Astrophysics Science Division Research Areas

Solar & Heliospheric Energetic Particles and Cosmic Rays

Cosmic Rays in the Heliosphere - Particles are accelerated in the solar system at shocks where co-rotating high-speed solar wind stream interact with slower solar, at shocks driven by CMEs, and at the solar wind termination shock. In addition to the study of acceleration processes, cosmic ray transport in the heliosphere is investigated as a necessary component to the understanding of other cosmic ray observations. Cosmic ray intensity can also provide a diagnostic of solar wind conditions complementary to conventional plasma and magnetic field measurements.

Solar Energetic Particles - Current experiments seek to understand the acceleration process in both solar flares and Coronal Mass Ejections (CMEs). They are also seeking to understand why the abundance of 3He can vary by orders of magnitude from flare to flare and why heavy ions are frequently enhanced in 3He-rich events.

Galactic Topics

Stars

Goddard Scientists study individual stars-- supermassive stars, Wolf-Rayet stars, chromospherically active stars, luminous blue variables-- and also stellar populations in the Milky Way and in nearby galaxies like M31. Using FUSE and HST, we study the X-ray-modified stellar winds from high-mass X-ray binaries the explosion debris from supernova 1987A, and molecular hydrogen in planetary nebulae.

Extremely massive stars play a role in chemical enrichment and galactic evolution. They mark the end of their lives as supernovae explosions in which a single supernova can equal the entire radiant output of a galaxy. Some members of this class have been suggested to produce the "hypernovae". The energy emitted in a "hypernova" is perhaps equivalent to the radiant energy output of an entire universe of galaxies. Such extraordinary explosions require stellar precursors of unusually large mass, and so should be rare. The Milky Way possesses one possible member of this class, the massive, luminous, and relatively nearby star, Eta Carinae. Eta Carinae is unstable, and is surrounded by ejecta from an eruption in the mid-19th century. X-rays are produced as the ejecta expands into the circumstellar medium near the star at speeds of 100-1000 km/s.

Stars researchers include: Ted Gull, Ken Carpenter, Mike Corcoran, Rosina Iping, Bill Danchi, Sally Heap, Randy Kimble, Allen Sweigart, George Sonneborn, Jon Morse, Derck Massa, Chuck Bowers, Jay Rajagopal, Aki Roberge

Compact Objects/Binaries

Compact objects (white dwarfs, neutron stars, and black holes), are an excellent laboratory for physics under extreme conditions. In particular, when they are in close binary systems, they can shine brightly in the high energy sky due to accretion - when matter from the binary companion falling into the deep gravitational potential wells of these compact objects, it can release a significant fraction of its rest mass energy in the process. GSFC researchers study accretion in binaries in a wide variety of situations using X-ray (Chandra, XMM-Newton, Suzaku, RXTE, Swift), UV (HST, FUSE), optical (ground-based), and IR (Spitzer) instruments. We see a wide range of dramatic phenomena from such systems, including pulsations from rapidly-spinning neutron stars, intense bursts from thermonuclear burning, eclipses, and dips due to occulting material on the disk edge. X-ray Spectroscopy and fast timing studies reveal a wealth of information about the physical processes taking place in these complex systems.

Studies of X-rays emitted from the vicinities of black holes rely on the application of General Relativity, and may one day strongly constrain the theory in the strong gravity limit. We develop 3-dimenensional numerical simulations of Einstein's gravitational field equations to model strong field binary black hole merger interactions and to calculate the resulting gravitational waveforms.

Studies of neutron star X-ray emissions have provided an increasingly tight constraint on the nuclear equation of state - how matter at the nuclear density really behaves. Some binaries involving two white dwarfs or one white dwarf and one neutron star are so compact that they are expected to be strong sources of gravitational waves for LISA, and will eventually merge. Merging white dwarfs, or perhaps some other variety of accreting white dwarfs, are progenitors of Type Ia supernovae and hence the studies of such systems have potential relevance to cosmology.

