How Stellar Activity can be Good for Life

Dr. Paul Rimmer

University of Cambridge, UK

Tuesday, Aug 7, 2018

Abstract

It is likely that the building blocks of life were formed photochemically from hydrogen cyanide on the surface of the Early Earth. This requires both sufficient UV light and a source of hydrogen cyanide (HCN). Flares and coronal mass ejections (CMEs) on stars are not always detrimental to habitability. CMEs ionize and dissociate molecular nitrogen, providing a source of atmospheric HCN that is orders of magnitude more efficient than photochemistry near a planet’s surface, where the HCN is needed. Additionally, when considering the rates to form sugars in the presence of the UV light and HCN, and the rates at which inert adducts form in the dark, and comparing with UV spectra of cool stars, we find that sufficiently active M dwarfs, with flares of energy greater than 5e34 erg with frequency greater than than once every 50 days, may provide enough energy to drive the formation of sugars. We are most interested in planets on which life started long ago, since it is unlikely we will be able to detect life that has just begun on an exoplanetary surface. Therefore it is important to have a good understanding of how flare rates change with stellar age.

Do we really need to worry about binary stars?

JJ Eldridge

Tuesday, Aug 21, 2018

Abstract

This answer to this question depends on who you ask but in nearly all parts of astrophysics the answer should be yes. Yet most stellar evolution models that are widely used today assume that stars are single. This is at odds with our growing understanding that most stars are in binary systems close enough the two stars can interact and experience very different evolution to that of single stars. I will discuss how the Binary Population and Spectral Synthesis (BPASS) code provides a tool to be able to include these different evolutionary pathways when studying stellar systems. I will show the importance of accounting for binary interactions by discussing a few examples. These will include stellar populations in HII regions, open clusters and globular clusters, galaxies near and far and the variety of both electromagnetic and gravitational transients.

Constraining Cosmic Reionization with Hubble, James Webb, and WFIRST

Brant Robertson

Tuesday, Aug 28, 2018

Abstract

Understanding cosmic reionization requires the identification and characterization of early sources of hydrogen-ionizing photons. Through a series of intense observational campaigns with Wide Field Camera 3 aboard Hubble Space Telescope we have now systematically explored the galaxy population deep into the era when cosmic microwave background (CMB) data indicate reionization was underway. High-redshift observations with HST including UDF12, CANDELS, and the Frontier Fields provide the best constraints to date on the abundance, luminosity distribution, and spectral properties of early star-forming galaxies. We synthesize results from these HST campaigns and the most recent constraints from Planck CMB observations to infer redshift-dependent ultraviolet luminosity densities, reionization histories, and the electron scattering optical depth evolution consistent with the available data. We will then preview how James Webb Space Telescope and eventually WFIRST will provide a new window into the reionization epoch and teach us about the physics of galaxy formation in the early universe.

The Search for Sources of IceCube Astrophysical Neutrinos

Erik Blaufuss

UMD

Tuesday, Sep 11, 2018

Abstract

The IceCube Neutrino Observatory instruments a cubic-kilometer of glacial ice under the Amundsen-Scott South Pole Station, Antarctica to detect neutrinos above ~100 GeV and perform astro-particle observations of the Universe. Astrophysical neutrinos are expected to be created in the birthplaces of high-energy cosmic rays, and point the way back to these elusive sources. Since IceCube's detection of a diffuse flux of high-energy astrophysical neutrinos in 2013, identifying their sources has been the primary science goal. This talk with will present the latest measurements of the astrophysical neutrino flux and highlight results from realtime alerts generated by astrophysical neutrino detections that trigger rapid follow-up observations by the community. In particular, a neutrino alert in September, 2017 triggered world-wide astronomical observations, and provide evidence that the Fermi-LAT identified blazar TXS 0506+056 is the first multi-messenger source producing neutrinos, as well as an accelerator of cosmic rays. Potential upgrades to IceCube will also be discussed, including the physics potential of a future IceCube-Gen2 facility at the South Pole.

A new dawn: gravitational-wave observations of binary systems on the ground and in space

Emanuele Berti

Tuesday, Sep 18, 2018

Abstract

The observation of compact binary mergers by the LIGO/Virgo collaboration marked the dawn of a new era in astronomy. LISA will fulfill this vision by opening a new observational window at low frequencies. The gravitational radiation emitted by compact binary systems in these two frequency windows encodes important information on their astrophysical formation mechanism. Furthermore, compact objects - whether in isolation or in binaries - are excellent astrophysical laboratories to probe our understanding of high-energy physics and strong-field gravity. I will highlight the potential of Earth- and space-based detectors to further our understanding of the formation and evolution of compact binaries. I will also discuss potential smoking guns of new physics in gravitational-wave detectors, and the theoretical and observational challenges associated with their search.

What's next for LIGO: from O3 to the next generation of gravitational wave detectors

Lisa Barsotti

MIT

Tuesday, Sep 25, 2018

Abstract

The LIGO gravitational wave detectors are undertaking a series of improvements with the goal of coming back on-line even more sensitive in their next Observing Run O3, scheduled for early 2019. In parallel, the world-wide gravitational wave community is ramping up the effort to prepare for the next generation of ground-based gravitational wave instruments. In my talk, I will give an update on the current status of the LIGO detectors, how the global network of detectors will evolve in the upcoming years, and prospects for improving their sensitivity by more than a factor of 10 in new facilities.

Fast Radio Bursts are Happening

Sarah Spolaor

West Virginia University

Tuesday, Oct 09, 2018

Abstract

Fast radio bursts (FRBs) are intense flashes of light almost as bright as an active galactic nucleus, but lasting only a few milliseconds. They appear to be coming from distant galaxies, and happen once every few seconds somewhere in the sky. Their first discovery happened exactly one decade ago, but in just the past few years our understanding of them has begun to unfold. In only the past year, the total number of detected FRB sources has doubled (now ~60). If we are able to localize FRBs to distant host galaxies and measure their distance, we might be able to use FRBs to map the ionization history of the Universe and study diffuse magnetic fields, among other applications. Importantly, localizing FRBs will also be critical for performing deep multi-wavelength follow-up, and identifying the FRB progenitor. The race is on to detect more FRBs, localize them, and discover what creates these mysterious flashes. The Realfast detector on the Karl G. Jansky Very Large Array is so far the only system with a demonstrated capability to localize a FRB to a host galaxy. This talk will provide an overview for the current context and future of this field, and review the promise of Realfast and other upcoming detectors to allow multi-wavelength follow-up and begin to allow the use of FRBs as probes of the Universe.