Directed Energy Planetary Defense

Directed Energy (DE) systems offer the potential for true planetary defense from small to km class threats. Directed energy has evolved dramatically recently and is on an extremely rapid ascent technologically. It is now feasible to consider DE systems for threats from asteroids and comets. DE-STAR (Directed Energy System for Targeting of Asteroids and exploration) is a phased-array laser directed energy system intended for illumination, deflection and compositional analysis of asteroids [1]. It can be configured either as a stand-on or a distant stand-off system. A system of appropriate size would be capable of projecting a laser spot onto the surface of a distant asteroid with sufficient flux to heat a spot on the surface to approximately 3,000 K, adequate to vaporize solid rock. Mass ejection due to vaporization creates considerable reactionary thrust to divert the asteroid from its orbit. DESTARLITE is a smaller stand-on system that utilizes the same technology as the larger standoff system, but with a much smaller laser for a dedicated mission to a specific asteroid. DESTARLITE offers a very power and mass efficient approach to planetary defense. As an example, a DE-STARLITE system that fits within the mass and size constraints of the Asteroid Redirect Mission (ARM) system in a small portion of the SLS block 1 launch capability is capable of deflecting an Apophis class (325 m diameter) asteroid with sufficient warning. A DESTARLITE using the full SLS block 1 launch mass can deflect any known threat

A population of dust-enshrouded objects orbiting the Galactic black hole

The central 0.1 parsecs of the Milky Way host a supermassive black hole identified with the position of the radio and infrared source Sagittarius A*, a cluster of young, massive stars (the S stars) and various gaseous features. Recently, two unusual objects have been found to be closely orbiting Sagittarius A*: the so-called G sources, G1 and G2. These objects are unresolved (having a size of the order of 100 astronomical units, except at periapse, where the tidal interaction with the black hole stretches them along the orbit) and they show both thermal dust emission and line emission from ionized gas. G1 and G2 have generated attention because they appear to be tidally interacting with the supermassive Galactic black hole, possibly enhancing its accretion activity. No broad consensus has yet been reached concerning their nature: the G objects show the characteristics of gas and dust clouds but display the dynamical properties of stellar-mass objects. Here we report observations of four additional G objects, all lying within 0.04 parsecs of the black hole and forming a class that is probably unique to this environment. The widely varying orbits derived for the six G objects demonstrate that they were commonly but separately formed

Directed energy missions for planetary defense

Directed energy for planetary defense is now a viable option and is superior in many ways to other proposed technologies, being able to defend the Earth against all known threats. This paper presents basic ideas behind a directed energy planetary defense system that utilizes laser ablation of an asteroid to impart a deflecting force on the target. A conceptual philosophy called DE-STAR, which stands for Directed Energy System for Targeting of Asteroids and exploration, is an orbiting stand-off system, which has been described in other papers. This paper describes a smaller, stand-on system known as DE-STARLITE as a reduced-scale version of DE-STAR. Both share the same basic heritage of a directed energy array that heats the surface of the target to the point of high surface vapor pressure that causes significant mass ejection thus forming an ejection plume of material from the target that acts as a rocket to deflect the object. This is generally classified as laser ablation. DE-STARLITE uses conventional propellant for launch to LEO and then ion engines to propel the spacecraft from LEO to the near-Earth asteroid (NEA). During laser ablation, the asteroid itself provides the propellant source material; thus a very modest spacecraft can deflect an asteroid much larger than would be possible with a system of similar mission mass using ion beam deflection (IBD) or a gravity tractor. DE-STARLITE is capable of deflecting an Apophis-class (325 m diameter) asteroid with a 1- to 15-year targeting time (laser on time) depending on the system design. The mission fits within the rough mission parameters of the Asteroid Redirect Mission (ARM) program in terms of mass and size. DE-STARLITE also has much greater capability for planetary defense than current proposals and is readily scalable to match the threat. It can deflect all known threats with sufficient warning

DE-STARLITE: A Directed Energy Planetary Defense Mission

This paper presents the motivation behind and design of a directed energy planetary defense system that utilizes laser ablation of an asteroid to impart a deflecting force on the target. The proposed system is called DE-STARLITE for Directed Energy System for Targeting of Asteroids and ExploRation – LITE as it is a small, stand-on unit of a larger standoff DE-STAR system. Pursuant to the stand-on design, ion engines will propel the spacecraft from low-Earth orbit (LEO) to the near-Earth asteroid (NEA). During laser ablation, the asteroid itself becomes the propellant ; thus a very modest spacecraft can deflect an asteroid much larger than would be possible with a system of similar mission mass using ion beam deflection (IBD) or a gravity tractor. DE-STARLITE is capable of deflecting an Apophis-class (325 m diameter) asteroid with a 15-year targeting time. The mission fits within the rough mission parameters of the Asteroid Redirect Mission (ARM) program in terms of mass and size and has much greater capability for planetary defense than current proposals and is readily scalable to the threat. It can deflect all known threats with sufficient warning

Is there a Dark Cusp at the Galactic Center? Constraining the Extended Mass Distribution in the Central 0.01 Parsecs of the Galactic Center Using Stellar Orbits