Compact Objects/Binaries researchers include: Tod Strohmayer, Craig Markwardt, John Cannizzo, Chris Shrader, Lorella Angelini, Nick White, Frank Marshall, Rich Kelley, Tim Kallman

Supernova Remnants

The violent explosion of a massive star at the end of its life is called a supernova. A supernova is one of the most energetic events in the universe, and causes a single star to briefly outshine the entire galaxy in which it is located. Supernova remnants are the dramatic objects produced by these violent explosions. The tenuous gas in the interior of the supernova remnant glows at X-ray wavelengths, and X-ray observations are a valuable source of information on the interactions between the explosion and the surrounding gas.

Acceleration of galactic cosmic rays by supernova remnants should be limited to about 10¹⁵ eV, because particles of higher energy cannot be contained, and therefore cannot be accelerated, within the remnants. This is supported by a change in the spectral shape at about this energy, which may indicate the presence of an additional source of cosmic rays, perhaps extragalactic in origin. The limits of supernova shock acceleration and the signature of any new sources are being actively studied.

Extrasolar Planets

Besides the many missions and programs aimed at planet detection, current exoplanet research at Goddard includes transit spectroscopy, searches for planets around white dwarfs, research in to the nature of the habitable zone, and theoretical studies of planet formation. A number of the extrasolar planets detected so far exhibit a transit across their parent star as seen from Earth. These planets have offered the deepest look yet into the nature of planets outside the solar system. Using the Spitzer Space Telescope, our team has recently detected one planet's secondary eclipse---the time when the planet disappears behind the star. This observation represents the first detected of radiation emitted from an extrasolar planet.

Exo-planet researchers include: Drake Deming, Marc Kuchner, Bill Danchi , Bruce Woodgate, Jeremy Richardson, Mark Clampin, Sally Heap, Chuck Bowers, Aki Roberge

Videos about the first detection of light from an exoplanet

Goddard's Astrobiology Node

Goddard's Solar System Exploration Division

Milky Way Galaxy

The electron-positron annihilation feature at 0.511 MeV is used to probe sources and conditions in the Milky Way's galactic center region. Produced as energetic cosmic rays illuminating interstellar clouds, diffuse gamma-ray emission can be used to infer the origin and flux of cosmic rays within the Galaxy.

Extra-galactic Topics

Galaxy Formation and Evolution

Galaxy formation and evolution covers a wide range of observations conducted with a wide variety of telescopes and techniques, and using both imaging and spectroscopy. Ongoing projects address such topics as the faint blue galaxy problem, the powering source of ultra-luminous infrared galaxies (ULIRGs), and the star formation history of the Universe. Examples of the observations used for these projects include the Hubble Deep Fields, Spitzer imaging and spectroscopy, and ground-based studies in the optical through millimeter.

Over cosmic time, the evolution of galaxies can be traced by measuring characteristics of their star formation - such as the star formation rate or their metal content. Science topics such as the history of the assembly of galaxies and the formation of the elements in the universe are addressed with galaxy evolution observations. Of particular power for such observations are those conducted in the far-infrared, since this long wavelength light escapes from the obscured cores of highly star forming galaxies. Recent observations with the SHARC-II submillimeter camera and upcoming observations with MUSTANG and GISMO millimeter cameras have added to the picture we have of the star formation history of the universe. Goddard is also involved in the SOFIA observatory via the HAWC and SAFIRE instruments that will provide far-infrared imaging and spectroscopy to shed more light on these topics.

Galaxy Formation and Evolution researchers include: Dominic Benford, Eli Dwek, Jon Gardner, Sally Heap, Harvey Moseley, Bill Oegerle, Johannes Staguhn (UMD), and Bruce Woodgate.

AGN

Active galaxies contain a core (or nucleus) of emission that is embedded in an otherwise typical galaxy. This core may be highly variable and bright compared to the rest of the galaxy. X-rays penetrate outward from the core and provide scientists with unique insights into the physical processes occurring there. At the very center of the galaxy core lies a supermassive black hole. Dense material accretes onto the black hole releasing large amounts of gravitational energy. X-rays coming from close to the black hole are gravitationally redshifted, introducing a characteristic distortion in spectral features, such as the relativistically broadened iron K fluorescence line.

