What is a Higgs and how was it discovered?

Sarah Eno

UMD

Tuesday, Sep 10, 2013

Abstract

The Large Hadron Collider (LHC), a proton-proton collider located in Geneva, Switzerland, began operation in 2008 and currently provides the highest center-of-mass energy in the world. During the summer of 2012, two of the experiments located at the LHC reported evidence for the production of a new particle whose properties seemed consistent with those predicted by the Standard Model for the Higgs Boson. In this talk, I will discuss these results, what more we can learn about this particle in the future, and the remaining mysteries of particle physics.

The Science of Gravitational Waves with Space Observatories

Ira Thorpe

GSFC

Tuesday, Sep 17, 2013

Abstract

After decades of effort, direct detection of gravitational waves from astrophysical sources is on the horizon. Aside from teaching us about gravity itself, gravitational waves hold immense promise as a tool for general astrophysics. In this talk I will provide an overview of the science enabled by a space-based gravitational wave observatory sensitive in the milli-Hertz frequency band including the nature and evolution of massive black holes and their host galaxies, the demographics of stellar remnant compact objects in the Milky Way, and the behavior of gravity in the strong-field regime. I will also summarize the current status of efforts in the US and Europe to implement a space-based gravitational wave observatory.

Cosmic Beauty and Blemishes

Marc Kamionkowski

JHU

Tuesday, October 22, 2013

Abstract

The vast majority of the wealth of cosmological information we have has come from power spectra (or equivalently, two-point correlation function), for the CMB temperature and for the mass distribution in the Universe today. But there is far more that can be sought in the future with the deluge of data from current and forthcoming surveys. I will discuss how the data can be used to look for new fields during inflation; to test geometrically for their properties; to seek parity breaking in the early and late Universe; to look for exotic dark-energy physics; to inquire about nontrivial cosmic topologies; to identify preferred-frame effects; etc. I will also then comment on a possible surprise in the CMB data.

Cold Exoplanets and Eccentric Rings

Marc Kuchner

GSFC

Tuesday, November 5, 2013

Abstract

The only way to find true Neptune analogs around other stars and study their orbits is to interpret images of debris disks, extrasolar analogs of the Kuiper belt. Crisp new HST and ALMA images of debris disks around nearby stars like Fomalhaut show narrow rings offset from the star. Surely these eccentric rings are dynamical signposts of exo-Neptunes, hidden or not so hidden, sculpting the rings. But new models of debris disks are changing our understanding of the exoplanet-debris disk connection. I'll describe SMACK, a new kind of debris disk model that tracks planetesimal collisions in 3D, and how these collisions confute our usual dynamical intuition about eccentric rings. Then I'll consider the possibility that many of these systems contain hidden amounts of gas. The "photoelectric instability" can sculpt rings in such disks with no need for planets at all.

The First Galaxies: Prospects for Understanding Them in the JWST Era

Jason Tumlinson

STScI

Tuesday, Novemver 19, 2013

Abstract

JWST is being built to see "First Light". This is true in more ways than one, for JWST will be able to probe the first galaxies at high redshift and their survivors in the local Universe. I will also consider how understanding the first stars and galaxies will rely not only on JWST but also other facilities that are expected in its era.

How NuSTAR Sees Neutron Stars: From Iron Lines to Cyclotron Lines

Felix Fuerst

Caltech

Thursday, November 21, 2013

Abstract

The Nuclear Spectroscopy Telescope Array (NuSTAR), launched in June 2012, is the first focusing high energy X-ray telescope in orbit. Thanks to its high sensitivity and good spectral resolution above 10keV, combined with a broad bandpass from 3-79 keV, it has already provided valuable insight in the physics of neutron stars. Highly magnetized neutron stars (B~10^12G) can have Cyclotron Resonant Scattering Features (CRSF), the only way to directly measure the magnetic field strength close to the surface of the neutron star. CRSF energies are typically between 10-60keV, the perfect energy range for NuSTAR, so that we can use it to precisely measure their energy and width. Additionally, their shape can be studied in detail, which might differ from a simple Gaussian optical depth profile. These results directly lead to constraints on the emission geometry of the accretion column. I will present results for Her X-1 and Vela X-1, two of the brightest cyclotron line sources in the sky, both showing extremely smooth lines. NuSTAR also covers the iron line region, and its spectral resolution is high enough to study the line width. In Low Mass X-ray Binaries the line originates from reflection of the accretion disk close to the neutron star, i.e., from deep down the gravitational potential. I will show spectra of Ser X-1 in which the iron K-alpha line is clearly broadened due to relativistic effects. This broadening lets us draw conclusion on the distance of the accretion disk to the neutron star and the neutron star mass itself.

