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Structure and Evolution of Normal & Active Galaxies
Structure and Evolution of Normal & Active Galaxies

Galactic structure and evolution involve analyses of whole galaxies as self-contained systems of dark matter, stars, and gas that evolve over billions of years. The history of a galaxy is shaped by its internal metabolic processes (star formation and death, gravitational interactions among all its components, and sometimes by an active black hole engine at its core) as well as by interactions with other galaxies, its environment, and the universe itself. Understanding how galaxies, especially the Milky Way, formed and evolved is key to understanding an ancient part of humankind's own origins.

Typically a hundred thousand light years across with the mass of a few hundred billion suns, each galaxy is home to most of the universe's many basic building blocks: interstellar gas and dust, stars and planets, neutron stars and black holes, and, often at the galaxy's center, an active supermassive black hole engine that may outshine the combined light from all its stars. These are the abundant but mysterious dark matter that dominate a galaxy's mass.

On a “small” scale, galaxy evolution is influenced by the death of old stars, which expel newly-created elements forged in their central furnaces, as well as the formation of new stars from enriched interstellar gas. This keeps the stellar population replenished over eons of time. A galaxy's shape is determined by how the stars and gas move within the gravitational field of the galaxy's (mostly dark) matter, and the rate at which it forms stars is determined by how much interstellar gas it has.

Occasionally, two galaxies collide and merge, leading initially to a rapid increase in the rate of star formation and a rapid funneling of gas fuel to the supermassive black hole engine in the center. This active galactic nucleus (or AGN) sometimes shines so brightly that all we can see on Earth is a quasar at its center. In fact, the radiation pressure and powerful jets generated by the AGN can drive out all the gas accreted in the merger, thereby shutting off the supply of gas that fueled star formation and nuclear activity in the first place.

On a very large scale, galaxies appear to have formed out of the expanding universe shortly after the Big Bang. So the study of galaxy evolution requires understanding not only star formation and supermassive black holes, but also cosmology -- the birth and evolution of the universe itself.

Featured Projects

The Nuclear Spectroscopic Telescope Array (NuSTAR) is the first focusing hard X-ray telescope in orbit, allowing true imaging in this largely unknown region of the spectrum. Currently, it is conducting a census of black holes on all scales, mapping newly-created radioactive material in nebulae from recently-exploded stars, and exploring jets of plasma ejected at nearly the speed of light from the most powerful AGN in order to understand what powers these giant engines.

spiral galaxy
NuSTAR (magenta) plus an optical image of the spiral galaxy IC 342, shows two very active black hole systems – too powerful to be stellar-mass black holes, but not powerful enough to be AGN. These may be candidates for the elusive “intermediate mass” black holes often predicted, but not yet confirmed to exist. Image Credit: NASA.

The Wide-field Infrared Survey Explorer (WISE) is a near- and mid-infrared (3.5 - 23 μm wavelength) space telescope launched by NASA in late 2009. It has found the most luminous galaxies in the universe (called hot dust obscured galaxies or “hot DOGs”), discovered 30,000 new dark solar system bodies (some very near the earth), determined the history of star formation in normal galaxies, and will be providing an infrared catalog for the even more powerful James Webb Space Telescope (JWST). Having lost all of its solid hydrogen cryogen in September 2010, WISE is now turned off, but analysis and archiving of the massive amounts of returned data is ongoing.

The two extremes of the WISE universe, and so much more in between. Top left: A top-down view of the Solar System, showing all the minor planets observed by WISE’s NEOWISE project (main belt asteroids [black dots]; known near-earth objects [green] and comets [blue]; WISE-discovered NEOS [red] and comets [yellow]). Top right: The current view of how many “killer” asteroids have been found so far (almost all of those larger than 1 km in size), half of those larger than 0.5 km, etc.). Bottom: The entire WISE infrared sky, showing the Milky Way along with the positions of “hot DOGs” – the most luminous galaxies in the universe (magenta dots). Between these two extremes WISE has studied almost everything else: the coolest brown dwarf stars, newly-forming stars, and normal and active galaxies. Image Credit: NASA.

Current Projects

The Cluster Lensing And Supernova Survey with Hubble (CLASH) is an innovative survey to place new constraints on the fundamental components of the cosmos using Hubble Space Telescope observations of distant clusters of galaxies.

Deep Space Network Ground Radio Telescopes
While the main job of NASA’s Deep Space Network (DSN) is to track distant spacecraft like Voyager, Cassini, and Spitzer, these communication antennas also can be used as ground radio telescopes either as single dishes or as some of the most powerful elements in world-wide Very Long Baseline Interferometry (VLBI) arrays, which also may include a space radio telescope as well (Space VLBI). JPL has built a new observing system for this network called the DSN Transient Observatory (DTO). Its goal is to detect radio transients (short [10 millisecond] but very powerful bursts of radio radiation) in the distant cosmos.

