mostly main-sequence (MS) B stars, traveling so fast that they will eventually escape from the Milky Way. Recently, it has been shown that the popular Hills mechanism, in which a binary system is disrupted via a close encounter with the supermassive black hole at the Galactic center, may not be their only ejection mechanism. The analyses of Gaia data ruled out a Galactic center origin for some of them, and instead indicated that they are extreme disk runaway stars ejected at velocities exceeding the predicted limits of classical scenarios (dynamical ejection from star clusters or binary supernova ejection). We present the discovery of a new extreme disk runaway star, PG 1610+062, which is a slowly pulsating B star bright enough to be studied in detail. A quantitative analysis of spectra taken with ESI at the Keck Observatory revealed that PG 1610+062 is a late B-type MS star of 4–5 M⊙ with low projected rotational velocity. Abundances (C, N, O, Ne, Mg, Al, Si, S, Ar, and Fe) were derived differentially with respect to the normal B star HD 137366 and indicate that PG 1610+062 is somewhat metal rich. A kinematic analysis, based on our spectrophotometric distance (17.3 kpc) and on proper motions from Gaia’s second data release, shows that PG 1610+062 was probably ejected from the Carina-Sagittarius spiral arm at a velocity of 550 ± 40 km s−1, which is beyond the classical limits. Accordingly, the star is in the top five of the most extreme MS disk runaway stars and is only the second among the five for which the chemical composition is known.

scholarly journals Hypervelocity stars in the Gaia era

2018 ◽  
Vol 620 ◽  
pp. A48 ◽  
Author(s):  
A. Irrgang ◽  
S. Kreuzer ◽  
U. Heber
Keyword(s):  
Radial Velocity ◽  
Galactic Center ◽  
Galactic Disk ◽  
Large Magellanic Cloud ◽  
Proper Motions ◽  
The Galaxy ◽  
Galactic Potentials ◽  
Kinematic Analyses ◽  
Ejection Mechanism ◽  
Runaway Stars

Context. Young massive stars in the halo are assumed to be runaway stars from the Galactic disk. Possible ejection scenarios are binary supernova ejections (BSE) or dynamical ejections from star clusters (DE). Hypervelocity stars (HVSs) are extreme runaway stars that are potentially unbound from the Galaxy. Powerful acceleration mechanisms such as the tidal disruption of a binary system by a supermassive black hole (SMBH) are required to produce them. Therefore, HVSs are believed to originate in the Galactic center (GC), the only place known to host an SMBH. Aims. The second Gaia data release (DR2) offers the opportunity of studying HVSs in an unprecedented manner. We revisit some of the most interesting high-velocity stars, that is, 15 stars (11 candidate HVSs and 4 radial velocity outliers) for which proper motions with the Hubble Space Telescope. were obtained in the pre-Gaia era, to unravel their origin. Methods. By carrying out kinematic analyses based on revised spectrophotometric distances and proper motions from Gaia DR2, kinematic properties were obtained that help constrain the spatial origins of these stars. Results. Stars that were previously considered (un)bound remain (un)bound in Galactic potentials favored by Gaia DR2 astrometry. For nine stars (five candidate HVSs plus all four radial velocity outliers), the GC can be ruled out as spatial origin at least at 2σ confidence level, suggesting that a large portion of the known HVSs are disk runaway stars launched close to or beyond Galactic escape velocities. The fastest star in the sample, HVS 3, is confirmed to originate in the Large Magellanic Cloud. Conclusions. Because the ejection velocities of five of our non-GC stars are close to or above the upper limits predicted for BSE and DE, another powerful dynamical ejection mechanism (e.g., involving massive perturbers such as intermediate-mass black holes) is likely to operate in addition to the three classical scenarios mentioned above.

scholarly journals Constraining the Variability and Binary Fraction of Galactic Center Young Stars

2016 ◽  
Vol 11 (S322) ◽  
pp. 237-238
Author(s):  
Abhimat K. Gautam ◽  
Tuan Do ◽  
Andrea M. Ghez ◽  
Jessica R. Lu ◽  
Mark R. Morris ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Adaptive Optics ◽  
Binary Systems ◽  
Main Sequence ◽  
Milky Way ◽  
Galactic Center ◽  
Young Stars ◽  
Early Type ◽  
Eclipsing Binary ◽  
Early Type Stars

AbstractWe present constraints on the variability and binarity of young stars in the central 10 arcseconds (~ 0.4 pc) of the Milky Way Galactic Center (GC) using Keck Adaptive Optics data over a 12 year baseline. Given our experiment’s photometric uncertainties, at least 36% of our sample’s known early-type stars are variable. We identified eclipsing binary systems by searching for periodic variability. In our sample of spectroscopically confirmed and likely early-type stars, we detected the two previously discovered GC eclipsing binary systems. We derived the likely binary fraction of main sequence, early-type stars at the GC via Monte Carlo simulations of eclipsing binary systems, and find that it is at least 32% with 90% confidence.

scholarly journals The Assembly History of the Milky Way Nuclear Star Cluster

2015 ◽  
Vol 12 (S316) ◽  
pp. 50-54
Author(s):  
A. Feldmeier-Krause ◽  
N. Neumayer ◽  
R. Schödel ◽  
A. Seth ◽  
P. T. de Zeeuw ◽  
...  
Keyword(s):  
Milky Way ◽  
Galactic Center ◽  
Star Clusters ◽  
Star Cluster ◽  
Reference Object ◽  
Early Type ◽  
Distinct Component ◽  
History Of ◽  
Early Type Stars ◽  
Integral Field Spectrograph