Galactic Cosmic Rays: From Earth to Sources

Terri Brandt

GSFC

Tuesday, November 26, 2013

Abstract

For over 100 years we have known that cosmic rays come from outer space, yet proof of their origin, as well as a comprehensive understanding of their acceleration, remains elusive. Direct detection of high energy (up to 10¹⁵eV), charged nuclei with experiments such as the balloon-born, antarctic Trans-Iron Galactic Element Recorder (TIGER) and the recently flown SuperTIGER have provided insight into these mysteries through measurements of cosmic ray abundances. The abundance of rare heavy elements with respect to certain intrinsic properties suggests that cosmic rays include a component of massive star ejecta.

Supernovae and their remnants (SNe & SNRs), often occurring at the end of a massive star's life or in an environment including massive star material, are one of the most likely candidates for sources accelerating galactic comic ray nuclei up to the requisite high energies. The Fermi Gamma-ray Space Telescope Large Area Detector (Fermi LAT) has improved our understanding of such sources by widening the window of observable energies and thus our view into potential sources' energetic processes. Since Fermi LAT surveys the whole sky, we are able to create the first systematic study of GeV emission in all regions containing known SNRs. Not only will this catalog, in combination with the wealth of multiwavelength data available, allow us to constrain SNRs' ability to accelerate cosmic rays, but it will also provide statistically-motivated insight into the inner workings of GeV-emitting SNRs.

Galaxy Mergers through Cosmic Time

Jennifer Lotz

STScI

Tuesday, December 3, 2013

Abstract

Galaxies grow with time through both discrete galaxy mergers and smooth gas accretion. The importance of mergers in defining the properties of today's galaxies remains an outstanding observational question. Estimates of the galaxy merger rate and its evolution can vary by factors of 10, depending upon the method and assumptions used to count mergers. Using physical-motivated timescales from a large suite of galaxy merger simulations, I am able to reconcile the discrepancies between different measurements of the galaxy merger rate over the past 8 billion years. However, the peak of massive galaxy formation occurred more than 10 billion years ago. I present new results from the Hubble Space Telescope on the role of galaxy mergers in forming the most massive galaxies at early times.

Pulsar Timing Arrays: No longer a blunt instrument for Gravitational Wave Detection

Andrea Lommen

Franklin & Marshall

Tuesday, December 10, 2013

Abstract

The limits that pulsar timing places on the energy density of gravitational waves in the universe are on the brink of limiting models of galaxy formation and have already placed limits on the tension of cosmic strings. Pulsar timing has traditionally focused on stochastic sources, but recent research has demonstrated that pulsar timing will (1) offer a rich variety of information on individual gravitational wave sources including waveform, direction and luminosity distance, (2) test alternative theories of gravity, (3) allow us to observe the same gravitational wave source at two different epochs separated by thousands of years. In other words, pulsar timing is a shrewd and versatile gravitational wave detection instrument.

The Origin of Titan

Doug Hamilton

UMD

Tuesday, December 17, 2013

Abstract

Titan is arguably the Solar System's most unusual satellite. It is fifty times more massive than Saturn's other moons and is the only satellite with a substantial atmosphere. Titan shares a unique resonance with nearby Hyperion, but otherwise sits in a particularly large gap between Rhea and Iapetus. Titan has the largest eccentricity of all Saturn's regular satellites and has a reasonably large orbital tilt; its distant neighbor Iapetus has an even more impressive eight degree free inclination. None of these peculiarities are even partially understood. Until now!