Stellar orbits around the supermassive black hole (SMBH) at Galactic center (GC) provide unique insight into the physics and astrophysics of SMBHs and how they interact with their host galaxies. In this dissertation, I use stellar orbits at the GC to directly measure the distribution of extended mass around the Milky Way’s central SMBH. Dynamical theories predict that there should be a steep increase in mass density, or a cusp, towards the center of relaxed stellar populations around supermassive black holes. While the theory of stellar cusp formation is well motivated by physics and therefore widely adopted, it has never been observationally verified in the direct vicinity (within 0.5 parsecs) of a supermassive black hole. Observational verification is important because the assumption that cusp models are correct underlies a wide range of calculations that impact understandings of astrophysical processes such as galaxy evolution, the growth of and dynamics around SMBHs, and the origins and rates of gravitational wave emission. The GC provides a unique laboratory to test cusp theories as it hosts stellar populations old enough to be dynamically relaxed, and is the only galactic nucleus close enough to measure the stellar density distribution of the innermost region around an SMBH. This work uses multi-star General Relativistic orbit fits to probe the extended mass within the central 0.01 pc around the SMBH at the GC. Assuming a canonical Bahcall-Wolf cusp with a power-law index of 1.5, measurements of orbital precession of the 16-year-period star S0-2 suggest ∼18,000 � 12,000 � 6,000 M⊙ of extended mass within the central 0.01 pc of the Galaxy. This measurement from S0-2 alone is consistent with predictions from dynamical theories and allows for the possibility of a dark cusp, though still allows for the possibility of a missing cusp (no extended mass) at the 2σ-level. One of the key advancements of this work is the ability to move beyond fits to S0-2 alone and simultaneously constrain multiple stars with a relativistic orbit model. Added constraints from additional stars make it possible to leave the power-law index of the density profile as a free parameter. Multi-star relativistic orbit fits with the power-law index left as a free parameter suggest evidence for a non-zero extended mass within the central 0.01 pc of the GC that follows a core-like density profile rather than a cusp-like density profile. The inferred value of extended mass is ∼60,000 � 20,000 � 6,000M⊙, following a density profile with a 1σ upper limit of γ=0.46 (2σ<0.76, 3σ<1.66)—consistent with the core-like profile inferred from observations of late-type stars in the GC. Updated values for the mass of and distance to the SMBH at the GC, which are fundamental parameters for modeling the central SMBH, are also presented: MBH = (4.18 � 0.03 � 0.01) � 10^6 M⊙ and R0= (8.16 � 0.04 � 0.01) kpc

A population of dust-enshrouded objects orbiting the Galactic black hole.

The central 0.1 parsecs of the Milky Way host a supermassive black hole identified with the position of the radio and infrared source Sagittarius A* (refs. 1,2), a cluster of young, massive stars (the S stars3) and various gaseous features4,5. Recently, two unusual objects have been found to be closely orbiting Sagittarius A*: the so-called G sources, G1 and G2. These objects are unresolved (having a size of the order of 100 astronomical units, except at periapse, where the tidal interaction with the black hole stretches them along the orbit) and they show both thermal dust emission and line emission from ionized gas6-10. G1 and G2 have generated attention because they appear to be tidally interacting with the supermassive Galactic black hole, possibly enhancing its accretion activity. No broad consensus has yet been reached concerning their nature: the G objects show the characteristics of gas and dust clouds but display the dynamical properties of stellar-mass objects. Here we report observations of four additional G objects, all lying within 0.04 parsecs of the black hole and forming a class that is probably unique to this environment. The widely varying orbits derived for the six G objects demonstrate that they were commonly but separately formed

Evidence of a Decreased Binary Fraction for Massive Stars within 20 milliparsecs of the Supermassive Black Hole at the Galactic Center

We present the results of the first systematic search for spectroscopic binaries within the central 2 × 3 arcsec ^2 around the supermassive black hole at the center of the Milky Way galaxy. This survey is based primarily on over a decade of adaptive optics-fed integral-field spectroscopy ( R ∼ 4000), obtained as part of the Galactic Center Orbits Initiative at Keck Observatory, and it has a limiting K ’-band magnitude of 15.8, which is at least 4 mag deeper than previous spectroscopic searches for binaries at larger radii within the central nuclear star cluster. From this primary data set, over 600 new radial velocities are extracted and reported, increasing by a factor of 3 the number of such measurements. We find no significant periodic signals in our sample of 28 stars, of which 16 are massive, young (main-sequence B) stars and 12 are low-mass, old (M and K giant) stars. Using Monte Carlo simulations, we derive upper limits on the intrinsic binary star fraction for the young star population at 47% (at 95% confidence) located ∼20 mpc from the black hole. The young star binary fraction is significantly lower than that observed in the field (70%). This result is consistent with a scenario in which the central supermassive black hole drives nearby stellar binaries to merge or be disrupted, and it may have important implications for the production of gravitational waves and hypervelocity stars

The Swansong of the Galactic Center Source X7: An Extreme Example of Tidal Evolution near the Supermassive Black Hole

We present two decades of new high-angular-resolution near-infrared data from the W. M. Keck Observatory that reveal extreme evolution in X7, an elongated dust and gas feature, presently located half an arcsecond from the Galactic Center supermassive black hole. With both spectro-imaging observations of Br- γ line emission and Lp (3.8 μ m) imaging data, we provide the first estimate of its orbital parameters and quantitative characterization of the evolution of its morphology and mass. We find that the leading edge of X7 appears to be on a mildly eccentric ( e ∼ 0.3), relatively short-period (170 yr) orbit and is headed toward periapse passage, estimated to occur in ∼2036. Furthermore, our kinematic measurements rule out the earlier suggestion that X7 is associated with the stellar source S0-73 or with any other point source that has overlapped with X7 during our monitoring period. Over the course of our observations, X7 has (1) become more elongated, with a current length-to-width ratio of 9, (2) maintained a very consistent long-axis orientation (position angle of 50°), (3) inverted its radial velocity differential from tip to tail from −50 to +80 km s ^−1 , and (4) sustained its total brightness (12.8 Lp magnitudes at the leading edge) and color temperature (425 K), which suggest a constant mass of ∼50 M _Earth . We present a simple model showing that these results are compatible with the expected effect of tidal forces exerted on it by the central black hole, and we propose that X7 is the gas and dust recently ejected from a grazing collision in a binary system