Named after Sir Frederick William Herschel, the Herschel telescope is a far-infrared and submillimeter (57 micrometers to 0.67 millimeters wavelength) telescope launched by ESA in early 2009. It has revealed new information about the earliest, most distant stars and galaxies, as well as those closer to home. Having lost all of its liquid helium cryogen in April 2013, Herschel is now turned off, but analysis and archiving of the massive amounts of data that it returned is ongoing.

The James Webb Space Telescope (JWST) could be the premier observatory in the next decade, following in Hubble's footsteps but working primarily in the red to mid-infrared region (0.6 - 27 microns wavelength). The Mid InfraRed Instrument (MIRI) works in a wavelength range similar to WISE (5 - 27 microns) and will take advantage of JWST's large 6.5 meter mirror. It can study every phase in the history of the Milky Way and other galaxies, from the first galaxies formed after the Big Bang, to those forming stars to the present day.

Long Wavelength Array (LWA-OVRO)
JPL and Caltech, in collaboration with UNM are building a large low frequency radio telescope array at the Owens Valley Radio Observatory. This facility is designed for transient radio source searches and technology development for future larger arrays to detect highly red-shifted neutral hydrogen from the cosmic Dark Ages.

The NASA/IPAC Teacher Archive Research Program (NITARP) gets high school and college teachers involved in authentic astronomical research. The program places small groups of educators with a professional astronomer who will serve as a mentor on an original research project using data from NASA missions. The educators then incorporate the experience into their classrooms and share their new knowledge with students and other teachers. To date, the research projects have involved a broad range of astronomy from star formation, to evolved stars, to active galactic nuclei. The program has resulted in five articles successfully published in the Astrophysical Journal.

Spitzer Space Telescope
In addition to studying the origin of stars and planets, the Spitzer infrared observatory also is used to study galaxies at distances so great that we are seeing them as they existed billions of years ago. All light from these galaxies is stretched by the expansion of the universe to about twice its normal wavelength. (For example, the emission line of oxygen with a wavelength of 0.501 μm and the H| | line at 0.656 μm are shifted to 1.0 and 1.3 microns. So, whereas local galaxies can be studied at optical wavelengths, it is better to study "high redshift" galaxies in the infrared. Spitzer has lost all of its cryogenic coolant, but the observatory is still being operated as a “warm” mission (only cooled to the temperature of cold space).

Theoretical Investigations
The behavior of normal and active galaxies also can be studied with JPL’s supercomputers and other forms of theoretical calculation. Indeed, it is with such studies, and detailed comparison with observations, that the greatest understanding of these objects is achieved. Similar to weather prediction or airplane aerodynamic studies on the earth, these astrophysical simulations build galaxy or black hole systems inside a supercomputer’s memory and use the laws of physics to determine how the system evolves. Sometimes the simulation follows the flow of cosmic fluid or the interaction of hundreds of thousands of star and dark matter “particles.”

Future Projects

Cosmic Dawn
JPL is developing several experiment concepts for observing the Dark Age – the period preceding the Epoch of Reionization (EOR), which refers to the period in the history of the universe during which the predominantly neutral intergalactic medium was ionized by the emergence of the first luminous sources. These sources may have been stars, galaxies, quasars, or some combination of the above. Experiment concepts include ground-based, lunar orbiting, and lunar surface instruments, with eventual observations and intensity mapping in both low frequency neutral hydrogen and high frequency CO.

JPL is participating in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), a collaboration aiming to detect and study the gravitational waves from supermassive black hole binaries. Such binaries are predicted to be the late-stage remnants of mergers of galaxies. The technique ensures precise pulsar timing by utilizing the world's largest radio telescopes, eventually possibly including radio antennas in NASA's Deep Space Network (DSN).

The Observatory for Multi-Epoch Gravitational lens Astrophysics (OMEGA) is an Explorer scale mission concept that aims to decipher the nature of the dark matter that makes up 25% of the mass of the universe. It will do so by using gravitational lensing observations of distant Active Galactic Nuclei (far behind nearby galaxies and clusters of galaxies) to map the granularity and distribution of dark structures in the nearby objects. This will reveal the physical properties of the dark matter particle(s).

The project scientists for Spitzer, Herschel, WISE, NuSTAR, JWST/MIRI, and the principal investigator on OMEGA all work at JPL.


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