Clusters of Galaxies

Most galaxies in the Universe do not exist in isolation but are gravitationally bound with other galaxies. Small associations, called groups, may have a few dozen galaxies which extend over a million light years. Larger and rarer associations may have thousands of galaxies which extend tens of millions of light years. X-ray emission arises from hot (10-100 million degrees) intracluster gas trapped in the potential well of the cluster. It is thought that the metals in clusters were formed by stars in elliptical galaxies and were driven out into the intracluster medium by supernovae winds. The total mass of clusters appears to be larger (by factors of 10-30) than can be accounted for by the visible matter in the galaxies and gas. Hence, clusters are believed to contain dark matter, in addition to the baryonic matter (the "ordinary" matter in the stars and gas). The properties of dark matter are not well understood and its presence is only detected through gravitational influence.

Galaxy Clusters researchers include: Ann Hornschmeier (Cardiff), Rich Mushotzky, Bill Oegerle

Gamma-Ray Bursts

Gamma ray bursts are sudden, brief flashes of gamma rays that occur about once a day at random positions in the sky. These bursts are still a mystery to astronomers; no one knows what causes them, or what physical forces are at work. All that is known is that they are among the most powerful explosions in the Universe.

Studies of GRBs from space have advanced dramatically with the recent results being return by the Swift observatory. The GRB research group in the ASD is leading the Swift GRB mission. . Key results include: (1) discoveries related to the nature of short gamma-ray bursts, (2) studies of the early universe from GRBs detected at large distances, (3) the discovery of the complex nature of GRB afterglows, (4) the detection of a nearby GRB in coincidence with a rare hyper-energetic supernova, (4) studies of the brightest gamma ray flash ever recorded, produced by a magnetar in our Galaxy, (5) the first sensitive survey of the hard x-ray sky leading to the finding that more than 1/2 of all AGN are obscured by gas and dust, and (6) the largest data base of UV observations of supernovae. Swift is expected to continue operating for 10 years.

With the new Fermi (formerly GLAST) mission, ASD scientists will again have considerable capabilities for GRB research, combining data from its specialized burst monitor (GBM) and its primary instrument (LAT). The GLAST Burst Monitor (GBM) is designed to observe has such a large field-of-view that it will be able to see bursts from over 2/3 of the sky at one time, providing locations for follow-up observations of these enigmatic explosions. The GBM works at a lower energy range than the LAT, so together they provide the widest range of energy detection in the gamma-ray regime for any satellite ever built. The launch is scheduled for the fall of 2007.

The ASD GRB research group is a major participant in the Energetic X-ray Imaging Survey Telescope (EXIST) mission concept study led by Prof. J. Grindlay (Harvard).

GRB researchers include: Lorella Angelini, David Band, Scott Barthelmy, Patricia Boyd, Tom Cline, Jay Cummings, Neil Gehrels, Stephen Holland, Hans Krimm, Frank Marshall, Jay Norris, Ann Parsons, Taka Sakamoto (NPP), Goro Sato (USRA), and Mike Stamatikos (NPP)

Cosmology

Cosmic Microwave Background

Cosmic Microwave Background (CMB) Research: Studies of the CMB from space have produced ground-breaking results on the conditions in the early universe. The CMB research group in the ASD led the COBE mission (including the Project Scientist, Principal and Deputy Investigators of the FIRAS and DIRBE instruments, and Deputy PI for the DMR instrument). The WMAP mission is a collaborative project between GSFC and Princeton University to map the microwave sky at 44 times the sensitivity and 33 times the angular resolution (13 arcmin) of COBE. Scientific papers from the first year of operation were published in a special issue of the ApJ, and included such results as: (1) full sky maps of the temperature anisotropy, (2) constraints on models of structure formation, the geometry of the universe and inflation, (3) detection of reionization after the Dark Ages, (4) accurate values of many cosmological constants, and (5) initial results on the polarization of the CMB. WMAP is still operating and taking high quality data. Results from the first 2 full years of data will be released in 2004.