AbstractWithin the central 10 pc of our Galaxy lies a dense cluster of stars, the nuclear star cluster. This cluster forms a distinct component of our Galaxy. Nuclear star clusters are common objects and are detected in ~ 75% of nearby galaxies. It is, however, not fully understood how nuclear star clusters form. The Milky Way nuclear star cluster is the closest of its kind. At a distance of only 8 kpc we can spatially resolve its stellar populations and kinematics much better than in external galaxies. This makes the Milky Way nuclear star cluster the perfect local reference object for understanding the structure and assembly history of nuclear star clusters in general. There are of the order of 107 stars within the central 10 pc of the Galactic center. Most of these stars are several Gyr old late-type stars. However, there are also more than 100 hot early-type stars in the central parsec of the Milky Way, with ages of only a few Myr. Beyond a projected distance of 0.5 pc of the Galactic center, the density of young stars was largely unknown, since only very few spectroscopic observations existed so far. We covered the central >4 pc2 (0.75 sq.arcmin) of the Galactic center using the integral-field spectrograph KMOS (VLT). We extracted more than 1,000 spectra from individual stars and identified >20 new early-type stars based on their spectra. We studied the spatial distribution of the different populations and their kinematics to put constraints on the assembly history of the Milky Way nuclear star cluster.

scholarly journals The Central Dark Mass of the Milky Way

2001 ◽  
Vol 205 ◽  
pp. 20-27
Author(s):  
A. Eckart ◽  
R. Genzel ◽  
T. Ott
Keyword(s):  
Milky Way ◽  
Compact Object ◽  
Early Type ◽  
Proper Motions ◽  
Solar Mass ◽  
Stellar Orbits ◽  
Stellar Cluster ◽  
Sagittarius A ◽  
Compact Radio Source ◽  
Early Type Stars

Measurements of the proper motions and radial velocities of stars in the central cluster of the Milky Way have revealed the presence of a 2-3 million solar mass black hole at the position of the compact radio source Sagittarius A* (SgrA*). The overall stellar motions do not deviate strongly from isotropy and are consistent with a spherical isothermal stellar cluster. Speckle spectroscopy with SHARP at the NTT and slit spectroscopy with ISAAC at the VLT suggests that several of them are early type stars. This is consistent with the idea that these stars are members of an early type cluster with small angular momentum and therefore are now in the immediate vicinity of SgrA*. Most recent data now allows to measure the curvatures of the stellar orbits for a few of the stars that are closest to the center and have the largest proper motions of up to 1400 km/s. The curvatures indicate that the stars indeed orbit the central compact object and will allow to further determine its mass and compactness.

scholarly journals Remarkable Symmetries in the Milky Way Disc's Magnetic Field

2011 ◽  
Vol 28 (2) ◽  
pp. 171-176 ◽  
Author(s):  
P. P. Kronberg ◽  
K. J. Newton-McGee
Keyword(s):  
Magnetic Structure ◽  
Large Scale ◽  
Milky Way ◽  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Field Structure ◽  
Field Pattern ◽  
Close Coupling ◽  
Sign Change

AbstractWe apply a new, expanded compilation of extragalactic source Faraday rotation measures (RM) to investigate the broad underlying magnetic structure of the Galactic disk at latitudes ∣b∣ ≲15° over all longitudes l, where our total number of RMs is comparable to those in the combined Canadian Galactic Plane Survey (CGPS) at ∣b∣ < 4° and the Southern Galactic Plane (SGPS) ∣b∣<1.5°. We report newly revealed, remarkably coherent patterns of RM at ∣b∣≲15° from l∼270° to ∼90° and RM(l) features of unprecedented clarity that replicate in l with opposite sign on opposite sides of the Galactic center. They confirm a highly patterned bisymmetric field structure toward the inner disc, an axisymmetic pattern toward the outer disc, and a very close coupling between the CGPS/SGPS RMs at ∣b∣≲3° (‘mid-plane’) and our new RMs up to ∣b∣∼15° (‘near-plane’). Our analysis also shows the vertical height of the coherent component of the disc field above the Galactic disc's mid-plane—to be ∼1.5 kpc out to ∼6 kpc from the Sun. This identifies the approximate height of a transition layer to the halo field structure. We find no RM sign change across the plane within ∣b∣∼15° in any longitude range. The prevailing disc field pattern and its striking degree of large-scale ordering confirm that our side of the Milky Way has a very organized underlying magnetic structure, for which the inward spiral pitch angle is 5.5°±1° at all ∣b∣ up to ∼12° in the inner semicircle of Galactic longitudes. It decreases to ∼0° toward the anticentre.

scholarly journals 10.2. High proper motions in the vicinity of Sgr A∗: unambiguous evidence for a massive central black hole

1998 ◽  
Vol 184 ◽  
pp. 433-434
Author(s):  
A. M. Ghez ◽  
B. L. Klein ◽  
C. McCabe ◽  
M. Morris ◽  
E. E. Becklin
Keyword(s):  
Black Hole ◽  
Milky Way ◽  
Galactic Center ◽  
Robust Method ◽  
Proper Motions ◽  
Central Black Hole ◽  
Milky Way Galaxy ◽  
The Galaxy ◽  
Sgr A

Although the notion that the Milky Way galaxy contains a supermassive central black hole has been around for more than two decades, it has been difficult to prove that one exists. The challenge is to assess the distribution of matter in the few central parsecs of the Galaxy. Assuming that gravity is the dominant force, the motion of the stars and gas in the vicinity of the putative black hole offers a robust method for accomplishing this task, by revealing the mass interior to the radius of the objects studied. Thus objects located closest to the Galactic Center provide the strongest constraints on the black hole hypothesis.

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