Soon after the Big Bang, the Universe became a space filled with "stuff:" neutral gas, dark matter, and radiation. After several hundred million years, primitive structures began to form from the first chemical elements, creating the first massive stars and eventually the first galaxies.

Compact Stellar Systems

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Studies of internal dynamics, stellar population and evolution of compact and dense stellar systems of different scales ranging from globular clusters and ultracompact dwarf galaxies to compact elliptical and massive compact galaxies.

Time Domain Astrophysics

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digitizing the Harvard plates

The Digital Access to a Sky Century @ Harvard (DASCH) project is pleased to release its second production data release (DR2), covering Galactic latitude b = +75 to +60deg, joining results from DR1 and the 5 "Development Fields" from which the hardware and software pipelines for DASCH were developed. These represent ~6% of the Harvard plate data (1885 - 1992; full-sky).

Interstellar Dust

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HETGS observations of Black Hole and Neutron Star systems

The compositional make-up of interstellar (ISM) dust and the relative abundances of chemical elements in astrophysical environments are not well understood. Since dust is a primary repository of the ISM, and is responsible for the chemical evolution of stars, planets, and life itself, it has a profound effect on many areas of astrophysical research from cosmology to star and planet formation. Powerful X-ray satellites (Chandra, XMM-Newton, Suzaku) pointed through dust at bright black hole (BH) and neutron star (NS) systems can be used to study ISM dust in unique ways

Dark Matter in Galaxies

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radio emission at 3cm wavelength in contours overlaid on a greyscale image from the Hubble Space Telescope'

For some time now, it has been known that most of the matter in galaxies is invisible--so called dark matter. Dark matter cannot be detected directly, its effects can only be inferred gravitationally. However, "weighing" a galaxy is no simple task. The phenomenon of gravitational lensing provides a powerful way to measure the dark matter in galaxies. Gravitational lensing occurs when the radiation from a distant source is bent by the gravity of a massive object, like a galaxy, that lies between us and the source.

Nearby Galaxies

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SA(s)c LINER galaxy NGC 7331

Nearby galaxies supply us with the opportunity to study galaxy dynamics and star formation on large scales, yet are close enough to reveal the details needed to make connections to the phenomena we observe around us in the Milky Way. Nearby galaxy studies therefore provide a better understanding of the physical properties of our own Galaxy, in which observations are often hampered by high obscuration from dust and by our location inside its disk.

Active Galactic Nuclei

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M87 is a giant elliptical galaxy near the center of the a large cluster of galaxies at a distance of 16 Mpc in the constellation Virgo. It is one of the first galaxies discovered to have an optical "jet", which is visible faintly as it protrudes through the bright optical emission from the stars in the galaxy. M87 contains the nearest active galactic nucleus (AGN) in the northern sky, offering the possibility of studying an AGN at the highest linear resolution.

VLBI Proper Motions

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Local Group of galaxies

Our Milky Way and Andromeda (M31) are the dominant galaxies in our "Local Group." Both galaxies have many small "satellite" galaxies, which are believed to orbit about them. The past history and future fate of the Local Group are not well known for two reasons. Firstly, the locations and motions of the galaxies in 3-dimensions are poorly determined. Secondly, while we can see normal matter from star-light and thermal emission from interstellar gas and dust, we now understand that there probably is more unseen "dark matter" in and around galaxies than normal matter.

Hot Interstellar Medium

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sky map produced by Rosat

Normal spiral galaxies such as our own Milky Way contain immense volumes of very hot gas, with temperatures of millions of degrees. We are beginning to understand the sources and life cycle of this gas, heated by supernova explosions and the winds from young, hot stars. It is still not clear, for example, how this gas, rich in newly synthesized elements such as carbon, oxygen, and iron, cools and is recycled into future generations of stars and planets (e.g.

Globular Clusters

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47 Tuc

Globular clusters, those dense clusters of ancient stars that are the oldest stellar systems in galaxies and our Milky Way, are rich targets for study with the Chandra X-ray Observatory. Their stellar densities are so high (a million times more stars per unit volume than in the solar neighborhood) that encounters between individual stars and between binaries (pre-existing) and single stars are frequent enough that binary populations including exotic objects (neutron stars and white dwarfs) are created ~100X more efficiently than in the Galaxy as a whole.

Milky Way X-Ray Sources

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ChaMPlane, Bulge Windows and Bulge Latitude Surveys