Kogut (PI), Fixsen, Limon, Mirel, and Wollack of ASD, in collaboration with Levin (JPL), Seiffert (JPL), and Lubin (UCSB) launched the Absolute Radiometer for Cosmology, AStrophysics, and Diffuse Emission (ARCADE), a balloon-borne instrument to measure the spectrum of the CMB at centimeter wavelengths. ARCADE searches for the signature of heating from the first generation of stars to form after the Big Bang. Successful flights in 2001 and 2003 showed the CMB to follow a blackbody spectrum down to 3 cm wavelength. A second-generation instrument is under construction and will launch in 2005.

Recently, Kogut (PI), Fixsen, Hinshaw, Limon, Moseley, Wollack (all ASD), Devlin (U Penn), and Irwin (NIST) were awarded a NASA/ROSS grant to fly a high-altitude balloon payload (PAPPA) to measure the polarization anisotropy of the CMB. The flight will search for the imprint of gravity waves produced during an inflationary epoch in the early universe and also characterize the polarized Galactic foregrounds.

Hinshaw (PI) leads a mission concept study for the Inflation Probe (aka CMBPOL), one of the Einstein Probes in the "Beyond Einstein" initiative in NASA's Structure and Evolution of the Universe theme. The goal of the inflation probe is to measure the amplitude of the B-mode polarization in the early universe, as direct support for the Inflation theory and to measure of the energy scale of Inflation.

Hinshaw (PI) is the Director of the Legacy Archive for Microwave Background Data Analysis (LAMBDA) Data Center, which strives to provide one-stop shopping for the CMB research community.

CMB researchers include: Bennett, Fixsen (SSAI), Hill (SSAI) Hinshaw, Kogut, Limon (SSAI), Mather, Mirel (SSAI), Moseley, Odegard (SSAI), Weiland (SSAI), and Wollack.

Dark Energy

In 1998, astronomers made an astounding discovery that shook the foundations of modern physics: contrary to expectations, the expansion of our Universe is revving up. We live in a runaway Universe, where the most distant observable galaxies are racing away from us at ever increasing speeds.

But what is causing this cosmic acceleration? No one knows for certain, but whatever dark energy actually is, detailed measurements reveal that it comprises a whopping 74% of our Universe's total mass-energy budget!

As the Universe's dominant form of energy, dark energy plays a crucial role in determining how the cosmos evolves, and it will determine whether our Universe expands forever or collapses upon itself.

The two teams who co-discovered cosmic acceleration in 1998 used ground-based optical telescopes to study Type Ia supernovae. Since then, NASA spacecraft including the Hubble Space Telescope, the Wilkinson Microwave Anisotropy Probe (WMAP), and the Chandra X-ray Observatory have played leading roles in probing the history of cosmic expansion, giving the scientific community independent confirmation that cosmic acceleration is for real.

NASA has developed the Beyond Einstein Program, a series of missions designed to probe fundamental questions about dark energy, black holes, and the very early Universe. One of the missions is the Joint Dark Energy Mission (JDEM), which will study dark energy. Two other Beyond Einstein missions, International X-ray Observatory (IXO, formerly Con-X) and the Laser Interferometer Space Antenna (LISA), will provide crucial independent measurements of dark energy.

Cracking the mystery of dark energy will revolutionize physics, and learning the Universe's dominant form of energy will stir the public's imagination. NASA spacecraft continue to explore the Universe in many different ways, and future NASA missions such as JDEM, Con-X, and LISA are poised to take the next giant leap in this quest for dark energy.

Dark Energy researchers include: Benford, Rauscher, Greenhouse, Woodgate, Sonneborn, Hinshaw, Gardner, Wiseman, Carpenter, Oegerle, Kashlinsky, Gehrels, Kimble, Felton, Bonfield, and Teplitz.