Astrophysics Seminar – Star Formation – 7th March
Title: The star-forming ISM: bottom-up versus top-down approaches
Speaker: Paul Clark (Cardiff University)
Time: 1:30pm on Tuesday 7th March 2017
Venue: Physics C36
Abstract:
Observations of the star formation activity in galaxies has revealed a relationship between the star formation rate and the surface density of the gas, especially when one looks at the cold, H2-dominated phase.
Although the physical process behind this phenomenon is not fully understood, it has been used by the galaxy formation community as a sub-grid model in the their numerical simulations. While this might work on large scales, and for `standard’ galaxy types, it fails when we look at the detailed structure within the galaxies. Milky Way star formation studies attempt to work from the bottom up, rather than the top down. In today’s talk, I will discuss recent results from numerical simulations and observational studies that shed light on the large-scale processes that regulate the star formation process in galaxies. From a theoretical viewpoint, I will compare the relative role of various feedback processes, such as photo heating of the ISM, supernovae and cosmic rays.
On the observational side, we will use Milky Way studies to show that much of the observed molecular gas in galaxies may not be involved in the star formation process at all.
Grainne Wilkinson
Physics Colloquium – “Reconfiguring the Fields of Astrophysical Objects: Magnetic Reconnection, Parallel Electric FIelds, and Turbulence”
Date: 07 March 2017, 3pm-4pm
Venue: Marcus Merriman LT
Speaker: Prof. Bob Ergun, University of Colorado
Abstract: Magnetic reconnection is a fundamental process that enables a change of magnetic topology in plasmas, which can result in a sudden, sometimes violent, release of energy. For example, magnetic reconnection initiates solar flares and coronal mass ejections. At magnetized planets, reconnection allows the for a robust energy exchange between the solar wind and the planet’s magnetosphere and can result in magnetic storms, magnetic sub-storms, and intense auroral displays. In astrophysical plasmas, reconnection can drive disk instabilities, energize jets, and result in strong particle acceleration. In laboratory plasmas, it is the root of “saw tooth” events in tokomaks. Because of its widespread importance, magnetic reconnection has been investigated for over one half of a century. However, a full understanding of the process has eluded us. As of now, it is best understood on ion scales in two dimensions. The electron-scale physics and the three-dimensional nature of magnetic reconnection are a topic vigorous investigation with laboratory experiments, space experiments, and numerical simulations.
The Magnetospheric Multiscale (MMS) mission, which has four spacecraft in a close tetrahedron, is designed to study the three-dimensional structure of magnetic reconnection focusing on the electron diffusion region. MMS has two phases, the first phase, which examines reconnection near the Earth’s sub-solar magnetopause, is now complete. The initial results have verified some of the electron-scale physics that was predicted by simulation in two dimensions. Deeper examination, however, shows that magnetic reconnection may be inherently a turbulent process in three dimensions as evidenced by strong magnetic field fluctuations, drift waves, and intense parallel electric fields. I discuss recent advances in our understanding of magnetic reconnection that have been enabled by MMS observations.
Grainne Wilkinson
Do you fancy acting as a judge at the IOP’s North West undergraduate Physics Challenge this year?
Derek Ward-Thompson at UCLan has asked me to circulate the invitation to staff here at Lancaster. It’s at Salford University on Wednesday 29th March from 10.30am till 3pm.
If interested, please contact Derek directly (dward-thompson@uclan.ac.uk)
Gráinne Wilkinson & Jim Wild